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Operational guidelines Plönninge biogas plant
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Operational guidelines for Plönninge
biogas plant
Release History
Version 1.0, June 2011
Any question about this document should be addressed to:
Bioprocess Control Sweden AB
Scheelevägen 22
SE-223 63 Lund
Sweden
Tel: +46 (0)46 163950
Fax: +46 (0)46 163959
E-mail: [email protected]
Web: www.bioprocesscontrol.com
Table of Contents
1 INTRODUCTION ............................................................................................................ 1
1.1 Description of the plant ............................................................................................... 1
2 DESCRIPTION OF THE OPERATIONAL UNITS .................................................... 3
2.1 Operational units for solid and liquid materials .......................................................... 5
2.1.1 Manure tanks 1 & 2 .............................................................................................. 6
2.1.2 Mixing tank .......................................................................................................... 7
2.1.3 Buffer tank .......................................................................................................... 15
2.1.4 Digester .............................................................................................................. 17
2.1.5 Digestate storage containers 1 & 2 ..................................................................... 19
2.2 Operational units for storage, purification, analysis and distribution of biogas ........ 21
2.2.1 Raw gas storage .................................................................................................. 21
2.2.2 Gas room ............................................................................................................ 23
2.2.3 Upgrading unit .................................................................................................... 25
2.2.4 High pressure gas storage ................................................................................... 26
2.2.5 Filling station ...................................................................................................... 27
2.2.6 Stirling engine .................................................................................................... 28
2.2.7 Gas burner .......................................................................................................... 29
2.2.8 Torch .................................................................................................................. 30
2.3 Control room .............................................................................................................. 31
2.3.1 Control cabinet ................................................................................................... 33
2.3.2 Work station ....................................................................................................... 34
2.4 Heating/cooling system ............................................................................................. 35
3 CONTROL PANEL ....................................................................................................... 36
3.1 Start menu .................................................................................................................. 37
3.2 Process overview (Huvud) ......................................................................................... 38
3.2.1 Mixing tank menu (Blandningstank) .................................................................. 39
3.2.2 Manure tank 1 (Pumpbrunn 2) ........................................................................... 41
3.2.3 Manure tank 2 (Pumpbrunn 3) ........................................................................... 43
3.2.4 Buffer tank menu (Bufferttank) .......................................................................... 45
3.2.5 Digester menu (Rötkammare) ............................................................................ 48
Digester settings menu ..................................................................................................... 49
3.2.6 Digestate storage unit (Efterrötkammare) .......................................................... 52
3.2.7 Gas measuring menu (Gasmätning) ................................................................... 55
3.2.8 Gas consumption menu (Gasanvändning) .......................................................... 58
3.3 Data logger (Logging) ............................................................................................... 60
3.3.1 Logger 1 ............................................................................................................. 61
3.3.2 Logger 2 ............................................................................................................. 62
3.3.3 Logger 3 ............................................................................................................. 63
3.4 Energy measuring (Energimätningar) ....................................................................... 64
3.4.1 Alarm list (Larm) ............................................................................................... 65
4 ANALYSIS AND MONITORING ............................................................................... 66
4.1 Determination of feedstock characteristics ................................................................ 66
4.1.1 pH ....................................................................................................................... 66
4.1.2 Moisture content ................................................................................................. 67
4.1.3 Total (TS) and volatile solids (VS) .................................................................... 68
4.1.4 Biochemical methane potential (BMP) test ....................................................... 69
4.2 Monitoring of process parameters in anaerobic digestion process ............................ 70
4.2.1 Temperature ....................................................................................................... 71
4.2.2 pH ....................................................................................................................... 71
4.2.3 Alkalinity ............................................................................................................ 71
4.2.4 Nutrients and toxins ........................................................................................... 72
4.2.5 Biogas flow and composition ............................................................................. 73
4.2.6 Volatile fatty acids (VFA) and dissolved hydrogen (DH) ................................. 74
4.3 Sampling and analysis ............................................................................................... 74
4.3.1 Sampling points .................................................................................................. 74
4.3.2 Analysis of liquid samples ................................................................................. 80
4.4 Analysis of gaseous samples ..................................................................................... 89
4.5 Online monitoring and data logging .......................................................................... 93
5 EVALUATION OF THE OPERATION AND PROCESS PERFORMANCES ...... 94
5.1 Process operation ....................................................................................................... 94
5.1.1 Organic loading rate (OLR) ............................................................................... 94
5.1.2 Hydraulic retention time (HRT) ......................................................................... 94
5.2 Process performances ................................................................................................ 95
5.2.1 Gas normalization .............................................................................................. 95
5.2.2 Gas productivity ................................................................................................. 95
5.2.3 Gas yield ............................................................................................................. 96
5.2.4 VS reduction ....................................................................................................... 96
5.3 Process stability ......................................................................................................... 97
6 DOCUMENTATION ..................................................................................................... 99
6.1 Navigation ............................................................................................................... 100
6.2 Sorting of raw data (Rådatasortering) ..................................................................... 101
6.3 Raw data (Rådata) ................................................................................................... 102
6.4 “Manual” data (Manuell data) ................................................................................. 103
6.5 Daily data (Dagsvärden) .......................................................................................... 105
6.6 Weekly data (Veckovärden) .................................................................................... 107
6.7 Monthly data (Månadsvärden) ................................................................................. 109
6.8 Printable document (Utskriftsformulär) .................................................................. 112
6.9 How to insert data from the data logger .................................................................. 113
6.9.1 Download data from Datalogger ...................................................................... 113
6.9.2 Insert data into Process_data.xlsm ................................................................... 116
7 METHODOLOGY FOR PROCESS IMPROVEMENTS ....................................... 120
7.1 Meetings .................................................................................................................. 121
8 OPERATIONAL ROUTINES .................................................................................... 122
8.1 Daily operational routines ....................................................................................... 122
8.2 Weekly operational routines .................................................................................... 133
9 PROCESS EVALUATION ......................................................................................... 136
9.1 Weekly evaluation ................................................................................................... 136
9.1.1 Saving the data for weekly evaluation ............................................................. 138
9.2 Monthly evaluation .................................................................................................. 142
9.3 Yearly evaluation ..................................................................................................... 143
1
1 INTRODUCTION
The Plönninge biogas plant serves as a demonstration and research site and was built to
promote small scale biogas production. It is situated at Plönninge Agricultural High School
and is operated in collaboration with Region of Halland.
Region of Halland has, together with Bioenergicentrum Halland, an ambition to promote
regional development related to renewable energy sources. The focus is on agricultural
enterprises and most of the work is carried out by Plönninge Agricultural High School. To
ensure that this facility can serve as a demonstration plant for future farm-based biogas plants
in the region and around the world, it is important that the plant can be run as efficiently as
possible and that the produced biogas can be fully utilized.
The purpose of this document is to serve as a support and a guide for operators at the
Plönninge biogas plant.
1.1 Description of the plant
General
The biogas plant in Plönninge is a small farm scale plant that has been in operation since
2004. It was constructed by Läckeby Water AB with the original objective of decomposing
remnant silage and cow manure from farms and other available waste products in the area.
The volume of the digester is 300 m3 with an expected gas production of 250-300 Nm
3/day.
The average retention time of the digester is around 30 days, depending on the availability of
manure.
Operation
Manure from around 80 cows is collected in a manure tank, which is then pumped into a
larger mixing tank. Furthermore, this is mixed, in the same tank, with more solid substrates
(e.g. silage or potatoes). Iron chloride (FeCl3) is also added to reduce the amount of hydrogen
suphide (H2S) in the produced biogas, by precipitation of FeS from sulphur-containing
compounds. The mixed material is then pumped further into a buffer tank where it spends
around one day before it is fed into the digester. The digester is top mixed with two sets of
impellers and it is kept at an average temperature of 37 ºC. As the material is fed into the
digester, digested slurry or digestate is removed into two serial connected storage units, where
it is stored for around half a year before it is used as a fertilizer to cultivate crops at the farm.
The produced gas is consumed in three different ways using the following systems: i) in a gas
burner for producing heat; ii) in a Stirling engine for producing electricity and heat; and iii) in
an upgrading unit for producing biomethane as a vehicle fuel.
2
Originally, only the gas burner was installed at the plant but, in order to promote the
production of higher value products, the Stirling engine and the biogas upgrading unit were
installed in 2008; the Stirling engine started operations in 2011.
3
2 DESCRIPTION OF THE OPERATIONAL UNITS
The most important operational units at the Plönninge biogas plant are presented in this
section. They have been divided into four categories:
1) Operational units for liquid and solid materials
2) Operational units for gas flows
3) Operational units in the control room
4) Heating / cooling system
An overview picture of the Plönninge biogas site, where some of the larger operational units
have been marked, can be seen in Figure 2-1.
Figure 2-1 Satellite photo (Google maps) of Plönnige biogas site.
A simplified process drawing of Plönninge biogas plant can be seen in Figure 2-2.
4
PS
LC
FI
LC
LC
LC
LS
TC
LC
TC
Pi FI
GFL1
DigesterRK1, 300 m3
Digestate storage 1ERK1, 1600 m3
FI Flow indicator
LC Level control
PS Tryckutlösare
LS Level switch
TC Temperature control
PI Pressure indicator
LC
Manure storageLT1, 1200 m3
TITI
Gas alarmTorch
Condensation trapSF1
Condensed water
Raw gas storage
GL1,
Iron chloride
Buffer tankBT1, 12 m3
Mixing tankPB1, 50 m3
Manure tank 1PB2, 12 m3
Manure tank 2PB3, 50 m3
PotatoesFruit &
Vegetables
Horse manure
Silage
Manual loading
Gas burnerGP1, 60 kW
FI
GF1
Condensation trapSF2
Condensed water
Digestate storage 2ERK2, 1500 m3
LC
P1
P2
P3
P4
P6
Stirling engineSM1, 8kW (36 kW)
Electric production
Water scrubberWS1
High pressure gas storage
Gas pump
X-ripper
P7
Figure 2-2 Simplified process drawing of the Plönnige biogas plant.
5
2.1 Operational units for solid and liquid materials
In this section all the operational units that handle the liquid and solid material in the
Plönninge biogas plant are listed and described. A summary of their properties can be seen in
Table 2-1.
Table 2-1 Summary of operational units handling liquid and solid material.
Abbreviati
on
Volume
(m3)
Mixing Heating Sensors Connections
in
Connections
out
Manure
tank 1
PB2 12
Recirculation No Level Stable (cow) PB1
Manure
tank 2
PB3 50
Recirculation No Level Stable (calf) LT1
Mixing tank PB1 50 Submersible
mixer,
recirculation
No Level PB2, Manual
loading
BT1
Buffer tank BT1 12 Recirculation No Level PB1 RK1, ERK1
Digester RK1 300 Mixer Yes Level, level
switch,
temperature (2)
BT1 ERK1
Digestate
storage 1
ERK1 1600 Submersible
mixer (2)
No Level RK1 ERK2
Digestate
storage 2
ERK2 1500 Mobile mixer No No ERK1 -
Manure
storage
LT1 1200 Mobile mixer No No PB2, PB3,
RK1
-
In total, there are eight operational units handling the solid and liquid material in Plönninge.
6
2.1.1 Manure tanks 1 & 2
Figure 2-3 Photos of manure tank 1.
A Housing covering the manure tank
B Tap for manure sampling
C Container used for loading the 1.7 m3 pilot plant (described in a separated document)
with manure
D Pipe for recirculation
E Motor for recirculation pump
F Manure tank (lid)
Role
The role of the manure tanks is to collect and store manure from the cow stables.
Dimensions
The manure from the cow stable is collected in two tanks (PB2 and PB3) that are situated
below ground. Both tanks have a rectangular shape with PB2 having a volume of 12 m3 and
PB3 having a volume of 50 m3.
Mixing
The tanks are mixed by recirculation of the content. The same pump is used for both
recirculating and removing content. This is controlled by an actuator that regulates a 3 way
valve.
Connections
Manure tank 1 (PB2) is connected to the main cow stable on the incoming side and the mixing
tank on the outgoing side.
7
Manure tank 2 (PB3) is connected to the calf stable on the incoming side and the manure
storage tank (LT1) on the outgoing side. The content can also be pumped to the buffer tank
(BT1) by manually regulating several valves.
Sensors
Both manure tanks have level sensors to monitor the occupancy of the tank and to make sure
that no flooding will occur or the pumps will go dry.
Regulation/Automation
The outgoing pump is regulated by the level in the manure tank and in the mixing tank. A
maximum and minimum level is specified by the user in the control panel. The minimum
level is important in order to avoid that the pump goes dry and the maximum level is
important in order to avoid flooding of the tank. If the level reaches the minimum level the
outgoing pump will be inactivated, whereas if it reaches the maximum level the outgoing
pump will be activated in order to reach an acceptable level in the mixing tank.
Operation
At the moment, only manure tank 1 (PB1) is in operation. The manure is pumped from the
manure tank into the mixing tank.
2.1.2 Mixing tank
Figure 2-4 Photo of mixing tank.
8
A Waste containers for fruit and vegetables
B Feeder band connecting the funnel and the mixing tank
C Loading funnel for waste
D Disintegration unit with cutting knifes
E Mechanical lid for covering mixing tank
F Mixing tank
G Container for FeCl3 solution
Role
The role of the mixing tank is to mix the solid substrates with the manure.
Dimensions
The mixing tank is situated below ground and has a cylindrical shape with a total volume of
50 m3. The tank is covered with a lid to minimize the odors and keep away the rain water.
Mixing
The mixing is carried out with a submersible mixer and recirculation of the content. As for the
manure tank, the same pump is used for recirculating and pumping away the content,
controlled with an actuator that regulates a T-valve. The submersible mixer is manually
operated using an on/off button placed next to the control panel.
Figure 2-5 Photo of the buttons for controlling the submersible mixer.
9
Connections
The mixing tank is connected to the manure tank 1 (PB2) on the incoming side and the buffer
tank on the outgoing side.
Sensors
The mixing tank has a level sensor to monitor the occupancy of the tank and to make sure that
it will not flood or that the pump goes dry.
Regulation/Automation
The outgoing pump is regulated by the level of the mixing tank and the buffer tank. A
maximum and minimum level is specified by the user in the control panel. The minimum
level is important in order to avoid that the pump goes dry and the maximum level is
important in order to avoid flooding of the tank. If the level reaches the minimum level the
outgoing pump becomes inactive, whereas if it reaches the maximum level the outgoing pump
will be activated in order to reach an acceptable level in the buffer tank.
Operation
In the mixing tank, the manure from manure tank 1 is mixed with all the solid substrates. The
substrates are manually added with the help of a front loader, or a lift system for certain
containers. When the lift system is used, the substrate is also passed through a disintegration
unit equipped with knives for reducing the size of the solid material.
To load substrate through the front loader, the cover has to be opened from an open/close
panel located next to the tank.
Miscellaneous
In the mixing tank, FeCl3 solution is added manually from a container placed next to the tank.
X-ripper (to be installed)
Figure 2-6 Pictures of the X-ripper (Vogelsang).
10
Role
The role of the X-ripper is to reduce the particle size of the added solid substrate. Its robust
design, using the proven double-shaft system, allows for economical shredding of large
amounts of solids in liquid media.
Connections
The X-ripper is connected to the mixing tank.
Operation
The solid material is loaded into the receiving funnel and shredded by the X-ripper before
falling into the mixing tank. More detail description needs to be added once the X-ripper is
installed on the site.
Supplier
Company: Vogelsang Sverige AB
Adress: Duvesjön 450
SE – 442 92 Romelanda
Contact
person
Klas-Göran Brevik
Tel: +46 (0) 31 7512 70 0
E-mail: [email protected]
11
Old macerator
Figure 2-7 Photo of old macerator.
Role
The role of the old macerator is also to reduce the particle size of the added solid substrate.
Connections
The old macerator is connected to the mixing tank.
Regulation/Automation
The old macerator is controlled manually from a control panel located next to the unit.
Operation
The solid material is loaded into the receiving funnel where it is ground down and fed into the
mixing tank.
12
Substrate handling units
Figure 2-8 Photos of substrate handling units.
A Bunker silos
B Lifting device for 200 L barrels
C 200 L barrels
D 140 L waste containers
E Loading of glucose from a 200 L barrel
Many different types of substrates are added to the mixing tank. The substrates are either
added directly to the mixing tank with a front loader, or via the old macerator unit or the X-
ripper. Examples of how several substrates are processed and handled can be seen in Table
2-2.
13
Table 2-2 Example of several processed substrates.
Storage Pretreatment Front loader Maximum
storage time
Silage Bunker silo No Yes Several months
Potatoes 140 L waste
container, bunker
silo
X-ripper, old
macerator
Yes/No (with old
macerator)
1 month
Fruit and Vegetables 140 L waste
container
Old macerator No 1 week
Jam 200 L barrel No Yes 1 month
Glucose 200 L barrel Heated (winter) Yes Several months
Horse manure Bunker silo No Yes Several months
FeCl3 solution container
Biogas from anaerobic digestion of animal waste (i.e. manure) typically contains 500 to 3000
ppm of H2S, depending on the composition of solid substrates. Removal of H2S is needed to
reduce air pollution, protecting at the same time the power generation equipment, and
increasing the safety of the operations.
Figure 2-9 Photo of FeCl3 solution container.
Role
The role of the FeCl3 solution is to reduce the levels of H2S in the produced gas. The iron
precipitates out the sulfur and prevents the production of H2S in the digester.
14
Connections
The FeCl3 solution container is connected to the mixing tank.
Regulation/Automation
The FeCl3 solution container is operated with a manually switched tap.
Operation
Every day, a certain amount of FeCl3 solution is added into the mixing tank by the operator.
The addition of the solution is regulated by opening and closing a tap.
Front loader
Figure 2-10 Photo of the front loader.
Role
The role of the front loader is to transport some of the solid material from its storage unit and
to load it into the mixing tank.
Operation
The front loader is shared by the whole farm and should only be operated by personnel with
proper training. It has a few different lifting devices for different types of material. A device
formed like a scoop is normally used to handle loose material, like silage and horse manure,
while a specially designed device with attachment points is used to handle liquid or semisolid
materials in barrels, such as jam and glucose.
Miscellaneous
The lifting device for loading loose material has weighting cells for controlling the loaded
amount of material.
Since the front loader is shared by the whole farm, it is important to be handled with care.
15
2.1.3 Buffer tank
Figure 2-11 Photo of the buffer tank.
A Buffer tank
B Motor for pump
C Actuator for T-valve
D T-valve
E Recirculation pipe
F Pipe to digester
Role
The role of the buffer tank is to provide an additional place for the substrate to mix and be
further disintegrated before pumped into the digester.
Dimensions
The buffer tank is situated below the ground and has a rectangular shape with a total volume
of 12 m3. The tank is covered with a lid to minimize the odors and keep away the rain water.
Mixing
The buffer tank is mixed by recirculation of the content. The same pump is used for
recirculating and pumping away the content. This is controlled by an actuator that regulates a
valve in a T-connection.
16
Connections
The buffer tank is connected to the mixing tank (PB1) on the incoming side and the digester
(RK1) on the outgoing side.
Sensors
The buffer tank has a level sensor to monitor the occupancy of the tank and to make sure that
no flooding will occur or that the pump will go dry.
Regulation/Automation
The outgoing pump is controlled from the control panel where the user can regulate the
frequency of pumping and the amount of material pumped in during each cycle. A maximum
and minimum level can also be provided by the user. If the level reaches the minimum level
the outgoing pump will become inactive, whereas if it reaches the maximum level the
outgoing pump will be activated.
A flow alarm is activated if the level does not decline as much as it should when the outgoing
pump is turned on.
17
2.1.4 Digester
Figure 2-12 Photos of the digester and digestate pump.
A Ladder for climbing to digester roof
B Biogas outlet pipe
C Top cover and motor for mixer
D Digester
E Manhole cover
F Digestate feeding pump
Role
In the digester, the anaerobic degradation of the organic material in to biogas is taking place.
Dimensions
The digester has a cylindrical shape with a total volume of 300 m3.
Mixing
The content of the digester is mixed by a top mixer with impellers at two different levels. The
speed of the mixer can be controlled.
At the top of the mixer there are two specially designed rotor blades which prevent formation
of floating hard layers inside the digester. More detail description needs to be added once
rotor blades are installed on the site.
18
Connections
The digester is connected to the buffer tank on the incoming side and digestate storage 1 on
the outgoing side. There is also an outgoing biogas pipe from the top of the digester.
Sensors
The digester has three sensors
Bottom temperature sensor
Top temperature sensor
Level sensor
Regulation/Automation
The operation of the digester is controlled mainly in three ways:
1) The level in the digester is maintained by controlling the pump for the outgoing
sludge. The sought level is entered in the control panel and is maintained by activating
or deactivating the outgoing pump.
2) The temperature in the digester is maintained by controlling a shunt valve that
regulates the flow of heating water. A PID controller regulates the shunt valve based
on the difference between the setpoint temperature and the actual temperature. The
setpoint temperature, along with the P (Proportional), I (Integral) and D (derivative)
constants can be entered in the control panel.
3) The top mixer is controlled by an on/off timer as well as a direction setting in the
control panel.
Operation
Normally, feeding from the buffer tank is set to give a retention time in the digester of around
30 days. The temperature is normally set to be around 37 ºC and the slurry volume is
normally set to be around 270 m3 (i.e. the height of the slurry level is about 760 cm).
Miscellaneous
The digester has a manhole cover at the bottom, where it is possible to enter in the digester
when it is empty. There is also a smaller manhole cover on the top. There is a ladder on the
side of the digester, allowing the possibility to climb onto the digester roof.
Supplier
Company: Svenska Neuero
Adress: Sätuna Storegården
521 98 Broddetorp
Contact
person
Stefan Persson
Tel: 046-249630
E-mail: [email protected]
19
2.1.5 Digestate storage containers 1 & 2
Figure 2-13 Photos of digestate storage container 1 (upper) and digestate storage container 2 (bottom).
A Cover of digestate storage 1
B Digestate storage container 1
C Digestate storage container 2
Role
In the digestate storage container 1 & 2, the digestate is stored when coming from the digester
until used as a fertilizer.
Dimensions
Digestate storage container 1 has a total volume of 1600 m3 and digestate storage container 2
a total volume of 1500 m3.
Mixing
Digestate storage container 1 has two submersible mixers that are regulated via the control
panel. Digestate storage container 2 has no mixing.
20
Connections
The digestate storage container 1 is connected to the digester on the incoming side and the
digestate storage container 2 on the outgoing side. The digestate storage container 1 can also
be connected to the manure storage tank and the buffer tank.
The digestate storage container 2 is connected to the digestate storage container 1 on the
incoming side. The digestate storage container 2 is emptied by pumping its content into the
fertilizer tanks.
Sensors
There is a level sensor in the digester storage container 1.
Regulation/Automation
The digestate storage container 1 is filled with digestate from the digester using a pump. The
content of the digestate storage unit 1 is then flown by gravity force into the digestate storage
container 2.
Operation
The digestate storage container 1 is filled first when the digestate is pumped out from the
digester.
Miscellaneous
No gas from any of the digester storage units is collected. The digester storage container 1 has
an open cover only for preventing the rain water and digester storage container 2 has no cover
at all. The digester storage container 2 is mainly emptied during spring and fall, when the
fertilizer is needed for cultivating crops.
21
2.2 Operational units for storage, purification, analysis and distribution of biogas
2.2.1 Raw gas storage
Figure 2-14 Photos of raw gas storage.
A Raw gas storage container
B Gas pipe from pilot plant
C Valve for connection to pilot plant
D Water block
Role
The role of the raw gas storage unit is to store the produced raw gas in order to maintain a
stable flow to the gas utilization units (upgrading, burner and Stirling engine).
Connections
The raw gas storage unit is connected to the gas system of the plant. The pressure in the raw
gas storage unit and the gas fan in the gas room determine if the gas flows out from the
storage unit or not.
22
Sensors
The raw gas storage unit has two sensors:
A Level sensor (%), which can measure how full the storage unit is.
A Pressure sensor (mbar), which measures the pressure in the raw gas storage unit.
Operation
The gas storage unit is filled as the biogas produced from the reactor. The emptying is
dependent on the gas level in the storage unit as well as the status of the gas utilization units.
Normally, the upgrading unit is prioritized and activated when the level in the gas
storage is above 60 % and deactivated at a level below 20 %.
The Stirling engine is normally activated when the upgrading unit cannot take any
more gas (i.e. high pressure storage is full) and is also normally activated at levels
above 60 % and deactivated at a level below 20 %.
The gas burner is the third in line and is normally activated when the level of the gas
storage is above 80 % and deactivated at a level below 20%.
The torch is ignited if the pressure in the gas storage gets too high.
Miscellaneous
The raw gas storage has a water block controlling the release in the atmosphere of the excess
gas (i.e. when the pressure in the storage unit exceeds 13-14 mbar).
23
2.2.2 Gas room
Figure 2-15 Photos of gas room.
24
A Gas filter
B Incoming gas pipe
C Outgoing gas pipe to upgrading unit
D Outlet for gas sampling
E Condensation trap
F Outgoing gas pipe to Stirling engine
G Flow meter for measuring the flow to gas burner
H Flow meter for measuring total gas flow
I Gas fan
J Outgoing gas pipe for torch
K Outgoing gas pipe for gas burner
Role
The gas room is the core of the gas system at the biogas site and contains most of the sensors,
valves and fans. The unit for removing condensation is also located in the gas room, where
the gas sampling also takes place.
Connections
The gas room is connected to the gas storage/digester on the incoming side and the upgrading,
Stirling engine, gas burner and torch on the outgoing side.
Sensors
Four sensors are placed in the gas room:
two pressure sensors
two flow meters
Miscellaneous
The gas room contains a gas filter to make sure no particles are coming into any of the gas
utilization units.
25
2.2.3 Upgrading unit
Figure 2-16 Photo of upgrading unit (water scrubber).
A Upgrading unit
B Scrubber column
C Gas compressor
Role
The role of the upgrading unit is to upgrade the biogas to biomethane by removing the carbon
dioxide (CO2). The technique used is water scrubbing, i.e. dissolving the carbon dioxide into
water at high pressure.
Capacity
The upgrading unit can handle raw gas flows up to 18 m3/hour.
Connections
The upgrading unit is connected to the raw gas storage unit on the incoming side and the high
pressure storage on the outgoing side.
Regulation/Automation
The upgrading unit is activated when the sought level in the raw gas storage is obtained and
the high pressure storage is not full (below 170 bar). This is carried out by opening a valve
and activating the fan in the gas room.
Supplier
Company: Biorega AB
Adress: L Rya
SE - 314 92, Långaryd
Homepage: www.biorega.se
Contact person: Peter Karlsson
Tel: +46 (0)371 430 11
Email: [email protected]
26
2.2.4 High pressure gas storage
Figure 2-17 Photo of high pressure gas storage unit.
A High pressure gas storage for biomethane
B Pressure sensor
Role
The role of the high pressure gas storage unit is to store the upgraded biomethane at a high
pressure (230 bar) so it can be filled into vehicles using the standard gas filling system.
Connections
The high pressure gas storage unit is connected to the upgrading unit on the incoming side
and the gas pump on the outgoing side.
Sensors
A pressure sensor is used.
Operation
The high pressure storage unit is filled up when the upgrading unit is active. It is emptied
when the gas pump from the filling station is used.
27
2.2.5 Filling station
Figure 2-18 Photo of the filling station.
A Filling pump
B Payment system for gas filling
Role
The filling station allows the filling of the upgraded biomethane in corresponding vehicles.
Connections
The filling station is connected to the high pressure gas storage unit on the incoming side.
Sensors
The filling station has a flow meter that measures the amount of gas that is filled into a car.
Operation
A valve on the filling device opening connects the high pressure storage unit to the gas tank in
the car. The pressure difference between the two systems makes the gas flow from the high
pressure storage unit into the car reservoir until an equal pressure is achieved.
28
2.2.6 Stirling engine
Figure 2-19 Photo of the Stirling engine.
Role
The role of the Stirling engine is to produce electricity by utilizing the compression and
expansion of gas given from the heat produced from the combustion of biogas.
Capacity
The production capacity of the Stirling engine is 8 kW electricity, whereas the total capacity
(including heat) is 36 kW.
Connections
The Stirling engine is connected to the raw gas storage unit on the incoming side. The heating
system is lead through the Stirling engine, where it absorbs some of the produced heat. Before
the heating water reaches stirling engine, it is lead through a cooler (see heating/cooling
system below) to make sure the incoming water is at a low enough temperature. The leftover
products from the combustion are released into the atmosphere through a chimney.
29
Regulation/Automation
The Stirling engine is activated when the sought level in the raw gas storage is obtained and
the prioritized gas utilization units (upgrading unit) cannot consume more gas. This is carried
out by opening a valve and activating the fan in the gas room.
2.2.7 Gas burner
Figure 2-20 Photo of the gas burner.
Role
The role of the gas burners is to combust the incoming biogas and produce heat in the heating
system.
Capacity
According to the specification, the capacity of the gas burner is supposed to be 60 kW.
However, normally a lower capacity, close to 50 kW, is obtained.
Connections
The gas burner is connected to the raw gas storage unit on the incoming side. The heating
system is lead through the gas burner were it absorbs the produced heat. The leftover products
from the combustion are released into the atmosphere through a chimney in the roof.
30
Sensors
The gas burner is equipped with temperature sensors.
Regulation/Automation
The gas burner is activated when the sought level in the raw gas storage is obtained and the
prioritized gas utilization units cannot consume more gas. This is carried out by opening a
valve and activating the fan in the gas room.
2.2.8 Torch
Figure 2-21 Photo of the torch.
A Torch for excess biogas
Role
The role of the torch is to burn of any excess gas the other gas utilization units cannot
consume. This is carried out to avoid the release of the gas into the atmosphere.
Capacity
The torch is designed to handle gas flows up to 10 m3/h.
Connections
The torch is connected to the raw gas storage on the incoming side. The leftover products
from the combustion are released into the atmosphere.
31
Regulation/Automation
The torch is activated when the pressure in the raw gas storage exceeds a certain limit. This is
carried out by opening a valve and activating the fan in the gas room. The pressure that
activates the torch is specified in the control panel.
2.3 Control room
32
Figure 2-22 Photos of the control room.
A Pipe and valve controlling the substrate entering the digester
B Pipe and valve controlling the substrate leaving the digester
C Moisture analyzer
D Gas composition analyzer
E Digestate sampling hose
F Digestate pump
G Stirling engine
H Shunt valve regulating the heating of the digester
I Control panel
J Gas burner
K Control cabinet
L Computers and printer
M Work station
The control room is the place where the operation of the biogas plant is controlled via the
control panel. This is also the location of the Stirling engine, gas burner, large parts of the
heating/cooling system, as well as for simple substrate analysis. The control room also
contains a work station with a computer, where all data can be entered and accessed. In the
control room a number of tools (e.g., moisture analyzer, pH meter, portable gas analyzer) are
also available.
33
2.3.1 Control cabinet
Figure 2-23 Photos of the control cabinet.
A Control cabinet
B Control panel
The control cabinet is the place for the electronic communication interface. Here all the
operational units are centrally controlled. A short description of some of the units in the
control cabinet is presented below.
PLC
The PLC (Programmable Logical Controller) is a local computer that controls all processes in
the plant. It receives incoming signals from sensors and sends out outgoing signals to control
pumps, valves, etc.
Relays
The relays determine if certain processes or units are active or not (e.g. motors, valves, etc).
This is performed with the help of electromagnets that open or close certain high voltage
electrical circuits using low voltage or low current circuits.
34
Digester top mixer frequency converter
It regulates the speed of the top mixer in the digester by regulating the frequency of its power
input. It operates within a 0-60 Hz interval.
2.3.2 Work station
Figure 2-24 Photo of the work station.
The work station is the place where all information regarding the process is gathered and
processed. The process data from the datalogger in the control panel can also be downloaded
onto a computer at the work station.
35
2.4 Heating/cooling system
Figure 2-25 Photo of the heating/cooling system.
A Shunt valve
B WM1
C Cooler
The heating/cooling system at the site is connected to the same system that Plönninge
Agricultural High School also uses. This makes it possible to easily utilize the extra heat
produced from the gas burner. A measuring device (WM1) measures the heat energy
produced and consumed by the plant by monitoring the incoming and outgoing heating water.
The only operational unit that is heated by the heating/cooling system is the digester. This
process is controlled by a shunt valve (A) that acts on signal from a PID controller in the PLC.
The heat energy that is consumed in the digester is monitored by the device WM1 (B).
The heating/cooling system is also used to cool the upgrading unit and the Stirling engine. To
make sure the Stirling engine can operate properly, a cooler (C) is connected to the
heating/cooling system just ahead of the engine. This is necessary since the Stirling engine
requires cold incoming water to be able to handle the excess heat produced in the
compression/expansion process.
36
3 CONTROL PANEL
Figure 3-1 Photo of control cabinet with control panel.
Many parts of the process can be monitored and controlled from the control panel. A touch
screen is used to navigate between the different menus. It is developed by Apptronic in 2004
and has been continuously updated over the years.
The control panel can be found on one of the control cabinet doors in the control room (Figure
3-1).
37
In this section all the menus in the control panel are described. The menus are presented with
a screenshot together with a table of all of their functionalities.
3.1 Start menu
Figure 3-2 Screenshot of start menu.
From the start menu (Figure 3-2) you can navigate between the four different main menus
(process overview, energy measuring, alarm list and system). A list of the functionalities in
the start menu can be seen in Table 3-1.
Table 3-1 Functionalities of the start menu.
Name Action Information displayed
A Översikt Go to process overview menu
B Energimätning Go to energy measuring menu
C Larm Go to alarm list
D System Go to system menu
38
3.2 Process overview (Huvud)
Figure 3-3 Screenshot of process overview (översikt) menu.
From the process overview menu (Figure 3-3) the different menus available in the control
panel including the operational panels, alarm list, data logger and energy measuring can be
accessed. In Table 3-2 a list of all functionalities in the process overview can be seen.
Table 3-2 Functionalities of process overview menu.
Name Action Information displayed
A Blandningstank Go to mixing tank menu Mixing tank pump on (green) or off (white)
B Pumpbrunn 2 Go to manure tank 1 menu Manure tank 1 pump on (green) or off (white)
C Prumpbrunn3 Go to manure tank 2 menu Manure tank 2 pump on (green) or off (white)
D Bufferttank Go to buffer tank menu Buffer tank pump on (green) or off (white)
E Rötkammare Go to digester menu
F Efterrötkammare Go to digestate storage menu
G Gasmätning Go to gas measuring menu Raw gas storage pressure (mbar)
H Gasanvändning Go to gas utilization menu
I Huvud Go to start menu
J Larm Go to alarm list
K Energimätning Go to energy measuring menu
L Loggning Go to data logger
Separate information displayed
1 “pump symbol” Pump to digestate storage on (green) or off (white)
2 Producerad energi Produced energy for the current day (kWh)
3 Förbrukad energi Consumed energy for the current day (kWh)
39
3.2.1 Mixing tank menu (Blandningstank)
Figure 3-4 Screenshot of the mixing tank menu.
From the Mixing tank (Figure 3-4) menu, the operation of the mixing tank can be controlled.
You can choose to have it in automatic mode (the pumping and mixing are automatically
controlled) or manual mode. A list of the functionalities in the mixing tank menu can be seen
in Table 3-3.
Table 3-3 Functionalities of mixing tank menu.
Name Action Information displayed
A Inställningar Mixing tank settings menu
B Driftsläge Change between automatic and manual operation of the pump
If pump operation is in automatic or manual mode
C Ventil AV1 Change between circulation and feeding
mode for the pump If pump direction is in circulation or feeding
mode
D Pump P1 Turn pump on or off in manual mode If pump is on (0) or off (1)
E Översikt Process overview menu
F Larm Alarm list
G Energimätning Energy measuring menu
H GP 1 Buffer tank menu
I PB2 Manure tank 1 menu
Separate information displayed
1 “Level indicator” Liquid level in mixing tank as well as lower and upper boundaries
2 Nivå i PB1 Liquid level and corresponding volume in mixing tank
3 “Valve symbol”
AV1
If pump direction is in circulation or feeding mode
4 “Pump symbol” P1 If pump is on or off
40
Mixing tank settings menu
Figure 3-5 Screenshot of the mixing tank settings menu.
Functionalities
From the mixing tank settings menu, instructions on how the mixing tank should be operated
can be set. Parameters such as circulation time for each feeding of material as well as the
upper and lower level boundary of the mixing tank can be controlled. A list of the
functionalities in the mixing tank menu can be seen in Table 3-4.
Table 3-4 Functionalities of mixing tank settings menu.
Name Action Information displayed
A Cirkulationstid Set time for circulation ahead of
feeding
Current time for circulation ahead of feeding
B Övre nivå i tank Upper boundary for liquid level Current upper boundary for liquid level
C Undre nivå i tank Lower boundary for liquid level Current lower boundary for liquid level
D Tillbaka Go back to the Mixing tank menu
41
3.2.2 Manure tank 1 (Pumpbrunn 2)
Figure 3-6 Screenshot of manure tank 1 menu.
Functionalities
From the manure tank 1 menu (Figure 3-6) the operation of the manure tank 1 can be
controlled. It can be operated in automatic mode (the pumping and mixing is automatically
controlled) or manual mode. A list of the functionalities in the manure tank menu can be seen
in Table 3-5.
Table 3-5 Functionalities of manure tank 1 menu.
Name Action Information displayed
A Inställningar Manure tank 1 settings menu
B Driftsläge Change between automatic and
manual operation of the pump
If pump operation is in automatic or manual
mode
C Ventil AV2/3 Change between circulation and
feeding mode for the pump
If pump direction is in circulation or feeding
mode
D Pump P2 Turn pump on or off in manual
mode
If pump is on (0) or off (1)
E Översikt Process overview menu
F Larm Alarm list
G Energimätning Energy measuring menu
H PB1 Mixing tank menu
I PB3 Manure tank 2 menu
Separate information displayed
1 “Level indicator” Liquid level in manure tank 1 as well as lower and upper boundaries
2 Nivå i PB2 Liquid level and corresponding volume in manure tank 1
3 “Valve symbol”
AV2
If pump direction is in circulation or feeding mode
4 “Pump symbol” P2 If pump is on or off
42
Manure tank 1 settings menu
Figure 3-7 Screenshot of manure tank 1 settings menu.
Functionalities
From the manure tank 1 settings (Figure 3-7) menu, the instructions on how the manure tank 1
should be operated can be set. Parameters such as circulation time before each feeding of
material as well as the upper and lower level boundary of the manure tank 1 can be controlled.
A list of the functionalities in the manure tank 1 menu can be seen in Table 3-6.
Table 3-6 Functionalities of manure tank settings menu.
Name Action Information displayed
A Cirkulationstid Set time for circulation (mixing)
before feeding
Current time for circulation (mixing) before
feeding
B Övre nivå i tank Upper boundary for liquid level Current upper boundary for liquid level
C Undre nivå i tank Lower boundary for liquid level Current lower boundary for liquid level
D Tillbaka Manure tank 1 menu
43
3.2.3 Manure tank 2 (Pumpbrunn 3)
Figure 3-8 Screenshot of manure tank 2 menu.
Functionalities
From the manure tank 2 menu (Figure 3-8), the operation of the manure tank 2 can be
controlled. It can be operated in automatic mode (the pumping and mixing is automatically
controlled) or manual mode. A list of the functionalities in the manure tank 2 menu can be
seen in Table 3-7. Table 3-7 Functionalities of manure tank 2 menu.
Name Action Information displayed
A Inställningar Manure tank 2 settings menu
B Driftsläge Change between automatic and
manual operation of the pump
If pump operation is in automatic or manual
mode
C Ventil AV5 Change between circulation and
feeding mode for the pump
If pump direction is in circulation or feeding
mode
D Pump P3 Turn pump on or off in manual mode If pump is on (0) or off (1)
E Översikt Process overview menu
F Larm Alarm list
G Energimätning Energy measuring menu
H PB1 Mixing tank menu
I PB3 Manure tank 1 menu
Separate information displayed
1 “Level indicator” Liquid level in manure tank 2 as well as lower and upper boundaries
2 Nivå i PB3 Liquid level and corresponding volume in manure tank 2
3 “Valve symbol” AV5 If pump direction is in circulation or feeding mode
4 “Pump symbol” P3 If pump is on or off
44
Manure tank 2 settings menu
Figure 3-9 Screenshot of the manure tank 2 settings menu.
Functionalities
From the manure tank 2 settings (Figure 3-9) menu, the instructions on how the manure tank 2
should be operated can be set. Among the parameters which can be set are the circulation time
for each feeding of material as well as the upper and lower level boundary of the manure tank
2. The functionalities presented in the manure tank 2 settings menu are listed in Table 3-8.
Table 3-8 Functionalities of the manure tank 2 settings menu.
Name Action Information displayed
A Cirkulationstid Set time for circulation ahead of
feeding
Current time for circulation ahead of feeding
B Övre nivå i tank Upper boundary for liquid level Current upper boundary for liquid level
C Undre nivå i tank Lower boundary for liquid level Current lower boundary for liquid level
D Tillbaka Manure tank 2 menu
45
3.2.4 Buffer tank menu (Bufferttank)
Figure 3-10 Screenshot of the buffer tank menu.
Functionalities
From the buffer tank menu (Figure 3-10), the operation of the buffer tank can be controlled.
The operation can be set in automatic mode (the pumping and mixing is automatically
controlled) or manual mode. A list of the functionalities in the buffer tank menu can be seen
in Table 3-9.
Table 3-9 Functionalities of the buffer tank menu.
Name Action Information displayed
A Inställningar Buffer tank settings menu
B Driftsläge Change between automatic and
manual operation of the pump
If pump operation is in automatic or manual
mode
C Ventil AV11 Change between circulation and
feeding mode for the pump
If pump direction is in circulation or feeding
mode
D Pump P4 Turn pump on or off in manual mode If pump is on (0) or off (1)
E Flödesmätning Go to Flödesmätning menu
F Översikt Process overview menu
G Larm Alarm list
H Energimätning Energy measuring menu
I PB3 Manure tank 2 menu
J RK1 Digester menu
Separate information displayed
1 “Level indicator” Liquid level in buffer tank as well as lower and upper boundaries
2 Nivå i PB3 Liquid level and corresponding volume in buffer tank
3 “Valve symbol” AV11 If pump direction is in circulation or feeding mode
4 “Pump symbol” P4 If pump is on or off
46
Buffer tank settings menu
Figure 3-11 Screenshot of the buffer tank settings menu.
Functionalities
From the buffer tank settings (Figure 3-11) menu, the instructions on how the buffer tank
should be operated can be set. The circulation time for each feeding of material as well as the
upper and lower level boundary of the buffer tank can be set here. The feeding to the digester
as well as setting from which operational unit the buffer tank is filled. A list of the
functionalities listed in the buffer tank settings menu can be seen in Table 3-8.
Table 3-10 Functionalities of the buffer tank settings menu.
Name Action Information displayed
A Cirkulationstid Set time for circulation ahead of
feeding
Current time for circulation ahead of feeding
B Övre nivå i tank Upper boundary for liquid level Current upper boundary for liquid level
C Undre nivå i tank Lower boundary for liquid level Current lower boundary for liquid level
D Beskickningsintervall Set how often the digester is fed Current setting for how often the digester is fed
(min)
E Beskickningsmängd Set how much is fed each time Current setting for how much is each time (m3)
F Nivåhållningsfunktion Set which tank that should feed to the
buffer tank
Current order of tanks that should pump to the he
buffer tank
G Nivåhöjning Set additional margin of height for
liquid filling when the lower boundary
level is reached
Current additional margin of height for liquid
filling when the lower boundary level is reached
H Tillbaka Buffer tank menu
47
Buffer tank flow measuring menu
Figure 3-12 Screenshot of the buffer tank flow measuring menu.
Functionalities
From the buffer tank flow measuring menu (Figure 3-12), the feeding of the digester can be
followed. A list of the functionalities listed in the buffer tank flow measuring menu can be
seen in Table 3-11.
Table 3-11 Functionalities buffer tank flow measuring menu.
Name Action Information displayed
A Tillbaka Back to buffer tank menu
Separate information displayed
1 Momentant flöde Current flow rate to digester
2 Beskickad mängd Volume counter for each individual feeding cycle
3 Dygnsmängd Volume fed to digester current day (starts at 00:00)
4 Total mängd Total amount fed to digester since flow meter was installed
48
3.2.5 Digester menu (Rötkammare)
Figure 3-13 Screenshot of the digester menu.
Functionalities
From the digester menu (Figure 3-13) the operation of the digester can be controlled. The
operation can be set to automatic mode (the pumping to the digestate storage is automatically
controlled) or manual mode. Changing the settings for the temperature control and the mixer
can also be performed in this menu. A list of the functionalities in the digester menu is
presented in Table 3-12.
Table 3-12 Functionalities of the digester menu.
Name Action Information displayed
A Inställningar Digester settings menu
B Driftsläge Change between automatic and
manual operation of the pump
If pump operation is in automatic or manual
mode
C Ventil AV11 Change between circulation and
feeding mode for the pump
If pump direction is in circulation or feeding
mode
D Pump P4 Turn pump on or off in manual
mode
If pump is on (0) or off (1)
E Temp I RK1 Digester temperature control
menu
Current temperature in digester
F “Mixer symbol” OM5 Mixer settings menu If mixer is on or off
G Översikt Process overview menu
H Larm Alarm list
I Energimätning Energy measuring menu
49
J BT1 Buffer tank storage
K ERK1 Digestate storage menu
Separate information displayed
1 “Level indicator” Liquid level in digester as well as lower and upper boundaries
2 Nivå i RK1 Liquid level and corresponding volume in digester
3 “Pump symbol” P6 If digestate pump is on or off
Digester settings menu
Figure 3-14 Screenshot of the digester settings menu.
Functionalities
From the digester settings (Figure 3-14) menu, the instructions on how the digester should be
operated can be set. The setpoint for the digester temperature and the lower level boundary
can be specified in this menu. A list of the functionalities in the digester settings menu can be
seen in Table 3-12.
Table 3-13 Functionalities of the digester settings menu.
Name Action Information displayed
A Undre nivå I tank Set lower boundary for liquid level Current lower boundary for liquid level (cm)
B Temp. börvärde Set temperature setpoint Current upper boundary for liquid level (ºC)
H Tillbaka Digester menu
50
Digester temperature menu
Figure 3-15 Screenshot of the digester temperature menu.
Functionalities
From the digester temperature menu (Figure 3-15), the set point for the digester temperature
can be set and the latest temperature trends can be followed. A list of the functionalities in the
digester temperature control menu can be seen in Table 3-14.
Table 3-14 Functionalities of the digester temperature control menu.
Name Action Information displayed
A Börvärde Set the digestate temperature setpoint Current digester temperature setpoint (°C)
B REGULATOR Go to digester temperature control menu
C Tillbaka Back to digester menu
Separate information displayed
1 Temp TC50 Current temperature in from lower sensor in digester
2 Temp TC51 Current temperature in upper sensor in digester
3 “Graph” Temperature trends for the upper and lower sensor for the last 4 days
51
3.2.5.1.1 Digester temperature control menu
Figure 3-16 Screenshot of the digester temperature control menu.
Functionalities
In the digester temperature control menu (Figure 3-16), the control parameters for the PID
controller that regulates the digester temperature can be modified. A list of the functionalities
in the digester temperature control menu can be seen in Table 3-15.
Table 3-15 Functionalities of the digester temperature control menu.
Name Action Information displayed
A K-värde Set the K constant (proportional coefficient) Current value for K constant
B I-värde Set the I constant (integral coefficient) Current value for I constant
C D-värde Set the D constant (derivative coefficient) Current value for D constant
D Samplingsperiod Set the sampling frequency (0=continuous) Current sampling frequency
E Min. Set the minimum controller output Current minimum output
F Max. Set the maximum controller output Current maximum output
Separate information displayed
1 Utstyrt värde Current controller output (signal to shunt valve)
2 Är Current digester temperature
3 Bör Digester temperature setpoint
4 Ut Current controller output (signal to shunt valve)
52
3.2.6 Digestate storage unit (Efterrötkammare)
Figure 3-17 Screenshot of the digestate storage unit menu.
Functionalities
From the digestate storage unit menu (Figure 3-17), the operation of the digestate storage unit
1 and the manually control of the mixers in the digestate storage unit 1 can be controlled. A
list of the functionalities listed in the digestate storage unit menu can be seen in Table 3-16.
Table 3-16 Functionalities of the digestate storage unit menu.
Name Action Information displayed
A Inställningar Digestate storage unit 1 settings
menu
B ERK1 till LT1 Pumping from digestate storage
unit to manure storage unit menu
C Omrörare OM60/61 Set digestate storage unit 1 mixers
on or off
If mixers is on (0) or off (1)
D Översikt Process overview menu
E Larm Alarm list
F Energimätning Energy measuring menu
G RK1 Digester menu
H GAS M Gas measuring menu
Separate information displayed
1 “Level indicator” Liquid level in digestate storage 1
2 Nivå i ERK1 Liquid level and corresponding volume in digestate storage 1
3 “Mixer symbol” OM60 If mixer OM60 is on or off
4 “Mixer symbol” OM61 If mixer OM61 is on or off
53
Settings menu of the digester storage unit
Figure 3-18 Screenshot of the digestate storage unit settings menu.
Functionalities
From the settings menu of the digestate storage unit (Figure 3-18), the instructions for the
operation of the digestate storage unit can be controlled by setting an upper level boundary.
When the upper level is reached, an alarm is activated. A list of the functionalities in the
digestate storage unit 1 settings menu can be seen in Table 3-17.
Table 3-17 Functionalities of the digestate storage settings menu.
Name Action Information displayed
A Övre nivå I tank Set upper boundary for liquid level Current upper boundary for liquid level (cm)
B Tillbaka Back to digestate storage menu
54
Pumping from digestate storage unit to manure storage unit (ERK1 till LT1)
Figure 3-19 Screenshot of pumping from digestate storage to manure storage menu.
Functionalities
From the settings menu of the digestate storage settings (Figure 3-19) menu, the instructions
on how to pump from the digestate storage unit to manure tank unit 1 are specified. Setting
pumping duration and time for starting and stopping the pump can also be performed in this
menu. A list of the functionalities in the menu for pumping from digestate storage unit to
manure storage unit can be seen in Table 3-18.
Table 3-18 Functionalities of the menu for pumping from digestate storage unit to manure storage unit.
Name Action Information displayed
A Pumpning ska pågå i Set duration time for pumping Current set duration time for pumping
B Starta Start and stop pumping If the pump can be started or stopped
C Tillbaka Back to digestate storage menu
Separate information displayed
1 Förlupen tid How long time the pump has been active since started
55
3.2.7 Gas measuring menu (Gasmätning)
Figure 3-20 Screenshot of the gas measuring menu.
Functionalities
From the gas measuring menu (Figure 3-20), the current gas flows, raw gas storage pressure
as well as operation of the torch can be followed. A list of the functionalities in the gas
measuring menu can be seen in Table 3-19.
Table 3-19 Functionalities of the gas measuring menu.
Name Action Information displayed
A GM1 Go to gas flow meter menu Current flow rate in flow meter 1
B GM3 Go to gas flow meter menu Current flow rate in flow meter 2 (gas
burner)
C Inställningar Go to gas measuring settings
menu
D Översikt Process overview menu
E Larm Alarm list
F Energimätning Energy measuring menu
G ERK1 Digestate storage menu
H GAS Gas utilization menu
Separate information displayed
1 PC1 Current pressure in raw gas storage
2 GFA1 If torch is on (green) or off (white) and current days online time of torch
3 GF1 If gas pump in on (green) or off(white)
56
Gas measuring settings menu
Figure 3-21 Screenshot of the gas measuring settings menu.
Functionalities
From the gas measuring settings menu (Figure 3-21), the raw gas storage pressure limit for
activating the torch can be set. A list of the functionalities in the gas measuring settings menu
can be seen in Table 3-20.
Table 3-20 Functionalities of the gas measuring settings menu.
Name Action Information displayed
A Tändning av gasfackla Set minimum raw gas storage
pressure for activation of torch
Current minimum raw gas storage
pressure for activation of torch (mbar)
B Tillbaka Go to back to gas measuring
menu
57
Gas flow meters menu
Figure 3-22 Screenshot of the gas flow meters menu.
Functionalities
From the gas flow meters menu (Figure 3-22), the process parameters of the two gas flow
meters in the system can be followed. A list of the functionalities in the gas flow meters menu
can be seen in Table 3-21.
Table 3-21 Functionalities of the gas flow meters menu.
Name Action Information displayed
A Tillbaka Back to gas measuring meter
Separate information displayed
1 Momentat (GM1) Current value for gas flow meter (total gas flow) (m3/h)
2 Dygnsvärde (GM1) Gas produced the current day (total gas flow) (m3/d)
3 Totalt (GM1) Total gas production of the plant (total gas flow) m3
4 Momentat (GM3) Current value for gas flow meter (gas burner) (m3/h)
5 Dygnsvärde (GM3) Gas produced the current day (gas burner) (m3/d)
6 Totalt (GM3) Total gas production of the plant (gas burner) (m3)
58
3.2.8 Gas consumption menu (Gasanvändning)
Figure 3-23 Screenshot of the gas consumption menu.
Functionalities
From the gas consumption menu (Figure 3-23), the gas consumption units can be monitored.
The status of several gas alarm systems can also be followed in this menu. A list of the
functionalities in the gas consumption menu can be seen in Table 3-22.
Table 3-22 Functionalities of gas consumption menu.
Name Action Information displayed
A Inställningar Go to gas utilization settings menu
B Översikt Process overview menu
C Larm Alarm list
D Energimätning Energy measuring menu
E GAS M Gas measuring menu
F PB1 Mixer tank menu
Separate information displayed
1 GASLAGER Level in raw gas layer (%)
2 GASVARNARE Level of gas alarm (not functioning)
3 GASPANNA If gas burner is on (green) or off (white) and on time the current day so far
4 STIRLING If stirling engine is on (green) or off (white) and on time the current day so far
5 FORDONSGAS If upgrading unit is on (green) or off (white) and on time the current day so far
59
Gas consumption settings menu
Figure 3-24 Screenshot of the gas consumption settings menu.
Functionalities
From the gas consumption settings menu (Figure 3-24), the settings controlling the levels for
the upgrading unit, Stirling engine and the gas burner can be set. This is carried out by
specifying a filling level of the raw gas storage unit at which the gas consumption should be
activated, as well as a corresponding level when it should be deactivated. A list of the
functionalities in the gas consumption settings menu can be seen in Table 3-23.
Table 3-23 Functionalities of gas flow meter menu.
Name Action Information displayed
A Start (Fordonsgasanl.) Set raw gas storage level to activate
upgrading unit
Current raw gas storage level to activate
upgrading unit
B Stopp (Fordonsgasanl.) Set raw gas storage level to deactivate
upgrading unit
Current raw gas storage level to
deactivate upgrading unit
C Start (Sterlingmotor Set raw gas storage level to activate
Stirling unit
Current raw gas storage level to activate
Stirling unit
D Stopp (Sterlingmotor Set raw gas storage level to deactivate
Stirling unit
Current raw gas storage level to
deactivate Stirling unit
E Max (Gaspanna) Set the maximum raw gas storage level
for the gas burner
Current the maximum raw gas storage
level for the gas burner
F Start (Gaspanna) Set raw gas storage level to activate gas
burner unit
Current raw gas storage level to activate
gas burner unit
G Stopp (Gaspanna Set raw gas storage level to deactivate gas
burner unit
Current raw gas storage level to
deactivate gas burner unit
H Gaslarm Set gas alarm level to give gas alarm Current gas alarm level to give gas alarm
I Tillbaka Back to gas utilization menu
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3.3 Data logger (Logging)
Figure 3-25 Screenshot of the data logger menu.
Functionalities
From the data logger menu (Figure 3-25) the three different loggers in the control panel can
be accessed. A list of the functionalities in the data logger menu can be seen in Table 3-24.
Table 3-24 Functionalities of data logger menu.
Name Action Information displayed
A Loggning 1 Go to Logger 1 menu
B Loggning 2 Go to Logger 2 menu
C Loggning 3 Go to Logger 3 menu
D Läs av nu View the latest collected data points
E Nollställ Erase the loggers
F Huvud Back to start menu
G Översikt Go to process overview menu
H Larm Go to alarm list
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3.3.1 Logger 1
Figure 3-26 Screenshot of the Logger 1 menu.
Functionalities
From the logger 1 menu (Figure 3-26), the parameters stored in the logger can be seen and
their trends for the four last days can be monitored. A list of the functionalities in the logger 1
menu can be seen in Table 3-25.
Table 3-25 Functionalities of logger 1 menu.
Name Action Information displayed
A Tillbaka Back to data logger menu
B Loggning 2 Go to logger 2 menu
C Loggning 3 Go to logger 3 menu
Separate information displayed
1 LOGGER 1 Parameters stored in logger 1
2 “Graph” Four day trend lines for parameters stored in logger 1
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3.3.2 Logger 2
Figure 3-27 Screenshot of the Logger 2 menu.
Functionalities
From the logger 2 menu (Figure 3-27), the parameters stored in the logger can be seen and
their trends for the four last days can be monitored. A list of the functionalities in the logger 2
menu can be seen in Table 3-26.
Table 3-26 Functionalities of logger 2 menu.
Name Action Information displayed
A Tillbaka Back to data logger menu
B Loggning 1 Go to logger 1 menu
C Loggning 3 Go to logger 3 menu
Separate information displayed
1 LOGGER 2 Parameters stored in logger 2
2 “Graph” Four day trend lines for parameters stored in logger 2
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3.3.3 Logger 3
Figure 3-28 Screenshot of Logger 3 menu.
Functionalities
From the logger 3 menu (Figure 3-28), the parameters stored in the logger can be seen and
their trends for the four last days be monitored. A list of the functionalities in the logger 3
menu can be seen in Table 3-27.
Table 3-27 Functionalities of the logger 3 menu.
Name Action Information displayed
A Tillbaka Back to data logger menu
B Loggning 1 Go to logger 1 menu
C Loggning 2 Go to logger 2 menu
Separate information displayed
1 LOGGER 3 Parameters stored in logger 3
2 “Graph” Four day trend lines for parameters stored in logger 3
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3.4 Energy measuring (Energimätningar)
Figure 3-29 Screenshot of the energy measuring menu.
Functionalities
From the energy measuring menu (Figure 3-29), the amount of energy that has been
consumed and produced can be monitored. A list of the functionalities in the energy
measuring menu can be seen in Table 3-28.
Table 3-28 Functionalities of energy measuring menu.
Name Action Information displayed
A Huvud Back to start menu
B Översikt Got to process overview menu
C Larm Go to alarm list
Separate information displayed
1 Totalvärden Readings of totally produced (blue) and consumed (red) energy
2 Dygnsvärden Readings of produced (blue) and consumed (red) energy for the current day
3 “Graph” Trend lines of the produced (blue) and consumed (red) energy
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3.4.1 Alarm list (Larm)
Figure 3-30 Screenshot of the alarm list.
Functionalities
From the gas alarm list (Figure 3-30) the gas consumption units can be monitored. The status
of several gas alarm systems can also be followed in this menu. A list of the functionalities in
the gas consumption menu can be seen in Table 3-29.
Table 3-29 Functionalities of alarm list.
Name Action Information displayed
A ESC Go back to previous menu
B “ Arrow up” Go up in list
C “Checkmark” Acknowledge alarm
D “Magnifying glass” Zoom in
E “Wristwatch” Display the time for the alarms
F “Arrow down” Go down in list
Separate information displayed
1 “Alarm list” Current alarms in list and if they are active (red) or acknowledged (grey)
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4 ANALYSIS AND MONITORING
There is an increasing need to analyze the liquid or solid raw materials before their use as
feedstock (substrates) in anaerobic digestion processes and also to monitor suitable process
parameters which can give early indications of imbalances in the microbial system and early
warnings of external disturbances.
4.1 Determination of feedstock characteristics
Biogas can be produced from a broad range of substrates that are suitable for anaerobic
digestion, e.g. manure, residual sludge, energy crops, municipal solid waste and industrial
waste. Operation of a pilot and/or full-scale anaerobic digester working on a single substrate
or in a co-digestion mode requires analysis of each substrate. The substrate should be
characterised with regard to pH, moisture content, total (TS) and volatile solids (VS) and also
to its potential to produce bio-methane.
4.1.1 pH
pH is a measure of the acidity/alkalinity of a solution. A neutral solution (H2O) has a pH of 7.
Alkaline or basic solutions have a pH higher than 7 and acidic solutions less than 7. pH is
defined as negative decimal logarithm of the hydrogen concentration in a solution; a low pH
indicates a high concentration of hydrogen ions [H+], while a high pH indicates a low
concentration.
pH = − log[H+] (1)
pH can be measured experimentally using a pH sensor, which consists of an ion-selective
electrode covered with a glass membrane and a reference electrode (e.g. calomel or silver
chloride electrode).The pH sensor measure a potential difference between the ion-selective
and the reference electrodes, and this potential difference is dependent of hydrogen
concentration according to the Nernst equation:
E = E0 +RT
nFln[H+] (2)
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Figure 4-1 Photo and schematic representation of a pH sensor.
The pH value of the substrate influences the growth of microorganisms; most methanogens
and acetogens grow best near neutral pH conditions, whereas acidogens prefer to live in weak
acidic conditions.
4.1.2 Moisture content
Moisture content (MC) is the quantity of water contained in a sample. The gravimetric
method is a widely used method for determination of trace amounts of water in a sample. This
can be done by drying a known amount of sample in an oven.
The moisture analyzer is based on the principle of thermogravimetric analysis: the sample is
weighted both before and after drying (using a 400 W halogen lamp as a heating source); the
water content is calculated as the ratio between the difference in amounts of the sample before
(mWet) and after drying (mDried) and the initial amount of sample, and the moisture content is
usually expressed as weight %.
𝑀𝐶 % =𝑚𝑊𝑒𝑡 −𝑚𝐷𝑟𝑖𝑒𝑑
𝑚𝑊𝑒𝑡× 100 (3)
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Figure 4-2 Photo of the moisture analyzer used for the determination of the total solids of a target sample.
The total content of solids is a measure of the amount of material remaining after all the water
has been evaporated.
𝑇𝑆 % =𝑚𝐷𝑟𝑖𝑒𝑑
𝑚𝑊𝑒𝑡× 100 = 100 − 𝑀𝐶 (%) (4)
4.1.3 Total (TS) and volatile solids (VS)
The dry matter, i.e. all inorganic and organic compounds, is often expressed as TS and can be
measured according to a standard protocol. For a given biomass sample, it is necessary to heat
the sample up to 105 °C in order to remove all water content.
VS is represented by the organic compounds in the sample. After finishing the TS
measurement, heating the sample up to 550 °C for two hours should be continued for burning
up the organic matter. The weight difference between the sample after heating at 105 and 550
°C reflects the VS content of the biomass.
The next three steps are usually followed to determine the TS and VS of a target sample:
1). Preparation
a) Heat a dish to 550 °C for 1 h.
b) Place the dish in a desiccator for cooling.
2). TS determination
a) Weigh the dish and record this value.
b) Add 2-3 ml of a representative sample into the dish.
c) Place the dish with the sample in an oven preheated to 105 °C and allow the volatiles
to evaporate for 20 h.
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Figure 4-3 The main steps performed for TS determination.
3). VS determination
a) Take the dish out of the oven and allow it to cool to room temperature in a desiccator.
b) Weigh the dish and record the value.
c) Transfer this dish into a furnace pre-heated to 550 °C (ignition).
d) After 2 h, take the dish out of the furnace and cool it to RT in a desiccator.
e) Weigh the dish and record the value.
Figure 4-4 The main steps performed for VS determination.
TS is calculated as the ratio between the amount of dried sample (mDried) and the initial
amount of wet sample (mWet), whereas VS is calculated as the ratio between the difference in
the amount of sample after drying and burning (mBurned) and the initial amount of sample.
𝑇𝑆 % =𝑚𝐷𝑟𝑖𝑒𝑑
𝑚𝑊𝑒𝑡× 100 (5)
𝑉𝑆 % =𝑚𝐷𝑟𝑖𝑒 𝑑−𝑚𝐵𝑢𝑟𝑛𝑒𝑑
𝑚𝐷𝑟𝑖𝑒𝑑× 100 (6)
4.1.4 Biochemical methane potential (BMP) test
A laboratory-scale procedure in which substrates are characterized and then evaluated using
the biochemical methane potential (BMP) analysis is usually carried out in the first step. This
test provides a preliminary indication of the biodegradability of a substrate and of its potential
to produce methane via anaerobic digestion.
The conventional BMP assay involves incubating a substrate inoculated with anaerobic
bacteria for a period of 30 to 60 days, commonly at 37 ºC, and monitoring the biogas
production and its composition throughout the test. Most such tests require a relatively high
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workload for manual sampling of the produced gas at different time points, followed by
analysis, data recording and processing.
The Automatic Methane Potential Test System (AMPTS) II follows the same analysing
principles as conventional biochemical methane potential tests, which make the results fully
comparable with common methods. However, in an AMPTS, the sampling, analysis and
recording are fully integrated and automated, the bio-methane production being recorded
continuously 24 h per day, 7 days per week with minimal workload. The system is able to
analyse substrates with or without pre-treatment in order to allow biogas producers to
determine the methane production potential and degradation profile of any substrate,
providing the optimum co-digestion possibilities, retention times and plant utilisation.
Figure 4-5 Photo of AMPTS and a screenshot with the graph page.
The AMPTS provides the following advantages over conventional BMP tests: (i) automated
analytical procedure, reducing workload and time, (ii) on-line and real-time data logging of
total biogas or bio-methane production and flow rate, (iii) user friendly interface for real-time
data display and analysis overview, (iv) high quality data allowing extracting process kinetic
information, (v) easy and low maintenance, (vi) cost effectiveness, (vii) possibility of
multiplexing, allowing simultaneous evaluation of co-digestion and substrate pre-treatment.
4.2 Monitoring of process parameters in anaerobic digestion process
Anaerobic digesters require monitoring of critical parameters (e.g. temperature, pH and
buffering capacity, the concentration of nutrients and inhibitors, gas composition) in order to
obtain an optimal production efficiency and biogas yield. However, due to the expensive
and/or time-consuming character of most analysis methods for anaerobic digestion, industrial
digesters are usually not extensively monitored and only few parameters may be continuously
measured, such as pH and gas flow. Therefore the loading rate of a digester has to be kept
relatively low for safety reasons.
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4.2.1 Temperature
Anaerobic treatment is normally carried out within two distinct temperature ranges: i)
thermophilic range, where the optimal temperature is about 55 ºC, and ii) mesophilic range,
where the optimal digestion occurs at about 37 ºC.
The advantages of thermophilic digestion over the mesophilic one include a high CH4
production rate and the support of a higher organic load. However, thermophilic digestion
appears unstable in comparison to degradation under mesophilic conditions due to
denaturation of enzymes at high temperature.
Besides the two temperature ranges mentioned before, methanogenesis is also possible at
temperatures below 20 ºC, under psycrophilic conditions, but occurs at lower rates. At this
low temperature, the enzymatic hydrolysis of organic matter rich in carbohydrates is also
slow. In conclusion, the mesophilic conditions are the most used for the anaerobic digestion
of organic materials.
4.2.2 pH
For the successful operation and control of the anaerobic fermentation it is essential to
measure the reactor pH since a change in pH is a good indicator of process stress for the
systems with low buffer capacity or alkalinity.
The pH of the reactor should be maintained close to neutrality in anaerobic processes
(between 6.8 and 7.4) to ensure stable operation. Each of the microbial groups involved in the
process has a specific pH region for optimal growth. For the acidogens the optimal pH is
around 6, whereas for the acetogens and methanogens the optimal pH is around 7. For
example, process overloaded results in excessive production of fatty acids and this will be
reflected in decreased pH if the buffering capacity of the fermentation liquid is low.
4.2.3 Alkalinity
Another important parameter in anaerobic digestion systems is alkalinity, which is a measure
of the capacity of a sample to resist a change in pH. For maintaining a neutral pH and a stable
operation of the reactor, the fermentation mixture should provide enough buffering capacity to
neutralize any possible volatile fatty acids (VFA). Carbonic acid (bicarbonate form),
dihydrogen phosphate, hydrogen sulphide and ammonia are the compounds that provide a
significant buffering capacity around pH 7.
Even if alkalinity represents the total concentration of bases in solution, it is expressed as ppm
or mg/L CaCO3. Alkalinity is determined by a titration method using a buret/digital titrator
and a pH meter. Titration is the addition of small quantities of the reagent (H2SO4 or HCl) to
the sample until the sample reaches a certain pH known as an endpoint (pH of 4.3).
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Figure 4-6 Photo of the digital titrator used for the determination of alkalinity.
Alkalinity (AK, expressed as mg CaCO3/L) is calculated as a function of the volume (Vacid)
and normality of standard acid (Nacid) which is used for titration.
CaCO3 (sample) + 2H+
(acid) → Ca2+
+ H2CO3
𝐴𝐾 = 𝑉𝑎𝑐𝑖𝑑 × 𝑁𝑎𝑐𝑖𝑑 ×50000
𝑚𝐿 𝑠𝑎𝑚𝑝𝑙𝑒 (7)
At pH 4.3, more than 99% of the bicarbonate system is converted to carbonic acid. If VFA are
present, more than 80% of the total VFA will be measured and this leads to overestimation of
the total alkalinity. Therefore a new end point is proposed, titration of a sample to a pH of
5.75. At this pH 80% of the bicarbonate will be converted to H2CO3 and VFA will have less
contribution on the alkalinity giving a better measure of the buffering capacity. For a stable
operation it is recommended to have partial alkalinity of 1200 mg CaCO3/L.
4.2.4 Nutrients and toxins
Efficient biodegradation requires that nutrients, such as N, P, and trace elements are available
in sufficient amounts. The most important nutrients are nitrogen and phosphorus and it has
been suggested as a rule of thumb, that COD:N:P ratio should be kept at a minimum of
250:5:1. The anaerobic digestion of a substrate with high nitrogen content (e.g. manure or a
feedstock with high protein content) will release ammonium and this will lead to ammonia
inhibition. Therefore, co-digestion of manure with carbohydrate rich-organic wastes will
improve the C/N ratio and will lead to a more efficient digestion. It has also been reported that
supplementation of trace elements, such as Ni and Co, stimulates anaerobic processes.
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Besides compounds which stimulate anaerobic digestion process, there are toxic compounds
which can inhibit the degradation. Methanogens are commonly considered to be the most
sensitive to toxicity, although all microorganisms involved in digestion can be affected.
The toxicity of NH3, H2S and VFA is pH dependent since only the non-ionized forms exhibit
microbial toxicity. Ammonia is toxic at a pH higher than 7. At pH 8, 10% is in free ammonia
which is more toxic than ammonium ion (90%). In general, free ammonia levels should be
kept below 80 ppm to avoid toxic effect. H2S and VFA (acetate, propionate, butyrate) are
toxic at pH below 7. As the pH decreases, the concentration of the undissociated form of the
acid increases relative to the ionized form. Digester failure occurs when the concentration of
the undissociated VFA (expressed as acetic acid) reach a level of 30 ppm. Volatile acid
accumulation has been used, therefore, as an indicator of system imbalance.
Heavy metal ions exhibit toxicity for the microorganisms by inactivating the sulphydryl
groups (thiolic groups) of their enzymes in forming mercaptides.
Methanogenic bacteria are very sensitive to O2. In an anaerobic digester, any O2 present in the
digester will be rapidly consumed by hydrolysing and acidogenic bacteria.
4.2.5 Biogas flow and composition
Monitoring of the biogas production rate and composition is common at pilot and full-scale
anaerobic digester facilities. Inhibition of methanogenesis would cause a decrease in gas
production and overloading would result in increased gas production at the beginning,
followed by a decrease when VFA have accumulated. The proportion of CH4 to CO2 in biogas
depends on the substrate. However, temperature, pH and pressure can also alter the gas
composition slightly. Typical gas composition for carbohydrate feeds are 55% CH4 and 45%
CO2, while for fats the gas can contain as much as 75% CH4.
Figure 4-7 Photos of the gas sampling port and the gas sensor.
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Even though measuring parameters such as biogas production and composition is common at
biogas plants, they have been shown not to be sensitive enough for process monitoring and
control. Due to limitations in mass transfer between liquid and gas phases, the gas-phase
concentration does not always reflect the actual concentration in the liquid.
4.2.6 Volatile fatty acids (VFA) and dissolved hydrogen (DH)
Propionate, butyrate and valerate are intermediate compounds from the acidogenic step and
can be converted further into CH4 and CO2 through the acetogenesis step. Accumulation of
these acids results in a decreased pH, leading to an increased amount of protonated VFA
which causes inhibition of degradation of the feedstock. Since accumulation of these
compounds reflects an imbalance between the microbial groups involved in the degradation,
monitoring of these intermediates is therefore a method of tracking the status of the process.
The concentration of dissolved hydrogen has also been shown to be a key factor in the
fermenter since its concentration affects thermodynamics and the degradation pathway of the
anaerobic process. Hydrogen works as both an intermediate and electron carrier in the
degradation process. High hydrogen concentrations can inhibit volatile acid degradation,
resulting in VFA accumulation. Thus, hydrogen accumulation can be suggested as an early
stage indicator of process imbalance and toxic inhibition.
Figure 4-8 Photo of a hydrogen sensor.
Selection of parameters for process monitoring and control depends on the reactor
configuration, the characteristics of the feedstock, and available sensors, as well as the
implemented control strategy, and may not be generally applicable. However, it is quite
common that several parameters are monitored at the same time, as they can provide
complementary information about process dynamics.
4.3 Sampling and analysis
4.3.1 Sampling points
At the Plönninge biogas site, the liquid samples can be collected mainly from four places (i.e.
manure tank, mixer tank, buffer tank and digester) whereas the gas sampling is carried out
from the condensation trap in the gas room.
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Sampling from the manure tank
For sampling from the manure tank a sampling stick and a bucket are required; a description
of the operational steps to be followed is presented below.
Figure 4-9 Photo of the sampling port from the manure tank.
1) In the control panel, access the manure tank menu and do the following tasks:
Figure 4-10 Screenshots of manure tank 2 menu with instructions on how to turn on the mixing.
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a) Make sure the level is high enough for using the pump. The level should be above 50
cm.
b) Turn the pump on manual mode.
c) Turn the pump on recirculation mode.
d) Start the pump and run it for at least five minutes.
2) Remove the cover of the manure tank.
3) Take a sample using the sampling stick. Immerse the stick a bit below the upper liquid
level and mix in order to get a more representative sample.
4) Empty the content of the sample stick in the bucket.
5) Place the cover back on the manure tank.
6) Take the bucket with the sample back into the control room for analysis.
7) In the control panel, perform the following steps:
a) Turn off the pump.
b) Turn the pump on automatic mode again.
Sampling from the mixing tank
For taking a sample from the mixing tank, a sampling stick and a bucket are required.
1) In the control panel, access the mixing tank menu and do the follwing tasks (same as for
manure tank):
a) Make sure the level is high enough for using the pump. The level should be above the
lower boundary.
b) Turn the pump on to manual mode.
c) Turn the pump on to recirculation mode.
d) Start the pump and run it for at least five minutes.
2) Turn on the submersible mixer.
3) Remove the cover of the mixing tank.
4) Take a sample using the sampling stick. Immerse the stick a bit below the liquid level and
mix in order to get a more representative sample.
5) Empty the content of the sample stick in the bucket.
6) Put the cover back on the mixing tank.
7) Take the bucket with the sample back into the control room for analysis.
8) Turn off the submersible mixer.
9) In the control panel, perform the following steps:
a) Turn off the pump.
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b) Turn the pump on automatic mode again.
Sampling from the buffer tank
For taking a sample from the buffer tank, a sampling stick and a bucket is required.
1) In the control panel, access the buffer tank menu and do the follwing tasks (same as for
manure tank):
a) Make sure the level is high enough for using the pump. The level should be above the
lower mark.
b) Turn the pump on to manual mode.
c) Turn the pump on to recirculation mode.
d) Start the pump and run it for at least five minutes.
2) Remove the cover of the buffer tank.
3) Take a sample using the sampling stick. Immerse the stick a bit below the liquid level and
mix in order to get a more representative sample.
Figure 4-11 Photo of the sampling stick immersed in the buffer tank.
4) Empty the content of the sample stick in the bucket.
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Figure 4-12 Photo of the sampling stick emptied in the bucket.
5) Put the cover back on the buffer tank.
6) Take the bucket with the sample back into the control room for analysis.
7) In the control panel, perform the following steps:
a) Turn off the pump.
b) Turn the pump on automatic mode again.
Sampling from the digester
For taking a sample from the digester, a bucket is required.
1) Make sure the valve of the digestate hose (situated behind the control room) is closed (the
tap is in the opposite direction to the hose).
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Figure 4-13 Photo of the valve of the digestate hose in “closed” position.
2) Go back inside and open (in the same direction as the hose) the valve and hold it open for
three seconds.
Figure 4-14 Photo of the pump from the control room.
3) Go outside, carefully open the valve (the tap should be in same direction as the hose) while
holding the hose outlet firmly into the collecting bucket. The digestate will now flow into the
bucket.
Figure 4-15 Photo of the valve of the digestate hose in “open” position and the bucket full with
a sample collected from the digester.
4) When no more digestate is flowing from the hose outlet, close the valve again.
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Figure 4-16 Photo of the valve of the digestate hose in “closed” position.
Sampling from the condensation trap (in the gas room)
For taking and analyzing a gas sample from the condensation trap, an MSA Altair 5IR sensor
is required.
Figure 4-17 Photo of the MSA Altair sensor for measuring CH4 and H2S concentrations in a gas sample.
4.3.2 Analysis of liquid samples
The only tests currently performed for raw materials, at the Plönninge biogas plant, are the
measurement of moisture content (which is indirectly a measure of the total solids) and the
pH. These measurements are performed using a moisture analyser (Kern MLB_N, version
2.1, Germany) and a pH sensor (Impo electronic, type 1510, Denmark), respectively.
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Figure 4-18 Photo of Kern MLB_N moisture analyser situated in the control room.
Determination of moisture content
1) Turn on the analyzer by pressing the On/Off button until digits appears on the display.
2) The analyser needs a pre-heating process before measurement. For that, place a sample tray
on the tray support and press the Start/Stop key to initiate the heating.
Figure 4-19 Photo of the moisture analyzer when the “Start” key is pressed for initiating the heating.
3) When the temperature of the analyser reaches equilibrium, a downward arrow is displayed
on the top right corner. Open the lid and place a sample tray previously kept at room
temperature in the tray support.
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Figure 4-20 Photo of the sample tray placed on the tray support of the moisture analyzer.
83
4) Press the Tare button and wait the value on the display to stabilize.
Figure 4-21 Photo of the “Tare” key from the moisture analyzer.
5) When a downward arrow appears on the top right corner of the display, the sample may be
placed in the sample tray. Make sure that the sample is properly mixed before sampling. Use a
proper sample quantity, e.g. 5-10 g.
84
Figure 4-22 Photo of the previously mixed sample added to the sample try of the moisture analyser.
6) When the display shows a stable value, close the heating cover to start the analysis. A
blinking bright light should appear inside the moisture analyser.
Figure 4-23 Photo of the sample before staring the moisture analyser.
7) When the change of moisture content per minute (drying rate) is below 0.1%, the
measurement is completed. Open the heating cover and remove the sample using the tray
handle. Turn off the analyzer by pressing the On/Off button.
8) Calculate the TS value by subtracting the displayed value of moisture content from 100.
85
Figure 4-24 Screenshot of the Excel file process_data.xlsm.
8) Enter the aquired TS value for the sample in the excel file process_data.xlsm.
86
Determination of pH
Figure 4-25 Photo of the pH sensor situated in the control room.
1) Turn on the pH sensor by pressing the On button until numbers appears on the display.
Figure 4-26 Photo of the pH electrode.
87
2) Remove the protection cap of the electrode. Place the sensor in the buffer standard
solution(s) and calibrate it (single- or two-point(s) calibration).
Figure 4-27 Photo of the protection cap of the pH electrode.
3) Place the electrode in the sample. Be sure that the membrane of the electrode is well
immersed in the liquid.
Figure 4-28 Photo of a pH electrode immersed in a liquid.
88
4) Place the sensor on a solid surface and make sure the electrode remains stable and doesn’t
get completely submerged.
Figure 4-29 Photo of a pH meter registering pH of a target sample.
5) Wait for the pH value to stabilize (normally takes 2-3 minutes).
6) Remove and rinse the electrode under running water.
7) Make sure that the protection plastic cap still contains storage liquid and place it back over
the membrane of the sensor.
Figure 4-30 Screenshot of the Excel file process_data.xlsm.
8) Enter the registered pH value for the sample in the Excel file process_data.xlsm
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4.4 Analysis of gaseous samples
The analysis of the biogas samples are performed using an MSA Altair sensor.
Figure 4-31 Photo of MSA Altair sensor for measuring biogas composition.
1) Turn on the MSA Altair sensor by pushing down on the button in the middle and holding it
for a few seconds until a sound is generated and the screen lights up.
Figure 4-32 Photo of MSA Altair sensor in “On” position.
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2) Perform a pump test by blocking the tube until the screen displays “Pump test OK”.
Figure 4-33 Photo of MSA Altair sensor in its “test” stage.
3) When the calibration is finished, the “FRISKLUFT SETUP” will appear on the display and
at that moment press the right button.
Figure 4-34 Photo of the gas outlet on the condensation trap.
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4) Open the valve for the gas outlet on the codensation trap.
Figure 4-35 The connection of the gas sensor with the gas outlet on the condensation trap.
5) Connect the sample unit to the gas outlet by placing the plastic tube of the sampling unit
inside the plastic tube of the gas outlet.
Figure 4-36 Photo of the display of the gas sensor.
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6) Wait for the values on the display to stabilize (this usually takes 1-2 minutes) and then note
the values for CH4 and H2S concentration.
Figure 4-37 Photo of the gas sensor placed in its holder for charging.
7) Place the sampling unit back in its holder for charging. Make sure that the green light is on.
Figure 4-38 Screenshot of the Excel file containing the registered values for CH4 and H2S
concentrations.
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8) Enter the registred values for CH4 and H2S concentrations in the Excel file
process_data.xlsm.
4.5 Online monitoring and data logging
Several process parameters are measured online to give information about the operation of the
plant. A number of these parameters are also locally saved in the computer of the control
panel.
Totally, there are three data loggers that save and store daily the measured values of 14
parameters (Table 4-1). There is a memory limit in the data logger which causes it to
overwrite older values after a certain time (after about 2-3 months). Therefore, it is important
to download the data on a regular basis.
Table 4-1 Parameters that are logged in the data logger.
Name in control panel Name in Excel filea Description
Logger 1 1 TC50 Temp1 Temperature digester bottom
2 TC51 Temp2 Temperature digester top
3 LC5 Nivå RK Level in digester
4 LC6 Nivå ERK Level in digestate storage unit 1
5 GM1 DYGN Gasflöde Daily gas production
6 GM3 DYGN Gasflöde panna Daily gas flow in gas burner
Logger 2 1 EM1 DYGN EM1 Consumed electricity by operational
units
2 WMM1 DYGN WMM1 Consumed heat energy by digester
3 WMM2 DYGN WMM2 Produced heat from plant
4 GP1 TID DYGN Tid gaspanna Gas boiler on time
5 FI5 DYGN Beskickning Amount fed to digester
Logger 3 1 STERLING TID DYGN Tid stirling Stirling engine on time
2 FORDON TID DYGN Tid uppgradering Upgrading on time
3 FACKLA TID DYGN Tid fackla Torch on time
a) Excel file for data handling in Plönninge. More information is given in section “6. Documentation”.
The data from the logger can be downloaded as a csv (comma separated values)-file that can
be open in Excel. A guide of how this conversion is carried out is presented in chapter 6.
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5 EVALUATION OF THE OPERATION AND PROCESS PERFORMANCES
5.1 Process operation
5.1.1 Organic loading rate (OLR)
The OLR is a measurement of how much organic material is loaded into the digester each day
and is expressed as 𝑘𝑔𝑉𝑆/𝑚𝑑𝑖𝑔𝑒𝑠𝑡𝑒𝑟3 /𝑑𝑎𝑦. This parameter considers both the concentration
and the amount of the incoming substrate and is independent of the digester size, thus
representing a very good parameter for regulating the feeding of the digester and in the same
time assessing the performances of the digester.
A recommended value to start with for a mesophilic process (35-39 ºC) is normally around 2-
3 𝑘𝑔𝑉𝑆/𝑚𝑑𝑖𝑔𝑒𝑠𝑡𝑒𝑟3 /𝑑𝑎𝑦; however, the processes should also be tested at higher levels of
ORL.
The OLR can easily be calculated by dividing the concentration of the incoming substrate
(𝐶𝑉𝑆 ,𝑠𝑢𝑏𝑠𝑡𝑟𝑎𝑡𝑒 ) with the inflow (𝐹𝑖𝑛 ) to the digester (Equation 8).
𝑂𝐿𝑅 =𝐶𝑉𝑆 ,𝑠𝑢𝑏𝑠𝑡𝑟𝑎𝑡𝑒
𝐹𝑖𝑛
(8)
5.1.2 Hydraulic retention time (HRT)
The HRT is a measurement of how long time the incoming material spends in the digester on
average. A too short HRT can lead to a washing-out of the bacteria (due to the fact that more
bacteria is leaving the digester than they can reproduced) which can cause digester crashes.
As a recommendation, the HRT should be kept above 20 days to make sure there is no risk of
bacteria cells washout. A longer HRT will also lead to a longer time for the bacteria to
degrade the substrate which in turn will increase the gas yield. However this will also lower
the productivity in most cases (see section 5.2). Therefore, it is important to find a good
balance for HRT.
The HRT can easily be calculated by dividing the average volume of liquid in the digester
(𝑉𝑙𝑖𝑞 ,𝑑𝑖𝑔𝑒𝑠𝑡 𝑒𝑟 ) to the average inflow (𝐹𝑖𝑛 ) (Equation 9).
𝐻𝑅𝑇 =𝑉𝑙𝑖𝑞 ,𝑑𝑖𝑔𝑒𝑠𝑡𝑒𝑟
𝐹𝑖𝑛
(9)
Table 5-1 Process operation parameters.
Recommended value Comment
OLR >3 kg VS/m3/day Varies from process to process, changes in
OLR should be conservative
HRT 30 days Should be kept above 20 days
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5.2 Process performances
There is a number of parameters used to evaluate the performances of a biogas plant. These
parameters are often standardized, making it possible to compare different plants with each
other and get a good understanding of what performances should be expected. The normalized
accumulated volume of gas, gas productivity and the reduction in VS are the most
representative parameters which are reviewed and evaluated in a daily, weekly and/or
monthly basis.
5.2.1 Gas normalization
Gas normalization is a way to get a standardized measurement of the gas volume or flow rate
by compensating for the effects of temperature and pressure. The pressure deviation is often
so small that it can be excluded. Since raw biogas contains small amounts of water vapor, this
effect should be also removed.
There are several standards for carrying out such compensation; below is the one accepted by
IUPAC (International Union of Pure and Applied Chemistry).
𝐹𝑏𝑖𝑜𝑔𝑎𝑠 = 𝐹𝑟𝑎𝑤 ,𝑏𝑖𝑜𝑔𝑎𝑠 ∙273.15
273.15 + 𝑇𝑏𝑖𝑜𝑔𝑎𝑠∙ 𝐾 (10)
𝐾 = 1 −10
8.19625−1730.630
𝑇𝑏𝑖𝑜𝑔𝑎𝑠 +233,426
1013
(11)
5.2.2 Gas productivity
The gas productivity is a standardized parameter to measure and compare how productive a
biogas digester is. It is a measurement that describes the amount of gas produced per reactor
volume and day with the unit 𝑁𝑚𝑔𝑎𝑠3 /𝑚𝑑𝑖𝑔𝑒𝑠𝑡𝑒𝑟
3 /𝑑𝑎𝑦 . Since the parameter considers the
volume of the digester, it may be used for comparison of performances of different biogas
plants. The parameter can be calculated from either the total volume of biogas and/or
methane. For standardization, the gas is usually normalized by compensating for the effect of
temperature, pressure and water content; the normalized values are around 9% lower than the
ones for the raw biogas.
A well performing plant has a biogas productivity (Pbiogas) of around 2-3 𝑁𝑚𝑔𝑎𝑠3 /𝑚𝑑𝑖𝑔𝑒𝑠𝑡𝑒𝑟
3 /
𝑑𝑎𝑦 and a methane productivity of 1-2 𝑁𝑚𝑔𝑎𝑠3 /𝑚𝑑𝑖𝑔𝑒𝑠𝑡𝑒𝑟
3 /𝑑𝑎𝑦 . However, these values
depend greatly of what type of substrate is used and the configuration of the plant. The gas
productivity (P) can be calculated by dividing the average normalized gas flow (F) with the
total volume of the digester (Vdigester) (Equations 12 and 13):
𝑃𝑏𝑖𝑜𝑔𝑎𝑠 =𝐹𝑏𝑖𝑜𝑔𝑎𝑠
𝑉𝑑𝑖𝑔𝑒𝑠𝑡𝑒𝑟 (12)
96
𝑃𝑚𝑒𝑡 ℎ𝑎𝑛𝑒 =𝐹𝑏𝑖𝑜𝑔𝑎𝑠 ∙ 𝑋𝑚𝑒𝑡 ℎ𝑎𝑛𝑒
𝑉𝑑𝑖𝑔𝑒𝑠𝑡𝑒𝑟
(13)
5.2.3 Gas yield
The gas yield is a standardized parameter to measure and compare how efficient a biogas
digester is. It is a measurement that describes the amount of gas produced per amount of
organic material and is expressed as 𝑁𝑚𝑔𝑎𝑠3 /𝑘𝑔𝑉𝑆 . Since the parameter considers how much
gas is produced per amount of organic material, it may be used as a comparison between
biogas plants digesting the same or similar substrates. Similarly to the gas productivity, this
parameter can be calculated with both total biogas and/or methane. For standardization, the
gas is usually normalized by compensating the effect of temperature, pressure and water
content; the normalized values are around 9% lower than the ones for the raw biogas.
A well performing plant usually has a biogas yield of 0.6-0.8 𝑁𝑚𝑔𝑎𝑠3 /𝑘𝑔𝑉𝑆 and a methane
productivity of 0.4-0.5𝑁𝑚𝑔𝑎𝑠3 /𝑚𝑑𝑖𝑔𝑒𝑠𝑡𝑒𝑟
3 /𝑑𝑎𝑦 . As mentioned above, these values depend
greatly on what type of substrate is digested. For a farm scale plant where manure and
carbohydrate rich substrates normally are digested, these values are normally somewhat
lower. A good way to find out what level to be expected is to perform a BMP analysis (see
section 4.1.4). A rule of thumb is that the process should have a similar or higher gas yield
compared to the gas potential from the BMP analysis to be considered as a well performing
process.
The gas yield can be calculated by dividing the average normalized gas flow with the organic
loading rate (OLR) (Equations 14 and 15):
𝑌𝑏𝑖𝑜𝑔𝑎𝑠 =𝐹𝑏𝑖𝑜𝑔𝑎𝑠
𝑂𝐿𝑅 (14)
𝑌𝑚𝑒𝑡 ℎ𝑎𝑛𝑒 =𝐹𝑏𝑖𝑜𝑔𝑎𝑠 ∙ 𝑋𝑚𝑒𝑡 ℎ𝑎𝑛𝑒
𝑂𝐿𝑅
(15)
5.2.4 VS reduction
The VS reduction is another measurement that indicates the efficiency of the anaerobic
process. It corresponds to the amount of the organic material that was digested during
fermentation. This is an especially interesting parameter if the focus is on waste reduction
instead of gas production.
The expected VS reductions depend greatly on the type of substrate digested.
The VS reduction can be calculated by dividing the difference between the incoming and
outgoing VS to the incoming VS (Equation 16). If the volumetric inflow and outflow can be
97
assumed to be the same (if the volume in the digester is constant) this can be calculated by the
same equation but with concentration of VS instead of the mass.
𝑉𝑆𝑟𝑒𝑑 =𝑉𝑆𝑖𝑛 − 𝑉𝑆𝑜𝑢𝑡
𝑉𝑆𝑖𝑛≈
𝐶𝑉𝑆 ,𝑖𝑛 − 𝐶𝑉𝑆 ,𝑜𝑢𝑡
𝐶𝑉𝑆 ,𝑖𝑛 (16)
Table 5-2 Process performance parameters.
Recommended value Comment
Gas productivity >1 Nm3/m
3/d
Methane productivity >0.6 Nm3/m
3/d
Total gas yield >0.5 Nm3/kgVS Depends greatly on type of substrate
Methane yield >0.3 Nm3/kgVS Depends greatly on type of substrate
VS reduction >60 % Depends greatly on type of substrate
5.3 Process stability
One of the most important aspects of having a well performing process is to have a stable
process. The losses in gas production can be substantial if the process gets disturbed. Aside
from that, a constant environment usually makes the microorganisms in the digestate perform
optimally.
pH is a well-known parameter to measure the stability of the anaerobic digestion process. This
is due to the fact that many of the bacterial groups (especially the methane producing bacteria)
are sensitive to pH levels outside the optimal intervals. For a stable process, the pH value
should be stable around 7-7.5. Normally, an instable process is suffering from decreasing pH
due to production of more intermediate products (i.e. VFA) than the methane producing
bacteria can consume. When the pH becomes low enough, the methane producing bacteria
gets inhibited, leading to more accumulation of VFA.
Measuring pH is a relatively simple and cheap method, giving a rather good indication of the
process’ status. However, in order to truly know the condition of a process, the concentrations
of VFA and total alkalinity (TA) (see section 4.2) also need to be measured.
The alkalinity is a measurement of the buffer capacity and therefore gives an indication of
how much VFA the process can absorb before the pH starts to drop. Normally, the alkalinity
is rather high in processes that are fed with cow manure since the manure often is rich in basic
ions.
The procedure demands a lab with titration equipments and is therefore not performed on
routine basis. However it is recommended to perform the test on the digestate at least three to
four times per year, preferably combined with the VFA analysis. It is however more
interesting to record the ratio between VFA and total alkalinity (see, VFA/TA) than just
alkalinity, since this relationship actually determines the effect on the pH value.
98
The gas composition partly provides information on how the intermediate steps are
performing. Normally, the composition is rather constant as long as a similar substrate is fed
to the process. However, if the methane concentration starts to decrease, it is a sign that the
process is not working under optimal conditions. A lower concentration of methane often
means that there is an inhibition of a methane producing step. A normal methane
concentration for the Plönninge biogas plant is 60-65 %.
Ammonium nitrogen (N-NH4) gives an indication of how much inorganic nitrogen is present
in the process. The concentration of ammonia is in direct correlation with the concentration of
N-NH4, depending especially on pH and temperature. Ammonia can be very toxic for the
biomass at higher concentrations. The values for N-NH4 should be lower than 2-3 g/L.
The temperature is an important parameter for the process to perform optimally. In a
mesophilic process, the temperature should be around 35 – 39 ºC. It is important to have
constant temperature even within this interval (in the interval of starting temperature ±0.5 ºC).
A constant temperature will allow the bacteria to perform optimally since they do not have to
adapt to temperature changes.
Table 5-3 Process stability parameters.
Recommended value Comment
Temperature 37 ⁰C Should be stable, max ± 1 ºC
VFA <4 g/l Depends on degree of adaption and alkalinity
VFA/TA <0.3 >0.3 indicates possible process instability
N-NH4 <2-3 g/l High values in combination with high pH is dangerous
pH 7.2-8.5 Should be stable
Methane
concentration
60-65 % Depends much on substrate, decreasing concentration gives
indication of problem
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6 DOCUMENTATION
In order to have a good understanding and follow up of the process operation, it is important
to keep a detailed logging of the recorded data. This will help to make a good review of
historical performance and learn lesson from the past on how the plant should be operated
better in future. For this purpose an Excel file template has been created in which all the
process data can be entered and saved for process evaluation (Table 6-1). The Excel file is
named Process_data.xlsm in this document.
Table 6-1 Different sheets in the Excel file template.
Sheet Comment Input Manual/Automatic
Rådatasortering Sort and remove duplicates in data from data
logger
Manual input
Rådata Place to paste the managed data from
“Rådatasortering”
Manual input
Manuell data Input analysis results and amounts of loaded
solid substrate
Manual input
Dagsdata Presentation of daily values from data logger Automatic
Veckodata Presentation of weekly process data Partly manual input
Månadsdata Presentation of monthly process data Automatic (VS/TS required)
Urskriftsformulär Printing form for manual data input -
Beräkningar Used for monthly data calculations -
This Excel file should be updated on daily basis with new results from the different analyses.
The data should then be reviewed on a weekly basis to get a good overview of the process
performances.
100
6.1 Navigation
To navigate among the different sheets in the Excel file template, click the name of the sheet.
Figure 6-1 Screenshot of the Excel-file, also displaying where to navigate between different sheets.
101
6.2 Sorting of raw data (Rådatasortering)
In this sheet the raw data from the data logger is first pasted (Figure 6-2). A macro function is
used automatically to remove all duplicates from the raw data and sort it based on the dates.
Figure 6-2 Screenshots of “Rådatasortering” sheet where (A) is empty and (B) is pasted and treated data.
102
6.3 Raw data (Rådata)
In this sheet the data managed in “Rådatasortering” are inserted. The data from the 3 different
loggers (i.e. loggers 1-3) are here combined.
Figure 6-3 Screenshot of “Rådata”-sheet where data from two data loggers (i.e. loggers 1-2) have been inserted.
103
6.4 “Manual” data (Manuell data)
In this sheet results from the liquid (i.e. TS, pH) and gas analysis (gas composition in %) as
well as the amounts of all manually loaded solid substrate. The results are grouped on months
(Figure 6-4) for a better overview.
Figure 6-4 Screenshot of all the “Manuell data”-sheet when the display is minimized to show only the monthly
values.
The daily values for each month (Figure 6-5) can then easily be displayed by clicking on the
corresponding ”+” sign on the left side of the sheet.
104
Figure 6-5 Screenshot of all the “Manuell data”-sheet when one month is expanded to show all daily inputs.
105
6.5 Daily data (Dagsvärden)
In this sheet the data from the data logger is displayed. The form uses the data read from
“Rådata” and recalculates it to more manageable units. The data is displayed as daily values,
then grouped into months.
An average value for each month is calculated for the various parameters (displayed in the
rows “Medel”). When possible, the parameters are also added together to give monthly sums
(displayed in the row “Total”).
Figure 6-6 Screenshot of “Dagsvärden”-sheet when the display is minimized to show only the monthly values.
The daily values for each month (Figure 6-7) can then easily be displayed by clicking on the
corresponding “+”sign on the left side of the sheet.
106
Figure 6-7 Screenshot of all the “Dagsvärden”-sheet when one month is expanded to show all daily inputs.
As mentioned above, the raw data is modified in the form to give more proper units. To avoid
using decimals the posts in the data logger are stored as larger numbers (e.g. 37 oC
corresponds to 3700 in the data logger). All the different actions performed to modify the raw
data are presented in Table 6-2.
Table 6-2 List of how the raw data is modified in “Dagsvärden”-sheet.
Parameter Action Raw data Treated data
Temp1 Divide by 100 to give ºC 3710 37.10
Temp2 Divide by 100 to give ºC 3710 37.10
Nivå RK Divide by 100 to give meter 721 7.21
Nivå ERK Divide by 100 to give meter 292 2.92
Gasflöde - - -
Gasflöde Panna - - -
EM1 - - -
WMM1 - - -
WMM2 - - -
Tid gaspanna - - -
Beskickning Divide by 10 to give m3/d 98 9.8
107
6.6 Weekly data (Veckovärden)
In this sheet the weekly data are grouped together (Figure 6-8). The user has to copy and paste
the data from “Manuell data” and “Dagsvärden” in this sheet (see the guide in section 9).
Figure 6-8 Screenshot of “Veckodata”-sheet when minimized to display only the weekly values.
The daily values for each individual week (Figure 6-9) can then easily be displayed by
clicking on the corresponding ”+”-sign on the left side of the sheet.
Figure 6-9 Screenshot of all the “Veckovärden”-sheet when one week is expanded to show all daily inputs.
108
Table 6-3. Parameters listed in the “Veckovärden”-sheet.
Parameter Unit Time period Comment
Added amounts
Total kg Day and week Sum of all substrates
Substrate 1 kg Day and week Sum
Substrate 2 kg Day and week Sum
Substrate 3 kg Day and week Sum
Substrate 4 kg Day and week Sum
Substrate 5 kg Day and week Sum
Substrate 6 kg Day and week Sum
Substrate 7 kg Day and week Sum
TS content
Manure tank %ww Day and week Average
Mixing tank %ww Day and week Average
Buffer tank %ww Day and week Average
Digester %ww Day and week Average
pH
Manure tank -log[H+] Day and week Average
Mixing tank -log[H+] Day and week Average
Buffer tank -log[H+] Day and week Average
Digester -log[H+] Day and week Average
Gas composition
Methane content %Vol Day and week Average
Carbon dioxide content %Vol Day and week Average
Hydrogen Sulphide ppmVol Day and week Average
Data logger
Temperature lower °C Day and week Average
Temperature upper °C Day and week Average
Level digester m Day and week Average
Level digestate storage m Day and week Average
Daily total gas production m3/d Day and week Average
Daily gas consumption burner m3/d Day and week Average
EM1 kWh/d Day and week Average
WMM1 kWh/d Day and week Average
WMM2 kWh/d Day and week Average
Daily On time gas burner min/d Day and week Average
Daily load to digester m3/d Day and week Average
Daily On time Stirling engine min/d Day and week Average
Daily On time upgrading min/d Day and week Average
Daily On time torch min/d Day and week Average
Weekly total gas production m3/week Day and week Sum
Weekly gas consumption burner m3/week Day and week Sum
EM1 kWh/week Week Sum
WMM1 kWh/week Week Sum
WMM2 kWh/week Week Sum
Weekly On time gas burner min/week Week Sum
Weekly load to digester m3/week Week Sum
Weekly On time Stirling engine min/week Week Sum
Weekly On time upgrading min/week Day and week Sum
Weekly On time torch min/week Day and week Sum
Process
parameters
VS/TS %TS Day and week Given by user
HRT days Day and week Average
OLR kgVS/m3/d Day and week Average
Total gas productivity m3/m3/d Day and week Average
Methane productivity m3/m3/d Day and week Average
VS reduction %VS Day and week Average
Total gas yield m3/kgVS Day and week Average
Methane yield m3/kgVS Day and week Average
109
6.7 Monthly data (Månadsvärden)
In this sheet all data for every month is summarized and displayed (Figure 6-10). Both the
average and total values are given.
The only input required is the average VS/TS ratio. All the other parameters are automatically
generated from the data recorded in “Rådata” and “Manuell Input” sheets.
In this sheet the average values for all parameters are given for each month and the whole
year (Medel). A monthly and a yearly total (Total) are also given for certain parameters.
Figure 6-10 Screenshot of “Månadsvärden”-sheet.
In Table 6-4 all the parameters displayed in the “Månadsvärden” sheet are listed.
110
Table 6-4 Parameters listed in the “Månadsvärden”-sheet.
Parameter Unit Time period Comment
A Added amounts
Total kg/month Month and year Sum of all
substrates
Substrate 1 kg/month Month and year Sum
Substrate 2 Kg/month Month and year Sum
Substrate 3 Kg/month Month and year Sum
Substrate 4 kg/month Month and year Sum
Substrate 5 kg/month Month and year Sum
Substrate 6 kg/month Month and year Sum
Substrate 7 kg/month Month and year Sum
B TS content
Manure tank %ww Month and year Average
Mixing tank %ww Month and year Average
Buffer tank %ww Month and year Average
Digester %ww Month and year Average
C pH
Manure tank -log[H+] Month and year Average
Mixing tank -log[H+] Month and year Average
Buffer tank -log[H+] Month and year Average
Digester -log[H+] Month and year Average
D Gas composition
Methane content %Vol Month and year Average
Carbon dioxide content %Vol Month and year Average
Hydrogen Sulphide ppmVol Month and year Average
E Data logger
Temperature lower °C Month and year Average
Temperature upper °C Month and year Average
Level digester m Month and year Average
Level digestate storage m Month and year Average
Ave daily total gas
production
m3/d Month and year Average
Ave daily gas consumption
burner
m3/d Month and year Average
EM1 kWh/d Month and year Average
WMM1 kWh/d Month and year Average
WMM2 kWh/d Month and year Average
Ave daily On time gas
burner
min/d Month and year Average
Ave daily load to digester m3/d Month and year Average
Ave daily On time Stirling
engine
min/d Month and year Average
Ave daily On time
upgrading
min/d Month and year Average
Ave daily On time torch min/d Month and year Average
F Data logger
Monthly total gas
production
m3/month Month and year Sum
Monthly gas consumption
burner
m3/month Month and year Sum
EM1 kWh/mont
h
Month and year Sum
111
WMM1 kWh/mont
h
Month and year Sum
WMM2 kWh/mont
h
Month and year Sum
Monthly On time gas
burner
min/month Month and year Sum
Monthly load to digester m3/month Month and year Sum
Monthly On time Stirling
engine
min/month Month and year Sum
Monthly On time
upgrading
min/month Month and year Sum
Monthly On time torch min/month Month and year Sum
G Process
parameters
VS/TS %TS Month and year Given by the user
HRT days Month and year Average
OLR kgVS/m3/d Month and year Average
Total gas productivity m3/m
3/d Month and year Average
Methane productivity m3/m
3/d Month and year Average
VS reduction %VS Month and year Average
Total gas yield m3/kgVS Month and year Average
Methane yield m3/kgVS Month and year Average
112
6.8 Printable document (Utskriftsformulär)
This sheet (Figure 6-11) is a printer friendly version of the “Manuell data”-sheet. It can be
used if the operator prefers to write down the data on paper before entering it into the Excel-
sheet.
Figure 6-11 Screenshot of “Utskriftformat”-sheet.
113
6.9 How to insert data from the data logger
The input of data from the data logger can be divided into two steps:
1. Download data from data logger.
2. Insert data into the Process_data.xlsm file.
Both these steps are presented below.
6.9.1 Download data from Datalogger
1. The data from the Datalogger need to be first downloaded from the local computer.
Use the shortcut called “Gasverk (logggiler)” located on the desktop (Figure 6-12).
Figure 6-12 Screenshot of desktop where “Gasverk (loggfiler)” shortcut is marked out.
2. A list of different files should appear (TEMP, ENERGI, LOGGER1, LOGGER2
LOGGER3) (Figure 6-13). Start to download a file by clicking on its name.
114
Figure 6-13 Screenshot of FTP catalogue with downloadable log files.
3. A window should appear where “open”, “save” or “cancel” can be selected (Figure
6-14). To download the document click on the “Spara”-button.
Figure 6-14 Screenshot of window that appears when clicking on logger1.SKV.
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4. Use the windows explorer to choose where you want to save the log file (Figure 6-15).
Preferably a folder for log files needs to be created first. Name the file with the logger
name and date. Click “Spara” for saving the data file.
Figure 6-15 Screenshot of “save as”-window that appears when “save” is chosen.
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6.9.2 Insert data into Process_data.xlsm
1. Open the downloaded log file (Figure 6-16).
Figure 6-16 Screenshot of log file in Excel.
2. Copy all the data and open the Process_data.xlsm and paste it in the top left cell (A1)
in the sheet “Rådatasortering” (Figure 6-17).
Figure 6-17 Screenshot of how to paste log file data in Excel.
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3. All the data should now be pasted into the sheet. To remove the duplicates access the
“view” menu (top menu board) and click on the “Macro”-symbol on the right side. In
the scroll menu that appears choose “View Macro” (Figure 6-18).
Figure 6-18 Screenshot of how to access Macros in Excel.
4. A new window containing a list of macros should now appear (Figure 6-19). Mark the
function called “Remove Duplicates” and then click on “Run”.
Figure 6-19 Screenshot of how to run the Macro “RemoveDuplicates” in Excel.
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5. The list without duplicates should now be displayed (Figure 6-20).
Figure 6-20 Screenshot of results after running Macro “RemoveDuplicates”.
1. To insert the data into the data handling algorithms of the Process_data.xlsm, copy all
the data besides the dates and go to the sheet called “Rådata”. There paste the data in
its correct position. Remember to paste the data at the location corresponding to the
correct date.
a. Logger1 starts with Temp 1 and should therefore be pasted there (Figure 6-21).
Figure 6-21 Screenshot of where to paste data from Logger1.
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b. Logger 2 starts with EM1 and should therefore be pasted there (Figure 6-22).
Figure 6-22 Screenshot of where to paste data from Logger2
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7 METHODOLOGY FOR PROCESS IMPROVEMENTS
In order to optimize the process it is important to first define a clear goal of the plant
operation, i.e. whether the purpose of plant operation is for energy production, waste handling
or combination of both. Plönninge biogas plant is defined as a demonstration plant at farm-
scale. There is a need not only to show the feasibility of producing vehicle fuel, electricity and
heat production, but also a need to use manure wastes as a part of the feedstock and to
demonstrate that the digested residues can be used as fertilizers for crops cultivation. In order
to achieve these goals, it is essential to maximize the biogas production at Plönninge biogas
plant.
Once the goal of plant operation is defined, it is important to apply a good methodology on
how to constantly improve the plant operation. There are several important aspects to be kept
in mind before defining the most suitable strategy for the operation of Plönninge biogas plant.
In general, the following aspects can give a big impact on plant operation and biogas
production:
i. Quality and quantity of the feedstock
ii. Whether there is suitable process/plant configuration and instrumentation to ensure
reasonable flexibility for plant optimization
iii. Right operational routine and follow up to ensure that plant operation can be
continuously improved
Plönninge biogas plant has a rather simple process and plant configuration based on selected
feedstock. The available instruments (i.e. sensors and actuators) can support the basic
requirement of plant operation. Although it is always possible to further improve the plant
configuration and instrumentation, it is assumed that the process optimization can be based on
the current process/plant configuration and instrumentation. The process optimization strategy
should therefore be focused on feedstock selection and right operation routine and follow up.
Feedstock
In order to achieve as high biogas production as possible, it is important to select feedstock
with high methane potential. In general, liquid cow manure has relative low methane
potential. It is therefore important to use more energetic and easy degradable feedstock,
depending of course on their availability at the Plönninge plant.
Operational routine and follow up
A higher biogas production can also be achieved by implementation of better loading regimes
with a constant pushing of the process, so the biomass throughput and energy throughput of
the plant can be increased whereas a stable operation can still be retained. Every week or
month should be seen as new test were the loading regimes is changed a little bit from the last
period and the effect of this change is continuously monitored. Depending on the
performances obtained, these changes should be considered permanent or be rejected. This
dynamics of the process parameter changes – continuous evaluation should be implemented
as a part of operational routine, so operational lesson in the past can be well recorded,
evaluated and follow up in order to improve future operation.
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7.1 Meetings
In order to have a good follow up of the plant operation, meetings should be held on a regular
basis among operators and all personnel should be involved. In these meetings the
performance of the plant and any potential problems should be reviewed and discussed.
Objectives and aims for the plant operation should also be set, and any deviation should be
evaluated.
Such meetings should at least be held once per month.
Topics that are recommended to be discussed during these meetings include:
Performance of plant on weekly and monthly base
Any deviation from the feedstock supply in terms of both quality and quantity?
Is there any problem with the operation in terms of technical, logistic and personnel aspects?
Any progress and lesson learn since the previous meeting?
Any improvement that can be foreseen?
Was the set goals reached?
Is the economic plan reached/on schedule?
Decide on new or keep old goals.
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8 OPERATIONAL ROUTINES
These operational routines list and describe all the tasks that should be carried out on a daily
and weekly basis at the Plönninge biogas plant.
8.1 Daily operational routines
In this section operational tasks that should be carried out each day are listed and described.
Preferably, these tasks are carried out at the beginning of the working day. It is important to
build up routines where all these tasks are carried out every day.
1. Perform a quick check of the biogas plant to make sure nothing went wrong during the
night. Look especially for flooding in any of the operational units.
2. Check the control panel of the SCADA system:
i. Check the alarm list If there is any alarm indication for a particular process
unit, please check whether it is possible to make any suitable tuning and
adjustment so the process unit can go back to the normal operational mode. If
there is no alarm indication, move on to the next point (Figure 8-1).
Figure 8-1 Screenshot of alarm list.
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ii. Check the conditions of the operational units
1. Digester level and temperature. Make sure the values are within the specified
levels (e.g., the same as or close to setpoints). If the values are not within the
default range, try to identify the reason and check whether it is possible to make
any suitable tuning and adjustment so that the digester level and temperature can
come back into the operational range (Figure 8-2).
Figure 8-2 Screenshot of digester menu.
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2. Check the filling level; if this is too high or too low, try to identify the reason
and evaluate whether it is possible to make any suitable tuning and adjustment
so that the slurry level of the buffer tank level can be brought back within the
optimal range (Figure 8-3).
Figure 8-3 Screenshot of buffer tank.
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3. Check the filling level; if this is too high or too low, try to identify the reason and
evaluate whether it is possible to make any suitable tuning and adjustment so that the
slurry level of the mixing tank level can be brought back within the optimal range
(Figure 8-4).
Figure 8-4 Screenshot of mixing tank.
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4. Manure tank level. Check the filling level; if this is too high or too low, try to
identify the reason and evaluate whether it is possible to make any suitable tuning and
adjustment so that the slurry level of the manure tank level can be brought back within
the optimal range (Figure 8-5).
Figure 8-5 Screenshot of manure tank 2 menu.
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i. Fill up the mixing tank by manually pumping sufficient amount of the content
from manure tank 1 as possible. Make sure that level in the mixing tank does
not get too high (Figure 8-6).
Figure 8-6 Screenshot of manure tank 1 and mixing tank menus with instruction on how to pump from manure
tank 1 to mixing tank.
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ii. Check the gas utilization. Make sure that the gas storage level is at a
reasonable level. If it is not, please check the reason and see whether it is
possible to make any suitable tuning and adjustment so that the gas storage
level is brought within the right range (Figure 8-7).
Figure 8-7 Screenshots of gas consumption and gas measuring menu.
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5. Turn on the submersible mixer (Figure 8-8).
Figure 8-8 Photo of showing how to turn on submersible mixer in mixing tank.
6. Go outside to the gas room and perform a gas composition test (Figure 8-9). Enter the
registered data in the file Process_data.xlsm in the computer.
Figure 8-9 Photos of the equipment used for the analysis of gas composition.
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7. Go outside to the mixing tank and add FeCl3 into the tank (Figure 8-10). This is
carried out by opening the tap and waiting for 5 seconds before closing the tap. Enter
the date and amount in the form placed in the mail box next to the FeCl3 container.
8.
Figure 8-10 Photos of FeCl3 solution adding.
9. Go outside to the front loader and load the X-Ripper with potatoes (the amount
decided at the operational meeting). Enter the loaded amount in the file
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Process_data.xlsm in the computer. More detail instruction needs to be added after the
installation of X-Ripper has been implemented.
10. Take a sample from the buffer tank and perform a quick-TS (using the moisture analyzer) and
a pH analysis, and enter the result in the file Process_data.xlsm in the computer (Figure 8-11).
Figure 8-11 Photos of buffer tank sampling and quick TS analysis with moisture analyser.
11. Fill up the buffer tank as much as possible by manually pumping feedstock from the
mixing tank (Figure 8-12). Make sure that the level in the buffer tank does not get too
high (e.g., not above 250 cm).
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Figure 8-12 Screenshots with instructions of how to pump from the mixing tank to the buffer tank.
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12. Turn off the submersible mixer in the mixing tank (Figure 8-13).
Figure 8-13 Photo of showing how to turn off submersible mixer in mixing tank.
8.2 Weekly operational routines
In this section operational tasks that should be carried out once or several times per week are
listed and described. Suggestions of which week days these tasks should be performed are
also given.
Monday
1. Look at the data from the previous week and decide on whether to keep the same
loading regime or make any adjustment if necessary.
2. Load the silage (if this is specified in the operational plan).
Tuesday
1. Take a slurry sample from the manure tank 1 and perform a quick TS (using the
moisture analyzer) and a pH analysis. Enter the data in the Excel file
Process_data.xlsm.
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Figure 8-14 Photo of quick TS test with moisture analyser.
3. Load any other substrate available (if this is specified in the operational plan).
Wednesday
4. Load the silage (if this is specified in the operational plan).
Thursday
1. Collect the waste containers with fruit and vegetables from the local ICA Maxi.
2. Add the fruit and vegetables to the mixing tank via the x-ripper.
Friday
1. Load the ensilage (if this is specified in the operational plan).
Task to perform before the weekend
1. Turn on the submersible mixer (from the switch located next to the control panel,
(Figure 8-8)); allow it to run for about 60 minutes in order to homogenize the
feedstock in the mixing tank.
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2. Fill up the buffer tank as much as possible. Make sure the level does not get too high.
3. Fill up the mixing tank as much as possible. Make sure the level in the manure tank
does not get to low and that the level in the mixing tank does not get to high.
4. Go outside the mixing tank and add a double dosage of iron chloride into the tank.
This is performed by opening the tap for 10 seconds. Enter the date and the amount of
iron chloride added in the form placed in the mailbox next to the iron chloride
container.
5. Add a double load of potatoes into the mixing tank via the x-ripper.
6. Do not forget turning off the submersible mixer in the mixing tank.
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9 PROCESS EVALUATION
9.1 Weekly evaluation
Evaluation of the plant performance should be carried out weekly. This should be performed
independently by the operator mainly or by a larger working group where other internal and
external process engineers might be involved. For weekly operational evaluation, the process
performance should be studied by comparing the plant performances of the latest week vs.
previous weeks. The purpose of the meeting should be to set an operational plan for the
coming week. The time for the meeting should be the same every week (preferably on
Monday morning in order to get a fresh start of the week and also maximize the number of
working days close to the operational changes).
Manipulating parameters, parameters that should be used for tuning the operation.
Response parameters, parameters that should be used to evaluate the performance of the plant
based on settings of manipulating parameters.
Other important parameters, parameters whose effect on the process should be
considered when the response from changes in operation can be observed.
The parameters that should be considered in the evaluation are listed below. The parameters
are dived into 3 different categories:
Manipulating parameters, parameters that should be used for tuning the operation.
Response parameters, parameters that should be used to evaluate the performance of
the plant based on settings of manipulating parameters.
Other important parameters, parameters whose effect on the process should be
considered when the response from changes in operation can be observed.
Table 9-1 Parameters considered in process evaluation (for description of parameters, please see section 5.1).
Manipulating parameters Response parameters Other important parameters
Feeding interval Methane productivity TS concentration in buffer tank
Size of each load Methane yield pH in digester
Amount of added solid
substrate
Total gas productivity Temperature in digester
Type of solid feedstock Total gas yield H2S concentration
HRT VS reduction
OLR Methane concentration
Manipulating parameters
The parameters that should be adjusted to alter the operation are the feeding rate and added
amount of solid substrate. These parameters will then have an indirect effect on the HRT
and the OLR which are important to consider in the evaluation. Especially the HRT should
be monitored to make sure it does not get too low (e.g., above 20 days) to avoid washout of
the bacteria. OLR is a more general parameter to know how hard the process is loaded and it
can be used to compare the operation with other plants.
The focus should be placed on adding as much solid substrate as possible to maximize the
OLR and still keep a long HRT. However, with this strategy it is important to control the TS
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concentration in the buffer and mixing tank since too high values could cause problems
with the pumps.
Response parameters
The most important response parameter to consider is the methane productivity. If it has
increased compared to the previous operational period it could be considered as a positive
result. However, the reason for the increase in methane production should also be
investigated. Another important parameter to consider is the methane yield since this gives
information of how efficient the process is.
Strategy for optimizing the operation
1. Increase the load:
a. Focus on adding as much as possible of energy rich substrate that is regional
abundant and can be accessible and easier to load into the digester.
b. Make sure that the TS content in the buffer tank does not get too high (not over
10%).
c. Closely monitor and follow up the operation in order to maximize the performances
of all process units.
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9.1.1 Saving the data for weekly evaluation
1. Open the Excel data file and in the sheet “Manuell data” copy the data from each day
of the previous week (Figure 9-1).
Figure 9-1 Screenshot of “Manuell data”-sheet where the values for 1 weeks are marked.
2. Go to the sheet “Veckodata” and open the week of interest by clicking on the ”+”-sign
on the left of the week number (Figure 9-2).
Figure 9-2 Screenshot of Veckovärden”-sheet in compressed form (click “+”-signs on right side to show daily
values for a week).
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3. In the top left cell (e.g., Silage for Monday) right click and choose “Paste Special”
(“Klistra in special”) (Figure 9-3).
Figure 9-3 Screenshot of how to paste the data from “Manuell data”-sheet into “Veckovärden”-sheet using
“Paste Special”.
4. Choose “Values” in the menu that opens (Figure 9-4).
Figure 9-4 Screenshot of “Paste Special” window that appears.
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5. Now the values should be pasted into the formula; an example is presented below
(Figure 9-5):
Figure 9-5 Screenshot of “Veckovärden”-sheet where the data from “Manuell data”-sheet has been pasted.
6. Next step is to paste the data from the DataLogger. This is carried out in the same way
as the manual data. Open the sheet “Dagsvärden” and copy the values for the specified
dates (Figure 9-6).
Figure 9-6 Screenshot of “dagsvärden”-sheet where the values for 1 weeks are marked.
7. Go back to the sheet “Veckodata” and right click on top left cell after the manual
inputs (e.g., Temp1 for Monday). Choose “Paste Special” and choose values again
(Figure 9-7).
Figure 9-7 Screenshot of how to paste the data from “Dagsvärder”-sheet into “Veckovärden”-sheet using “Paste
Special”.
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8. The values should now be inserted in the form; an example is presented below (Figure
9-8).
Figure 9-8 Screenshot of “Veckovärden”-sheet where the data from “Dagsvärden”-sheet has been pasted.
9. In order to calculate the process parameters a value for VS/TS (% of VS per TS) needs
to be entered. This is inserted in the top row under the column “VS/TS” (Figure 9-9).
Figure 9-9 Screenshot of to enter VS/TS value in “Veckovärden” sheet.
10. After this, given that all other necessary data is in place, the process parameters should
automatically be calculated (Figure 9-10).
Figure 9-10 Screenshot of “Veckovärden”-sheet showing the calculated process paramteters.
11. All the data for that specific week is in place and the performances can be evaluated.
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9.2 Monthly evaluation
A review of the plant operation should be carried out on monthly basis by the operator or
process engineers. This monthly evaluation should be performed from more plant-wide and
systematic aspects and give a good overview on total mass and energy outputs, as well as
operational economic over a one-month period. The data can then be compared with historical
data from the previous months in order to set up a strategy to maintain a good operation
and/or get further improvement (if possible). It is recommended to present and discuss the
monthly evaluation during the first weekly meeting of next month.
In Manipulating parameters, parameters that should be used for tuning the operation.
Response parameters, parameters that should be used to evaluate the performance of
the plant based on settings of manipulating parameters.
Other important parameters, parameters whose effect on the process should be
considered when the response from changes in operation can be observed.
The parameters that should be considered in the evaluation are listed. The parameters are
dived into 3 different categories:
Mass throughput, in this category parameters that reflect the amount of feedstock
entering and of digestate exiting the reactor, type of feedstock and their characteristics
(VS, TS, pH, BMP), feedstock load regime, etc should be summarized.
Energy throughput, parameters reflecting the totally produced biogas volume,
specific biogas production rate, utilization of biogas (heat, vehicle fuel, electricity),
electricity consumption, heat consumption, etc should be summarized.
Economical aspects, in this category parameters reflecting the operational costs
(material, electricity, manpower, logistic, equipment depreciation, etc.) and potential
income sources (electricity, vehicle fuel, heat, digestate as fertilizer) should be
summarized.
Table 9-2 Examples of parameters that should be considered in process evaluation.
Mass throughput Energy throughput Economic aspect
Feedstock volume Biogas volume Operational cost
Feedstock type Specific biogas production rate Saving from electricity generation
Solid content of feedstock Heat production Saving from heat production
Digestate volume Electricity production Potential income from vehicle fuel
OLR Biomethane production Potential income from digestate
Electricity consumption
Heat consumption
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9.3 Yearly evaluation
A yearly review of plant operation should also be carried out by operators or process
engineers. This should be very similar to monthly evaluation; however the time scale is over
12 months and should give a good overview on the total mass and energy throughputs, as well
as on operational economic parameters. The data can be compared with historical data from
the previous years in order to set up a yearly strategy to maintain a good operation and/or get
further improvement (if possible).
In Manipulating parameters, parameters that should be used for tuning the operation.
Response parameters, parameters that should be used to evaluate the performance of
the plant based on settings of manipulating parameters.
Other important parameters, parameters whose effect on the process should be
considered when the response from changes in operation can be observed.
The parameters that should be considered in the evaluation are listed below. The parameters
are dived into 3 different categories:
Mass throughput, in this category parameters reflecting the amount of feedstock
entering and digestate exiting the reactor, type of feedstock used and their
characteristics (VS, TS, pH, BMP), feedstock loading regime, etc should be
summarized.
Energy throughput, parameters reflecting the total produced biogas volume, specific
biogas production rate, utilization of biogas (heat, vehicle fuel, electricity), electricity
consumption, heat consumption, etc should be summarized.
Economical aspects, in this category parameters reflecting the operational cost
(material, electricity, manpower, logistic, equipment depreciation, etc.) and potential
income sources (electricity, vehicle fuel, heat, digestate as fertilizer) should be
summarized.
Table 9-3 Examples of parameters that should be considered in process evaluation.
Mass throughput Energy throughput Economic aspect
Feedstock volume Biogas volume Operational cost
Feedstock type Specific biogas production rate Saving from electricity generation
Solid content of feedstock Heat production Saving from heat production
Digestate volume Electricity production Potential income from vehicle fuel
OLR Biomethane production Potential income from digestate
Electricity consumption
Heat consumption