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1
BIOGAS TECHNOLOGY
BASICS - RURAL DIGESTERS -
HIGH RATE DIGESTERS
Text Book: K.M. Mital, Biogas Systems,
Principles & Applications, 1996, New Age
Intrnl.. N.Delhi.
3
National Project on Biogas Development
To promote and disseminate information
about biogas technology specifically, the
government organised the National Project
on Biogas Development nation-wide, and
several NGO's have been active in
implementing the programme on the ground.
Active dissemination was also undertaken by
the Khadi and Village Industries Commission
(KVIC), in the context of rural development
from small-scale income generating
opportunities.
4
Applications of Biogas:
1. Cooking fuel- Design of Burner.
2. Lighting Fuel- Mantle lamp.
3. After removal of traces of H2S, NH3 and water vapour, fuel gas can be used for running stationary I. C. Engines.
I. C. Engines are used with pump for water supply or with generator for power.
4. Purified & filled in CNG cylinders, biogas is a useful automobile fuel for short journeys.
5
Purpose of RURAL BIOGAS PLANTS
ENERGY RECOVERY:
FOR COOKING, LIGHTING, PUMPING, OR POWER- - WITH BURNER, MANTLE LAMP, ENGINE-PUMP AND GENERATOR
HYGIENIC DISPOSAL OF ANIMAL WASTE AS MANURE
SUBSTITUTES FOR FUELWOOD & KEROSENE
________________________________________
Another text book: Nijaguna, B.T., Biogas
Technology, New Age International publishers
(P) Ltd., 2002.
6
Eliminating firewood burning in kitchen
by use of clean burning gas fuel.
A clean and particulate-free source of energy
also reduces the likelihood of chronic
diseases that are associated with the indoor
combustion of biomass-based fuels, such as
respiratory infections, ailments of the lungs;
bronchitis, asthma, lung cancer, and
increased severity of coronary artery disease.
7
FEED FOR BIOGAS PLANT: WET
BIODEGRADABLE WASTE
Biogas systems offer an integrated system that
lends itself to a rural setting; the plants can be
maintained with a variety of organic residues, from
humans, animals, crops and domestic food waste.
It is a viable option for solid waste disposal in areas
of rapid urbanisation also.
It may be possible to manage BGS and modify by
individuals within the community, preferably the
plant owner, and reliance on 'outside' assistance
kept to a minimum.
8
FEED FOR BIOGAS PLANT: WET
BIODEGRADABLE WASTE
DOMESTIC ANIMAL WASTES: Excreta of
cow, pig, chicken etc
MANURE, SLUDGE: Canteen and food
processing waste, sewage
MUNICIPAL SOLID WASTE: After separation
of non-degradable
9
FEED FOR BIOGAS PLANT: WET BIODEGRADABLE WASTE (continued)
WASTE STARCH & SUGAR SOLUTIONS:
• Fruit processing, brewery, press_mud-from
sugar factory etc
• Sludge from activated sludge aerobic wwt
OTHER INDUSTRIAL EFFLUENTS:
• Pulp factory waste liquor,
• Leather industry waste.
10
WET FERMENTATION:
FEED HAS SUBSTRATE TOTAL SOLID
CONCENTRATION, ( TSC) = 8 TO 9 %
FOR COW DUNG, RATIO OF DUNG TO WATER
= 1:1
FOR SUCH A SLURRY, BIOGAS PRODUCED
IS:
IN SUMMER AT 47 C, 0.06 M3 PER KG DUNG
ADDED PER DAY
IN WINTER AT 8 C, 0.03 M3 PER KG DUNG
ADDED PER DAY
11
DRY FERMENTATION OR SOLID STATE
FERMENTATION :
FEED SUBSTRATE TOTAL SOLID CONCENTRATION, ( TSC) OF 20 TO 30 %, A MIX OF COW DUNG AND A WIDE VARIETY OF AGRO-RESIDUES.
FOR CATTLE DUNG AND MANY AGRO-RESIDUES AT INITIAL CONCENTRATIONS OF TSC BETWEEN 16 TO 25 % BIOGAS PRODUCTION HAS BEEN DEMONSTRATED SATISFACTORILY IN SMALL BATCH TYPE AND PLUG FLOW TYPE DIGESTERS.
12
STAGES OF MICROBIAL DECOMPOSITION: 1. HYDROLYSIS OF BIOPOLYMERS [CARBOHYDRATES, PROTEINS] TO MONOMERS 2. CONVERSION OF SUGARS, AMINO ACIDS, FATTY ACIDS TO HYDROGEN, CO2, AMMONIA AND ACETIC, PROPIONIC AND BUTIRIC ACIDS 3. CONVERSION OF H2, CO2, ACETIC ACID TO CH4 AND CO2 MIXTURE
14
Questions on BGT
What properties of biogas have to be improved before it is used as an engine fuel?
Write short notes on (i) Feedstock for biogas, (ii) Dry and wet fermentation, (iii) Microbial and biochemical aspects.
Discuss the operating parameters for biogas production by anaerobic digestion.
15
TYPES OF RURAL BIOGAS PLANTS
FIXED DOME: JANATHA, DINABANDHU
FLOATING DRUM: K.V.I.C
COMBINED FEATURES: PRAGATI
17
The Planning Research and Action Division (PRAD)
based in Uttar Pradesh, developed the 'Janata' fixed-
dome plant, based on a modified design widely used in
China.
Key features of the Janata model, is the fixed-dome. With
this design, the inlet and outlet tank volumes are
calculated for minimum and maximum gas pressures
based on the volumes displaced by the variation of gas
and slurry within the system.
The Janata system is about 30% cheaper to construct
than a KVIC model of the same capacity with added
advantages that there are no moving parts, making local
construction possible and maintenance easy. Janata
plant is more appropriate for small-scale users.
22
The basic plant, which came to be known as the
KVIC model, consists of a deep well, and a floating
drum, usually made of mild steel. The system
collects the gas, which is kept at a relatively
constant pressure. As more gas is produced, the
drum gas holder consequently rises. As the gas is
consumed, the drum then falls. The biomass slurry
moves through the system, as the inlet is higher
than the outlet tank, creating hydrostatic pressure.
Only completely digested material can flow up a
partition wall, which prevents fresh material from
'short-circuiting' the system, before flowing into the
outlet tank.
27
• COMBINES FEATURES OF KVIC &
DEENABANDU,DEVELOPED IN
MAHARASHSTRA
• LOWER PART: SEMI-SPHERICAL IN
SHAPE WITH A CONICAL BOTTOM
• UPPER PART: FLOATING GAS HOLDER
• POPULARIZED IN MAHARASHTRA,
UNDARP, PUNE
Pragati rural biogas plant
30
DRY FERMENTATION OR SOLID
STATE FERMENTATION :
FOR CATTLE DUNG AND MANY
AGRO-RESIDUES AT INITIAL
CONCENTRATIONS OF Total Solid
Content BETWEEN 16 TO 25 %
BIOGAS PRODUCTION HAS BEEN
DEMONSTRATED SATISFACTORILY
IN SMALL BATCH TYPE AND PLUG
FLOW TYPE DIGESTERS.
31
Fresh biomass added to
The top of decomposing
Biomass bed becomes
acidogenic zone. Effluent
taken from bottom.
Methanogenic zone is in
the middle having high
SRT. Compaction of fresh
biomass gives high wet
density within a short
period.
35
Table: Different types of biogas plant recognized by MNES
(Ministry of Non-Conventional Energy Sources). After Gate,
1999.
1. Floating-drum plant with a cylinder digester (KVIC model).
2.Fixed-dome plant with a brick reinforced, moulded dome
(Janata model).
3. Floating-drum plant with a hemisphere digester (Pragati
model).
4. Fixed-dome plant with a hemisphere digester (Deenbandhu
model).
5. Floating-drum plant made of angular steel and plastic foil
(Ganesh model).
7.Floating-drum plant made of pre-fabricated reinforced
concrete compound units.
8. Floating-drum plant made of fibreglass reinforced polyester.
36
Subsidies were granted on plants upto 10 Cu.m (a large
family-sized system), and usually for the models recognized
by the government, as listed in table, though there may be
regional differences. Allowances were paid towards
investment costs, to every user and for every biogas plant
that was installed, in what may be interpreted as a measure
of intent to promote biogas technology, and perhaps the most
critical instrument in determining initial uptake. The extent of
the allowance was dependent on the size of plant, socio-
economic status of the user, and geographical region,
according to rules worked out by central government.
37
Limitations for Use of rural BGT
The family size biogas program cannot cater to the
needs of the poor, as these groups fail the technical
requirements to maintain a viable plant. For even
the smallest-sized plant, three to four cattle are
needed to provide the necessary quantity of dung.
Less than this and the plant are not economically or
operationally viable. Constraints may also exist in
the provision of space and water that are likewise
necessary for a biogas plant. According to Moulik,
the smallest 3 cu.m family size plant requires about
27 sq.m of land.
38
HIGH RATE BIOGAS PLANTS FOR INDUSTRIAL
WASTE WATER TREATMENT
As part of biological waste treatment, reduces high BOD content to
make it suitable for aerobic biological treatment.
Faster disposal / recycling of waste water with partial recovery of
energy as fuel [biogas]
_______________________________________________________
Reference: Effluent Treatment & Disposal: I Ch. E, U.K.,
Symposium Series No 96, 1986, P 137-147, ‘Application of
anaerobic biotechnology to waste treatment and energy production’,
Anderson & Saw.
41
TYPES OF HIGH RATE BIOGAS PLANTS
ANAEROBIC CONTACT
ANAEROBIC FILTER:UPFLOW,
DOWNFLOW
UPFLOW ANAEROBIC SLUDGE BLANKET
ANAEROBIC FLUIDISED/ EXPANDED BED
ANAEROBIC ROTATING CONTACTOR
48
Hybrid reactor
The hybrid reactor can be used for a wide variety of industrial effluents and it is possible to maintain the desired pH conditions for both the acidogens and the methanogens. The inert matrix material increases the retention of the granular sludge and prevents the washout of the microbial population. By choosing a suitable highly porous packing material with a large specific surface, the adhesion of microbes can be greatly improved and the concentration of activated sludge in the reactors can be considerably enhanced.
49
Hybrid reactor The rate of mass transfer is
also higher owing to the increased contact time between the feed and the microbes.
As the material which
immobilizes the microbes can capture most of the sludge when the slurry passes through the reactor, the loss of sludge is minimized. Apart from the advantages of simplicity in operation and design, the hybrid reactor
also works out to be more economical than fixed bed
system at the industrial scale.
51
What criteria is applied in selecting a rural
biogas plant of a small family size?
Why is biogas is not supplied in cylinders like
LPG? Can we use same stove for both?
Explain hydraulic and solid retention time for
a fixed film biogas digester.
In a flood prone area, what type of small
biogas plant would you use?
Questions on BGT
52
ANAEROBIC ROTATING
BIOLOGICAL DISC CONTACTOR
IT CONSISTS OF A
SERIES OF DISCS OR
MEDIA BLOCKS MOUNTED
ON A SHAFT WHICH IS
DRIVEN SO THAT THE
MEDIA ROTATES AT RIGHT
ANGLES TO THE FLOW OF
SEWAGE.
55
Features of biogas lamp:
Brightness depends on gas pressure, air to
gas ratio, extent of mixing etc. Proper
nozzle adjustment is necessary to achieve
required light intensity.
Lamps designed for 100 candle-power,
consume 0.11 to 0.15 m biogas per hour.
56
Biogas for electricity Generation
One kwh can be generated from 0.7m3 of
biogas to light 15 bulbs [60watts] for one
hour.
For lighting, power route is better than
direct burning
Economical for large sized plants,
requires high initial capital investment.
57
Purification of biogas for storing in CNG
cylinders.
Removal of CO2: Scrubbing with limewater
or ethanol amine solution.
Removal of H2S: Adsorption on a bed of iron
sponge and wood shavings.
Removal of H2O:-
For the removal of moisture, pass the gas,
through the crystals of white silica gel.
58
Biogas as I.C. engine Fuel
• Traces of H2S, NH3, water vapor to be removed
by absorption/adsorption.
• With modified fuel injection system, in stationary
diesel or petrol engine biogas can be used.
• In Diesel engine, dual fuel mode is needed.
• After initial start up with petrol, engine can
run on biogas
59
Operating parameters
Retention time: The ratio of volume of slurry in the digester to the volume fed into and removed from it per day is called retention time. Thus a 20 liter digester is fed at 4 litres per day so that the volume of digester is constant the retention time is 5 days. The required retention time is normally 30 days for mesophilic
(25-35oC) conditions.
Volumetric organic loading rate: This can be expressed as kg Vs per volume per day based on the % weight of organic matter added each day to the digester volume.
Digester loading rate %= (Per cent of organic matter in feed)/(Retention Time)
Loading rate range is 0.7 to25 kg VS/ m3 / Day