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PROCESS MOISTURE ANALYZER
PROCESS MOISTURE ANALYZERS
Measuring moisture in gas or HC liquids in hazardous areas
Copyright Caltech 2014
PROCESS MOISTURE ANALYZER
EExd ConstructionSafety by containment
Channel 1 gas inlet & outlet
Channel 2 gas inlet & outlet
Cable glands
Through-glass user interface
Channel 1 dew-point &
pressure sensor
Channel 2 dew-point & pressure sensor
EExd enclosure
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PROCESS MOISTURE ANALYZER
Control Unit Sensor Assemblies
IS work by using barriers
User interface
Safe area Hazardous area
Optional pressure transmitter
Sensor block
Dew-point transmitter
Electrical connections
Power port and
switch
Built-in I.S. barriers
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PROCESS MOISTURE ANALYZER
Gas analysers requireCareful sample system design
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PROCESS MOISTURE ANALYZER
Natural Gas Production
Glycol dehydration process monitoring - onshore & offshore
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PROCESS MOISTURE ANALYZER
Liquefied Natural Gas Production
• Molecular sieve dehydration prior to liquefaction
• LNG re-gasification at receiving terminals
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PROCESS MOISTURE ANALYZER
Refineries and Petrochemical Processing
• Petroleum Refinery– Isomerisation naphtha– Reformer re-cycle H2
• HDPE plant – ethylene
• BTX processes– benzene, toluene and
xylene
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PROCESS MOISTURE ANALYZER
Other Applications:
• Pipeline Drying• Offshore export pipeline natural gas• Transmission pipeline monitoring• Fiscal metering of gas• Gas storage facilities• Hydrogen cooling• CNG filling stations• Industrial gases• Welding gases
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PROCESS MOISTURE ANALYZER
Measurement Principle – background• Liquids consisting of non-polar molecules such as
hydrocarbon chain or hydrocarbon rings do not mix with water.
• Liquid Hydrocarbons can absorb a certain amount of water vapour (dissolved moisture) and thus have a limited saturation concentration.
• Dissolved moisture acts as a gas, exerting a partial pressure with corresponding dew-point temperature.
• Saturation concentration is specific to the liquid and highly dependant on temperature.
Oil & Water Do Not Mix
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PROCESS MOISTURE ANALYZER
Measurement Principle –Henry’s Law
In chemistry, Henry's law is one of the gas laws. It was formulated by William Henry of Manchester, England in 1803.
At a constant temperature, the amount of a given gas dissolved in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.
Henry’s law is applicable for organic liquid when the moisture content at saturation does not exceed 1%
S
W
S P
P
C
C
Copyright Caltech 2014
PROCESS MOISTURE ANALYZER
Measurement Principle – Henry’s Law
Henry’s Law is used for determining the Weight Portion of moisture in total Liquid
C = Moisture concentration in ppmWCs = Saturation moisture concentration in ppmW at the temperaturePw = Water vapour pressure from sensor measurementPs = Saturation water vapour pressure at the temperature
K = Cs/Ps (Henry constant)
The impedance sensor measures Pw. To calculate C, the Cs must be known.
WS
S PP
CC
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PROCESS MOISTURE ANALYZER
Measurement Principle –Solubility Data (CS value) Example
Calculated saturation concentration of typical LPG propane and butane mixtures
0100200300400500600700
0 10 20 30 40 50
Temperature of liquid, deg. C
Cs,
pp
mW
PropaneButane70%C3-30%C480%C3-20%C490%C3-10%C4
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PROCESS MOISTURE ANALYZER
Measurement Principle –Calculation Example
Cyclohexane with measured dew point of –20oC and analysis temperature of +30oC:
Moisture content in ppmW = CS/PS x PW
CS for cyclohexane at 30oC sample temperature = 194 ppmW
PW at –20oC measured dew point = 103 Pa
PS at 30oC sample temperature = 4247 Pa
ppmW = 194 x 103/4247 = 4.7 ppmW
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PROCESS MOISTURE ANALYZER
Can be ATEX IS or EExd
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PROCESS MOISTURE ANALYZER
Control Unit Sensor Assemblies
I.S. Construction
User interface
Safe area Hazardous area
Temperature transmitter
Sensor block
Dew-point transmitter
Electrical connections
Power port and
switch
Built-in I.S. barriers
Copyright Caltech 2014
PROCESS MOISTURE ANALYZER
EExd and I.S. HC Liquid Sampling System
• Again careful design required.
• Temperature stabilisation needs to be considered
• Sample can return to systems-cost benefit
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PROCESS MOISTURE ANALYZER
Petrochemical Plants
• Hydrocarbon feed stock
• Hydrocarbon products
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PROCESS MOISTURE ANALYZER
Liquid Fuels
• Aero/jet fuel• Heating oil
• LPG ‘autogas’
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PROCESS MOISTURE ANALYZER
Other Applications:
• Prevents acid formation during reactor process• Controls moisture in solvents for polymer production• Liquid fuels to avoid supply line blockage• Lubricant oils for preventative maintenance• Transformer oil to prevent insulation breakdown• Solar power heat transmission media
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PROCESS MOISTURE ANALYZER
Quartz Crystal Moisture Analyzers
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PROCESS MOISTURE ANALYZER
Quartz Sensor Technology
• A quartz crystal is sensitised with a thin film of hygroscopic material.
• Water molecules are adsorbed into the hygroscopic layer deposited on the surface.
• The change in mass modifies, in a very precise and repeatable manner, the oscillation frequency.
• The moisture concentration is measured as a change in the oscillation frequency
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PROCESS MOISTURE ANALYZER
Measurement Principle –Sensor Construction
Sensor Crystal
Reference Crystal
Primary Δf = fReference Crystal – fSensor Crystal
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PROCESS MOISTURE ANALYZER
Measurement Principle –Sensor Construction
• Compact design & easy access for serviceability
• Sensor block contains the following elements:
Sensor and reference quartz crystal
3 solenoid valves
Moisture generator
Oscillator electronics
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PROCESS MOISTURE ANALYZER
Measurement Principle –T Variation Effect
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PROCESS MOISTURE ANALYZER
• Oven contains the following elements:
Sensor block
Mass flow meter
Capillaries
Temperature probe
Heater
Fan
Measurement Principle –Oven Construction
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PROCESS MOISTURE ANALYZER
Measurement cycle (phase 1)Dried sample flow
Measurement cycle (phase 2)Sample flow
Dryer
Flow Meter
Measurement Δf = primary Δfsample – primary Δfdry
•30/30 sec measurement cycle•Non-equilibrium for fast response•Self-cancelling effect for contamination
60sec
Measurement Principle – Measurement Cycles
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PROCESS MOISTURE ANALYZER
Calibration cycle (phase 1)Dried sample flow
Calibration cycle (phase 2)Calibration flow
Dryer
Flow Meter
Measurement Δf = primary Δfdry – primary Δfcal
•Moisture generator with calibrated value•Calibration adjusted based on measured Δf and the known moisture level
Moisture Generator
Measurement Principle – Auto Calibration Cycles
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PROCESS MOISTURE ANALYZER
QMA2020 Construction
Dry Gas inlet
Cable glands
Through-glass user interface
Electronics
Sensor oven assembly
EExd enclosure
Cable glands
Sample inlet
Gas outlet
Mole-sieve dryer
PROCESS MOISTURE ANALYZER
Application – Glycol Dehydration of Natural Gas
Application: Glycol Dehydration / Moisture Monitoring in Natural Gas
Problem: The circulation rate of the glycol must be balanced against flow rate of the natural gas and the amount of water to be removed.
Specification:30-1000ppmVPressure: 200-1500 psig
Installation: Outdoors or in instrument shelter. Div 2 / Zone 1 areas. Offshore Div 1 / Zone 1.
Required Sampling system:- Heated Pressure Regulation- Liquid Separator- Contaminant Trap- Asymmetric timing- Insulated or htd sample lines
PROCESS MOISTURE ANALYZER
Application – Molecular Sieve Dehydration
Application: Mole Sieve dehydration / Moisture Monitoring in Natural Gas
Problem: Time-based bed regenerations cost money, permit process upsets, shorten bed life.
Specification:0-100ppmVPressure: 200-1500 psig
Installation: Outdoors or in instrument shelter. Div 2 / Zone 1 areas. Offshore Div 1 / Zone 1.
Required Sampling system:
- Heated Pressure Regulation- Contaminant Trap- Asymmetric timing- Insulated or htd sample lines
Sampling System Block diagram, drawing or picture
PROCESS MOISTURE ANALYZER
Application – Custody Transfer of Natural Gas
Application: Moisture Monitoring in pipeline quality Natural Gas
Problem: Gas quality specs must be met before entry into transport pipelines. Excess moisture forms hydrates and causes corrosion.
Specification:30-1000ppmVPressure: 200-1500 psig
Installation: Outdoors or in instrument shelter. Div 2 / Zone 1 areas. Offshore Div 1 / Zone 1.
Required Sampling system:
-Heated Pressure Regulation-Liquid Separator-Contaminant Trap-Asymmetric timing-Insulated heated sample lines
Copyright Caltech 2014
PROCESS MOISTURE ANALYZER
QMA2020 – Refinery Catalytic Reforming
Application: Moisture Monitoring in H2 Recycle Streams
Problem: Excess or insufficient moisture in catalytic reforming impacts catalyst activity and life.
Typical Range: 10-20ppmVTemperature: ambient
Installation: Outdoors, typically in Div 1 / Zone 1 areas
Sampling System Block diagram, drawing or picture
Required Sampling system:-Isolation of Sample System with nitrogen purge for use during catalyst regeneration-Pressure Regulation-Contaminant trap-Asymmetric timing
Copyright Caltech 2014
PROCESS MOISTURE ANALYZER
Application – Propylene
Application: Moisture Monitoring in Propylene Gas Streams
Problem: Water is a contaminant to most processes utilizing propylene; especially reactions used to produce polypropylene.
Typical Range: 0-10ppmVTemperature: ambient
Installation: Outdoors, typically in Div 1 or 2 / Zone 1 areas
Required Sampling system:
-Pressure Regulation-Super-dryer-Symmetric timing-Heated sample transport lines
Copyright Caltech 2014
PROCESS MOISTURE ANALYZER
EthyleneApplication: Moisture Monitoring in Ethylene Gas Streams
Problem: Water is a contaminant to most processes utilizing Ethylene; especially reactions used to produce plastics.
Typical Range: 0-10ppmVTemperature: ambient
Installation: Outdoors, typically in Div 1 or 2 / Zone 1 areas
Required Sampling system:
-Pressure Regulation-Super-dryer-Symmetric timing-Heated sample transport lines
Copyright Caltech 2014
PROCESS MOISTURE ANALYZER
Application – LNGApplication: Moisture Monitoring in re-gasification process
Problem: process monitoring and custody transfer / quality assurance purposes
Typical Range: 0-25ppmV
Installation: Outdoors, typically in Div 2 / Zone 1 areas
Required Sampling system:
-Heated Pressure Regulation-Contaminant Trap-Asymmetric timing-Insulated or htd sample lines
Copyright Caltech 2014
PROCESS MOISTURE ANALYZER
Other Applications:
Hazardous area• Industrial gas production• Olefins production• LNG production / Re-vaporization• And many more...
Non hazardous area• High purity gas production• Industrial gas production• Electronic gases• Air separation plants• Catalyst bed protection• Semiconductor grade gases• Cylinder gases• Speciality gases• Process dryers• Hydrocarbon gases• And many more...
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PROCESS MOISTURE ANALYZER
What is the Hydrocarbon Dew point?
The dew point is the temperature at which hydrocarbon condensates firstbegin to form when natural gas is cooled, at constant pressure.
Similar of course for water, but water has no retrograde curve
-40 -30 -20 -10 0 +10
Water and HC liquidspresent in gas
HC liquidspresent ingas
Wholly gaseous
Temperature, oC
Pres
sure
, Ba
ra
H2O Dewpoint
HC Dewpoint
0
10
20
30
40
50
60
70
80
Retrograde Phase Envelope
Hydrocarbon and Water Dewpoint in Natural Gas
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Hydrate formations
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Compressor damage
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PROCESS MOISTURE ANALYZER
Hydrocarbon dew point control in gas turbines
•A major industrial application for natural gas is as the feed energy source for combined cycle gas turbine power plant, producing electricity.
• Often 50ºF of superheat is required to prevent HCL’s forming
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PROCESS MOISTURE ANALYZER
Hydrocarbon Dew point Reduction Plant
Well HeadNGL
Separator
Glycol Contactor
10-15MPa
J.T. Valve
P= 3 to 5 MPa
L.T.S.
Condensate
Compressor
Transmission Pipeline
7 to 15 MPa
Water dew point reduction
Hydrocarbon Dewpoint reduction
After extraction from the gas field, natural gas is processed to remove water and heavy hydrocarbon components, before transmission through the pipeline network. This diagram shows a typical plant for the removal of both excess moisture and heavy hydrocarbons
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PROCESS MOISTURE ANALYZER
What the processing achieves
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How can hydrocarbon dew point be measured?
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Equation of state calculation from extended GC analysis: Sample, analyse, calculate
Mol%C1 Methane CH4 88C2 Ethane C2H6 5C3 Propane C3H8 2C4 Butane C4H12 1C5 Pentane C5H14 0.3C6 Hexane C6H16 0.1C7 Heptane C7H16 0.03C8 Octane C8H18 0.01C9 Nonane C9H20 0.001C10 Decane C10H22 0.0003C11 Undecane C11H24 0.0000C12 Dodecane C12H26 0.0000
CO2 1.5H2O 0.005 (50ppm)H2S 0.0001N2 2.0O2 0.08
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3 calculations 3 results
In addition the presence ofaromatics such as toluene and benzene can affect the result
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PROCESS MOISTURE ANALYZER
Optical Condensation Dew Point Meter
Temperature, oC
mg/
Nm
3
0
20
40
60
80
100
120
140
160
-30 -20 -10 0 +10 +20
Liquid to gas ratio
Temperature,
mg/
Nm
3
0
20
40
60
80
100
120
140
160
-30 -20 -10 0 +10 +20
Temperature. C
LGR
mg/m3
AB C
Hydrocarbon tail forms B~C
C is the lowest theoretical pointcould be 20ºC higher than firstvisible quantity.
It is accepted practice to regress the Line to point A to eliminate the tailAnd arrive at an over all DP
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PROCESS MOISTURE ANALYZER
The DARK SPOT Technique
Wetted withCondensate
Light Source Detector
Dry
Light Source Detector
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The DARK SPOT Technique
The dark spot forming
- - - -
- - -
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PROCESS MOISTURE ANALYZER
CONDUMAX Hydrocarbon Dewpoint Analyser
Confronting the issues:• High sensitivity - DARK SPOT
Technique• Facility to produce an ‘LGR plot’
- sensitivity calibration routine• Decoupling the sample flow
rate/cooling rate inter-relationship - fixed volume sample analysis
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
10 15 20 25 30 35 40 45 50
Optical Surface Temperature, deg.F
Sig
nal
Ch
ang
e, m
V
Trip point setting at 275mV (Factory Default)
Optical Surface Temperature, °F
Sign
al C
hang
e, m
V
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PROCESS MOISTURE ANALYZER
CONDUMAX II Hydrocarbon Dewpoint Analyser
Control Unit
Remote interface
Sampling System
Sensor Assembly
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PROCESS MOISTURE ANALYZER
Inside the optical sensor cell
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PROCESS MOISTURE ANALYZER
The End
Thanks
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