PROCESS MOISTURE ANALYZERS Measuring moisture in gas or HC liquids in hazardous areas

Transcription

1 PROCESS MOISTURE ANALYZERS Measuring moisture in gas or HC liquids in hazardous areas

2 EExd Construction Safety by containment PROCESS MOISTURE ANALYZER Channel 1 dew-point & pressure sensor Through-glass user interface Channel 1 gas inlet & outlet Channel 2 dew-point & pressure sensor EExd enclosure Channel 2 gas inlet & outlet Cable glands

3 IS work by using barriers User interface Control Unit Sensor Assemblies Optional pressure transmitter Built-in I.S. barriers Sensor block Electrical connections Dew-point transmitter Power port and switch Safe area Hazardous area

4 Gas analysers require Careful sample system design

5 Natural Gas Production Glycol dehydration process monitoring - onshore & offshore

6 Liquefied Natural Gas Production Molecular sieve dehydration prior to liquefaction LNG re-gasification at receiving terminals

7 Refineries and Petrochemical Processing Petroleum Refinery Isomerisation naphtha Reformer re-cycle H2 HDPE plant ethylene BTX processes benzene, toluene and xylene

8 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

9 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

10 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 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. C C S P P W S Henry s law is applicable for organic liquid when the moisture content at saturation does not exceed 1%

11 Measurement Principle Henry s Law Henry s Law is used for determining the Weight Portion of moisture in total Liquid C C P S W C = Moisture concentration in ppmw C s = Saturation moisture concentration in ppmw at the temperature P w = Water vapour pressure from sensor measurement P s = Saturation water vapour pressure at the temperature K = C s /P s (Henry constant) S P The impedance sensor measures P w. To calculate C, the Cs must be known.

12 Measurement Principle Solubility Data (C S value) Example Calculated saturation concentration of typical LPG propane and butane mixtures Cs, ppmw Temperature of liquid, deg. C Propane Butane 70%C3-30%C4 80%C3-20%C4 90%C3-10%C4

13 Measurement Principle Calculation Example Cyclohexane with measured dew point of 20 o C and analysis temperature of +30 o C: Moisture content in ppm W = C S /P S x P W C S for cyclohexane at 30 o C sample temperature = 194 ppm W P W at 20 o C measured dew point = 103 Pa P S at 30 o C sample temperature = 4247 Pa ppm W = 194 x 103/4247 = 4.7 ppm W

14 Can be ATEX IS or EExd

15 I.S. Construction User interface Control Unit Sensor Assemblies Temperature transmitter Built-in I.S. barriers Electrical connections Sensor block Dew-point transmitter Power port and switch Safe area Hazardous area

16 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

17 Petrochemical Plants Hydrocarbon feed stock Hydrocarbon products

18 Liquid Fuels Aero/jet fuel Heating oil LPG autogas

19 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

20 Quartz Crystal Moisture Analyzers

21 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

22 Measurement Principle Sensor Construction Sensor Crystal Reference Crystal Primary Δf = f Reference Crystal f Sensor Crystal

23 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

24 Measurement Principle T Variation Effect

25 Measurement Principle Oven Construction Oven contains the following elements: Sensor block Mass flow meter Capillaries Temperature probe Heater Fan

26 Measurement Principle Measurement Cycles Dryer Measurement cycle (phase 1) Dried sample flow 60sec Flow Meter Measurement cycle (phase 2) Sample flow Measurement Δf = primary Δf sample primary Δf dry 30/30 sec measurement cycle Non-equilibrium for fast response Self-cancelling effect for contamination

27 Measurement Principle Auto Calibration Cycles Dryer Moisture Generator Calibration cycle (phase 1) Dried sample flow Flow Meter Calibration cycle (phase 2) Calibration flow Measurement Δf = primary Δf dry primary Δf cal Moisture generator with calibrated value Calibration adjusted based on measured Δf and the known moisture level

28 QMA2020 Construction EExd enclosure Mole-sieve dryer Electronics Sensor oven assembly Through-glass user interface Cable glands Cable glands Gas outlet Sample inlet Dry Gas inlet

29 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: ppmV Pressure: 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

30 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. Required Sampling system: - Heated Pressure Regulation - Contaminant Trap - Asymmetric timing - Insulated or htd sample lines Specification: 0-100ppmV Pressure: psig Installation: Outdoors or in instrument shelter. Div 2 / Zone 1 areas. Offshore Div 1 / Zone 1. Sampling System Block diagram, drawing or picture

31 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. Required Sampling system: Specification: ppmV Pressure: psig Installation: Outdoors or in instrument shelter. Div 2 / Zone 1 areas. Offshore Div 1 / Zone 1. -Heated Pressure Regulation -Liquid Separator -Contaminant Trap -Asymmetric timing -Insulated heated sample lines

32 QMA2020 Refinery Catalytic Reforming Application: Moisture Monitoring in H 2 Recycle Streams Problem: Excess or insufficient moisture in catalytic reforming impacts catalyst activity and life. Typical Range: 10-20ppmV Temperature: ambient Installation: Outdoors, typically in Div 1 / Zone 1 areas Required Sampling system: -Isolation of Sample System with nitrogen purge for use during catalyst regeneration -Pressure Regulation -Contaminant trap -Asymmetric timing Sampling System Block diagram, drawing or picture

33 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: 0-10ppmV Temperature: 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

34 Application: Moisture Monitoring in Ethylene Gas Streams Ethylene Typical Range: 0-10ppmV Temperature: ambient Problem: Water is a contaminant to most processes utilizing Ethylene; especially reactions used to produce plastics. Installation: Outdoors, typically in Div 1 or 2 / Zone 1 areas Required Sampling system: -Pressure Regulation -Super-dryer -Symmetric timing -Heated sample transport lines

35 Application: Moisture Monitoring in re-gasification process Problem: process monitoring and custody transfer / quality assurance purposes Application LNG 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

36 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...

37 Hydrocarbon and Water Dewpoint in Natural Gas What is the Hydrocarbon Dew point? The dew point is the temperature at which hydrocarbon condensates first begin to form when natural gas is cooled, at constant pressure. Similar of course for water, but water has no retrograde curve Pressure, Bara H 2 O Dewpoint Water and HC liquids present in gas Retrograde Phase Envelope HC liquids present in gas Wholly gaseous HC Dewpoint Temperature, o C

38 Hydrate formations

39 Compressor damage

40 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

41 Hydrocarbon Dew point Reduction Plant PROCESS MOISTURE ANALYZER Water dew point reduction Hydrocarbon Dewpoint reduction Well Head 10-15MPa Glycol Contactor Separator NGL P = 3 to 5 MPa J.T. Valve L.T.S. Condensate Transmission Pipeline 7 to 15 MPa Compressor 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

42 What the processing achieves

43 How can hydrocarbon dew point be measured?

44 Equation of state calculation from extended GC analysis: Sample, analyse, calculate Mol% C 1 Methane CH 4 88 C 2 Ethane C 2 H 6 5 C 3 Propane C 3 H 8 2 C 4 Butane C 4 H 12 1 C 5 Pentane C 5 H C 6 Hexane C 6 H C 7 Heptane C 7 H C 8 Octane C 8 H C 9 Nonane C 9 H C 10 Decane C 10 H C 11 Undecane C 11 H C 12 Dodecane C 12 H CO H 2 O (50ppm) H 2 S N O

45 3 calculations 3 results In addition the presence of aromatics such as toluene and benzene can affect the result

46 Optical Condensation Dew Point Meter PROCESS MOISTURE ANALYZER LGR mg/m mg/nm 3 mg/nm It is accepted practice to regress the Line to point A to eliminate the tail And arrive at an over all DP Liquid to gas ratio Hydrocarbon tail forms B~C A B C Temperature, C is the lowest theoretical point Temperature. C could be 20ºC higher than first visible quantity Temperature, o C

47 The DARK SPOT Technique Light Source Detector Light Source Detector Dry Wetted with Condensate

48 The DARK SPOT Technique PROCESS MOISTURE ANALYZER The dark spot forming

49 CONDUMAX Hydrocarbon Dewpoint Analyser 1500 Confronting the issues: High sensitivity - DARK SPOT Technique Facility to produce an LGR plot - sensitivity calibration routine Decoupling the sample flow rate/cooling rate interrelationship - fixed volume sample analysis Signal Change, mv Signal Change, mv Trip point setting at 275mV (Factory Default) Optical Surface Temperature, deg.f Optical Surface Temperature, F

50 CONDUMAX II Hydrocarbon Dewpoint Analyser PROCESS MOISTURE ANALYZER Sampling System Sensor Assembly Remote interface Control Unit

51 Inside the optical sensor cell

52 The End Thanks