Process Description
Natural Gas Compression Plant Overview
The Natural Gas Compression Plant program represents a typical gas processing facility that removes associated hydrocarbon liquids from natural gas streams from production wells. The produced natural gas is compressed by a set of 3-stage reciprocating compressors. Additional condensate produced by cooling at higher pressures is removed and the gas is sent to a gas pipeline for distribution to natural gas processors and other users. The removed liquids (condensate) are collected in a Make Tank where water, hydrocarbons and dissolved gases are separated. The separated water and hydrocarbons are stored in tanks.
The Natural Gas Compression Plant also includes the following utility systems:• Fuel gas system
• Flare system
• Instrument Air System
The feed mainly contains a range of alkane hydrocarbons: methane through hexane. Nitrogen, carbon dioxide and water vapor are also present in small concentrations. The feed to the Natural Gas Compression Plant is normally in 2 phases, gas and condensate, with the lighter compounds in the gas phase and heavier compounds in the condensate phase.
• The main purposes of the Natural Gas Compression Plant are to:
• Separate the condensate present in the feed from gas wells
• Remove any entrained condensate from the condensate separation step
• Compress the natural gas from well pipeline pressure to transmission pipeline pressure
• Meter the produced natural gas sent to the gas transmission pipeline
• Collect condensate removed in the first two operations
• Separate water from the condensate
• Store the separated condensate and water
A portion of the feed ethane, propane and butane and nearly all of the heavier hydrocarbon compounds in the feed gas are recovered as condensate. The removal of condensate in the Natural Gas Compression Plant minimizes the possibility of liquids accumulating in the downstream natural gas pipeline.
Feed gas and condensate from the pipeline from the production wells flows through plant inlet isolation valve XV-804 and enters the Slug Catcher, D-801 which separates condensate in the feed. The slug catcher is a large horizontal drum outfitted with a collection sump to collect the condensate. The separated gas is sent to the Cyclonic Gas Separator, D-802. Condensate removed in D-801 is sent to the Make Tank, T-862.
The Cyclonic Gas Separator, D-802 removes droplets of entrained condensate in the gas coming from the Slug Catcher using internal cyclones to remove nearly all the entrained condensate. The condensate removed in the Cyclonic Gas Separator is sent to the Make Tank. A small flow of natural gas is taken off as fuel gas for the Natural Gas Compression Plant.
The natural gas from the Cyclonic Gas Separator is sent to three electric motor-driven Gas Compressors, K-811, K-821 and K-831. Each gas compressor is a three-stage reciprocating compressor outfitted with suction drums and discharge air coolers for each stage of compression (refer to Schematic #5). Condensate collected in the suction drums of the Gas Compressors is sent to the Make Tank.
The compressed natural gas is sent to the Discharge Separator, D-841 to separate condensate produced from cooling the 3rd stage discharge gas. Because this condensate tends to have significant concentrations of dissolved light gases, it is sent back to the Slug Catcher so that these dissolved gases can be recovered.
Compressed gas from the Discharge Separator then passes through the Gas Dehydration Unit, X-841 to remove most of the water in the compressed gas. The Gas Dehydration Unit is not simulated in detail. Gas from the Gas Dehydration Unit is sent to the Dehydration K.O. Drum, D-842 to remove any drying solvent that carries over from the Gas Dehydration Unit. The collected solvent (water-based) is sent to the Slug Catcher to recover any dissolved light gases contained in the solvent.
Dried natural gas from the Dehydration K.O. Drum is sent to the Gas Meter Skid, A-851 and then into the Gas Pipeline through plant outlet isolation valve XV-855.
Make Tank, T-862 collects liquid from Slug Catcher, the Cyclonic Gas Separator and the Gas Compressors’ suction drums. The Make Tank is a vertical, cylindrical tank that acts as a three-phase separator to separate dissolved light gases from the feed streams. Water in the feed will coalesce and fall to the bottom of the Make Tank. The hydrocarbons will float on the water layer. Near the top of the Make Tank, a carryover pipe drains off the hydrocarbon layer to the Condensate Tank T-863. The water at the bottom of the Make Tank is drained off to the Water Tank T-861. Periodically, the contents of the Water and Condensate Tanks are taken off by truck.
The flashed gases from the Make Tank are sent to the VRU (Vapor Recovery Unit), X-861. The VRU is not simulated in detail. Any liquids recovered by the compression and cooling of flash gas in the VRU are returned to the Make Tank. Any non-condensable gases from the VRU are routed to the Flare System.
The Natural Gas Compression Plant ESD System controls the plant isolation valves XV-804 and XV-855. These are motor-operated valves which are opened and closed by ESD control logic. Interlock logic will automatically initiate an isolation of the Natural Gas Compression Plant and lock out the operator from introducing feed to the Natural Gas Compression Plant until the shutdown conditions are cleared. The interlock logic will also stop the motors of the three Gas Compressors. Alternatively, the operator can initiate a manual isolation of the Natural Gas Compression Plant.
The following utilities are fully integrated with the gas and condensate processing sections described above.
Refer to Schematic #14 in the “Process Schematics” section below. The Fuel Gas System distributes a small flow of gas taken from the Natural Gas Compression Plant to the Flare System.
Refer to Schematics #15 and #16 in the “Process Schematics” section below. The Flare System collects vented gases and pressure safety valve releases from the equipment in the Natural Gas Compression Plant. The HP Flare Header handles releases from equipment that normally operates at high pressure while the LP Flare Header handles all the other releases. The HP Flare Header is outfitted with a liquid K.O. drum and pumps which send any collected liquids to disposal facilities at battery limits. Gases collected by the HP and LP Headers are sent to the Flare Stack for combustion prior to release to atmosphere.
Refer to Schematic #17 in the “Process Schematics” section below. The Instrument Air System provides compressed, dry air to the pneumatic control valves in the Natural Gas Compression Plant. In case of a low air supply pressure, control valves will move to their air-fail position.
The detailed description of the principles of operation of these units and systems is provided below.
Slug Catcher
Feed Gas Valves
Raw natural gas from the Feed Gas Pipeline at battery limits passes through the pipeline block valve MOV-800, through a check valve to inlet Natural Gas Compression Plant isolation valve XV-804, and then into the Slug Catcher D-801. A bypass valve HV-804 is provided to pressure up the Natural Gas Compression Plant prior to introducing high pressure natural gas into the plant. The bypass valve is automatically closed whenever XV-804 is detected to be fully opened.
PIG Receiver R-801
The PIG Receiver R-801 is used to collect (receive) a PIG during pipeline inspections. PIG stands for pipeline inspection gizmo. The PIG is launched (inserted) at the far end of the pipeline (not simulated) and travels through the pipeline to gather information about the condition of the pipeline. A barred-T connection of the pipeline prevents the PIG from traveling to MOV-800 in case R-801 is not set up to receive the PIG. Normally, R-801 is not in service.
Slug Catcher D-801
The Slug Catcher D-801 is a long horizontal gas-liquid separator drum. Gas from the Slug Catcher is routed to the Cyclonic Gas Separator D-802. Separated liquid is collected in sump (boot) attached to the bottom of the drum. The collected liquid contains light hydrocarbons and water and is taken off to Make Tank, T-862 through control valve LV-801.
The Slug Catcher is protected from overpressure by pressure safety valve PSV-801. A hand-controlled valve HV-801 allows the Slug Catcher to be depressured to flare if needed.
Cyclonic Gas Separator
Cyclonic Gas Separator D-802
The natural gas from the Slug Catcher D-801 has small amounts of entrained liquid in it. The gas flows through block valve LV-807 and control valve FV-857 and enters the side of Cyclonic Gas Separator D-802. Internal cyclones within the vertical vessel remove nearly all of any residual entrained liquid in the gas from D-801 using cyclonic action. Liquid removed by the cyclones is collected in the bottom of D-802 while the dry gas exits the cyclones in the upper half of D-802.
Most of the dry gas is sent off to the three Gas Compressors K-811, K-821 and K-831 via a distribution header. A small flow of dry gas is taken off as fuel gas and sent to the Fuel Gas System. The collected liquid (condensate) is sent to the Make Tank T-862 through control valve LV-802.
The Cyclonic Gas Separator is protected from overpressure by pressure safety valve PSV-802. A hand-controlled valve HV-802 allows the Cyclonic Gas Separator to be depressured to flare if needed.
Gas Compressors
Refer to Schematics #5 and #7 through #9 in the “Process Schematics” section below. Schematic #5 is an overview of the three Gas Compressors and schematics #7 through #9 show the detailed instrumentation and control schemes of the Gas Compressors.
All three Gas Compressors are identical process- and instrumentation-wise. They only differ by their tag numbers. Normally, Gas Compressors No. 1 & No. 2 (K-811 and K-821) are in operation.
Gas Compressors K-811, K-821 & K-823
The Gas Compressors are 3-stage reciprocating compressors. Each stage consists of a suction drum, a reciprocating compressor cylinder and a discharge cooler.
1ST Stage
Natural gas from the Cyclonic Gas Separator D-802 flows from the inlet header through a check valve, an isolation valve (XV-811, XV-821 & XV-831), through the suction pressure control valve (PV-811, PV-821 & PV-831) and into the 1st Stage K.O. Drum (D-811, D-821 & D-831). The suction drums separate any entrained liquid in the natural gas from the Cyclonic Gas Separator. The separated condensate is collected in the bottom of the drum and is taken off to the Make Tank T-862. Normally a small flow rate of condensate is collected in the operating 1st Stage K.O. Drums.
Reciprocating compressors use pistons to compress the gas. Reciprocating compressors are constant volume machines meaning that for the same suction conditions (pressure, temperature) they will compress roughly the same volume of gas, irrespective of the discharge pressures of the stages. The sweep volumes of each stages’ compressor pistons are designed to be progressively smaller because the gas density increases with suction pressure. To adjust the flow rate handled by each compressor, clearance pockets are built into the cylinders. These clearance pockets provide extra clearance volume (the volume of the cylinder outside the piston’s sweep volume). Therefore, the total clearance volume of a cylinder can be dynamically changed by activating and deactivating these clearance pockets. The higher the clearance volume, the lower will be the volumetric efficiency of the cylinder resulting in a lower volumetric rate of gas compressed by the cylinders. The loading (i.e. volumetric rate relative to its maximum rate) of each compressor is adjusted through a single hand controller which manages the activation/deactivation of the individual clearance pockets in the cylinders of each stage of the Gas Compressors.
Because of the heat of compression, the discharge temperatures from the 1st Stage compressor cylinders are significantly increased and must be reduced before the gas enters the 2nd stage cylinder. Hot gases from the 1st Stage cylinders flow into the 1st Stage Coolers (E-811, E-821 & E-831). These are air-cooled heat exchangers whose fan motors are automatically turned on and off with the compressors’ motors. Louvers on the air cooler are adjusted to control the outlet temperatures of the 1st Stage Coolers.
2ND Stage
Cooled gas from the 1st Stage Coolers enters the 2nd Stage K.O. Drums (D-812, D-822 & D-832). Any condensate produced by the cooling of natural gas at the discharge pressure of the 1st Stage is separated in the drums and routed to the Make Tank, T-862. Normally, no condensate is produced by the 1st Stage Coolers.
Gases from the 2nd Stage K.O. Drums flow into the 2nd Stage cylinders and are compressed to a higher pressure.
The hot gases from the 2nd Stage cylinders are cooled in 2nd Stage Coolers (E-812, E-822 & E-832). These air coolers operate identically to the 1st Stage Coolers.
3RD Stage
Cooled gas from the 2nd Stage Coolers enters the 3rd Stage K.O. Drums (D-813, D-823 & D-833). Any condensate produced by cooling of natural gas at the discharge pressure of the 2nd Stage is separated in the drums and routed to the Make Tank, T-862. Normally, a significant flow of condensate is produced by the 2nd Stage Coolers.
Gases from the 3rd Stage K.O. Drums flow into the 3rd Stage cylinders and are compressed to a higher pressure.
The hot gases from the 3rd Stage cylinders are cooled in 3rd Stage Coolers (E-813, E-823 & E-833). These air coolers operate identically to the 1st & 2nd Stage Coolers. The outlet gases and condensate from the 3rd Stage Coolers pass through check valves, an outlet isolation valve (XV-812, XV-822 & XV-832), to a collection header and on to the Discharge Separator, D-841 where the condensate will be separated from the compressed gas.
Discharge Separator
Discharge Separator D-841
The compressed gas/condensate streams from the Gas Compressors K-811, K-821 & K-831 are collected in the Gas Compressor discharge header and routed into the Discharge Separator D-841. The condensate produced by the cooling of natural gas at the discharge pressure of the 3rd Stage is separated in D-841 and routed to the inlet of the Slug Catcher D-801 to recover dissolved light gases in the condensate.
The Discharge Separator is protected from overpressure by pressure safety valve PSV-841. A hand-controlled valve HV-841 allows the Discharge Separator to be depressured to flare if needed.
Gas Dehydration Unit X-841
High pressure natural gas from the Discharge Separator is normally routed through isolation valve XV-841 and through the Gas Dehydration Unit, X-841. The Gas Dehydration Unit is not simulated in detail. Its purpose is to remove most of the water vapor in the natural gas prior to passing it into the downstream transmission pipeline. This helps avoid the formation of hydrates (ice-like solid mixtures) in the pipeline. In most gas dehydration units, a circulating water-based solution such as TEG (tri-ethylene glycol) is used to absorb the water in a contacting tower/column. The dry gas is sent on to the Dehydration K.O. Drum D-842.
In case of problems in the Gas Dehydration Unit, the natural gas can be bypassed around the unit using isolation valve XV-842 to route natural gas directly to D-842.
Dehydration K.O. Drum D-842
The Dehydration K.O. Drum D-842 separates any dehydrating solution leaving in the dry gas from the Gas Dehydration Unit and removes any condensate in the gas from the Discharge Separator D-841 bypassed around the Gas Dehydration Unit. The collected liquid is routed to the inlet of the Slug Catcher D-801 to recover any dissolved light gases in the dehydrating solution/condensate.
The Dehydration K.O. Drum is protected from overpressure by pressure safety valve PSV-842. A hand-controlled valve HV-842 allows the Discharge Separator to be depressured to flare if needed.
Gas from D-842 passes on to the Gas Meter Skid A-851.
Gas Metering
Gas Meter Skid A-851
The gas from the Dehydration K.O. Drum D-842 is sent to Gas Meter Skid A-851 unit prior to flowing into the gas pipeline at battery limits. There are 2 metering runs in A-851. Normally both runs are in operation. MOV-857A/B are used to isolate the meter runs as necessary (e.g. running at reduced rate).
The design composition of the produced gas is 95.5 volume % methane, 2.9 volume % ethane, 0.8 volume % propane, 0.4 volume % carbon dioxide, 0.0 volume % nitrogen with balance (0.4 volume %) consisting of heavier hydrocarbons.
PIG Launcher L-851
Gas from A-851 normally flows through Natural Gas Compression Plant isolation valve XV-855 and through pipeline block valve MOV-858 into the Gas Pipeline at battery limits. When the Gas Pipeline needs to be inspected, a PIG can be launched from PIG Launcher L-851, through MOV-859 and into the Gas Pipeline. Normally L-851 is not in service.
Storage Tanks
Make Tank T-862
Make Tank, T-862 collects liquid from Slug Catcher, the Cyclonic Gas Separator, the Fuel Gas K.O. Drum and the Gas Compressors’ suction drums. Except for the drain from the Fuel Gas K.O. Drum which is intermittent and manually controlled, these streams pass through the three isolation valves XV-861, XV-862 and XV-863 which are automatically closed to prevent the Make Tank from being overfilled. The Make Tank is a vertical, cylindrical tank that acts as a three-phase separator to separate dissolved light gases from the feed streams.
Water in the feed streams will coalesce and fall to the bottom of the Make Tank. The hydrocarbons will float on the water layer. Near the top of the Make Tank, a carryover pipe drains off the hydrocarbon layer through hand valve HV-867 to the Condensate Tank T-863. The water at the bottom of the Make Tank is drained off to the Water Tank T-861 through hand valve HV-866. The piping between the Make Tank and the Water Tank contains a vertical U-bend to act as a seal to prevent flow when the level of the Make Tank is very low, typically at startup when all the tanks are empty, and the Make Tank is starting to receive condensate.
Flashed vapor from the top of the Make Tank is sent to a header connecting the tops of the three tanks in the Storage Tanks area. This equalizes the pressure of the tanks so that liquids will easily flow by gravity flows from the Make Tank to the Water Tank and the Condensate Tank. The pressure of the vapor header is normally set by the pressure of the Vapor Recovery Unit X-861. In case of an overload of the Vapor Recovery Unit’s capacity, an automatic pressure controller will vent excess flash gas off to the Flare System through control valve PV-861.
The Make Tank is outfitted with a pressure safety valve PSV-862 which will vent flash gas to atmosphere at a safe location in case the combined capacities of the Vapor Recovery Unit and control valve PV-861 are exceeded.
Vapor Recovery Unit (VRU) X-861
The Vapor Recovery Unit (VRU) X-861 is a packaged unit that will condense heavier components out of the flash gas from the Make Tank and return them to the Flash Tank. The VRU is not simulated in detail. It is assumed to be always running.
Gas is routed from the tanks’ vapor header through hand control valve HV-863 and into the VRU. Normally HV-863 is fully open. Condensate produced by the VRU is automatically pumped to the inlet line to the Make Tank T-862. Non-condensable gas (mainly methane) is automatically routed to the Flare System and burned prior to being released to atmosphere.
Water Tank T-861
The Water Tank T-861 is a vertical cylindrical tank of the same dimensions as the Make Tank and holds produced water from the Make Tank. Its contents are periodically loaded out to trucks through hand valve HV-864 and sent to a central water processing facility.
Condensate Tank T-863
The Condensate Tank T-863 is a vertical cylindrical tank of the same dimensions as the Make Tank and holds produced condensate from the Make Tank. Its contents are periodically loaded out to trucks through hand valve HV-865 and sent to a central condensate processing facility.
Fuel Gas System
Fuel Gas Heater E-901
Fuel gas is supplied directly from the Cyclonic Gas Separator D-802 through isolation valve XV-901 to Fuel Gas Heater E-901. The flow of fuel gas is relatively small to meet the needs of pilot gas and header purge gas of the Flare System. E-901 is a small electric heater that uses an ON/OFF thermostat-type system to heat the fuel gas. The fuel gas is heated above its hydrocarbon dewpoint so as to avoid condensate forming in the fuel gas system. Warmed fuel gas is sent to the Fuel Gas K.O. Drum D-901 through control valve PV-901.
Fuel Gas K.O. Drum, D-901
Any condensate in the fuel gas from E-901 is removed in Fuel Gas K.O. Drum D-901. A boot on D-901 collects any condensate. Normally there is no condensate in the gas to D-901. Condensate is manually drained as needed to the Make Tank T-862 through control valve HV-901.
Fuel gas is distributed to the flare system as follows:
• As supply gas to the Pilot Flame Generator X-955
• As sweep gas for the HP Flare Header
• As sweep gas for the LP Flare Header
The Fuel Gas K.O. Drum is outfitted with a pressure safety valve PSV-901 which will vent fuel gas to the LP Flare Header in case of overpressure.
Flare System
HP Flare Header
The HP Flare Header collects vents and PSV (pressure safety valve) releases from the following equipment that operates at high pressure:
• Slug Catcher D-801
• Cyclonic Gas Separator D-802
• Discharge Separator D-841
• Dehydration K.O. Drum D-842
• Gas Meter Skid A-851
Also, a small flow rate of fuel gas from Fuel Gas K.O. Drum D-901 is injected through control valve FV-960 at the beginning of the HP Flare Header to keep a continuous flow of gas through the header. The fuel keeps air from infiltrating from the Flare Stack FS-952 back into the HP Flare equipment which can result in an explosion within the HP Flare System piping and equipment.
Liquids K.O. Drum D-951
PSV releases and vents into the HP Flare Header flow into the HP Liquids K.O. Drum D-951 to separate any liquids that make have flowed from the source equipment (e.g. in case of high liquid level in the equipment) or liquids formed during the auto-chilling of the high-pressure PSV release/vent gases. Vapors are routed to the Seal Drum D-952 and then to the Flare Stack FS-952.
K.O. Liquids Pumps P-951A/B
K.O. Liquids Pumps, P-951A/B pump accumulated liquids in D-951 to disposal facilities at battery limits. These pumps are electric motor-driven centrifugal pumps. The pumps automatically start to keep the level of D-951 in a safe range during any release. P-951A will automatically start first on high level. If the level becomes very high, P-951B will be started. The pumps can also be operated manually as needed.
LP Flare Header
The LP Flare Header collects vents and PSV (pressure safety valve) releases from the following equipment that operate at low pressure:
• Fuel Gas K.O. Drum D-901
• Make Tank T-862 vapor header
• Vapor Recovery Unit X-861
Also, a small flow rate of fuel gas from Fuel Gas K.O. Drum D-901 is injected through control valve FV-954 at the beginning of the LP Flare Header to keep a continuous flow of gas through the header. This keeps air from infiltrating from the Flare Stack FS-952 back into the LP Flare equipment which can result in an explosion within the LP Flare System piping and equipment.
The LP Header is connected to the piping that brings HP Header release gas from D-951 to the Seal Drum D-952.
Seal Drum D-952
The Seal Drum is partitioned with a vertical baffle separating two sides. Utility water from battery limits feeds the left side of the drum through control valve FV-961. The left side of D-952 is normally full of water which spills over the baffle to the right side of the Seal Drum. This forms a water seal over the inlet piping of the release from D-951. This helps prevent air from infiltrating back through to the HP and LP flare headers. In normal operation, the sweep gases from the HP and LP Headers bubble up through the water seal and up the Flare Stack FS-952 which sits atop D-952. In the event of a major gas release to the Flare System, the water seal will be blown until the release flow diminishes.
A small opening is cut in the base of the baffle to allow drainage of water from the seal-side at shutdown.
Seal Water Pumps P-952A/B
Water collected in the right side of the Seal Drum is pumped to disposal via Seal Water Pumps, P-952A/B. The Seal Water Pumps are electric motor driven pumps and are of the same capacity. Normally, only one pump is in service.
Flame Generator X-955
Pilot Flame Generator X-955 uses a small flow of fuel gas from Fuel Gas K.O. Drum D-901 to maintain a flame that will ignite the HP and LP Header purge gases, vent gases and PSV release gases. X-955 employs an electronic spark generator that cycles every few seconds to ensure the pilot flame is always lit.
Flare Stack FS-952
Net gas from D-951 and the LP Flare Header flows through the water seal of Seal Drum D-952 and up Flare Stack FS-952 which sits atop of D-952. Ambient air mixes into the flare stack at the top and is ignited by Pilot Flame Generator X-955. Normally, the small amount of fuel gas that sweeps the HP and LP Flare Headers is burned by FS-952.
Instrument Air System
Overview Of Instrument Air System
The Instrument Air System provides instrument air to the Natural Gas Compression Plant’s control valves. The system generally does not affect the operation of the Natural Gas Compression Plant except in case of low instrument air pressure where control valves will move to their air-fail position.
Packaged Air Compressors C-981A/B deliver compressed air to the Air Supply Header at a constant flow rate. C-981A is normally in operation with C-981B on standby.
The Air Supply Header distributes compressed air to the Service Air Supply Header. Service air is used for general use within the plant. The Air Supply header is also connected to the Air Receiver TK-982 and supplies air to the Instrument Air Header via Air Dryers V-983A/B. The Air Dryers use a desiccant (drying beads) to remove moisture from the air flowing to the Instrument Air Header.
The Air Receiver TK-982 serves as a large air reservoir for the Instrument Air System so that in case of a failure of one of the Packaged Air Compressors the air pressure will not drop quickly. This allows time for the operator to start the standby Air Compressor without any effect on Natural Gas Compression Plant’s control valves. TK-982 is outfitted with a self-regulating pressure control valve PCV-984 which will regulate the pressure of TK-982 by venting excess air to atmosphere.
Packaged Air Compressors, C-981A/B
These packaged air compressor systems are simulated as a “black box”. When a compressor is running, it will deliver compressed air to the Air Supply Header at a constant flow rate. Also, the maximum temperature in the system is calculated based on whether the compressor is running and based on the pressure of the Air Supply Header. C-981A is normally in operation with C-981B on standby.
Air Supply Header
The Air Supply Header distributes compressed air to the Service Air Supply Header via solenoid-operated valve PV-982. Service air is used for general use within the plant. Normally, 50% of the air flow from one Air Compressor is distributed to the Air Supply Header. The Air Supply header is also connected to the Air Receiver TK-982 and supplies air to the Instrument Air Header via Air Dryers V-983A/B. Normally 50% of the air flow from one Air Compressor is distributed to the Instrument Air Header.
Air Receiver, TK-982
The Air Receiver TK-982 serves as a large air reservoir for the Instrument Air System so that in case of a failure of one of the Packaged Air Compressors the air pressure will not drop quickly. This allows time for the operator to start the standby Air Compressor without any effect on Natural Gas Compression Plant’s pneumatic control valves.
TK-982 is outfitted with a self-regulating pressure control valve PCV-984 which will regulate the pressure of TK-982 to be around 120 PSIG. This valve vents excess air to atmosphere.
Air Dryers, V-983A/B
The Air Dryers, V-983A/B use a desiccant (drying beads) to remove moisture from the air flowing to the Instrument Air Headers. The Air Dryers are always assumed to be in operation. The pressure drop across the Air Dryers is normally 11.2 PSI.
Instrument Air Supply Header
The Instrument Air Supply Header supplies air to the pneumatic control valves in the Natural Gas Compression Plant. The pressure of the header is normally around 106 PSIG.