Process Description
Gas pipeline Overview
Supplier No. 1 is located at the west end of the West Leg of the pipeline. Supplier No. 1 normally supplies 100 MMCFD of natural gas to the Gas Pipeline. The west end of the pipeline normally operates at 865 PSIG.
Compressor Station No. 1 handles all the flow of natural gas coming from Supplier No. 1 via the West Leg. Compressor Station No. 1 consists of two centrifugal Booster Compressors K-101A/B which can be operated in series or parallel operation. Normally only one of the compressors is in operation. The inlet pressure to Compressor Station No. 1 is normally 800 PSIG. The outlet pressure of Compressor Station No. 1 is normally 959 PSIG.
The natural gas from Compressor Station No. 1 enters the western end of the Central Leg. Supplier No. 2 is connected into the Central Leg approximately midway along the pipeline leg. Supplier No. 2 normally supplies 75 MMCFD of natural gas to the Gas Pipeline. The combined flow from suppliers No. 1 and 2 are sent to Compressor Station No. 2 at the east end of the Central Leg.
Compressor Station No. 2 consists of two centrifugal Booster Compressors K-201A/B which can be operated in series or parallel operation. Normally only one of the compressors is in operation. The inlet pressure to Compressor Station No. 2 is normally 800 PSIG. The outlet pressure of Compressor Station No. 2 is normally 1,071 PSIG.
The natural gas from Compressor Station No. 2 enters the western end of the East Leg. Supplier No. 3 is connected into the East Leg approximately midway along the pipeline leg. Supplier No. 3 normally supplies 75.0 MMCFD of natural gas to the Gas Pipeline. The combined flow from suppliers No. 1, 2 and 3 (250 MMCFD) are sent to the Terminus at the east end of the East Leg. After being metered at the Terminus, the natural gas is sent to a distribution system at battery limits. The Terminus normally operates at 700 PSIG.
A natural gas storage cavern is connected to the East Leg of the pipeline just before the Terminus. In case the natural gas cannot be taken off to the distribution system after the Terminus, the natural gas can be sent to Cavern C-701 so that the flow rates from Suppliers No. 1, 2 and 3 do not have to be reduced. Depending on the pressure of the natural gas in the Cavern, Injection Compressor K-701 may be put in service to move the natural gas from the Eat Leg into the Cavern. Similarly, Retrieval Compressor K-702 may be put in service to return natural gas from C-701 back to the East Leg as needed. A Line Heater is provided to warm up cold natural gas from that returns from the Cavern when the Cavern pressure is much higher than the pressure of the East Leg.
Supplier No. 1
Supplier No. 1 supplies natural gas to the West Leg of the pipeline. The flow of gas passes through flow control valve FV-011 and on to Filter F-001 to remove any solids suspended in the gas prior to entering Supplier No. 1 Meter Run MR-001. MR-001 uses a turbine flow meter to accurately measure the volumetric flow of the natural gas entering the West Leg of the pipeline. A densitometer on the metering skid measures the density of the natural gas so that the mass flow into the pipeline can be calculated from the volumetric flow given by the turbine flow meter. Motor-operated valves MV-011 and MV-2000 are located at the inlet of the Filter F-001 and at the outlet of Meter Run No. 1 MR-001 so that the flow from Supplier No. 1 can be stopped in case of normal shutdown or in case of an emergency. The piping for the supply line and the meter run are located at grade.
West Leg
Natural gas from Supplier No. 1 Meter Run MR-001 flows through piping and enters the beginning of the West Leg of the Gas Pipeline just upstream of isolation valve MV-2001 which is located at grade. The Western Leg of the Gas Pipeline system is 16 inches in diameter and 50 miles. It runs at approximately a constant elevation from beginning to end. The pipeline runs underground after MV-2001 and is 8 feet under the surface of the land.
There are four more motor operated isolation valves, MV-2001, MV-2002, MV-2003 and MV-2004 on the Western Leg. The pipeline emerges from underground at each isolation valve and returns underground after the valve. This allows the valve to be accessed at the surface for maintenance and repair. A gate valve is used for each valve with a motor actuator. The motor opens or closes the valve in 30 seconds to isolate sections of the pipeline in case of an emergency (e.g. a leak or fire near the pipeline property) or maintenance on a section of the pipeline.
Note that the pipeline MOVs normally are outfitted with an equalization line and hand valves in parallel to the MOV at the valve station in case there is very high differential pressure across the MOV when it is closed. The equalization line is used to manually direct gas to the low-pressure side of the valve. This is done because a large differential pressure across the MOV will inhibit the opening of the disk inside the gate valve assembly. The force of the motor pulling the disk can often result in damage to the seal trim on the disk. Opening the equalization line reduces the pressure difference across the MOV to avoid damage when opening the MOV. The equalization line and its valves are not simulated. It is assumed these local operations are performed as necessary.
West Leg PIG Launcher L-001 is located at the beginning of the Western Leg of the pipeline above grade just before MV-2001. A small supply line from MR-001 passes through hand valve HV-013A (a gate valve) to provide gas to push the PIG (pipeline inspection gizmo) out of the launcher and into the Western Leg as needed. A PIG can be used for inspection and for cleaning the pipeline, depending on its design.
The PIG launcher consists of a pipe with a larger diameter than that of the Western Leg and is fitted with a swing cover plate at the larger end for loading the PIG. On the simulator, loading of the PIG by swinging the cover plate and inserting the PIG is accomplished with HV-013C. These operations are always done in the field but are presented to the operator on the simulator so that the basic operation of PIG loading and launching can be practiced. The launcher also has a transition piece that tapers to the diameter of the pipeline. Hand valve HV-013B isolates the launcher from the Western Leg. The Western Leg is constructed such that the PIG can travel smoothly in the natural gas flowing through the pipeline to the West Leg PIG Receiver R-001 at the end of the Western Leg. Normally all the valves for L-001 are closed. Note that a PIG launcher also has vent, drain and equalization valves along with pressure gauges for local operation (draining, venting, purging, filling). These are excluded on the simulator and all appropriate local operations for loading and launching the PIG are assumed to be performed correctly.
After the last segment of the West Leg, the pipeline emerges to the surface and enters the West Leg PIG Receiver R-001. R-001 is essentially a mirror image of West Leg PIG Launcher R-001. Flow from the pipeline is routed into R-001 through HV-014A. R-001 is also outfitted with a small line and valve HV-104B to allow natural gas flow into R-001 so that the PIG will enter.
The main flow from the Western Leg diverts through a barred tee upstream of HV-014A and is sent to Compressor Station No. 1. Barring (lengths of steel bar) on the tee prevents the PIG from flowing into the side port of the tee. Natural gas flow from R-001 through HV-014B is combined with the flow to Compressor Station No. 1. Normally all the valves for R-001 are closed. Note there is no unloading function for R-001 because this is assumed done in the field after a PIG is received in R-001.
Compressor Station No. 1 Controls
Compressor Station No. 1 consists of two variable speed centrifugal compressors that can operate in either series or parallel. Each compressor is outfitted with a discharge air cooler to cool the natural gas before it is sent to the Central Leg. The purpose of Compressor Station No. 1 is to boost the pressure of the natural gas coming from the West Leg of the pipeline so that the flow rate of natural gas through the West Leg can be maintained as the natural gas travels on to the Central Leg. The operation of the compressor station is highly automated for purposes of ease of operation and improved safety.
Natural gas normally flows from the West Leg to Compressor Station No. 1 through the compressor station’s inlet motor operated valve (MOV) MV-2005I. Direct flow from the West Leg to the Central Leg is made by bypassing the Compressor Station No. 1 which will open the mainline MOV MV-2005M. Natural gas flows from MV-2005I through Filter F-101 which removes any suspended solids that may be present in the gas from the West Leg.
Knockout Drum D-101 removes any liquids present in the natural gas leaving Filter F-101. This prevents potential damage to the Booster Compressors.
The gas normally flows from D-101 to No. 1 Booster Compressor K-101A. K-101A is outfitted with suction and discharge valve MOVs (MV-101AS and MV-101AD). Both valves are open when K-101A is running. K-101A is a centrifugal compressor outfitted with an electric motor powered by a variable frequency drive (VFD). The VFD powers both K-101A and K-101B. In normal operation, the speed of K-101A is adjusted to maintain the inlet pressure to Compressor Station No. 1. The VFD adjusts the frequency of the electric power to the motor and therefore adjusts the speed of K-101A. In case the VFD is not in operation, electric switchgear will directly connect power from the utility supply to the motor and it will run at full speed.
No. 1 Discharge Air Cooler E-101A is outfitted with a fan to blow air through the cooler. The motor of the fan runs whenever K-101A motor is running. The cooled gas from E-101A is normally sent to the discharge line of the Compressor Station whenever Booster Compressor K-101B is not running.
In case K-101A and K-101B are not running, gas flow from D-101 will automatically bypass K-101A and K-101B through a check valve in the bypass line around the compressors.
Booster Compressor K-101B can also directly take gas leaving D-101 and operate in parallel to K-101A. Alternatively, K-101B can be lined up in series with K-101A. To do this, tie valve HV-101 is opened to route discharge gas from E-101A to the suction of K-101B. A check valve between the suction lines of K-101A and K-101B ensures that gas from E-101A does not recycle back to the suction of K-101A. Also, a check valve between the discharge lines of K-101A and K-101B ensures that discharge gas from K-101B does not recycle back to the suction of K-101B. To operate K-101B in parallel to K-101A, the tie valve HV-101 is fully closed.
Booster Compressor K-101B is identical to K-101A and normally serves as a standby spare. K-101B’s suction and discharge valves (MV-101BS, MV-101BD) are identical to those of K-101A as is its Discharge Air Cooler E-101B.
Cooled gas from E-101A and E-101B and any gas bypassing K-101A/B are combined and routed through the compressor station’s outlet MOV MV-2005O to join with the mainline piping passing around the compressor station through mainline valve MV-2005M. The boosted natural gas then flows to the Central Leg of the Gas Pipeline.
Upstream of MV-2005O, a gas recycle line is routed through anti-surge control valve XV-102 to Knockout Drum D-101. XV-102 is regulated by an anti-surge controller XIC-102. Normally XV-102 is closed and no gas is recycled to D-101.
Central Leg
Natural gas from Compressor Station No. 1 flows through piping and enters the beginning of the Central Leg of the Gas Pipeline just upstream of isolation valve MV-2006 which is located at grade. The Central Leg of the Gas Pipeline system is 16 inches in diameter and 50 miles long. It runs at approximately a constant elevation from beginning to end. The pipeline runs underground after MV-2006 and is 8 feet under the surface of the land. There are four more motor operated isolation valves, MV-2007, MV-2008, MV-2009 and MV-2010 on the Central Leg. The pipeline emerges from underground at each isolation valve and returns underground after the valve. This allows the valve to be accessed at the surface for maintenance and repair. A gate valve is used for each valve with a motor actuator. The motor opens or closes the valve in 30 seconds. These valves are used to isolate sections of the pipeline in case of an emergency (e.g. a leak or fire near the pipeline property). MV-2008 is located on the tie-in line from Supplier No. 2 Meter Run MR-002 which is located mid-way between MV-2007 and MV-2009.
Central Leg PIG Launcher L-002 is located at the beginning of the Central Leg of the pipeline above grade just before MV-2006. L-002 PIG operations are not simulated.
After the last segment of the Central Leg the pipeline emerges to the surface and enters the Central Leg PIG Receiver R-002. R-002 PIG operations are not simulated.
The flow from the Central Leg is sent to Compressor Station No. 2.
Supplier No. 2
Supplier No. 2 supplies natural gas to the Central Leg of the pipeline. The flow of gas passes through flow control valve FV-021 and on to Filter F-002 to remove any solids suspended in the gas prior to entering Supplier No. 2 Meter Run MR-002. MR-002 uses a turbine flow meter to accurately measure the volumetric flow of the gas entering the Central Leg of the pipeline. A densitometer on the metering skid measures the density of the gas so that the mass flow into the pipeline can be calculated from the volumetric flow given by the turbine flow meter. Motor-operated valves MV-021 and MV-2008 are located at the inlet of the Filter F-002 and at the outlet of Meter Run No. 2 MR-002 so that the flow from Supplier No. 2 can be stopped in case of normal shutdown or in case of an emergency. The piping for the supply line and the meter run are located at grade. Flow from MR-002 continues through a short run of pipe above grade to the tie-in with the Central Leg.
Compressor Station No. 2 Controls
Compressor Station No. 2 is identical in configuration to Compressor Station No. 1. It consists of two variable speed centrifugal compressors that can operate in either series or parallel. Each compressor is outfitted with a discharge air cooler to cool the natural gas before it is sent to the East Leg. The purpose of Compressor Station No. 2 is to boost the pressure of the natural gas coming from the Central Leg of the pipeline so that the flow rate of natural gas through the Central Leg can be maintained as the natural gas travels on to the East Leg. The operation of the compressor station is highly automated for purposes of ease of operation and improved safety.
Natural gas normally flows from the Central Leg to Compressor Station No. 2 through the compressor station’s inlet motor operated valve (MOV) MV-2011I. Direct flow from the Central Leg to the East Leg is made by bypassing the Compressor Station No. 2 which will open the mainline MOV MV-2011M. Natural gas flows from MV-2011I through Filter F-201 which removes any suspended solids that may be present in the gas from the Central Leg.
Knockout Drum D-201 removes any liquids present in the natural gas leaving Filter F-201. This prevents potential damage to the Booster Compressors.
The gas normally flows from D-201 to No. 2 Booster Compressor K-201A. K-201A is outfitted with suction and discharge valve MOVs (MV-201AS and MV-201AD). Both valves are open when K-201A is running. K-201A is a centrifugal compressor outfitted with an electric motor powered by a variable frequency drive (VFD). The VFD powers both K-201A and K-201B. In normal operation, the speed of K-201A is adjusted to maintain the inlet pressure to Compressor Station No. 2. The VFD adjusts the frequency of the electric power to the motor and therefore adjusts the speed of K-201A. In case the VFD is not in operation, electric switchgear will directly connect power from the utility supply to the motor and it will run at full speed.
No. 2 Discharge Air Cooler E-201A is outfitted with a fan to blow air through the cooler. The motor of the fan runs whenever K-201A motor is running. The cooled gas from E-201A is normally sent to the discharge line of the Compressor Station whenever Booster Compressor K-201B is not running.
In case K-201A and K-201B are not running, gas flow from D-201 will automatically bypass K-201A and K-201B through a check valve in the bypass line around the compressors.
Booster Compressor K-201B can also directly take gas leaving D-201 and operate in parallel to K-201A. Alternatively, K-201B can be lined up in series with K-201A. To do this, tie valve HV-201 is opened to route discharge gas from E-201A to the suction of K-201B. A check valve between the suction lines of K-201A and K-201B ensures that gas from E-201A does not recycle back to the suction of K-201A. Also, a check valve between the discharge lines of K-201A and K-201B ensures that discharge gas from K-201B does not recycle back to the suction of K-201B. To operate K-201B in parallel to K-201A, the tie valve HV-201 is fully closed.
Booster Compressor K-201B is identical to K-201A and normally serves as a standby spare. K-201B’s suction and discharge valves (MV-201BS, MV-201BD) are identical to those of K-201A as is its Discharge Air Cooler E-201B.
Cooled gas from E-201A and E-201B and any gas bypassing K-201A/B are combined and routed through the compressor station’s outlet MOV MV-2011O to join with the mainline piping passing around the compressor station through mainline valve MV-2011M. The boosted natural gas then flows to the East Leg of the Gas Pipeline.
Upstream of MV-2011O, a gas recycle line is routed through anti-surge control valve XV-202 to Knockout Drum D-201. XV-202 is regulated by an anti-surge controller XIC-202. Normally XV-202 is closed and no gas is recycled to D-201.
East Leg
Natural gas from Compressor Station No. 2 flows through piping and enters the beginning of the East Leg of the Gas Pipeline just upstream of isolation valve MV-2012 which is located at grade. The East Leg of the Gas Pipeline system is 16 inches in diameter and 50 miles long. It runs at approximately a constant elevation from beginning to end. The pipeline runs underground after MV-2012 and is 8 feet2.40 meters under the surface of the land. There are four motor operated isolation valves, MV-2013, MV-2014, MV-2015 and MV-2016 on the East Leg. The pipeline emerges from underground at each isolation valve and returns underground after the valve. This allows the valve to be accessed at the surface for maintenance and repair. A gate valve is used for each valve with a motor actuator. The motor opens or closes the valve in 30 seconds. These valves are used to isolate sections of the pipeline in case of an emergency (e.g. a leak or fire near the pipeline property). MV-2014 is located on the tie-in line from Supplier No. 3 Meter Run MR-003 which is located mid-way between MV-2013 and MV-2015.
East Leg PIG Launcher L-003 is located at the beginning of the East Leg of the pipeline above grade just before MV-2012. L-003 PIG operations are not simulated.
The flow from MV-2016 flows through the last segment of the East Leg to the Storage and Terminus areas of the Gas Pipeline.
Supplier No. 3
Supplier No. 3 supplies natural gas to the East Leg of the pipeline. The flow of gas passes through flow control valve FV-031 and on to Filter F-003 to remove any solids suspended in the gas prior to entering Supplier No. 3 Meter Run MR-003. MR-003 uses a turbine flow meter to accurately measure the volumetric flow of the gas entering the East Leg of the pipeline. A densitometer on the metering skid measures the density of the natural gas so that the mass flow into the pipeline can be calculated from the volumetric flow given by the turbine flow meter. Motor-operated valves MV-031 and MV-2014 are located at the inlet of the Filter F-003 and at the outlet of Meter Run No. 3 MR-003 so that the flow from Supplier No. 3 can be stopped in case of normal shutdown or in case of an emergency. The piping for the supply line and the meter run are located at grade. Flow from MR-003 continues through a short run of pipe above grade to the tie-in with the East Leg.
Cavern Controls
R-003 East Leg Pig Receiver
Natural gas flows from MV-2016 on the East Leg through the last segment of approximately 10 miles. The East Leg emerges to the surface and enters the East Leg PIG Receiver R-003. R-003 PIG operations are not simulated. Flow from the East Leg normally flows past R-003 to the Terminus of the pipeline located a short distance from R-003.
D-701 Knockout Drum
Upstream of R-003 there are takeoff and return lines to the Cavern Storage Area on the East Leg. The takeoff and return lines are 8 inches in diameter and will not pass a larger diameter PIG from the East Leg. The takeoff line passes through MOV MV-701 and continues to Knockout Drum D-701 which removes any liquid that might be present in the takeoff gas from the East Leg.
K-701 Cavern Injection Compressor
From D-701, natural gas flows to the Cavern Injection Compressor K-701. K-701 is used to send natural gas from the East Leg of the Gas Pipeline to the Cavern C-701 in order to build gas inventory during low natural gas demand times of the year. Normally, no gas is being sent to the Cavern. K-701 is outfitted with suction and discharge MOVs MV-703S and MV-703D.
When the Cavern pressure is below the pressure of the East Leg, direct injection of pipeline gas to the Cavern can be made through control valve FV-704 without needing to put K-701 into service. FV-704 also can be manually opened when K-701 is running in order to recycle a portion of the discharge gas from K-701. This allows control of the gas takeoff rate from the East Leg while K-701 is running.
C-701 Cavern
The net natural gas flow from K-701 and FV-704 is combined and piped to the Cavern C-701 which is a large underground natural formation of high volume that can hold high pressure natural gas without a significant loss of gas. The Cavern is normally storing natural gas at 2,000 PSIG. The practical maximum pressure of the Cavern is 2,500 PSIG. The practical minimum pressure of the Cavern is 300 PSIG. Note that the storage capacity of the Cavern is made smaller on the simulator compared to real caverns so that the pressure response of the natural gas in the Cavern may be more readily observed in a typical classroom training session in response to operator actions on the simulator.
MOV MV-704 is used to isolate the injection piping from the Cavern.
Retrieval of natural gas from the Cavern is made through MOV MV-710 which isolates the Cavern from the gas retrieval section.
K-702 Cavern Retrieval Compressor
When the Cavern pressure becomes less than the pressure of the East Leg, the Cavern Retrieval Compressor K-702 is used to retrieve natural gas from the Cavern. K-702 is a motor-driven reciprocating compressor. It is outfitted with suction and discharge MOVs MV-711S and MV-711D. The discharge gas from K-702 is cooled in Discharge Air Cooler E-702. The motor of E-702’s fan runs whenever K-702’s motor is running. The cooled retrieval gas from E-702 is sent to the East Leg of the Gas Pipeline through MOV MV-702.
F-711 Line Heater
When the Cavern pressure is higher than the East Leg pressure, retrieval gas will be routed through control valve FV-713 to Line Heater F-711. F-711 is an indirectly fired heater which warms cold retrieval gas that results from depressuring through control valve FV-713 (Joule-Thomson effect). The cold gas must be warmed to prevent the possibility of brittle fracture of the pipeline. A glycol/water solution is warmed in the lower part of F-711 using combusted fuel gas which transfers heat through firetubes immersed in the glycol solution. The heated glycol solution rises by convection (warmer liquids are less dense) and bathes the warming tubes in the upper section of F-711. Heater transfers from the glycol solution to the cold retrieval gas flowing through the warming tubes. The cooled glycol solution then circulates down back to the firetubes in the lower section of F-711. The fuel gas passes through control valve TV-714 from battery limits. The details of the burner system for F-711 are not simulated.
The warmed retrieval gas from F-711 is also sent through MOV MV-702 to the East Leg of the Gas Pipeline.
Terminus
The Terminus is the very end of the Gas Pipeline at the end of the East Leg. All the equipment is above grade. Flow from the East Leg Filter F-004 to remove any solids suspended in the natural gas prior to entering Terminus Meter Run MR-004. MR-004 uses a turbine flow meter to accurately measure the volumetric flow of the natural gas taken from the East Leg of the pipeline. A densitometer on the metering skid measures the density of the natural gas so that the mass flow into the pipeline can be calculated from the volumetric flow given by the turbine flow meter. Flow then continues from MR-004 through pressure control valve PV-041. Motor-operated valves MV-2017 and MV-041 are located at the inlet of the Filter F-004 and at the outlet of Terminus Meter Run MR-004 so that the flow from the East Leg of the pipeline can be stopped in case of normal shutdown or in case of an emergency. Flow from MR-004 continues through a short run of pipe above grade to piping that transfers the natural gas to the downstream distribution system at battery limits.