Process Description
Simtronics’ Gas Terminal simulation includes the following processing systems commonly found in gas terminal facilities:
• Slug Catcher
• Cyclonic Gas Separator
• Condensate Separator
• Gas Meter Skid
• Mercury Removal Unit
• Condensate Meter Skid
In addition, the following utility systems are simulated:
• Fuel Gas System
• Closed Drain System
• Flare System
• Instrument Air System
These process and utility sections are fully integrated, and, therefore, the Gas Terminal simulation enables realistic and comprehensive training for operators to master startup, normal shutdown, and emergency shutdown operations. The natural gas and condensate characteristics can be varied to impact conditions throughout the process systems. A rich set of faults is provided to permit training for response to a wide variety of operational problems.
A full range of operations can be learned and practiced on the Gas Terminal simulator. These include normal, startup, shutdown, and emergency shutdown procedures.
The rest of this manual describes the simulated Gas Terminal process and provides detailed operating procedures and exercises for training.
Gas Terminal Overview
The Gas Terminal program represents a typical gas processing facility that removes associated hydrocarbon liquids from raw natural gas streams from production wells. The conditioned natural gas from the Gas Terminal is sent to a gas pipeline for distribution to natural gas processors and other users. The removed liquids (condensate) are collected, treated to remove mercury, and pumped to a liquid pipeline for distribution to condensate processors.
The Gas Terminal also includes the following utility systems:
• Fuel gas system
• Closed Drain System
• Flare system
• Instrument Air System
• Oily Water System
• Dissolved Air Flotation Unit (DAF)
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 Gas Terminal 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 Gas Terminal are to:
• Separate the condensate present in the feed from gas wells.
• Remove any entrained condensate from the condensate separation step.
• Meter the produced natural gas sent to the downstream gas pipeline.
• Collect condensate removed in the first two operations.
• Pump and treat the condensate in the Mercury Removal Unit.
• Meter the condensate sent to the downstream condensate pipeline.
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 Gas Terminal 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 terminal isolation valve XV-804 and enters the Slug Catcher which separates condensate in the feed. The slug catcher consists of a set of long parallel pipes which slant into a large diameter pipe to collect the condensate. The parallel pipes of the Slug Catcher also have a vertical pipes attached which direct the feed gas to the Cyclonic Gas Separator, D-802. This arrangement of parallel pipes allows handling widely varying flow rates (slugs) of condensate in the feed pipeline compared to a conventional gas-liquid separation drum which would be very large and expensive owing to the high pressure of the process.
The Cyclonic Gas Separator removes droplets of entrained condensate in the gas coming from the Slug Catcher, D-801, using internal cyclones. The natural gas, free of condensate, is sent to the Gas Meter Skid and then into the Gas Pipeline through terminal isolation valve XV-805. A small flow of natural gas is taken off as fuel gas for the Gas Terminal before the Gas Meter Skid. Any excess condensate collected in D-802 can be sent to the Closed Drain System.
Condensate Separator collects liquid from the large-diameter collection pipe of Slug Catcher, D-801 and from the Cyclonic Gas Separator. D-803 is a three-phase separator and produces an oily water phase in its boot. D-803 operates at a slightly lower pressure than D-801 and D-802, so a small amount of the condensate received from these two vessels will flash off as vapor. The vapor is sent off to a Gas Recovery Unit at battery limits. The net condensate is collected at the end opposite the Condensate Separator and is pumped through the Mercury Removal Unit before passing through the Condensate Meter Skid and then into the Condensate Pipeline through terminal isolation valve XV-819. The oily water separated from the condensate on the feed side of D-803 is sent to the Closed Drain System.
The Gas Terminal ESD System controls the terminal isolation valves (XV-804, XV-805, XV-808 and XV-819). These are motor-operated valves which are opened and closed by ESD control logic. Interlock logic will automatically initiate an isolation of the Gas Terminal and lock out the operator from introducing feed to the Gas Terminal until the shutdown conditions are cleared. Alternatively, the operator can initiate a manual isolation of the Gas Terminal.
The following utilities are fully integrated with the gas and condensate processing sections described above.
The Fuel Gas System distributes a small flow of gas taken from the Gas Terminal to the Flare System.
The Closed Drain System collects any drained liquid from process units in the Gas Terminal, flashes the liquid in the Closed Drain Drum and sends any produced vapor to the LP Flare Header. Collected is sent to the Closed Drain Storage Tank and can be pumped to the Flare System Liquids K.O. Drum as needed.
The Flare System collects vented gases and pressure safety valve releases from the equipment in the Gas Terminal. 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. Gasses collected by the HP and LP Headers are sent to the Flare Stack for combustion prior to release to atmosphere.
The Instrument Air System provides compressed, dry air to the pneumatic control valves in the Gas Terminal. In case of a low air supply pressure, control valves will move to their air-fail position.
The Oily Water System separates oily components from the process water from the Gas Terminal by settling the water in a series of tanks and sumps to allow most of the oil that is dispersed in the water to coalesce and separate into an immiscible phase that floats on the water. The water is then sent to the Dissolved Air Flotation (DAF) Unit to remove the last amounts of oil still dispersed in the water. The separated oil is collected and pumped to the Flare System.
The Dissolved Air Flotation (DAF) Unit treats the water produced by the Oily Water System using an added flocculant which promotes coalescing of the remaining oil in the water. These coalesced oil droplets are brought to the surface of the DAF Basin using circulating water saturated with a small flow of ambient air. The air-saturated water is injected back into the DAF basin where the flocculated water enters the basin. Small air bubbles form because the pressure is lower in the basin than in the Air Saturator Tank. These small air bubbles help lift the coalesced oil to the top of the basin where it is skimmed off. The clarified water from the DAF Basin is then sent to the DAF Surge Tank and pumped to discharge facilities at battery limits. The float oil from the DAF Basin is recovered in the DAF Float Tank and pumped back to a sump in the Oily Water System.
Instrumentation
This section describes the controls and instruments of the Gas Terminal.
Slug Catcher
Feed Gas Pipeline
The pressure of pipeline feed gas is indicated on PI-800. Switch MOV-800 opens and closes pipeline inlet valve MOV-800. PI-806A indicates the pressure between MOV-800 and Gas Terminal inlet isolation valve XV-804. The position of XV-804 is indicated on XI-804 which reflects the open and closed limit switches on the stem of XV-804. XI-804 will indicate as OPEN, TRVL or CLSD depending on these switches. XV-804 is controlled by Gas Terminal control logic (see Gas Terminal Control below). The opening of startup bypass valve HV-804 is controlled by HIC-804. HIC-804 is locked in manual mode with an output of 0% whenever XV-804 is in the OPEN position. This ensures HIC-804 will not be left open in case there is a Gas Terminal trip which requires all pipeline gas flow to the terminal to be stopped.
PIG Receiver R-801
The inlet pipeline valve MOV-801 to PIG Receiver R-801 is opened and closed with switch MOV-801. The outlet valve MOV-802 of PIG Receiver R-801 is opened and closed with switch MOV-802. ZI-801 is an indicate-only switch to show whether or not a PIG arrival has been detected in R-801.
Slug Catcher D-801
The temperature of gas and condensate to the Slug Catcher D-801 is indicated on TI-801. The pressure of De-entrained gas leaving D-801 is indicated on PI-801.
The level of liquid in the collection header of D-801 is normally controlled by LIC-801A whose output is sent to low signal selector LY-801. LY-801 compares the output of LIC-801A with the output of LIC-803B which keeps the Condensate Separator D-803 from being overfilled. The lowest of these two outputs adjusts the position of LV-801.
Normally LIC-801A is in control of LV-801.
The flow of liquid through LV-801 is indicated on FI-808.
In case the level of condensate in the Slug Catcher becomes too high, LIC-801B reduces the flow rate of gas to the Gas terminal through low signal selector FY-805 (see Schematic #4). Normally, the setpoint of LIC-801B is set at 80% while the setpoint of LIC-801A is set at 50%. LIC-801A and LIC-801B share the same transmitter for their PVs.
An independent level instrument LAH-801 is provided as a trip to the Gas Terminal interlock.
The flow rate of gas to the Cyclonic Gas Separator D-802 is indicated on FI-801. Hand controller HIC-801 adjusts the position of control valve HV-801 on the vent line to the HP Flare Header.
Cyclonic Gas Separator
Cyclonic Gas Separator D-802
Switch MOV-807 opens and closes the inlet block valve to Cyclonic Gas Separator D-802.
Low signal selector FY-807 adjusts the position of control valve FV-807. FY-807 selects the lowest of Slug Catcher high level controller LIC-801B’s output (see Schematic #3) and the output of selector FX-807 from the Gas Meter Skid A-801 (see Schematic #5). Normally, the signal from FX-807 controls the position of FV-807. This control valve controls the flow of gas from the feed pipeline.
PI-802 indicates pressure of D-802. TI-802 indicates the temperature of the gas leaving D-802. Hand controller HIC-802 adjusts the position of control valve HV-802 on the vent line to the HP Flare Header. FI-809 indicates the flow rate of gas to the Fuel Gas System.
LIC-802A normally controls the level of the condensate collected in D-802 by adjusting the position of control valve LV-802A. Its setpoint is normally 50%. FI-802A indicates the flow of condensate through LV-802A.
LIC-802B shares the same PV with LIC-802A and controls the same level in case the level in D-802 becomes high. Its setpoint is normally 80%. LIC-802B adjusts the position of control valve LV-802B. FI-802B indicates the flow of condensate through LV-802B.
An independent level instrument LAH-802 is provided as a trip to the Gas Terminal interlock.
Gas Metering
Gas Meter A-801
Hand switches MOV-807A/B open and close the isolation valves MOV-807A/B on the “A” and “B” runs of Gas Meter Skid A-801, respectively. Normally both meter runs are in operation. One of the meter runs may be taken out of operation at lower rate operation, if desired, to maintain the operating meter run in a flow range where the meter is most accurate (near its design flow which is 46.7 MMSCF/D).
FI-807A/B indicate the volumetric flow rates of gas through meter runs “A” and “B”, respectively. FS-807 is a computing unit that sums these two indications which is then indicated on FIC-807.
PIC-805 indicates the pressure at the outlet of A-801.
FX-807 is an A/B signal selector that selects between the outputs of FIC-807 and PIC-805 to become the control signal to low signal selector FY-807 (see schematic #4). Switch HS-807 selects which controller output is used for controlling the position of control valve FV-807 via FY-807.
Normally HS-807 is in the “FIC” position so that FIC-807 controls the flow of gas from the feed pipeline. If HS-807 is placed in the “PIC” position, PIC-805’s output will regulate control valve FV-807. This control mode is not usually used unless there is some situation where the Gas Terminal will effectively be used to control the pressure of the downstream gas pipeline.
The analyzer at the outlet of the A-801 measures the sales gas from the terminal:
• AI-801 VOL % Methane (C1)
• AI-802 VOL % Ethane (C2)
• AI-803 VOL % Propane (C3)
• AI-804 VOL % Carbon dioxide (CO2)
• AI-805 VOL % Nitrogen (N2)
• AI-806 VOL PPM Water (H2O)
• AI-807 Hydrocarbon dewpoint in DEG F
PI-806B indicates the pressure downstream of Gas Terminal gas outlet isolation valve XV-805. XV-805 is controlled by Gas Terminal control logic (see Gas Terminal Control below). The position of XV-805 is indicated on XI-805 which reflects the open and closed limit switches on the stem of XV-805. XI-805 will indicate as OPEN, TRVL or CLSD depending on these switches.
Hand switch MOV-808 opens and closes the gas pipeline isolation valve MOV-808.
PI-809 indicates the Gas Pipeline pressure.
Hand controller HIC-805 adjusts the position of HV-805. Normally HV-805 is fully closed. HIC-805 is used to depressure the Gas Meter Skid at shutdown.
PIG Launcher L-801
The outlet pipeline valve MOV-801 from the PIG Launcher L-801 is opened and closed with switch MOV-809. ZI-809 is an indicate-only switch to show whether or not a PIG launch has been detected in L-801.
Condensate Separator
Condensate Separator D-803
Switch XV-801 opens and closes inlet condensate isolation valve XV-801. Switch XV-802 opens and closes inlet condensate isolation valve XV-802. Both of these switches are locked in the CLSD position in case there is high level in D-803 (see Interlock I-803 below).
The pressure of D-803 is controlled by PIC-803 by adjusting the position of control valve PV-803. Downstream of PV-803, XV-808 is controlled by Gas Terminal control logic (see Gas Terminal Control below). The position of XV-808 is indicated on XI-808 which reflects the open and closed limit switches on the stem of XV-808. XI-808 will indicate as OPEN, TRVL or CLSD depending on these switches.
PI-808 indicates the pressure of piping to the Recovery Unit at battery limits.
FI-803 indicates the flow through PV-803. TI-803 indicates the temperature of the gas leaving D-803.
Hand controller HIC-803 adjusts the position of HV-803. Normally HV-803 is fully closed. HIC-803 is used to depressure the Condensate Separator at shutdown.
The level of condensate is normally controlled by LIC-803A which adjusts the setpoint of FIC-809 which controls the flow through the Condensate Meter Skid A-802 (see Schematic #7). LIC-803B is a high level override controller that shares the PV of LIC-803A. LIC-803B is used by low selector LY-801 to reduce the condensate flow from the Slug Catcher D-801 (see Schematic #3). The setpoint of LIC-803B is normally 80% while the setpoint of LIC-803A is 50%.
In the event of a significant loss of outflow capacity of condensate from D-803, LIC-803B will reduce the condensate flow from the Slug Catcher. As a result, the Slug Catcher’s level will increase and cause LIC-801B to cause the feed flow rate to the terminal to be reduced via low signal selector FY-807 until the condensate flow from the Slug Catcher matches the reduced outflow capacity from D-803.
The level of condensate in D-803 on the inlet side of the overflow weir in D-803 is indicated on LAH-806 which is provided as a trip to the Gas Terminal interlock (see Interlock I-801 below). LIC-805 controls the interface level of water in the boot of D-803 by adjusting the position of control valve LV-805. The flow of water through LV-805 is indicated on FI-805.
Condensate Transfer Pumps P-803A/B
Hand switches HS-803A/B start and stop the motors of P-803A/B, respectively. Normally, only P-803A is in operation. FI-804 indicates the flow of condensate from P-803A/B.
Hand switches MOV-803A/B open and close the suction MOVs (motor operated valves) on these pumps, respectively.
Condensate Filters F-803A/B
Switches HV-811A/B open and close the block valves of F-803A/B respectively. Normally, only HV-811A is open.
PDI-810 indicates the pressure drop across the Condensate Filters.
Mercury Removal Unit
Mercury Removal Unit X-801
Hand switch MOV-812 opens and closes the inlet block valve to X-801. Hand switch MOV-815 opens and closes the outlet block valve from X-801. Hand controller HIC-812 adjusts the position of X-801 bypass control valve HV-812.
PI-811 indicates the inlet pressure to X-801 and HV-812. PI-816 indicates the outlet pressure of X-801 and HV-812.
Condensate Pre-filter F-812
PDI-812 indicates the pressure drop across Condensate Pre-filter F-812.
Condensate Filter Coalescer/Separator F-813
PDI-813 indicates the pressure drop across Condensate Filter Coalescer/Separator F-813.
LAHL-813 indicates the water interface level of F-813. This instrument is used to open and close control valve LV-813. Switch LV-813 is used to open and close LV-813. Switch HS-813 is an auto/manual switch to have LV-813 automatically open and close LV-813 when HS-813 is in the AUTO position. In AUTO mode, the valve will be opened when the level of F-813 reaches 60% and closed when it reaches 20%. Switch LV-813 can be manually operated in AUTO mode as long as the level of F-813 is between the high and low limits.
Mercury Removal Vessel V-814
PDI-814 indicates the pressure drop across Mercury Removal Vessel V-814.
Condensate Post-filter F-815
PDI-815 indicates the pressure drop across Condensate Post-filter F-815.
Condensate Metering
Condensate Meter Skid A-802
Hand switches MOV-818A/B open and close the isolation valves MOV-818A/B on the “A” and “B” runs of Condensate Meter Skid A-802, respectively. Normally both meter runs are in operation. One of the meter runs may be taken out of operation at lower rate operation, if desired, to maintain the operating meter run in a flow range where the meter is most accurate (near its design flow which is 2.854 MBPD).
FI-818A/B indicate the volumetric flow rates of condensate through meter runs “A” and “B”, respectively. FY-818 is a computing unit that sums these two indications which is then used as the PV for FIC-818.
Condensate Meter Skid A-802
Hand switches MOV-818A/B open and close the isolation valves MOV-818A/B on the “A” and “B” runs of Condensate Meter Skid A-802, respectively. Normally both meter runs are in operation. One of the meter runs may be taken out of operation at lower rate operation, if desired, to maintain the operating meter run in a flow range where the meter is most accurate (near its design flow which is 2.854 MBPD).
FI-818A/B indicate the volumetric flow rates of condensate through meter runs “A” and “B”, respectively. FY-818 is a computing unit that sums these two indications which is then used as the PV for FIC-818.
FIC-818 controls the condensate flow from A-802 by adjusting the position of control valve FV-818. FIC-818 is normally in cascade mode and receives its setpoint from LIC-803A to control the level of condensate in Condensate Separator D-803.
PI-819 indicates the pressure between FV-818 and condensate outlet isolation valve XV-819.
XV-819 is controlled by Gas Terminal control logic (see Gas Terminal Control below). The position of XV-819 is indicated on XI-819 which reflects the open and closed limit switches on the stem of XV-819. XI-819 will indicate as OPEN, TRVL or CLSD depending on these switches.
Hand switch MOV-820 opens and closes the condensate pipeline isolation valve MOV-820.
PI-822 indicates the pressure of the condensate pipeline.
PIG Launcher L-802
The inlet valve MOV-822 to the PIG Launcher L-808 is opened and closed with switch MOV-822.The outlet pipeline valve MOV-821 from PIG Launcher L-802 is opened and closed with switch MOV-821. ZI-821 is an indicate-only switch to show whether or not a PIG launch has been detected in L-802.
Gas Terminal Control
XIC-801 is a switch that is used to change the position of motor-operated Gas Terminal isolation valves XV-804, XV-805, XV-808 and XV-819 as follows:
• When XIC-801 is placed in the RUN position, all the Gas Terminal inlet and outlet isolation valves will be commanded to open.
• When XIC-801 is placed in the STOP position, all the Gas Terminal inlet and outlet isolation valves will be commanded to close.
• It normally takes 30 seconds for the valves to fully open or close.
• If any of the valves do not attain their commanded position within 60 seconds, the respective sequence error alarm for the affected valves (XA-804, XA-805, XA-808, XA-819) will sound.
• If a trip of the Gas Terminal occurs (I-801), XIC-801 will be locked in the STOP state until the interlock is reset.
Monitoring of ambient combustible gas concentration is performed at the Gas Terminal. XA-881 will alarm if a significant gas concentration is detected. XAH-881 will alarm if excessively a high concentration of combustible gas is detected and is provided as a trip to the Gas Terminal interlock.
Fuel Gas System
Fuel Gas Heater E-901
Switch XV-901 is an indicate-only switch that shows the position of E-901 inlet isolation valve XV-901. XV-901 is controlled by Interlock I-901.
TIC-901 is a controller that when in automatic mode will turn E-901 control switch TS-901 ON and OFF to maintain the outlet temperature around the setpoint of TIC-901 within a deadband of +/- 0.9 DEG F. When TIC-901 is in manual mode, switch TS-901 is maintained in the OFF position.
Switch HS-902 is the master power switch of E-901 and must be ON for the heater to work.
Fuel Gas K.O. Drum D-901
PIC-901 controls the pressure of D-901 by adjusting the position of control valve PV-901. Normally PIC-901’s setpoint is 58 PSIG.
PAH-901 independently indicates and alarms the pressure of D-901 and is a trip sensor for Interlock I-901.
LI-901 indicates the level of condensate in D-901.
LAH-901 independently indicates and alarms the level of condensate in D-901 and is a trip sensor for Interlock I-901.
Hand controller HIC-901 adjusts the position of HV-901 to drain condensate from D-901 to the Closed Drain Drum D-921. Normally HV-901 is fully closed.
FI-901 indicates the flow of fuel gas from D-901 to all the fuel gas users.
Closed Drain System
Closed Drain Drum D-921
LIC-921 controls the level of condensate in D-921 by adjusting the position of control valve LV-921.
LIC-923 controls the interface level of water in the boot of D-921 by adjusting the position of control valve LV-923.
Closed Drain Tank T-922
Hand switch MOV-921 opens and closes the inlet isolation valve MOV-921 on the line from D-921.
Hand switch MOV-922 opens and closes the inlet isolation valve MOV-922 on the line from the Oily Water System.
LI-922 indicates the level of condensate in T-922.
P-923A/B
Hand switches MOV-923A/B open and close the suction MOVs (motor operated valves) on P-923A/B, respectively.
Hand switches HS-923A/B start and stop the motors of P-923A/B, respectively. Normally no pump is in operation.
FI-923 indicates the flow rate of condensate from P-923A/B to the Liquids K.O. Drum D-951 of the Flare System.
Flare System
HP Flare Header
FIC-960 controls the flow of purge fuel gas to the header by adjusting the position of control valve FV-960.
D-951
Hand switch MOV-953 opens and closes the inlet block valve MOV-953 on the condensate line from P-923A/B.
PI-951 indicates the pressure of D-951. FI-953 indicates the flow of gas from D-951 to Seal Drum D-952.
LIC-951 indicates the level of liquid in D-951 by controlling the position of control valve LV-951. LIC-951 is automatically placed into automatic mode under the control of Interlock I-951.
HP Flare Header
FIC-960 controls the flow of purge fuel gas to the header by adjusting the position of control valve FV-960.
D-951
Hand switch MOV-953 opens and closes the inlet block valve MOV-953 on the condensate line from P-923A/B.
PI-951 indicates the pressure of D-951. FI-953 indicates the flow of gas from D-951 to Seal Drum D-952.
LIC-951 indicates the level of liquid in D-951 by controlling the position of control valve LV-951. LIC-951 is automatically placed into automatic mode under the control of Interlock I-951.
LAH-951 independently indicates the level of liquid in D-951. It is used by control interlock I-951 to start P-951A/B.
P-951A/B
Hand switches MOV-951A/B open and close the suction MOVs (motor operated valves) on P-951A/B, respectively.
Hand switches HS-951A/B start and stop the motors of P-951A/B, respectively. These switches can be operated at any time, irrespective of the state of Interlock I-951.
FI-951 indicates the flow of liquids from P-951A/B to disposal facilities at battery limits.
X-955
Hand switch HS-955 turns HP Pilot Flame Generator X-955 on and off.
FI-955 indicates the flow rate of fuel gas to X-955.
XI-955 indicates the intensity of the pilot flame produced by X-955.
FS-952
TI-955A/B indicate the temperature in the vicinity of the tip of the HP Flare Stack.
XI-956 indicates the flame intensity at the tip of the HP Flare Stack.