SPM-1400 Centrifugal Compressor

Process Description


The SPM-1400 Centrifugal Compressor Process Simulation can be configured to compress a variety of process gases by varying the molecular weight. The default configuration is for dry air.

Air passes through a suction valve before entering the suction drum. If the process gas demand is less than the minimum recommended compressor flow (surge point), then the makeup gas will mix with the kickback flow. The gas then passes through a cooler, where the temperature is lowered to prevent excessive compressor discharge temperatures. Any condensate present in the gas will be knocked out in the suction drum before the gas enters the compressor.

The compressed gas is then drawn off from the discharge side of the compressor by users. In the event of a decrease in process gas demand by the users, a minimum compressor flow line (kickback or spillback) is provided to allow the recycling of gas to prevent compressor surging. A vent/flare line is also provided to prevent an over-pressuring of the system.



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Process Specifications


Approximately 500 MSCFH of air is to be compressed from a suction pressure of 250 PSIG to a discharge pressure of 500 PSIG. All of the gas is sent to a downstream process which is maintained at 375 PSIG. The compressor speed required to accomplish this task is 5343 RPM. Compressor suction temperature is maintained at 100 Deg F, and the compressor discharge temperature is 260 Deg F.

Equipment Specifications


The centrifugal compressor is driven by a steam turbine. The machine is capable of rotating at a maximum speed of 10000 RPM, however it should be tripped at about 8000 RPM to prevent damage to the equipment. At design conditions, the compressor is operating at approximately 70% of maximum capacity.

All the valves in the system have linear flow characteristics. The vent/flare line has been given sufficient capacity to completely vent the system down in an emergency.

The cooler has been designed with sufficient capacity to maintain the suction temperature of the gas within tolerable limits, even when the compressor is running on total kickback.
Instrumentation


Flow to the suction drum is maintained by suction pressure controller PIC-301. The suction flow is indicated by FI-101. Supply gas pressure and temperature are indicated by PI-101 and TI-101 respectively. The supply gas block valves can be opened and closed with switches HV-101 and HV-102.

Kickback flow, which is indicated by FI-501, is controlled by FIC-301 which indicates total compressor flow.

Vent/flare flow is controlled by over-pressure controller PIC-701 and is indicated by FI-701. The vent/flare block valves can be opened and closed with the switches HV-701 and HV-702.

Flow to the process is controlled by FIC-601. The downstream process pressure is indicated by PI-601. The process block valves can be opened and closed with the switches HV-601 and HV-602.

Steam flow to the turbine is controlled by speed controller SIC-401. The steam block valves can be opened and closed with the switches HV-401 and HV-402.

Cooling water flow to the cooler is controlled by TIC-202 and indicated by FI-201. Cooling water supply temperature is indicated by TI-203 and cooling water return temperature is indicated by TI-204. The cooling water block valves can be opened and closed with the switches HV-201 and HV-202.

Compressor discharge temperature is indicated by TI-501 and compressor discharge pressure is controlled by PIC-501.
Advanced Controls

There are a number of ways of controlling a centrifugal compressor. The following is a description of a number of common methods.

Compressor suction pressure is controlled by suction pressure controller PIC-301, which modulates the flow to the suction drum. Compressor suction may also be allowed to float by placing PIC-301 in manual and maintaining the position of the suction valve constant.

Compressor discharge pressure is maintained by PIC-501 which is cascaded to the compressor speed controller SIC-401 in a master-slave type arrangement. The compressor may be operated at constant speed and the discharge pressure may be allowed to float, by placing SIC-401 in automatic mode. Alternatively, discharge pressure may be maintained with the vent/flare pressure controller PIC-701.

Faults


All faults can be failed high or low to any degree with any of 8 fault function generators (step change, square wave, staircase, stairs, ramp, sawtooth, slope, or sine wave). Faults can be programmed to start and/or stop at various times during a simulation exercise.

  • Fault 1: Valve V-101 %
  • Fault 2: Valve V-102 %
  • Fault 3: Valve V-201 %
  • Fault 4: Valve V-202 %
  • Fault 5: Valve V-401 %
  • Fault 6: Valve V-402 %
  • Fault 7: Valve V-601 %
  • Fault 8: Valve V-602 %
  • Fault 9: Valve V-701 %
  • Fault 10: Valve V-702 %
  • Fault 11: TI-101 Supply
  • Fault 12: TI-203 Cool Wtr
  • Fault 13: PI-101 Supply
  • Fault 14: PI-601 Process
  • Fault 15: Coolr Heat Trans
  • Fault 16: PC301 Transmitter
  • Fault 17: PC501 Transmitter
  • Fault 18: SC501 Transmitter
  • Fault 19: FC301 Transmitter
  • Fault 20: Molecular Weight
  • Fault 21: Surge Point
  • Fault 22: Valve V-301 %
Training Exercises


You may create a virtually unlimited number of scenarios and training exercises by programming the faults described in the previous section. You can then establish performance standards for each one of those exercises. Simtronics provides a number of exercises with established performance standards for each process simulation. The objective, time to complete the exercise, cause, effect, solution, and procedure for each exercise is documented. You may modify these procedures to more closely reflect your particular process plant operating procedures.

  • Exercise 1: Design
  • Exercise 2: Cold Start
  • Exercise 3: Suction Valve Ramps Closed
  • Exercise 4: Pressure Transmitter PIC-501 Fails