SPM-500 Flash Tank

Process Description


The objective of the SPM-500 Flash Tank Process is to separate a mixture of the two paraffins hexane (C6) and heptane (C7) by virtue of the difference in their boiling point temperatures. The separated products are then sent to other units for further processing.



Click here to view the schematic display

 
Process Specifications


A mixture of approximately 300 GPM of 46 WT % hexane and 54 WT % heptane is to be separated into its constituent components. The mixture is supplied at a temperature of 85 Deg F. A total of approximately 420 ACFM of hexane rich vapor at 80 PSIG and 319 Deg F is to be produced. A total of approximately 220 GPM of heptane rich liquid at 80 PSIG and 319 Deg F is to be produced.
Equipment Specifications


The unit consists of a feed preheater (E-401), a flash tank (T-501), an overhead vapor line, and a bottoms liquid line.

The mixture flow loop is modulated by a flow control valve (V-401) with parabolic flow characteristics. The overhead vapor line is modulated by a pressure control valve (V-501) with quick opening flow characteristics. The bottoms liquid line is modulated by a level control valve with linear flow characteristics. The unit (valves, piping, and vessel) has been designed to process a maximum of approximately 500 GPM of feed. Sufficient upstream pressures and pre-heating capacity are provided to accomplish this task.

The flash tank (T-501) is a cylindrical tank 4 feet in diameter by 12 feet in height. The flash tank has a total capacity of 150 cubic feet or 1128 gallons of fluid. At design conditions the flash tank provides approximately 2 minutes of holdup running half full.

Block valves with bypasses are provided for both the vapor (HV-501 and HV-502) and liquid (HV-503 and HV-504) lines.

Instrumentation


The mixture feed flow loop is outfitted with a composition analyzer that measures weight percent hexane and heptane (AI-305 and AI-306 respectively). Feed temperature is controlled by TIC-406 and flow is controlled by flow controller FIC-401.

The overhead vapor line is outfitted with a composition analyzer that measures weight percent hexane and heptane (AI-501 and AI-502 respectively). Flash Tank pressure is regulated by pressure controller PIC-501. Vapor rate is measure by FI-501. Vapor flow can be blocked in by block valves HV-501 and HV-502. Downstream pressure is measured by PI-502.

The bottoms liquid line is outfitted with a composition analyzer that measures weight percent hexane and heptane (AI-503 and AI-504 respectively). Flash Tank level is controlled by level controller LIC-501. Liquid rate is measure by FI-502. Tank temperature and tank bottom pressure are measured by TI-501 and PI-503 respectively. Liquid flow can be blocked in by block valves HV-503 and HV-504. Downstream pressure is measured by PI-504.
Advanced Controls

The flash tank pressure may be regulated manually by modulating the pressure control valve (PIC-501 controller output), or the pressure controller (PIC-501) may be placed in automatic. In this manner, flash tank pressure may be specified (PIC-501 setpoint), with no further adjustments required by the operator.

Likewise, the flash tank level may be maintained manually by modulating the level control valve (LIC-501 controller output), or the level controller (LIC-501) may be placed in automatic. In this manor, flash tank level may be specified (LIC-501 setpoint), with no further adjustments required by the operator.

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: WT % C6 AI-305
  • Fault 2: E-401 Heat Transfer
  • Fault 3: TC406 Transmitter
  • Fault 4: Valve V-501 %
  • Fault 5: Valve V-502 %
  • Fault 6: Valve V-503 %
  • Fault 7: Valve V-504 %
  • Fault 8: Vapor PI-502
  • Fault 9: Liquid PI-504
  • Fault 10: PC501 Transmitter
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: Block Valve V-501 Fails Closed
  • Exercise 4: TC406 Transmitter Reads Low