19. A process that is being considered for construction has been through several

Question

19. A process that is being considered for construction has been through several technicl reviews; block flow, process flow, and piping and instrumentation diagrams are available for the process. Explain the changes that would have to be made to the three principal diagrams if during a final preconstruction review, the following changes were made: a. The efficiency ofa fired heater had been specified incorrectly as 92% instead of 82%. b. A waste process stream flowrate (sent to a sludge pond) was calculated incorrectly and s now 30% greater than before. c. It has been decided to add a second (backup) drive for an existing compressor. d. The locations of several control valves have changed to allow for better operator accss. . During a retrofit of an existing prosess a verrol uno

Explanation / Answer

a) In the process flow diagram, the amount of heated materials flowing out will decreases due to the drop in efficiency

b) In the process flow diagram, the outlet waste stream calculations have to repeated again. If this outlet contains significant amount of the waste which is greater than the tolerable values of the waste, a new waste separation process has to included in all the three sheets to meet the environmental standards.

c) The changes should be included in both the block flow and piping and instrumentation diagrams. In case of the power required for the compressor is not met by the first drive, the instrumentation and control shown in PI diagram can access the second drive

d) This changes will affect the process flow and PI diagrams significantly. The valves have to be located correctly on the process flow and the PI diagram as it determines the flowrates of the various streams and also the control actions to be taken in the plant.

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