A process instrumentation diagram of a flash drum is shown in Figure. Steam is condensed in a steam coil to vaporize a portion of the liquid feed, and the liquid product is removed by a pump. There are control valves for the steam flow, vapor product, liquid product, feed flow, and the steam chest (which allows the steam chest to be rapidly evacuated in emergency situations). Determine which of the five valves should be fail-close (F/C) or fail-open (F/O) for safe operation, for each of three cases:
(a) The safest conditions are achieved by the lowest temperature and pressure in the flash vessel.
(b) Vapor flow to downstream equipment can cause a hazardous situation.
(c) Liquid flow to downstream equipment can cause a hazardous situation. Discuss various scenarios of air failure (or powerfailure).
