Hi all,
I have a difficult question regarding to select a suitable pump for closed drain vessel service in gas distribution center.
The closed drain vessel was installed at 3m below the ground. In Feed design, 2 diaphragm pumps were designed to pump the hydrocarbon to the burn pit. There was not any calculation for these pumps available in Feed.
Because of serving hydrocarbon, client requires Pumps must be API 676 type, hence diaphragm is not accepted.
We are doing calculation and provide data for Mechanical, and because the pump is installed at ground, and the vessel is at lower position. The calculated NPSHa is "-" 2.8 m. Mechanical could not find any suitable pump for this service.
We have tried to bring down the pumps to the same level with the vessel however some safety concerns have been raised and client refused that option.
Another idea is to choose the vertical pumps and installed on top of vessel. I do not agree because it impact the instrumentation in the vessel as well as easy to cause fire if there is a leakage gas. (the low-pressure gas is connected to LP flare header and flare stack).
some questions have been raised what if we bring the closed drain vessel to ground floor, the pump can be a typical centrifugal, and if drained liquid from other process equipment can flow by gravity during maintenance or not? if the liquid flows by different pressure, then why not just install at ground level? Closed drain receiving liquid from filter Seperators, Fuel gas vessel, pipe and HP Knock-out drum. (=> this will impact piping and civil and structure because other equipment needs to be lifted to higher level)
PIDs is attached for your reference.
It would be great if i can have your opinion in this case. Thanks in advance for any discussion and opinion.
Cheers,
Linda