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Vacuum Pump Non-Condensible Loads

Vacuum Pump Non-Condensible Loads

Vacuum Pump Non-Condensible Loads

(OP)
Greetings,

Working on a prelimiary design for a new processing facility - reactor followed by 3 distillation columns. Need to develop a sized equipment list for approximate total installed costs.

The columns are to be operated under vacuum conditions and working on sizing vacuum pumps for the application. The systems are totally condensed and vapor pressures in the reflux drum are low so at this point looking for an air leakage estimate to get a decent idea of required pump capacity.

Have little else to go on at this point so attempting to use the air leakage curves published by the Heat Exchange Institute as a starting point but the resulting leakage numbers seem very low. For one situation we have a column with an estimated internal volume of ~ 350 ft3 to be operated at 50 mmHg. Based on the system volume and operating pressure the HEI curves predicts the leakage rate at ~ 7 lb/hr or about 31 ACFM. Comparing to vacuum pump specs on P&ID's from other processes thinking this capacity should be an order of magnitude higher. Realize safety factors should be applied but the ACFM result just seems way off.

Admittedly in uncharted territory here as first time using the HEI charts so looking for some insight.

Does anyone have vacuum pump sizing experience using the HEI charts?

Are there better air leakage estimate guidelines for early capacity sizing?

Thanks,

JoeChem

RE: Vacuum Pump Non-Condensible Loads

The figures from HEI apply for properly sized and maintained vacuum system. It doesn't really make a lot of sense to use numbers which are an order of magnitude above these figures. Some resources recommend to add 2-5 lb/hr on top of the number as calculated by HEI, to account for various additional connections throughout the system.

A great resource on this subject is "Encyclopedia of Chemical Processing and Design: Volume 61 - Vacuum System" by J.J.McKetta. Some parts are published online (see https://books.google.ro/books?id=RNXyYP8EA2EC&... in particular pages 19-52.

The image below is from GEA Vacuum Systems and they refer to HEI standards as well, with consideration given to relative number of flanged vs. welded connections. See original resource, page 2 at: http://produkte.gea-wiegand.de/GEA/GEACategory/146...





Dejan IVANOVIC
Process Engineer, MSChE

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