Q & A > Question Details
We need to build very small vacuum distillation unit . We cannot find out how many of oil will crack and we cannot evaluate how many m3 of gases will be generated . So our questions:
What should be a capacity of vacuum pump in m3 per 1t/h ?
How many gases are usually released ?
or give examples from your plants.

16/10/2014 A: Kaushik Purohit, RIL, Kaushik.Purohit@ril.com
Co-relations are given in reference “refinery process modeling" by Gerald L. Kaes, first edition.
17/04/2012 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
The vapors are:
- air leakage
- non-condensible hydrocarbons from cracking
- condensible hydrocarbons from cracking
- dissolved gases in the feed
- steam
- vaporized top tray liquid
- entrained top tray liquid
For the eductor or vacuum pump data sheet, it is customery to furnish the following:
non-condensible hydrocarbon
condensible hydrocarbon
Both lbs/h and mol wt. are included for each.
How to calculate or estimate those figures?
E&C companies and some consultants have developed a set of curves for this purpose. The curves correlate feed rate, flash zone temperature, and the gas or vapor rate needed for a data sheet. Typical compositions of the various vapors are used. In the company where I used such curves, the data for generating the curves were collected by visiting many operating vacuum units and collecting operating and laboratory data. Since then, heavier crudes have/are being produced and processed. Since flash zone temperatures for those crudes are lower than with other crudes, the curves have corrections because the heavier crudes have no less propensity to cracking at those lower temperatures.
Your favorite E&C company or process consultant can make the necessary calculations for you.