Wednesday, January 19, 2011

Great article on Heat Integration in CEP

The December 2010 issue of CEP (Chemical Engineering Progress) has a good article on heat integration. Disclaimer, I am a friend of the author (Alan Rossiter). Rossiter's article is a very understandable explanation of pinch analysis, a topic that is confusing to the uninitiated.

The concept of pinch analysis is that you don't need to use steam for all your heating needs, or cooling water for all your cooling needs. You might have 'hot' process streams that need to be cooled, and 'cold' process streams that need to be heated. Pinch analysis suggests that you will save energy if you use the 'cold' process stream as a utility for the 'hot' process stream, rather than purchasing steam and cooling water. While that may sound simple…most people find the next steps, performing the pinch analysis, difficult to understand.

Rossiter does a wonderful job showing us how to perform pinch analysis, and shows that the use of this method is not as difficult as we think. He explains how to understand the composite curve for 'heat sinks' and 'heat sources. He shows how you can perform a retrofit study, to see the potential benefits to integrating heat on an existing crude column.

Some of our customers have done pinch analysis before, some are interested in it.

Want to do it in CHEMCAD? We have the ability to generate a composite curve (fig 1, in Rossiter's article). You can specify the value for deltaTmin, the distance between the hot and cold curves. You can specify that some of the streams on the flowsheet should be ignored when you generate the composite curve; you wouldn't want to include a steam flow rate on the theoretical composite curve. When you're ready to explore alternate configurations, draw out a flowsheet with heat exchangers and match streams (Fig 3, Rossiter). We don't automatically match streams for you; we feel that an engineer needs to make that decision.

I suggest that anyone involved with utilities (or crude columns) and process simulators take the time to read Rossiter's article; it might give you money saving ideas.

PS While you are looking at recent issues of CEP, you could also take a look at page 59 of the Nov '10 issue, for a picture of the CHEMCAD Technical support team at AIChE's Process Technology Conference. Better yet, check out the back cover of January '11 CEP.