Chemical Engineering Progress February, 2010
An article in the February 2010 issue of Chemical Engineering Progress, "Producing Electricity and Chemicals Simultaneously" by Herbert W. Cooper (pp. 24-32), prompted quite a few letters from readers and generated much discussion. Because of space constraints, we were not able to print all of them in the magazine. Two appear in the May issue (pp. 4-5).
Here is another letter that we received. The author's reply appears as the first comment.
To the Editor:
We read with interest the recent article "Producing Electricity and Chemicals Simultaneously" in the February 2010 issue of CEP which examines the possibility of doing simultaneous chemical (methanol) and electricity production in one facility and concludes that the economics are poor based on today's costs. We believe that the author's conclusions are not necessarily correct as he has overlooked certain factors in his analysis. If we consider running two different plants in parallel using the same raw material, then it is clear that, depending on the costs and sales prices of the products, one process will always perform economically better than the other. As a result, there is no apparent advantage in having a mixed product plant. It only becomes profitable to have a mixed product plant when there are significant synergies and integration between the two operations and processes. The author restricts his analysis to a plant that produces electricity only and one that produces electricity and methanol simultaneously. From the outset we can predict that the optimum is either an electricity only plant or a methanol only plant as the author does not consider integration of the electricity and methanol plants. If we look at the author's mixed product plant the only synergy that seems to have been exploited is using the off gases from the methanol plant to make electricity, which is not necessarily a large benefit. Our research group has been looking into integrated methanol and electricity plants for several industrial clients and believe there are potentially large advantages to integrating the processes in several situations. For instance, there are considerable synergies if we were to make the methanol plant a once through plant and then combust the off gases (which are abundant due to equilibrium limitations) for electricity production. In this case, as one does not have a recycle system one does not have to do air separation, with at most oxygen enrichment. Also the steam generated from the methanol synthesis can be used in the electricity generation. The possibilities for process combinations are virtually endless and need to be explored in depth, and with insight. We have developed tools to look at the targets (Glasser et al., 2009) or what is theoretically possible, for such situations and so are able to scan the possibilities very rapidly and with a minimum of information. An important point to recall is that simply using the established flow-sheets for the process and putting them together will rarely if ever result in an optimal mixed product plant. Our work has shown that the optimum flow-sheets often become radically different for each of these combinational cases and these reveal the real synergies in the mixed product plants. These mixed product plants certainly can begin to look very attractive from a suitability and economic perspective. The possibilities for making radical improvements on the way we currently do things are out there if we are open minded in our approach. Part of this thinking requires that we move away from a cut and paste design approach and work on the development of new processes even for established technologies. The thinking and technologies that were available 50 years ago, and those in the market today are in many case quantum leaps apart, but often existing process are not adjusted beyond incremental improvements to take advantage of this. Another example of such possible world changing technology is the integration of air separation and methane reforming proposed by Air Products with the application of their ITM technology. Yours sincerely, David Glasser, Diane Hildebrandt, Brendon Hausberger, Bilal Patel, Centre of Material and Process Synthesis, Department of Chemical and Metallurgical Engineering, University of the Witwatersrand, Johannesburg, South Africa Benjamin J Glasser, Department of Chemical and Biochemical Engineering, Rutgers University, Piscataway, New Jersey, USA Reference: Glasser D., Hildebrandt D., Hausberger B., Patel B. and Glasser B., (2009), Invited Perspectives Article: Systems Approach to Reducing Energy Usage and Carbon Dioxide Emissions. AIChE Journal, 55 (9), 2202-2207.
Please let us know what you think.
Comments
Dear Professor Glasser et al.,
Thank you for sharing your thoughts about the subject; I agree with some of them and disagree with others, as discussed below.
I do remain comfortable that my conclusions are correct and while there are inevitably factors that were considered but not specifically included in the published version of the analysis, I have addressed the ones I deemed to be of practical importance, and offer the following elaborations.
You note that when “running two different plants in parallel using the same raw material, then it is clear that, depending on the costs and sales prices of the products, one process will always perform economically better than the other.” and later “From the outset we can predict that the optimum is either an electricity only plant or a methanol only plant…” These are narrowly true, but overlook some non-technical but important realities. One is that costs and sales prices change frequently, and occasionally to large extents; today’s best product choice is often different from tomorrow’s. Flexibility to emphasize one or the other has a real economic value, particularly since massive electric storage is not yet practical. Secondly, there are major cultural differences between utility companies and chemical companies with respect to the risk/reward balance and governmental regulation of prices and investments. Having a company from each sector participate in a common project, although contentious, may well provide synergies in rebalancing various business decisions.
There are issues I have with respect to the comments about the synergies that are necessary to obtain advantages in a mixed product plant: As you state, “The possibilities for process combinations are virtually endless and need to be explored in depth, and with insight.” Obviously, one can devise a great many process sequences for producing multiple products such as chemicals and electricity from a given feedstock. Several of these might appear to offer large economic benefits from increased process integration of material and thermal flows. My “insight” is that there is a real phenomenon of having a plant whose subsystems are overly integrated, making it exceedingly difficult, if not impossible, to meet start-up and part-load operational requirements. This has, unfortunately, occurred numerous times. Conversely, once-through processes offer simpler operation and frequently lower capital expenses. Whether or not these are offset by sacrificing the advantages of recycling streams that have already been partially processed depends on many project-specific economic factors; a case-by-case analysis, rather than broad generalizations, is required to properly assess the situation. Having said this, the process flow sheets on which the presented analysis were based do in fact include a practical amount of high pressure/temperature steam generation from the gasifier effluent gas cooler, some medium pressure compressed air extraction from the gas turbine’s air compressor to supplement the air feed to the Air Separation Unit, and use of purge gases.
Finally, I as a reasonably experienced chemical engineer (and many others in the technoeconomic world) certainly agree that we need to “…move away from a cut and paste design approach and work on the development of new processes even for established technologies…. but often existing process are not adjusted beyond incremental improvements to take advantage of this.” However, as much as I support new process development from intellectual and business perspectives, I’ve also come to realize that incremental improvements very often lead to meaningful economic benefits over time, carry low technology risks, and are more readily financeable. I’m sure you are not minimizing their importance, particularly when considering multi-billion dollar investments as an alternate approach.
My impression is that any disagreements between us are not related to technology-based issues but are more centered on evaluations of operational problems and broad business issues.
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From LinkedIn Discussion: The first thing that immediately pops to mind, is the number of paper mills that produce all their own power and often sell the surplus back to the grid.http://bit.ly/9JRNBu
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From the Author:
Yes, this is relatively common in their cogeneration plants, and indeed the revenues realized through this are critical to the projects' financial viability. These cogeneration plants, however, are virtually all based on simple combustion of black liquor and wood waste in conventional boilers. Hopeful;ly at least the larger plants are considering the benefits gasification may provide, including opening the door to production of other chamicals from the H2 and CO that leave the gasifier.
A reasonable number of papers have now been published on this approach. The US EPA, moreover, is now funding "Technology Assessment for Gasification of Aqueous Sludge from Paper Mills"
Herbert W. Cooper,
President - Dynalytics Corp.
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