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This discussion tracks a material flow through the steam system, starting with feed and continuing with steam generation, steam uses and, finally, condensate recovery.
Refinery and petrochemical plant engineering staffs must understand complex-wide steam systems, and they should seek to improve the performance of these systems. Here, the adaptation of existing facilities in response to process changes in the refinery or petrochemical complex is examined.
Pursuant to the January 2013 article, "Improve your plant-wide steam network," this article is concerned with improving the performance of existing steam equipment. Several articles 1-3 have been written over the years regarding ways to improve steam systems. These articles have mainly focused on specific elements or "pieces" of the total system, and they touch on the timeless issues of boiler performance, steam turbines, steam reboilers/heaters, letdowns, process uses, condensate recovery, steam traps, deaerating, etc. Also highlighted are some aspects that generally receive less attention, or that are altogether ignored.
Steam system weaknesses and inefficiencies
Industry has not developed a specific metric that defines overall steam system performance. For the most part, it is left to the knowledge and experience of the engineers and operators to observe and develop improvements. Since the "utility system" engineer is frequently chosen from the ranks of younger engineers, and since operations personnel are responsible for their process area only and not the refinery-wide steam system, progress can be slow.
After completing all the steps discussed in Part 1 of this article, the total system is understood--but what comes next? How does one go about improving the system? There are a number of items to look for and consider. The following discussion tracks a logical material flow through the steam system, starting with the feed (i.e., cold, demineralized water), and continuing with steam generation, steam uses (and abuses) and, finally, condensate recovery.
Preheating treated makeup water to deaerator. Most energy-conservation schemes in refining come down to one of two approaches: either not using the energy in the first place, or recovering more energy from the multitude of streams being cooled in air or water coolers. In the latter case, the limitation is not the heat available, but rather having sufficient DeltaT to recover the heat (i.e., second law of thermodynamics efficiencies, commonly referred to...