Jake recently had graduated college and started his first job. His new company assigned him to one of its large sites. There, Jack, a senior engineer who had been at the site his entire career, would mentor Jake.
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One of the areas both were responsible for was a methanol distillation or finishing process. Methanol, created in previous steps, was pumped to this final refining area to produce product for customers. Because it was a very low-pressure distillation process, the temperature of the steam and condensate in the reboiler also were low. Earlier in the process, heat recovered from the reformers generated steam. Then, the steam was let down through several stages of power generation to provide the boil-up for the distillation operation. Condensate from the process then was sent to the process sewer.
Winter Woes
The small amount of flash steam created hazards during winter weather. In light of a national energy crisis at the time, an energy conservation push closely targeted any losses. Installing a flash cooler on the line to the sewer resolved the hazard issue. Engineers put in a used heat exchanger at ground level with the condensate line piped to the exchanger. And, then, problems started.
When the heat exchanger began banging and jumping, Jack was called to the site. Eventually, the movement caused the inlet piping to fail; the condensate spilled into the area, resulting in even more problems on that cold day. Jack had the condensate diverted back through the original sewer dump while he began to deal with the water hammer issue. Because Jake had just graduated, Jack asked him to do a little research on water hammer and directed him to some of the company’s resources on the subject.
In the meantime, Jack went back to finding a quick solution. He installed a sparger into the inlet line and piped cooled condensate to the sparger. Weld repairs were made and the heat exchanger returned to service. Jack gradually introduced condensate into the sparger and reached an equilibrium point where the banging and shaking stopped. It was temporary — but it solved the problem for the time being.
Multiple Issues Discovered
Jake had begun researching the water hammer issue. Jack had sent him to one of the corporate experts who showed Jake where to find the information as well as how to begin the manual calculation and modelling process. Jake began the calculations but ran into a problem due to lack of information for the model; Jack filled in the missing data. Together, they worked through the complex analysis until they had a clear picture of what was happening. Through this experience, Jake learned not only how to perform the analysis but also how to be a mentor to a younger engineer.
So, what did they discover? First, the heat exchanger was oversized. It was bought cheap but resulted in too much capacity, causing flash steam in the condensate to quickly condense leading to the severe water hammer. Second, the piping to the heat exchanger had been sized according to the inlet to the exchanger rather than for the actual flow of condensate. This led to a large cross section with the pipe operating much like a drain with only partially filled conditions. As it entered the heat exchanger, a rise in elevation then closed off the pipe, capturing flash steam in a bubble that then collapsed, further aggravating the water hammer problem. Third, river water was used as condensing medium. The water was fairly warm in the summer but when winter rolled in the temperature difference along with the oversized heat exchanger resulted in major bubble collapses within the heat exchanger. And finally, while the sparger could mitigate the problem, it required constant modulation based on multiple variables including process rate, river temperature, ambient temperature, etc.
They developed a solution but, unfortunately, the cost was not in the budget. The plant had been scheduled for shutdown three years before Jake arrived; however, operation continued because the facility set to replace it experienced start-up delays, forcing the older plant to continuing operating at low rates. Nevertheless, it was a great learning experience for a young engineer both from a technical perspective as well as forming one of the bases for future mentoring. (For more on mentoring and sound advice from the field, visit www.ChemicalProcessing.com/voices/field-notes/.)
