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Comment Separation Processes

Magic trays, brown solvent

By Chemical Engineering |

Every five years or so, a call would come in and once again I would be troubleshooting a certain extraction unit in Canada — usually in the dead of winter. This particular unit had a liquid-liquid extractor, a stripper, a vacuum regenerator and the usual complement of pumps, pipes, valves, vessels, heat exchangers, raccoons and crows. Some of you might remember the extractor from my Crow’s Nest column ( CE, February 2011, p. 21). The natural state of the extraction solvent was clear and slightly yellow. With time, however, oxygen would creep into the unit, especially via the vacuum regenerator. Organic acids would form. The acids would eat any carbon steel that they encountered. Iron oxide and carbonaceous materials would accumulate in the solvent, which would turn from yellow to green to brown and then black. Eventually the solvent would look and feel like the three-year old engine oil in my 1974 Ford Falcon. One troubleshooting visit was in response to a complaint about reduced recovery. The unit was shut down for the annual turnaround. My colleague, Reese, and I decided to enter and inspect the extractor at three manhole locations, starting with the top manhole. The top manhole was open. According to our drawings,…
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