Modeling a Propane-Propylene Splitter

I had been hired to review the design for a new 12,000 BSD propane-propylene splitter for a chemical plant in Convent, Louisiana. The tower was intended to be a replacement for an existing 10,000 BSD propylene-propane splitter. The incremental capacity of2000 BSD would economically justify the 3,000,000 investment for the new splitter. 

I asked the operators why the existing tower was limited to its current 10,000 BSD capacity. They responded by noting that above 10,000 BSD of feed, the concentration of propane in the propylene overhead product (see Fig. 51.1) would exceed the 2 percent specification. 

I asked the operators to increase the splitter feed rate by 500 BSD to 10 00 BSD. When they complied, the concentration of propane in the overhead propylene product increased from 2 to 3 percent. 

000 BSD We have to keep the reflux ratio constant as we increase the feed rate, I explained. 

000 BSD of reflux. It s part of the Black Box. These sorts of parameter limits are imbedded in the computer control logic, explained the board operator. Frank Skorski spent a lot of time on the computer control of this splitter. I imagine Frank knew a hell of a lot more about computer control than you. He was the computer control engineer here in Convent for 12 years. Norm, I don t think you should be second-guessing Mr. Skorski.  

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