December 28, 2006
Ammonia present in the rich feed to an amine stripper, even in the ppm range, tends to build up in the upper section of the stripper between the condenser and the rich amine feed leading to operating problems. Simulators such as ProMax which can model amine units reflect the operational problems as difficult convergence of the stripper. Usually a liquid purge stream from the stripper reflux is used to remove some of the ammonia from the stripper and avoid the ammonia build-up in the condenser loop. In the simulator, the easiest method of modeling a purge stream is to insert a Splitter between the condenser liquid and the reflux back to the column. Then attach a purge stream to the splitter. The Splitter should be set such that 1 to 10% of the reflux is sent to the purge stream. To prevent much of the ammonia in a feed stream from ever even entering the plant, many plants use a water wash for any feed stream containing significant amounts of ammonia. Whenever modeling a plant with feeds containing ammonia, be sure to find out if the plant is actually using a feed wash because it is very important to include it in the simulation to obtain accurate results. The difference in stripper results can be very dramatic. If more ammonia appears in the simulation than in the actual plant, the required reboiler duty could appear to be too high by as much as a factor of two or three.
Authored by Lili Lyddon - BR&E Technical Support / Help Author