Crystallization is a process used intensively with cooling provided by an ammonia refrigeration system. One of the particular concerns at the plant was the possibility of a catastrophic release of ammonia. With receivers, condensers, surge tanks, and accumulators for the chillers, coolers and filtrate recycle subcoolers, there are approximately 35 safety/relief valves which could “blow.” Conceivably several could blow simultaneously. During a release both liquid ammonia and/or ammonia vapor would be encountered. Based on the largest valves in the system, a single-valve release could discharge approximately 315 Ibs. of liquid ammonia in two minutes (157.5 Ib/min., equivalent to about 3500 acfm of vapor).
The worst-case ammonia release would occur during a plant fire, with pressures rising and relief valves “popping.” Once liquid ammonia is released fire fighting becomes infinitely more difficult. The aim was to ensure that this problem would never arise. An emergency ammonia release plan was therefore, needed. Part of the plan involved obtaining the proper safety equipment and training personnel in its use. Just as important was the attempt to contain and control the released ammonia. A six person Ammonia Project Team was created to come up with a practical solution.
The plan was to “cap the well”— pipe all relief valves into a header designed to accept discharges from several valves at once. The header would lead the discharges to the treatment equipment. Since ammonia collection points are spread around the complex, in the compressor building, the solvent building and other areas, it became evident that the scrubber should logically be located outdoors. With all these preliminary factors determined, the next step was to find the optimum treatment system.