Process for heat recovery from ammonia stripper in andrussow process

A process for purifying a crude hydrogen cyanide product comprising hydrogen cyanide, ammonia, and from 25 to 50 vol. % water, the process comprising the steps of:

• contacting in an ammonia absorber at least a portion of the crude hydrogen cyanide product with an absorbing solution to produce an ammonia-rich stream containing ammonia and water, and an ammonia absorber overhead stream containing hydrogen cyanide;
• separating in an ammonia stripper at least a portion of the ammonia-rich stream to vaporize ammonia and water into an ammonia stripper overhead and a lean stream;
• passing the ammonia stripper overhead through a waste heat boiler to generate steam having pressure of less than 400 kPa, preferably from 180 kPa to 380 kPa, and to partially condense the ammonia stripper overhead into a liquid stream;
• passing at least a portion of the ammonia absorber overhead stream into an ammonia scrubber to remove residual ammonia to produce an ammonia scrubber off-gas stream;
• absorbing in a hydrogen cyanide absorber at least a portion of the ammonia scrubber off-gas stream in dilute acidified water to produce a hydrogen cyanide absorber off-gas stream and a hydrogen cyanide absorber tails stream containing hydrogen cyanide;
• separating in a hydrogen cyanide stripper at least a portion of the hydrogen cyanide absorber tails stream to obtain an intermediate stream, wherein the steam from the waste heat boiler is directed to a calandria of the hydrogen cyanide stripper;
• and
• recovering in a hydrogen cyanide enricher column a purified hydrogen cyanide product from the intermediate stream.

A process for purifying a crude hydrogen cyanide product comprising hydrogen cyanide, ammonia, and from 25 to 50 vol. % water, the process comprising the steps of:

• recovering ammonia from the crude hydrogen cyanide product using at least one lean solution and generating steam having pressure of less than 400 kPa by cooling an ammonia-water solution;
• recovering hydrogen cyanide using acidified water from at least a portion of the crude hydrogen cyanide product;
• and
• directing the generated steam to drive the separation of hydrogen cyanide and acidified water.

A heat integration apparatus, comprising:

• an ammonia absorber for contacting a crude hydrogen cyanide product comprising hydrogen cyanide, ammonia, and water with an absorbing solution to produce an ammonia-rich stream containing ammonia and water, and an absorber overhead stream containing hydrogen cyanide;
• an ammonia stripper for separating at least a portion of the ammonia-rich stream to vaporize ammonia and water into an ammonia stripper overhead and a lean stream;
• a waste heat boiler for generating steam by passing the ammonia stripper overhead therethrough, wherein the steam has a pressure of less than 400 kPa, and for partially condensing the ammonia stripper overhead into a liquid stream;
• an ammonia scrubber for removing residual ammonia from at least a portion of the ammonia absorber overhead stream to produce an ammonia scrubber off-gas stream;
• a hydrogen cyanide absorber for contacting a portion of the off-gas stream with dilute acidified water to produce a hydrogen cyanide absorber off-gas stream and a hydrogen cyanide absorber tails stream containing hydrogen cyanide;
• a hydrogen cyanide stripper for separating at least a portion of the hydrogen cyanide absorber tails stream to obtain a hydrogen cyanide stream, wherein the hydrogen cyanide stripper has a calandria;
• and
• a pipe for directing the steam from the waste heat boiler to the calandria.