| 摘要 |
In an ammonia synthesis process a nitrogen-hydrogen gas is reacted partially over a catalyst at a pressure in the range 30-120 bar abs, ammonia is separated as liquid after cooling the reacted synthesis gas and unreacted synthesis gas is recycled. The liquid ammonia is evaporated in heat exchange with reacted synthesis gas to provide the required cooling effect. Such heat exchange is effected using a heat exchange surface (as in a plate-fin heat exchanger) of at least 1.5 m2 per kg mol per hour of ammonia to be condensed, with cold-end temperature approach of less than 8 DEG C. and a hot-end temperature approach of less than 5 DEG C. whereby exploit the heat effect of, inter alia, the non-ideality of ammonia to provide product gaseous ammonia at a convenient pressure with minimal mechanical refrigeration. |
