GB1217219A - Process for recovering excess ammonia in urea synthesis - Google Patents

Abstract

1,217,219. Recovering excess ammonia in urea synthesis. MITSUI TOATSU CHEMICALS Inc. 6 Aug., 1968 [10 Aug., 1967; 5 March, 1968], No. 37497/68. Heading C2C. The invention comprises a process for recovering excess ammonia in a urea-synthesis wherein carbon dioxide is reacted with a stoichiometric excess of ammonia in a synthesis zone at a urea-forming temperature and pressure, the excess ammonia contained in the resulting ureasynthesis effluent is separated as ammonia gas at a pressure lower than the said urea-forming pressure, the separated ammonia gas is cooled to form liquid ammonia and the liquid ammonia is recirculated to the synthesis zone for re-use therein, which includes separating the said excess ammonia from the said urea-synthesis effluent at a pressure substantially equal to the vapour pressure of ammonia at a condensation temperature at which the quantity of heat generated in the condensation of the ammonia gas is substantially equal to the quantity of heat required to elevate the temperature of the liquid ammonia raw material and mixing the thus separated ammonia gas with the liquid ammonia raw material, thereby condensing the said ammonia gas to form liquid ammonia at a high temperature. The separation of the said excess ammonia may be conducted at a gauge pressure of 40-120 kg./cm.<SP>2</SP>, for example, by adiabatically expanding said urea synthesis effluent, or by subjecting the ureasynthesis effluent to distillation at a temperature of 140-180‹ C.