Patent ID: 8313722

Claim:
A process of removing NO x from a combustion gas stream using gaseous ammonia by producing ammonia from urea, by a process which comprises: (a) heating an aqueous solution of urea, or a mixture of urea, containing biuret or ammonium carbamate on site, in a hydrolysis reactor such that a gaseous ammonia-containing product is obtained which is essentially free of urea, biuret, or ammonium carbamate, the temperature and pressure being maintained by the input of heat to the reactor; (b) separating the gaseous ammonia-containing product from the liquid phase aqueous reaction media at the operating pressure; (c) retaining the liquid phase reaction medium in the reactor for further conversion to gaseous ammonia and carbon dioxide while feeding additional aqueous solution to the reactor; and (d) withdrawing the gaseous ammonia and carbon dioxide-containing product separated in step (b) at a controlled rate to meet ammonia demand requirements for removal of NO x from a combustion gas stream; wherein the temperature in the hydrolysis reactor is not controlled but is allowed to vary to match the demand requirement for ammonia and in which the reactor operating pressure is varied as function of the demand requirement for ammonia or reactor operating temperature such that adequate water is maintained in the hydrolysis reactor for hydrolysis of urea, and wherein the equilibrium solution concentration is maintained by a pressure-temperature relationship so that the product gas temperature is always above the dew point of the product gas.