Process to produce ammonia from urea

Abstract

In a process for generating ammonia from urea which process 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, and/or recycling at least a portion of the said reaction medium back into the reactor, a urea dissolver, or the feed solution to the reactor for further conversion; and (d) withdrawing the gaseous ammonia and carbon dioxide-containing product separated in step (b) at a controlled rate to meet demand requirements; the improvement 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 pressure is varied as function of the demand requirement for ammonia or reactor operating temperature.

1 . In a process for producing ammonia from urea which process 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, and/or recycling at least a portion of the said reaction medium back into the reactor, a urea dissolver, or the feed solution to the reactor for further conversion; and   (d) withdrawing the gaseous ammonia and carbon dioxide-containing product separated in step (b) at a controlled rate to meet demand requirements;   
     the improvement 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 pressure is varied as function of the demand requirement for ammonia or reactor operating temperature. 
   
   
       2 . The process of  claim 1  comprising the improvement 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 pressure is varied as function of the demand requirement for ammonia or reactor operating temperature to maintain adequate water in the hydrolysis reactor for hydrolysis of urea. 
   
   
       3 . The process of  claim 1  wherein the reactor has gaseous ammonia containing take off provided with a restriction adapted to open and close to allow for the flow of product gas to match the ammonia demand requirements. 
   
   
       4 . A process of  claim 1  wherein the pressure is maintained at or above the equilibrium pressure of the feed solution. 
   
   
       5 . A process of  claim 1  wherein the pressure is maintained at or below the equilibrium pressure of the feed solution. 
   
   
       6 . A process of  claim 1  wherein the pressure temperature relationship is set by a function that maintains a relatively constant liquid concentration in the reactor independently of the ammonia production rate. 
   
   
       7 . A process of  claim 1  wherein the pressure set point is as a function of the reactor temperature. 
   
   
       8 . A process of  claim 1  wherein the pressure set point is set by the ammonia generation needed from the reactor. 
   
   
       9 . A process of  claim 1  wherein the feed solution is in the range of 20 to 72% urea. 
   
   
       10 . A process of  claim 1  wherein the solution is created in the reactor by feeding either urea or a concentrated urea and a separate source of water. 
   
   
       11 . A process of  claim 1  wherein a solution is withdrawn from the reactor either for use or mixing to make a urea feed solution for the reactor. 
   
   
       12 . A process of  claim 1  wherein the operating temperature varies from 230 deg F. to 550 deg F. 
   
   
       13 . A process of  claim 1  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. 
   
   
       14 . A process of  claim 1  wherein the urea feed does not have formaldehyde or formaldehyde compounds. 
   
   
       15 . A process of  claim 1  wherein the urea feed has formaldehyde or formaldehyde compounds. 
   
   
       16 . In a process for removing nitrogen oxides from a combustion gas stream which process 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, and/or recycling at least a portion of the said reaction medium back into the reactor, a urea dissolver, or the feed solution to the reactor for further conversion;   (d) withdrawing the gaseous ammonia and carbon dioxide-containing product separated in step (b) at a controlled rate; and   (e) contacting the gaseous ammonia-containing product with the combustion gas stream at a rate which essentially matches the demand requirement of nitrogen oxides removal in said combustion gas stream;   
     the improvement 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 pressure is varied as function of the demand requirement for ammonia or reactor operating temperature. 
   
   
       17 . The process of  claim 16  comprising the improvement 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 pressure is varied as function of the demand requirement for ammonia or reactor operating temperature to maintain adequate water in the hydrolysis reactor for hydrolysis of urea. 
   
   
       18 . The process of  claim 16  wherein the reactor has gaseous ammonia containing take off provided with a restriction adapted to open and close to allow for the flow of product gas to match the ammonia demand requirements. 
   
   
       19 . A process of  claim 16  wherein the pressure is maintained at or above the equilibrium pressure of the feed solution. 
   
   
       20 . A process of  claim 16  wherein the pressure is maintained at or below the equilibrium pressure of the feed solution. 
   
   
       21 . A process of  claim 16  wherein the pressure temperature relationship is set by a function that maintains a relatively constant liquid concentration in the reactor independently of the ammonia production rate. 
   
   
       22 . A process of  claim 16  wherein the pressure set point is as a function of the reactor temperature. 
   
   
       23 . A process of  claim 16  wherein the pressure set point is set by the ammonia generation needed from the reactor. 
   
   
       24 . A process of  claim 16  wherein the feed solution is in the range of 20 to 72% urea. 
   
   
       25 . A process of  claim 16  wherein the solution is created in the reactor by feeding either urea or a concentrated urea and a separate source of water. 
   
   
       26 . A process of  claim 16  wherein a solution is withdrawn from the reactor either for use or mixing to make a urea feed solution for the reactor. 
   
   
       27 . A process of  claim 16  wherein the operating temperature varies from 230 deg F. to 550 deg F. 
   
   
       28 . A process of  claim 16  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. 
   
   
       29 . A process of  claim 16  wherein the urea feed does not have formaldehyde or formaldehyde compounds. 
   
   
       30 . A process of  claim 16  wherein the urea feed has formaldehyde or formaldehyde compounds.