| 摘要 |
An integrated process for the synthesis of urea and melamine, wherein: urea is synthesized with a stripping process in a high-pressure synthesis loop comprising a reactor, a stripper and a carbamate condenser, and the urea solution leaving said stripper is sent to a recovery section to produce a concentrated urea product and a recovered carbamate solution; at least part of said urea product is converted to melamine, and the off-gas from the synthesis of melamine are recycled to the urea synthesis by mixing with the gas phase from the stripper and with said recovered carbamate solution, thus forming a mixed flow which is then condensed in said carbamate condenser, and the condensate is eventually directed to the reactor. |
| 主权项 |
1) A process for the combined synthesis of urea and melamine, wherein:
urea is synthesized from ammonia and carbon dioxide with a stripping process, said stripping process including at least the steps of reacting ammonia and carbon dioxide in a reaction section, to form an aqueous solution comprising urea, ammonium carbamate and unconverted ammonia, and treating said solution in a stripping section, obtaining a urea solution and a gas phase containing ammonia and carbon dioxide, also including a step of condensation in a condensation section, at least a portion of synthesized urea is used to produce melamine in a tied-in melamine plant, obtaining also a flow of melamine off gas which contain ammonia and carbon dioxide, and said flow of melamine off gas is recycled back to said process for the synthesis of urea, either in a gaseous state or in a liquid state after condensation, wherein at least a portion of said gaseous phase obtained from the stripping process is fed directly to said reaction section in a gaseous state, and wherein said urea solution leaving the stripping section is further processed in at least one recovery section obtaining a liquid carbamate solution and a more concentrated solution, and at least a portion of said concentrated solution is used to produce melamine, and wherein the melamine off gas are recycled to the process for synthesis of urea by: mixing said flow of melamine off gas with a portion of said gas phase from the stripping treatment, and with at least a portion of said liquid carbamate solution coming from said recovery section, thus obtaining a gaseous-liquid mixed flow, condensing said mixed flow in said condensation section, obtaining a condensate, and feeding said condensate to said reaction section. |
