Process and plant for the synthesis of urea and melamine
AssigneeCasale SA
InventorsPaolo Bertini, Gabriele Di Carlo
Life of this patent
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Abstract
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.
Claims14
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 a first 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 a first 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 second portion of said gaseous phase from the stripping treatment, and with a second 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.
A modification of a urea plant operating according to a stripping process, said urea plant including at least a reactor, a stripper and a condenser, the urea plant further comprising at least one recovery section where a urea solution leaving the stripper is further processed, a liquid carbamate solution and a more concentrated urea solution being obtained in said at least one recovery section, and the modification including at least the steps of:
- adding a tied-in melamine plant which converts into melamine a portion of the urea synthesized by said urea plant;
- recycling the off gas containing ammonia and carbon dioxide withdrawn from of said melamine plant to the urea plant, and
- directing a first portion of the gaseous phase separated in withdrawn from separated in the stripper of the urea plant, containing ammonia and carbon dioxide, to the reactor of the urea plant, the modification further including:
- mixing said off gas withdrawn from the melamine plant with a second portion of said gaseous phase from the stripper, and with a portion of said liquid carbamate solution obtained from said at least one recovery section, thus forming a gaseous-liquid mixed flow which is condensed in said condenser of the urea plant.
Dependencies are inferred from the claim text.