Urea production system and method for absorbing melamine tail gas

Abstract

The invention relates to a urea production system and method for absorbing melamine tail gas, and belongs to the field of urea production. The urea production system comprises a urea synthesis section, a recycle recovery section, an evaporation section, an evaporation condensate recovery section and a desorption and hydrolysis section; the urea synthesis section comprises a liquid ammonia buffer groove, an ammonia condenser, a first adsorption tower, a liquid ammonia preheater, a urea synthesis tower, a carbomate preheater and an inert gas refining purifier; the recycle recovery section comprises a predistillation tower, a second separation tower, a flash evaporator, a first absorption external cooler, a first section evaporator, a two-circulation first condenser, a two-circulation secondcondenser and a tail absorption tower; the predistillation tower is adopted to reduce the water volume entering into the synthesis tower, the flash evaporator is added, the urea is concentrated, a waterpower ejector is used to vacuumize and recycle ammonia and carbon dioxide in the tail gas, the ratio of H2O and CO2 is reduced, and the conversion rate of the CO2 is improved; the system load is reduced; and under the condition of not additionally supplementing the carbon dioxide, and the tail gas from a triamine device by condensation and absorption is taken as a raw material of urea production.

Description

technical field [0001] The invention belongs to the field of urea production, and relates to a system and method capable of smoothly absorbing the tail gas produced by a melamine device and simultaneously using the tail gas as a raw material to synthesize urea. Background technique [0002] Melamine is an important chemical product. A large amount of tail gas will be produced during the production of melamine with urea as raw material. The chemical equation of the reaction is as follows: [0003] 6CO(NH 2 ) 2 →C 3 N 3 (NH 2 ) 3 +6NH 3 +3CO 2 . [0004] The production of 1 ton of melamine usually requires 1.05 tons of ammonia and 1.15 tons of carbon dioxide mixed gas. Ammonia and carbon dioxide are the raw materials for the production of urea. Using the tail gas produced by the triamine plant, the synthesis of urea is carried out again without adding fresh carbon dioxide. The molten urea produced is returned to the triamine plant for recycling as raw materials, effec...

AI Technical Summary

Problems solved by technology

[0006] (1) Into urea high pressure system H 2 O / CO 2 Ratio increased significantly and dropped seriously, causing the load of low-pressure decomposition to increase;

[0007] (2) The water balance of the original system is destroyed, resulting in difficulties in the operation of the high-pressure system;

[0008] (3) It is difficult to control the heat balance of the urea synthesis tower itself, resulting in low temperature of the urea synthesis tower and affecting the urea synthesis reaction;

[0009] (4) The load of the low pressure system increases, the amount of material circulation increases, and the energy consumption of the system increases

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