Medium-pressure recovery process of low steam/carbon ratio-three-section adsorption-evaporative ammonia-cooling carbamide production

Abstract

The invention discloses a medium-pressure recovery process of carbamide production, comprising four process steps: condensation adsorption, separation, medium-pressure adsorption and ammonia condensation recovery; wherein the temperature of the condensation adsorption is improved to 105 DEG C from 90 DEG C to 95 DEG C of traditional process, the medium-pressure adsorption is improved into three-section adsorption from two-section adsorption, and an ammonia condenser of the ammonia condensation recovery is changed into an evaporative ammonia condenser from a tubular heat exchanger, so as to lead steam / carbon mole ratio in ammonium carbamate solution recycled and returned to a carbamide synthesis tower in a system to be reduced to 1.5 from 2.0, the carbon dioxide content in gas phase exhausted from a medium-pressure adsorption tower is greatly reduced, and is decreased within 5ppm from 100ppm, thereby being beneficial to improving the carbamide synthetic ratio and reducing the investment and consumption; in addition, the operation is convenient and safe.

Description

technical field [0001] The invention discloses a medium-pressure recovery process in urea production, which belongs to the technical field of urea production. Background technique [0002] The reaction of industrial production of urea is carried out in two steps. The first step is to generate the intermediate product ammonium carbamate (abbreviated as methyl ammonium) by the reaction of ammonia and carbon dioxide. The reaction formula is: [0003] 2NH 3 (liquid)+CO 2 (gas) = ​​NH 4 COONH 2 (liquid)+Q 1 [0004] The second step generates urea by methylammonium dehydration, and its reaction formula is: [0005] NH 4 COONH 2 (Liquid)=CO(NH 2 ) 2 (liquid)+H 2 O(liquid)-Q 2 [0006] The first step reaction is a reversible strong exothermic reaction, the reaction speed of forming ammonium carbamate is relatively fast, and it is easy to reach chemical equilibrium, and after reaching the chemical equilibrium, the degree of conversion of carbon dioxide into ammonium carb...

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Problems solved by technology

The second step reaction is a reversible micro-endothermic reaction, which needs to be carried out in the liquid phase, the reaction speed is slow, and it takes a long time to reach chemical equilibrium, and there is reverse back mixing in the synthesis tower, even if chemical equilibrium is reached, all Ammonium carbamate is dehydrated into urea

[0011] In the existing medium-pressure recovery process, the molar ratio of water to carbon in the recovered ammonium carbamate solution is high, which is not conducive to reducing energy consumption; at the same time, the two-stage absorption process of bubbling absorption and fine washing is not conducive to improving the output of the medium-pressure absorption section. Ammonium carbamate solution concentration and reduce the content of carbon dioxide in the medium-pressure absorption tower gas, because the solubility of carbon dioxide in liquid ammonia is extremely small, the carbon dioxide contained in the tower gas will generate ammonium carbamate crystals in the process of ammonia condensation Block equipment and pipelines, make urea production impossible, and cause corrosion to the equipment in contact

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