Low-temperature, high-efficiency and energy-saving low-pressure decomposition process for urea production

Abstract

The invention relates to the field of further utilization of a desorption hydrolysis gas phase and desorption purified water heat in urea low-pressure decomposition in the urea production process, andspecifically relates to a low-temperature, high-efficiency and energy-saving low-pressure decomposition process for urea production. The process includes five process steps: mass heat transfer of upper-section filler, low-pressure decomposition heating, mass heat transfer of desorption hydrolysis gas, carbon dioxide gas stripping of lower-section filler and separation. A reaction mixture is heated to 130-135 DEG C in a low-pressure decomposition heater, most of ammonium carbamate in the solution is decomposed into NH3 and CO2, and free ammonia is distilled out; after carbon dioxide gas stripping is performed on the gas-liquid mixture which is obtained through heating decomposition of the low-pressure decomposition heater, the remaining ammonium carbamate in the solution is decomposed intoNH3 and CO2, free ammonia is obtained through gas stripping, and the content of NH3 in the solution in a low-pressure decomposition tower is lower than 0.6% by weight. The urea low-pressure decomposition process has low investment of equipment, a high decomposition rate of ammonium carbamate, a high evaporation rate of total ammonia and low consumption of steam.

Description

technical field [0001] The invention relates to the field of further utilization of low-pressure decomposition gas produced in the urea production process, and specifically relates to a low-pressure decomposition process for urea production using low-pressure decomposition heat, three-stage heating, and one-stage air lift. 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 rel...

AI Technical Summary

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

[0010] Existing low-pressure decomposition tower, because only one section packing section is designed, the CO in the urea methylammonium liquid 2 and NH 3 Decomposition and separation, there is NH 3 Problems such as incomplete decomposition, gas-liquid entrainment, and high decomposition temperature (the NH in the urine at the bottom of the low-pressure decomposition tower 3 The content is about 1.0%, and the decomposition temperature is about 145°C), the low-pressure decomposition steam consumption is high, and the load of the recovery section is heavy

[0011] The traditional low-pressure decomposition process for urea production adopts steam direct heating decomposition and separation methods, which leads to high consumption of decomposition steam and poor decomposition efficiency

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