Process of directly preparing urea by tripoly cyanamide

Abstract

This invention relates to a urea preparation methods which directly use melamine assembly end gas, including high pressure synthesis, midst-low-pressure decomposition, condensing pressure, low pressure condensate recovery steps. First absorbing and condensing melamine assembly end gas (composition: NH3: 40 to 45%; CO2: 35 to 40%, and the rest of H2O) into ammonio liquid; and then mix ammonio liquid with liquid ammonia and passive air as raw materials of urea synthesis; at last to preheat this mixture to 180 ~ 195 deg C, and sent into tower of urea synthesis of high-pressure, generate urea solution.

Description

technical field [0001] The present invention relates to by-product tail gas (containing: CO) in the production process of melamine 2 , NH 3 and H 2 O) a technology and equipment for direct synthesis of urea solution. Background technique [0002] Due to the production characteristics of melamine, the by-products in its production process contain CO 2 and NH 3 No matter it is the advanced high-pressure method technology or the numerous low-pressure method technologies in my country at present, the treatment of a large amount of by-product tail gas is a great technical problem. [0003] Some melamine manufacturers try to separate the by-product tail gas of melamine into pure NH 3 , CO 2 , but the process technology is complicated, the process flow is long, the equipment investment is large, and the separated CO 2 The ammonia contained in it is difficult to return to the process production device for use, and direct discharge will cause a lot of economic waste, and it ca...

AI Technical Summary

Problems solved by technology

However, due to the large amount of water contained in the by-product tail gas of melamine production, the circulating water volume of the system is increased to a certain extent when it is co-produced with other existing urea plants, and at the same time it causes H in the urea synthesis tower. 2 O / CO 2 The improvement of the urea synthesis tower leads to the CO 2 The decline in conversion rate; especially with the expansion of melamine production capacity, the load of the recovery system will be greatly increased, which will bring unacceptable changes to the operating parameters of the entire device, which will eventually lead to the deterioration of the working conditions of the entire urea system

Taking a large-scale urea plant (520,000 tons / year) as an example, the by-product tail gas of melamine in the low-pressure process is sent to the existing urea plant, and after adding water to the low-pressure system to absorb and condense, it is sent to the high-pressure section through a high-pressure methylammonium pump, so that the high-pressure The flow rate of the ammonium ammonium pump is increased to the rated flow rate, which makes the operation of the urea plant inflexible and has a great impact on production management; at the same time, the addition of water-containing tail gas makes the H 2 O / CO 2 From the original 0.41 to 0.7, eventually resulting in the CO in the urea synthesis tower 2 Conversion rate decreased from 58% to around 55%

[0005] With the enlargement of the melamine plant, the existing urea plant must be modified in order to co-produce with the existing urea plant. Relying on the original patentee to transform the existing large-scale urea plant, not only need to pay a lot of technical costs, but also need to increase some Important equipment, and there are still technical risks and difficulties in implementing the transformation of the existing urea plant to deal with melamine tail gas

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