Optimum method for co-producing melamine and urea

Abstract

The invention relates to an optimum method for co-producing melamine and urea, the melamine production technology is characterized by comprising a gas phase quenching or solid phase quenching low pressure circulation method which takes urea as a raw material, an European science and technology high pressure method or a DSM low pressure method, and an urea device is a CO2 air stripping urea device. The optimum method has the following technical effects that the urea device enables matched reformation according to maximal coproduction melamine capability, and the productivity is increased by near 25% after merging with melamine tail gas, the capacity expansion reformation on synthesis ammonia is not required, because that a medium pressure decomposition system and an urea pre-concentration device are added, the vapor of urea per ton and unit consumption of electricity are not increased.

Description

technical field [0001] The invention is suitable for the improvement of production and energy saving of the carbon dioxide gas stripping urine device and the recycling of ammonia and carbon dioxide tail gas discharged from the melamine production process or methylamine liquid co-production of urea. technical background [0002] The melamine reaction process with urea as raw material produces a large amount of ammonia and carbon dioxide by-products, and at the same time, due to the need to supplement part of the ammonia gas during the process operation, it is necessary to discharge 1.05 tons of ammonia and 1.15 tons of carbon dioxide mixed gas for the production of 1 ton of melamine, commonly known as tail gas; Ammonia and carbon dioxide gas are the raw materials for urea production, so the co-production of melamine and urea is the most suitable in terms of resource allocation. However, due to the different production processes of melamine, the co-production of urea from melam...

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Problems solved by technology

Improved gas phase quenching process Although the exhaust gas pressure is increased to above 0.3MPa (A), if it is discharged from the outlet branch of the carrier gas compressor, it can reach above 0.6MPa (A), but to merge the exhaust gas of the large-scale melamine plant into the urea plant, either The tail gas is compressed to above 1.8MPa for medium-pressure absorption, or the tail gas is absorbed at low pressure and then subjected to medium-pressure desorption and concentration above 1.8MPa, or ammonia-carbon separation; desorption concentration and ammonia-carbon separation require more than 4 tons of melamine tail gas 2.0MPa steam, such a high steam consumption seriously restricts the development of this process route. Although the energy consumption of the direct compression of tail gas is much lower than that of the low-pressure absorption and medium-pressure analysis process, due to the small volume flow and narrow flow path of the tail gas compressor , the melamine tail gas contains viscous impurities that are difficult to separate, which are easy to stick to the impeller of the turbine compressor, seriously affecting the long-term stable operation of the melamine tail gas compressor, so the melamine gas phase quenching process is used in the tail gas co-production urea process Without achieving the perfect unity of low energy consumption and long-term operation, they were forced to produce some products such as ammonium bicarbonate, ammonium chloride, and ammonium nitrate, which have low fertilizer efficiency and are not conducive to long-distance transportation. The production of 1 ton of melamine requires 3 tons of urea, which is equivalent to 1.5 tons of urea changed from high-efficiency nitrogen fertilizer to low-efficiency nitrogen fertilizer, increasing the transportation volume

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