Method for producing ammonium phosphate by utilizing low-grade low-concentration raffinate

Abstract

The invention discloses a method for producing ammonium phosphate by using low-grade and low-concentration raffinate acid, in which low-grade raffinate acid with a P2O5 concentration of 22% to 24% is sent as washing liquid to the washing system of an ammonium phosphate device to circulate and absorb tail gas When the neutralization degree of the raffinate washing liquid is 0.6-0.9, it is sent to the concentration device, heated and concentrated until the P2O5 concentration is 26%-30%, and the concentrated slurry is mixed with concentrated phosphoric acid in the neutralization reactor Used in the production of ammonium phosphate products. Using low-grade and low-concentration raffinate to absorb ammonia and dust in the tail gas of the ammonium phosphate unit and then heating and concentrating can solve the problem of acid-insoluble scale layer that is difficult to clean during the concentration process with low-grade and low-concentration raffinate, making it possible to use low-grade The cost of producing ammonium phosphate with low-grade and low-concentration raffinate is greatly reduced; and it can also save the amount of washing water required by the tail gas treatment system of the ammonium phosphate plant, further reducing the production cost of the entire ammonium phosphate plant.

Description

technical field [0001] The invention relates to a method for producing ammonium phosphate, in particular to a method for producing ammonium phosphate by utilizing low-grade and low-concentration raffinate. Background technique [0002] At present, most of the wet purification of phosphoric acid adopts the solvent extraction method, and a large amount of raffinate will be produced in the production, and the main digestion method of these raffinate is to produce chemical fertilizers. According to the different production materials and processes, the P of raffinate 2 o 5 Concentrations vary greatly. At present, there is a technology of using raffinate acid to produce granular monoammonium phosphate or diammonium phosphate, and the raffinate P 2 o 5 The concentration reaches more than 37%, derived from the P 2 o 5 The wet-process phosphoric acid purification produced by high-grade phosphate rock with a content of more than 32% is not suitable for the utilization of low-conc...

AI Technical Summary

Problems solved by technology

[0003] Due to the increasingly scarce phosphate rock resources, most enterprises use P 2 o 5 For low-grade phosphate rock with a content of less than 30%, the concentration of wet-process phosphoric acid produced from this type of phosphate rock is about 40%. After purification by solvent extraction, the by-product raffinate P 2 o 5 The concentration is only about 23%, and it contains a large amount of impurities such as calcium sulfate and pyroxenite type compounds. Because the raffinate acid is not only low in grade but also low in concentration, it cannot be directly used in traditional ammonium phosphate production equipment, otherwise it will be used later. It will cause the product quality to fail to meet the requirements, and the nutrient and water content of the product is seriously unqualified; in addition, the water content of low-grade low-concentration raffinate acid is too high, which will lead to difficulties in the water balance of the ammonium phosphate production unit, and great pressure on environmental protection

Although the water content of raffinate can be reduced by heating and concentrating, the P of raffinate can be increased. 2 o 5 concentration, it can be directly sent to the neutralization reactor of the ammonium phosphate plant of the neutralization slurry concentration method for the production of ammonium phosphate products, but because the impurities in the raffinate acid are easily formed on the inner wall of the concentration heat exchanger after high temperature concentration Hard, dense, acid-insoluble scale layer that is difficult to remove. When the scale is serious, the tubes will be blocked and the concentration operation cannot continue.

The main phases of the scale layer are calcium sulfate, magnesia-type compounds, amorphous silicides and iron-aluminophosphate, which are mixed with each other and bonded together to form hard and dense acid-insoluble process rocks. It is extremely difficult, which makes it difficult for the heat exchanger to work stably for a long time, which greatly increases the cost of utilizing raffinate through the concentration method

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