Equipment and process for recovery of fluorine from flue gas of hydration absorption of phosphorus in kiln-method phosphoric acid technology

Abstract

Disclosed is a device and process for fluorine recovery from smoke after phosphorus absorption by hydration in a kiln process for the production of phosphoric acid, wherein the device comprises a first-stage and second-stage fluorine absorption tower, which are both fluidised counter-current washing towers; the first-stage fluorine absorption tower mainly consists of a fluorosilicic acid washing pipe and a fluorosilicic acid separation tank; the top of the separation tank is provided with a smoke outlet, and at the bottom thereof a fluorosilicic acid liquid outlet is connected to the fluorosilicic acid washing pipe via a circulating and conveying pipeline; the main structure of the second-stage fluorine absorption tower is similar to that of the first-stage fluorine absorption tower, the top of the second-stage fluorosilicic acid separation tank is provided with a defoaming layer and a smoke outlet, and at the bottom thereof a fluorosilicic acid liquid outlet is in communication with a nozzle in the second-stage fluorosilicic acid washing pipe and the fluorosilicic acid separation tank in the first-stage fluorine absorption tower via a circulating and conveying pipeline. The fluorine recovery process of the present invention comprises multiple operations of a first-stage fluorine absorption, a first-stage gas-liquid separation, a second-stage fluorine absorption, and a second-stage gas-liquid separation etc. The present invention has the advantages of simple structure, low investment cost, high raw material utilisation rate, and good fluorine recovery effects etc.

Description

technical field [0001] The invention relates to a device and a process for recovering fluorine-containing substances from flue gas, in particular to a device and a process for recovering fluorine from flue gas after hydration and phosphorus absorption in a kiln phosphoric acid process (KPA). Background technique [0002] At present, there are two main methods for the industrial production of phosphoric acid in the world. (1) Phosphoric acid production by wet method: that is, using sulfuric acid to decompose phosphate rock to obtain dilute phosphoric acid and CaSO 4 ·nH 2 O is the main solid waste (referred to as phosphogypsum), and dilute phosphoric acid is concentrated to obtain wet-process phosphoric acid containing about 54% phosphoric acid. The main disadvantages of this process are: first, it consumes a large amount of sulfuric acid; second, the waste residue phosphogypsum cannot be effectively utilized, and the entrained sulfuric acid, phosphoric acid and soluble flu...

AI Technical Summary

Problems solved by technology

The main disadvantages of this process are: first, it consumes a large amount of sulfuric acid; second, the waste residue phosphogypsum cannot be effectively utilized, and the entrained sulfuric acid, phosphoric acid and soluble fluoride are all soluble in water, and are easily washed away by rain after natural stacking. It causes serious pollution to the environment; thirdly, the impurity content of phosphoric acid in the product is relatively high, and it is generally only used for the production of fertilizer; fourthly, in order to ensure the economy of the product, high-grade phosphate rock must be used

The main disadvantages of thermal phosphoric acid production: one is to consume a lot of electric energy; the other is to separate the P 4 The gas also contains a large amount of fluoride (SiF 4 and HF present) and a small amount of unprecipitated gas P 4 , which will cause serious pollution to the atmospheric environment; third, the gas containing a large amount of CO is directly burned and emptied, which is a great waste of energy; fourth, in order to ensure the economy of production, it is also necessary to use high-grade phosphate rock

[0005] However, our research shows that the above-mentioned kiln phosphoric acid process is difficult to realize in large-scale industrial application and practice, and its main defects are:

The hydration acid collection process of kiln-process phosphoric acid was mainly based on the method of heat-process phosphoric acid collection in the past, but there is a big difference between the kiln flue gas of kiln-process phosphoric acid and the flue gas after the thermal process phosphoric acid yellow phosphorus is burned: first, P in kiln flue gas 2 o 5 The concentration of the flue gas is lower, and the flue gas volume of the former is 3 to 4 times that of the latter at the same scale of output; second, the composition of the flue gas out of the kiln process phosphoric acid is complex, containing fluorine, dust, SO 2 Other impurities

Therefore, if the traditional thermal phosphoric acid collection method is still used, there will be many problems: first, the flue gas volume of thermal phosphoric acid is small, and the flue gas flow rate of the corresponding equipment is low. If it is directly applied to the kiln phosphoric acid process, The size of the equipment system will be quite large. The equipment system is not only complex in structure, but also has high investment and operating costs; secondly, the content of impurities in the flue gas of kiln phosphoric acid is complex, and the corrosiveness of spray acid is stronger. The blockage of equipment and pipelines by solid impurities requires further improvement in the acid collection process and equipment structure; more importantly, the kiln flue gas from kiln-process phosphoric acid also contains fluorine-containing substances that are harmful to humans (named as SiF 4 and HF forms), which need to be recycled while avoiding environmental pollution

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