Phosphoric Acid Plant Equipment

一. Phosphorus, phosphate fertilizer, phosphate industry

Phosphorus is a widely used chemical raw material product and occupies an important position in the national economy. Yellow phosphorus has lively properties and strong chemical properties, and can produce a variety of products. At present, more than half of the yellow phosphorus in the world is mainly used to make phosphoric acid and phosphate, which are used in the fertilizer industry, detergent, food industry, pharmaceutical industry, pesticides and phosphates. Industries such as the electronics industry, textiles, glass, metallurgy and ceramics also have an increasing demand for phosphates. In addition, yellow phosphorus compounds can be made into incendiary bombs and smoke bombs, etc., and occupy a certain position in national defense.

二. The production process of phosphoric acid

2.1 Thermal phosphoric acid production

The production process of thermal phosphoric acid can be simplified as follows: the production of phosphorous yellow phosphorus in an electric furnace, combustion, absorption and hydrolysis of phosphoric acid.

2.1.1 Complete combustion method: (one-step method)

The furnace gas containing elemental phosphorus from the electric furnace is directly burned, and the CO in the furnace gas is also burned together

This method is not used in industry due to poor heat utilization (phosphoric anhydride is strongly corroded, and a large amount of reaction heat cannot be used).

2.1.2 Liquid phosphorus combustion method (two-step method)

Common industrial processes, the first: yellow phosphorus burning phosphorus pentoxide to cool and absorb phosphoric acid, also known as water cooling process; the second: yellow phosphorus burning phosphorus pentoxide to cool phosphoric acid, absorb phosphoric acid, also known as acid cooling process.

Thermal phosphoric acid generally contains >85% phosphoric acid with high concentration and pure quality. It is the main raw material of phosphoric acid for food and pharmaceutical industries. Thermal phosphoric acid is produced with elemental phosphorus. 1 ton of elemental phosphorus (1.38 tons of 100% phosphoric acid can be produced) requires power consumption of 12500-15000KWH, which is a high energy consumption industry.

2.2 Wet phosphoric acid production

It is obtained by decomposing phosphate rock with inorganic acid: commonly used nitric acid, hydrochloric acid, sulfuric acid and fluosilicic acid. Since calcium sulfate has a small solubility and is easy to separate from phosphoric acid, wet-process phosphoric acid actually refers to phosphoric acid obtained by decomposing phosphate rock with sulfuric acid. Depending on the slurry temperature, phosphoric acid concentration, sulfuric acid dosage and other conditions, calcium sulfate hydrate has three forms:

三.The production process is as follows:

2.2.1 Dihydrate material process: multi-slot or single-slot process, no back-slurry process and back-slurry process, vacuum cooling and air cooling process. The product generally contains 28~32% P2O5, and the total phosphorus recovery rate: 93%~97%. Widely used in various countries.

2.2.2 Hemihydrate-dihydrate process: CaSO4 is first formed into hemihydrate crystallization, and then hydrated and recrystallized into dihydrate. Total phosphorus recovery rate: 98%~98.5%.

2.2.3 Dihydrate-semihydrate process: Phosphorus total recovery rate: about 99%.

2.2.4 Hemihydrate process: high concentration phosphoric acid 40%~50%P2O5 can be obtained, ammonium phosphate or heavy calcium can be directly produced, and a large factory of 1300T/dP2O5 has been built.

1.1 Pump structure selection

According to the characteristics of the medium and the stirring conditions in the reaction tank, the material and reasonable structure of the pump flow parts with wear resistance and corrosion resistance should be selected. Under the condition that the solid content of phosphoric acid medium is less than 3%, the corrosion resistance of ultra-low carbon molybdenum tri-titanium and aluminum di-titanium is excellent, but under the condition that the solid content of phosphoric acid slurry is 25% to 35%, the wear resistance Not high, the service life is shortened. Therefore, special attention should be paid to the medium and working conditions when selecting the material of the pump flow parts.

1.2 The choice of speed

When the pump speed is high, it will accelerate the wear and corrosion of the flow components such as the volute and impeller. Most of the rotational speeds of pumps used in phosphoric acid plants in my country and those used in foreign ammonium phosphate plants are 1460 r/min and 970 r/min. Therefore, on the premise of satisfying the head and flow, the pump with low speed should be selected as much as possible.

1.3 Selection of vertical pump and horizontal pump

Compared with vertical pumps, horizontal pumps have the following advantages:

1.3.1 The price is lower, usually 1/2 to 1/3 of the vertical pump under the same head and flow conditions, or even up to 1/4.

1.3.2 The length of the cantilever shaft under the vertical pump support frame is limited, and it is usually troublesome to control the liquid level in production.

1.3.3 If the vertical pump cannot be directly installed on a large tank, the vertical pump must be set up, and the medium is placed on the small tank of the vertical pump by opening the side of the lower part of the large tank, which will increase investment and waste manpower and material resources. .

1.4 Selection of pump impeller type

Since ammonium phosphate slurry, slurry and phosphoric acid usually contain solid particles, when the temperature drops, the solubility decreases and precipitates out, and it is easy to form a hard scale layer on the impeller of the pump, especially the volute. Therefore, in the ammonium phosphate phosphate In the device, the open impeller is generally used, especially in the reaction tank of the phosphoric acid plant and the phosphoric acid filtration system, the open impeller must be selected; the ammonium phosphate slurry pump should also use the open impeller.

2. Selection of wet-process phosphoric acid sludge separation equipment

The solid impurities that settle out during the storage of wet phosphoric acid are called sludge, which can block equipment, pipelines and transportation tools, and affect product quality. Therefore, sludge separation must be carried out in the production of wet phosphoric acid.

The principles of equipment selection should generally be satisfied: less investment, high efficiency, small footprint, simple operation, relatively complete sludge separation, and low liquid content in the filter cake. Due to the relatively small driving force of the vacuum filtration equipment, when the fine crystalline particles block the filter cloth, the operation will not be able to proceed, which cannot meet the needs of phosphoric acid sludge separation. Therefore, according to the process requirements, the equipment selects a pressurized filter. After research and analysis, the following three types of pressure filters can be considered.