Introduction to Yellow Phosphorus Production Process

Introduction to Yellow Phosphorus Production Process

The raw materials for producing yellow phosphorus are phosphate rock, coke (white coal), and silica. Coke (white coal) is both a reducing agent and a conductor in the production of yellow phosphorus by electric furnace (submerged arc furnace) method; Silica is a solubilizer that can lower the melting point of slag and facilitate slag removal. The main chemical component of phosphate rock is calcium fluorophosphate, with the general formula Ca5F (PO4) 3.

The grade of phosphate rock (expressed as P2O5 content) generally requires a P2O5 content of ≥ 28%, Fe2O3<%, and CO2<5% (all of the above indicators are calculated on a dry basis and checked upon arrival at the plant). When phosphate ore is fed into the furnace, the H2O content is less than 2% and the particle size is 5-35mm.

The fixed carbon content in coke (white coal) is generally required to be greater than 80% (calculated on a dry basis and checked at the time of entry), and the mechanical strength should be good. When coke (white coal) is fed into the furnace, the H2O content is less than 2% and the particle size is 3-25mm.

The SiO2 content of silica should be greater than 97%, and the particle size should be 5-35mm when entering the furnace. The entry indicators of the three raw materials are mainly achieved through crushing, screening, drying, etc. After passing the inspection, they are separately stored in different warehouses for backup.

The main chemical reaction of phosphorus production by electric furnace (submerged arc furnace)  method is: 4Ca5F (PO4) 3+21SiO2+30C 3P4 ↑+30CO ↑+SiF4 ↑+20CaSiO3. Phosphate ore, silica and coke (white coal) that meet the production process requirements are released in batches from the storage bin according to a certain proportion, and then mixed into a uniform mixture and transported to the electric furnace bin.

The mixture is continuously fed into a closed micro positive pressure electric furnace (submerged arc furnace)  through seven discharge pipes that connect the electric furnace body and the silo in a uniform distribution. The three-phase electrodes (three or six) of the electric furnace work at around their rated power, causing the mixture entering the electric furnace to undergo a reduction reaction at 1400-1500 ℃. The generated slag and phosphorus iron are regularly discharged from the furnace, and the phosphorus iron is recovered at the slag channel. The slag enters the slag pool (or water quenched slag pool) and is promptly picked up and transported away.

Generated yellow phosphorus CO、 Silicon tetrafluoride and other gases (known as furnace gas) escape from the reaction melting zone, pass through the continuously replenished mixture in the upper part of the furnace (known as the furnace gas filter layer), and carry a part of the mechanical impurities in the mixture (at this time, the furnace gas temperature generally drops to below 260 ℃). They enter the series of three absorption towers through the air duct and are cooled by circulating sewage with low turbidity, suitable temperature and pressure. Yellow phosphorus condenses into droplets and enters the bottom phosphorus receiving tank together with mechanical impurities, which is crude phosphorus.

Crude phosphorus is heated, stirred, and clarified with steam in a refining pot, and then pure phosphorus is deposited at the bottom of the pot. After that, it enters the condensation tank and is cooled to form the product yellow phosphorus.

Finally, the finished phosphorus is measured and packaged. CO and other gases (i.e. exhaust gas) are divided into two paths through a total water seal. One path is further purified and used as fuel, usually released when not in use.