Study On Demisting And Continuous Arsenic Removal From Thermal Process Phosphoric Acid Production

Phosphoric acid is one of the most important intermediate products in the process of phosphorus chemical industry, one of the main raw material for the production of phosphate and fertilizer. The primary means of making phosphoric acid are furnace and wet process. Furnace process is relatively wet process with the advantages of high purity, low levels of impurities, mainly used in the production of food grade phosphoric acid, electronic grade phosphoric acid and specialty phosphates. With the improvement of people’s living standards and the development of electronic industry, furnace phosphoric acid market demand continues to increase. However, it has some defects, such as the larger energy expenditure and high cost. Energy saving and consumption reduction are the focus of scientific research for developing thermal process phosphoric acid.The collecting of acid mist is an important process in furnace phosphoric acid. Venturi scrubber is a key device for this process, but it collect of acid mist at high pressure loss. Arsenic is the main impurity affecting the purity of thermal process phosphoric acid, the content of it is an important index to measure the quality of phosphoric acid. Stirred tank reactor is a key device for arsenic removal, but it has some defects, such as the larger energy expenditure, limited capacity, uncontinuous produce, etc.A homemade dynawave scrubber and SK static mixture are used as research object, the collecting of acid mist by dynawave scrubber and arsenic removal from phosphoric acid by SK static mixture are systematical investigated, respectively. The results obtained are shown as follows:(1) The dynawave scrubber has a good effect in collecting of acid mist, the highest demisting efficiency can be achieved at circulating phosphoric acid concentration and temperature are 32%,30 ℃. The demisting efficiency increased with the increasing gas flow and liquid gas ratio. The device begin into the bubble operating area when liquid gas ratio is 3.5 L/m3 and gas flow is 2900 m3/h, the stabilized can be formed only when liquid gas ratio is 4.5 L/m3 and gas flow is 3000 m3/h, the demisting efficiency in this operating condition is about 99.5%, the pressure drop is about 5000 Pa.(2) The largest effect of demisting efficiency is gas flow, followed by liquid gas ratio, the phosphoric acid of concentration and temperature has little effect on it. The temperature of demisting gas in the range of 40±5 ℃ at the bubble operating area. The liquid gas ratio and gas flow have little influence for the variation of temperature.(3) The arsenic removal efficiency of SK static mixture is high and the time is short. It increases initially and decreases with the increase flow, and increases initially and keeps constant with the increase P2S5/AS. The content of arsenic is 0.0079 mg/kg when flow rate and P2S5/AS are 0.60 m3/h,3, respectively, far below the index of food grade phosphoric acid. It not only can save space, but also can save investment employ SK static mixture to remove arsenic in phosphoric acid.