Utilization value and corrosivity of yellow phosphorus tail gas

At present, the method of industrialization of yellow phosphorus production is the electric furnace method, whose advantages are particularly prominent in areas with sufficient power supply.

The main chemical reactions of phosphorus production by electric furnace are:

4Ca5F(PO4)3＋21SiO2＋30C1400－1500℃3P4↑＋30CO↑＋SiF4↑＋20CaSiO3

The production of one ton of yellow phosphorus will produce about 2500 to 3000 cubic meters of tail gas, the main component of which is carbon monoxide, with a content of up to 85% to 92%. Its calorific value is equivalent to 5500 to 6500 cubic meters of urban gas, with a calorific value of 10.5 to 11 MJ/m3, which is much higher than half water gas, and its utilization value is very high. Therefore, yellow phosphorus tail gas is a good heat source and raw material for the production of carbon 1 chemicals. One of the main measures taken by the phosphorus chemical industry to cope with the financial crisis is to address the comprehensive utilization of yellow phosphorus furnace exhaust gas. Moreover, China's current environmental protection policy situation no longer allows direct venting and combustion, which not only wastes energy seriously and pollutes the atmosphere, but also does not comply with the national concept of developing a circular economy and promoting energy conservation and emission reduction.

At present, the technical direction of comprehensive utilization of yellow phosphorus tail gas is useful as a heat source, the development of carbon 1 chemicals, and tail gas power generation. Yellow phosphorus tail gas steam boilers have been used in Guizhou, Yunnan, and other places since 2010. It is understood that after installing a yellow phosphorus tail gas steam boiler in a yellow phosphorus plant, the energy-saving efficiency has reached 75% to 80%. It can be seen that the utilization rate of heat energy generated by the combustion of yellow phosphorus tail gas into steam is very high.

In addition to CO, yellow phosphorus tail gas contains many impurities, such as inorganic sulfur (S, H2S, SO2), organic sulfur (CH4SH, COS), SiF4, PH3, P4, HF, CH4, CO2, O2, N2, cyanide, and raw material dust. Generally, total sulfur is 0.8~8.0 g/m3, and total phosphorus is 0.5~1.5 g/m3.

Due to the complex composition of yellow phosphorus tail gas, high corrosivity to equipment, immature purification processes, and large investment in purification projects, most enterprises have adopted yellow phosphorus tail gas steam boilers as energy conservation and emission reduction methods, but the complex and frequent corrosion has plagued yellow phosphorus enterprises.

After spraying water to collect phosphorus and wash gas from yellow phosphorus tail gas, most corrosive media elements such as fluorine, phosphorus, and sulfur can be removed, but there are still small amounts of phosphorus, sulfur, and trace amounts of fluorine that are difficult to remove. The yellow phosphorus tail gas steam boiler adopts a boiler structure that separates combustion and heat exchange. This structure can avoid the erosion and corrosion of high-temperature flame on boiler equipment and the combustion and corrosion of elemental phosphorus on the tubes. However, it is still inevitable that high-temperature flue gas will cause oxidative corrosion and hydrogen embrittlement on the tubes, as well as the acid dew point corrosion of low-temperature flue gas on the economizer and flue stack. Eventually, equipment such as tubes, energy-saving devices, and flues are frequently replaced, resulting in unstable processes, low production efficiency, and even the entire boiler being scrapped.