China has the world's richest phosphate resources. Its reserves, output and market share of yellow phosphorus all rank first in the world. The smelting process of yellow phosphorus generates a large amount of tail gas, which is rich in CO and has a relatively high calorific value. However, due to the complex composition of yellow phosphorus tail gas, the difficulty in purification and the high investment, most yellow phosphorus producers directly release the tail gas for combustion. Take 2008 as an example. The actual production capacity of yellow phosphorus in China was 824 tons, and the emission of tail gas was approximately 2.23 billion cubic meters. Direct combustion and discharge would mean a loss of 235PJ of thermal energy. On the one hand, it would cause waste of energy and resources; on the other hand, it would cause environmental pollution, which does not meet the national requirements for energy conservation, environmental protection and the development of a circular economy. Especially since the implementation of the "Yellow Phosphorus Industry Access Conditions" in 2009, it has been clearly stipulated that the tail gas of yellow phosphorus cannot be directly discharged for combustion. It must be rationally utilized through resource utilization, and the comprehensive utilization rate of tail gas in new facilities should reach over 90%. Therefore, the recovery and utilization of yellow phosphorus tail gas have been elevated to an unprecedented height.
02. Utilization of yellow phosphorus tail gas
If yellow phosphorus tail gas can be rationally utilized, it will become a valuable secondary resource. Because it is rich in C0, its calorific value is 10.5-11.7MJ/m³, which is much higher than that of semi-water gas and can be used as fuel. Meanwhile, the CO, H and other substances in the tail gas of yellow phosphorus are also excellent chemical raw materials, and the comprehensive utilization channels are very extensive.
(1) Direct combustion emissions
Due to the complex composition of yellow phosphorus tail gas, with a wide variety of harmful impurities, its purification and separation are somewhat difficult. Moreover, the purification process is complex and the investment in purification projects is large, which to some extent hinders the effective utilization of yellow phosphorus tail gas. In the early days, most yellow phosphorus producers directly burned and discharged it, especially in some smaller enterprises. This treatment method was very common, and some even discharged it directly without burning, resulting in energy waste and environmental pollution. The access conditions for the yellow phosphorus industry issued in 2009 explicitly prohibited this kind of tail gas treatment method.
(2) As fuel
Due to the high calorific value of yellow phosphorus tail gas, the temperature of the mixed flue gas generated by combustion is also relatively high, and it can be appropriately used as a heat source to replace coal. It can be used to dry raw materials such as phosphate rock and coke, heat water for the production process of yellow phosphorus, dry phosphate, etc. It can also be used to sinter raw materials. The flue gas after being cooled by heat absorption is then treated by dust removal facilities and discharged, ultimately achieving the transformation of waste into treasure and reverse auxiliary production. Overall, this method can significantly reduce the energy consumption in the production of yellow phosphorus and minimize the pollution caused by the direct venting of tail gas to the surrounding environment. It also has the advantages of simple process technology, low requirements for production equipment, low investment, and convenient management. The obvious drawback is that the potential of tail gas is not fully utilized, and the added value of the thermal energy provided is low.
03. Power generation from yellow phosphorus tail gas
Yellow phosphorus tail gas power generation technology is an energy utilization technology. By collecting, pressurizing and purifying the tail gas emitted during the production of yellow phosphorus, It is sent to the combustion chamber of the internal combustion engine, mixed with air and then burned. The high-temperature and high-pressure gas produced by the combustion drives the piston of the internal combustion engine to move back and forth. Through mechanical structures such as connecting rods, the linear reciprocating motion of the piston is converted into the rotational motion of the crankshaft, thereby generating mechanical energy and then converting it into electrical energy.
This technology reduces pollution from the source, avoids unorganized emissions of exhaust gas or waste gas and waste residue produced by torch combustion, lowers the cost of subsequent environmental protection treatment, and achieves a win-win situation of economic and environmental benefits. It is an important path for the green transformation of the yellow phosphorus industry.
