In order to ensure the safe production of coal mines, it is necessary to supply a large amount of fresh air to the underground coal mine to dilute the concentration of biogas and eliminate harmful gases. This depends on ventilation. Almost all coal mine exhaust gas is directly discharged into the atmosphere, which not only causes environmental pollution, but also wastes a large amount of available gas resources. The US Environmental Protection Agency estimates that in 2002, for example, the global coal mine ventilation gas emissions were more than 17.3 billion cubic meters, equivalent to 237 million tons of carbon dioxide emissions into the atmosphere. Among them, 11 major coal-producing countries accounted for more than 88%: China ranked first with 6.7 billion cubic meters, followed by 2.6 billion cubic meters in the United States, 2.2 billion cubic meters in Ukraine, and 700 million cubic meters in Russia and Australia. Poland and Kazakhstan reached 400 million cubic meters and 300 million cubic meters respectively.
There are many technologies available for oxidizing coal mine exhaust gas. The US Environmental Protection Agency is evaluating the optimal airflow, biogas concentration, and effective market use.
The most promising is the wind reverse reactor technology. This technique utilizes the principle of regenerative heat exchange between the hard bed of gas and heat exchanger media. The exhaust gas flows in one direction, passes through the reactor, and the temperature rises until the gas is oxidized. When the oxidized gas heat product continues to flow toward the far side of the hard bed, it loses heat until the wind flow automatically reverses, eventually emitting air, carbon dioxide, water and heat. Heat can be supplied to the local area, or a gas turbine can generate electricity. Based on experimental and field experience, the airflow reverse reactor can be operated with a venting gas concentration as low as 0.1%. In the United States, this mature technology is about to be put into commercial use.
Mine exhaust gas can also be used directly as fuel gas for power generation. Commercial applications have proven to be technically feasible and the process is simple, although it is limited in reducing the amount of greenhouse gases. Australia's Anping Coal Mine uses 10% of the exhaust gas for many internal combustion engines. Exhaust gas (concentration: 0.7%) does not require processing, and can be directly used to generate electricity from internal combustion engines and generator units that use coal mine gas and old pond gas (plus natural gas if necessary) as the main fuel.
Some companies have become or are developing gas turbines that use exhaust gas as their main fuel. Some technologies use a catalyst to burn exhaust gas. Some techniques use gas on an external burner without a catalyst, but the effect is lower than the standard turbine temperature, so there is still a problem of insufficient combustion. .
At present, some developers say they can use mine exhaust gas with a gas concentration of 1% to 1.6%, or a mixture of mine exhaust gas and high concentration gas. There are also developers working on the use of exhaust gas with a gas concentration of 0.8% or less. If the gas concentration is high, the turbine can use up to 80% of the total fuel, and at low concentrations, only 20% of the total fuel can be used.
Another technology that has been developed to demonstrate the use of exhaust gas is the combination of coal gangue and exhaust gas in the converter, and the heat obtained can meet the needs of 1.2 megawatts of turbine power. Depending on the proportion of coal gangue exhaust gas, the equipment can be used as an auxiliary technology or main technology to utilize exhaust gas. It does not need to replenish gas or increase the concentration of exhaust gas to maintain operation.
The concentrator is another new technology that economically uses exhaust gas. A concentrator can increase the concentration of exhaust gas by 20 times. This may be advantageous for blending with low concentration exhaust gas for lower fuel turbines, or for increasing the concentration to undiluted gas. The key is how to improve the efficiency of increasing the concentration of exhaust gas. At present, although the experiment to increase the efficiency of increasing the exhaust gas concentration by 0.1% to 1.0% has made some progress, it is not satisfactory.
There are also a number of ways to use the exhaust gas to produce protein and supplement animal feed.
The use of exhaust gas to generate electricity, or the use of exhaust gas to reduce greenhouse gas emissions, can not only greatly improve the environment, turn waste into treasure, but also obtain considerable economic benefits, the economic significance and practical significance of exhaust gas utilization technology is Unquestionable.
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