Coalbed methane is called coal mine gas in coal mine. According to the new resource evaluation results, China's onshore CBM resources amount to 36.8 trillion cubic meters, which is equivalent to the onshore conventional natural gas resources (38 trillion cubic meters), second only to Russia and Canada. The main component of coalbed methane is methane. When the concentration of methane in the air reaches 5%-16%, it will explode in open fire, which is the source of coal mine gas explosion accident.
The greenhouse effect of coal bed methane (CBM) is about 21 times that of carbon dioxide (CO2) when it is discharged directly into the atmosphere without application. Coal mine gas power generation can not only effectively deal with coal mine gas accidents, improve the safe consumption conditions of coal mine, but also help to increase the supply of clean energy, reduce greenhouse gas emissions, and achieve multiple purposes of maintaining life, resources and environment.
I. Low Concentration Gas Power Generation Technology
Coal mine gas consists of high concentration gas and low concentration gas. High concentration gas refers to the gas whose concentration is more than 25%, and low concentration gas refers to the gas whose concentration is less than 25%. More than 60% of the gas in our country is low concentration gas containing less than 25% methane. According to the requirements of coal mine safety regulations, the gas concentration below 25% can not be stored and delivered, let alone applied.
Gas Generator Set
There are two problems to be dealt with in the demand of low-concentration gas power generation. One is that each coal mine is different and changing at any time. It is difficult for traditional generating units to "respond to changes with unchangeability"; the other is the problem of safe transmission of low-concentration gas.
The low-concentration gas generator unit adopts the technology of electric control gas mixer, which can automatically control the air-fuel ratio to adapt to the change of gas concentration. At the same time, it also deals with the safe delivery technology of low-concentration gas, and uses the fine water mist technology to deal with the safe delivery problem of low-concentration gas in the air.
II. Fundamental Request for Low Concentration Gas Power Generation
Firstly, according to the request of the national coal mine safety management department, the gas drainage system is installed, and the gas drainage system must operate normally; secondly, the gas drainage volume of the gas drainage system is about 1 million m3/year, and the gas concentration is between 6-25%. If these two conditions are reached, the foundation of gas power station can be established. If gas power station is established, the benign cycle of coal mine can be carried out, which is "promoting extraction by application and promoting safety by extraction".
III. Investment and Return of Gas Power Station
Power plant investment: 3000-4000 yuan/KW; unit guarantees continuous operation power of 400 kW, annual operation time can reach more than 300 days;
The annual generating capacity of a generating unit is 3 million kwh (consuming 1 million m3/year of pure gas);
The annual generating income of a generating unit is 1.2 million yuan (the electricity price is 0.4 yuan/KWh).
The annual operating cost of a generating unit includes oil consumption, personnel salary, equipment maintenance, equipment depreciation, etc. The generating cost is about 0.10 yuan/kWh.
Annual operating cost and cost of a generating unit = 0.10 yuan/kWh *3 million kWh = 300,000 yuan
Annual revenue of a generating unit:
Annual Income = Annual Generation Income - Annual Total Cost Cost = 1.2-300,000 yuan = 900,000 yuan
4. Application and Benefit of Waste Heat in Gas Power Station (Take 700GFW Unit as an Example)
1. Application Principle of Waste Heat
The exhaust gas of gas generating unit carries a large amount of heat in the process of cleaning from the inside of the unit. The exhaust temperature is about 550 C. Superconducting heat pipe evaporator is used to recover the heat in the exhaust gas of the unit, and 0.6 MPa steam is produced for users to use.
2. Design Scope
The design scope of the exhaust heat recovery system for gas generating units includes the design, selection and arrangement of all pipelines, accessories and equipment of the whole waste heat recovery system from the inlet of the water tank to the steam outlet flange of the steam separator in the power station.
3. Calculation of Waste Heat
The calculation shows that each superconducting heat pipe evaporator can produce 0.6 MPa steam of 0.6 tons/hour.
4. Major equipment
Superconducting heat pipe evaporator
XFZFQ-1.0-0.6 superconducting heat pipe evaporator with heat transfer area of 138 m2 and design pressure of 1.15 MPa is selected for the 700 GFW unit.
5. Water quality request
According to the request of GB1576-2001 "Water Quality Standard for Industrial Boilers", the feed water of heat pipe evaporator should be stopped. The total hardness of the feed water is less than 0.6 mmol/l and the oxygen content is less than 0.1 mg/l. Softening water preparation system is designed in waste heat application system. After disposal, the water quality can reach the application request.
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