China has abundant coalbed methane resources, ranking third in the world. Every year, more than 13 billion cubic meters of gas are emitted during coal mining, equivalent to approximately 16 million tons of standard coal.
In the past, apart from heating, there was no reasonable utilization method for coalbed methane, and it was not fully utilized. Therefore, the vast majority of gas was discharged into the atmosphere, which cost money, wasted resources, and polluted the environment.
The development and utilization of coal mine gas has the following important significance:
1) China's conventional oil and natural gas resources are relatively scarce. Over the past 20 years, the Chinese economy has developed rapidly, and the demand for energy has also increased. In recent years, China's dependence on the international energy market has been increasing. In order to maintain sustained and rapid economic growth, it is necessary for China to develop new energy sources and change the existing unreasonable energy structure;
2) The development and utilization of coal mine gas has considerable economic benefits. At present, the prices of conventional energy such as crude oil, natural gas, and coal are constantly rising both domestically and internationally. The development and utilization of coal mine gas can be carried out along with coal mining projects, saving engineering costs;
3) Coal mine gas is the main culprit of coal mine accidents. 70-80% of domestic coal mine accidents are caused by gas explosions or outbursts. Increasing coal seam gas extraction can reduce the gas content in the mine tunnel and effectively prevent accidents from occurring;
4) The main component of coal mine gas is methane, which is one of the main greenhouse gases. Its damage to atmospheric ozone is 22 times that of CO2. If coal mine gas is developed and utilized, carbon emissions can also be reduced.
With the exploration and mining of coal resources, coal mine gas has been extensively discovered as an associated resource. Coal mine gas is divided into four categories based on its methane concentration: one is surface extraction of coalbed methane, with methane concentration greater than 80%, mainly used for civilian, automotive fuel, power generation, etc; The second type is gas extracted during coal mining, with methane concentrations between 30% and 80%, known as high concentration coal mine gas, mainly used for civilian, chemical, power generation, combustion, etc; The third category refers to the extraction and discharge of methane during coal mining, with a methane concentration greater than or equal to 3% and less than 30%, known as low concentration gas. Currently, a small portion is used for power generation, while the majority is directly discharged; The four types are methane emitted from coal mine ventilation systems with a concentration below 1%, known as "ventilation gas", which is directly released. At present, the research on depleted wind oxidation power generation technology is still in its infancy.
Key technologies for coal mine gas power generation
The key technologies for coal mine gas power generation can be summarized into three categories: gas mixing, automatic control, and safety fire prevention, which are further divided into the following: equal vacuum membrane mixing technology; Venturi electric control mixer mixing technology; Electric control technology for double butterfly door mixer; Gas low-pressure intake mixing technology; Low pressure and high flow pilot pressure regulation control technology; Gas flame retardant technology
Main technical characteristics of gas generator set
1) Automatic air-fuel ratio adjustment technology
Implement closed-loop control of engine air-fuel ratio through computer, and design large-diameter gas intake channels for low concentration gas. Gas and air are controlled separately by electric butterfly doors. When the concentration of CH4 changes, the engine automatically monitors the combustion status in real time. The control unit issues instructions and the actuator adjusts the gas channel to change the gas intake amount, achieving the goal of automatically adjusting the mixture ratio and keeping the engine air-fuel ratio in an ideal state. The entire process is automatically implemented. Units without automatic air-fuel ratio adjustment technology theoretically cannot be applied to gas power generation, and practice has also proven that there are no successful cases of units without automatic air-fuel ratio adjustment technology being used domestically.
2) Low pressure intake technology
In response to the low pressure of gas extraction, the unit adopts the technology of mixing gas and air before pressurization to adapt to the low pressure of coal mine gas. The application of this technology can achieve the goal of directly using coal mine gas extraction and power generation. When the gas pressure reaches above 3kPa before the pressure regulating valve, it can meet the usage conditions without the need for additional pressurization devices, reducing investment. Units that do not adopt this technology require pressurization devices, which increases investment; At the same time, when the pressure of low concentration gas increases, the explosion limit quickly widens, increasing safety hazards, consuming electricity, and reducing power generation efficiency.
3) Lean combustion technology
By reasonably matching the gas distribution system and utilizing the new concept combustion chamber technology and cylinder temperature control technology with independent intellectual property rights, lean combustion is achieved together, reducing heat load, improving the adaptability of the unit to gas and the thermal efficiency of the unit, greatly enhancing its power and reliability. Units that do not adopt this technology are prone to detonation and are sensitive to the humidity of gas, resulting in difficulty or discontinuity in ignition, which directly affects the reliability of unit operation.
4) Anti tempering technology
The company has developed a metal corrugated belt gas pipeline specific flame arrester for the characteristics of low concentration gas, which is used for three ignition points of the engine to prevent engine backfire. This specialized flame arrester has been approved by the National Fire Administration.
5) Digital ignition technology
This technology is a patented technology of Shengli Power Machinery Co., Ltd. The ignition system is used in conjunction with products from ALTRONIC Corporation in the United States. Through worldwide use, it has been proven that this system has high reliability, especially suitable for high-power units, ensuring sufficient gas combustion and reliable operation of the units. This ignition system is particularly suitable for multi cylinder models, allowing each cylinder to work in good condition and unleash the performance of the machine.
2.3.3 Safety of Low Concentration Gas Power Generation Technology
1) The safety of the crew itself
The design of the 500GF1-3 gas generator set fully embodies the design principles, taking into account the flammability and explosiveness of gas, especially low concentration gas. The unit itself has multiple safety protection devices:
Short circuit protection; Overcurrent protection; Undervoltage protection; Reverse power protection; Generator thermal protection; TEM protection system.
2) Safety of low concentration gas transportation system
① Process of fine water mist conveying system
Gas enters the gas transmission pipeline through a water level self controlled water seal flame arrester and a metal corrugated belt gas pipeline dedicated flame arrester. The water in the parallel gas pipeline is pressurized by a water pump and continuously forms mist in the gas pipeline through a water mist generator. Fine water mist and gas are mixed and transported in pipelines. Fine water mist condenses and is circulated after dehydration by a dehydrator.
② Wet water level automatic control group firearm
③ Metal corrugated gas pipeline special flame arrester
④ Fine water mist fire extinguishing technology
⑤ Circulating dehydration technology
⑥ Pressure control technology for gas conveying system
⑦ Monitoring technology for fine water mist transportation
Economic Benefit Analysis of Gas Generator Unit
General parameters
Unit operating time: Considering the normal maintenance and upkeep of the unit, the unit operating time is calculated at 7200 hours per year.
Unit operating power: The long-term operating power of the unit is 1000 kilowatts (the unit can output rated power when the atmospheric pressure is 100 kPa, the ambient temperature is 25 ℃, the relative humidity of the air is 30%, and the gas quality meets relevant regulations. It can also work continuously for 12 hours at rated power and operate for a long time at 90% of the rated power.).
Unit depreciation: Generally, if the overhaul cycle of a unit is greater than 30000 hours, it can undergo three major overhauls, and the service life is calculated as 10 years. The depreciation cost is about 200000 yuan per year.
Electricity price: Under the current national policy, the on grid electricity price for gas generators is:
0.38 (basic grid electricity price)+0.25 (national financial subsidy, calculated according to regional financial policies)=0.63 yuan/kW. h;
Taking into account the actual electricity usage of the coal mine and fully considering the self generation and self use of the power station, the electricity price can be calculated at approximately 0.5 yuan/kW. h to offset the electricity bill
Economic Benefit Analysis of Single Gas Generator Unit Operation
The long-term operating power of a single 1100GF-WK2 gas generator set is calculated at 1000kW.
Unit heat consumption rate: ≤ 10MJ/kW. h, converted to electricity generation, each standard cubic meter of pure gas can generate 3.3-3.5 kWh of electricity.
At a CH4 content of 100%, a single unit consumes approximately 303 m3 of gas per hour during operation;
Annual power generation: 1000kW × 7200h=7.2 million (kW. h)
Annual power generation output value: 720 × 0.5=3.6 million yuan
Operating cost: can be controlled within 550000 yuan. The average operating cost per kilowatt hour is around 0.075 yuan.
The specific analysis is as follows:
Equipment depreciation cost: Depreciation cost is calculated at 200000 yuan per year.
Accessory cost: mainly includes the engine oil filter, air filter, etc. Considering the damage and replacement of some components, the average accessory cost from unit production to scrapping is 50000 yuan/year.
Maintenance cost: Depending on the specific situation of the unit during use, it includes medium maintenance (once every 10000-12000 hours, with a cost of 100000 yuan/unit) and major repairs (once every 20000-25000 hours, with an average cost of 200000 yuan/unit). The average maintenance cost is (10+20) × 4 ÷ 10=120000 yuan/year.
Maintenance costs: including personnel salaries, etc. The power station has one station master and six unit maintenance workers, with two people per shift, implementing an 8-hour work system; Two maintenance workers, one machine and one electricity. There are a total of 9 people, with an average annual salary of about 30000 yuan. The annual maintenance cost of the power station is about 270000 yuan, and the average cost per unit is calculated based on the capacity of the power station. If the power station consists of 4 units, the cost per unit is about 67500 yuan.
Oil cost: The annual oil cost for a single unit is approximately 60000 yuan.
Gas cost: mainly includes pipeline maintenance cost, purification cost, etc., which can be controlled within 20000 yuan per unit.
Maintenance and other auxiliary equipment: maintenance and other auxiliary equipment such as gas transmission system, cooling system, power system, etc., calculated at 25000 yuan.
The total operating cost of the unit is: 20+5+12+6.75+6+2+2.5=542500 yuan.
The average cost is 542500 yuan ÷ 7.2 million kilowatt hours ≈ 0.075 yuan/kW. h
Annual profit of a single gas generator set: 3.6 million yuan -542500 yuan=3.0575 million yuan.
In addition, the power station can increase economic benefits by extracting CO2 emission reduction funds through supporting waste heat recovery devices and CDM projects.
Waste heat utilization output value: The unit is equipped with waste heat recovery devices to achieve cogeneration of heat and power. It can generate about 0.8 tons of steam per hour (pressure of 0.4-0.6Mpa); The steam price is calculated at 200 yuan/ton, which can save 1.152 million yuan in steam costs throughout the year.
conclusion
Through the implementation of this gas power generation project, the safety issues of coal mine gas and the environmental pollution caused by gas drainage have been effectively solved. Through cogeneration, a circular economy has been developed, and the comprehensive utilization rate of energy has been improved.
Developing green electricity represented by gas power generation is in line with the industry policies encouraged by the country. Through efficient utilization of resources, it increases the efficiency of enterprises, reduces production costs, and is beneficial to environmental protection. It is a green and environmentally friendly project that benefits the country, the people, and society.