Discussion on the green and low-carbon development path of coal mine under the background of "double carbon"

Abstract: Aiming at the transformation and development of coal enterprises under the goal of carbon peaking and carbon neutrality, this paper analyzes the current situation of coal enterprises and points out the common problems existing in various coal enterprise groups based on the characteristics of capacity reduction, closure and withdrawal of mines and active mines. From the aspects of energy conservation, environmental protection and comprehensive utilization of resources, the countermeasures and suggestions on clean and efficient utilization of coal during the "14th Five-Year Plan" period are put forward. So as to better cope with the transformation of enterprises under the dual-carbon situation, and promote the steady development of the coal industry.

Coal has long been regarded as the necessity of energy consumption in China, which supports the development of national economy. On September 22, 2020, at the General debate of the 75th session of the United Nations General Assembly, China announced to the world that China will strive to peak its carbon dioxide emissions before 2030, and strive to achieve carbon neutrality before 2060. In the "14th Five-Year Plan" and the outline of the 2035 vision goals, the extensive formation of green production and life style, and the stable decline of carbon emissions after peaking have become important contents, and "carbon peaking" and "carbon neutrality" have become important strategic goals for the country's development in the next three decades.

In recent years, the CPC Central Committee and The State Council have attached great importance to the construction of ecological civilization and the clean and efficient use of coal. After the proposal of peak carbon neutrality, coal enterprises pay more attention to energy conservation, environmental protection and comprehensive utilization of resources, and the idea of ecological civilization gradually runs through all aspects of enterprise development. The production energy in mining areas can be reduced by strictly controlling the energy use index, promoting the substitution of energy-saving equipment, utilizing waste heat and pressure, and developing comprehensive utilization of resources. In the promotion of ecological environmental protection in mining areas, enterprises have further increased the investment in ecological environmental protection, all coal gangue comprehensive utilization power plants have achieved ultra-low emissions, land reclamation work has been promoted in an orderly manner, the main pollution sources in mining areas have also achieved positive results, and the mining area environment has been significantly improved. There are also new highlights in the comprehensive utilization of resources, the use of coal gangue, fly ash resources to carry out phase-change thermal storage material technology application, solve the problem of coal gangue and fly ash large-scale accumulation in mining areas, the use of oil shale refining waste residue to produce soil amendments, and broaden the technical content and added value of solid waste utilization.

1. Development status of coal enterprises

1.1 Production operation

Coal enterprises are the main force in the low-carbon transformation of the coal industry, and the main body responsible for coping with and realizing the dual-carbon goal. Under the dual-carbon goal and supply guarantee situation, the overall operation of coal enterprises in the country is stable and orderly.

In 2022, the operating income of coal enterprises above designated size in China will reach 4.02 trillion yuan, an increase of 19.5 percent year-on-year, and the total profit will reach 1.02 trillion yuan, an increase of 44.3 percent year-on-year. On the coal supply side, domestic production reached another record high. In 2022, the national raw coal output will be 4.56 billion tons, an increase of 10.5%, as shown in Figure 1.

1.2 Closure of production capacity and industrial transfer

The coal industry has obvious problems related to mine closure and withdrawal, and there is pressure on industrial transfer. From the situation of mine closure and withdrawal, the problems of asset disposal, personnel transfer resettlement and subsequent ecological protection derived from coal mine closure and withdrawal are still very prominent. Concentrated performance is:

(1) After the policy withdrawal or closure of the mine, there are policy obstacles to the write-off of the corresponding assets and debts of the coal mine, and the supporting mechanism for the complete withdrawal of the coal mine remains to be improved.

(2) Due to the large number of workers in coal mines, the pressure of personnel transfer and resettlement after the closure of mines is huge, the number of jobs that can be provided by industrial transfer is limited, the way to transfer and resettlement of personnel through re-employment is relatively limited, and the financial pressure of enterprises for personnel resettlement is relatively large. Once the coal price goes down or the main business of coal changes, the pressure of maintaining stability will be greatly increased.

(3) The ways and methods of closing and exiting the coal industry transfer are not high in technical content, most of them are closely related to the main coal industry, and the newly transferred industries are small in volume and scale, making it difficult to form an alternative pattern of new industries.

2. Green and low-carbon development path

Since the two-carbon goal was proposed, coal enterprises have actively explored new development paths, and the concept of green and low-carbon runs through all aspects of coal mine production, and has achieved some results in the disposal and utilization of coal gangue, mine water, and gas. Taking a state-owned coal mine as an example, the paper analyzes the green and low-carbon development path of coal mine under the background of carbon peak carbon neutrality.

2.1 Coal gangue disposal and utilization

Since the production of the self-built mine, the gangue in the mining area has been piled up as solid waste. The gangue mountain is about 60m high, the storage capacity is about 700,000 m3, and the area is more than 40,000 square meters. The high storage, large storage capacity and large area not only pollute the environment, but also restrict the development of the coal mine economy. To this end, on the one hand, the enterprise actively organizes cadres and workers to carry out ecological restoration and management of mining areas, gangue hills and surrounding areas, transplanting more than ten kinds of trees, with a green area of tens of thousands of square meters, by laying sprinkler pipes and installing sprinklers at multiple points, to achieve full coverage of gangue hills spray pipe network, and regularly open the spray dust reduction, effectively reducing the dust pollution of gangue hills. On the other hand, the exposed sites not covered by plants are fully covered with air filter, and the management of the rescue team is arranged through the daily inspection of gangue hills, and the damaged air filter is covered in time. At the same time, the enterprise also actively expand the disposal and utilization channels of coal gangue, through the sale of surrounding building materials factories, power plants for brick and power generation, the annual consumption of more than 250,000 tons, the gangue mountain is expected to be basically eliminated within 3~5a, to achieve economic efficiency and solid waste accumulation negative growth win-win.

2.2 Mine water treatment and comprehensive utilization

(1) As one of the large water mining areas, the mine has a mine water and domestic sewage treatment station. In recent years, in order to improve the wastewater treatment capacity, a new mine water efficient swirl treatment system has been added, and the treated mine water and domestic sewage have been discharged up to the standard. At the same time, in order to save underground fresh water resources, according to the influence of factors such as the outlet point of mine water and whether it is affected by coal mining pollution, enterprises have adopted the comprehensive utilization of "classified treatment, improve the comprehensive utilization rate and utilization value, and realize the local resource utilization of mine water", and the treated water is used for water supply, wetland park, water plant, production and life of mining area and agricultural irrigation.

(2) Implementation of mine water waste heat utilization heat pump system project. In the process of mining, the treatment of mine drainage and the phenomenon of mine thermal damage are common problems. Therefore, in order to ensure the normal work of underground personnel and machinery, the mine water should be treated in time. There is a lot of heat energy in the waste water discharged from the mine and the return air of the mine, the waste heat generated in the coal mining, the recovery of waste heat energy, combined with the water source heat pump system, can convert a large number of low temperature heat energy that can not be directly used into useful high temperature heat energy, for the winter heating of the mining area, wellhead antifreeze and summer air conditioning system, not only can replace the boiler room, reduce the pressure of environmental pollution, but also can drop Low production energy consumption of enterprises, improve the economic benefits of enterprises, truly achieve green environmental protection (no combustion, no smoke exhaust, no waste emissions), high efficiency and energy saving (1kW power consumption, can get more than 4~6kW heat or cold), a multi-purpose machine (heating, cooling and domestic hot water).

2.3 Gas extraction and utilization

Coal mine gas is one of the main hazards in the process of mine production, the concentration of 5%~16% in the open fire explosion, its main component is methane, the greenhouse gas effect is 21 times that of carbon dioxide, methane emissions on the climate and environment. How to turn "waste" into treasure is a difficult problem that enterprises need to solve in the pursuit of high-quality development. As early as the 1980s, a ground gas pumping pump station was established in the mine, and the pumping pump station was reformed in 2011. At present, four gas pumping pumps are installed in the gas pumping station, which can realize two working and two standby (parameters are shown in Table 1). The normal operation of the gas extraction system in the mine, the capacity of gas pumping station, standby pump and extraction pipe network can meet the needs of gas control in the mine area.

In view of the characteristics of hard coal quality in some areas of the main treatment face, the mine actively promotes the use of mechanical cavitation devices, and innovatively puts forward the comprehensive treatment technology of "loosening blasting + mechanical reaming cavitation" in cross-layer drilling, and improves the gas permeability of coal seam by implementing integrated measures of blasting and expansion. In addition, through the multi-level management mechanism of the mine, the four key links of "fine drilling, strong coal punching, tight hole sealing and pumping in place" are the main grasping points, and multiple measures are taken simultaneously to greatly improve the utilization of gas extraction in the mine.

Mine gas power generation increased from 3.3464 million kW·h in 2021 to 12.3634 million kW·h in 2022, an increase of 3.69 times; According to the calculation of 0.71 yuan /(kW·h), the utilization of gas power generation in 2022 will increase the efficiency of the mine by nearly 8.77800 yuan. From January to April 2023, the total mine gas power generation has completed 4,703,500 kW·h, which has increased mine efficiency by 3,339,400 yuan, as shown in Figure 2.

At present, the gas concentration of the extraction system is 20%~30%, the pure gas flow rate is 18m3/min, the average daily power generation is about 45,000 kW·h, and 1m3 gas can generate 1.95kW·h, which can increase the efficiency of the mine by 30,500 yuan per day. In addition, according to the relevant provisions of the local coal mine gas prevention and control management measures, the mine will replace the pump whose gas extraction pump capacity does not meet the relevant requirements at this stage.

3 Policy Suggestions

In the process of promoting green and high-quality development, the scale and business indicators of coal enterprises may show a downward trend in a certain period of time, but the investment in ecological restoration, pollution prevention and control, and safety production will still be more and more large, accounting for a higher proportion of costs, and the burden will be more and more heavy. It is suggested that the corresponding policy support can be given in ecological restoration, subsidies for comprehensive utilization of gas and mine water, tax on solid waste stacking of gangue mountain, and fund support for coal mine safety renovation.

4 Conclusion

On the whole, the status of coal resources as the ballast and underpinning stone of China's energy security will not change in the short term. Coal enterprises are faced with both difficulties and opportunities. At present, the problems existing in various coal enterprises are much the same, and the enterprises lack a deep analysis of the impact of the 3060 target, and their preparation is also insufficient. Under the new situation, coal enterprises can learn from each other in the process of transformation and development, and at the same time, they should grasp the overall situation, adhere to the policy orientation, and make dynamic adjustments according to the actual situation of enterprises, so as to lay a solid foundation for achieving the goal of carbon peak carbon neutrality and promoting high-quality development of enterprises.