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Under the “dual carbon” goal, China’s energy structure is accelerating transformation and upgrading, and new energy represented by solar energy, wind energy, geothermal energy is gradually replacing traditional coal, oil, gas and other fossil energy. Promoting the optimal combination of coal and new energy is a new requirement for achieving the “double carbon” goal, and also an important path for the green and low-carbon transformation of coal mines in the future. Based on the analysis of the energy distribution characteristics of coal-endowed areas in China, it is found that the fossil energy distribution areas dominated by coal are often also areas rich in solar energy, wind energy, thermal energy and other new energy, which are suitable for large-scale development of new energy in in coal-endowed areas. The research results are as follows: ① Put forward the concept of full life cycle energy development in coal-endowed areas, divide the energy development process in coal-endowed areas into three stages: coal, coal and new energy optimization combination, and new energy, and build a general framework for new energy development in coal-endowed areas; ② In terms of solar energy development, the theoretical reserves and development potential of solar energy in the mining area are evaluated based on the overlapping relationship between the coal occurrence and the solar energy resource rich area, and a hierarchical comprehensive utilization scheme of solar energy coupled with photochemical utilization, such as distributed/centralized photovoltaic power generation, solar thermal utilization and solar hydrogen production, is proposed to achieve diversified and efficient conversion and utilization of solar energy and collaborative mining with coal resources; ③ In terms of geothermal energy development, the potential of geothermal energy development in coal-endowed areas is evaluated based on the overlapping relationship between the coal bearing area and the geothermal energy resource rich area. In combination with the formation mechanism, distribution law and mining situation of the mine geothermal, a collaborative development system of deep mineral resources and geothermal resources is established to form a comprehensive application scheme for the graded mining of mine geothermal energy and the cascade utilization of thermal users, including the hot water type, rock temperature type and mixed type of the mine, realizing the strategic transfer of “harm” to “benefit” of mine geothermal; ④ In terms of wind energy development, the potential of wind energy development in the mining area is evaluated based on the overlapping relationship between the coal occurrence and the wind energy resource rich area, and the application approaches of wind power generation, wind water lifting, and wind heating technologies in the coal bearing area are proposed, and the wind energy utilization framework for power supply, water cycle power, heating self-sufficiency, and grid connected power generation of underground and underground facilities is constructed; ⑤ Considering that the roof is generally managed by the caving method in the current underground coal mining, and the caving space cannot be effectively used for underground energy storage, a technical path of energy storage in the goaf of the mine is proposed, which is “advanced planning of energy storage reservoir → construction of energy storage reservoir using functional backfilling→ Energy storage and release operation control”; ⑥ In view of the complex and changeable characteristics of multi energy complementary integrated energy system (MCIES) in coal-endowed areas, a heterogeneous energy flow coupling model of energy production and supply units in coal-endowed areas is established, the mathematical expressions of different energy hubs in MCIES are unified, and the energy management and optimization logic method and operation mode of MCIES in coal-endowed areas are proposed. This paper aims to explore the combination path of coal and new energy, demonstrate the feasibility of large-scale development of new energy in coal-endowed areas, endow coal bearing areas with the function of energy supply in the whole life cycle, and form a new mode of energy industry development of coal enterprises integrating “mine-wind-light-heat-storage”.

Malic acid is a dicarboxylic acid that is widely used in food, pharmaceutical and chemical industries. We studied the effects of overexpression of carboxylation pathway genes and inactivation of malic enzymes on the aerobic production of malic acid. Over expression of phosphoenolpyruvate (PEP) carboxylase (ppc) generated strain E21, which increased malic acid production from 0.57 g/L to 3.83 g/L. Then pyc gene from Coryenbacterium glutamicus and pck gene from Actinobacillus succinogenes were overexpressed in E21 separately. The resulting strains E21 (pTrcpyc) and E21 (pTrc-A-pck) produced 6.04 and 5.01 g/L malate with a yield of 0.79 and 0.65 mol/mol glucose, respectively. Deleting two malic enzymes (encoded by maeA and maeB) also led to an increase of 36% in malic acid production with a production of 5.21 g/L. However, the combination of malic enzymes deletion and pyc overexpression could not further increase the yield of malic acid. After optimization of fermentation conditions, strain E21 (pTrcpyc) produced 12.45 g/L malic acid with a yield of 0.84 mol/mol which is 63.2% of the theoretical yield.