Coal-to-natural gas has greater advantages

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Currently, in China, the methods for converting coal into energy products include power generation, coal-to-oil conversion, coal-to-methanol and dimethyl ether production, and coal-to-natural gas production. The energy efficiency, from lowest to highest, is as follows: coal-to-oil (34.8%), coal-to-dimethyl ether (37.9%), coal-to-methanol (41.8%), power generation (45%), and coal-to-natural gas (50%–52%). Coal-to-gas has the highest energy efficiency; it is the most effective way to utilize coal, as well as the optimal method for producing coal-based energy products. In terms of water consumption per unit heat value, the water usage per gigajoule ranges from lowest to highest as follows: coal-to-natural gas (0.18–0.23 tons), coal-to-oil (0.38 tons), coal-to-dimethyl ether (0.77 tons), and coal-to-methanol (0.78 tons). Coal-based natural gas has the lowest water consumption per unit of heat value, making it the most water-efficient energy source; this is of great significance for the development of the coal chemical industry in western regions where coal is abundant but water is scarce. Since the methanation unit for coal-to-natural gas produces a large amount of high-pressure steam, this steam is used to drive the air separation turbines, reducing the use of boilers and fuel coal. In the methanation unit, almost 84% of the waste heat is recovered in the form of high-pressure steam, while only 0.5% of the waste heat needs to be cooled using cooling water; thus, the heat recovery efficiency of the entire system is very high. At the same time, a large amount of excess low-pressure steam can be used for power generation. In coal-based methanol, dimethyl ether, and synthetic oil plants, almost all of the high-pressure steam required for air separation is supplied by boilers, with virtually no excess low-pressure steam available. To this end, coal-to-natural gas can **reduce CO2 emissions from boilers and power generation**. For example, in coal-to-natural gas projects that utilize water-coal slurry gasification technology, the production capacity is 1.6 billion cubic meters of natural gas per year; the excess low-pressure steam is used for power generation, producing 480 million kWh of electricity annually, which is equivalent to a reduction of 451,200 tons of CO2 emissions ； This project generates 542 tons per hour of steam at 9.8 MPa as a by-product of methanation, resulting in an annual reduction of 1.38 million tons of CO2 emissions. Furthermore, coal-to-natural gas can be transported via pipelines on a large scale; it is energy-efficient, environmentally friendly, safe, and has low transportation costs. Methanol, dimethyl ether (under pressure in liquid form), and oils are all flammable and explosive liquid products; their transportation is difficult and costly, and transport safety is a matter of concern. Therefore, in terms of product transportation, coal-to-natural gas has an advantage.