Make rational use of coke oven gas to develop a circular economy

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One of the traditional coal gasification technologies is coking, which involves using coking coal to produce coke and coke oven gas through dry distillation in a coking oven; the coke is then used in blast furnaces for iron production. However, some manufacturers are keen on using coke oven gas to produce methanol, and this practice is gaining momentum in independent coking plants. Research has found that compared to methanol production from coal gas, methanol production from coke oven gas still has many drawbacks. Therefore, producing methanol from coal gas is the best option for processes that serve as substitutes for petroleum. In coking plants, the gas produced by gasification units is supplied together with coke oven gas; this allows a large amount of excess coke oven gas to be used for the production of direct reduced iron, which is then supplied to steel mills as a high-quality feedstock. A coal-oil-iron circular economy, based on coal gasification, using coking as an energy conversion method, taking the production of oil substitutes as an opportunity, and aiming for a revolution in steel technology, will be of great significance for the rapid development of China’s national economy. 1 Review of the existing kerosene-iron circular economy (1) The existing kerosene-iron circular economy is based on the coking industry, where valuable coking coal is used in coking ovens to produce coke and coke oven gas. Coke is supplied to blast furnaces to produce blast furnace iron (non-pure iron) as raw material for steelmaking. Coke oven gas is used to produce methanol, which is then used to manufacture dimethyl ether as a substitute for petroleum. (2) The coke oven gas used in methanol production is manufactured from precious coking coal; as a result, a large amount of coking coal is consumed, which increases the cost associated with coke oven gas and thereby raises the production cost of methanol. (3) The process technology for producing methanol from coke oven gas has the following problems: First, due to the high sulfur content in coke oven gas (especially organic sulfur), multi-stage desulfurization processes are complex, the process flow is lengthy, which in turn increases the investment costs. Secondly, the production process of methanol requires deep desulfurization of coke oven gas, with the sulfur content in the purified gas (including organic sulfur) needing to be below 0.1 ppm. Therefore, a large amount of catalyst is required during the desulfurization process, increasing the cost allocation for methanol. Thirdly, the hydrogen content in coke oven gas is between 56% and 58%; during methanol synthesis, the carbon-hydrogen ratio is unbalanced, resulting in a low utilization rate of hydrogen. The aforementioned problems are due to the characteristics of coke oven gas; therefore, it is necessary to change the feed gas. (4) During the blast furnace iron-making process, coke comes into direct contact with molten iron; most of the sulfur and impurities in the coke end up in the molten iron. As a result, the iron produced in blast furnaces is not pure iron, which poses significant challenges in the desulfurization and impurity removal processes during steelmaking. This situation needs to be changed urgently. 2 A new model for the circular economy of kerosene and iron (1) The new model for the circular economy of kerosene and iron is based on coal gasification technology; non-coking coals (lignite, bituminous coal, etc.) are gasified in Enfield or Texaco furnaces to produce gas or syngas. Gas is used to replace coke oven gas, while syngas is used to produce methanol. Large amounts of excess coke oven gas can be used to produce directly reduced iron, which can replace blast furnace iron as a feedstock for steelmaking. The scientific integration of traditional ironmaking technologies with direct reduction ironmaking technologies can maximize both economic and social benefits. (2) The coal-to-gas process uses non-pulverized coals such as lignite and long-flame coal as raw materials. These raw materials are abundant and inexpensive, and in terms of replacing coke oven gas, they can help save a large amount of coking coal. (3) Gasifiers such as the Ender furnace and the Texaco furnace combine a gasifier, a gas converter, and a water gas generator in one unit. Organic compounds and sulfides in gas are converted into hydrogen, carbon monoxide, and elemental sulfur through cracking, transformation, and reforming. Since elemental sulfur is easier to remove than organic sulfur, it is possible to **simplify the process flow for methanol synthesis**. Since the gasification process heats the material to the conversion and synthesis temperatures at the same time, it is possible to save 15%–20% in energy consumption compared to using cold coke oven gas for methanol production; thus, producing methanol from coal gas is far superior to producing it from coke oven gas. (4) Under the new process, both the coking plants in steel companies (metallurgical coking plants) and independent coking plants (which account for 70% of the country’s coke production capacity) should install gasification units of appropriate scale to produce coal-based gas. Coal gas with different compositions is supplied together with coke oven gas. The produced syngas is used to manufacture methanol, while the excess coke oven gas is used to produce directly reduced iron. (5) When using coke oven gas to produce direct reduced iron with the HYLZR technology, it is only required that the sulfur content in the gas be kept between 15 and 20 mg/m3; therefore, there is no need for advanced desulfurization of the coke oven gas, which **simplifies the desulfurization process**. Due to the high hydrogen content in coke oven gas, the gas consumption per unit of directly reduced iron is only 618 m3/t. (6) Modern steel mills require large quantities of directly reduced iron. Once the directly reduced iron produced from coke oven gas meets the needs of steelmaking, it also creates favorable conditions for the integration of coking plants and steel mills. 3 Kerosene-Iron Circular Economy Process Diagram of the kerosene-iron circular economy process (see the overview section in this site’s “Technical Treasury”). The coal gas produced by metallurgical coking plants is mixed with blast furnace gas and supplied to CCPP and various heating furnaces to replace coke oven gas. Excess coke oven gas is used to produce direct reduced iron as a high-quality feedstock for steelmaking. The metallurgical coke produced by coking plants is supplied to blast furnaces for iron production, while the molten iron generated by these furnaces is fed to steel mills and subsequent rolling processes. Some low-calorific value coal gas produced by independent coking plants is used to heat the coke ovens, and it can replace up to 50% of the gas generated by the coke ovens themselves. This excess coke oven gas can be used to produce directly reduced iron, meeting the urgent needs of steel mills. Most of the syngas produced by coal-to-gas furnaces is used to manufacture methanol as a substitute for petroleum. 4 Conclusions (1) Developing a large-scale circular economy for kerosene and iron is conducive to the rational utilization of coal resources, the development of petroleum substitutes, the proper use of gas, and the production of large amounts of hydrogen; this helps to save coal resources and energy, while also promoting the development of hydrogen utilization technologies. (2) Replacing coke oven gas with coal gas in the production of methanol can simplify the manufacturing process for methanol, reduce its production costs, and free up large amounts of valuable coke oven gas for use in the direct reduction of iron. (3) The technology for producing directly reduced iron using coke oven gas is mature, and the production process is short. Due to the high hydrogen content in coke oven gas, it can reduce the production costs of directly reduced iron, and will surely become a production process route for directly reduced iron that suits China’s national conditions. (4) The widespread use of direct reduced iron to replace blast furnace iron will bring about revolutionary changes in steel production. Reputable manufacturers that have compared direct reduced iron production with blast furnace iron production have found that raw material consumption can be reduced by 25%, steel output can increase by 35%, and carbon dioxide emissions can be cut by 38%. This undoubtedly plays a significant role in promoting technological innovation and independent innovation within China’s steel industry.