Current Development Status of Coal-to-Oil Technology

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This post was last edited by liaifeng on 2018-9-10 at 20:23. The current status of developments in coal-to-oil technology: As international oil prices continue to reach record highs (hovering above $130), this has further spurred the rapid development of projects aimed at replacing oil on a global scale. However, traditional coal-to-oil production raises many concerns, as it requires 3 to 4 tons of coal to produce 1 ton of oil, resulting in an energy efficiency of only 50%, and it needs 9 to 15 tons of water. However, with the advancement of science and technology, it is possible to solve this problem that has plagued people by combining various processes and adopting new approaches. 1. Introduction to coal-to-oil technology: Coal liquefaction is divided into indirect liquefaction and direct liquefaction. Direct coal liquefaction requires higher quality coal than indirect liquefaction, but it has a simpler process, higher thermal efficiency, and a higher yield of liquid products ； Coal indirect liquefaction has less stringent requirements regarding coal quality compared to direct liquefaction, but it involves a longer process, and its thermal efficiency and liquid yield are lower than those of direct liquefaction. 1.1 Indirect liquefaction method: Coal indirect liquefaction involves first gasifying coal to produce syngas (CO + H2), which is then converted into organic hydrocarbons through catalytic synthesis (such as F-T synthesis). Coal types are highly adaptable for indirect coal liquefaction, and the operating conditions during this process are mild; a typical synthetic process for indirect coal liquefaction is carried out at 250°C and 15–40 atmospheres of pressure. Furthermore, the relevant synthesis technologies can also be used for the conversion of natural gas and other carbon-containing organic compounds, yielding synthetic products of high quality with low pollution. The coal indirect liquefaction oil synthesis technology has been widely industrialized abroad. Leveraging its abundant coal resources, South Africa has built synthetic oil plants that consume nearly 42 million tons of coal per year, producing around 5 million tons of synthetic oils and 2 million tons of chemicals. In terms of technology, South Africa’s SASOL company has gone through four stages: fixed-bed technology (1950–1980), circulating fluidized bed (1970–1990), fixed-fluidized bed (1990–), and slurry bed (1993–). 1.2 Direct liquefaction method: Direct liquefaction is the process of converting coal directly into liquid fuel through high-pressure hydrogenation. In 1913, German chemist Bunge was the first to study the high-pressure hydrogenation of coal, obtaining the world’s first patent for coal liquefaction. By 1944, the oil production capacity of Germany’s direct coal liquefaction plants had reached 4.23 million tons per year, supplying two-thirds of Germany’s aviation fuel and 50% of the fuel needed for cars and armored vehicles during World War II. The discovery of large quantities of cheap oil in the Middle East starting in the 1950s made direct coal liquefaction temporarily less competitive, while the world oil crisis of the 1970s further hindered the development of coal liquefaction technology. The representative coal direct liquefaction processes in the world are Germany’s IGOR process, the U.S.’s HTI process, and Japan’s NEDOL process. The common feature of these new liquefaction processes is that the reaction conditions for coal liquefaction are much milder than those in traditional liquefaction processes, resulting in reduced production costs; intermediate scale-up tests have already been completed. . 2. Comparison of the economic viability of coal-to-oil conversion and existing issues 2.1 Comparison of economic viability of coal-to-oil conversion Table 1 shows a technical and economic comparison between direct and indirect liquefaction methods using Shenhua coal. As can be seen from the table, the cost per ton of oil produced by the direct method is 1,400 yuan, while it is 1,600 yuan for the indirect method. 5 to 6 tons of water are required per ton of oil produced, compared to 9 to 12 tons in the indirect method. The direct method allows 2.4 tons of coal to be used to produce 1 ton of oil, whereas the indirect method requires 4.4 tons of coal. When coal is converted into oil using the direct liquefaction method, the utilization rate of its thermal energy is 47.6%, whereas it is only 28.6% under the indirect liquefaction method; in other words, most of the thermal energy is consumed during the process of converting coal into oil. It is precisely because coal-to-oil production requires a large amount of water and results in huge energy waste that it is **difficult for us to make the decision to invest on a large scale in such an industry. Since the direct method has high requirements for coal quality and necessitates coal of better quality, its application is limited by the available raw materials. 2.2 Problems in coal-to-oil production The main challenge facing coal liquefaction projects in the future is how to reduce water consumption and ensure sustainable environmental development. Next is addressing the issue of carbon dioxide emissions. The production process of coal-to-oil generates large amounts of carbon dioxide; 7 to 8 tons of carbon dioxide are emitted for every ton of oil produced. As a partner of Shenhua, the South African company Sasol has also only made some attempts in the areas of water conservation and carbon dioxide emissions reduction. Before 2012, developing countries such as China **might make commitments to reduce carbon dioxide emissions, which would have a direct impact on coal liquefaction projects like those of Shenhua and Yankuang. However, we should view the pollution issues associated with coal-to-oil projects in a fair and objective manner; in terms of air pollution, power plants are far more problematic than coal liquefaction projects ； In terms of water consumption, both fertilizer production projects and coal-to-methanol processes consume more water than coal-to-oil processes. Therefore, it seems unfounded to blame coal-to-oil production for high water consumption; the key issue is that the locations where such projects are built do not allow for an adequate balance between coal and water resources. 3. Introduction to current coal-to-oil technologies: Given the numerous problems associated with previous coal-to-oil methods, many private and foreign-funded research institutions claim to have developed new coal-to-oil technologies. 3.1 Introduction to the New Process of Shaanxi Jinchao Investment Company 3.1.1 Technical Features Shaanxi Jinchao Investment Company in China has collaborated with the Center for Materials and Process Synthesis at the University of Golden Mountain in South Africa to develop a new technology for converting coal into oil suitable for use in China. The innovative approach of this technology lies in the use of new chemical methods to improve energy efficiency. The new chemical method combines traditional raw materials such as coal and natural gas (or gas waste from coal mines), allowing the hydrogen-to-carbon ratio to be adjusted; it also eliminates the recycling steps in the synthesis process. The current mature synthesis process is: coal + water + oxygen → synthesis gas is produced → hydrocarbons + carbon dioxide are formed. In this process, carbon dioxide is an exhaust gas that not only reduces the efficiency of converting coal into hydrocarbons but also pollutes the atmospheric environment. At the same time, the increase in carbon dioxide emissions requires more coal to produce each ton of hydrocarbons, raising operating costs. The new method simplifies the process flow, reducing technical risks and operating costs. Currently, the technological upgrades carried out by industry leaders in coal-to-oil conversion focus on the reactors used in the synthesis process; however, the cost of these reactors accounts for no more than 10% of the total investment required for the entire enterprise, while innovations in new process flows can save 15% to 30% in investment costs. In fact, the company combines mature natural gas-to-oil technology with coal-to-oil technology, making full use of the high hydrogen-to-carbon ratio in natural gas to compensate for the lack of hydrogen in coal, thereby significantly reducing the amount of water required for hydrogen production in conventional coal liquefaction processes. From the perspective of technological innovation, this approach falls under the category of combined processes. 3.1.2 Technical analysis: By contacting the company, it was initially learned that it is conducting pilot tests in Baoji. Since we were unable to contact the relevant technicians, we will analyze its water-saving performance from a theoretical perspective for now. Assuming that coal is composed entirely of carbon, about 0.17 tons of hydrogen are required to produce 1 ton of coal oil; this hydrogen is supplied by natural gas. Assuming that natural gas is composed entirely of methane, 1.4 tons of natural gas are needed. That is, through rough theoretical calculations, coal can be liquefied using a ratio of natural gas to coal of 1.4:1. Of course, these are just analyses from a chemical perspective; in reality, the weight ratio of natural gas to coal is likely to be much greater than 1.4. 4 As can be seen from the above theoretical analysis, it is actually more appropriate to refer to this technology as natural gas liquefaction; its technical feature lies in the significant reduction of production costs achieved by adding coal. Our country is poor in natural gas**, so it is not very practical for us to develop natural gas liquefaction. To produce 3 million tons (**the maximum output for coal-to-oil as specified by the Regulatory Commission), 1.75 million tons of natural gas would be required. The fact that some people in our country are suggesting the use of gasification to produce natural gas further illustrates that there are many questions surrounding the application of this technology. Furthermore, building a production facility for 3 million tons per year of petroleum products under this process is estimated to require an investment of up to 26 billion yuan. 3.2 Hefeng Group Co., Ltd.’s liquefaction technology – Hefeng Group has developed a liquefaction technology for lignite. It claims that no water is required throughout the entire production process (traditional coal-to-oil production technologies use hydrogenation processes, which require more than 10 tons of water per ton of oil produced); in this technology, water is used only for the cooling system and is not wasted ； The production equipment uses conventional petrochemical equipment, featuring small size, low land occupation, low investment, short construction period, and rapid results. However, since only lignite can be used as a raw material, and China’s production of lignite is low, it is not suitable for wide-scale adoption. At present, the low-temperature pyrolysis project for lignite with an annual production capacity of 5 million tons, which is to be built by Hulunbuir Dongneng Chemical Co., Ltd., is planned to require a total investment of 925.87 million yuan. The project will process 5 million tons of lignite per year, producing 2 million tons of semi-coke, 300,000 tons of tar, 12,500 tons of crude benzene, and 550 million cubic meters of gas. Once the project is put into operation, its output value can reach 1.4 billion yuan. It can be seen that the technical level of its liquefaction technology is average. 3.3 Shaanxi Yulin Shenmu Jinjie Tianyuan Chemical Co., Ltd. This company makes use of the local coal tar resources and employs an upright furnace distillation process to produce semi-coke, coal tar, and coke oven gas. Hydrogen is generated from coke oven gas, and then, through two-stage hydrogenation and tail oil cracking techniques, coal tar and hydrogen are subjected to hydrogenation reactions in the presence of catalysts. As a result, fuels such as diesel, naphtha, and liquefied gas are obtained, thereby achieving integrated production of coal, coke, and oil and increasing the added value of coal tar. At the same time, the waste gas generated during the production process can be recycled, and there is zero discharge of industrial wastewater, thereby completely eliminating the pollution problems associated with traditional coal tar processing. Coal tar is an oily liquid formed during the coking process, composed of more than 500 types of aromatic hydrocarbons; it has not yet been fully utilized in industry. It is reported that the two-stage hydrogenation tail oil cracking technology used by Shenmu Jinjie Tianyuan Chemical Co., Ltd. is the first of its kind in China, with a conversion rate of 93% for coal tar – meaning that 1 ton of coal tar can produce 930 kilograms of refined oil. At present, the 250,000 tons per year medium-temperature coal tar lightening plant is under commissioning, producing over 200 tons of fuel diesel and naphtha per day, and will soon reach full production capacity. Although many industry experts believe that the commissioning of the medium-temperature coal tar lightening project, which can be regarded as a \"Yulin version of coal-to-oil production,\" opens up new avenues for the deep processing of coal and coal tar and for extending the coal chemical industry chain, thereby holding great significance for the development of alternative oil resources in China, we believe that this is merely a post-treatment process for coal tar and cannot be linked to the liquefaction of coal; at best, it can be classified as part of the coal chemical industry. 3.4 Aqueous-phase Fischer-Tropsch reaction: Focusing on low-temperature and aqueous-phase research, a research group from the School of Chemistry and Molecular Engineering at Peking University started with Fischer-Tropsch reactions in ionic liquids, and in 2005 developed ultra-long-lasting nanocatalysts for Fischer-Tropsch reactions that remained active at 150°C. Later, the research group came up with a completely new idea of conducting the reaction in an aqueous medium, and succeeded two years later. The new approach proposed by this research achievement offers a new direction for the future industrial development of Fischer-Tropsch synthesis. As a key technology for the major industrial process of coal-to-oil via indirect liquefaction, once the new Fischer-Tropsch synthesis technology is scaled up for industrial use, it is entirely possible that it will replace the entire existing industrial Fischer-Tropsch synthesis system. However, although this achievement has attracted attention worldwide, it will still take a long time before it can be put into practical use. 4. Conclusion As mineral resources become increasingly scarce, the search for alternative energy sources will show a rapid growth trend. We also believe that humanity will surely be able to find alternative forms of energy. In terms of the source of energy, it all comes from solar energy; the various materials we use today are merely carriers of that energy. If we had advanced fast charging technologies for storing electricity, as well as hydrogen storage technologies, we might not need to look for new energy sources anymore. But we are even more convinced that through technological progress, we will surely be able to find a new energy technology suitable for our era.