Current status and research trends of kerosene co-processing technology

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Current Status and Research Trends of Kerosene Co-refining Technology 1. Advantages of kerosene co-refining technology: As global oil resources tend to become heavier and of lower quality, and given China’s shortage of oil resources with coal being the main energy source, efficient conversion of such heavy and low-quality oils as well as the clean utilization of coal resources are important issues that need to be addressed urgently in the field of energy. The coal-kerosene co-processing technology alters the conventional processing modes of direct coal liquefaction and slurry-phase hydrocracking of heavy oils. It makes full use of the synergistic effects between coal and oil in hydrocracking reactions. Coal powder is uniformly dispersed into heavy oils such as low-quality oils, coal tar, naphthenic heavy oils, or petroleum residues; a single pass through the reactor suffices for the hydrocracking reaction, thereby producing light oil products and enabling efficient conversion of both coal and heavy oils. The advantages of this technology are mainly reflected in five aspects: a synergistic effect between coal and heavy oil, high raw material conversion rate, high production efficiency, high product quality, and low production costs. (1) There is a synergy between coal and heavy oil. Heavy oils generally contain relatively high amounts of heavy metals such as Ni and V, as well as heteroatoms such as N and S; these substances can easily cause catalyst poisoning and deactivation ； In the coal-hydrocarbon co-processing system, coal powder can not only adsorb heavy metals from heavy oil, but also adsorb coke particles generated during the reaction, thus serving as a coke carrier that somewhat delays the deactivation of the catalyst ； Elements such as Ni, Fe, and S can act as catalysts in the coal liquefaction process. (2) High raw material conversion rate. The conversion rates of both coal and heavy oil are greater than 90%, which is higher than those in direct coal liquefaction or the hydroprocessing of residuum in a slurry bed reactor. (3) High production efficiency. The kerosene co-processing technology is a single-pass processing method; it eliminates the need to recycle large amounts of light oil fractions as solvents in direct coal liquefaction. This allows for efficient utilization of the reactor volume, resulting in a significant increase in processing capacity. (4) High product quality. The cetane number of diesel produced via the hydrocracking of heavy oil in a suspended bed is relatively high compared to that obtained through the direct coal liquefaction process. The presence of heavy oil in the coal-kerosene co-processing system enhances the diesel yield. Therefore, the coal-kerosene co-processing technology addresses the issues of low cetane numbers and overly uniform molecular structures in diesel products derived from direct coal liquefaction. (5) Low production costs. The heavy oil in the co-refining system, after hydrogenation, serves as a hydrogen supply solvent in the coal liquefaction process, which can reduce hydrogen consumption and significantly improve the hydrogen utilization rate. The kerosene co-refining process has attracted attention from countries around the world due to its numerous technical advantages. Research on coal kerosene co-processing technologies abroad began early, with representative processes including HTI process developed by HTI in the United States, PYROSOL process developed through a collaboration between CED in Canada and GFK in Germany, and CANMET process developed by CANMET in Canada. The development in this field started late in China, but significant progress has been made in recent years; examples include the kerosene co-processing technology developed by Shaanxi Yanchang Petroleum, as well as the kerosene co-processing technology from the Coal Chemical Engineering Branch of the China Coal Research Institute. The former has already completed its industrial demonstration phase. The rapid development of these processes is expected to accelerate the industrial application of kerosene co-refining technology. 2. Typical processes for kerosene co-refining 2.1 HTI process 2.1.1 Development progress HTI Corporation began preliminary research on the HTI process in 1974, drawing on the fundamental research, engineering development, and operational experience from the H-Oil process for heavy oil hydrocracking, the H-Coal process for direct coal liquefaction, and the CCITSL process. Using high-pressure reactors, a small-scale continuous plant with a capacity of 25 kg/d, and a pilot plant with a capacity of 3 t/d, systematic studies were conducted on the compatibility among different kerosene types, their reaction characteristics, and the process conditions. Based on these findings, the engineering design for a commercial demonstration plant was carried out. Later, this process attempted to incorporate recycled plastics into the reaction system for hydrocracking; not only could this address the problem of plastic pollution, but it could also increase the yield of light oils from the reaction products, further reducing the costs associated with the kerosene cracking process. It thus holds good prospects for development. 2.1.2 Technical features: The HTI process utilizes a unique two-stage fluidized bed reactor, which enables the online loading and unloading of catalysts. This ensures high catalytic activity within the reactor and facilitates deep conversion of the feed materials. The HTI process flow is shown in Figure 1. The kerosene slurry is mixed with H2 after passing through a preheater, and then fed into a first-stage fluidized bed reactor containing a Co-Mo/Al2O3 catalyst. Hydroprocessing is carried out at a reaction temperature of 435–450°C and a hydrogen pressure of 12–18 MPa ； It then enters a second-stage fluidized bed, where hydrocracking takes place in the presence of a Ni-Mo/Al2O3 catalyst to remove heteroatoms such as S and N. Table 1 shows a comparison of the operating conditions and product yields between the HTI process and the direct coal liquefaction process. As can be seen from Table 1, the design of the two-stage series-connected fluidized bed reactors and the development of highly active catalysts enable higher degrees of conversion of coal and oil. Compared with direct coal liquefaction, the HTI process can achieve a higher liquid yield while maintaining essentially the same coal conversion rate, and it can also effectively reduce the gas yield. Table 1 Comparison of operating conditions and product yields for the HTI process and the direct coal liquefaction process 2.2 The CANMET process 2.2.1 Development progress In 1981, CANMET established a small-scale experimental unit with a capacity of 1 kg/h to initiate research on the technology of co-processing coal with kerosene; it studied the impact of process conditions on product yield and quality, and verified the economic viability of this co-processing approach ； Subsequently, a long-term operation of 50,000 hours was carried out on a 0.5 t/d pilot plant to investigate the scaling laws of the process, and feeding trials were conducted on a small-scale demonstration plant of 25 t/d. Currently, under conditions of a relatively low coal feed ratio, the CANMET process has been put into industrial use; a 250,000 t/a industrial demonstration plant has been built at the Port Talbot refinery in Canada. 2.2.2 Technical Features: The technical feature of the CANMET process is the use of FeSO4·7H2O powder as a catalyst, along with a suspension bed as the reactor, which enables low-pressure operation during the coal liquefaction process. The basic process flow of the CANMET process is shown in Figure 2. Kerosene slurry, FeSO4·7H2O powder, and H2 are fed together into the bottom of the fluidized-bed reactor, where hydrocracking takes place at a reaction temperature of 435–455°C and a reaction pressure of 13.6 MPa; the liquid yield can reach 74.3%. The use of a fluidized bed reactor not only maximizes the utilization of the reactor volume, but also ensures the uniformity and stability of the temperature within the reactor ； FeSO4·7H2O powder, used as a catalyst, exhibited the ability to promote hydrogenation conversion and delay coking under conditions of low pressure and low hydrogen consumption. This not only reduced the capital investment costs for the facility but also effectively lowered operational expenses. 2.3 The PYROSOL process
2.3.1 Development progress
Based on a summary of the technical challenges associated with previous coal liquefaction processes—such as high hydrogen consumption, high operating pressures, low coal content in the coal-oil slurry feedstock, and the significant impact of ash content in coal on the process—CED and GFK jointly developed the PYROSOL process around 1985. The PYROSOL process has demonstrated technical feasibility in autoclaves, pilot-scale units, and a 120 kg/d pilot plant; it is the most economical technology for kerosene co-processing. 2.3.2 Technical features: The PYROSOL process is a combined processing technology consisting of three stages: liquefaction of coal and heavy oil, mild hydrocracking, and hydroprocessing-delayed coking. Its basic process flow is shown in Figure 3. The ash-removed coal powder is thoroughly mixed with heavy oil and disposable Fe catalysts, passed sequentially through two series-connected direct-contact preheaters, and then subjected to a mild hydrocracking reaction at a reaction temperature of 380–420°C and a reaction pressure of 8–10 MPa. Approximately 65% of the heavy fractions of the reaction products (unconverted coal or heavy oil, Fe catalysts that can be discarded, ash, etc.) undergo further hydrodesulfurization delayed coking reactions under conditions of a reaction temperature of 480–520°C and a reaction pressure of 8–10 MPa. The design of the ash removal unit and the three-stage combined processing unit enhances the adaptability of the PYROSOL process to various feedstocks, while significantly reducing hydrogen consumption to approximately 1% of the reaction feedstock. 2.4 The Co-processing Technology of Petroleum Kerosene from Yanchang Petroleum 2.4.1 Development Progress In April 2011, Yanchang Petroleum introduced advanced foreign suspended-bed hydrocracking technology. By drawing on the characteristics of both single-coal direct liquefaction technology and heavy oil suspended-bed hydrocracking technology, it began research and development on kerosene co-processing technology. It has since built a pilot plant with a capacity of 150 kg/day as well as an industrial demonstration plant with an annual capacity of 450,000 tons. Pilot-scale experiments showed that using FCC slurry and Xiwan coal as raw materials, at a reaction temperature of 468°C, a reaction pressure of 22 MPa, and a coal mass fraction of 45%, the coal conversion rate was greater than 94%, the conversion rate of heavy oil (>525°C) was greater than 90%, the conversion rate of asphaltenes was nearly 90%, and the total liquid yield reached over 70%. The industrial demonstration plant successfully completed the entire production process in January 2015, producing qualified products; it is currently in the stage of process optimization and operational refinement. This technology combines heavy oil processing techniques with modern coal chemical engineering techniques, opening up a new pathway for the petrochemical and coal chemical industries and promoting the development of energy chemical technologies; it holds great potential for industrial application. 2.4.2 Technical Features The basic process flow of the extended petroleum kerosene co-refining process is shown in Figure 4. This process uses medium- and low-rank coal along with heavy oil as raw materials, and employs an online integrated technology of suspended-bed hydrocracking and fixed-bed hydroisomerization; the suspended-bed processing stage makes use of an efficient Fe-based catalyst-additive system. The kerosene slurry and fresh H2 pass through preheating systems respectively before entering a series of plug-flow suspended-bed reactors, where they undergo hydrocracking at a reaction temperature of 450–470°C and a reaction pressure of 18–22 MPa. The light products are separated using a high-temperature and high-pressure separator before being fed directly into a fixed-bed reactor for hydroprocessing. Highly efficient Fe-based catalyst-additive systems can provide more activated hydrogen; the additives can act as a carbon carrier in the reaction, effectively delaying coking and tar formation in the reactor and separation systems, thereby achieving high conversion rates for coal with high inert content and heavy oils. 2.5 Other processes: Although the development of some kerosene co-refining processes has been suspended or terminated, understanding the development process or technical characteristics of these processes is beneficial for carrying out further research and development efforts, thereby advancing the industrial application of kerosene co-refining technology. In 1979, Chevron proposed the Chevron two-stage kerosene co-processing technology. The greatest feature of this process is that it relies solely on the metal-active components contained in the kerosene slurry, without the need for any external catalysts. The hydrocracking reaction takes place in a single-stage suspension bed reactor at a reaction temperature of 425–480°C and a reaction pressure of 10–20 MPa. After water, gases, and light oil fractions are removed from the reaction products, they enter the second reactor (a fixed-bed or fluidized-bed reactor), where further hydrocracking reactions take place at a reaction temperature of 350–400°C. Based on the technology of direct coal liquefaction, the Coal Chemical Engineering Branch of the China Coal Research Institute developed in 2007 a co-processing technique for coal and oil, which mainly consists of a coal hydrogenation liquefaction process and a hydrogenation upgrading process for liquid oils. In the coal hydrogenation liquefaction process, dispersed bimetallic or multimetallic catalysts are used, while in the hydrogenation upgrading process for liquid oils, supported catalysts of the Ni-Mo, Ni-Co, or Ni-W series are employed; the hydrogenation upgrading is carried out at reaction temperatures of 330–390°C and reaction pressures of 10–15 MPa. Compared with direct coal liquefaction technology, this method can increase the coal conversion rate by 1%–5%, and raise the yield of light and medium-quality oils in the reaction products by more than 5%. ARC Company has successfully developed a two-stage kerosene co-reaction process using Co/H2O (steam) – H2, which expands the options available for hydrogen sources. The kerosene slurry is first solvated in a Co/H2O (steam) atmosphere, and then undergoes catalytic hydrogenation in a second-stage reactor [16]. Experimental results from the 48 kg/d pilot plant show that using Co/H2O (steam) in place of H2 enables the reduction of operational costs while increasing the coal conversion rate and the quality of the liquid product.