Comparison of coal-to-syngas technologies

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Author/Source: Chen Ying1, Ren Zhaoyuan2 (1. Yankuang Lunan Fertilizer Factory, Tengzhou, Shandong 277527)； 2. Coal slurry gasification and coal chemical industry **engineering research. Date: 2009-1-13. Texaco’s coal slurry gasification technology, Shell’s pressurized coal gasification technology, and GSP gasification technology are all typical clean coal gasification methods, each with its own characteristics. Companies should make a reasonable choice when upgrading or building new facilities, taking into account factors such as the type of coal, ash melting point, scale of the installation, product portfolio, and investment requirements. The following provides an analysis and evaluation of the aforementioned gasification technologies, as well as their selection and application, for your reference. 1 Shell gas-flow bed pressurized pulverized coal gasification: There are no successful examples of this process being used in fertilizer production abroad. Sinopec Baling Branch was the first company to introduce this technology for the production of fertilizer raw materials. To date, 18 companies in the country have introduced this technology (device). However, this process adopts the waste boiler route; since the synthetic feed gas contains little steam, only 14% at 3.0 MPa ； Therefore, a large amount of steam must be added in the subsequent shift process for the production of synthetic ammonia, and some steam is also required in the shift process for methanol production. This results in a complex process as well as inefficient use of energy within the system. Hubei Shuanghuan Technology Co., Ltd. was the first manufacturer to go into official operation, starting trial runs in May 2006. It has been reported that during the testing phase, issues such as leaks in the water wall at the burner location occurred, problems with the coal transfer system led to an imbalance in the oxygen-to-coal ratio and excessive furnace temperature, severe corrosion of the water wall tubes at the slag outlet, blockages inside the coolant pipes, and damage to the burner protection shields arose. Projects that introduce this technology require large investment. In May 2006, Guizhou Tianfu signed a contract with Shell; the scale of the gasification unit was 170,500 m3 of CO+H2 per hour, with an investment of 970 million RMB, which is 1.8 times the investment required for a gasification unit of similar scale using water-coal slurry. The gasification unit has a complex equipment structure and a long manufacturing cycle. The gasifier, conduits, and internal components of the waste boiler are manufactured in Spain and India; the production cycle is 14–18 months, with a shipping time of 3 months ； The pressure shell can be manufactured domestically, but the materials still need to be imported, and the production cycle is also long ； The degree of localization of equipment, instruments, and materials lags far behind that of water-coal slurry gasification. A long construction period (3–5 years) will result in a longer repayment cycle for the enterprise, increasing its financial burden. Among Sinopec’s Baling Branch, Hubei Shuanghuan, and Liuzhou Chemical Co., Ltd., which signed contracts with Shell in 2001, only Shuanghuan carried out trial operations in May 2006 ； Among Sinopec Hubei Fertilizer Branch, Sinopec Anqing Branch, Yuntianhua Group Company, and Yunwei Group Zhanhua Branch, which signed contracts with Shell in 2003, only Anqing began operating its boilers in October 2006. The author believes that the Shell gasification unit lacks the support of mature applications in chemical production, and it will take a considerable amount of time to master it. Before the introduction of the 300 kt/a ammonia synthesis plant at Shaanxi Weihua Group, although Lunan Fertilizer Plant already had experience using Texaco gasifiers in China, it still took 5 years, from the time of completion and commissioning in 1996 to 2000, to reach the designed capacity of 300 kt/a. Therefore, it is estimated that the process of digesting, absorbing, and reaching full capacity for Shell’s gasification technology will also be lengthy, and it will not take less time than it did for Texaco’s gasification technology back then. It is evident that blindly following this trend to introduce such technologies is equivalent to paying a high price to conduct large-scale demonstrations of their industrial application by Shell, which carries significant risks. 2. GSP gas flow bed pressurized coal gasification: Since 2005, three companies – Ningxia Coal Industry Group Company, Anhui Huaihua Group Company, and Jiangsu Linggu Chemical Co., Ltd. – have signed contracts with German Future Energy to adopt the GSP gasification technology. The key technical parameters of this technology are roughly on the same level as those of Shell gasification, while its investment cost lies between that of Shell gasification and coal-water slurry gasification. The main difference is that Shell features multiple nozzles arranged opposite each other on the side walls, using a synthesis gas upward-flow waste heat boiler configuration ； GSP, on the other hand, is a single-nozzle top spray system that uses a syngas downward quenching process. Since GSP employs a quenching process, which is more suitable for chemical production, it is favored and recommended by many experts. This technology is similar to Shell’s technology; there are no successful examples of its application in powder coal gasification, which means it carries significant risks. Whoever introduces it first will be responsible for carrying out industrial demonstrations for GSP. For various reasons, the GSP introduction contracts signed by Huaihua, Linggu, and Future Energy have been suspended, and they have turned to seeking water-coal slurry gasification technology. Therefore, more caution is needed when choosing this technology. 3 Coal-water slurry gasification technology 3.1 Texaco coal-water slurry gasification technology The Texaco gasifier uses coal-water slurry with a concentration of 60% as raw material, features top injection at a single nozzle, a hot wall made of refractory bricks, and a quenching process. When this technology was introduced to China in the late 1980s, four industrial plants were already in operation internationally, including those for cold-water IGCC power generation in the United States, the Isman CO carbonylation plant, and the Ube ammonia synthesis plant in Japan. At the end of the 1980s, Lunan Fertilizer Plant introduced Texaco water-coal slurry gasification technology for the first time to produce synthetic ammonia. The project was meticulously designed by the First Institute of the former Ministry of Chemical Industry; the degree of localization reached over 90%. Testing began in 1993, and by 1995 the annual production volume exceeded the design target. The load was then increased rapidly to over 130% and maintained at that level, with a single furnace being able to operate continuously for more than 130 days at a time, achieving an annual operation rate of 90%. During the first 6 years after commissioning, the average operating time was 326.8 days (327 days on average in Ube, Japan), and it once achieved a record of operating two reactors without any backup units, with each reactor having an average annual operating time of 306 days. In 1995, it was awarded the **First Prize for Scientific and Technological Progress**, as an acknowledgment of the outstanding achievements in China regarding the adaptation, improvement, and localization of technologies in Texaco gasification plant design and equipment, as well as in operational management. The successful demonstration at Lunan Fertilizer Plant facilitated the further adoption of Texaco’s water-coal slurry gasification technology in China, marking the beginning of clean coal gasification in the country. Currently, there are 24 operating units in China that use this technology, and 10 units under construction. 3.2 New type of opposed-four-nozzle gasification furnace. The development of this type of water-coal slurry gasification furnace was a key research project during the “Ninth Five-Year Plan” period; pilot studies were carried out jointly by Yankuang Lunan Fertilizer Factory and East China University of Science and Technology, resulting in multiple invention patents. After evaluation, assessment, and acceptance by relevant authorities, it was deemed to fill a gap in domestic technology and represent an international leader in this field. “It enters the industrial demonstration phase during the 15th plan period. The 3 furnaces built by Hualu Hengsheng and Yankuang Guotai are now in normal industrial operation, with 7 furnaces under construction at present. 3.2.1 Operation status of Hualu Hengsheng’s gasification unit: The gasification section of Hualu Hengsheng’s domestic large-scale nitrogen fertilizer production project is equipped with 3 water-coal slurry gasifiers, all with a capacity of 750 t/d and a pressure of 6.5 MPa; two of them are in operation while one serves as a backup. One of these gasifiers is a new type of opposite-nozzle gasifier, which was successfully put into operation on December 1, 2004, with full-scale operation commencing on June 2, 2005. By July 2006, the four-nozzle gasification unit had accumulated over 5,800 hours of operation, corresponding to an annual operation rate of 67.85%, which was higher than the average operation rate of the other two furnaces; the longest operation time for a single furnace was 1,380 hours. In March 2006, an on-site assessment was conducted by ** on the domestic production project for large-scale nitrogen fertilizers; the carbon conversion rate of the gasification unit was 99.9%, the content of useful gas components was above 84%, and the carbon content in the slag was less than 5%. This gasification unit generates an additional profit of 50,000 yuan per day compared to a Texaco water-coal slurry gasification unit of the same scale. Hualu Hengsheng’s domestic production project for large-scale nitrogen fertilizers won the Special Prize for Scientific and Technological Progress in the chemical industry in 2006. 3.2.2 Operation status of the Yankuang Guotai gasification unit: Yankuang Guotai, in collaboration with East China University of Science and Technology, undertook the “10th Five-Year Plan” **“863” project – an industrial facility for multi-nozzle opposed water-coal slurry gasification technology along with related infrastructure. This facility uses two 1,150 t/d gasification reactors with a pressure of 4.0 MPa; it is capable of producing 240 kt/year of methanol and 71,800 kW of power, which supplies the 200 kt/year acetic acid production plant. The gasifier achieved successful commissioning on July 2, 2005, and began operations officially on October 16; the maximum continuous operating time for a single unit exceeded 1,650 hours. As of November 15, 2006, the operation rate was 96%, with 230 kt of methanol and 170 kt of acetic acid produced in that year. On December 11, 2005, this project passed the on-site assessment by experts from the “863” project, which is part of the major initiatives under the 10th Five-Year Plan’s **High-Tech Research and Development Program” focused on the development of new water-coal slurry gasification technologies, for its industrial demonstration plant with a capacity of one thousand tons. 3.2.3 Comparison of Key Parameters with Texaco Gasification Technology The comparison of key parameters between the domestic four-nozzle gasification technology and Texaco gasification technology is shown in Table 1. http://www.nmtech.com.cn/jishuwang/upload1/070913901222737.jpg Based on the analysis of Table 1: ① LuHua Texaco, Guotai Four-Nozzle, and LuHua Pulverized Coal pilot projects all used Beisu washed coal, allowing for good comparability; the key technical parameters of Guotai Four-Nozzle lie between those of Texaco’s water-coal slurry gasification and pulverized coal gasification, showing significant improvements over Texaco’s method ； ②Both Hualu Hengsheng’s Texaco furnace and its four-nozzle furnace use the same type of coal – Shenfu coal slurry; the trends in the comparison results are similar, and even more pronounced ； ③Hualu Hengsheng Texaco, Shanghai Coking Texaco, and Weihe Texaco use the same or similar types of coal, and their main gasification parameters are at a similar level, indicating that the coal slurry gasification technology is highly mature and well mastered by these plants. Compared with foreign coal-water slurry gasification technologies, the technical features and advantages of the four-nozzle coal-water slurry gasification unit are mainly as follows. ①A comparison of the operational data from the Guotai four-nozzle gasification furnace and the Luhua Texaco furnace shows that the content of useful gas components increased by 2%–3%, CO2 content decreased by 2%–3%, the carbon conversion rate increased by 2%–3%, specific oxygen consumption was reduced by 7.9%, and specific coal consumption was reduced by 2%. 2%. ②The gasifier has a wide adjustable load range and strong adaptability, which facilitates the scaling up of the plant. ③The liquid level of the washing and cooling fluid in the composite bed remains stable, effectively preventing fluctuations in the liquid level in the quenching chamber of the Texaco furnace, as well as issues related to water and ash contamination ； The temperature ratio of the crude syngas to the black water is 10°C lower than that of Texaco, indicating good heat and mass transfer performance. ④The staged synthesis gas preliminary purification is energy-efficient, highly efficient, features low pressure drop, and provides good separation performance. ⑤Direct heat exchange with slag water is superior to Texaco indirect heat exchange; the temperature difference between the exhaust gas from the evaporative hot water tower and the temperature of the ash water is only 4°C. This approach overcomes the problem of scaling and blockage that often occurs in indirect heat exchange equipment, and it also improves the heat exchange efficiency (the maximum temperature difference between the two phases in a Texaco flash vapor condenser is 60°C) ； ⑥The technology transfer fee is only about 1/3 of that of Texaco. 3.2.4 Comparison with Texaco gasification island investments: A comparison is made based on Tianchen Company’s estimates for the investments in Jinling and Guotai gasification islands (see Table 2); the Jinling Texaco gasifiers consist of 3 units, with a daily coal consumption of 1,200 tons and a pressure of 4.0 MPa ； Two Guotai four-nozzle gasification furnaces, with a daily coal consumption of 1,150 tons and a pressure of 4.0 MPa. http://www.nmtech.com.cn/jishuwang/upload1/070913901565093.jpg A comparison shows that, with roughly the same gas production capacity, and excluding software costs, a single four-nozzle furnace requires an additional investment of 7 to 10 million yuan. The software licensing fee for Nissan’s 3.6 million m3/h gasifier of the Texaco type (operated in a 2+1 configuration) is 46 million yuan; the cost of software and services amounts to 8 million yuan, resulting in a total of 54 million yuan, which translates to 18 million yuan per unit. The software cost for four nozzles is 1/3 of that for a Texaco gasifier, amounting to 6 million yuan per unit. When comparing the total investment of the two types of furnaces, the four-nozzle gasification furnace costs 2–5 million yuan less per unit than the Texaco gasification furnace. 3.2.5 Comparison with Texaco gasifier maintenance costs During the normal industrial operation phase of the gasifiers, based on the experience with the Luhua Texaco gasifier, the annual maintenance costs of the two types of gasifiers are compared in Table 3 (comparison of key items). It can be seen that the annual maintenance cost for the four-nozzle gasification system is slightly higher than that of the Texaco gasification system. 3.2.6 Lifespan of the arch bricks in the four-nozzle gasifier After the four-nozzle gasifier was put into demonstration operation, the problems encountered were basically the same as those faced during the initial operation of the Texaco furnace at Luhua; experience and existing regulations were available to guide handling. The only new issue was the short lifespan and rapid erosion of the arch bricks. The four-nozzle furnace at Hualu Hengsheng was in operation until January 2006 when the arch bricks were replaced, having accumulated a total operating time of 3,200 hours. Another reason for the early replacement was to stagger the brick replacement times with those of the other 2 Texaco furnaces. The Guotai B# gasifier has been in operation for 1,178 hours (49 days and 2 hours); it was replaced due to excessive temperature at the dome head and severe brick erosion ； The A# gasifier also had its dome bricks replaced after more than 700 hours of operation. By analyzing and comparing the design and operational data of the pilot plant for coal gasification using Luhua powder, Hualu Hengsheng, and Guotai’s three facilities (see Table 4) ； Conduct laboratory cold testing and hot testing ； Axial velocity distribution in the upper space of the test furnace, the time it takes for the four flow streams to reach the top after colliding, and the height to which the flame rises, etc ； By comparing some data with those of the Texaco furnace, it is believed that the rapid erosion of the arch bricks in the Guotai four-nozzle gasification furnace is mainly caused by the small height-to-diameter ratio in the upper part of the furnace, the high initial oxygen velocity from the nozzles, the impact of upward flow streams, and the effects of high temperatures. Through extensive analysis, comparison, and experimental studies, it is concluded that the initial oxygen velocity at the nozzle should be controlled at around 100 m/s, and the upper space should be extended by 1,300 mm, so as to adjust the height-to-diameter ratio in the upper part of the furnace from the original 1.04 to ≥1.61. The total thickness of the heat-exposed brick lining on the cylinder wall of the Guotai four-nozzle gasification furnace is 235 mm. After operating for over 6,000 hours, the erosion depth at the most severely affected areas is only 50–60 mm. With 80% of the lining remaining to be replaced, the furnace’s service life can reach 16,000 hours (667 days) ； The condition of its cone bottom bricks is also far superior to that of the Texaco furnace’s cone bottom, with a service life of over 10,000 hours. 3.2.7 Other issues (1) Issues regarding the furnace diameter and length of four-nozzle furnaces: The nozzles, furnace diameter, and furnace length of any gasification furnace are all designed to match the intended operating load. Within a certain range of production loads, the flow field and temperature field in the area where the counterflow streams meet must be in an ideally suitable state relative to the furnace’s geometry, in order to achieve optimal gasification efficiency and a satisfactory service life for the refractory bricks. The residence times in the gasification chamber of the four-nozzle furnace and the Texaco furnace are 8 s and 3–5 s, respectively, while their particle residence time distributions are 0.2–3 s and 0–3 s, respectively. The residence time in the Texaco furnace is too short, and there is short-circuiting of particles, so the gasification efficiency is affected to some extent ； The GSP furnace has this problem too. GE has now adjusted the furnace diameter and height of Texaco gasifiers, such as the φ3.2m/φ3.8m furnace models in recent years. (2) Requirements for the manufacture and assembly of nozzles and issues related to furnace wall tiles: The requirements for the design, manufacture, and installation of nozzles in a four-nozzle furnace are identical to those of the Texaco gasification furnace. Problems that occurred during the initial commissioning of the four-nozzle gasification furnace, such as damage to the burner tips and the refractory bricks in the burner chamber, were mainly due to excessive installation errors in the three-channel gaps of the burners; in some areas, the inner and outer nozzles came too close together, resulting in a crescent-shaped gap and severe uneven flame distribution. However, experiments have shown that as long as the deviation in the overall installation of the four nozzles is less than 4°, it has no effect on the tiles opposite to them. 4 Conclusion Through analysis and comparison, as well as the demonstration operation of the four-nozzle furnace, we have gained full confidence in furnace types developed independently in China with complete independent intellectual property rights. It is believed that the four-nozzle gasifier is a mature type of furnace, possessing internationally leading technology in the field of water-coal slurry gasification. Comparing several types of furnaces, the four-nozzle gasification furnace is more suitable for coal chemical production; therefore, the author highly recommends this type of furnace.