Features and Applications of Ende Powder Gasification Technology

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Features and Applications of Ende Powder Gasification Technology Author/Source: Zhou Yongshun (Anshan Coking Refractory Materials Design and Research Institute, Anshan 114002, Liaoning) Date: 2002-3-16 -------------------------------------------------------------------------------- 1 Current Status of Powder Gasification Technology in China At present, most small and medium-sized fertilizer plants in China still use fixed-bed, atmospheric-pressure, intermittent gasification furnaces for gas production; this technology is relatively outdated, and the exhaust gases it produces pollute the environment. Most of the raw materials used for gas production are anthracite coal from Jincheng, Shanxi, with a small amount coming from anthracite coal in regions such as Ningxia and Guizhou; coke is also used in some cases. Coal types other than smokeless lump coal are widely distributed in China, but currently very few of these coal types are used to produce synthetic ammonia. The high price of smokeless lump coal is an important factor restricting the production costs of small and medium-sized nitrogen fertilizers in our country. How can this situation be changed? One approach is to introduce advanced foreign coal gasification technologies, such as Texaco water-coal slurry gasification, Shell pulverized coal gasification, and Lurgi pressurized coal gasification. The common feature of these three gasification technologies is the use of pressurized gasification with pure oxygen, large production capacity per furnace, and advanced technology. However, the investment is high, and significant requirements are placed on the scale of the facility; the minimum scale is an annual production of 200 kt of synthetic ammonia, with typical annual production amounts exceeding 300 kt of ammonia. Due to the high investment costs associated with introducing gasification equipment, it is difficult to achieve this solely through the efforts of the company itself without **financial support. The coal gasification technologies available in China include the solid heat carrier method developed by Dalian University of Technology for processing lignite ； The coke-carried heat gas generation process developed by Tsinghua University ； Gas production using a gray carrier circulating fluidized bed developed by Beijing Lantian Xinyuan Technology Co., Ltd ； The fluidized-bed water-gas furnace gasification technology promoted by Zhengzhou Yongtai Energy New Equipment Company, as well as the ash-polymerized fluidized-bed gasification furnace developed by the Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences, and so on. Our institute has been involved in experimental research on some of these technologies, as well as in their engineering design. Overall, most of these pulverized coal gasification technologies are still at the stage of industrial or semi-industrial testing, or at a small-scale pilot project level. Even those technologies that have been incorporated into engineering designs and put into operation either operate on a small scale or have been in use for only a short period of time. For example, the fluidized-bed water gasifier gasification technology has been put into operation in Zhengzhou and Nanyang, but the maximum production capacity of a single gasifier is 1,000–1,700 m3/h; therefore, multiple gasifiers need to be installed for the renovation of fertilizer plants. Moreover, this technology is currently used in urban gas production, and there is still a lack of experience in its successful application in ammonia synthesis plants. Although the gray pyrolytic fluidized bed gasification technology has been used by Shaanxi Chenghua Co., Ltd. to upgrade the feedstock route for 80 kt/a ammonia synthesis, it is still in the stage of small-scale industrial demonstration from a technical perspective, and lacks experience in large-scale industrial application and long-term operation. Our country already has a foundation for developing powder gasification, but the infrastructure for scaling up and implementing it on an industrial scale is weak, which means it will take some time. 2 Characteristics of the Ender powder gasification technology: In the early 1950s, North Korea introduced two Winkler gasifiers with a capacity of 10,000 m3/h from the Soviet Union. Through years of practical exploration and numerous modifications to the original Wenkler gasifier, a practical powder coal gasification technology with its own characteristics was developed, namely the Ende powder coal gasification technology. Compared to traditional Winkler gasifiers, it features three major improvements. One approach is to transform the bottom of the furnace into a cone of a specific shape, eliminating the existing grate and replacing it with air distribution nozzles in order to address issues such as slag formation at the furnace bottom and uneven heating, thereby increasing the production capacity of each furnace ； The second is to add a cyclone dust removal return device at the outlet of the generating furnace in order to reduce the carbon content in the carried-out material ； Thirdly, it involves changing the layout of the waste heat boiler to reduce wear on the boiler tubes and extend its operational life. Years of practical production experience have shown that the Ende powder gasification technology possesses the following characteristics. (1) High production capacity: The maximum gas output per furnace can exceed 40,000 m3/h. (2) It operates stably and reliably, with low maintenance requirements. The elimination of the grate prevents slag formation at the bottom of the furnace. The gasification furnace consists only of a furnace body lined with refractory material and a removable nozzle; it has no transmission components or vulnerable parts, so it requires little maintenance to achieve a high continuous operation rate, generally exceeding 90%. (3) It offers great operational flexibility, making it easy to start and stop the furnace. The production load of the gasification furnace can be adjusted within the range of 40% to 110% of the design load. (4) Lignite, bituminous coal, non-caking coal, or weakly caking coal with a thickness of 0–10 mm can be used, which greatly expands the range of available coal sources and significantly reduces the production costs of gas. 3 Comparison of Ende powder coal gasification technology with other technologies: Compared with foreign technologies such as Texaco slurry coal gasification, Shell powder coal gasification, and Lurgi pressurized coal gasification, Ende powder coal gasification technology offers a wider range of coal suitability, simpler treatment of waste materials, less environmental impact, and is mature and reliable, making it suitable for large-scale production. However, the Ende furnace operates at atmospheric pressure and at relatively low temperatures; as a result, the conversion rate of carbon is lower than that of gasification furnaces abroad which operate under high temperature and high pressure conditions. In most areas of our country, the local coal price is low; therefore, it is reasonable to sacrifice some gasification efficiency in order to achieve better overall economic benefits. Compared with foreign powder coal gasification technologies, the Ende powder coal gasification technology is not very advanced, but it suits China’s national conditions and represents a practical new technology. Compared with existing coal gasification technologies in the country, its prominent features are its maturity and reliability, the ability to be used for large-scale production, extensive operational experience in synthesizing ammonia over the long term, and a high concentration of useful components in the produced gas – with CO+H2 accounting for 70% and methane content around 2%. The Ende powder gasification project designed by our institute for Jiaogua Gas General Factory in Jingdezhen City, Jiangxi Province, came online for normal operation in February 2001. This furnace uses air gasification, with raw material being long-flame coal from Yima, Henan Province, to produce gas with a low calorific value. The design capacity of this furnace is 10,000 m3/h, and the actual operating load can be adjusted within a range of 30% to 150%. The gas generator operates stably and easily, meeting or exceeding all design specifications, resulting in a significant reduction in the cost of coal gas production. Since the technical equipment has been fully domesticated, the investment required for Ende’s pulverized coal gasification technology is much lower compared to Texaco’s water-coal slurry gasification and Shell’s gasification technologies. Taking a gasifier for 40,000 m3/h of syngas (90 kt/a of ammonia production) as an example, the investment in an Endo powder coal gasifier is only 23.44 million yuan, while that for a Texaco water-coal slurry gasifier is around 78 million yuan; the investment for a Lurgi gasifier is about 45 million yuan. Shell does not have gasifiers of this scale. When converted to a gasification unit with an annual ammonia production of 300 kt, the investment for the gasification part in a facility producing 90 kt of ammonia is approximately 75 million yuan. The investment for an Ende powder gasifier is only 30% to 50% of that for an imported gasifier. Compared with the fixed-bed batch water-gas furnace process, Ende powder gasification units are generally installed outdoors, eliminating the need for investment in building construction ； The steam generated is more than sufficient, eliminating the need for an investment in a boiler room ； Since it is a continuous operation, the investment in a buffer gas tank can be avoided. However, powder coal gasification requires oxygen-enriched air supply, which entails increased investment in the oxygen production system ； Generally, coal powder needs to be dried, which increases the investment in coal drying systems. 4 Energy-saving measures proposed by our institute for this process: In order to reduce project costs, we took the following considerations into account in the engineering design. (1) On the basis of meeting the requirements related to coal gasification, coal should be selected locally whenever possible; if conditions permit, pulverized coal in the 0–13mm range should be purchased from coal mines, or arrangements should be made with the coal mines to have it crushed and screened on-site so that qualified material can be acquired. This can save investment in the coal preparation system. (2) Since the moisture content of coal to be fed into the furnace is required to be less than 8%, a coal drying device needs to be installed. However, in some areas the moisture content of coal does not meet the requirements only during the rainy season; in such cases, the coal drying facilities can be simplified, such as by installing rain shelters at the coal storage sites or using simple coal warehouses. (3) Since the operating cycle of the Ende furnace is over 90%, only the waste heat boiler requires regular maintenance. Some companies can determine the maintenance schedule for the waste heat boiler by scheduling regular inspections of the gas-using equipment, without needing to use the furnace itself. (4) The source of oxygen should preferably be pressure swing adsorption air separation for oxygen production. This technology is already well-developed. Compared with the cryogenic method, it requires less space, is easier to install, and has a shorter construction period. The total investment for PSA units with a capacity of 4000 m3/h or less is 20%–30% lower than that for cryogenic units. The purity of the oxygen produced can reach 93%–95%, and the cost of oxygen production is around 0.3 yuan per m3. (5) For the renovation of old gas stations, especially large ones, existing gas station facilities should be utilized as much as possible depending on funding availability, in order to reduce project costs. After comprehensive comparison, at the same scale, the capital investment for the Ende powder gasification technology is comparable to or slightly higher than that of the water gas furnace process using fixed-bed batch production. In terms of operating costs, Texaco gasification involves a coal slurry preparation process, and the nozzles and refractory bricks in the gasifier need to be replaced regularly. Shell dry powder gasification includes coal grinding and drying processes, while Lurgi pressure gasification requires wastewater treatment, all of which increase the operating costs. Ende coal gasification is a atmospheric pressure gasification process; coal powder can be fed directly into the furnace, and the gasifier has no rotating or wearing parts, which reduces operating costs. One of its drawbacks is that syngas needs to be pressurized, which increases some operating costs, and the utilization rate of coal is also lower than that in Texaco and Shell’s gasification processes. The cost of raw coal generally accounts for 40% to 50% of the cost of gas production. Since the Ende powder coal gasification technology can be applied to pulverized coal, especially low-quality lignite, the purchase cost of raw materials is 50%–60% lower than that of lump coal, thereby significantly reducing the cost of gas. Furthermore, the operating efficiency of the Endre furnace is over 90%, resulting in lower maintenance costs. The number of employees required is also 1/3 less than that of fixed-bed gasifiers of similar scale, which is another factor contributing to reduced production costs. 5 Production Applications and Economic Benefits: Taking the estimated engineering investments, production costs, and economic benefits of several projects designed by our institute as examples. The pulverized coal gasification unit designed by our institute for the Jingde Coking Gas Complex has a production capacity of 10,000 m3/h of air gas; the project investment amounted to 12 million yuan. The cost of producing gas is 0.12 yuan/m3 (with the coal price at 240 yuan/t), and the internal rate of return on the total investment (after taxes) is 25.4% ； The total investment payback period is 3.84 years (including a 1-year construction period). The pulverized coal gasification project at Fushun Carbon Factory has a designed capacity of 10,000 m3/h of air gas; the investment in this project amounts to 14.3 million yuan. The cost of producing gas is 0.104 yuan/m3 (with the coal price set at 174 yuan/t). The internal rate of return on total investment (after taxes) is 33.57%, and the payback period for the total investment is 4 years (including a 1-year construction period). The Fushun Special Steel Coal Gasification Project has a designed capacity of 40,000 m3/h and consists of three series; one series will be put into operation in the first phase to produce semi-water gas (with a calorific value of 6,270 kJ/m3). A gas production facility with a capacity of 4,000 m3/h has been built. The investment in this project amounts to 75 million yuan. The cost of producing gas is 0.135 yuan/m3 (based on a coal price of 140 yuan/t). The internal rate of return on total investment (after taxes) is 29.72%, while the payback period for the total investment is 4.37 years (including a 1-year construction period). This is the situation regarding the production of industrial gas; if it is used to produce ammonia synthesis gas, it will increase the capital investment in oxygen production systems as well as the cost of oxygen used in production. The preliminary estimates are as follows. If the annual production of synthetic ammonia is 30 kt, a 10,000 m3/h End gasifier can be used, along with an oxygen production unit based on pressure swing adsorption with a capacity of around 2,000 m3/h; the total investment for this project is approximately 24 million yuan. If the annual production of synthetic ammonia is around 90 kt, a gasifier with a capacity of 40,000 m3/h can be used, along with an air oxygen production unit capable of handling about 6,000 m3/h of air; the total investment for such a project is approximately 85 million yuan. If the price of raw coal is 170 yuan per ton and the cost of oxygen is 0.3 yuan per m3, the cost of syngas is around 0.15 yuan per m3. The cost of gas produced by fixed-bed water gasifiers is at least 0.2 yuan per m3 or more.