Development and current status of gasification technology

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Liu Weiping (Shandong Hongri Akang Chemical Co., Ltd., Linyi 276021) 1 Preface The domestic ammonia and methanol industries have undergone years of development; currently, various raw materials such as coal, natural gas, and coke oven gas are used for production. Given that China’s energy profile is characterized by a shortage of oil and gas while coal resources are relatively abundant, coal still plays a dominant role as a raw material in China’s ammonia and methanol industries. Regarding gasification process technologies, the main types currently in use are fixed-bed, fluidized-bed, and pneumatic-bed systems. As for furnace types, there are fixed-bed batch gasifiers, as well as systems such as Ash Fusion, Texaco, and End gasifiers. Each gasification method has its own characteristics, and different manufacturers in China employ these various methods. 2 Overview of Domestic Gasification Technologies 2.1 Fixed-Bed Batch Gasification (UGI) (1) Technical Overview This is the earliest type of gasification technology adopted in China, and it is also the most widely used method for generating gas in methanol and ammonia synthesis plants across the country; it accounts for over 70% of the current ammonia production capacity. After years of development, this technology has become quite mature, and the equipment is now fully domestically produced. The fixed-bed intermittent gasification gas production system mainly includes devices for feeding raw coal, gas production, gas purification and dust removal, as well as waste heat recovery. The production process involves atmospheric pressure batch gasification. Each gas generation cycle consists mainly of five stages: blowing, upper blowing, lower blowing, secondary upper blowing, and cleaning blowing, with a cycle time typically ranging from 120 to 150 seconds. Depending on the different control processes, water gas and semi-water gas with varying compositions can be produced. This technology uses a solid-state ash discharge method; since air is used as the oxidant, the carbon utilization rate is low, the decomposition rate of steam entering the furnace is low, and the carbon content in the ash is high, typically around 20%. Since it is a atmospheric-pressure batch gas production process, the production capacity of each individual unit is low; depending on the specifications of the furnace, the gas output per unit ranges from 4000 to 12000 Nm3/h, with the effective gas content of the produced gas being between 60% and 85%. This gas production method uses anthracite coal from Shanxi as raw material; the particle size of the coal is required to be between 20 and 80 mm, with a moisture content of less than 8%. Currently, more than 600 enterprises in China employ this technology. (2) Advantages and disadvantages of the technology: This technology requires low investment and has a short construction period. By utilizing the reaction between air and carbon, the need for expensive air separation units is eliminated, resulting in the lowest investment among all current gasification technologies. Generally, the investment required for a synthetic ammonia plant with a capacity of 10×10 Kt/year in terms of gasification systems is around 30 million yuan, which in turn reduces the depreciation costs associated with production. Since smokeless lump coal is used as the raw material, and this type of coal is expensive, its availability is limited; moreover, the low utilization rate of the raw material and high energy consumption result in high production costs, which represents the biggest drawback of this technology. Gas production uses atmospheric pressure and batch gasification, which limits the size of the installation. Additionally, the short continuous operating time of the equipment results in heavy maintenance requirements, as well as the need for specialized furnaces for the equipment. The device causes significant environmental pollution, there is a high level of dust at the site, the operating conditions are poor, and the technology used is relatively outdated. 2.2 Eunde Furnace (1) Technical Overview: The Eunde coal-fired fluidized bed gasification technology is a gasification process that was developed and improved over time by the ’7·7’ Chemical Plant in Eunde County, North Hamgyong Province, North Korea, based on the original Wenker coal-fired fluidized bed gasifiers. This gasification technology was introduced to China in the 1990s by Liaoning Ende Engineering Construction Co., Ltd. This type of furnace uses coal powder as raw material and different gasifying agents to produce air gas, semi-water gas, and water gas, which are respectively used as gas for industrial heating furnaces, as fuel for domestic use, and as synthesis gas for chemical industries. At present, all components of this device have been domestically produced. The gas generation system of the Ende furnace mainly consists of raw coal preparation, gas generation, preliminary gas purification, and the accompanying air separation unit. The production process involves atmospheric pressure gasification at an operating temperature of 900–1000 °C; solid ash discharge is used, with the carbon content in the ash being less than 10%. The effective gas content of the produced coal gas ranges from 65% to 70%. For a plant with a gas production capacity of 40,000 Nm3/h, if one gas generation furnace is used, the total investment for the entire coal gasification system is approximately 80 million yuan, of which the Endler furnace accounts for about 32 million yuan and the air separation system accounts for 30 million yuan. If two gas generation furnaces with a capacity of 20,000 Nm3/h are used, the total investment for the entire system is approximately 90 million yuan. The raw materials used in this technology are mainly lignite, long-flame coal, and non-sticky and weakly sticky bituminous coals. The ash content of the coal is required to be less than 30%, it must have a high ash fusion point (ST > 1250 °C), and good chemical activity at low temperatures (greater than 85% at 950 °C, and greater than 95% at 1000 °C). The current production capacities of this equipment are 10,000 Nm3/h, 20,000 Nm3/h, and 40,000 Nm3/h. Considering the impact that equipment maintenance can have on the operational stability of the plant, it is common for a single plant to use two or more gas generation furnaces, so that a failure in one unit does not result in the shutdown of the entire plant. To date, 18 units have been installed in China, of which more than 7 are used in ammonia synthesis plants. China’s first gas generation unit for Ende furnaces was put into operation in Jingdezhen, Jiangxi Province in 2001, with a capacity of 10,000 Nm3/h. Subsequently, gasification units for Ende furnaces were also built and brought online by various chemical enterprises such as Heilongjiang Heihua Group Co., Ltd., Jilin Changshan Fertilizer Group Co., Ltd., Anhui Huaihua Group Co., Ltd., Heilongjiang Beifeng Group Ningan Chemical Company, and Jilin Beifang Gas. (2) Advantages and disadvantages of the technology: Since the gas generation technology using the Ende furnace can be fully domestically produced, its investment is low; the cost of a 10×10 Kt/a ammonia synthesis plant is approximately 70–80 million yuan, which is less compared to other continuous gas generation methods. In terms of raw materials: This type of furnace uses lignite and long-flame coal as raw materials, whose prices are lower than those of Shanxi white coal, thereby allowing for reduced costs in gas production. However, it requires strict standards regarding properties such as the viscosity of the raw coal. Currently, these types of coal are mainly found in regions such as Jilin, Inner Mongolia, Guangxi, Yunnan, and Yima in Henan. As a result, the use of such raw materials limits the widespread adoption of this gas production method, which is also one of its main drawbacks. The current maximum gas generation capacity is 40,000 Nm3/h. Since it operates under atmospheric pressure, this approach offers significant advantages over the fixed-bed batch gasification furnaces that are widely used in China; on the other hand, it also imposes certain limitations on the enlargement of such furnaces. Considering the operational stability of the installation, a typical system uses two or more gas generation furnaces, which increases the investment and floor space required as well as the complexity of operation. 2.3 Gray Melting Polymerization Gasification Technology (1) Technical Overview: The gray melting polymerization technology is a gasification technology with independent domestic intellectual property rights, developed jointly by institutions such as the Shanxi Institute of Coal Chemistry under the Chinese Academy of Sciences and Shaanxi Qinjin Technology Co., Ltd. Currently, several companies in China are using this technology to produce synthetic ammonia or methanol. The ash fusion fluidized bed pulverized coal gasification system mainly includes raw coal preparation, coal feeding system, gasifier, ash discharge system, dust removal system, waste heat recovery system, and washing and purification equipment. This technology uses oxygen-enriched or pure oxygen for continuous gas production, with a gas generation pressure of 0.03–1.00 MPa. The operating temperature is generally maintained at around 1100 °C, which should be 100 °C lower than the ash melting point. A solid-state ash discharge method is employed; the carbon content in the ash is less than 10%, the carbon conversion rate exceeds 90%, and the effective gas content ranges from 72% to 78%. The gas contains no tar or heavy hydrocarbons, has a low phenol content, and results in minimal wastewater generation. The production capacity of a single unit, calculated in terms of ammonia synthesis, ranges from 3×10Kt/year to 10×10Kt/year. Given the frequent need for equipment maintenance, it is common to equip a single plant with two or more gas generation furnaces in order to ensure the continuous and stable operation of the plant. For a 10×10 kt/a ammonia synthesis plant, the investment in the ash pyrolysis gas generation system ranges from 150 million to 250 million yuan, of which the investment in the air separation system accounts for over 40%. This technology requires that the particle size of the raw coal be such that >6mm particles account for <1%, and particles <1mm account for <40%. The ash content is required to be 10%–40%, and the cinder characteristics should be 1–6 (with 2–4 being preferred). The external moisture content is ≤5%, and the ash fusion temperature (ST) is ≥1250 °C. The coal types used include lignite, bituminous coal, sub-bituminous coal, anthracite, and coke dust, offering broad adaptability. Currently, the coal types employed in industrial installations include Huating bituminous coal from Gansu, Binxian bituminous coal from Shaanxi, caking bituminous coal from Datong in Shanxi, Tang’an anthracite from Shanxi, as well as high-ash bituminous coal from Pingdingshan. The consumption indicators are shown in Table 1. http://pub2.hi2000.com/upload1/0711261445405856.jpg (2) Advantages and disadvantages of the technology: This is a new type of coal gasification technology developed in China with complete independent intellectual property rights; as a result, all the equipment can be manufactured domestically, resulting in relatively lower investment costs. As this is a relatively new gasification technology, it is currently undergoing continuous improvement and maturation, offering good market prospects. However, due to its short period of adoption and the limited number of manufacturers using it, there is still little experience in terms of its design, production, and application. This technology eliminates the reliance on Shanxi white coal as a raw material, but it still has certain requirements regarding properties such as the ash fusion point and ash content of the coal; there are thus many restrictions on the raw materials, which in turn hinders the widespread adoption of this technology. At present, this technology is mainly based on atmospheric pressure gasification, while low-pressure gasification is in the stage of being promoted and applied. The production capacity of individual units is relatively low, and larger-scale implementation is still some time away. At present, due to the short service life of the central tube in this equipment, it needs to be replaced every three months to six months, which results in a short continuous operation period for the equipment and frequent start-up and shutdown cycles. Additionally, in order to ensure the stable operation of the system, more than two gas generation furnaces are required per unit. The CO2 content in the gas produced by this gas generator generally exceeds 20%, which is more than twice as high as that in the semi-water gas produced by current fixed-bed gasification methods; as a result, the capacity of the subsequent decarburization unit has to be increased significantly. 2.4 Shell Gasification Technology (1) Technical Overview: Research on Shell gasification technology began in the 1970s. Following numerous pilot tests, scale-up trials, and the construction of demonstration plants, an industrial facility with a capacity of 250 MW was built in 1989 at the De Moerkerk combined cycle power plant in the Netherlands; this facility came online in 1998. This technology belongs to the fluidized bed technology category; its process flow mainly includes the pretreatment of raw coal, pressurization and feeding of coal, coal gasification, ash removal, gas purification, desulfurization, as well as supporting systems for water treatment, air separation, and nitrogen production. The gas generation pressure used is 2.0–4.0 MPa, with the operating temperature ranging from 1400 to 1600°C. Liquid slag removal technology is employed; the carbon content in the slag is less than 1%. Dry coal powder is used as the feed material, and the carbon conversion rate reaches 99%, with the effective gas content in the syngas being approximately 90%. The effective gas ratio oxygen consumption is approximately 340 Nm3 per 1000 Nm3 (CO + H2), and the coal consumption is about 590 kg per 1000 Nm3 (CO + H2). Regarding Shell’s gasification technology, in addition to one industrial plant abroad, domestic companies have, since 2001, introduced 12 sets of 13 Shell furnace units, including those at the Liuzhou Fertilizer Plant in Guangxi, the Hunan Dongting Nitrogen Fertilizer Plant of Sinopec, China Shenhua Coal-to-Oil Co., Ltd., the Hubei Zhijiang Fertilizer Plant of Sinopec, the Anhui Anqing Chemical Complex of Sinopec, the Dalian Dahuahua Company’s ammonia synthesis plant, Yunnan Yuntianhua Group, and Yunnan Zhanhua Group. The production capacity of these units ranges from 20×10kt/a to 50×10kt/a, and they are primarily used in ammonia synthesis and methanol production facilities. Factors such as the transfer of patented technologies, a low rate of domestic production of equipment, and the need to import key equipment contribute to making this technology the most capital-intensive coal gasification unit in China at present. The coal gasification system associated with a 20×104 t/year ammonia synthesis plant requires an investment of around 350–400 million yuan, of which approximately 100 million yuan is invested in the air separation system. (2) Advantages and disadvantages of the technology: It has a wide range of coal adaptability, with almost no requirements regarding the raw coal; bituminous coal, subbituminous coal, lignite, and petroleum coke can all be gasified. It also tolerates a broad range of coal ash fusibility levels, and can handle coals with high ash content, high moisture content, and high sulfur content as well – a feature that other coal gasification technologies cannot match. However, for coals with a high ash fusion point, fluxes (such as lime) must be added to lower the ash fusion point. Therefore, from an economic perspective, it is still necessary to select certain types of coal. By using pressurized gasification, oxygen consumption is low and the production capacity per furnace is high, making it suitable for large-scale production. Currently, the coal feeding rate per unit of equipment can reach 2000 t/d, with a corresponding ammonia synthesis capacity of 1500–1600 t/d. Due to the use of a water-cooled wall structure, there is no need for refractory brick lining. Additionally, there are no moving parts inside the gasifier, which means that the burners used in this gasifier have a long service life, typically exceeding one year. This allows the equipment to operate continuously for extended periods without the need for spare units, and this is also a significant difference from other coal gasification technologies. However, since the commissioning time for similar devices in China is shorter, this point still needs to be verified through actual operation. The Shell gasifier uses multiple nozzles, typically 4 to 6 in number, which are arranged in pairs symmetrically, granting the unit a high degree of operational flexibility. High-temperature gas production ensures that the gasification reaction proceeds thoroughly; as a result, the resulting coal gas contains few by-products, no heavy hydrocarbons, and causes little environmental pollution. The key equipment for this gasification technology must be manufactured abroad, and components such as nozzles and coal powder valves are also entirely imported. The low degree of localization of these devices results in the highest investment costs among current domestic coal gasification technologies, causing depreciation to account for a large proportion of the product costs. At the same time, the construction period for such facilities is long, usually three years or even more. This is the biggest drawback of this technology. Due to the use of dry feeding, it features a high carbon conversion rate, high thermal efficiency, low heat loss, low energy consumption, and a high content of useful gas. However, since the waste-heat recovery system is used in the gasifier, the hydrogen-to-carbon ratio of the produced gas is around 0.5, which is too low. The hydrogen-to-carbon ratio required for methanol production should be above 2, and for ammonia synthesis, all of the CO needs to be converted. Therefore, the gas produced by this facility requires a subsequent conversion unit that consumes large amounts of steam to carry out the conversion of CO. Therefore, from the perspective of gas composition, this technology is more suitable for power generation units rather than for producing chemical products such as methanol and synthetic ammonia. Currently, abroad there is only one industrial plant using this technology for combined cycle power generation; there are no actual production plants using it for the synthesis of ammonia and methanol. As a result, when introducing this technology in China for the production of ammonia and methanol, there is a lack of targeted design and production experience, which leads to higher investment costs and more complex processes, thereby preventing the full realization of the advantages of this technology. 2.5 Texaco Water-Coal Slurry Pressurized Gasification (1) Technical Overview GE Texaco’s water-coal slurry pressurized gasification technology was developed in the early 1950s by the American company Texaco, based on the partial oxidation gasification of heavy oil; it was subsequently put into industrial use in countries such as Japan, Sweden, and Italy. In 1998, the company joined forces with the China Water-Coal Slurry Gasification and Coal Chemicals Center to establish Texaco Gasification Services Co., Ltd., aimed at introducing and promoting the company’s water-coal slurry pressurized gasification technology. This technology belongs to the fluidized bed pressurized gasification category; its process flow mainly includes coal grinding and slurry preparation, slurry storage and transportation, coal gasification and syngas washing, slag treatment systems, as well as supporting air separation units. There are three processes for utilizing heat in gasifiers: quenching, waste heat recovery, and a combination of quenching and waste heat recovery. The appropriate process can be selected based on the product to be produced. For plants that manufacture synthetic ammonia and methanol, the quenching process is generally used, resulting in a high gas-to-vapor ratio as well as a high hydrogen-to-carbon ratio in the obtained gas. The gasifier uses wet feeding and liquid slag discharge technology, with the coal slurry having a moisture content of approximately 30% to 40%. The gas generation pressure of the device ranges from 2.5 to 6.5 MPa, with 4.0 MPa devices being more common. The normal operating temperature of a gasifier is 1300–1400°C, which is 50–100°C higher than the ash melting point of the feed coal. The effective oxygen consumption is 336–410 m3 (CO+H2) per km3, and the coal consumption is 550–620 kg per (CO+H2) km3. The effective content of gases is 80%–84%, and the carbon conversion rate exceeds 97%. Due to high-temperature gasification, the methane content in the gases is very low (CH4 content ≤ 0.1%), there is no tar, resulting in minimal environmental impact and facilitating gas purification. In 1989, China introduced its first Texaco water-coal slurry pressurized gasification unit at the Yankuang Lunan Fertilizer Plant. To date, more than a dozen enterprises, including Shanghai Coking Plant, Shaanxi Weihe Fertilizer Plant, Huainan Fertilizer Plant, Jihua Company’s Fertilizer Plant, and Jinling Petrochemical, use Texaco gasification technology to produce chemical products such as synthetic ammonia and methanol. Due to the use of pressurized gasification, the gasification furnace has a simple structure, which results in high production capacity per furnace. Currently, the maximum coal feeding rate in domestic plants is 1,000 t/day, while that in international plants is 2,000 t/day. One gasification furnace can produce (20–30) × 10kt of methanol per year. Since this device has been in use in China for many years and the degree of domestic production of its components is high, reaching over 90%, the investment required for such devices is relatively low. The investment for a gasification furnace system with a coal feeding rate of 500 t/d and a gasification pressure of 4.0 MPa is approximately 70 million yuan ； The investment for a gasification furnace system with a coal feeding rate of 1,000 t/d and a gasification pressure of 4.0 MPa is approximately 110 million yuan. One of the features of this technology is its wide adaptability to different types of coal; bituminous coal, anthracite, sub-anthracite, anthracite, high-sulfur coal, as well as low-quality coals with low ash fusion points and petroleum coke can all be used as feedstocks for gasification. However, not all types of coal are suitable for this purpose. To ensure the long-term stable operation of the system, coals with low ash content, low ash melting point, and good viscosity-temperature properties are generally more appropriate for this technology. Therefore, it is usually required that the ash content of the raw coal be below 20%, and its ash melting point below 1300°C. (2) Advantages and disadvantages of the technology: The Texaco process has been in use in China for over a decade, so there is extensive experience in aspects such as design, equipment manufacturing, installation, commissioning of the plants, and operation related to this technology. It is a mature and reliable technology, with a high degree of localization of the equipment. At present, the key factor affecting the long-term stable operation of the Texaco gasification unit is the short operating cycle of the gasifier burners. The operating cycle of the gasifier burner generally does not exceed two months, and the burner needs to be replaced due to issues such as nozzle wear and cracks. This is the main reason why the Texaco gasification plant requires a backup burner, which in turn leads to increased investment in the plant as well as higher operating costs. Currently, the service life of fire-resistant bricks used abroad is up to two years, while in China it is around one year. The cost of replacing these bricks accounts for more than half of the total maintenance costs associated with the installation, and the replacement process takes more than a month. In addition, issues such as scaling in the black water system and water presence in the gasification furnace also affect the continuous and stable operation of the installation. The gasifier of this technology has only one burner, resulting in lower operational flexibility. 2.6 Four-nozzle opposed water-coal slurry gasification technology (1) Technical overview: This gasifier was developed jointly by East China University of Science and Technology, Yankuang Lunan Fertilizer Plant, China Tianchen Chemical Engineering Company, and other organizations; it represents a coal gasification technology with independent domestic intellectual property rights. It is a fluidized-bed pressurized gasification technology that has been improved upon the basis of Texaco’s water-coal slurry gasification technology; it is equivalent to the domestically developed version of Texaco’s technology. The first pilot installation of this technology was put into operation in October 2005 at Yankuang Lunan Fertilizer Plant. The facility is equipped with two gasification units, with a daily coal input of 1,000 tons; it produces 24×10kt of methanol per year, and it also includes a power generation unit. It has been operating normally for over a year now, and it represents a relatively new gasification technology. At present, aside from Yankuang Lunan Fertilizer Plant which uses this technology to produce methanol, a second coal gasification unit with a daily coal input of 650 tons and an operating pressure of 6.5 MPa was built at Hualu Hengsheng in 2004; it is currently operating properly. Meanwhile, several domestic companies have also adopted or plan to adopt the multi-nozzle opposed water-coal slurry gasification technology to build coal chemical plants or IGCC facilities. The proposed facilities include Jiangsu Linggu Group’s project for producing 40×10kt of synthetic ammonia per year, Tengzhou Phoenix Fertilizer Co., Ltd.’s project for producing 60×104t of alcohol-ammonia, and Zhenjiang Sopco Group’s project for generating gas for acetic acid production on a scale of 60×10kt. It is evident that this technology is being adopted at a rapid pace in China, indicating good prospects for its use in the future. This technology belongs to a fluidized bed pressurized gasification unit, with wet feeding and liquid slag discharge. The coal gasification system mainly consists of a water-coal slurry preparation unit, a four-nozzle opposed coal gasification unit, a preliminary coal gas purification unit, a slag-containing water treatment unit, and a supporting air separation unit. Vaporization pressure: 3.0–6.5 MPa; operating temperature: 1200–1300°C. The residue contains ≤5% carbon, with an effective gas content of ≥83% and a carbon conversion rate of ≥98%. The oxygen consumption per unit volume of effective gas (CO + H2) is 360–380 m3/km3, while the coal consumption per unit volume of effective gas is 540–570 kg/km3. (2) Advantages and disadvantages of the technology: Since this technology was developed on the basis of the original Texaco gasification technology, some of its advantages, such as a wide range of suitable raw coals and high production capacity per unit of equipment, have been well retained. This technology is an improvement based on the Texaco water-coal slurry gasifier, addressing the main issues associated with Texaco’s technology. Improvements were made to the main issues associated with Texaco’s technology, such as low startup rates due to single nozzles, limited operational flexibility, high operating costs resulting from short lifespans of refractory bricks, and water presence in the gasifier. Based on the current operation status, significant improvements have been seen in all of these issues. This technology possesses independent intellectual property rights, which means that the licensing costs compared to patented technologies are significantly lower. At the same time, there is also a substantial increase in the degree of localization of equipment and materials. The nozzles and refractory bricks used in this technology are domestically produced, which accordingly reduces operating costs and shortens the supply cycle. Due to the use of the four-nozzle technology, the investment required for coal gasification plants is higher, exceeding that of the Texaco technology by 20% to 30%. During operation of the unit, severe erosion of the arch bricks in the gasification furnace and overheating of the furnace arch occurred, thereby affecting the operational stability of the unit. This technology is newly developed; currently, industrial-scale installations have been in operation for a relatively short time, so there is limited experience in terms of design and operation. Some data can only be accurately determined after the installations have been operating for a longer period of time. 2.7 Other coal gasification technologies (1) Two-stage dry coal powder pressurized gasification technology: This two-stage dry coal powder pressurized gasification technology is a coal gasification method with independent intellectual property rights, developed by the Xi’an Thermal Power Research Institute. With the support of domestic power companies and scientific research institutions, research on this technology began in 1994; an experimental unit was built in 1997, and a pilot plant with a coal processing capacity of 36–40 t/day was constructed in 2004. At present, a demonstration plant with a coal feeding capacity of 1000 t/day is under construction. Based on the current situation, this technology is designed for coal-based power generation, and the demonstration plant is also intended for power generation purposes. Industrial-scale plants for the production of ammonia and methanol are still some time away from being realized. (2) GSP fluidized bed gasification technology: The GSP fluidized bed gasification technology is a coal gasification method that was developed starting in 1975 by the German Fuel Institute (DBI) in Germany; it is primarily suitable for gasifying low-quality lignite. In 1991, this technology was acquired by the German company Norr, which carried out systematic improvements on it. This technology belongs to the fluidized bed pressurized gasification category; it uses dry coal powder as raw material and employs a single burner for gas production. The gasifier is equipped with water-cooled internal components, operates at a pressure of 2.8 MPa and a temperature of 1400°C, and has 6 years of experience in using lignite as raw material for gasification. The largest GSP gasifier currently in use has a coal feeding capacity of 720 tons per day. Due to the use of water quenching, the investment required is much lower than that of Shell furnaces, making it more suitable for coal chemical production. Currently, there are 3 companies in the world that use the GSP gasification technology, but none of them use it for coal gasification. Only one unit has 6 years of experience in gasifying lignite, and there is no record of long-term gasification of coals with different properties. There is a lack of practical engineering experience in design and operation, and it is necessary to establish a demonstration unit for long-term operational testing. (3) LURGI pressurized gasification technology: The LURGI gasification method is the earliest pressurized gasification technique to be adopted in the world. It was first proposed by the German company LURGI, and the first industrial plant of this type was put into operation in Germany in 1936. It is a fixed-bed gasifier with an operating pressure of 2.5–3.5 MPa, utilizing a dry ash discharge method. The Lurgi gasification method is primarily used for gasifying lignite, as well as coal that is non-caking or weakly caking. The raw coal required has high thermal stability, good chemical activity, a high ash fusion point, high mechanical strength, and should be non-caking or weakly caking; in addition, lump coal must be used, which imposes restrictions on the types of coal that can be utilized and their properties. Although the Lurgi process features a large number of industrial installations, mature technology, and extensive production experience, it is more suitable for urban gas use due to its low gasification temperature, which results in a low content of useful components (CO+H2) in the gas. It also has high levels of benzene, phenols, and tar in the gas, presents complex challenges in terms of wastewater treatment, and has a high methane content; as such, it is not appropriate as a feed gas for the production of synthetic ammonia and methanol. (4) Pressurized gasification technology for multi-component slurries: This technology was developed by the Northwest Institute of Chemical Engineering and represents a coal gasification method with independent intellectual property rights. Research on this technology began in the late 1960s and lasted for over thirty years. It belongs to the wet fluidized-bed pressurized gasification technique. In this process, solid or liquid carbon-containing materials (such as coal/petcoke/petroleum asphalt/oil/coal liquefaction residues, etc.) are combined with a flowing phase (water/waste liquid/effluent) to form a slurry; additives such as dispersants/stabilizers/pH regulators/wetting agents/emulsifiers are then added to this slurry. This mixture undergoes a partial oxidation reaction with oxygen, resulting in a feed gas whose main components are CO and H2. Such gas can be used for ammonia synthesis, methanol production, hydrogen generation, oil synthesis, and combined-cycle power generation. Its basic production equipment is similar to that of the water-coal slurry pressurized gasification technology, belonging to the gas generation method with a single burner in a fluidized bed configuration. The typical composition of the multi-component slurry is 60%–65% coal, 10%–15% oil, 20%–30% water, with a viscosity of ≤2500 cP. By the end of June 2006, the multi-feed slurry gasification technology had been put into industrial use in more than a dozen industrial plants on the Chinese mainland, including synthetic ammonia plants with capacities of (3–30)×10kt/year, methanol plants with capacities of (20–60)×10kt/year, and coal-to-oil plants with a capacity of 50×10kt/year. Three sets of industrial plants are already operating steadily; this represents a promising gasification method, yet there are still certain limitations regarding the raw materials used. 3 Points to Consider When Choosing Gasification Technology. At present, various gasification technologies each have their own characteristics and applicable ranges; there is yet no gas production method that stands out significantly in terms of overall performance. This is also a major factor behind the diversity of gas production methods used in China today. When choosing the gas generation method, the following points can be considered. (1) First and foremost, the coal gasification method should be determined based on the characteristics of the raw materials; it is not appropriate to decide on the coal gasification method first and then select a suitable coal type. Currently, several plants in China have encountered this reversed approach, where insufficient understanding of the coal types to be used was available during plant design, resulting in the inability to use local coal after the plant started operating, and thus the need to transport coal from other locations. For the raw coal to be used, it is necessary to have a clear understanding of various factors such as its origin, quality, reserves, production volume, ex-factory price, arrival price, and supply stability. The physical and chemical properties of the coal – including carbon content, calorific value, thermal stability, caking property, and ash content – are all factors that affect gas production; specific values are obtained through testing. By comprehensively comparing these various factors, it is possible to determine which type of coal offers the best overall benefits. (2) Depending on the products obtained from gasification, it is used for power generation, producing fuel gas, or for manufacturing methanol and synthetic ammonia. Since the pressure and gas composition of the raw material gas produced by gasification in different furnace types vary, they are suitable for various industrial applications. Determining the appropriate type of furnace: some types are suitable for power generation, some are suitable for use as fuel gas, and some can be used to produce raw gas for coal chemical products. (3) Determine the production scale and capacity of the product. Different gasification technologies have varying effects on the economies of scale of the facilities to be built; at the same time, the associated investment costs, construction timelines, and market adaptability also differ. (4) In general, when choosing a gas production method, enterprises should consider the specific circumstances of their situation, conduct a comprehensive analysis of the project in question, and take a thorough understanding of various factors such as raw materials, technology, market conditions, and environmental considerations. By optimizing these aspects, it is possible to avoid or reduce investment risks and enable enterprises to achieve maximum benefits. Decision-making regarding the choice of gas production method should not be based on just one factor alone, as this could lead to irreparable losses. This post was last edited by lcs000212 on 2007-12-10 15:21]