The technological development path of gasification using Tsinghua furnace gas

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This post was last edited by Qinghua Lu on 2016-8-8 at 09:57. The path of technological development in coal gasification by Qinghua Lu. Source: Beijing Yingde Qingda Technology Co., Ltd. I. Overview Currently, coal accounts for about 66% of China’s total primary energy consumption, with the total coal consumption amounting to approximately 3.7 billion tons. China’s energy characteristics are an abundance of coal, a shortage of oil, and limited natural gas; the coal-dominated energy consumption structure is unlikely to change significantly in the short term. With the continued advancement of industrialization and urbanization, requirements regarding the control of total energy consumption and environmental constraints are becoming increasingly stringent. Therefore, accelerating the clean and efficient utilization of coal, as well as developing technologies for its comprehensive utilization, has become an important task for China at present. Among the various coal utilization technologies, gasification is the key and leading technology for the clean conversion of coal. Our country is the largest user of coal gasification technology in the world. Coal gasification serves as the foundation for developing process industries such as coal-based chemical products, coal-based liquid fuels, synthetic natural gas, IGCC power generation, hydrogen production, and direct reduction ironmaking. As a major coal-consuming country, coal gasification is a core technology for China to achieve efficient and clean utilization of coal; it is also a crucial technology for addressing environmental pollution caused by coal combustion. Gasification technology is also one of the most important and crucial process steps in the development of modern coal chemical industry. Its selection, as well as its stable, efficient, and economical operation, are crucial to the success or failure of the project. The gasification technologies currently popular in the petrochemical industry fall into two main categories: the water-coal slurry refractory brick technology and the dry powder water-cooled wall technology. However, both of these technologies have their own shortcomings. Compared to these two technologies, the second-generation Tsinghua furnace that utilizes water-cooled wall gasification technology based on water-coal slurry takes full advantage of all the benefits of water-coal slurry refractory bricks and dry-powder water-cooled wall technology, while simultaneously avoiding their shortcomings. It represents a coal gasification technology with independent intellectual property rights in China, one that surpasses international advanced levels in this field. With the widespread use of this Tsinghua furnace in the petrochemical industry, it will further promote the development of China’s coal chemical industry, enabling the country to occupy a leading position in coal gasification technology. II. The development history of the Tsinghua furnace: Starting in 2001, Tsinghua University and Beijing Dali Ke Technology Co., Ltd. began preliminary research and development work on gasification technology. In 2011, Yingde Gas Group, the largest independent industrial gas supplier in China, took over the responsibilities previously held by Beijing DaliKe Technology Co., Ltd. It established a new industry-university-research alliance for the Qinghua Furnace, and founded Beijing Yingde Qingda Technology Co., Ltd. This company is responsible for the exclusive operation of the gasification technology related to the Qinghua Furnace, and it works together with Tsinghua University on the research and development as well as promotion of subsequent technologies associated with this furnace. The Department of Thermal Engineering at Tsinghua University has long been committed to research and development in the fields of coal combustion, coal gasification, and clean coal technologies. It has undertaken numerous **key scientific and technological research projects**, as well as projects funded by the National Natural Science Foundation, the 863 Program, and the 973 Program. As a result, it has achieved many important results that are leading domestically and reach international advanced levels. With the support of the **863 Program (2002AA529050), in 2002 research on the model of the first-generation Tsinghua furnace, experiments on the cold-flow field, numerical simulations, and experiments on hot-state simulation were completed, and some technical challenges in the industrialization process were resolved. Innovatively, the concept of staged air supply widely used in the combustion field and the structural design of vertical cyclone furnaces were applied to coal gasification, overcoming the key technical challenges in this field and breaking the foreign monopoly on fluidized bed coal gasification technology; as a result, patents for coal gasification with independent intellectual property rights were developed. A complete set of experimental methods for the research and development of gasification technology has been established, resolving the key switching technology for staged oxygen supply ； Theoretical and experimental studies were conducted on the combustion of an oxygen jet in flammable gases under a strongly reducing atmosphere, addressing the key technical issues related to back-flame combustion of the oxygen jet ； The parameters describing the effect of pressure on the kinetics of the carbon-steam gasification reaction under pressurized conditions were corrected, thereby establishing a more complete and reliable overall kinetic model for gasifiers ； Further improved the coal variety adaptability of the water-coal slurry gasifier ； Design guidelines and process design packages for the oxygen-staged gasification process were developed. Yingde Gas Group has a team of senior engineering and technical personnel with extensive experience in chemical engineering design and operation. They have been engaged in the development of chemical technologies and processes as well as in production operations for a long time, possessing rich experience in chemical engineering design, operation, and relevant technical expertise in the fields of chemistry and coal gasification. Beijing Yingde Qingda Technology Co., Ltd., established by Yingde Gas Group and Tsinghua University, has been authorized by Tsinghua University to be the exclusive operator of the Tsinghua furnace gasification technology. It is responsible for the design of process schemes for the Tsinghua furnace as well as providing technical support and improvements for the engineering implementation, thereby addressing various engineering issues that arise during the industrialization process. Large-scale industrial units utilizing the first-generation refractory brick gasification technology of the Tsinghua furnace (a non-slag/slag hierarchical gasification technology) have been put into operation at Datang Hulunbuir (Project 18/30), Ordos Jinchengtai Chemical Co., Ltd. (the first phase involving a 600,000-ton methanol production facility), and Shanxi Yangquan Fengxi Fertilizer Industry (Group) Linyi Branch. To date, all three units have been operating stably. In December 2007, the first-generation Tsinghua furnace technology underwent an evaluation by the China Petroleum and Chemical Industry Association; it was deemed to have reached an internationally advanced level. In 2009, this technology was recognized by the China Nitrogen Fertilizer Industry Association as a technology to support the development of the industry, and it won the first prize for scientific and technological progress from the Petrochemical Industry Association in that same year. 　 The 180,000-ton/year ammonia and 300,000-ton/year urea project of Datang Hulunbuir Fertilizer Co., Ltd. utilizes the first-generation Tsinghua coal gasification technology. The project involves the construction of two gasification furnace systems operating at 4.0 MPa with a diameter of 2,800 mm, along with supporting systems for coal slurry preparation and slag water treatment. The Datang Hulunbuir (Project 18/30) uses local lignite from Hulunbuir as the coal feedstock for gasification. Compared to bituminous coal and anthracite, lignite has a lower price and higher reactivity, but its calorific value is relatively low and its moisture content is high, typically ranging from 25% to 60%. 　　In order to make better use of China’s lignite resources, in recent years various coal gasification technologies such as fixed-bed gasification, fluidized-bed gasification, and pulverized coal gasification – both domestically and internationally – have been employed in numerous practical projects for the utilization of lignite. However, all these coal gasification technologies require some degree of pre-treatment of the lignite before it is fed into the furnace, and they involve high investment costs. In particular, some of these technologies consume large amounts of fresh water and generate significant amounts of wastewater, posing considerable environmental challenges for coal chemical projects. 　 For many years, the petrochemical industry has been seeking a technology that can be used to apply lignite in coal chemical processing at low cost, with high efficiency and in an environmentally friendly manner. It was not until 2012 that a successful application of the first-generation Tsinghua furnace gasification technology brought hope to people. In June 2012, at Datang Hulunbuir Fertilizer Co., Ltd., the world’s first lignite water-coal slurry gasification plant was successfully fed with feedstock on the very first attempt. And in January 2013, successful 240-hour parallel operation of the two brown coal gasifiers was achieved. At the end of 2015, Datang Hulunbuir Fertilizer Company received yet more good news: the world’s first lignite water-coal slurry gasification unit, Project 18.30, achieved full operational capacity ahead of schedule! 　 In the water-coal slurry fluidized bed gasification technology that preceded Tsinghua’s furnace gasification technology, when lignite was used as the raw material, its high moisture content made it difficult to form a slurry; the concentration of the resulting coal slurry was not high, typically around 53%. Traditional views at that time held that coal slurries with a concentration lower than 58% could not be used in this gasification technology. However, at Datang Hulunbuir Fertilizer Co., Ltd., the Tsinghua coal gasification unit operates stably; it utilizes the lignite resources of Hulunbuir City as its basis and employs lignite from Dongming Mine as the gasification feedstock. The coal slurry concentration ranges from 46% to 51%. Having been in successful operation since its commissioning in June 2012, it demonstrates significant progress made by Tsinghua’s coal gasification technology in the development and utilization of low-concentration water-coal slurry, represented by lignite. It serves as an important engineering example, providing a viable path for China to utilize advanced and environmentally friendly coal gasification technologies to process difficult-to-treat lignite resources. 　 The results achieved by Tsinghua furnace technology in the application of lignite have attracted the attention of more companies in the industry. In July 2013, the 1.35 million tons per year synthetic ammonia production project of Inner Mongolia Wulantai’an Energy and Chemical Co., Ltd. opted for the second-generation Tsinghua furnace technology (water-cooled wall gasification technology using coal slurry). This project utilizes lignite available locally in Xingan League as raw material, with a coal slurry concentration of 53%. Before launching the construction project, Ulan Tai’an Energy and Chemical Co., Ltd. spent nearly four years on technical selection, conducting technical and economic evaluations of more than a dozen gasification technologies from home and abroad. It was ultimately determined that the Tsinghua furnace is the most suitable gasification technology for the lignite in Xingan League. Also in 2013, the 200,000-ton per year ethylene glycol production project of Xinjiang Tianye Company, as well as the 1,4-butanediol project of Xinjiang Guotai Xinhua Mining Co., Ltd., chose Tsinghua furnaces as the gasification technology for production; they used Xinjiang lignite with a slurry concentration of 53%. The application technology of low-concentration water-coal slurry has now become a trump card for the second-generation Tsinghua boilers to gain a foothold in the market. In 2005, Tsinghua University began research and development on the second-generation Tsinghua furnace. The water-coal slurry water-cooled wall technology used in this second-generation furnace features a combustion chamber with a water-cooled wall structure; the internal components of the gasifier itself constitute a membrane-type water-cooled wall, which is installed within the pressure-bearing shell of the entire gasifier. During the operation of the gasifier, the layer of ash that solidifies on the membrane wall in the gasification reaction zone can protect the water wall, preventing the water wall tubes from being eroded by molten slag, thereby achieving an effect of using slag to counteract slag. On August 22, 2011, the world’s first water-cooled wall coal-water slurry gasifier was successfully commissioned at Shanxi Yangmei Fengxi Fertilizer Industry. It entered stable operation right from its first operation, fully fulfilling the objectives of its research, development, and design. The planned maintenance on January 9, 2012, led to a miracle in the coal chemical industry: the first time that the plant operated safely, stably, and continuously for 140 days. On September 3, 2012, the China National Petroleum and Chemical Industry Federation organized relevant experts in Beijing to hold an appraisal meeting for the scientific and technological achievement of the “Qinghua furnace coal-water slurry gasification technology with water-cooled walls”. Tests conducted over 72 hours of continuous operation showed that the device operates smoothly, features a high level of automation, is safe and reliable, and has good control performance ； Lower investment and operating costs, with good adaptability to different coal types ； The entire device utilizes independently developed Chinese technology and domestic equipment, with a localization rate of 100%. The test results met the design specifications: specific oxygen consumption of 404.3 Nm3 O2/1000 Nm3 (CO+H2), specific coal consumption of 605.0 kg coal/1000 Nm3 (CO+H2), effective content of syngas (CO+H2) at 78.46%, and carbon conversion rate of 97.6%. The appraisal committee concluded that this gasifier technology is highly innovative and possesses independent intellectual property rights. It also combines the advantages of both water-coal slurry refractory bricks and dry powder water-cooled wall gasifiers; thus, it exhibits excellent overall performance. The technology brings notable economic and social benefits, and its overall level ranks among the world’s best. Therefore, the committee unanimously agreed to approve this technology for certification. In terms of feed methods, the high-pressure entrained flow gasification technology can be divided into two types: coal water slurry feeding (wet process) and dry powder feeding (dry process). The wet coal slurry feeding method features stable and reliable flow delivery, ensuring that the oxygen-to-coal ratio in the gasifier remains within a controllable range, thereby guaranteeing the stable operation of the gasifier. Dry feeding makes use of high-pressure dense-phase conveying; the flow of pulverized coal is unstable, which can easily lead to an imbalance in the oxygen-to-coal ratio inside the gasifier, affecting the safety of its operation. At the same time, wet feeding enables high-pressure operation, with mature commercial units for gasification systems operating at pressures of 4.0 MPa, 6.5 MPa, and 8.7 MPa. At present, the maximum pressure in dry powder feed gasifiers is only 4.0 MPa. Increasing the pressure in the gasification system can reduce the size of the equipment, lower the energy consumption during system operation, and enable isobaric synthesis in chemical processes. From a protective structure perspective, gasifiers can be divided into refractory bricks and water-cooled walls. With the water-cooled wall structure, the operating temperature of the gasifier can reach 1500°C or higher, thereby **expanding the gasifier’s adaptability to various coal types and reducing the raw material costs for operation. The operating temperature of a refractory brick gasifier must not exceed 1400°C. The successful development and commissioning of the second-generation Tsinghua furnace – the slurry-cooled wall Tsinghua furnace – have fundamentally resolved the stability issues associated with dry-feed cooled-wall gasifiers, as well as the problems related to coal variety compatibility in wet-feed refractory-brick gasifiers ； The gasification of \"high-carbon, high-ash, and high-sulfur\" coal was achieved, enabling the use of locally sourced coal for gasification and reducing the cost of coal fed into the furnace ； At the same time, the technical characteristics of the water-cooled wall gasification technology for water-coal slurry are in line with the current trend toward the clean and efficient utilization of coal. In 2012, the coal water slurry water-cooled wall Tsinghua furnace gasification technology was included in the Ministry of Industry and Information Technology’s \"Implementation Plan for the Promotion of Advanced Gasification Energy-saving Technologies\". In 2015, the Ministry of Industry and Information Technology and the Ministry of Finance jointly issued the \"Action Plan for Clean and Efficient Utilization of Coal in the Industrial Sector (2015–2020)\\", and the Tsinghua furnace with water-cooled walls for coal slurry was included among the 21 reference technologies for efficient coal utilization in industrial applications. III. Principle of Tsinghua Furnace Gasification Technology: The Tsinghua Furnace gasification technology uses coal as a raw material, and pure oxygen as a gasifying agent to carry out high-temperature partial oxidation reactions in a gasification furnace. This process produces process gas whose main components are CO and H2. After being cooled in a water bath and washed in a scrubber tower, the clean process gas is sent to downstream units as feed gas. The water-coal slurry gasification process is a non-catalytic partial oxidation process. High-purity oxygen and coal water slurry are mixed using a specially designed combustion nozzle and then injected into the gasifier, where they undergo partial oxidation reactions under high temperature and pressure to produce crude gas containing CO and H2 as its main components. The main reactions occurring in the gasifier between the coal slurry and oxygen are as follows: CmHnOsr + m/2 O2 → m CO + (n/2 – r) H2 + r H2S; CmHnOsr → (m/4 – r/2) CH4 + (m – n/4 + r/2) C + H2S; C + O2 → CO2 + Q; C + O2 → CO + Q; CO + O2 → CO2 + Q; C + CO2 → 2 CO – Q; C + H2O → CO + H2 – Q; CO + H2O → H2 + CO2 – Q; CO + H2O → CO2 + H2 + Q; CO + H2 → CH4 + H2O + Q; CO + H2 → CH4 + CO2 + Q; CO2 + H2 → CH4 + H2O + Q; C + H2 → CH4 + Q; H2 + O2 → H2O + Q; CH4 + O2 → CO2 + H2O + Q. There are three main reactions taking place in the gasifier: the oxidation of carbon, the decomposition of water vapor, and the reduction of carbon dioxide. The oxidation of carbon releases a large amount of heat, which is used to sustain the other two endothermic reactions as well as to maintain the high temperature inside the gasifier. The products of the gasification reaction are mainly CO + H2, along with small amounts of gases such as H2O(g), CO2, H2S, CH4, and N2. A fluidized bed is a reactor for gasification with co-current flow of two phases. The coal slurry and gasifying agent are uniformly mixed, then atomized through a special nozzle into the reaction chamber, where they ignite instantaneously, resulting in a flame reaction at temperatures ranging from 1300–1700°C. Oxygen and water-coal slurry are mixed through a nozzle and then enter the gasifier, where gasification occurs within a few seconds. To achieve a high conversion rate, partial oxidation is employed to release energy, keeping the gasifier at a temperature above the melting point of coal ash for the reaction to occur. The reaction temperature is determined based on the requirements of the coal type selected, while the gasification pressure is set according to the needs of the process. The gasification reaction occurs very rapidly; solids remain in the furnace for only a few seconds on average. The crude syngas produced as a result of this reaction contains little methane, usually less than 0.1%, whereas the conversion rate of carbon is as high as 98%. Due to the high reaction temperature, no condensable by-products such as tar, phenol, and higher hydrocarbons are formed, resulting in less environmental pollution and lower wastewater discharge. The gasification process is divided into three parts: the pulp preparation stage, the gasification stage, and the ash water treatment stage. Raw coal, water, and a small amount of additives are ground in a coal mill to produce a coal slurry with a concentration of 58–65%. Under the action of high-pressure coal slurry pumps, this slurry is fed through a process burner into the water-cooled wall gasifier ； The oxygen supplied from the air separation unit enters the gasifier through process burners; the coal slurry and oxygen undergo a gasification reaction within the gasifier. The syngas and slag produced are cooled and washed in a quench chamber located at the bottom of the gasifier. The cooled syngas then enters the washing and purification system via syngas pipelines ； The cooled slag is regularly discharged into the slag pool through lock hoppers and slag discharge pipelines; the black water containing fine slag enters the slag treatment system, where it is processed before being returned to the system for reuse. Figure 1 – Schematic diagram of the pulp preparation process. Figure 2 – Schematic diagram of the gasification process: http://ydqd.yingdegas.com/chinese/DataBase/UploadFile/20160808091722822.jpg Figure 3 – Schematic diagram of the ash water treatment process. IV. Technical features of the Tsinghua furnace with water-cooled walls for water-coal slurry use. 4.1 High safety level: The use of water-coal slurry as feed material ensures safe and reliable operation, avoiding problems such as instability in pulverized coal feed, flammability, explosiveness, and wear-related leaks. The water wall adopts the mature suspended vertical tube structure used in the field of thermal engineering, which ensures the safety of water circulation while avoiding complex thermal expansion issues. The water circulation is designed for natural circulation operation, with forced circulation as an alternative; in the event of an accident, it can switch to natural circulation to ensure the safe operation of the water wall to the greatest extent possible. 4.2 Strong adaptability to different coal types: The gasification temperature is not restricted by refractory materials; in actual industrial operations, temperatures of up to 1520°C (or even higher) have been achieved. The gasification reaction proceeds rapidly, with a high carbon conversion rate. It has good adaptability to various coal types, allowing it to handle coals with high ash content, high ash fusion point, and high sulfur content. This facilitates the local production of gasified coal. 4.3 High system operational efficiency: The unit operates continuously and stably. The burner head has been specially treated, ensuring a continuous operating cycle of over 120 days; there is no need to shut down the plant for repairs due to the replacement of refractory bricks, allowing an annual operating time of up to 8,000 hours. 4.4 Environmentally friendly and eco-efficient: The reaction temperature is relatively high, resulting in a low residual carbon content. No condensable by-products such as tar, phenols, or higher hydrocarbons are generated. Therefore, it causes minimal environmental pollution, produces less wastewater, which is easy to collect and treat ； Meanwhile, the pulping section can utilize various types of hard-to-treat organic wastewater. 4.5 Fast system startup: The combined ignition and heating process is simplified, with ignition and feeding procedures being carried out in one integrated step. The feeding and ignition of water-coal slurry utilize a unique \"fire ignition\" technology, allowing the gasifier to reach full capacity in just five hours from a cold state. 4.6 Energy savings: The gasification pressure is high, and it is not affected by the raw material delivery system; thus, a more appropriate choice can be made based on the requirements of subsequent processing stages. This allows for synchronization with the pressure in methanol synthesis, thereby reducing energy consumption. It is capable of processing coal with high ash content, high ash fusion point, and high sulfur content; it facilitates the local production of gasification coal, reduces transportation costs, and increases the value of the coal by several times ； It reduces the need to replace refractory bricks, saving over 3 million yuan in replacement costs each year ； 4.7 Investment savings: The gasification unit is 100% domestically produced. Compared to other pressurized coal gasification technologies currently in operation in China, it reduces investment costs by 30–50%. 4.8 Technical details are well handled: In the industrialization process of Tsinghua Furnace gasification technology, there have been many innovations in detailed design. For instance, the gas distributor at the bottom of the scrubber ensures thorough mixing of ash water and coal gas, thereby guaranteeing the effectiveness of coal gas scrubbing ； The annular groove distributor in the flash tank is designed to facilitate maintenance of the flashing system ； The liquid seal design for vacuum flash evaporation prevents the flash tank from getting clogged, and these detailed improvements enable the vaporization system to operate stably over long periods of time. V. Successful promotion of the Tsinghua furnace’s slurry water-cooled wall technology: The coal gasification technology used in the Tsinghua furnace represents a new achievement resulting from the integration of thermal engineering and chemical engineering principles. This type of gasifier with a slurry water-cooled wall exhibits good adaptability to different types of coal, enabling the use of local coal sources and thereby reducing raw material costs. It offers an innovative approach for the cleaner utilization of coal, allowing make use of the abundant resources of high-calorific, high-carbon, and high-ash content coals. Based on a gasifier with a daily coal input of 1,000 tons, a reduction of 100 yuan per ton in the price of raw coal results in cost savings of over 30 million yuan per year for each such gasifier in terms of raw coal expenses. By replacing refractory bricks with water wall tubes, the maintenance costs for refractory bricks are reduced. The service life of refractory bricks is usually around 1.5 years, and the cost of replacing them each time is approximately 2 million yuan. If the service life of the water wall is considered to be 10 years, overall calculations show that maintenance costs can be saved by over 1 million yuan per year. Compared with gasifiers using refractory bricks, the water-cooled wall gasifier for water-coal slurry offers significant economic and social benefits after operation. Coal gasification is one of the key technologies for the clean conversion of coal. The water-cooled wall Tsinghua furnace for coal slurry features a wide range of coal compatibility, high gasification efficiency, low pollution emissions, high efficiency and cleanliness, as well as stable operation. Compared with other similar technologies, it offers advantages such as lower investment costs and higher availability rate. Thus, it provides coal chemical enterprises with a new type of coal gasification technology that requires less investment and results in lower operating costs, enhancing the competitiveness of these enterprises in the market. It also contributes to the development of the local economy, helps protect the ecological environment, and plays a positive role in boosting the local economy and increasing fiscal revenue, offering significant social benefits. By taking advantage of the structural features of the water-cooled wall Qinghua furnace for coal-water slurry, it is possible to easily modify existing gasification furnaces equipped with coal-water slurry refractory bricks, which provides broader prospects for the promotion and application of such water-cooled wall Qinghua furnaces. Tsinghua furnace gasification technology was developed for the cleaner utilization of coal, and it has blazed a trail of innovation by making use of the abundant coal resources characterized by high calorific value, high ash content, and high sulfur content. The second-generation water-cooled wall gasification technology using water-coal slurry has been put into operation at Yangmei Fengxi in Shanxi, Tianye in Xinjiang, and Yangmei Jishan. Contracts have also been signed with more than a dozen companies, including Shijiazhuang Yingding, Weifang Yingde Company, Karamay Yingde Company, CNOOC Tianye Chemical Co., Ltd., Jiangsu Debang Xinghua Chemical Technology Co., Ltd., Shandong Jincheng Chemical Technology Co., Ltd., Hebei Zhengyuan Chemical Group Company, Yangquan Coal Industry (Group) Co., Ltd., and Xingan League Wulantai’an Energy and Chemical Co., Ltd. Currently, technical upgrades to the water wall systems in the water-coal slurry refractory brick furnaces at Xinsheng Coal Chemical Co., Ltd. of Guizhou Shuicheng Mining Group, Haolianghe Branch of Heilongjiang Beidahuang Agriculture Co., Ltd., and Anhui Huaihua Northwest Energy Chemical Company are underway. This will provide broader prospects for the promotion and application of the Tsinghua furnace technology with water-cooled walls for water-coal slurry. The Xinjiang Tianye project with an annual production capacity of 200,000 tons of ethylene glycol is constructed on a scale featuring an effective synthesis gas (CO+H2) output of 120,000 Nm3/h in the production area. The gasification unit employs the Tsinghua furnace gasification technology with water-cooled walls for coal slurry; the gasifier operates at 6.5 MPa and has a diameter of 2800 mm, and it is designed as a double-unit setup without a backup unit. The designed production capacity of each individual gasifier is 1500 t/day in terms of coal input. Using local lignite from Xinjiang, the slurry formation concentration when using lignite alone is 53%; by adding coke dust, this concentration can be increased to over 58%. Figure 4: Two Tsinghua-type gasification units at Xinjiang Tianye. Coal type used for operation: Shenhua coal. Industrial analysis values: Moisture content – Marwt%: 24.4; Ash content – Adwt%: 6.56; Volatile matter content – Vdwt%: 30.99; Fixed carbon content – FCdwt%: 62.45. Elemental analysis values: Carbon content – CCdwt%: 75.71; Hydrogen content – HHdwt%: 3.7; Nitrogen content – NNdwt%: 0.54; Sulfur content – SSdwt%: 0.58; Oxygen content – OOdwt%: 12.91; Chlorine content – CLCldwt%: 0.014; Arsenic content – AsAsdug/g: 0.35. Lower heating value – Qnet.ar MJ/kg: 20.01. Grinding index – HGI/100. Ash fusion temperature – DT°C: 1250; Softening temperature – ST°C: 1280; Flowing temperature – FT°C: 1300. Concentration of slurry produced using conventional slurry preparation methods – %: 53.04. Apparent viscosity of conventional coal slurry (100 s^-1, 25°C) – mPa·s: 954. Table 1: Specifications of the lignite used as raw material by Xinjiang Tianye. In August 2015, the first Tsinghua-type furnace equipped with a water-cooled wall for coal slurry processing at Xinjiang Tianye was successfully commissioned after just one week of operation, and all subsequent processes were put into operation as well. By October 2015, the two Tsinghua-type furnaces were operating in parallel, producing more than 120,000 Nm3/h of useful gas. As of March 2016, the gasifier had been in continuous operation for over 100 days, achieving the design goal of stable, long-term, and efficient operation. Key technical parameters: Slurry concentration: 58% (with 40% coke dust); effective gas composition: CO+H2≥78%; specific oxygen consumption: ≤420 Nm3/1000 Nm3 (CO+H2); specific coal consumption: ≤620 kg/1000 Nm3 (CO+H2); carbon conversion rate: ≥98%; combustible content in slag: ≤5%. To date, the water-cooled wall Tsinghua furnace for coal-water slurry has achieved successful industrial operation over long periods of time at Xinjiang Tianye. Through its successful operation at Xinjiang Tianye, the Tsinghua furnace has achieved a comprehensive energy consumption level that is among the best in China for the gasification of brown coal in Xinjiang. VI. Development prospects of Tsinghua furnace gasification 1. Renovating the outdated production capacity of small and medium-sized nitrogen fertilizer enterprises. Traditional coal chemical industries mostly use atmospheric pressure fixed-bed gasification technology, which is characterized by high energy consumption, high emissions, high pollution, and low efficiency – what is commonly referred to as the \"three highs and one low\". Under the multiple pressures of \"three highs and one low,\" it is imperative to adjust the structure of traditional coal chemical industries and pursue industrial upgrading; currently, over 500 enterprises in China that use fixed-bed gas generation technologies are facing the need for such upgrades. Moreover, the pressurized coal gasification furnace is difficult for small and medium-sized nitrogen fertilizer companies, which already face operational challenges, to adopt due to its high investment costs. Therefore, the low-cost water-cooled wall Tsinghua furnace gasification technology using water-coal slurry will become the preferred technology for many such companies as well as gas production facilities. Compared to fixed-bed gas generation, by changing the type of raw coal used and reducing consumption, the cost per ton of ammonia can be reduced by more than 500 yuan; for a plant with an annual production capacity of 200,000 tons of synthetic ammonia, this can result in annual cost savings of 100 million yuan. By adopting water-cooled wall Tsinghua furnace gasification with water-coal slurry, it is not only safe and environmentally friendly with a long operation cycle, but also reduces investment and operating costs. This will greatly improve the production efficiency of enterprises, help protect the ecological environment, and contribute to the development of the local economy and the increase in local fiscal revenue, thus bringing about positive social and economic benefits. 2. The overall gasification technology in modern coal chemical industry: Coal chemical projects generally feature high coal consumption, large water usage, and significant emissions of wastewater, waste gases, and solid waste. Among the \"three wastes\" emitted in coal chemical industries, there are many harmful components, making their treatment difficult. For example, in the case of coal-to-natural gas production, aside from water-coal slurry gasification, if fixed-bed and fluidized-bed gasification methods are used, wastewater treatment poses a significant challenge; it has even been included in the **\"863\" science and technology research program. Although there are many wastewater treatment processes for coal chemical industry in China at present, their operational performance is generally unstable, let alone achieving \"zero discharge\". Due to the difficulties in solving wastewater treatment issues, several coal chemical projects in the country have seen their commencement or operation repeatedly delayed. 　　At present, in China, for gasification technologies other than water-coal slurry gasification – such as the Lurgi furnace, BGL furnace, Space furnace, GSP furnace, SHELL furnace, and Endress furnace – steam must be added during the gasification process. The water required for this steam needs to be desalinated; fresh water is processed to produce boiler water, and the utilization rate of water is less than 80%. In water-scarce regions such as Inner Mongolia and Xinjiang, where the water contains a high level of salts, the utilization rate of water is even lower. In the context of increasingly stringent environmental regulations and growing water scarcity, wastewater treatment and water conservation requirements are likely to become one of the key factors determining the success or failure of a coal chemical project. 　　In terms of dry powder gasification technology, during the coal powder preparation process, fuel gas or other media are used to remove the excess moisture from the coal, with a drying level of around 2% being generally required. This amount of water is especially precious in areas with scarce water resources such as Inner Mongolia and Xinjiang, yet there is still no method for its recovery to date. To maintain the dryness of the coal powder pipeline, steam tracing is required for the coal powder transfer pipeline; some of the condensate cannot be recovered, resulting in waste. 　 In Tsinghua furnace gasification, most of the water is added in the form of coal water slurry; there are no special requirements regarding the moisture content of the coal, and the quality of the water used for this purpose is not very stringent. Generally, untreated organic wastewater is used for slurry preparation, which offers environmental benefits. Dry powder gasification involves removing the excess moisture from the coal, after which the required amount of moisture is added gradually. The moisture needed in the gasification furnace must be supplied in the form of high-pressure superheated steam, while the water required in the conversion stage must be supplied as superheated steam or boiler water. Therefore, compared with Tsinghua furnace gasification, dry powder gasification requires higher quality water and a larger amount of water than coal water slurry gasification. Regarding the currently popular coal-to-natural gas projects, it is generally believed that the Ruhr process involves 8% to 12% methane, making it economical to produce coal-to-natural gas. However, the Ruhr process can only utilize lump coal with a size of 8 mm to 50 mm; a large amount of fine coal generated during coal mining cannot be used, and the process produces large quantities of phenol-containing wastewater that is difficult to treat. The water-coal slurry gasifier uses semi-enclosed coal feeding, wet coal grinding, and fluidized bed gasification, resulting in minimal pollution throughout the process. Neither gasification nor conversion requires steam; the coal slurry can be prepared using alcohol-containing wastewater, and the amount of waste water generated is low. The pollutants present in this wastewater are limited in number, with a COD level of only 200–760 mg/L, making it easy to treat through biological methods. By utilizing the water-cooled wall Tsinghua furnace gasification technology for water coal slurry, first of all, the pulverized coal generated during coal mining can be utilized ； Second, the difficult-to-treat wastewater generated by the Lurgi furnace can be treated ； Third, it can save some investment in wastewater treatment ； Fourth, it can help reduce the operating costs of some wastewater treatment facilities. 　　Therefore, for specific coal-to-natural gas projects, experts recommend that an equilibrium should first be established between lump coal and pulverized coal, based on the caking degree of the raw coal and the amount of pulverized coal used. If there is still excess pulverized coal after this balancing process and no other way to utilize it, the gasification unit should adopt a dual-furnace configuration that relies primarily on fixed-bed gasification technology, with Tsinghua furnace gasification technology as a supplementary option. At the same time, it is necessary to balance the amounts of fresh water and wastewater in order to enable their recycling. 　 VII. Conclusion: The competition in the world today boils down to a struggle for energy resources. Experience is the best teacher; China currently has over 1,000 boilers of various types, which means it possesses a wealth of experience and lessons learned. Coal gasification is the key technology for the clean conversion of coal, and its selection, as well as its stable, efficient, and economical operation, are crucial to the success or failure of a project. The successful operation of the water-cooled wall gasification technology for water-coal slurry has opened an innovative path for the clean development and utilization of abundant \"high-carbon, high-sulfur, and high-ash\" coal resources. It has significantly enhanced China’s influence and speaking power in the field of coal gasification worldwide, providing strong technical support for the efficient and green use of coal itself.