Types of vaporization furnaces

According to statistics, there seem to be over 50 types of gasification furnaces, which can be said to be widespread

I. Advantages and Disadvantages of Various Coal Gasification Processes In China, there are coal gasification technologies that have been industrialized, for which demonstration units have been established or pilot plants have been tested; there are also those based on technology imported from abroad, as well as technologies with independent intellectual property rights developed in China. These include atmospheric-pressure fixed-bed batch coal (or coke) gasification technology, atmospheric-pressure fixed-bed oxygen-enriched continuous coal (or coke) gasification technology, Lurgi fixed-bed pressurized coal gasification technology, ash-polymerized fluidized-bed pulverized coal gasification technology, Endel bubbling-bed (Winkler) pulverized coal gasification technology, GE Texaco slurry pressurized coal gasification technology, multi-feedstock slurry pressurized coal gasification technology, multi-nozzle (four burners) slurry pressurized coal gasification technology, Shell dry coal powder pressurized coal gasification technology, GSP dry coal powder pressurized coal gasification technology, two-stage dry coal powder pressurized coal gasification technology, and four-nozzle opposed dry coal powder pressurized coal gasification technology. Essentially, all the coal gasification technologies available abroad are present in China, as well as those that do not exist abroad. There are many gasification process technologies, making it difficult to decide on which one to use. First of all, we cannot simply believe the claims made by patent holders; there is no universal gasification furnace in the world yet. Various gasification technologies have their own characteristics and advantages and disadvantages, as well as specific areas of application. The promotion of patent holders should involve filtering out the irrelevant and false information to retain only what is genuine. Only those solutions that have withstood the test of long-term, stable and high-level production in practice, and that are economically viable while also complying with environmental standards and local environmental regulations, can be considered reliable. Below are the advantages and disadvantages of these technologies respectively. 1. Atmospheric pressure fixed-bed batch coal (or coke) gasification technology: This is one of the main methods used in China for producing nitrogen fertilizers. It features the use of air and steam at atmospheric pressure for batch gas production; the raw material required is coal or coke in the form of lumps with a size of 25–75 mm. This method results in low utilization efficiency of the incoming raw materials, high energy consumption, complex operation procedures, low gas production per furnace, and serious air pollution due to the need for blowing air and releasing gases. From a developmental perspective, it is a process that will be phased out gradually. 2. Oxygen-enriched continuous gasification technology using atmospheric-pressure fixed-bed anthracite (or coke). This technology evolved from batch gasification; it features the use of oxygen-enriched gas as the gasifying agent and continuous gasification. The raw material can be anthracite or coke with a particle size of 8–10 mm, which improves the utilization rate of the incoming raw materials. It causes no pollution to the atmosphere, requires less maintenance work, results in lower maintenance costs, and is suitable for areas where anthracite is available. It represents an improvement over existing atmospheric-pressure fixed-bed batch gasification technologies. 3. Luchi fixed-bed coal pressure gasification technology is mainly used for gasifying lignite, as well as coal that is non-caking or weakly caking. It requires the raw coal to have high thermal stability, good chemical activity, a high ash fusion point, and high mechanical strength; it is suitable for producing city gas and fuel gas. Since the gas produced contains tar, with a hydrocarbon content of around 1% and a methane content of about 10%, and since the separation of tar and the treatment of phenol-containing wastewater are quite complex, it is not recommended for use in the production of syngas. 4. Ash fusion fluidized bed coal gasification technology: The Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences, began researching this technology in the 1980s. In 2001, an industrial demonstration unit with a single furnace capable of producing 20 Kt of synthetic ammonia per year was put into operation, marking the realization of industrial application for this technology. Its advantages include wide adaptability to different types of coal – coal with particle sizes of <6–8 mm can be used – and it operates as a fluidized bed gasifier. The temperature of the bed layer reaches around 1100°C, while the central jet creates localized high-temperature areas within the bed with temperatures reaching 1200–1300°C. The coal ash does not melt; instead, it fuses together to form spherical or lump-shaped residues that are then discharged. The bed temperature is 100–200°C higher than that in an Ends gasifier. It can gasify lignite, bituminous coal and anthracite with low chemical reactivity, as well as petroleum coke. Additionally, it requires relatively low investment and has low production costs. The disadvantages are that the gasification pressure is at normal and low levels. Long-term operation tests at a pressure of 1.0 MPa were completed in December 2007, enabling the acquisition of operational experience. It is a Φ2400 gasification furnace with a coal feeding rate of 500–600 t/d. The operating pressure is still relatively low; further tests are needed to increase the gasification pressure. Currently, the gasification capacity per furnace is low, and the CH4 content in the product gas is high (1.5–2%). Although measures have been taken to recycle fly ash into the furnace for gasification, a significant amount of fine ash is still discharged from the second cyclone separator. Issues related to environmental pollution, as well as the storage and comprehensive utilization of fly ash, still need to be addressed further. This technology is suitable for small and medium-sized nitrogen fertilizer plants to change their raw material sourcing by utilizing local or nearby coal resources. 5. Ende powder gasification technology: The Ende furnace is essentially an improved version of the Winkler bubbling-bed gasifier, and it is suitable for gasifying lignite and long-flame coal. The raw coal used should be non-caking or weakly caking in nature, with an ash content of less than 25–30%, a high ash fusion point (ST greater than 1250°C), and good chemical activity at low temperatures (greater than 85% at 950°C and greater than 95% at 1000°C). To date, a total of 13 sets with 22 gasifiers have been built or are under construction in the country, of which 16 have already come online. It belongs to a fluidized bed gasifier, with the temperature in the middle of the bed ranging from 1000 to 1050°C. Currently, the largest gasifier uses oxygen-enriched gasification to produce 40,000 m³/h of semi-water gas. The disadvantages include a vaporization pressure at atmospheric pressure, a relatively low gasification capacity per furnace, a CH4 content in the product gas as high as 1.5–2%, large amounts of fly ash, as well as issues related to environmental pollution and the storage and comprehensive utilization of fly ash that need to be addressed. It is hoped that we won’t follow the same path taken by the Jilin Fertilizer Plant and Lanzhou Fertilizer Plant in terms of environmental pollution. This technology is suitable for small- and medium-sized nitrogen fertilizer plants located near lignite deposits to switch their raw material sources. 6. GE Texaco water-coal slurry pressurized gasification technology: This technology belongs to the category of fluidized-bed pressurized gasification. The raw coal is ground into a water-coal slurry, which is then pumped to a single burner at the top of the gasifier where it is burned to produce gas. The processes of transporting the raw coal, preparing the slurry, and pumping it into the gasifier are much simpler compared to dry-coal pressurized gasification methods such as those used by Shell and GSP; it is also safer, more reliable, and requires less investment. The production capacity per furnace is high; currently, the largest gasifier internationally has a daily coal feed rate of 2,000 tons, while the maximum capacity of gasifiers put into operation in China is 1,000 tons/day. The capacity of the gasifier in the design is up to 1600 t/d. It has a wide range of adaptability to raw coal; bituminous coal, anthracite, sub-anthracite, anthracite, high-sulfur coal as well as low-ash-melting-point inferior coals and petroleum coke can all be used as feedstock for gasification. However, the raw coal is required to have a low ash content, an ash fusion point of less than 1300°C in a reducing atmosphere, and good viscosity-temperature properties for the ash slag. Industrial production units are in stable, long-term operation at vaporization pressures ranging from 2.5 to 8.5 MPa; once built and put into operation, these units can carry out normal and stable production. There are two forms of heat utilization in gasification systems. One is the waste heat boiler type, which can recover the sensible heat contained in the gas to produce high-pressure steam, and it is suitable for combined cycle power generation ； The other type is the water-quenching type; the water-to-gas ratio of the syngas produced in this case is as high as 1.4, making it suitable for the production of chemical products such as hydrogen, synthetic ammonia, and methanol. The gasification system does not require externally supplied superheated steam or N2 or CO2 for transporting the coal feedstock used in gasification. The overall thermal efficiency of the gasification system reaches 94–96%, which is higher than that of Shell dry powder coal gasification (91–93%) and GSP dry powder coal gasification (88–92%). The gasifier has a simple structure and is lined with refractory bricks. There are no rotating components or complex membrane-type water-cooled wall internals in the gasifier, so it is easy to manufacture and inexpensive; no continuous combustion of liquefied gas or fuel gas (syngas) is required during startup, shutdown, or normal operation. Gas dust removal is relatively simple; it doesn’t require costly high-temperature and high-pressure fly ash filters, thus reducing investment costs. The carbon conversion rate reaches 96-98% ； The effective gas components (CO+H2) account for approximately 80-83% ； The oxygen consumption per unit of effective gas (CO+H2) is 336–410 M3/Km3, while the coal consumption per unit of effective gas (CO+H2) is 550–620 Kg/Km3. Abroad, 6 plants with 15 gasifiers have been built and put into operation. In China, 7 plants with 21 gasifiers have been completed and commissioned; additionally, 4 plants with 13 gasifiers are currently under construction or in the design phase. The final products generated by these operational plants include ammonia, methanol, acetic acid, acetic anhydride, hydrogen, carbon monoxide, fuel gas, and combined-cycle power generation. Since their commissioning, all plants have been operating continuously, stably, and for extended periods of time. The localization rate of equipment has exceeded 90%. Given this high localization rate and the relatively low investment costs compared to other pressurized gasification plants, the ratio of construction costs between coal-water slurry pressurized gasification with a standby gasifier and dry pulverized coal pressurized gasification without a standby gasifier is approximately Shell process : GSP process : multi-nozzle coal-water slurry pressurized gasification process : GE coal-water slurry process = (2–2.5) : (1.4–1.6) : 1.2 : 1. China already possesses extensive engineering and technical expertise, and has trained a large number of organizations as well as engineering and technical personnel skilled in this field, covering areas such as design, equipment manufacturing, construction and installation, coal type evaluation, trial firing, and turnkey project management. As a result, the cycle from construction, completion and commissioning to normal, continuous operation is relatively short, which is what project owners desire. The disadvantage is that the raw coal used for gasification is restricted by the refractory brick lining of the gasifier, making it suitable only for coals with a low melting point. The carbon conversion rate is low. The specific oxygen consumption and specific coal consumption are higher. The service life of refractory bricks in gasification furnaces is relatively short, typically 1–2 years; domestically produced bricks last around one year, and there is room for improvement. The service life of the burner in the gasification furnace is relatively short; generally, after 2 months of use, the furnace has to be shut down for inspection, maintenance, or replacement of the burner tip, which is an area that requires improvement. 7. Pressurized gasification technology for multi-component slurries: This technology was developed by the Northwest Institute of Chemical Technology and holds independent intellectual property rights. Its basic production equipment is similar to that of the water-coal slurry pressurized gasification technology, and it belongs to the type of gas generation using a single burner in a fluidized bed. A typical multi-component slurry consists of 60-65% coal, 10-15% oil, and 20-30% water. However, the author believes that the method of adding oil when preparing multi-component slurries does not conform to China’s current policy of substituting coal for oil in the nitrogen fertilizer industry to change the raw material route; thus it is undesirable and needs to be improved. 8. Multi-nozzle (four burner) water-coal slurry pressurized gasification technology: During the “Ninth Five-Year Plan” period, East China University of Science and Technology, Yankuang Lunan Fertilizer Plant, and China Tianchen Chemical Engineering Company undertook the key scientific and technological research project titled “Development of a new type of (multi-nozzle opposed) water-coal slurry gasifier”. It belongs to the gas flow bed type with multiple burners for gas generation, and the gasification furnace is lined with refractory bricks. Following its successful development, a gasification furnace system with a gasification pressure of 6.5 MPa and a daily coal processing capacity of 750 tons was constructed at Shandong Dezhou Hualu-Hengsheng Chemical Co., Ltd. The system was officially put into operation in June 2005 and has been functioning well ever since. Two gasification furnace systems with a gasification pressure of 4.0 MPa and a daily coal processing capacity of 1,150 tons were constructed at Yankuang Guotai Chemical Co., Ltd. in Tengzhou, Shandong. They were successfully commissioned on July 21, 2005, and have been in operation ever since. Upon evaluation and testing, it was found that when using North Star washed coking coal as the feedstock for gasification, multi-nozzle water-coal slurry pressurized gasification yields better performance compared to single-nozzle pressurized gasification. The gasification performance metrics are shown in Table 1. Table 1 compares the results of multi-nozzle gasification and single-nozzle gasification: Parameter – Multi-nozzle gasification – Single-nozzle gasification (Texaco); Effective gas (CO+H2) content/%: 84.9 vs. 82–83; Carbon conversion rate/%: >98 vs. 96–98; Effective gas per unit coal consumption/kg/km3: 535 vs. approximately 547; Effective gas per unit oxygen consumption/m3/km3: 314 vs. approximately 336. Table 2 shows the analysis results of the coal used for gasification. Parameters and their values: Industrial analysis, Element analysis, Ash fusion point/°C, Moisture (Mad)/%/2.18, Total sulfur (Stad)/%/2.84, DT 1090, Ash content (Ad)/%/7.32, Carbon content (Cad)/%/74.73, ST 1100, Volatile matter (Vdaf)/%/45.44, Hydrogen content (Had)/%/5.13, HT 1120, Fixed carbon content (FC)/%/49.46, Oxygen content (Oad)/%/8.77, FT 1130, Nitrogen content (Nad)/%/1.20. Compared to single-nozzle gasifiers, multi-nozzle gasifiers allow for a reduction of about 2.2% in coal consumption and 6.6% in oxygen consumption, which is quite attractive. Adjusting the load simultaneously is more flexible than in a single-nozzle gasifier. Suitable for gasifying coal with a low ash melting point. A total of 11 projects have been completed or are under construction, involving 30 gasifiers. 3 units with 4 gasification furnaces have been successfully put into operation. The coal feeding rate of the largest gasifier under construction is 2,000 t/d at 6.5 MPa. However, the problem that has emerged at present is the relatively rapid wear of the refractory bricks at the top of the gasification furnace ； And for a gasifier with the same diameter and production capacity, its height is greater than that of a GE Texaco single-nozzle gasifier; in addition, there are three more nozzles along with the corresponding high-pressure coal slurry pumps, coal slurry valves, oxygen valves, check valves, cut-off valves, and interlock control instruments. The investment required for a gasifier with a coal feeding rate of 1,000 tons per day is about 20–30 million yuan higher than that of a single-nozzle gasifier system. Compared to a coal gasification plant with 3 gasifiers, each having a coal feeding rate of 1000 t/d and capable of processing 2000 t of raw coal per day, the investment cost increases by approximately 60–90 million yuan. There are also higher annual maintenance costs, in addition to an increase in the fixed costs per unit of product produced. However, this technology is an independent intellectual property right unique to our country; the cost associated with technology transfer is much lower compared to adopting GE’s water-coal slurry gasification technology, making it quite competitive. This technology needs to be further improved and refined in actual production practices. 9. Shell’s dry coal powder pressurized gasification technology: Shell’s dry coal powder pressurized gasification technology belongs to the fluidized bed pressurized gasification technology. Volatile bituminous coal, anthracite, semi-anthracite, petroleum coke, and coal with a high ash fusion point. The coal feedstock used in the furnace is dry coal powder that has been dried and ground. Dry coal powder enters from the lower part of the gasifier; it involves upward gas generation with multiple burners. At present, the largest gasifiers abroad have a capacity to process 2,000 tons of coal per day, with a gasification pressure of 3.0 MPa. There is only one unit abroad that has been used for commercial combined-cycle power generation, and no records exist of systems operating at higher gasification pressures. This gasification furnace uses a water-cooled wall and has no refractory brick lining. A waste heat boiler is used to cool and recover the sensible heat of the gas, generating steam as a by-product; the gasification temperature can reach 1400–1600°C, and the gasification pressure can reach 3.0–4.0 MPa. This allows for the gasification of coal with high ash melting points, but it is still necessary to add limestone to the raw coal as a flux. This type of furnace was originally designed for combined cycle power generation. Since the beginning of this century, 19 gasifier units have been the subject of technology import contracts in China; their end products include synthetic ammonia and methanol, with a gasification pressure ranging from 3.0 to 4.0 MPa. It is characterized by the use of dry coal powder as feed, which is pneumatically conveyed into the furnace using high-pressure nitrogen; strict explosion-proof requirements apply to the coal powder conveying system ； The gasifier burner features multiple nozzles, with 4 arranged symmetrically, allowing for flexible load adjustment ； To prevent the molten and sticky fly ash entrained with the high-temperature gas from adhering to the heat exchange surfaces of the gas transfer ducts and the tube walls of the waste heat boiler downstream of the gasifier, part of the gas at 300–3500°C after high-temperature dust removal is mixed with part of the water-washed gas at 160–1650°C. The temperature of the resulting mixture is approximately 2000°C; this mixed gas is pressurized using a return gas circulation compressor and sent to the top of the gasifier, where it cools the syngas discharged from the gasifier to 900°C before entering the waste heat boiler heat recovery system. The volume of returned gas is quite large, accounting for 80–85% of the gas output from the gasification unit. This places extremely stringent demands on the operating conditions of the recycle gas compression equipment; it not only requires high investment and consumes more energy, but also has many components prone to malfunctions ； The syngas exiting the waste heat boiler is passed through a high-temperature, medium-pressure ceramic filter to remove any entrained fly ash at high temperatures. Such ceramic filters not only require high initial investment but also involve substantial maintenance efforts and high maintenance costs. The maintenance workload for waste heat boilers is also heavy; they experience many malfunctions, and the maintenance costs are high. It is stated that the carbon conversion rate can reach 98-99% ； Gasifiable lignite, bituminous coal, anthracite, petroleum coke ； The efficiency of cold gas is as high as 80-83% ； The effective gas components of syngas (CO+H2) account for around 90%. The consumption of effective gas (CO+H2) is 550–600 Kg/Km3, while the oxygen consumption is 330–360 M3/Km3; when using coal from Xinmi, Henan, the coal consumption is 709 Kg/Km3. The specific oxygen consumption is 367.2 Nm3/Km3. It should be noted here that, for any gasification technology, the specific values of coal consumption and oxygen consumption mentioned in the literature are data obtained under specific conditions. The exact figures can only be determined after testing the coal actually used. When comparing different options, the calculation methods specific to the gasification process can be employed, and evaluations should be based on data related to the same type of coal. ) ； 120-150 Kg/Km3 less than steam consumption ； 880-900 Kg/Km3 of steam can be produced as a by-product. The problem is that the licensor has only one power generation unit abroad, and lacks any track record in coal chemical production ； The gas combined cycle power generation unit (Demkolec) at the Buggenum power plant of Dutch utility Enexis serves as a peak-shaving power plant; in addition to the coal-to-gas power generation system, there is also a fuel oil power generation system as a backup. Therefore, the Shell gasification unit introduced by our country features only one gasifier operating in a single train, with no spare gasifier. Sufficient attention should be paid to whether it can achieve continuous and stable operation throughout the year in coal chemical production. If coal chemical production has to be shut down and restarted frequently as a result, with fewer operating days per year for the plants, the economic losses for those plants will be considerable. The investment in a system that does not use a furnace is 2 to 2.5 times that of a GE Texaco gasification unit or a multi-nozzle coal-water slurry gasification unit that employs a furnace. The high-temperature gas emitted from the gasification furnace is sent to large, expensive waste heat recovery boilers to produce steam via heat recovery; if this steam is to be used in coal chemical processes, it must be fed back into the subsequent carbon monoxide conversion system. However, if it is used for producing synthetic ammonia and hydrogen, the amount of steam generated is not sufficient. At the same time, a separate medium-pressure superheated steam system is also required to supply the superheated steam for gasification. In my opinion, Shell’s dry coal powder pressurized gasification technology equipped with a waste heat boiler is not suitable for coal chemical production at present and requires improvement. Therefore, when choosing a gasification scheme, owners and engineering companies should not rely solely on the opinions of patent holders. Instead, they need to conduct a technical and economic evaluation of the entire project process, taking into account factors such as the investment costs and electricity consumption differences of the air separation system, those of the coal grinding system, those of the coal drying system, those of the coal conveying system, the investment differences between coal preparation and conveying systems, the coal consumption and investment associated with the steam supplied to the gasifier, as well as the investment and energy consumption differences in the carbon monoxide conversion process. Only by considering all these factors can a correct conclusion be reached. In our country, units using the Shell dry coal powder pressurized gasification process have started trial production one after another since 2006; there are already several such units, but they have not yet achieved long-term stable and normal operation. The main reason is the long system process and the complex structure of the equipment. When gasifying coal with high ash content and high ash fusion point. This gives rise to issues such as whether the water wall can be evenly slagged; ash accumulation in the gas transfer pipes at the top of the gasifier and in the waste heat boiler; the dust removal efficiency and capacity of high-temperature and high-pressure dry fly ash filters; what to do with the large amount of fly ash generated daily; the frequent malfunctions of the quench gas compressors; and problems with the black water system used for water washing, cooling, and dust removal. This process was first applied in the chemical industry (especially for the production of synthetic ammonia, methanol, and hydrogen). The requirements regarding dust removal and purification, as well as the need for stable and continuous operation over long periods, are much higher in this sector compared to power generation. For power generation, fuel (or natural gas) generators can be used as a backup; however, in chemical production, a large-scale enterprise relies on just one set of gasification equipment with a complex structure and high demands on its control system, without any backup furnaces, which means that production cannot be guaranteed. For a new set of equipment to move from production initiation to stable normal operation, a running-in period is certainly necessary, but it should not be too long; otherwise, it will be difficult for the enterprise to cope. I believe that improvements can first be made to the raw coal, targeting the source of frequent failures; by using coal with low ash content and low ash melting point as raw material, it is possible to develop strategies for achieving stable and high production over long periods of time. Second is to add a backup gasifier that uses a quenching process. It is difficult to convert an existing Shell furnace to use a quenching process; instead, a gasifier with multiple nozzles for downward gas production should be used, as this is easier to implement. 10. GSP dry coal powder pressurized gasification technology: The GSP dry coal powder pressurized gasification technology belongs to the fluidized bed pressurized gasification category. The raw coal fed into the furnace is dry coal powder that has been dried and ground; this dry coal powder enters from the top of the gasification furnace, and gas production takes place through a single burner in a downward flow pattern. The gasifier is equipped with water-cooled internal components. The largest GSP gasifiers available abroad are capable of processing 720 tons of lignite per day; they operate at a pressure of 2.8 MPa and a temperature of 1400–1500°C. To regulate the furnace temperature, superheated steam must be supplied into the gasifier. There is 6 years of experience (1984–1990) in gasification using lignite as a feedstock. It is reported that when gasifying coal with a high ash fusion point, limestone can be added to the raw coal as a flux. Due to the use of a water quenching process, the investment required is much lower compared to Shell furnaces; the investment ratio between Shell furnaces and GSP furnaces is (1.43–1.56):1. This approach is suitable for coal chemical production. It is reported that the carbon conversion rate can reach 98–99%, and it is capable of gasifying lignite, bituminous coal, subbituminous coal, anthracite, petroleum coke, and tar. The efficiency of cold gas production is as high as 80–83%, with the effective gas composition (CO+H2) accounting for around 90%. The consumption of effective gas (CO+H2) per unit volume of coal is 550–600 Kg/Km3, oxygen consumption is 330–360 M3/Km3, and steam (superheated steam) consumption is 120–150 Kg/Km3. Under normal conditions, liquefied gas or other flammable gases are burned to facilitate ignition, prevent stalling, and ensure safe production. According to available literature, for example, in the case of a gasification unit capable of processing 720 tons of lignite per day, 777.7 Kg of liquefied gas is required per hour, which amounts to 19 tons per day. At a cost of 5,000 yuan per ton of liquefied gas, this results in expenses of 95,000 yuan per day, or 28.5 million yuan per year. If liquefied gas is used only at the start of operation while domestic coal gas is used during normal production, and based on calorific value calculations, approximately 3,500 Nm3 of domestic coal gas are consumed per hour. At a coal price of 450 yuan per ton, the cost of this domestic coal gas amounts to around 0.45–0.5 yuan per Nm3. This results in daily expenses of 38,000–42,000 yuan, or 11.4 million–12.6 million yuan per year – a considerable amount. The water-cooling wall coils of this gasifier are cooled by water at a pressure of 4.0 MPa and a temperature of 2500°C; no steam is generated within the coils, with only low-pressure steam at 0.5 MPa being produced in the external cooling water circulation system. Currently, there are 3 companies in the world that use the GSP gasification technology, but none of them use it for coal gasification. The plant at the Heihe Pump Gasification Plant has only 6 years of experience in gasifying lignite; it has no experience in gasifying coal with high ash content and high ash fusion point over extended periods of time. A demonstration unit needs to be established for long-term operational testing. When selecting coal for gasification, coal with low ash content and low ash melting point should be given priority. Domestically, Shenhua Ningxia Coal Industry Group Co., Ltd. has decided to adopt the GSP dry coal powder pressurized gasification technology to build a 830 Kt/a dimethyl ether plant, with a first-phase capacity of 600 Kt/a for methanol production; the coal feed rate per furnace is approximately 2000 t/d, making it the first commercial demonstration facility of this type. I hope this project will be completed soon and put into operation smoothly. 11. Two-stage dry coal powder pressurized gasification technology: This technology was developed by Xi’an Thermal Power Research Institute Co., Ltd., and it possesses independent intellectual property rights. In 1997, a test unit with a capacity of 0.7 t/d was built, and pressurized gasification tests were conducted on 14 typical types of thermal coal. In 2004, a pilot plant with a coal processing capacity of 36–40 t/h was built. Gasification tests were conducted on four types of coal powder, and the plant passed the 168-hour continuous operation test, having operated for a total of over 2,200 hours. The following technical parameters were achieved: carbon conversion rate ≥ 98.3%, effective gas (CO+H2) consumption per unit of coal = 520 Kg/Km3, oxygen consumption per unit of coal = 300 M3/Km3, effective gas (CO+H2) content ≥ 91%, and cold gas efficiency ≥ 83%. Coal types that can be gasified include lignite, bituminous coal, subbituminous coal, anthracite, as well as coals with high ash content and high ash fusion temperature. The moisture content of coal types suitable for gasification ranges from 4% to 35%, their ash content ranges from 5% to 31%, and their ash fusion temperature ranges from 1200°C to 15,000°C. The gasification pressure is 3.0–4.0 MPa, and the gasification temperature ranges from 1300 to 1700°C. No tar, phenol, or similar substances are produced. The typical composition of the syngas is 62.38% CO, 29.36% H2, 2.76% CO2, 0.26% CH4, 4.87% N2, and 0.37% H2S and other components. It is characterized by two-stage gasification, in which dry coal powder (accounting for 80-85% of the total coal amount), superheated steam, and oxygen are injected into the bottom of the gasifier through four symmetric burners to carry out the first stage of gasification and melt the slag. The generated gas rises to the middle part of the gasifier, where coal powder accounting for 15-20% of the total coal amount and superheated steam are injected. Two-stage gasification is carried out using the sensible heat of the gas rising from the lower section; at the same time, the high-temperature gas coming from the lower section, at 1400°C, is rapidly cooled to 900-1000°C. This replaces the cycle synthesis gas cooling process used in Shell’s gasification technology, allowing for cost savings as well as improved efficiency in terms of cold gas production and thermal efficiency ； The gasifier features a water-cooled wall structure, and its drawback is that the CH4 content in the syngas is high, which is unfavorable for the production of synthetic ammonia, methanol, and hydrogen. Waste heat boiler-type gasification units are suitable for combined cycle power generation. A demonstration unit consisting of a two-stage dry coal powder pressurized gasifier with a coal feeding rate of 2,000 tons per day (waste heat boiler process) has been selected for Huaneng Group’s “green coal power” project. Another demonstration unit, a two-stage dry coal powder pressurized gasifier with a coal feeding rate of 1,000 tons per day (quenching process), has been chosen for Inner Mongolia Shilin Chemical Co., Ltd.’s project to produce 300 Kt of methanol per year. It is hoped that these two demonstration units will be able to start operating successfully as planned. 12. Four-nozzle opposed dry coal pressurized gasification technology: This technology is an independent intellectual property-based coal gasification method developed through close collaboration among East China University of Science and Technology, Yankuang Lunan Fertilizer Plant (Engineering Research Center for Slurry Gasification and Coal Chemicals), and China Tianchen Chemical Engineering Company. The pilot plant has a coal handling capacity of 15–45 tons per day; it is located at the Yankuang Lunan Fertilizer Plant, and on December 21, 2004, it passed the 72-hour operation test conducted by the expert committee assigned by the Ministry of Science and Technology. The gasifier is a hot-wall furnace lined with refractory bricks. Dry coal powder is introduced into the gasifier from the upper part through four burners, and the resulting syngas flows downward, passes through water quenching, and then exits the gasifier. It belongs to the fluidized bed gasification furnace type. Tests were conducted using coal intended for production in the Texaco coal-water slurry gasification industrial plant at Yankuang Lunan Chemical Fertilizer Plant as raw material. The coal quality data is shown in Table 3: Table 3: Proximate analysis. Tests were carried out in the pilot plant using nitrogen and carbon dioxide as carrier gases. The gasification temperature is 1300–1400°C, and the gasification pressure is 2.0–3.0 MPa. The obtained process data are shown in Table 4: Table 4: Obtained process data. When nitrogen is used to transport dry coal powder, the nitrogen content in the syngas is 4–7%. When carbon dioxide is used as the carrier gas, the nitrogen content in the syngas is 0.7-0.9%. This type of gasifier is a hot-wall gasifier, suitable for gasifying coal with a low ash fusion temperature. In terms of technical specifications, it does not differ significantly from multi-nozzle pressurized coal-water slurry gasifiers; however, it involves additional investment and consumption related to superheated steam, as well as extra investment and energy consumption associated with pressurized nitrogen or carbon dioxide as a carrier gas. Some more work needs to be done on the cold fireplace in order to achieve satisfactory results. 13. Aerospace Furnace HT-L dry coal powder pressurized gasification technology: The Aerospace Furnace HT-L dry coal powder pressurized gasification technology is a patented technology developed by the 11th Research Institute of the China Aerospace Science and Technology Corporation. This furnace type combines the advantages of both Texaco and Shell technologies. It uses dry coal powder as raw material and can handle all types of coal. It features a single burner, a quench process, and water-cooled walls that generate steam; it is similar to the GSP furnace. The gasification temperature ranges from 1400–1700°C, with a maximum of 1850°C. The gasification pressure is 3.7 MPa. The thermal efficiency is η = 95%, the carbon conversion rate is 99%, and the content of useful gases (CO + H2) is ≥90%. 2050 m³ of syngas can be used to produce 1 ton of ammonia. The coal consumption for raw materials is 10% lower than that of Texaco, with the residual carbon in the slag being ≤0.5%, whereas it is 3% for Texaco; thus, the total coal consumption is 15% lower, and oxygen consumption is 20% lower. This technology employs advanced pulverized coal gas flow bed gasification technology for coal preparation, coal transportation, the fuel adjustment system, and the radiation section of the gasifier, while the ash and slag water treatment system, as well as the washing and purification processes, utilize the quenching process technology of the water-coal slurry gasification process – combining the advantages of the two most advanced gasification technologies in the world today. It has advantages in localizing raw coal, optimizing the process route, reducing investment, and using domestic equipment for key components. II. Selection and Evaluation of Gasification Process Technologies The evaluation of gasification process technologies must be based on whether they belong to clean gasification technologies. To date, it can be said that no universal type of gasifier or technology has been found. Various types of gasifiers and gasification technologies each have their own characteristics, advantages, and disadvantages, as well as their suitability for different types of coal and for the final products obtained after gasification. In selecting a process technology scheme, one must choose a process that has undergone extensive testing, industrial demonstration, and practical industrial production. It is necessary to select, based on merit, clean coal gasification technologies that are energy-efficient, cost-effective in terms of investment and operation, highly efficient, and cause no or only minimal environmental pollution that can be easily managed. When conducting evaluations, we must carry out technical and economic analyses from the perspective of the entire plant’s overall process; it is absolutely unacceptable to provide partial and unobjective assessments based solely on a particular gasification technology. At the same time, it is absolutely imperative not to rely solely on the one-sided explanations provided by patent holders and to conduct a partial and incomplete technical-economic evaluation. When the Texaco water-coal slurry pressurized gasification technology was introduced back then, the patent holders also presented their technology; apart from lignite with a high moisture content, other types of coal could be used for gasification. For coals with a high ash fusion point, limestone could be added as a flux to lower the ash fusion point and enable gasification. At that time, Lunan Fertilizer Factory used locally produced 75 coal, which has a high ash content and high ash fusion point, as raw material in an effort to overcome the challenges associated with gasifying coal with such high ash content and ash fusion point; it did not focus on finding coal varieties with lower ash content and lower ash fusion point. As a result, post-commissioning experience showed that it is possible to produce coal mixed with limestone according to the 75% ratio, but gasification operations and slag removal are difficult, making long-term stable operation challenging. Later, locally produced bituminous coking coal with a low ash melting point, as well as mixed coals from Luoling, Jiesuo, and Jingting, were found, and production has remained stable and normal ever since. The Weihe Fertilizer Plant was designed to use coal from Huangling, Shaanxi, as raw material. It was also difficult to achieve stable operation over long periods due to the high ash content and high ash melting point; later, by using Huating coal from Gansu, production became stable and normal. The same is true for the introduction of Shell gasification technology in recent years; the patent holders emphasize that thanks to the use of a water-cooled wall gasifier, the gasification temperature can be raised to 1500–1600°C, no backup furnace is required, the burners have a long lifespan, and it is possible to gasify coal with high ash content and high ash fusion points, although a flux needs to be added. It emphasizes lower coal consumption, lower oxygen consumption, higher efficiency of cold gas utilization, and the ability to produce medium- and high-pressure steam as a by-product. However, it does not explain the actual situation where this type of waste heat boiler-based gasification process is only suitable for combined cycle power generation, with a fuel-fired power generation system required as a backup. Moreover, a separate medium-pressure superheated steam boiler must be installed to supply the superheated steam required by the gasification furnace; this results in high investment costs. Additionally, when such boilers are used in coal chemical production, the steam recovered from the waste heat boilers has to be sent back to the subsequent carbon monoxide conversion system. In applications such as hydrogen production and synthetic ammonia manufacturing, the amount of steam generated as a by-product is not sufficient. This coal gasification process is not suitable for coal chemical production. Based on the characteristics of the various coal gasification process technologies mentioned above, we can classify them into several types. 1. The gasification process technologies that will be phased out include the atmospheric-pressure fixed-bed batch coal (or coke) gasification technology. 2. Gasification process technologies suitable for small and medium-sized nitrogen fertilizer plants to change their raw material sources and carry out technical upgrades include atmospheric-pressure fixed-bed anthracite (or coke) oxygen-enriched continuous gasification technology, ash-polymerization gasification technology, and Ende pulverized coal oxygen-enriched gasification technology. 3. Gasification process technologies suitable for combined cycle power generation include GE Texaco’s waste heat boiler-type pressurized slurry gasification technology and Shell’s waste heat boiler-type pressurized dry coal powder gasification technology. 4. The pilot tests have been completed; what remains is to establish demonstration plants and make further improvements to test the gasification process technologies in commercial operation. These technologies include the two-stage dry coal powder pressurized gasification technology and the four-nozzle opposed dry coal powder pressurized gasification technology. 5. Internationally and domestically, multiple commercialized plants have been operating steadily over long periods. Their coal gasification capacity reaches 1,000–2,000 tons of coal per day. Suitable technologies for large-scale coal gasification include GE Texaco’s pressurized coal water slurry gasification technology (operating at pressures of 4.0, 6.5, and 8.5 MPa), multi-component slurry pressurized gasification technology, and multi-nozzle (four burners) coal water slurry pressurized gasification technology (operating at pressures of 4.0 and 6.5 MPa). 6. Abroad, there is 6 years of experience in the commercial operation and gasification of lignite; gasification technology that can be applied to other types of coal (especially those with high ash content and high ash fusion point) also exists. In China, demonstration units are being established to test these technologies under long-term commercial operation conditions. There is the GSP dry coal powder pressurized gasification technology. 7. Gasification process technologies suitable for producing town gas and fuel gas include the Lurgi fixed-bed coal pressure gasification technology. III. Technical and Economic Comparison of Four Coal Gasification Processes Here, two dry coal powder pressurized gasification processes, Shell and GSP (the Shell method uses a waste heat boiler system, while the GSP method employs a quenching system), are compared with two slurry coal pressurized gasification processes, multi-nozzle and GE (both using quenching systems), from a technical and economic perspective. The basis for this comparison is: The results of the comparison show that: 1. For use in coal chemical production, the investment required for dry coal powder pressurized gasification is higher than that for slurry coal pressurized gasification ； The investment in the waste heat boiler process is higher than that in the quench process ； The investment in multi-nozzle coal water slurry pressurized gasification is higher than that of GE coal water slurry pressurized gasification ； The software cost for the Shell method is much higher than that of the other three methods ； The investment ratios (including software costs) for coal gasification plants are as follows: Shell:GSP:Multi-Nozzle:GE = 2.14:1.46:1.16:1. When comparing the comparable unit costs per Nm³ of (CO+H₂), the Multi-Nozzle coal-water slurry method and the GE method yield the lowest values at 0.422 and 0.423 yuan respectively; the Shell method has the highest cost at 0.496 yuan, while the GSP method falls in between at 0.442 yuan. The production cost of the Shell method is about 84-85 million yuan higher per year compared to the water-coal slurry method. 3. Since the multi-nozzle method and the GE method have a high degree of localization of equipment and materials, they require less investment. If the GSP method can also increase the localization rate of its equipment and materials, the plant investment and costs are expected to be further reduced. 4. The gasification efficiency of multi-nozzle water-coal slurry pressurized gasification is higher than that of single-nozzle water-coal slurry pressurized gasification; therefore, coal and oxygen consumption are lower, while the carbon conversion rate is higher. 5. The dust removal, black water flash evaporation, and heat recovery processes of multi-nozzle coal-water slurry pressurized gasification are superior to those of the other three gasification processes. Comparison table of consumption indicators for four coal gasification processes (comparable aspects). Note: The consumption of liquefied gas or coal gas used for routine safety precautions has not been included in the GSP method. Comparison table of investments required for four coal gasification processes (comparable aspects). Estimation table of costs per Nm³ of (CO+H₂) for four coal gasification processes (comparable aspects). Note: The consumption of liquefied gas or coal gas used for routine safety precautions has not been included in the GSP method. IV. Selection of raw coal types. The development of coal chemical industry, coal-to-oil production, and coal-to-olefins all rely on coal gasification; thus, the issue of selecting appropriate coal types must be addressed. We must absolutely avoid following the old path where nitrogen fertilizer industries primarily relied on anthracite from Jincheng, Shanxi. It is necessary to adapt measures to local conditions, using materials available locally; it is advantageous to develop coal chemical industries in areas where there are coal resources or where such resources can be found nearby. There is an issue of selecting the best coal type. In terms of gasification process technologies, China has all the gasification process technologies available in the world. There is no country in the world that **possesses so many gasification technologies – some of which are imported from abroad, while others are developed independently.** Especially in recent years, research and design institutions in China have developed various coal gasification technologies with independent intellectual property rights. Each of these technologies has its own characteristics, advantages, and disadvantages, as well as suitable types of coal for application. The issues to be considered when selecting coal types are as follows: 1. Utilizing locally available coal, sourcing it from nearby locations, and ensuring a stable supply are the primary considerations when choosing coal types for coal chemical projects. If one decides on what type of gasifier to use first and then selects the appropriate coal type, it reverses the order of consideration. These are the lessons that need to be learned from China’s current long-term reliance on anthracite from Jincheng, Shanxi, for nitrogen fertilizers. 2. We need to understand the quality, reserves, production volume, and ex-factory price of the coal produced by local coal mines, as well as the distance between the coal mines and the factory sites, the transportation methods used, and the transportation capacity. We also need to estimate the cost of the coal upon arrival at the factory, and conduct an analysis and evaluation of the coal quality. To evaluate coal quality, a comprehensive analysis of it is necessary, including industrial analysis, elemental analysis, determination of ash fusion point (both in an oxidizing and a reducing atmosphere; since the environment in coal gasification reactions is reducing, it is important to determine the ash fusion point under reducing conditions), viscosity-temperature characteristics of coal ash, grindability index of coal, thermal stability and cohesion, determination of coal’s chemical reactivity, and tests on coal’s slurry-forming properties. It also compares various coal sources in terms of coal quality, reserves, production volume, ex-mine price, transportation costs, etc., to analyze their advantages and disadvantages. If there is coal suitable for gasification in neighboring provinces, it can be considered as a raw material for gasification, even if the coal price is slightly higher. 3. Generally speaking, fluidized bed gasifiers are suitable for large-scale operation, and all fluidized bed gasifiers discharge slag in a molten state. Therefore, when selecting coal types, we should first consider coal with a low ash content and a low ash fusion point. Since the ash content in coal has a significant impact on the economic efficiency of factories, for example, using coal with 30% ash content requires 20% more transportation costs compared to coal with 10% ash content ； In the production process, more raw coal and oxygen are required to melt the ash and remove it from the gasification furnace ； The area of the cinder storage site also needs to be increased ； Regarding coal prices, the reality is that pricing is not strictly based on quality; there is little difference in price between coal with high ash content and that with low ash content. Therefore, it is a wise decision for some factories to use washed coking coal with low ash content as raw material. 4. When selecting raw coal, be careful not to create difficulties for yourself. According to the patent holder, their coal gasification technology can be used to gasify coal with high ash content and high ash fusion point; therefore, we chose coal with high ash content and high ash fusion point. If there is coal with low ash content and a low ash melting point nearby, why not use it? 5. Different types of coal have suitable gasification technologies available for selection; we need to conduct a technical and economic comparison based on factors such as the coal reserves in the mine, the extractable reserves, annual production volume, transportation conditions, reliability of supply, and coal prices. Since coal of this type can be used in various coal gasification technologies, it is necessary to conduct a technical and economic comparison of the entire production process based on the quality of that specific coal type. It is important to avoid relying on technical data provided by patent holders or from general literature, as well as avoiding limited technical and economic evaluations focused only on the coal gasification stage. A scientific, comprehensive, and objective assessment of the entire production process is essential in order to make the right choice. V. Environmental issues related to gasification units: At the current level of technology, large coal chemical enterprises should opt for gasification furnace technologies that utilize pressurized fluidized bed melting slag discharge systems. More mature process technologies include GE water-coal slurry pressurized gasification (quenching process) and multi-nozzle water-coal slurry pressurized gasification (quenching process), as well as Shell dry coal powder pressurized gasification, which is currently undergoing tests to determine its suitability ； The demonstration units under development include GSP dry coal powder pressurized gasification (quenching process) and two-stage dry coal powder pressurized gasification (quenching process) ； The multi-nozzle dry coal powder downward gas generation process (quenching process) that has passed pilot-scale testing. These devices all have several sources of contamination. The first is the coarse slag discharged after slag quenching; for example, in Shell dry coal powder pressurized gasification, the amount of slag generated accounts for 60% of the total ash content in the coal, while in water coal slurry pressurized gasification and GSP, this figure is 85%. As long as it is properly stored and ways are found for its comprehensive utilization (such as using it as a building material for roads or as a raw material for cement), it will not cause environmental pollution. The second issue is the fly ash discharged from high-temperature and high-pressure fly ash filters in systems such as Shell’s dry coal powder pressurized gasification unit. The amount of fly ash discharged by such systems accounts for approximately 34% of the ash content in the coal. Taking as an example a system that processes 2,000 tons per day of dry coal powder with a 20% ash content, 136 tons of fly ash are discharged daily; finding effective ways to utilize this fly ash is an important issue that companies need to address. If they are piled up carelessly without fixed users, it will cause pollution to the surrounding environment. Thirdly, as for the black water discharged by the system, it can be recycled after flocculation and sedimentation; however, some of the gray water still needs to be treated to remove ammonia and cyanide before it can be discharged, and this is a problem that can be solved. The sedimented ash in the black water, after pressure filtration to form a filter cake, can be discharged for comprehensive utilization or supplied as fuel. The H2S carried away with the syngas can be removed and recovered during the subsequent acid gas removal from the syngas. As for the small amount of H2S-containing waste gas discharged from the black water flash drum, it can be recovered and comprehensively utilized or sent to a flare for combustion and discharge. VI. On the issue of coal-based synthetic natural gas: Recently, professionals in the coal chemical industry have been actively discussing the topic of coal-based synthetic natural gas, and I would like to share my own views as well. 1. I believe the manufacturing cost issue is the first thing to consider. Theoretically, 4 M3 of (CO+H2) can only produce 1 M3 of CH4 (synthetic natural gas). 1 ton of standard coal can generate 400 M3 of synthetic natural gas; when pressurized gasification using coal slurry is employed, and assuming a cost of 100 yuan per ton for the raw coal, the production cost of synthetic natural gas is approximately 1.00 yuan per M3. At a price of 200 yuan/ton, the production cost of synthetic natural gas is approximately 1.22 yuan/m³. At a price of 250 yuan/ton, the production cost of synthetic natural gas is roughly 1.325 yuan/m³. At present, the cost of natural gas extraction in our country is around 0.4–0.5 yuan per M3. The management fees (which depend on the length of the pipelines) are approximately 0.3–0.88 yuan per M3, while the costs associated with distribution and storage in cities are about 0.3 yuan per M3. Thus, the total cost of natural gas comes to 1–1.68 yuan per M3, with the retail price of natural gas in Tianjin being 2.2 yuan per M3. Based on these figures, projects for producing synthetic natural gas, where the price of such synthetic natural gas is set at 1–1.35 yuan per M3, are only feasible in areas where the price of raw coal is below 100–250 yuan per ton, or in locations where it is possible to construct facilities directly at the coal mines. 2. As for the gasification technology applicable to synthetic natural gas, the reaction for producing synthetic natural gas is (CO + 3H2 = CH4 + H2O); in other words, 4 cubic meters of (CO + H2) are required to produce 1 cubic meter of CH4 (synthetic natural gas). The production process necessarily involves a CO conversion reaction of the synthetic natural gas obtained after gasification. The syngas produced by pressurized gasification of dry coal powder contains approximately 55–64% CO and 26–30% H2 ； The syngas produced by the pressurized gasification of water-coal slurry contains approximately 43–46% CO and 35–38% H2. It shows that the investment and steam consumption for CO conversion are higher in pressurized dry coal gasification compared to pressurized slurry coal gasification. In the gasification process, the investment required for the waste heat boiler system is higher than that for the quenching system; moreover, the high-pressure steam produced as a by-product must be returned to the syngas to participate in the CO conversion reaction. Obviously, the coal gasification process using a waste heat boiler is not suitable for producing synthetic natural gas. For the transport of dry coal powder in pressurized gasification, high-pressure N2 is used for pneumatic conveying; all of this N2 enters the gasification system. The synthetic natural gas produced contains 9-14% or more N2, with a CH4 content of only 84-85%. In contrast, synthetic natural gas produced by pressurized gasification using coal water slurry can have a CH4 content of over 97%. Some people have considered using CO2 for the pneumatic transport of dry coal powder, but this would require additional investment in CO2 recovery and compression. Clearly, the investment required for the pressurized gasification process using dry coal powder is higher than that for the pressurized gasification process using coal slurry. 3. In summary, the coal gasification process technologies currently suitable for large-scale production of synthetic natural gas are as follows: among the mature technologies are GE slurried coal pressurized gasification (quench process) and multi-nozzle slurried coal pressurized gasification (quench process) ； Demonstration units are being established; the process technologies that still need to be tested through long-term production practice include GSP dry coal powder pressurized gasification (quenching process) and two-stage dry coal powder pressurized gasification (quenching process).