Operation status of the space furnace gasification technology

Thread Content

Production application of the HT-L gasification technology: The HT-L gasification process is a simple, efficient, and practical gasification method developed by the 11th Aerospace Research Institute. It builds on advanced technologies from Dutch SHELL, German GSP, and American TEXACO gasification processes, utilizing its own proprietary coil-type water-cooled wall gasifier. The application of this process in coal chemical projects is described as follows: I. Process Introduction 1. Coal Grinding and Drying System The process flow, operating principle, and control parameters of the coal grinding and drying system are identical to those of the SHELL process. Two such systems are operated, one in use and one as a backup; each system has a capacity of 35 tons per hour. The goal is to produce coal powder with a particle size of less than 90 microns, where over 80% of the particles are of this size, and the water content is less than 2%. No separate limestone is added to the system; instead, granular limestone is fed onto the coal conveyor belt using a belt scale and via ratio adjustment, where it then enters the coal grinder for grinding. 2. Pressurized conveying system: The process flow, operating principle, and control parameters of the pressurized conveying system are identical to those of the SHELL process. Its purpose is to use pressure differences to transport the produced qualified coal powder to the gasifier for combustion and gasification. The difference is that V1205 has three legs; these three lines convey the fluid, which then converges at the burner and is sprayed into the furnace chamber in a spiral pattern through the gaps in the burner ring. 3. Vaporization and purification: The burner design is the same as that of GSP; vaporization is achieved using a single burner in a top-firing configuration. The vaporization furnace employs the TEXACO quenching process. When the pressure in the furnace reaches 1 MPa, coal powder mixed with oxygen and steam enters the furnace at a specific oxygen-coal ratio. After stabilizing the pressure for 1 hour, slag formation occurs. There are 8 temperature monitoring points in the furnace, which can be used as references for the vaporization temperature as well as to determine the status of slag formation. The designed gasification temperature is 1400–1600°C, with a gasification pressure of 4.0 MPa. The hot crude gas is quenched together with the slag at the lower part of the gasifier, where they are separated as well. During this quenching process, the quenching water evaporates, and the gas becomes saturated with water vapor; its temperature upon leaving the gasifier is 199°C. After being washed in a Venturi scrubber and a scrubbing tower, the syngas, with a temperature of 194°C and a solid content of less than 0.2 mg/m3, is sent on to the shift reaction stage. 4. Sludge and ash water treatment system: The process flow, operating principle, and control parameters of the sludge and ash water treatment system are identical to those of the TEXACO process. The slag is passed through a slag breaker, then through a high-pressure to low-pressure lock hopper, and sent to a slag skimmer for slag-water separation; the water is recovered and reused ； The gray water passes through high-pressure flash evaporation and vacuum flash evaporation before reaching the sedimentation tank; the clear water is recovered as cooling water. The slurry is subjected to vacuum filtration to produce a filter cake. II. Technical Features 1. Adaptability of raw materials: According to the designers, this process is adaptable to a wide range of coal types; bituminous coal, anthracite, and lignite can all be gasified, and it is also suitable for coals with high ash content, high moisture, and high sulfur levels. Longyu has used two types of coal for production: Shenmu Carbon Factory coal and Yongmei Xinqiao coal. The operating conditions are stable, and the effective gas content generally meets the design requirements. However, since the coal from Shenmu Carbon Factory has a low ash content (<10%), slag deposition is not very good; slag deposition is acceptable in the upper part of the furnace, but hardly occurs in the lower part. The operation time of Yongmei Xinqiao coal is relatively short, so it cannot fully reflect its slagging tendency. Attached are the coal quality analyses from Shenmu Carbon Factory and Yongmei Xinqiao: moisture, sulfur content, ash content, volatile matter, and fixed carbon. For Shenmu Carbon Factory, these values are 5.72, 0.83, 8.73, 35.88, and 50.37 respectively; for Xinqiao Mine, they are 1.47, 0.84, 22.56, 8.84, and 67.13 respectively. 2. Capacity per unit facility: The designed production capacity of each gasification unit is 42,000 NM3/h of useful gases (CO+H2), which allows for the production of 150,000–200,000 tons of methanol per year. Research is currently underway on gasification technologies and equipment that would enable an annual methanol production capacity of 350,000 tons. 3. The design yields a high carbon conversion rate of 98%, with the residual carbon in the slag kept at 1-2%; the actual residual carbon levels were 2.74%, 3.98%, and 1.59% ； The designed effective gas content is 90%, of which CO accounts for 70% and H2 accounts for 20%; the actual values are shown in the syngas analysis below: Syngas, Oxygen, Nitrogen, Carbon Monoxide, Hydrogen, Carbon Dioxide. Shenmu Coal Plant: 0.01, 6.12, 52.57, 27.0, 14.3; Xinqiao Mine: 0.02, 2.53, 54.92, 27.13, 15.4. Note: The medium used for transporting coal powder is carbon dioxide, with a load of 60%. 4. Thermal efficiency: The overall thermal efficiency is 95–96%, while the actual efficiency of cooled syngas is 80–83%. The steam production is only 3 T/H; most of the heat is transferred to the quenching water through the raw syngas and slag, resulting in heat loss. 5. Oxygen consumption: The designed oxygen consumption for producing each thousand cubic meters of useful gas is 330–360 Nm3. In actual production, coal from Xinqiao Mine is used, and the data on the amount of useful gas produced and the oxygen consumed are calculated at 60% load; the resulting oxygen consumption per thousand cubic meters of useful gas is 382.45 Nm3. 6. Coal consumption: The original design used Hebi coal with a fixed carbon content of 74% as the raw material, resulting in a coal consumption of 600 Kg/KNm3 of useful gas. In actual production, Xinqiao mine coal is used; calculations are based on the useful gas produced at 60% load, as well as data regarding coal and oxygen usage, showing that 693 Kg of coal is required per thousand cubic meters of useful gas. 7. Wastewater discharge: The design calls for 9.76 tons of wastewater to be discharged to the treatment facility per hour; in actual operation, the maximum discharge volume reaches 20 tons per hour, but the average discharge is less than 10 tons per hour, thus meeting the design requirements. 8. Water wall of the gasification furnace: The water wall of the gasification furnace is of coiled-tube type, with an inner diameter of DN40 for the water pipes, ensuring even distribution of water flow and preventing blockages that could lead to low water flow and subsequent tube rupture. However, the resistance is high and the heat exchange efficiency is poor. III. Key Equipment and Instruments 1. Coal Grinding Mill: The coal grinding mill uses the Shenzhong G168 model, which performs well. At loads below 70%, the pressure on the grinding rollers is set at 6.5 MPa; at loads above 70%, this pressure increases to 7.5 MPa ； Over 80% of the coal powder produced through grinding is less than 90μm, of which that with a size of ≤40μm accounts for 3–27%, typically around 10%. The after-sales service is poor. 2. Burners: The burners of the HT-L gasification furnace are manufactured by the 11th Aerospace Research Institute itself; they are similar to the German GSP gasification burners, with only a slight change in the direction in which the coal powder is injected. An integrated pilot burner, start-up burner, and coal burner is used, with the pilot burner located in the center. Natural gas at 0.2 MPa is utilized for the pilot burner, while natural gas at 1.7 MPa from the outlet of the natural gas compressor is used for the start-up burner. Once the furnace pressure reaches 1.0 MPa, all three coal powder supply lines are activated simultaneously (since there is only one oxygen supply line, the oxygen-to-coal ratio is controlled based on the total amount). After coal feeding begins, the pilot burner is turned off. The designer said that the part of the burner that usually gets damaged is the burner tip, which needs to be replaced every six months to a year (the price wasn’t specified). During the three months of testing, three burners have been replaced; it is said that there is nothing wrong with the burners themselves, but this was done to reduce the resistance posed by them as part of the testing process. 3. HT-L gasification furnace: The gasification furnace uses a top-firing design; as long as the pressure difference at the burner is maintained, the burner generally will not get damaged. The water wall is of the coiled type; the circulating water distribution tubes lead out four DN40 water pipes in a relatively even manner. These four pipes surround each other in parallel to form the water wall, with studs and fins between the pipes, onto which refractory material is attached. There are eight temperature measurement points in total in the furnace, with the temperature sensors embedded in the surface of the refractory material. The temperature readings can reach 1200°C, but the designers require that this temperature not exceed 1000°C; if it does exceed 1000°C, it indicates poor slag attachment or overheating of the furnace. It is reported that the temperature reading at the heating element in the aerospace furnace in Linquan, Anhui, showed 1800°C, and the water wall was quickly damaged. The lower part of the furnace employs TEXACO’s quenching process, which serves to wash and cool it. 4. Slag extractor: The slag extractor is from Qingdao Sizhou. Due to the short operating time, low load, and low ash content in the raw coal, no problems have arisen with the equipment itself. However, the capacity of the slag water pump is insufficient, which leads to overflow of slag water; it is planned to replace it with a slag water pump from a factory in Shijiazhuang (originally from Shanghai Kaiquan Pumps). 5. Coal powder mass flow meter: The coal powder mass flow meter uses the German SWR type, which relies on microwave measurement. Instead of using a speed meter and a density meter to obtain data separately and then performing calculations in the PLC, this device integrates the speed meter and the density meter, providing direct data output. The data collection is stable, but the values obtained are slightly lower than the actual values. The originally planned U.S.-made thermoelectric products were not used. 6. Coal powder control valve: The coal powder control valve uses the German brand SUFU, just like in our factory, but there has been one instance where the valve stem was damaged due to blockages by debris. 7. Coal powder three-way valve: The coal powder three-way valve is a product of Beijing Aerospace 11th Research Institute; it operates slowly, with a response time of more than 15 seconds on average. Our factory uses valves from Denmark, whose response time is around 10 seconds. 8. The steam flow meter in the gasification furnace gives inaccurate readings; the operators at Longyu lack experience in controlling the oxygen-coal ratio based on steam production, so they rely on changes in furnace temperature and the composition of the syngas. IV. Issues: 1. The screw conveyor does not operate stably, and problems such as blockages and broken screws occur frequently; it is planned to replace it with one from Nanjing. 2. If one out of the three coal powder circulation pipelines fails, the furnace must be shut down to prevent uneven burning that could damage the water wall and burners; this poses significant difficulties for long-term operation. It is therefore essential to ensure that the coal powder is clean, so as to avoid clogging of the coal powder valves. There was a case where the capacitive level gauge of V1204 failed, causing the coal powder valve to get clogged and leading to a shutdown. 3. Due to the low steam production, flow measurement is inaccurate; when using carbon dioxide to transport coal powder, there are no reference parameters available for adjusting the oxygen-to-coal ratio, resulting in blind operation. 4. After two flashes, the temperature of the gray water drops to 70–80°C; after sedimentation, it is sent to a vacuum filter. The high water temperature can cause the filter cloth to deform, shift out of place, or get damaged as a result of folding. 5. Due to the low steam production and low pressure in the external steam pipeline network, no further attempts have been made to increase the gasification load at present. 6. The mass flow rate meter for coal powder is in tons per hour, which causes excessive fluctuations in the oxygen-coal ratio during cascade control; therefore, the control of the oxygen-coal ratio is now done manually. V. Promotion and Application Analysis 1. The HT-L coal gasification process is a pulverized coal pressurized gasification technology independently developed by the 11th Academy of Aerospace, tailored to China’s national conditions. Although there is no pilot plant, the technologies involved in each unit have a solid design foundation and extensive operational experience, enabling direct industrial production without any design flaws or operational bottlenecks. 2. Low investment required. The total investment for Henan Longyu’s 150,000-ton methanol project is 640 million yuan, of which 310 million yuan is allocated to the gasification unit; this amount is one-third less than the investment required for a SHELL-based plant of similar scale. Simple structure and easy to operate. 3. High degree of localization. Many of the equipment in the HT-L gasification unit, such as the pulverized coal lock-hopper valve, slag crusher, burner, gasification furnace, pulverized coal circulation three-way valve, slag-water circulation pump, quenching water pump, boiler water circulation pump, and hot air stove, were designed, manufactured, or commissioned for manufacture by the 11th Academy of Aerospace Technology in Beijing. These devices operate smoothly and are easy to maintain, and they have also promoted the development of related industries; they hold great significance for advancing China’s economic and technological progress. 4. Although the HT-L gasification process has low thermal efficiency and significant heat losses, technical improvements can be made during future operation and design by adding waste heat recovery devices to reduce energy consumption. In summary, the HT-L gasification process is economical and reliable, making it worthy of promotion and application