Solutions to current problems in gasification
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Problems with water-coal slurry: The gasification of water-coal slurry presents issues such as low efficiency, high oxygen consumption, high requirements for coal quality, and a short lifespan of refractory bricks. This is mainly because nearly 40% of the water in coal water slurry absorbs a large amount of heat, making it difficult to maintain the thermal balance of the gasification reaction; hence, a refractory brick lining is required. Water-coal slurry gasification technology and the inner layer of refractory bricks are interdependent; without a high-quality refractory brick lining, the efficiency of water-coal slurry gasification will be very poor. However, using refractory bricks is like putting on a tight constraint, with its negative effects. To maintain a certain service life of the refractory bricks, the operating temperature inside the furnace is restricted and must not exceed 1400°C. The slurry concentration imposes requirements on the slurry-forming properties of coal ； There are also requirements regarding the ash content and ash fusion point in coal, among others; these requirements narrow down the range of suitable coals. Therefore, the core problem with coal water slurry feed is that it contains too little combustible material and has a low calorific value. The fundamental issue is to increase the combustible content of the coal slurry. One approach is to use high-calorific-value, low-ash cleaned coking coal (such as that from Lunan Fertilizer Plant) and petroleum coke (such as that from Jinling Petrochemical) ； Something can also be done to the liquid, such as creating an oil-in-water coal slurry, with the aim of increasing the calorific value of the coal slurry. Once the calorific value of the coal slurry is increased to be almost comparable to that of coal, water-cooled membrane walls can also be used in the gasifier, eliminating the need for refractory bricks. This results in lower oxygen consumption and coal consumption, as well as an expanded range of coal types that can be used. The issue of low vaporization efficiency with a single nozzle: Both the Texaco furnace and the GSP furnace use direct injection with a single nozzle, whereas the technology developed by East China University of Science and Technology employs dual-nozzle injection. The capacity of a single nozzle is always limited; to increase the capacity of a single furnace, multiple nozzles represent an ideal solution. For large-volume furnaces such as Shell’s ones that burn 4,000 tons of coal per day, it is being considered to add a pair of nozzles, resulting in a configuration with 6 nozzle pairs. For the GSP gasification process, multiple nozzles should also be considered at large capacities. The spray pattern results in an increase in the relative velocity of the gas-solid phase due to the collision and deflection of the gas flow, which facilitates the gasification reaction. This has been proven by the operation results of the multi-nozzle opposed gasifier at East China University of Science and Technology, with an increase in carbon conversion rate. Of course, in the design of the top structure for multi-nozzle opposed-nozzle furnaces, corresponding measures should be considered to address the rapid damage to the refractory bricks, such as increasing the height-to-diameter ratio of the upper space, deciding whether to use horizontal opposed-nozzle arrangement or a slightly inclined one, and determining whether local water cooling is necessary. The issue of high costs associated with upward-flow waste boilers: By using this type of boiler, it is possible to recover a large amount of sensible heat from the high-temperature gas, thereby generating high-pressure steam and achieving higher thermal efficiency. However, in an upflow fluidized-bed gasifier for waste boilers, most of the molten ash droplets are carried away by the airflow. To prevent blockages in the waste heat boiler system and the gas outlet, these droplets are usually first quenched into solid slag particles before being removed. Gas cooling, waste heat recovery, and slag dust removal make this system large, complex, and expensive. In current Shell gasifiers, large ceramic filtration units are used to remove slag dust, requiring regular pulse backwashing. This process is generally considered more suitable for producing gas used in IGCC power generation, with the main focus being on maximizing thermal efficiency; when it is used for producing chemical synthesis gas, corresponding improvements must be made. The downward water quenching process features simple equipment, and the large amount of water vapor carried in the gas can be used for subsequent CO conversion; it is generally considered suitable for syngas production.
For the gasification of petroleum coke, what type of furnace is suitable? Based on experience, Texaco seems to be a better choice; in terms of raw material diversity and efficiency, Shell appears to be superior. What about GSB furnaces or space furnaces?
It’s feasible; it would be better if more details could be provided
In the design of the top structure for multi-nozzle opposed-nozzle furnaces, appropriate measures should be considered to address the rapid deterioration of refractory bricks, such as increasing the height-to-diameter ratio of the upper space, deciding whether to use horizontal opposed-nozzle arrangement or a slightly inclined one, and determining whether local water cooling is necessary. I’m not sure if Huazhong University of Science and Technology has conducted experiments in this area. With horizontal spray, there is indeed a phenomenon of excessively high temperatures at the vault; if the spray is directed at a slightly downward angle, this problem of excessive vault temperature should be solvable. But then how should the oxygen level at the center be controlled?
I. Atmospheric pressure ash pyrolysis technology at Tianjin Alkali Plant: The Tianjin Alkali Plant produces 900,000 tons of soda ash and 80,000 tons of synthetic ammonia per year. There are currently two atmospheric-pressure ash fusion gasification furnaces, model Φ3000/4200, with one in operation and one as a backup. The designed daily coal feeding rate for a single gasifier is 250 t/d, while the actual coal feeding rate is approximately 230 t/d ； It is designed to produce 40,000 tons of synthetic ammonia per year, with an operating pressure of 0.01 MPa and an operating temperature of around 1000°C. Construction of the gasifier began in July 2003; it was put into trial operation in June 2005, and officially commenced operations in March 2006. The capacity of the air separation unit is 10,000 Nm3/h; this unit was in place during the early stage of plant construction, with an investment of around 50 million yuan. The air separation unit consumes approximately 0.49 kWh/Nm3 of electricity. The total investment for the two gasification units, along with slag treatment and raw coal processing, is approximately 50 million yuan (excluding land costs and interest expenses). A single furnace can operate continuously for about 45 days, with an ideal annual runtime of 145 days; however, in such a scenario the equipment suffers severe wear and tear. Under favorable operating conditions, the residual carbon in the ash can reach 2%; under poor operating conditions, it can go as high as 30–40%, while under normal conditions it is around 10%. This unit produces approximately 2 tons per hour of steam at 1.3 MPa; in addition to being used for gas generation, it can also supply 700 kg per ton of NH3 to external parties. The resulting slag and the fine ash after washing in the scrubber tower are sold directly, while the wastewater is reused. The main problems encountered during the operation of this device are severe wear on the pipelines of the primary and secondary cyclone dust collectors, a relatively small heat exchange area in the furnace cooler, high temperature of the gas at the outlet, severe wear and corrosion in the secondary waste heat boiler, severe corrosion in the tertiary waste heat boiler, and frequent blockages in the spiral coal feeding system. The service life of the burner in this furnace is 8–9 months, while the maintenance period is 7–10 days. Some of the economic indicators and parameters in operation are shown in the attached table. II. Yankuang Guotai Multi-nozzle Water Coal Slurry Technology in Tengzhou, Shandong: Yankuang Guotai in Tengzhou, Shandong, is designed to produce 200,000 tons of acetic acid, 240,000 tons of methanol, and 80,000 kilowatts of thermal power per year. There are currently 3 Φ3200 multi-nozzle water-coal slurry gasifiers in operation, with two in use and one as a backup. The designed daily coal input is 1150 t/d, the maximum capacity is 1500 tons, and the actual coal input is 900 t/d. The parent company of this group, Lunan Fertilizer Factory, was the first in the country to introduce Texaco gasifiers in 1993; it used anthracite from 1993 to 1996, and after 1996 switched to high-sulfur bituminous coal supplied by Yankuang Group. These gasifiers have been in operation for over 10 years now. The multi-nozzle water-coal slurry gasifier at East China University of Science and Technology is essentially an improvement on the Texaco design, with coal slurry nozzles among others; it features four nozzles arranged in an opposite configuration. The design pressure is 4.0 MPa, the actual operating pressure is 3.7 MPa, the operating temperature is approximately 1300°C, and the dried slag is discharged in a wet manner. Construction of the facility began in August 2003; it was tested in July 2005, went into official operation in September 2006, and reached full capacity in 2007. It uses local high-sulfur bituminous coal with a volatility of around 30% and a low calorific value of approximately 25 MJ/kg. It has been working properly until now. In 2007, the enterprise achieved remarkable economic results. The air separation unit utilizes cryogenic technology, with equipment based on the technology of the French company Air Liquide. Its designed capacity is 60,000 Nm3/h, while the actual capacity can reach 63,000 Nm3/h. The investment required for this unit is 300 million yuan. It is designed to supply two furnaces; if used to supply three furnaces, its capacity will be insufficient (each furnace requires 24,000–25,000 Nm3/h). The air separation process is driven by turbines, and the cost of oxygen is 0.38 yuan per Nm3. The power consumption per ton of methanol is approximately 1000 kWh/t of alcohol, while the coal consumption per ton of alcohol is ≤1.5 t/tCH3OH. The gasifier in this plant can operate continuously for 60–83 days per unit. The main problem with this technology is that the refractory bricks in the gasification furnace tend to wear out, requiring regular replacement; this process takes a long time and is costly. It is understood that the operating cycle of the nozzles in this factory is 60–80 days, and they are replaced during short downtime periods, with the replacement process taking approximately 8 hours ； The vault bricks need to be replaced 3 times every 2 years, and the repair time is approximately 1 month ； The cylinder bricks have been in use for 3 years now without any replacement. It is stated that the furnace has the following requirements for coal: it must have good slurry-forming properties, and its ash fusion temperature (FT) should not exceed 1350°C. To date, more than a dozen sets of contracts have been signed for enterprises under construction, and several of them have already started operations. Upon visiting the gasification furnace site, it was evident that the production area and equipment were extremely clean, to the point where they could be described as spotless. Some of the economic indicators and parameters related to the operation of this plant are shown in the attached table. III. HT-L Space Furnace Technology: The space furnace technology was developed by Beijing Aerospace Wanyuan Coal Chemical Engineering Company, drawing on the technologies and experience of Texaco and Shell. The upper part of the furnace features a shell-like water-cooled wall; the large coils are coated with silicon carbide refractory material, while the lower part uses a Texaco-type molten slag water-cooled shock crushing and separation system. Adopting rocket engine nozzle technology, with a single nozzle mounted at the top, three coal inlet pipes, and a high-pressure dry powder storage tank for supplying coal. According to Chief Engineer Lu, the nozzle’s lifespan can reach ten years. Due to the effect of the silicon carbide-coated water wall, it serves to protect the wall by using slag against slag, eliminating the problem of high-temperature wear of refractory bricks. The design pressure of the gasifier is 6.5 MPa, with an operating temperature of 1400–1850°C. The effective gas content of the produced coal gas can exceed 90%, while the residual carbon in the slag can be less than 1%. It is said that the 150,000-ton methanol gasification unit includes an investment of 250 million in air separation equipment; the annual maintenance cost is 8 million. It operates at high gasification temperatures and has no requirements regarding the type of coal used, with lower costs achieved when the ash content is below 18% (14%). Beijing Aerospace Wanyuan Coal Chemical Engineering Company introduced this technology at the beginning of 2006. There are currently two demonstration units in Linquan, Anhui, and Puyang, Henan; trial operation is scheduled for June 2008, with full production to begin in August 2008. This technology is still in the development stage, and some key technical parameters are shown in the attached table. Appendix: Technical Categories, Products, Raw Coal, Operating Pressure, Operating Temperature, Air Separation System, Gasifier, Composition of Raw Coal, Inbound Price, Design Capacity (Nm3), Investment Cost, Specifications, Daily Coal Consumption per Unit Gasifier, Gas Production Rate per Unit Gasifier (Nm3/h), Investment Cost. Tianjin Alkali Plant – Continuous Gasification using Ash Fusion; 80,000 tons of ammonia and 190,000 tons of soda ash produced. Shanxi Datong bituminous coal: FCad50%, Aad25%, Vad20%; Lower calorific value of ~21 MJ/kg; Price: 480 yuan/t; Operating pressure: 0.01 MPa; Operating temperature: 1000°C; Design capacity: 10,000 Nm3; Investment cost: 50 million yuan; Two gasifiers of diameter Φ3000/4200, one in operation and one as backup; Coal consumption: 250 t, with actual amount fed into the gasifier being around 230 t; Gas production rate: 15,500–100 million Nm3/h (including air separation system, slag treatment system, and raw material processing; land and interest costs not included). Yuncheng Guotai Water-Coal Slurry Process: 200,000 tons of acetic acid, 200,000 tons of methanol, and 80,000 kW of thermal power generated. Yuncheng and Shenmu bituminous coal: FCad55–65%, Aad21–22%, Vad28–32%; Ash fusion point ≤1350°C; Lower calorific value greater than 25 MJ/kg; Price: 600 yuan/t; Operating pressure: 4.0 MPa; Operating temperature: 1200–1300°C; Design capacity: 60,000 Nm3; Investment cost: 300 million yuan; Three gasifiers of diameter Φ3200, two in operation and one as backup; Actual coal consumption: 1150 t, with actual amount fed into the gasifier being around 900 t; Gas production rate: 80,000 Nm3/h; Investment cost: 340 million yuan (two gasifiers, including slag treatment system; air separation system not included). Anhui Linquan Aerospace Furnace Technology: 300,000 tons of methanol produced; Ash content: 16–18%; Lower calorific value of ~22 MJ/kg; Operating pressure: 4.5 MPa; Operating temperature: 1400–1850°C; Design capacity: 20,000 Nm3; Investment cost: 85 million yuan; Two gasifiers of diameter Φ2800, each operating at 70% capacity; Coal consumption: 800–1000 t; Investment cost: 80,000 million yuan, or 250 million yuan (for a single gasifier, including air separation system and technical fees)
Now, the industrialization of coal powder gasification is feasible, and four-nozzle cold-wall furnace coal powder gasification can solve the aforementioned problems.
Hehe, what a great post! It’s exactly the information I needed; it would be even better if it were more detailed
When selecting a furnace type, considerations such as its advancement, forward-looking features, safety and environmental friendliness, practicality, and reliability must be taken into account. A comprehensive comparison of various options and a thorough technical and economic evaluation should be carried out, taking into account the type of coal used as raw material as well as the capabilities of the enterprise, in order to determine the most suitable furnace type and minimize risks while maximizing benefits. TEXACO already possesses the gasification technology in China, having accumulated extensive experience; the equipment manufacturing, installation, and project implementation processes are fast, and there is ample experience in operating the systems, which means that it takes less time to reach full operational capacity. The main issues are the need for a certain type of coal to be used, as well as relatively low gasification efficiency, higher oxygen consumption, and a short lifespan for the refractory bricks. However, some of these problems have been resolved due to the early adoption of this technology in China ； For SHELL, its gasification technology offers advantages in terms of coal variety and environmental protection; its biggest drawbacks are high investment costs, excessive equipment expenses, as well as high power consumption required for drying, coal grinding, pressurizing the syngas used for high-pressure nitrogen and back-firing cooling ； For the GSP gasification technology, its main structure consists of a single-nozzle bottom-fed dry coal powder pressurized fluidized bed gasification system. The main issues are the limited capacity of each furnace and shortcomings in terms of long-term operational performance. In the plants that have been put into operation to date, the capacity of each furnace is only 720 tons of lignite per day, and the duration of operation recorded is not very long either ； Regarding the HT-L gasification technology, which was developed by the Beijing Institute of Aerospace Propulsion under the China National Space Administration, the design of its gasification furnace combines the advantages of SHELL and TEXACO. Two units are currently under construction, and their performance remains to be observed.