Comparison between Shell and Texaco

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The hell gasification process is carried out under high temperature and pressure; it is one of the more advanced second-generation gasification technologies in the world today. (1) The % dry powder feed has a high degree of adaptability to different coal types; bituminous coal, subbituminous coal, and lignite can all be gasified. It requires a lower ash fusion point for the coal compared to other gasification processes. (2) High vaporization temperature: The vaporization temperature is 1400–1600°C, with a pressure of 30–4.0 MPa; the carbon conversion rate can reach over 99%, and the proportion of useful gases (CO + H2) in the gas can reach 90%. (3) Low oxygen consumption: The oxygen consumption per ton of coal is 600–650 m3 (for Shenfu coal); therefore, the scale of the air separation unit required for it is slightly smaller than that needed for water-coal slurry. (4) Dry coal powder downward injection nozzle, with cooling protection. Shell gasifiers use multiple nozzles arranged symmetrically, typically four to six. The designed service life of the nozzle is 8000 hours. (5) Gasifier: The gasification pressure per unit gasifier is 3.0–4.0 MPa, with a daily coal processing capacity of 1,000–2,000 tons. It features a water wall structure without refractory brick lining, requiring less maintenance and allowing for a longer operating cycle. (6) Quenching and cooling of high-temperature gas: The mixed gas formed by gasification contains 40% slag, which is rapidly cooled to 900°C using quenching gas to prevent the liquid slag from adhering to the walls during solidification. (7) Waste heat boiler: The waste heat boiler has a water-tube structure and is used to recover the sensible heat of high-temperature gas. (8) Thermal efficiency issue: Approximately 83% of the heat energy in the gasification furnace is converted into syngas, while about 15% of the heat energy is recovered as high-pressure or medium-pressure steam; the overall thermal efficiency is around 98%. (9) Control System: The gasification process makes use of an advanced control system, including DCS, ESD, PLC, etc., to ensure that the gasification operates under optimal conditions. (10) Fly ash: The raw gas exiting the waste heat boiler enters a dry dust collector, where the fly ash is recovered using high-efficiency fly ash filters and then vaporized again. (11) Slag and wastewater: The slag discharged at high temperatures from the gasification furnace becomes glass-like particles after quenching; it has stable properties and has a relatively minor impact on the environment. Gassed sewage contains little cyanide and is easy to treat. Problems existing: (1) The application of this technology in ammonia synthesis is limited to domestic markets only, resulting in some distorted data. There needs to be a process of digestion and absorption, including equipment selection, construction management, and perhaps a learning process from trial operation to normal operation. ⑵ The internal components of the key gasification equipment (gasification furnace, waste heat boiler, gas transfer ducts, gas return chamber) are manufactured abroad, resulting in a longer construction period ； Burners, coal powder valves, slag valves, ash valves, etc., are entirely dependent on imports ； The transportation and lifting of large-scale equipment (the three major components, fly ash filters, high-pressure nitrogen buffer tanks) are relatively difficult. ⑶The investment is large and the level of automation is very high, being 1.4 to 1.5 times that of Texaco. ⑷The inner diameter of the water wall tubes is small, at only 7 mm, which requires high standards for the quality of water supplied to the boiler. ⑸The large amount of high-pressure or ultra-high-pressure nitrogen used partially offsets its energy-saving advantages. (6) Medium requirements: Coal with a low ash melting point, good activity, and low ash content is an appropriate type of coal for Shell gasification. Features of the Texaco process: (1) Wide adaptability to coal. In domestic production, bituminous coal is primarily used; there are no strict requirements regarding the activity of the coal, but certain requirements exist concerning its ash fusion point (ST3 is generally below 1250 °C). (2) Continuity of production. Texaco uses continuous feeding and liquid slag discharge. Slag discharge does not affect the operation of the gasifier. Domestic use is generally limited by the service life of the burner, which is usually around 50 days of continuous operation. (3) Reduced gas compression power consumption. Common pressure grades include: 2.7 MPa, 4.0 MPa, 6.5 MPa, 8.5 MPa, etc. The pressure after gasification is high, which allows for significant savings in compression energy consumption in subsequent processes. (4) High gasification strength. The equipment is compact in size, has a tight layout, and offers high production capacity. A ￠3200mm gasification furnace, operating at a pressure of 4.0 MPa, can produce 760 tons of synthetic ammonia per day. (5) High degree of automation. To ensure the safe operation of the device, the system is equipped with many interlocks. (6) High heat recovery rate. (7) The one-time investment is low, but the patent fees are high. The prominent problems with this process are: 1. The refractory bricks on the fire-facing side of the gasification furnace have a short service life, typically around one and a half years, and must be replaced partially or entirely, which is costly. 2. The thermocouples in the furnace chamber of the vaporization furnace have a short service life. 3. The Texaco burner has a short service life. It generally lasts for about 50 days. 4. Black water pipelines are prone to clogging, scaling, and erosion. 5. The quenching ring is prone to cracking, with the fire-facing side suffering from perforation caused by high-speed incoming water flow and high-temperature deformation. 6. Water streaking occurs to varying degrees in the quench chamber, limiting the high-load operation of the vaporization furnace. GSP gasification is a medium to large-scale gasification technology that was developed by the former **German GDR Fuel Research Institute and put into commercial operation. It combines all the advantages of Texaco and Shell, but this technology is currently used only for power generation. There is no precedent for its use in ammonia synthesis projects at present. Manufacturer used and performance: Texaco. Type of plant, Name of plant, Location, Capacity per furnace (coal/t/d), Date of construction, Heat recovery method, By-products. For industrial production: Lunan Fertilizer Plant, Shandong – 160, 1991; Cold quenching, Ammonia. Shanghai Coking Plant, Shanghai – 450, 1995; Cold quenching, Fuel gas. Weihe Fertilizer Plant, Shaanxi – 650, 1996; Cold quenching, Ammonia. Jinling Petrochemical, Nanjing – 500, 2005; Cold quenching, Ammonia. Huahua Group Co., Ltd., Anhui – 450, 2000; Cold quenching, Ammonia. Shell. Type of final product, Processing capacity (t/d), Number of gasifiers. Raw materials, Date of commissioning. Yingcheng, Hubei – Synthetic ammonia, 1000. Liuzhou, Guangxi – Synthetic ammonia, 1100. Yueyang, Hubei – Synthetic ammonia, H2, 2000. Zhijiang, Hubei – Synthetic ammonia, Methanol, 2000. Kunming, Yunnan – Synthetic ammonia, 2700. Dalian, Liaoning – Methanol, 1200. Zhenyi, Yunnan – Synthetic ammonia, 2700. Anqing, Anhui – Synthetic ammonia, H2, 2000. Shenhua, Inner Mongolia – H2. Yongcheng, Henan – Methanol. Xinxiang, Henan – Methanol. Yima, Henan – Methanol. Tianjin Bohai – Synthetic ammonia, Methanol