New dry powder gasification furnace: capable of handling both upper and lower processes”

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New Type of Dry Powder Gasification Furnace Capable of Handling Both Types of Coal Sources/Author: China Chemical Industry News Date: June 23, 2016 Clicks: 176 Reduction in fly ash and wastewater emissions On June 19, reporters learned from Beijing Xingrongtai Chemical Technology Co., Ltd. that the company’s new generation of coal gasification technology for low-quality coal has been successfully applied in the technical renovation project of the circulating fluidized bed gasification furnace at Tongliao Jinmei Chemical Co., Ltd., a facility capable of producing 150,000 tons per year of ethylene glycol along with 100,000 tons per year of oxalic acid. The 62,500 Nm3/h capacity gasification furnace, which uses lignite as raw material, was operated on a trial basis for 219 hours; it withstood various operating conditions successfully, and all related technologies have become fairly mature. The system operates continuously and stably, meeting most of the design requirements, which marks the successful development of this new generation of dry powder coal gasification furnaces by China. 　　　According to Tai Xuelin, general manager of Beijing Xingrongtai Chemicals, this technology uses a special circulating fluidized bed gasifier to replace the drying and grinding units in existing fluidized bed dry coal gasification technologies. It also possesses a primary gasification function, allowing the coal gas and coal powder produced by the circulating fluidized bed gasifier to be further gasified at a high temperature of around 2000°C. This approach eliminates the need for drying and grinding, as well as the need to add fluxes, thereby enabling the gasification of dry coal at even higher temperatures. 　　　 Tai Xuelin said that Tongliao Jinmei Chemical Co., Ltd. uses lignite as raw material and possesses 3 circulating fluidized bed gasification units for pulverized coal. Before the renovation, the 3 units consumed approximately 100 tons of lignite per hour, produced around 100,000 Nm3 of gas, and generated about 30 tons of fly ash. Most of the resulting fly ash enters the sedimentation tank along with the hydraulic ash removal system and washing water, turning into wet ash. The calorific value of these coal ashes is over 2,000 kcal, with a residual carbon content between 20% and 30%; the difficulty in handling wet ashes and ash water poses a significant challenge for the company. “Traditional circulating fluidized bed gasification is a low-temperature and atmospheric-pressure process that fails to completely decompose the organic substances in coal, posing significant environmental hazards. ”Tai Xuelin said. 　 Tai Xuelin told reporters that this project not only reduces the levels of organic pollutants such as residual carbon in fly ash, the amount of fly ash, and ammonia nitrogen in wastewater, thereby significantly decreasing environmental pollution, but it also boosts the conversion efficiency of carbon in coal and the content of useful gases in raw gas. It further reduces oxygen and coal consumption, helping enterprises to cut costs and save energy. Beijing Xingrongtai Company provided the patent license, as well as the technical modification plans for the primary gasification furnace and the technical design for the autothermal gas and coal powder counter-current fluidized bed gasification furnace. China Tianchen Engineering Co., Ltd. was responsible for the design of the supporting systems. From May 24 to June 2, 2016, the system underwent 219 hours of continuous and stable trial operation. Preliminary trial production shows that the composite powder gasification technology requires approximately 570 kg of lignite equivalent to standard coal per thousand cubic meters of useful gas produced, with an oxygen consumption of around 340 Nm3, an electricity consumption of about 30 kWh, and a cooling water consumption of roughly 15 tons per cycle ； The water consumption per use is around 0.75 tons ； Approximately 1,000 kg of sub-high-pressure steam at 5.4 MPa and 540°C is produced as a by-product. The fly ash and carbon residue in the gas are less than 1%; the ammonia nitrogen content in the gasification cycle water is only about 10% of that in conventional circulating fluidized bed gasifiers. The suspended solids in the gasification cooling water amount to around 0.3% of those in conventional circulating fluidized bed gasifiers, and there is no discharge of phenolic or petroleum-based wastewater. “Based on technical considerations and pilot operation results, once the crushing and screening of raw coal come online and the particle size of the coal fed into the furnace meets the design specifications, the coal consumption and oxygen consumption per thousand cubic meters of useful gas can be reduced by about 10%, while the content of useful gas can increase by around 10 percentage points; other types of consumption can also be further reduced. ”Tai Xuelin said. 　 　　　 Link: Technical characteristics of the composite powder gasification furnace. The composite powder gasification furnace is a dry powder gasification unit composed of an internal-circulation fluidized-bed powder gasification furnace, a self-heating counter-current gas-coal fluidized-bed gasification furnace, and their associated facilities. This gasification unit employs fluidized-bed pulverized coal gasification technology to partially gasify pulverized coal, producing high-temperature gas and coal powder. These are then fed into a self-heating counter-current gas-coal fluidized bed gasifier. In this reactor, the high-temperature gas reacts with oxygen to produce carbon dioxide and water vapor; at the same time, a high-temperature zone of over 2000°C is created. At such high temperatures, the coal powder reacts chemically with carbon dioxide and water vapor to produce carbon monoxide and hydrogen, thereby enabling the gasification of coal at even higher temperatures. Since the reaction between coal powder and carbon dioxide and water vapor is an endothermic reaction, the temperature of the gas leaving the high-temperature reaction zone gradually decreases. The temperature of the gas exiting the gasifier is already **below the ash melting point, allowing the valuable chemical energy in the raw coal to be converted into chemical energy in the gas to the greatest extent possible, thereby achieving a higher efficiency for cold gas production. Since the gasification temperature is around 2000°C, it is not necessary to add fluxes in order to carry out the slag gasification process successfully; this results in a higher carbon conversion rate, less fly ash, lower carbon content in the fly ash, and lower carbon content in the slag. Since the refractory bricks in the slag fluidized bed gasifier are not subjected to slag erosion, their service life is **extended**. Since the primary gasifier is a fluidized-bed pulverized coal gasifier that uses a screw feeder for feeding, apart from lignite with a moisture content higher than 25%, the feed coal only needs to be crushed. This eliminates the risk of explosions that can occur during the drying and grinding of pulverized coal, as well as the environmental pollution issues associated with the exhaust gases and dust generated by such drying and grinding systems.