The application of four-nozzle water-coal slurry gasification technology in our company

Thread Content

Wang Zhihua (Jiangsu Linggu Chemical Co., Ltd.) 1 The current development of gasification technology: With the progress of human society, petroleum products are widely used to power cars, airplanes, and other engines. At the same time, modern petrochemical industries, which are now inseparable from modern life, continue to consume enormous amounts of oil; the depletion of Earth’s oil and gas resources is an imminent threat. The massive release of greenhouse gases into the atmosphere has triggered a crisis in the climate and the human living environment. Therefore, how to reduce humanity’s excessive reliance on oil and natural gas, delay the depletion of these resources, and find new alternative energy sources are issues that countries around the world are striving to address. With the continuous advancement of science and technology, a range of new energy and energy-saving technologies have been developed to date, particularly in the fields of coal chemical and biochemical energy technologies, which have seen rapid progress. Some companies around the world, through more than a decade or even several decades of relentless effort, have finally developed several new coal gasification technologies that allow coal to be used as a substitute for oil and natural gas, and which can also be utilized for nearly a hundred years. The new coal gasification technologies share the following common features: first, they replace the traditional atmospheric-pressure coal gasification technique that has been in use for nearly a century; the gasification pressure is increased to 4.0–8.0 MPa, which allows for a significant reduction in energy consumption in the subsequent processing steps ； Secondly, it significantly improves the utilization rate of coal, helping to conserve coal resources; the carbon conversion rate can be increased from 70%–80% to 94%–99% ； Thirdly, the combination of gasification with emerging raw gas processing technologies enables the removal of the vast majority of environmentally harmful substances, as well as their recovery and reuse. Under these circumstances, the energy structure of our country is also undergoing profound changes. Given China’s current situation of abundant coal, limited oil, and scarce gas as primary energy sources, there is a consensus on making good use of coal as a main energy source and raw material for the chemical industry. Driven by new coal gasification units, a large number of facilities for producing fertilizers, methanol, and other chemicals using coal as raw material, as well as coal liquefaction projects, are being built at full speed. Methanol can not only be used as a fuel but also used to produce ethylene and propylene through MTO and MTP technologies. These products, which were originally made from oil, began to be produced using coal as a raw material, **reducing the production costs of ethylene and propylene; this has triggered a new revolution in the history of the petrochemical industry. In addition, clean fuel DME and the like can also be produced. There are also several large-scale projects under construction for coal liquefaction, which involves converting coal into oil, including direct liquefaction and indirect liquefaction. In addition to building new facilities, some fertilizer and chemical plants that previously used oil as a raw material are adopting new gasification technologies to transform their raw material supply chains; even some facilities that use natural gas as a raw material are undergoing gasification upgrades. In the development of modern coal chemical technology, although China started late, it has achieved remarkable results in recent times, especially since the beginning of this century, in terms of research and development in the field of coal gasification as well as the exploration of new types of coal gasification technologies. Some of these technologies are even more advanced and mature than those used abroad. 1.1 Technologies using water-coal slurry as a gasification feedstock 1.1.1 The four-nozzle water-coal slurry gasifier technology developed jointly by East China University of Science and Technology and Yankuang Group – after successful testing on the pilot scale at the Shandong Lunan Water-Coal Slurry Gasification and Coal Chemicals Engineering Research Center, a 72-hour operation test was conducted on this pilot unit in October 2000. The results of this test showed that at operating pressures of 1.6 MPa and 2.0 MPa, the proportion of useful gas components (CO + H2) reached approximately 83% ； Carbon conversion rate: >98% ； Specific oxygen consumption Nm3O2/1000 Nm3(CO+H2): ~380 ； Coal consumption per 1000 Nm3 of (CO+H2), in kg of coal: ~550 ； Vaporization display temperature: ~1280°C, temperature difference inside the furnace: ~100℃ ； Device gas production rate: ~2.2 Nm3 of dry gas per kg of coal ； The above data show that China’s four-nozzle coal water slurry gasification technology, which features independent intellectual property rights, is significantly superior to the Texaco coal water slurry gasification technology. However, due to the short operation time, the lifespan of the refractory bricks and quenching rings cannot be assessed in the short term. As the ash melting point of the raw coal is low, the furnace temperature is lower than that of the Texaco gasifier; therefore, the lifespan of the refractory bricks and quenching rings will be longer than that in a Texaco gasifier. Subsequently, the four-nozzle water-coal slurry gasifier was successfully applied in the Hualu Hengsheng ammonia synthesis project and the 240 kt methanol project of Yankuang Group Guotai Chemical. The main drawback that arises when the device is enlarged is that the refractory bricks in the upper area of the four-nozzle opposed burner are prone to damage due to the influence of air currents. To address this issue, improvements have been made to the third furnace at Guotai Chemical by lengthening the upper section of the burner, which is expected to resolve the problem. Since 2006, the adoption of four-nozzle water-coal slurry gasifiers has progressed rapidly, with companies such as Linggu Chemical, SOPH, and Phoenix having successively adopted these gasifiers. 1.1.2 Two-stage oxygenation water-coal slurry gasification furnace technology: The two-stage oxygenation water-coal slurry gasification furnace technology, developed jointly by Beijing Dalike Technology Co., Ltd. and Tsinghua University, has also been granted a patent. Pilot tests have shown that the main advantage of this gasification furnace is that, since the amount of oxygen introduced into the furnace together with the water-coal slurry is lower than that in conventional Texaco furnaces and four-nozzle furnaces, the temperature of the coal slurry nozzles is correspondingly lower. As a result, the cooling water jacket is less likely to be damaged, which not only helps to extend the lifespan of the coal slurry nozzles but also extends the lifespan of the bricks used in the furnace dome. This creates conditions for long-term operation of such coal slurry furnaces ； Oxygen is added again at an appropriate position below the coal slurry nozzle in the gasifier to meet the total oxygen requirement for gasification. The secondary oxygenation process has achieved satisfactory results in pilot plant tests, and it is set to be put into operation in methanol production facilities in the second half of 2007. 1.2 Progress of dry powder gasification technology in China 1.2.1 The secondary coal powder-fed water-cooled wall gasifier developed by Xi’an Thermal Power Research Institute and Xi’an Jiaotong University. After a series of research experiments, a pilot plant of this type was established in 2004; it features a vertical water-cooled wall. During the first feeding of coal powder and oxygen, an excess of oxygen is used, resulting in high temperatures of 1500–1700°C. Before leaving the top of the gasifier, coal powder is added a second time to achieve an appropriate ratio between coal powder and oxygen. Due to the reduction reaction between the coal powder and the high-temperature syngas already present, a large amount of heat is absorbed, causing the temperature of the process gas to drop. Typically, the outlet temperature of the gasifier can be maintained at around 900°C by controlling the amount of coal powder added in the second stage. 1.2.2 Multi-nozzle pulverized coal water-cooled wall gasifier: Given that dry powder coal gasification offers advantages such as lower energy consumption and greater adaptability to different types of coal, the Shandong Lunan Slurry Coal Gasification and Coal Chemicals **Engineering Research Center is also conducting pilot tests on four-nozzle pulverized coal water-cooled wall gasifiers. It is certain that once the design of the water wall is resolved in multi-nozzle powder gasification furnaces, the advantages of dry powder gasification will become apparent. It combines the benefits of Shell’s dry powder gasification process, which uses rapidly cooled coal slurry to produce syngas, and is thus more energy-efficient and effective, especially for producing gas used as raw materials in the chemical industry. Compared to the single coal powder nozzle in GSP gasifiers, multi-nozzle gasifiers are easier to scale up, but the design of the multi-nozzle water wall requires careful consideration. 2 Four-nozzle water-coal slurry gasifier and the choice of Linggu Chemical 2.1 Four-nozzle water-coal slurry gasifier The four-nozzle water-coal slurry gasification process also uses pure oxygen and water-coal slurry as raw materials; it employs a fluidized bed reactor to carry out a partial oxidation reaction under pressurized, non-catalytic conditions, resulting in crude gas whose main components are carbon monoxide and hydrogen. Similar to the Texaco water-coal slurry gasification process, this crude gas is particularly suitable as synthesis gas for ammonia and methanol production, as well as as a feed gas for hydrogen production; it can also be used as fuel gas for IGCC power generation. The pressure for four-nozzle gasification can range from 4.0 to 8.0 MPa, with a temperature of around 1360°C. At such high temperatures, the chemical reaction rate is relatively fast, while the vaporization rate is controlled by the transport process. To this end, by arranging the nozzles opposite to each other and optimizing the structure and dimensions of the furnace, a turbulent flow is generated within the furnace to enhance mixing and mass transfer processes, as well as to create an optimal flow pattern inside the furnace. The furnace volume of the four-nozzle gasification furnace is designed to be larger than that of the Texaco furnace, resulting in a longer residence time for the reactants. All these factors combined give the four-nozzle gasification furnace better process and engineering performance compared to the Texaco gasification furnace. Four-nozzle water-coal slurry features a high effective gas content, a high carbon conversion rate, and a longer service life for refractory bricks compared to Texaco furnaces. The washing and cooling unit for gas consists of a composite bed made up of a spray bed and a bubbling bed, which provides excellent performance in suppressing water and ash contamination in the gas. The preliminary gas purification unit consists of a mixer, a cyclone separator, and a water scrubber, and features high efficiency and energy savings. The core equipment of the slag-containing heat recovery system and the slag removal unit is the evaporative hot water tower, which employs a process where steam comes into direct contact with the returned graywater. This approach offers advantages such as high graywater temperature, efficient utilization of steam, resistance to blockage by ash and slag, energy savings, and a long operational lifespan. 2.2 Selection of Linggu Chemical Industry Linggu Chemical Industry Co., Ltd. is fully aware of the advantages of the four-nozzle water-coal slurry gasification furnace. With East China University of Science and Technology and Yankuang Guotai Chemical Industry as its technical backbones, it is able to construct the gasification unit successfully, as well as ensure smooth commissioning and operation that is safe, stable, long-lasting, and at full capacity. So we ultimately decided to choose the four-nozzle water-coal slurry gasifier technology. After Linggu Chemical adopted the four-nozzle gasifier, several other companies followed suit; to date, a total of 10 companies have adopted this type of gasifier, as shown in Table 1. http://pub2.hi2000.com/upload1/0804231529038051.jpg 2.3 Advanced technologies enable clean production. Since advanced pressurized gasification technology is employed in this transformation project, corresponding advanced syngas treatment processes can also be used. The crude syngas obtained from the gasification unit is treated using advanced sulfur-resistant shift processes as well as low-temperature methanol washing processes for desulfurization and decarbonization; almost all of the sulfur contained in the raw coal is recovered as elemental sulfur. As a result, compared to traditional atmospheric-pressure gasification processes, **pollution of the atmosphere by sulfur oxides is reduced** ； The black water generated during the gasification process is, aside from most of which being recycled, partially treated using an improved biochemical treatment process; as a result, the COD of the wastewater discharged meets the standard of ≤50×10—6, and NH3-N is ≤20×10—6, which are well below the **emission standards. COD before wastewater treatment according to the design≤