Introduction to multi-nozzle water-coal slurry gasifier

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Shandong Yankuang Group Co., Ltd. (Slurry Gasification and Coal Chemicals ** Engineering Research Center), in collaboration with East China University of Science and Technology, has successfully developed a new type of multi-nozzle opposed slurry gasification technology with independent intellectual property rights, based on the digestion and adaptation of Texaco’s slurry gasification technology. This technology is one of the most advanced fluidized-bed gasification technologies in the world. It will serve as a key and leading technology for the technological upgrading of China’s fertilizer industry, as well as for the development of coal liquefaction, integrated gasification combined cycle power generation (IGCC), and coal-based cogeneration technologies. It will **promote the advancement of coal chemical technology in China and drive technological progress in related industries. 1 Introduction to the Multi-nozzle Opposed Gasification Furnace 1.1 Gasification Flow Field In the laboratory, the flow field within the gasification furnace was studied using a large acrylic model of an opposed gasification furnace with a diameter of 1000 mm; it was found that this flow field can be divided into a jet zone, a impact zone, impact flow zones (two upper and two lower), six recirculation zones, a backflow zone, and a pipe flow zone, as shown in Figure 1. Research shows that the impact zone is the area within the gasifier where mixing between different fluid streams is most intense, and it enhances the atomization and mixing processes in the gasifier in the following ways. (1) The relative movement of oxygen and coal slurry within the impact zone generates shear force, which promotes further fragmentation of the coal slurry droplets and improves the atomization process. (2) Four jet streams combine through impingement to form an impinging jet stream, whose axial velocity decays more rapidly; as a result, the residence time distribution of the fluid within the furnace improves, that is, the \"short-circuiting\" phenomenon is suppressed. (3) The particle oscillation phenomenon occurring within the impact zone results in a relatively longer residence time for the particles. (4) The velocity fluctuations are severe within the impact zone, and the turbulence intensity is at its highest, indicating the best mixing effect. 1.2 Gasification reaction mechanism: After water-coal slurry and oxygen enter the gasification chamber, six physical and chemical processes take place sequentially: atomization, heat transfer, evaporation, removal of volatiles, combustion, and gasification. The first five processes occur at a relatively fast rate and are essentially completed in the five flow pattern regions numbered 1, 2, 3, 4, and 5. While the gasification reaction takes place in these five regions as well, it primarily occurs in the tubular flow region. The gasification process of coal slurry particles in the gasifier involves steps such as turbulent dispersion of the particles, oscillatory motion, convective heating, radiant heating, evaporation of the coal slurry and release of volatiles from the particles, gas-phase reactions of the volatile products, multiphase reactions of the coal char, and the formation of ash and slag. This technology was tested on a pilot scale at Lunan Fertilizer Plant using a distributed control system, and the results showed that the pilot plant operated smoothly and safely, with an advanced process design ； Under the same coal type and slurry concentration conditions, compared with the Texaco unit introduced by Lunan Fertilizer Plant, its volume fraction of useful gases (CO + H2) increased by 1.5%–2.0%, the carbon conversion rate increased by 2%–3%, and oxygen consumption was reduced by 2.0%–7.0%. Technical parameters such as the composition of useful gases, carbon conversion rate, specific oxygen consumption, and specific coal consumption all showed significant improvements. 2 Industrial applications: Currently, there are 4 multi-nozzle opposed water-coal slurry gasification furnaces in operation, one of which belongs to Shandong Dezhou Hualu Hengsheng Chemical Co., Ltd., with a daily coal processing capacity of 750 t ； 3 units at Shandong Yankuang Guotai Chemical Co., Ltd., with a daily coal processing capacity of 1,150 t. 2.1 Application at Shandong Hualu Hengsheng Chemical Co., Ltd. Through a patent licensing arrangement, and with the support of the **NDRC’s ‘Tenth Five-Year Plan’ project for the development of key technical equipment, the multi-nozzle opposed water-coal slurry gasification technology was applied in Shandong Hualu Hengsheng Chemical Co., Ltd.’s project to achieve domestic production of large-scale nitrogen fertilizers. One multi-nozzle opposed water-coal slurry gasification unit (6.5 MPa) was constructed; this unit successfully started operating with its first feed in December 2004, began full-scale operation on June 2, 2005, and in March 2006, **organized an on-site assessment of the project aimed at ensuring domestic production of nitrogen fertilizers. The assessment results show that the carbon conversion rate of the gasifier is 99.9%, the volume fraction of useful gases is 84%, and the carbon content in the slag is less than 5%. It generates approximately 50,000 yuan more in economic benefits per day compared to water-coal slurry gasification units of similar scale. 2.2 Application at Yankuang Guotai Chemical Co., Ltd. 2.2.1 Project Overview During the 10th Five-Year Plan period, following the approach of using projects to drive research and development, and using research and development to advance projects, Yankuang Group Co., Ltd. decided to construct a multi-nozzle opposed water-coal slurry gasifier with a capacity of 1,150 tons of coal per day and a pressure of 4.0 MPa. This was accompanied by a methanol production project with an annual capacity of 240 kt and a gas power generation project with a capacity of 71.8 MW; the total investment in these projects was 1.6 billion yuan. This is the first demonstration project for a coal gasification combined heat and power system in our country. It involves two projects under the **\"863\" program**: namely, the \"Industrial Demonstration Unit for New Water-Coal Slurry Gasification Technology\" and the \"Research, Development, and Demonstration of Key Technologies for Coal Gasification for Power Generation and Methanol Production.\" The former project commenced construction on May 1, 2003, with China National Third Chemical Engineering Construction Company being responsible for the construction of the gasification unit and the air separation unit. The gasification unit was designed by China Tianchen Chemical Engineering Company; the gasifier was manufactured by Harbin Boiler Factory, while the refractory bricks were produced by Gaonai Factory of Luoyang Refractory Materials Research Institute and Xinxiang Refractory Materials Factory ； The air separation unit was designed by China Hualu Engineering Company, and an air separation unit with an internal compression process using 60,000 m3/h (standard conditions) liquid oxygen pumps was selected ； The air compressors and air boosters in the air separation unit are driven by 40 MW fully condensed steam turbines, ensuring smooth startup and stable operation ； The synthesis unit employs advanced international low-pressure methanol synthesis technology, while the synthesis tower utilizes a patented technology from East China University of Science and Technology – an adiabatic isothermal methanol synthesis reactor ； Methanol distillation employs an energy-saving three-column process. The internal components of the distillation tower use structured packing ； The NHD process is used for the removal of acidic gases (H2S and CO2) ； The sulfur recovery process utilizes the Claus + SCOT sulfur recovery technology. This industrial demonstration project passed the 168-hour on-site industrial operation test organized by the China Petroleum and Chemical Industry Association in December 2005. 2.2.2 Process Flow The process flow of the industrial demonstration unit for the coal gasification power generation and methanol co-production system is shown in Figure 2. Coal, water, and coal slurry additives are fed into the coal mill to produce a coal slurry with a mass fraction of 60%–65%; this slurry is then pressurized by a coal slurry feed pump and sent to the 4 process burners ； Pure oxygen from the air separation unit is divided into 4 streams, which, after flow regulation, are fed into the process burners. The water-coal slurry is injected into the gasifier together with oxygen through process nozzles, where a shock reaction zone is formed to carry out partial oxidation reactions. The resulting crude syngas and slag move downward together into the gasifier’s quench chamber; most of the slag solidifies as it is cooled in a water bath, falling to the bottom of the quench chamber. It then passes through a static slag breaker before being collected in a hopper for regular disposal ； The crude syngas bubbles at the liquid level in the quench chamber of the gasifier before exiting that chamber; it then enters a impact mixer and a cyclone separator, and is subsequently sent to a washing tower for dust removal. The syngas with a dust content of less than 1 mg/m3 (under standard conditions) is divided into two streams: one stream is sent to the gas power generation unit, while the other is sent to the methanol production unit. The water gas used in combined cycle power generation with gas turbines/steam turbines is hydrolyzed in an organic sulfur hydrolysis tank before being sent to the NHD desulfurization system. The desulfurized gas is then fed into the gas turbine to generate electricity, while the flue gases go directly into a waste heat boiler to produce steam; this steam is fed into the steam network to drive a steam turbine for power generation. The water gas used for methanol production undergoes sulfur-resistant shift reaction and NHD desulfurization and decarburization; the resulting qualified syngas is compressed by a compressor before being fed into the methanol synthesis reactor, with the pressure in the methanol synthesis system being 5.0 MPa. 2.2.3 Operation Status: Construction of the new multi-nozzle opposed water-coal slurry gasification unit officially began on May 1, 2003 ； In July 2005, the gasification unit achieved successful first-time feeding, the process flow was established, and it operated continuously for 80 hours ； After the accompanying 240 kt/a methanol plant came online on October 15, 2005, it quickly reached its design capacity; in 2006 it produced 234 kt of methanol and generated 230 million kW·h of electricity. It reached its designed capacity in the first year of operation, indicating that the technology is mature and reliable. Currently, the entire plant is operating stably and has far exceeded its designed capacity; 99.5 kt of methanol was produced in the first four months of 2007, with an annual production volume reaching 300 kt. By the end of 2007, China’s first new type of multi-nozzle opposed coal slurry gasifier with a daily processing capacity of 1,150 tons of coal had been operating stably and continuously for 68 days at Yankuang Guotai Chemical Co., Ltd. The process burners were in use continuously for 85 days, setting a new record for the continuous operation time of this type of gasifier. Additionally, pressure-driven startup technology was implemented; to date, 10 such operations have been carried out, saving nearly 7 million yuan in costs. Guotai’s third gasifier (C# unit) was put into operation on September 3, 2007. Based on the current situation, the benefits of raising the roof height are already evident: compared to the initial period after the replacement of the roof bricks in unit B#, the wall temperature at the roof of unit C# has decreased by approximately 47°C, indicating that the working conditions for the refractory bricks in the upper space have improved significantly, which should ensure a long service life for these bricks. During the initial operation of the plant, both the A# and B# gasification furnace domes encountered a problem in which the dome refractory bricks were eroding at a rate faster than normal. Through the joint efforts of East China University of Science and Technology and Yankuang Group Co., Ltd., the design of the dome refractory bricks/precast blocks was modified on four occasions under the existing equipment conditions; the structure of the process burners was adjusted, and operating procedures were optimized. Currently, the continuous service life of the process burners is 85 days, while the lifespan of the dome refractory bricks is around 5,000 days. The refractory bricks in the straight-section area have not been replaced since October 2005. After nearly two years of operation of the multi-nozzle opposed water-coal slurry gasification unit at Chongkuang Guotai Chemical Co., Ltd., all the problems that arose in the initial stage of operation have been **solved**. At present, the facility is in good operating condition, with advanced process parameters; the system operates safely and stably, and its operation and control methods are advanced and flexible, resulting in excellent economic benefits. The operation of the multi-nozzle opposed water-coal slurry gasification technology at Yankuang Guotai Chemical Co., Ltd. demonstrates that this technology is mature and ready for large-scale market application. 2.2.4 Operating Characteristics (1) The volume fraction of the active gases (CO + H2) in the syngas reaches 84.9%, which is 2.0%–3.0% higher than that in single-nozzle water-coal slurry gasifiers. (2) The carbon conversion rate reaches 98%–99%. The mass fraction of combustibles in the slag of single-nozzle water-coal slurry gasifiers is generally between 25% and 40%, while that in the slag of multi-nozzle opposed water-coal slurry gasifiers is usually between 5% and 15%, with an average value below 10%. (3) 1.35 t of coal is consumed per ton of methanol, while at Yankuang Lunan Fertilizer Plant, which uses a single-nozzle water-coal slurry gasifier, 1.45 t of coal is consumed per ton of methanol. (4) Multi-nozzle opposed water-coal slurry gasifier is more suitable for large-scale applications. Since a single-nozzle water-coal slurry gasifier has only one process nozzle, increasing the gasification load is limited, and enlarging the burner gap will affect the atomization effect. When the mass fraction of coal slurry is 59.0% and 1500 t of coal is processed per day, the effective gas volume fraction in the single-nozzle coal slurry gasifier is below 80%, while the mass fraction of combustibles in the slag is above 25%. (5) In a multi-nozzle opposed coal water slurry gasifier, when one pair of burners fails (the failure is not due to issues with the burners themselves), the other pair of burners can maintain production in the downstream system; the failed burner can be reactivated under pressure. In contrast, a single-nozzle coal water slurry gasifier has only one process burner, and when that burner fails, the entire gasifier must be taken out of service. If there is no backup unit in the system, this will result in the shutdown of the entire system, leading to significant losses associated with starting up and shutting down the system. (6) Due to the significant difference in its flow field compared to single-nozzle water-coal slurry gasifiers, multi-nozzle opposed water-coal slurry gasifiers allow high-temperature thermocouples to have a longer service life, with an average service life of ≥2 months. (7) The gas purification and slag-containing water treatment processes are advanced. To date, the sulfur-resistant shift catalysts are still performing well, and it is expected that they can continue to be used for another year without issues. 3. Development prospects: The multi-nozzle opposed water-coal slurry gasification technology, which possesses complete independent intellectual property rights and is the first of its kind in the world, is at an international advanced level in the field of water-coal slurry gasification. The industrial demonstration plant built for this technology has successfully been put into commercial use, enabling China to have its own large-scale coal gasification technology for the first time; this marks that China now has the capability to compete with foreign gasification technologies. The multi-nozzle opposed water-coal slurry gasification technology possesses unique advantages and strong market competitiveness. It is widely applicable in the production of coal-based syngas, and is particularly suitable for large-scale coal chemical plants and coal-based combined production systems, offering very broad application prospects. Currently, a total of 27 multi-nozzle opposed water-coal slurry gasifiers are under design and construction, and several other companies intend to adopt this technology.