Current Status of High-Efficiency and Clean Coal Powder Combustion Technologies and Products in Our Country

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Abstract: This paper provides an overview of the recent developments in technologies such as clean combustion of coal powder, flue gas desulfurization and denitration, and dust removal, both domestically and internationally. It also presents the current status of related technologies and products in China. 　　The paper focuses on the research and engineering applications in coal powder distribution technology and high-efficiency clean combustion technology carried out by this institution during the \"Eighth Five-Year Plan\" and \"Ninth Five-Year Plan\" periods, as well as the achievements obtained. These include: 1. Status of development of basic research facilities: construction of coal-related basic research facilities, introduction of the atmospheric pressure entrained flow gasification and combustion simulation apparatus (AEFGC) from the Dutch ECN, introduction of the 640 MJ combustion apparatus (CRF) from Canada, and development of other facilities for research on gas-solid two-phase flows and aerodynamic properties. 2. Research progress: Undertaken multiple research projects, including two main topics and four sub-topics within **key research projects designated by the Science and Technology Commission, as well as several key research tasks assigned by the former Ministry of Electric Power. The main research areas include: adjustable and controllable coal powder distribution technology, concentration technology, high-efficiency and low-pollution combustion technology, energy-saving technology, mixed coal combustion technology, desulfurization technology, dust removal technology, and other control technologies. 3. Application status: It introduces the engineering application results of the aforementioned technical products in 600MW, 300MW, and 200MW units respectively, and provides a brief overview of the performance of each type of technical product. In addition, this paper also puts forward suggestions on the development direction of **clean coal combustion technology during the 10th Five-Year Plan period**, and introduces the key research areas and development directions of this institution. Preface: In recent years, as countries have placed increasing emphasis on environmental protection, movements to control pollution and safeguard the environment have emerged worldwide. New environmental protection technologies and products continue to emerge, while new challenges are also constantly arising. Coal powder combustion plays an important role in pollution emissions, and it has always been a key focus as well as a challenge in pollution control. Many **have made it a central task in their efforts to address environmental pollution, and have achieved relatively significant results. It is predicted that from 2000 to 2010, coal will still account for around 70% of China’s demand for primary energy, and this proportion could drop below 50% by 2050; however, the absolute amount of coal consumed will still **increase**. Therefore, for our country**, to control the overall environmental protection indicators, it is first necessary to curb pollution caused by coal combustion; the way forward lies in vigorously developing clean coal technologies aimed at the efficient and clean use of coal. Over the more than decade of continuous development in clean coal technology, many products and complete sets of technologies have been developed both domestically and internationally. There are advanced coal sorting technologies, coal slurry technologies, coal gasification, and coal liquefaction technologies. There are also technologies such as circulating fluidized bed, pressurized circulating fluidized bed, and integrated gasification combined cycle. In addition, there are flue gas purification technologies at various levels of efficiency, as well as technologies for the comprehensive utilization of fly ash. Considering the current situation in our country, high-efficiency and clean coal powder combustion as well as flue gas purification technologies are likely to have broad application prospects in the near future. Current status of high-efficiency and clean coal powder combustion technology and flue gas purification technology. High-efficiency and clean coal powder combustion as well as flue gas purification technologies include high-efficiency combustion technology, low-NOx combustion technology, flue gas desulfurization technology, flue gas denitration technology, dust removal technology, etc. A brief introduction is as follows: Generally speaking, high-efficiency coal powder combustion technology and low-NOx combustion technology are two mutually contradictory techniques. To reduce NOx generation and emissions, it is essential to keep the temperature in the combustion zone from being too high. However, low-temperature combustion affects the combustion rate of coal powder; the goal is to optimize the application of these two techniques together to achieve the best overall results, which in practice requires controlling the entire process of coal powder combustion. It ensures the stability of coal powder ignition, has a low combustion temperature, and at the same time provides a sufficiently long combustion time at a certain temperature to ensure complete combustion. The more advanced combustion technologies available in the world today take these factors into account to a large extent. Among those that use direct-flow burners, ABB-CE employs the inertial separation effect of the primary air elbow; a perforated partition is installed at the outlet of the elbow to divide the coal powder airflow into two streams – one rich at the top and one lean at the bottom – thereby creating upper and lower rich-lean coal powder burners. An axially adjustable V-shaped baffle is also installed at the nozzle, and by properly organizing the secondary air, a combustion process that is stable, efficient, and results in low NOx emissions is achieved ； Japan’s Mitsubishi Heavy Industries (MHI) has developed the PM-type burner, which utilizes the centrifugal force of elbows to divide the primary air into two streams of different concentrations, upper and lower; meanwhile, the use of flue gas recirculation and overall staged combustion within the furnace also yields good results. Those that primarily use swirl burners include FW Company, which utilizes cyclones to increase the concentration of primary air entering the main burner and to reduce the primary air velocity, thereby ensuring the stability of ignition of the coal powder stream and controlling the amount of NOx generated ； Other types that find extensive industrial use include B&W Company’s PAX type swirl coal burner, Japan’s IHI Company’s swirl coal burner with a wide adjustment range, and Germany’s Steimiller Company’s multi-stage air supply swirl burner. All of the above industrial products can ensure that NOx emissions remain below 400 mg/Nm3, and they feature high combustion efficiency. The low-NOx combustion technologies currently under development abroad can control the NOx generation level at around 200 mg/Nm3, which represents a fairly high level. However, since many advanced countries around the world have set strict standards for NOx emissions, it is difficult to meet these limits merely by improving combustion techniques; as a result, some boiler units are equipped with flue gas denitration systems at the rear. In recent years, our country has also developed many types of low-NOx combustion technologies. Representative ones include stratified coal powder burners, such as horizontal stratified burners, vertical stratified DC burners, swirl burners, and controllably stratified swirl coal powder burners. However, due to issues such as the variety of coal types in our country, these technologies have encountered some problems in practice; even coal-fired power units manufactured using similar foreign technologies face the same issues. Through efforts, a set of combustion technologies for stable combustion at low loads with low NOx emissions, which possesses a certain degree of adaptability to different types of coal, has been developed and put into industrial use for lignite boilers. These technologies enable NOx emissions to be kept below 400 mg/Nm3, while maintaining a combustion efficiency of over 99%, which is quite advanced. Flue gas desulfurization, denitration, and dust removal are the three main aspects of flue gas purification. In flue gas desulfurization, wet desulfurization holds an absolute dominant position, accounting for over 90% of the market in developed countries. Other desulfurization technologies include semi-dry desulfurization, calcium injection in the furnace with tail wetting, flue gas recirculating fluidized bed method, and electron beam ammonia method. From a development perspective, wet flue gas desulfurization remains dominant due to its high performance metrics, while the circulating fluidized bed desulfurization method for flue gas also gradually gains a share of the market thanks to its comprehensive technical and economic advantages, and it will be increasingly widely used in the future. For our country, it is best to adopt wet flue gas desulfurization technology and equipment from the start for newly built power units ； The modification of the units depends on the sulfur content of the coal type; for high-sulfur coal, the flue gas-circulated fluidized bed method can be used, while for low-sulfur coal, calcium injection into the furnace combined with wetting at the exhaust end can be employed. In particular, the numerous water film dust collectors that are already in use can have their value fully utilized. In terms of flue gas denitration, selective reduction reactors are generally used abroad to remove most of the nitrogen oxides from flue gas, while other methods are still in the stage of development and research. Due to constraints such as funding and site availability in the domestic market, there are no precedents for industrial applications at present, and the capacity to build demonstration units does not exist yet. In terms of flue gas dust removal, as developed countries impose increasingly strict requirements on dust emission levels and the efficiency of removing ultra-fine particles, many countries have gradually replaced electrostatic precipitators with pulse-jet bag filters, a practice exemplified by countries such as Australia and the United States. Our country plans to replace the cyclone dust collectors or water film dust collectors used in a large number of medium-sized units with electrostatic dust collectors in the near future, with the requirement that the exhaust dust concentration should not exceed 200 mg/Nm3, and no requirements exist for floating dust. For the proposed Dalian Taishan pressurized circulating fluidized bed boiler, the Chinese side plans to use pulse reverse-blow bag filters in order to achieve high performance. **Research activities and the application of results during the \"Eighth Five-Year Plan\" and \"Ninth Five-Year Plan\" periods at the Power Plant Combustion Engineering Technology Center; Introduction to the research facilities. Whether it is mechanism research or pilot-scale tests, they can be divided into three categories: aerodynamic characteristic tests, gas-solid two-phase flow characteristic tests, and coal combustion characteristic tests. Therefore, the center constructed three separate test halls to meet the specific requirements of each type of test. The aerodynamic performance testing hall covers an area of 800 m2 and is equipped with a main air supply system; the total air flow rate is 50,000 Nm3/h. It is divided into four areas: the area for studying the flow characteristics of individual burners, the area for examining flow patterns inside the furnace, the area for optimizing structures to reduce energy consumption and flow resistance, and the area for testing measurement devices, dampers, as well as other product technologies. The testing instruments include the Dandy 3D hot-wire system, PIV system, and other conventional instruments. To date, more than 30 bench test studies have been completed, and good results have been achieved in numerous field applications. In addition, there are other supporting mechanism research test benches and flow field calculation software, etc. The gas-solid two-phase flow test hall covers an area of 500 m2 and is equipped with a main air supply system. The total air volume is 35,000 Nm3/h, the pressure head is 10,000 Pa, and the powder supply rate can reach 200 kg/h. The available powders include silicon carbide, coal dust, and power plant fly ash. Research can be conducted on the development of burners with variable intensity, improvements to cyclone separators and dust collectors, as well as on electrostatic dust collection and bag filter dust collectors; studies on the flow characteristics of desulfurization towers can also be carried out, along with wear testing. In addition, there are separate test benches for coal powder distributors, test benches for automatically adjustable cascade louver coal powder distributors, and other mechanism test benches. The testing instruments include a laser holography system, a sheet light source imaging system, a Coulter particle size analyzer, an optical fiber concentration analysis system, a flow field pattern reproduction and analysis system, as well as other conventional testing systems for concentration and flow fields. The coal combustion characteristics test hall covers 700 m2 and can be divided into three main sections. The first major part involves the introduction of the Coal Combustion Pilot Test System unit (CRF) from Ontario Hydro in Canada. The coal consumption is 20 kg per hour, with a thermal power of 0.2 MW. The device consists of a raw coal drying system, a raw coal crushing system, a powder production system, a combustion system, primary and secondary air systems, a flue gas treatment system, an in-furnace calcium injection system, a flue gas dust removal system, a flue gas composition testing system, and a control system. The testing system and control system utilize the Rosemount online flue gas analysis system as well as other flow, temperature, and pressure sensors; all of these inputs are fed into a computer, which then performs online dynamic adjustments to all variables in order to meet the requirements of the tests. This device can comprehensively and accurately simulate the entire process of raw coal drying, crushing, grinding, powder transportation, combustion, and flue gas treatment. It enables focused evaluation and research on the impact of operating parameters and fuel quality on combustion stability, burnout degree, sediment formation, pollutant generation, as well as particle emission and collection. Furthermore, it facilitates the development of new low-NOx combustion technologies, in-furnace calcium injection techniques, and other flue gas treatment methods. This system features a high degree of automation, advanced control and testing instruments, as well as good reproducibility in experiments, enabling extensive technical development and research; it is one of the more advanced coal combustion testing systems available internationally. Currently, the center has made further modifications to this testing setup: it has rebuilt the combustion system, increased the combustion power to 0.3 MW, added a humidification and activation device at the exhaust gas outlet, installed a flue gas desulfurization system using the suspension method, and is conducting new research. The second major component is the atmospheric pressure entrained flow gasification and combustion simulation apparatus (AEFGC), developed in collaboration with the Dutch Energy Foundation (ECN). It is equipped with an integrated, premixed, multi-stage flat-flame gas burner that consumes approximately 5 grams of coal per hour. By providing different mixtures of gas and powder at various stages, it simulates the initial heating rate, premixing, and gaseous environment that particles experience in actual processes, serving as a foundation for studying the behavior of individual particles. It is equipped with a gas analysis system, a powder feeding system, a testing system, and other advanced control systems. The third section consists of basic research facilities, including a thermogravimetric/differential thermal synchronous analysis laboratory, and laboratories for the rapid analysis of fuel elements as well as the analysis of other properties of fuels. Experimental studies and analyses can be conducted on the ignition characteristics of coal, the burnout rate, the kinetics of combustion reactions, and the mechanisms of desulfurization. In addition to these physical studies, the center has also assigned specialized personnel to carry out numerical simulation research on flow, diffusion, and combustion. It has imported from Germany a set of numerical simulation software including NOx generation prediction, and has achieved certain results. Research and Application Status During the “Eighth Five-Year Plan” and “Ninth Five-Year Plan” periods, the center undertook over a hundred vertical and horizontal research projects, as well as projects related to production improvement and industrial manufacturing. Among them are **seven sub-projects under the key research projects of the Science and Technology Commission for the Ninth Five-Year Plan**, and **two demonstration production line construction projects from the Planning Commission**. In addition, over a hundred papers have been published domestically and internationally, and the individual has received numerous awards from the **Science and Technology Commission**, **electricity companies**, Northeast Electric Power Group Company, Liaoning Province’s Science and Technology Commission, and Shenyang City. Here is a brief introduction to the key research topics and their applications. Development of low-NOx combustion technology with overall low classification – This project is a sub-topic of the key research project during the “Ninth Five-Year Plan” period. The research aims to develop a practical technology that separates the coal powder ignition zone from the combustion zone as a whole, thereby achieving stable combustion at low loads, low NOx emissions, improved coal powder combustion efficiency, reduced slag formation within the furnace, and increased power output of the unit. Through various research methods such as theoretical analysis, numerical simulation, laboratory mechanism studies, and pilot-scale tests, Chinese and German experts jointly developed an engineering modification plan, which was then implemented on Unit 2 of the Yuanbaoshan Power Plant. This boiler was manufactured by the German company Steimueller, with a rated evaporation capacity of 1814.25 t/h; it came online in 1986. As the largest thermal power unit in the country at that time, it faced serious problems such as severe slagging inside the furnace, excessive overheating of the reheater, a boiler output of only 75% of its rated value, and NOx emissions of over 1000 mg/Nm3. After the implementation of the renovation plan, all the aforementioned problems were resolved. Furthermore, the implementation of the renovation plan is relatively easy. The completion of this project has enabled the center to achieve good results in understanding the combustion characteristics of lignite, organizing the combustion structure effectively, reducing pollutant emissions, and minimizing slag formation. Research on adaptive low-NOx coal powder combustion technology. This project is a sub-topic of the key research project under the **9th Five-Year Plan**. Typical low-NOx combustion technologies do not change with variations in coal type, nor do they adjust in response to changes in load. As a result, in situations where there are significant variations in coal type and load, contradictions such as nozzle slagging or poor low-NOx combustion performance inevitably arise. In this project research, a two-stage concentration method was adopted for coal powder: the first stage consists of an automatically adjustable enhanced-concentration device or forced distributor, while the second stage is a basic concentrator. Combining the two methods enables a continuously adjustable concentration ratio that changes in sync with variations in load and coal type, thus achieving a controllable combustion process. This enables functions such as adjustable thermal load along the furnace height, improved combustion efficiency, low-NOx combustion, reduced reheat water demand, prevention of slag formation inside the furnace, and good stable combustion performance at low loads. This technology and products are suitable for the combustion and coal grinding systems of fan coal mills; when implemented, they should be used in conjunction with the FDD intelligent flow measurement devices developed by the center to ensure proper adjustment of secondary air, etc. This technical product has been applied to two 300MW units and three 200MW units, yielding considerable economic and social benefits in all cases. Development of a coal powder distributor that is adjustable, controllable, capable of achieving even distribution, uniform current flow, and low resistance; this project is also a sub-topic of the key research projects under the **“Ninth Five-Year Plan”**. For medium-speed coal mills or double-inlet double-outlet ball coal mills, it is a requirement specified in the design standards for CE boilers to ensure that the total amount of coal powder, the coal powder concentration, and the deviation in coal powder fineness across all burners in the same mill are no more than 10%. This is also a necessary condition to ensure small variations in the thermal power output of each burner, identical ignition conditions, prevention of slag formation inside the furnace, and the proper application of modern low-pollution combustion technologies. Developing this key technology involves many disciplines and technical fields. Previously, only the United States, Germany, and Japan in the world were able to turn this technology into commercial products. Through mechanism research and pilot-scale modeling studies, the center has developed a series of complementary products such as WF-type coal powder distributors, primary air isolation valves, control valves, and quick-shut valves, designed for 200MW, 300MW, and 600MW units respectively. The aforementioned products resolved the issue of replacing the original German-made coal powder distributors at Chaoyang Power Plant. They also addressed problems such as slag formation, tripping caused by fan reversal, and loss of water in the furnace at Tieling Power Plant’s 300MW units, as well as issues related to the coal powder distributors for the domestically produced 600MW units at Yuanbaoshan Power Plant. The development of this technology provides equipment and technical support for the safe, clean, and efficient operation of large thermal power units. Research on anti-wear technologies for combustion pulverization systems. This is also a sub-project of a key research project during the \"Ninth Five-Year Plan\" period; the aim of this project is to develop economical, wear-resistant, and safe pulverization system equipment in order to extend the lifespan of the wear-prone components in coal mills. Through research, fully developed repairable medium-speed coal mill rolls and other products have been created, and they are widely used in several large thermal power plants around Shenyang. Development of flue gas desulfurization equipment for thermal power plants. This project is a key local research initiative under the **Science and Technology Commission’s Ninth Five-Year Plan**. Its core objective is to develop desulfurization equipment and technologies that suit China’s national conditions and characteristics, in order to provide technical foundations for large-scale industrial upgrades. Through several years of research, experiments were conducted on pilot-scale test rigs for calcium injection inside the furnace for desulfurization, as well as for wetting and activating the flue gas after calcium injection inside the furnace, as well as for flue gas desulfurization using the suspension method. The key aspects of these technologies and processes were identified, and preliminary designs for engineering upgrades and key equipment were developed, laying the groundwork for subsequent work. Development of integrated dust removal and desulfurization application technology. This project is a Sino-Canadian cooperation project. In the 1970s and 1980s, our country built a large number of small and medium-sized power units that used water film dust collectors for dust removal. In recent years, due to environmental protection requirements, there is an urgent need to improve their dust removal efficiency. This project utilizes mature foreign technology; the original venturi tube is removed from the design and replaced with a washing chamber and a new type of venturi tube, while the cleaning water system is provided by a newly added water circulation system. The resistance of the entire flue gas system is no greater than that of the original system, the total water consumption increases by less than half, and the dust removal performance is on par with that of a four-electrode field electrostatic precipitator. Furthermore, a desulfurization agent can be added to the water circulation system, with an expected desulfurization efficiency of over 60%; calcium injection equipment can also be installed in the furnace, achieving a total desulfurization efficiency of over 80%. In this way, existing equipment is utilized, the **standards are met, and breakthroughs have been achieved in the application of simple desulfurization technologies, yielding significant overall benefits. The demonstration project for this initiative is currently in the process of design and implementation. In addition to the six projects mentioned above, the center has also achieved results in other areas of automated control, such as high-efficiency and low-pollution combustion technologies, energy-saving technologies, coal blending combustion technologies, reliability management systems, computerized fuel management systems, automated coal conveying systems, and computerized power system drawing management systems. These technologies have been widely applied in power plants, yielding significant direct and indirect economic and social benefits. Some thoughts on the development direction of clean coal combustion technology during the 10th Five-Year Plan period. Regarding the desulfurization issue, **a long-term and stable policy should be formulated and strictly implemented to promote the large-scale and industrial development of desulfurization technologies and equipment. It also mobilizes resources to work together on efforts to localize the equipment for wet flue gas desulfurization technology, as well as on developing complete sets of solutions for CFB desulfurization technology, and uses economic incentives to encourage the development of new desulfurization technologies and processes as well as their practical application in projects. Given the constraints of the national conditions, while vigorously promoting high-efficiency and clean combustion technologies in newly built units, it is also necessary to intensify the renovation of existing units. In particular, mandatory measures should be taken regarding NOx emissions in order to advance the use of high-efficiency, clean, and low-NOx combustion technologies and reduce the impact of acid rain. Reforms to improve dust removal efficiency must take into account the situation after flue gas desulfurization in the future. Current upgrades focus on the adoption of electrostatic precipitators; if non-wet desulfurization technologies are used to upgrade the units in the future, the efficiency of electrostatic precipitation will be significantly affected. It is necessary to consider establishing demonstration projects using integrated dust removal and desulfurization technologies, and attempts should also be made to demonstrate the use of new filter bag-type dust collectors. Integrate energy-saving technologies with clean coal technologies in an organic manner, taking each other into account. Research and develop advanced clean coal technologies such as coal-fired combined cycles and coal conversion, to lay a technical foundation for their large-scale application in the next century. Vigorous research efforts should be undertaken in the field of clean energy; the technological capabilities related to clean energy sources such as solar and wind energy should be improved so that their products can reach a commercial level, and efforts should be made to promote their widespread use.