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“Introduction to the Industry Standard \"Technical Requirements for Fluidized Bed Combustion Equipment\" by Tian Ziping and Chen Yongguo, School of Mechanical and Power Engineering, Shanghai Jiao Tong University. Abstract: The article provides a brief overview of the main contents of the standard and gives a detailed explanation of the technical requirements specified therein. “The industry standard for \"Technical Requirements for Fluidized Bed Combustion Equipment\" was formulated by summarizing China’s more than 30 years of experience in developing fluidized bed boilers and incorporating advanced foreign technologies. Its purpose is to improve the combustion efficiency and safety reliability of fluidized bed combustion systems, as well as to reduce environmental pollution. Keywords: standards, technical specifications, fluidized bed combustion units, boilers 1 Introduction Circulating fluidized bed boilers have seen rapid development at home and abroad due to their efficient and clean combustion technology. Fluidized bed combustion systems in our country have a development history of over thirty years. Over the past decade, various boiler manufacturers have introduced foreign technologies, enabling this field to develop more rapidly in China and giving rise to a variety of different approaches. However, there are no technical specifications for the combustion equipment of fluidized bed boilers in China yet. Taking the introduction of advanced foreign technologies through the Global Environment Facility’s (GEF) project to provide technical assistance to China for efficient industrial boilers as an opportunity, work is now being carried out to formulate these technical specifications. The fourth sub-item (Bio-fluid type) and the ninth sub-item (CPC type) of the projects introduced by the GEF are circulating fluidized bed boiler projects; the technological advantages of these systems should be considered as important aspects of these technical specifications. Additionally, the relevant technologies, experiences, and lessons learned over more than 10 years by over a dozen boiler manufacturers in China in the design and manufacture of circulating fluidized bed boilers, as well as their operational techniques, should also be included in these technical specifications. The formulation of these technical specifications aims to systematize and standardize advanced foreign technologies as well as the experience gained by various institutions in China, thereby promoting the development of fluidized bed technology. The fluidized bed combustion unit specified in these technical conditions serves as a combustion unit component for boiler products. The development history of fluidized bed combustion systems in our country has progressed from bubbling fluidized beds in the 1960s and 1970s to circulating fluidized beds in the 1980s and 1990s. Bubbling fluidized beds are still used in small and medium-sized boilers that burn low-quality fuels such as coal gangue, lignite, and waste ； Circulating fluidized beds are widely used in medium and large-sized boilers due to their high combustion efficiency, desulfurization efficiency, and ease of scaling up. These technical requirements take both types of fluidized beds into account, with a focus on the circulating fluidized bed. This standard was proposed and taken under responsibility by the National Boiler Standardization Technical Committee (CSBTS/TC 73). Drafting units of this standard: Shanghai Jiao Tong University, Jinan Boiler Group Co., Ltd., Shanghai Boiler Factory Co., Ltd., Beijing Kangpei Combustion Equipment Co., Ltd. 2 Introduction to Standard Content 2.1 Scope Explains the content and applicable range of the standard. The standards specify the technical requirements for the design, inspection, painting, packaging, installation, testing, and acceptance of fluidized bed combustion equipment used in boilers. The standards apply to fluidized bed combustion equipment for steam boilers with a evaporation capacity of 6 t/h to 130 t/h, and for hot water boilers with a heating capacity of 4.2 MW to 116 MW. For fluidized bed combustion equipment of steam boilers (hot water boilers) with other evaporation rates (heat supply rates), this standard may be referred to. 2.2 Referenced Standards List the relevant referenced standards, which, by being cited in this standard, become part of its provisions. This simplifies the standard content and ensures good coordination and consistency with relevant referenced standards. 2.3 Definitions Define the technical terms used in this standard. Definitions are provided for the specialized structures of this combustion equipment, such as fluidized bed combustion devices, air distribution systems, return valves, separators, and other related components, as well as for specialized terms such as circulation ratio, grading separation efficiency, internal circulation, external circulation, cross-sectional flow velocity in the fluidized bed, and fluidized bed combustion temperature. 2.4 Technical Requirements: The main section of this standard. Specific requirements are set forth for the performance, technical parameters, and structural design of fluidized bed combustion equipment. In particular: (1) Data recommendations are provided for key technical parameters such as the \"cross-sectional flow velocity in the coal-fired fluidized bed\" (fluidization air velocity), the \"combustion temperature in the fluidized bed\" (bed temperature), and the \"recycling ratio\" ； (2) Technical requirements have been established for key structural elements such as air distribution plates, air nozzles, separators, return valves, and slag coolers ； (3) Recommendations and corresponding technical requirements are provided for operational issues such as wear prevention, thermal expansion, ignition, desulfurization, and water circulation. 2.5 System Design: The proper operation of fluidized bed combustion equipment relies on the coordination of various related auxiliary machines and instruments; hence, a separate chapter is dedicated to this topic. Technical requirements are specified for the systems related to ensuring the proper operation of fluidized bed combustion equipment, such as fuel preparation, limestone preparation, safety protection, and monitoring instruments. 2.6 Painting, Packaging, Transportation, and Storage: In addition to the general requirements for conventional boiler equipment, packaging reinforcement requirements are specified for various specialized thin-walled components such as expansion joints, non-water-cooled air chambers, air ducts, and separators. 2.7 Installation of fluidized bed combustion equipment: In addition to the general requirements, fluidized bed combustion equipment operates under high wind pressure; therefore, it is necessary that it possess good sealing properties. 2.8 Performance tests: Considering the characteristics of fluidized bed operation, specific requirements are outlined for determining the critical fluidization air volume and conducting tests on air distribution uniformity. 2.9 Inspection and Acceptance: Requirements are set for the quality of the equipment, particularly regarding the quality assurance of the purchased components used in it. 3 Standard Technical Requirements 3.1 General Performance Requirements (1) Meet the combustion requirements specified in the design and operation parameters regarding the boiler’s evaporation capacity or heat output, and be able to operate safely over the long term; (2) The combustion efficiency shall not be lower than the guaranteed value specified in the technical agreement; (3) The emissions of boiler dust, flue gas darkness, and gaseous pollutants shall comply with the provisions of GWPB 3 \"Emission Standards for Air Pollutants from Boilers\" or GB 13223 \"Emission Standards for Air Pollutants from Thermal Power Plants\". 3.2 Design value of “cross-sectional flow velocity in a coal-fired fluidized bed” (fluidization air velocity): For a bubbling fluidized bed without ash reburning, in order to reduce losses due to mechanical incomplete combustion, the cold-state air velocity should be maintained between 0.7 m/s and 0.9 m/s ； When there is fly ash reburning, it should be controlled at 0.8 m/s to 1.1 m/s. For circulating fluidized beds, the cold-state wind speed should be controlled between 0.9 m/s and 2.0 m/s. For fluidized bed boilers that burn biomass fuels, petroleum coke, etc., the appropriate fluidization air velocity should be calculated aerodynamically based on their physical properties. 3.3 The design value of the “fluidized bed combustion temperature” (bed temperature) depends on the type of fuel and whether desulfurization is applied. During desulfurization, the temperature should be kept below 900 ℃; when desulfurization is not carried out, it should be maintained at 1000 ℃ or lower, and at least 200 ℃ lower than the ash fusion deformation temperature DT(t1). 3.4 The selection of the design value for the \"circulation ratio\" affects the heat transfer and output within a circulating fluidized bed boiler. Factors such as the calorific value of the fuel, its ash content, thermal stability, and particle size distribution, the fluidization air velocity, whether tubes are installed, the separation efficiency of various separators, as well as the requirements regarding combustion efficiency and desulfurization efficiency, must all be taken into consideration. For the coals with a wide particle size distribution currently used in our country (usually 0 mm to 10 mm), an external furnace circulation system can utilize particle sizes ranging from 3 to 40. For high-quality coals with low ash content and petroleum coke, limestone is used as the material for external furnace circulation, in which case particle sizes of 20 or more are advisable. 3.5 Structure of fluidized bed combustion equipment: The air distribution device, whether of water-cooled or non-water-cooled design, must have good sealing properties and be able to withstand the wind pressure in the air chamber as well as the weight of the bed material. The wind cap should be made of heat-resistant and wear-resistant materials. The design of the air cap and its openings should meet the requirements for fluidizing solid particles and preventing them from flowing back. A fire-resistant, wear-resistant layer should be installed between the small holes in the air cap and the distribution plate, in order to reinforce the air cap and protect the distribution plate. When a sliding connection is used between the air distribution plate and the furnace water wall, there should be a proper heat expansion mechanism in place, as well as good sealing. For all pipes connected to the furnace body, such as secondary air ducts, return material ducts, ignition air ducts, feed pipes, etc., their layout and support systems must take into account thermal expansion compensation ； The connections between the two ends of the cyclone separator located at the furnace outlet and the furnace body must take into account free expansion between them, while ensuring a good seal. 3.6 Layout of the door opening platform: The arrangement of the observation ports should allow for monitoring of the fuel combustion process as well as the separation and return of fly ash. Ignition: Observation and operation platforms should be installed in the dense-phase area above the burner and air distribution plate. The manholes should be arranged to facilitate access for maintenance personnel to the air chamber, the dense-phase area of the furnace, and the separation devices, and platforms for personnel to enter and exit should be provided. 3.7 Return material device: The separator should be designed based on the required grading separation efficiency, and an appropriate type should be selected to meet the requirements regarding material circulation, combustion efficiency, desulfurization efficiency, and flue gas flow resistance. Due to space constraints in small boilers, an internal circulation system can be used ； For boilers with space for arrangement, an external circulation system or two-stage (multi-stage) separation can be employed. Return valves usually use non-mechanical valves, such as L-type, U-type, J-type, H-type valves, etc. The solid particles are fluidized by return air (including loosening air and conveying air) and conveyed back to the furnace. The height of the return material point above the air distribution plate varies depending on the coal type and fly ash particle size. For poorly burnable fuels, as well as fly ash and limestone particles with large particle sizes, the return material point should be placed closer to the air distribution plate. 3.8 Ignition burner: A water-cooled air distribution device can be used in conjunction with an under-bed ignition burner; the flame from this burner must not enter the air chamber. Instead, it heats the bed material using hot gases resulting from the mixing of smoke and primary air, thereby achieving fluidized ignition. Non-water-cooled air distribution devices can be equipped with bed-mounted heating burners, which require burners with high flame stiffness and strong penetration power. 3.9 Anti-wear measures: Parts prone to wear due to particle erosion, such as the wind caps, the furnace wall in the dense-phase zone, the inner surfaces of the separators, the tubes exposed to the airflow, and the water-cooled wall tubes, should be fitted with heat-resistant anti-wear materials or equipped with anti-wear structures; their service life should be at least as long as one major maintenance cycle. 221 3.10 Slag cooler: To enable the comprehensive utilization of the discharged ash and slag, a slag cooler with air cooling, water cooling, or a combination of both can be used. Its slag discharge temperature can be determined according to the requirements of the process flow; to ensure the reliability of the slag removal system, it is generally kept below 250 °C. 3.11 Desulfurization requirements: In fluidized bed combustion equipment, for fuels with high sulfur content, limestone should be used for desulfurization in accordance with the requirements regarding sulfur dioxide emissions specified in GWPB3 \"Emission Standards for Air Pollutants from Boilers\" or GB 13223 \"Emission Standards for Air Pollutants from Thermal Power Plants\". Limestone particles are generally required to be in the range of 0 mm to 2 mm, with particles larger than 1 mm accounting for no more than 10% of the total. 3.12 Reliability requirements for the heated surfaces: The tubes embedded in the furnace and the water-cooled wall tubes of the separator must ensure reliable water circulation. For membrane wall fins, the fin tip temperature of the tube should be below the heat resistance limit allowed for the steel material. 4 Standard Content Description (1) The gas-solid separation device referred to in these technical specifications is the gas-solid separator located within the boiler itself, and it is a key component of circulating fluidized bed combustion equipment. Research institutions and manufacturers both at home and abroad have conducted extensive research on this topic over the long term; utilizing various principles such as centrifugal separation, inertial separation, and gravitational separation, a variety of products have been developed. Its technical requirements focus on separation efficiency, flue gas resistance, heat and wear resistance, etc. These separation devices have their own advantages and disadvantages in terms of technology and structure. Taking the cyclone separator as an example, it is relatively mature in terms of technology, with a separation efficiency of over 99% ； However, the smoke resistance is relatively high, ranging from 1000 Pa to 1500 Pa, and it takes up a lot of space. A low-temperature cyclone separator for exhaust gas has also been developed, which can be installed in the smoke chamber at the rear of the boiler, thereby allowing medium-capacity circulating fluidized bed boilers to have a more compact structure. To meet the requirements of larger size and reduced startup time, it is possible to use water-cooled or steam-cooled tubes as the framework, coat them with wear-resistant and heat-resistant materials on the inside, and cover them with insulation material on the outside. There are also other inertial separators, as well as various separators that combine inertial separation with centrifugal separation; they come in different types and are suitable for different applications. These technical specifications only provide principle-based regulations and recommendations regarding performance requirements. (2) The combustion efficiency of fluidized bed combustion equipment is an important technical indicator, which is highly valued by both boiler manufacturers and users. Due to the many influencing factors, different combustion methods (bubble fluidized bed, circulating fluidized bed), different types of fuel, different boiler capacities, and whether desulfurization is employed can all cause significant variations in combustion efficiency. Therefore, these technical specifications stipulate that the requirements specified in the order contract must be met. The general technical requirements for industrial boilers specify the thermal efficiency values for fluidized-bed boilers; corresponding requirements can also be set for the combustion efficiency of fluidized-bed combustion equipment in accordance with these specifications. (3) The technical term \"circulation ratio\" has different definitions, such as the ratio of the amount of fly ash exiting the furnace to the amount of coal fed. Given that both internal furnace circulation and external furnace circulation are applicable, these technical specifications define it as the ratio of the amount of material involved in the circulation to the amount of coal fed. Abroad, circulating fluidized bed boilers often use very high circulation ratios. In the early stages of introducing foreign technology in our country, there was an excessive focus on high cycle rates; moreover, low-quality coal with a wide particle size distribution was used. Due to its low calorific value, a large amount of coal had to be supplied (large denominator), and because of the wide particle size distribution, only a small amount of material could participate in the cycling process (small numerator). As a result, it was impossible to achieve high cycle rates. Therefore, recommended values are provided under these technical conditions, taking into account national conditions, and these ranges are broad enough to allow for selection based on specific circumstances. For the coals with wide particle size distribution currently used in our country, an off-furnace circulation system can be employed with a range of 3 to 40. For high-quality coal with low ash content, limestone can be used as the circulating material for extracombustion cyclone separation of petroleum coke, with a value of over 20 being suitable. Experts have differing opinions on whether the technical term \"cycle rate\" should be used in these technical specifications. Of course, when designing a fluidized bed boiler, the circulation ratio is determined based on the aerodynamic calculations of the cross-sectional flow velocity in the fluidized bed and the gas-carrying separation, as well as the separation efficiency of the gas-solid separator, taking into account the properties of the solid particles. Just as in the calculation of boiler water circulation, the circulation ratio can be determined from the circulation water velocity. In both cases, the cycle rate serves as a criterion for the designer’s decision-making. Moreover, domestic users and manufacturers 222 are also actually used as criteria for judgment. Therefore, this technical term is used in these technical specifications. (4) Recommended key technical parameters and their rationale: Through extensive research and investigations, as well as by seeking the opinions and suggestions of relevant technicians and experts, the following key technical parameters have been recommended: a. “Fluidized bed combustion temperature” (bed temperature): It should be kept below 900°C during desulfurization, and below 1000°C when desulfurization is not required; moreover, it must be at least 200°C lower than the ash fusion deformation temperature DT(t1). Wuxi Boiler Factory, during desulfurization: 870℃ ； 950°C for Sichuan Boiler Factory without desulfurization; 850°C – 870°C with desulfurization℃ ； Without desulfurization: 920°C for Hangzhou Boiler Factory; 900°C for Harbin Boiler Factory; 871°C for CPC type; 827°C – 844°C for Bio-fluid type (Knauf Gypsum Board Factory). b. “Circulation ratio”: For the coals with a wide particle size range currently used in China (usually 0 mm to 10 mm), a circulation ratio of 3 to 40 can be adopted when using an external circulation system. For high-quality coals with low ash content or petroleum coke, limestone is used as the material for external circulation, and a ratio of over 20 is advisable. Harbin Boiler Factory, CPC type, 16.8; Jiangxi Boiler Factory of Jianglian Group, 5 – 20; Jinan Boiler Group Co., Ltd., 10 – 20. c. “Cross-sectional flow velocity in the coal-fired fluidized bed” (cold-state fluidization wind speed): In a bubbling fluidized bed where there is no ash reburning, the cold-state wind speed should be maintained between 0.7 m/s and 0.9 m/s ； When there is fly ash reburning, it should be controlled at 0.8 m/s to 1.1 m/s. For circulating fluidized beds, the cold-state wind speed should be controlled between 0.9 m/s and 2.0 m/s. Wuxi Boiler Factory: Circulating fluidized bed, 0.8 m/s – 1.1 m/s; Hangzhou Boiler Factory: Circulating fluidized bed, 1.1 m/s – 1.3 m/s; Beijing BAWI Boiler Factory: Circulating fluidized bed, 1.04 m/s. 5 Conclusion: The formulation of the \"Technical Specifications for Fluidized Bed Combustion Devices\" will play a positive role in promoting the gradual standardization and regularization of fluidized bed boiler products. It is hoped that during the implementation process, various units will continue to submit their suggestions and opinions to further revise and improve it. 【Author Introduction】 Tian Ziping, Professor at Shanghai Jiao Tong University and supervisor of doctoral students. Graduated from the Department of Power Engineering at Xi’an Jiaotong University in July 1964. I have been engaged in the development and research of boiler equipment for over 30 years. It has been highly effective in developing fluidized bed combustion technology for its successful application in power generation boilers. It has won 1 second prize and 1 third prize in the Science and Technology Progress Awards, 1 first prize in the Shanghai Science and Technology Progress Award, the Shanghai Talent Cultivation Award, as well as 5 provincial and ministerial-level science and technology achievement awards. Was awarded the title of Advanced Worker in the field of science and technology in Shanghai. Won the first prize for outstanding industry-university-research projects in Shanghai. 8 books have been published. More than 80 papers have been published.