Circulating fluidized bed boiler furnace staged combustion system

Abstract

The present invention discloses a circulating fluidized bed boiler furnace segmented combustion system, which is composed of a membrane water-cooled wall, a horizontal air distribution plate at the bottom, and an angled feeding and spreading area at the front wall of the water-cooled wall. Compared with a traditional circulating fluidized bed boiler, after the fuel enters the furnace, it first undergoes a preheating, evaporation, and spreading process, and then falls into the combustion space above the air distribution plate at the bottom of the furnace under the action of gravity for fluidized combustion. For circulating fluidized bed boilers that burn biomass fuels or garbage fuels with high moisture content, this system can fully dry, burn, and burn out fuels with high moisture content and difficult ignition, so that the agglomerated fuel can be fully spread in the furnace combustion space, improve combustion uniformity, and reduce air distribution plate temperature deviation, thereby effectively solving the problem of air distribution plate coking, improving boiler combustion efficiency, and improving economy. At the same time, the system can control the combustion situation in the furnace, control the flue gas temperature level and oxygen content by adjusting the air volume at various locations, thereby reducing nitrogen oxide emissions.

Description

Technical Field

[0001] The invention relates to the field of circulating fluidized bed boilers, in particular to a circulating fluidized bed boiler furnace segmented combustion system, which is applied to biomass and garbage power generation equipment. Background Art

[0002] With the rapid development of society, the world's demand for energy is increasing, and fossil fuels can no longer meet the growing energy demand. Therefore, the development of renewable energy has become the focus of attention around the world. Among them, biomass fuel and garbage fuel power generation technology has been widely used. Due to the characteristics of high moisture content, low calorific value, various shapes and sizes, and a lot of debris in biomass fuel and garbage fuel, when burning these fuels, conventional circulating fluidized bed boilers are prone to debris agglomeration, coking of air distribution plates, clogging of slag pipes, and large combustion fluctuations, resulting in uneven bed temperature distribution, uneven fluidization, incomplete combustion, and uneven furnace temperature distribution, which in turn reduces the thermal efficiency of the boiler, exceeds the pollutant emission standard, and even causes emergency shutdown of the boiler.

[0003] The circulating fluidized bed boiler furnace staged combustion system is one of the effective ways to solve the above problems. The system is designed for biomass fuel and urban garbage fuel, suitable for the characteristics of these fuels, can effectively solve the treatment problems of agricultural waste and urban garbage, and has broad application prospects. Summary of the invention

[0004] In order to overcome the shortcomings of traditional circulating fluidized bed boilers when burning biomass fuels and garbage fuels, such as incomplete combustion, easy coking, and uneven furnace temperature distribution, the present invention provides a circulating fluidized bed boiler furnace segmented combustion system, which can improve combustion efficiency and make the temperature distribution of air distribution plates uniform, without coking, and more uniform fluidization.

[0005] The present invention adopts the following technical solution:

[0006] A circulating fluidized bed boiler furnace segmented combustion system, including a furnace composed of membrane water-cooled walls, the combustion area in the furnace is divided into four areas, area one is a preheating, drying and feeding area, located in the fuel inlet area, located on the front wall of the boiler, and is an angled feeding and feeding area, the water-cooled wall of area one is provided with a feeding port, a feeding plate and a secondary primary fluidizing air duct, the feeding plate is provided with a feeding cap, the feeding port is connected to the furnace, the secondary primary fluidizing air duct is connected to the furnace through the feeding cap, the fuel enters the furnace from the feeding port, and is preheated, dried and spread in this area; area two is a combustion fluidizing area, located at the lower air distribution plate Area one is the suspended combustion area, which is located above the air distribution plate. A fluidizing hood is provided above the air distribution plate, and a main primary fluidizing air duct is provided below the air distribution plate. The fuel is stably burned and fluidized in this area. Area three is the suspended combustion area, which is located above the air distribution plate. Lower secondary air ducts and return ports are provided on the front and rear water-cooled walls of area three. The fuel entering the boiler is suspended and burned in this area. Area four is the burnout area, which is located at the top of the combustion area in the furnace. Upper secondary air ducts are provided on the front and rear water-cooled walls of area four. The fuel is burned in this area, and the flue gas carrying a large amount of heat rises, and heat exchange is carried out between the working medium in the furnace and the water-cooled wall.

[0007] Preferably, the angle formed by the broadcasting plate and the horizontal direction is inclined downward by 15° to 45°.

[0008] Preferably, the material broadcasting hood is an inclined hood, which is arranged in an oblique step-like manner on the corner of the preheating and drying material broadcasting area.

[0009] The use principle of the present invention is: after the fuel enters the furnace from the feed port, the small particle fuel is directly burned in area three, and then enters area four to burn out. Large particles, irregular fuels and fuels with high water content that are difficult to burn out first complete the preheating, drying and spreading process in area one, and then the fuel enters area two through area three under the action of gravity. During the falling process, the fuel further undergoes the preheating, drying and spreading process. During the process, the fuel temperature increases, the water in the fuel evaporates and the water content decreases, and the fuel is evenly dispersed in the furnace space, so that the fuel entering area two is easy to fully burn and evenly distributed, and then the fine ash and fine particle fuel produced by the combustion pass through area three and area four in turn under the action of the primary air at the bottom of the furnace, and finally the ash-containing flue gas produced by the combustion leaves the furnace, and the fine ash separated by the boiler cyclone separator re-enters area two through the return port, and this cycle continues. The hot air required for combustion is sent into the furnace in a segmented and multi-layer air distribution method, and the primary air is sent into the furnace through the main primary fluidization air duct and the secondary fluidization wind box, and is used as the boiler fluidization air. The secondary air is sent into the furnace through the lower secondary air duct and the upper secondary air duct and used as the boiler secondary air. This segmented and multi-layer air distribution method can meet the functions of fuel diffusion, combustion product fluidization, and timely adjustment of air volume, which is conducive to controlling combustion and furnace temperature levels.

[0010] The present invention can be effectively applied to circulating fluidized bed boilers that burn biomass fuel or garbage fuel. After adopting the above technical solution, compared with the traditional circulating fluidized bed boiler fuel that needs to go through the preheating, drying, and spreading process before entering the combustion area for combustion, the present invention evaporates the water content of the fuel before combustion, increases the fuel temperature, and evenly spreads the large-particle fuel in the furnace combustion space, so that the fuel burns fully, the temperature distribution of the air distribution plate is uniform, the material is fluidized uniformly, and the large-particle fuel agglomerates to avoid incomplete combustion, effectively solve the problems of coking and slag blockage caused by burning these fuels, improve boiler efficiency, and reduce the boiler accident shutdown rate.

[0011] The present invention can control the combustion by adjusting the primary air volume and secondary air volume of the boiler, thereby effectively controlling the temperature level and oxygen content in the furnace within a reasonable range, inhibiting the generation of nitrogen oxides, and being beneficial to reducing the original emission of nitrogen oxides from the boiler, so that the original emission concentration of nitrogen oxides is within 120mg / Nm 3 At the same time, the flue gas temperature in the furnace can be controlled at around 900°C, which is beneficial to improving the efficiency of the SNCR system and further reducing the nitrogen oxide emissions of the boiler.

[0012] The beneficial effects of the present invention are as follows: First, the fuel of the present invention has a wide range of applications, and is particularly suitable for biomass fuels and urban garbage fuels with high moisture content, low calorific value, various shapes and sizes, and a lot of debris.

[0013] Secondly, after the preheating, drying and spreading process, the fuel is easy to ignite and burn fully. The temperature of the air distribution plate is evenly distributed, and the fluidization in the furnace is even, which avoids coking and slag blockage, improves the combustion efficiency of the boiler and improves economy.

[0014] Thirdly, the present invention adopts a segmented and multi-layer air distribution method, which is beneficial to the fuel burnout and fluidization of the combustion products. Each level of air distribution can be adjusted separately, which can improve the boiler control ability, ensure stable combustion, and improve combustion efficiency.

[0015] Fourthly, the present invention can reduce the original emission of boiler nitrogen oxides, so that the pollutant emissions meet the requirements of national standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a structural schematic diagram of the present invention;

[0017] Figure 1 In the middle, 1. membrane water-cooled wall, 2. fluidizing air hood, 3. broadcasting air hood, 4. feeding port, 5. return port, 6. main primary fluidizing air duct, 7. secondary primary fluidizing air duct, 8. lower secondary air duct, 9. upper secondary air duct, I. preheating and drying broadcasting zone, II. combustion fluidizing zone, III. suspension combustion zone, IV. burnout zone. DETAILED DESCRIPTION

[0018] The technical solution of the present invention is further described in detail below through specific embodiments and in conjunction with the accompanying drawings:

[0019] Example: As attached Figure 1 As shown, a circulating fluidized bed boiler furnace staged combustion system, the furnace is composed of a membrane water-cooled wall 1, the lower part of the furnace is composed of a membrane water-cooled wall 1 to form a horizontal air distribution plate, above which a fluidizing air hood 2 is arranged, and below which a main primary fluidizing air duct 6 is arranged. The area of ​​the furnace front feed port 5 is composed of a membrane water-cooled wall 1 to form an angled membrane wall, a feed hood 3 is arranged above the feed area below the feed port 4, and a secondary primary fluidizing air duct 7 is arranged below it. A return port 5 is provided on the rear wall water-cooled wall of the suspended combustion zone III, and a lower secondary air duct 8 is provided on the front and rear wall water-cooled walls. An upper secondary air duct 9 is provided on the front and rear wall water-cooled walls of the burnout zone IV. At the same time, the inner water-cooled wall of the combustion zone is coated with refractory castables to protect the water-cooled wall pipes from being damaged by wear and high temperature.

[0020] When the boiler is running, the fuel enters the furnace from the feed port 4 in front of the furnace, and the fuel with smaller particles is directly burned in the suspended combustion zone III and then burns out in zone IV. The remaining large-particle fuel is spread in the preheating and drying broadcasting zone I under the action of the broadcasting wind of the broadcasting wind cap 3, and then enters the combustion fluidization zone II through the suspended combustion zone III under the action of gravity. Under the action of the primary and secondary winds, the large-particle fuel is further mixed and diffused, so that the fuel finally burned in the combustion fluidization zone II is evenly distributed in the combustion space on the air distribution plate. The flue gas and fine ash generated after the combustion of this part of the fuel are fluidized under the action of the primary wind at the bottom of the furnace, flow upward, and enter the furnace for heat exchange through the combustion fluidization zone II, the suspended combustion zone III, and the burnout zone IV in turn, and then the fine ash separated by the boiler cyclone separator re-enters the furnace through the return port 5, and the cycle continues.

[0021] When the boiler is running, the primary hot air required for combustion enters the furnace in two ways. One part enters from the main primary wind box 6 at the bottom of the furnace, and is used as the main fluidizing air of the boiler through the fluidizing air cap 2 to fluidize the materials in the furnace. The other part of the primary air enters from the secondary primary fluidizing air duct 7 below the angled water-cooled wall in front of the furnace, and is used as the boiler broadcasting air through the broadcasting air cap 3 to fluidize the small-particle fuel and spread the large-particle fuel in the furnace space. The secondary hot air required for combustion enters from the lower secondary air duct 8 and the upper secondary air duct 9 in front of and behind the furnace in two layers, and is used as the boiler secondary air.

[0022] After the fuel enters the furnace, it will first go through the process of preheating, evaporation, and dispersion before it can burn. Since the secondary air sent into the furnace and the temperature inside the furnace are much higher than the temperature of the fuel entering the furnace, the fuel can be preheated under the action of high temperature, and the water in the fuel evaporates. At the same time, the fuel can be evenly dispersed in the furnace combustion space under the action of air distribution during the falling process, and finally evenly distributed on the air distribution plate at the bottom of the furnace, so that the fuel can be evenly and fully burned, the air distribution plate temperature is evenly distributed, the fluidization is even, and the air distribution plate will not coke due to uneven temperature distribution. At the same time, the combustion of the agglomerated fuel after dispersion will not cause the slag discharge pipe to be blocked, which can effectively improve the combustion efficiency and improve the economy of the boiler.

[0023] When the boiler is running, the combustion can be precisely adjusted by adjusting the primary and secondary air volumes at each stage, thereby achieving the effect of controlling the combustion conditions, making the temperature level in the furnace uniform and controlled at around 900°C, the oxygen content controlled within a reasonable range, and reducing the boiler's nitrogen oxide emissions, so that the original NOx emission concentration is 120mg / Nm 3 the following.

[0024] The above-described embodiment is only a preferred solution of the present invention and does not limit the present invention in any form. There are other variations and modifications without exceeding the technical solution described in the claims.

Claims

1. A circulating fluidized bed boiler furnace staged combustion system, comprising a furnace consisting of a membrane water-cooled wall (1), characterized in that: The combustion area in the furnace is divided into four areas. Area one is the preheating, drying and spreading area (I), which is located in the fuel inlet area and the front wall of the boiler. It is an angled feeding and spreading area. A feed port (4), a feed plate and a secondary primary fluidizing air duct (7) are provided on the water-cooled wall of area one. A feed cap (3) is distributed on the feed plate. The feed port (4) is connected to the furnace. The secondary primary fluidizing air duct (7) is connected to the furnace through the feed cap (3). The fuel enters the furnace from the feed port (4) and is preheated, dried and spread in this area. Area two is the combustion fluidizing area (II), which is located in the lower air distribution plate area. A feed port (4), a feed plate and a secondary primary fluidizing air duct (7) are provided on the water-cooled wall below the feed plate. An air distribution plate, a fluidizing air cap (2) is provided above the air distribution plate, and a main primary fluidizing air duct (6) is provided below the air distribution plate. The fuel is stably burned and fluidized in this area; Area three is a suspended combustion area (III), which is located above the air distribution plate. A lower secondary air duct (8) and a return material port (5) are provided on the front and rear water-cooled walls of Area three. The fuel entering the boiler is suspended and burned in this area; Area four is a burnout area (IV), which is located at the top of the combustion area in the furnace. An upper secondary air duct (9) is provided on the front and rear water-cooled walls of Area four. The fuel is burned in this area, and flue gas carrying a large amount of heat rises, and heat exchange is performed between the working medium in the furnace and the water-cooled wall; When the boiler is in operation, the fuel enters the furnace from the feeding port in front of the furnace. The fuel with smaller particles is directly burned in the suspended combustion zone (III) and then enters the burnout zone (IV). The remaining large-particle fuel is dispersed in the preheating and drying feeding zone (I) under the action of the feeding wind of the feeding wind cap, and then enters the combustion fluidization zone (II) through the suspended combustion zone (III) under the action of gravity. Under the action of the primary air and the secondary air, the large-particle fuel is further mixed and diffused, so that the fuel finally burned in the combustion fluidization zone (II) is evenly distributed in the combustion space on the air distribution plate. The flue gas and fine ash generated after the combustion of this part of the fuel are fluidized under the action of the primary air at the bottom of the furnace, flow upward, and enter the furnace for heat exchange through the combustion fluidization zone (II), the suspended combustion area (III), and the burnout zone (IV) in turn. Then, the fine ash separated by the boiler cyclone separator re-enters the furnace through the return port, and the cycle continues. The angle formed by the seeding plate and the horizontal direction is inclined downward by 15° to 45°; The material broadcasting hood (3) is an inclined hood, which is arranged in an oblique step-like manner on the corner of the preheating and drying material broadcasting area (I).

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