Biomass fuel-assisted sludge incineration circulating fluidized bed boiler

Abstract

This invention discloses a circulating fluidized bed boiler for sludge incineration with biomass fuel combustion, which solves the problems of large fluctuations in the calorific value of sludge combustion and how to scientifically and rationally co-fire sludge fuel and biomass fuel in the furnace. A sludge fuel inlet (19) is provided on the front wall of the furnace above the cyclone separator return port (17) of the high-temperature adiabatic cyclone separator (2), and a sludge fuel feeder (20) is connected to the sludge fuel inlet. A biomass fuel inlet (21) is provided on the front wall of the furnace above the sludge fuel inlet (19), and a biomass fuel feeder (22) is connected to the biomass fuel inlet (21). A single row of secondary air inlets (23) is provided on the front and rear walls of the furnace above the biomass fuel inlet (21). The tail flue is divided into a high-temperature section flue and a low-temperature section flue. A high-temperature metal cartridge dust collector (3) is provided between the high-temperature section flue and the low-temperature section flue.

Description

Technical Field

[0001] This invention relates to a circulating fluidized bed boiler, and more particularly to a circulating fluidized bed boiler that uses biomass fuel for combustion of sludge. Background Technology

[0002] Municipal sludge is a byproduct of urban wastewater treatment. With the advancement of urbanization, the production of municipal sludge is increasing. How to safely and properly treat and dispose of municipal sludge, and truly achieve sludge reduction, harmlessness, and resource utilization, has become a major issue that urgently needs to be addressed in the environmental field. Sludge incineration has a good volume reduction effect and can effectively decompose toxic and harmful organic matter in sludge. It is the most promising way to reduce, harmlessly utilize, and utilize sludge. Various circulating fluidized bed boilers for sludge incineration have emerged in the current technology.

[0003] In circulating fluidized bed boilers for sludge incineration, the calorific value of the continuously fed sludge typically fluctuates between 500-1000 kcal, exhibiting a significant range and causing excessive furnace temperature fluctuations, leading to unstable boiler operation. Current technologies typically address this issue by co-firing coal or natural gas; however, this approach suffers from high operating costs and carbon emission limitations. Biomass pellets, with their low cost and low carbon footprint, present a novel approach to co-firing biomass fuel with sludge. However, biomass fuel has a relatively low density. Existing technologies include pre-mixing biomass fuel with sludge to create a blended fuel, which is then burned in the furnace. However, this method requires investment in fuel blending and production processes. Sludge incineration equipment is expensive to operate, and it is difficult to produce fuel with stable calorific value; the problem of large fluctuations in sludge calorific value still exists. The design furnace temperature of sludge incineration boilers is generally around 900 degrees Celsius to adapt to the characteristics of sludge combustion. Municipal sludge has high water content, high ash content, and low and unstable calorific value, which leads to difficulties in combustion when it is burned in a boiler. Biomass fuel, on the other hand, has a higher calorific value and lower ash content, and the use of biomass for combustion assistance can effectively solve the problem of sludge incineration difficulties. However, how to effectively combine the two, what kind of feeding method to adopt to control the overall calorific value of the fuel, and how to design the boiler furnace structure to achieve stable co-combustion of sludge and biomass fuel in the furnace are the primary issues that need to be considered in the design of circulating fluidized bed boilers for sludge incineration using biomass fuel for combustion assistance.

[0004] Sludge has a high ash content, producing a large amount of fly ash upon combustion. Furthermore, the inlet temperature of the working fluid (cold water, ambient air) in the low-temperature economizer and air preheater's low-temperature heating surfaces is relatively low. When the humid flue gas produced after sludge combustion passes through the outer wall of the inlet of the low-temperature heating surface, a large amount of dew will condense. These dew droplets will adsorb a large amount of dust particles from the flue gas, and the large amount of fly ash produced after sludge combustion will adhere to the tube walls of the low-temperature heating surface, clogging it. In addition, sludge combustion produces a large amount of carbon dioxide (C). O gas is present, and the flue gas velocity in the furnace is relatively fast, resulting in a large amount of CO gas entering the tail flue. How to treat the CO gas in the tail flue to achieve compliance with CO standards in the exhaust gas is a challenge that needs to be addressed. Furthermore, in the tail flue of a conventional circulating fluidized bed boiler, a high-temperature superheater / high-temperature reheater, a low-temperature superheater / low-temperature reheater, an economizer, and an air preheater are typically arranged sequentially along the flue gas flow direction. The flue gas flow from the furnace, passing through a cyclone separator, and flowing into the tail flue is then processed by the aforementioned... In hot-surface heat release, the flue gas temperature gradually decreases from 850-900℃ to around 150℃ at the flue gas outlet. However, when burning high-alkali fuels, the alkali metal elements in the fuel mainly enter the flue gas in the form of gaseous alkali metal compounds. When the flue gas temperature is between 650-800℃, the gaseous alkali metal compounds condense into liquid. At this time, if they encounter heating surfaces with high wall temperatures, such as superheaters and reheaters, the liquid alkali metal compounds will adhere to these heating surfaces, forming a complex and hard eutectic, and further adsorbing fly ash from the flue gas, causing severe fouling of the high-temperature heating surfaces, affecting heat exchange, and disrupting the normal flue gas flow path. Biomass fuel is a high-alkali fuel, and the proportion of alkali metal oxides in fly ash is relatively high. If a sludge incineration boiler uses biomass fuel for combustion, flue gas with a high alkali metal content will be introduced into the flue gas, leading to the above situation. Therefore, how to design and lay out the tail flue of a sludge incineration boiler with biomass combustion has become a difficult problem for technicians in this field. Summary of the Invention

[0005] This invention provides a circulating fluidized bed boiler for sludge incineration with biomass fuel combustion, which solves the technical problems of large fluctuations in the calorific value of sludge combustion and how to scientifically and rationally co-fire sludge fuel and biomass fuel in the furnace to achieve stable combustion in the boiler.

[0006] The present invention solves the above technical problems through the following technical solutions: The overall concept of this invention is as follows: Based on the characteristics of sludge fuel and biomass fuel, a coordinated structure is designed for the dense phase zone feeding in the furnace and the return material from the cyclone separator, allowing sludge fuel and biomass fuel to be fed into the furnace separately. Before ignition of the sludge incineration circulating fluidized bed boiler, bottom material is laid on the air distribution plate. Then, the biomass pellet fuel is ignited first using oil ignition. When the furnace temperature rises above 850°C, sludge fuel is then fed in, ensuring that the sludge fuel's entry point into the furnace is positioned above the cyclone separator return material's entry point, and the biomass pellet fuel's entry point into the furnace is positioned above the sludge fuel's entry point. A single row of secondary air inlets is arranged above the material drop point to create a combustion structure where the rising sludge is co-fired with the biomass fuel entering the furnace after the sludge fuel is fed in. By monitoring the furnace temperature and the ratio of primary to secondary air, the biomass fuel feed rate is controlled, and the furnace temperature is stabilized at around 900℃ to achieve full and stable combustion of the sludge. Because municipal sludge has a high water content (absolute humidity of about 25%) and high ash content, it produces a large amount of CO during combustion. Furthermore, the furnace combustion temperature reaches over 900 degrees Celsius. After co-firing with biomass fuel, alkali metal elements in the flue gas enter the flue gas in the form of gaseous alkali metal compounds. This invention addresses the mixed flue gas, characterized by high humidity, high fly ash content, high CO content, and the presence of gaseous alkali metal compounds, by comprehensively considering three main aspects: cooling, dust removal, and CO elimination. The tail flue design focuses on flue temperature and flow rate control, aiming to achieve dust removal at the front end of the flue. Three series-connected water-cooled front flues are used to achieve graded flow rate control of the flue gas, thereby realizing multi-stage dust removal and CO elimination. The first two sections of the three high-temperature water-cooled flues are designed as water-cooled empty flues, ensuring that the flue gas temperature is reduced to below 600 degrees Celsius after passing through these sections before entering the furnace. In the third high-temperature flue, the high-temperature heating surface is arranged in the third end flue where the flue temperature drops below 600 degrees Celsius, avoiding the liquefaction of gaseous alkali metal compounds in the flue gas on the high-temperature heating surface. By controlling the flue gas flow velocity, most of the dust is removed in the first three high-temperature water-cooled flues. The flue gas discharged from the first three water-cooled flues is then discharged into a high-temperature metal cartridge dust collector, and the flue gas flow velocity is controlled at 2-3 meters per second, achieving good staged dust removal. Finally, the basically clean flue gas after dust removal is discharged into a U-shaped low-temperature flue, where a low-temperature economizer and air preheater with low-temperature heat exchange surfaces are installed, thereby solving the problem of blockage of the low-temperature heating surface.

[0007] A circulating fluidized bed boiler for sludge incineration with biomass fuel combustion includes a circulating fluidized bed boiler furnace, a high-temperature insulated cyclone separator, and a tail flue. A sludge fuel inlet is located on the front wall of the furnace above the return port of the cyclone separator, and a sludge fuel feeder is connected to the sludge fuel inlet. A biomass fuel inlet is located on the front wall of the furnace above the sludge fuel inlet, and a biomass fuel feeder is connected to the biomass fuel inlet. A single row of secondary air inlets is located on the front and rear walls of the furnace above the biomass fuel inlet. The tail flue is a split-type design, consisting of a high-temperature section and a low-temperature section, with a high-temperature metal cartridge dust collector installed between the two sections.

[0008] The high-temperature section flue consists of a first high-temperature vertical downward flue, a second high-temperature vertical upward flue, and a third high-temperature vertical downward flue, which are arranged side by side and connected end to end. All three flues are water-cooled film-walled flues. The first and second high-temperature vertical upward flues are empty flues with water-cooled film walls. A low-temperature superheater and a high-temperature economizer are installed in the third high-temperature vertical downward flue. The low-temperature section flue is a U-shaped steel plate flue, in which a low-temperature economizer and an air preheater are installed.

[0009] A first ash remover is installed at the connection between the lower end of the first high-temperature vertical downward flue and the lower end of the second high-temperature vertical upward flue, and a second ash remover is installed at the bottom of the third high-temperature vertical downward flue.

[0010] An operating method for a biomass fuel-assisted sludge incineration circulating fluidized bed boiler, comprising the following operating steps: Step 1: Lay the furnace bottom material on the air distribution plate, heat the furnace bottom material to the ignition temperature of the biomass fuel using an oil ignition burner, and feed biomass fuel into the furnace through the biomass fuel feeder. After the furnace temperature continues to rise steadily, continuously feed biomass fuel into the furnace through the biomass fuel feeder to continue raising the furnace temperature, and then stop using the oil ignition burner. The sludge fuel is sludge fuel with a moisture content of 40%-45% and in soil-like form; the biomass combustion aid is granular fuel with a particle size of less than 10 cm. The second step is to start the sludge fuel feeder when the furnace temperature reaches 850°C, and continuously feed sludge fuel into the furnace. The sludge fuel has a moisture content of 40%-45% and is in soil-like form. The sludge falling into the sludge feeding point is heated by the high-temperature furnace bottom material, the moisture evaporates, and after rising under the action of primary air, it merges with the biomass fuel that has just entered the furnace and is ignited, thus realizing the mixed combustion of sludge fuel and biomass fuel. The third step involves the return ash, after being separated by a high-temperature insulated cyclone separator, falling through the return port of the cyclone separator into the area below the sludge discharge point, thus continuously replenishing the high-temperature bottom material in the lower part of the furnace. The return ash, sludge fuel, and biomass fuel are disturbed and mixed in the dense phase zone of the furnace, achieving complete combustion of the sludge. Step 4: The flue gas temperature entering the first high-temperature vertical downward flue from the outlet of the high-temperature adiabatic cyclone separator is 910℃. This flue gas descends along the first high-temperature vertical downward flue, makes a 180-degree turn at its lower end, and then ascends along the second high-temperature vertical upward flue. At the 180-degree turn, the flue gas temperature is 700℃. After another 180-degree turn at the upper end of the second high-temperature vertical upward flue, the flue gas enters the third high-temperature vertical downward flue, where the temperature is 610℃. The flow velocity of the flue gas in the first and second high-temperature vertical downward and upward flue is 7 m / s. After the fly ash in the flue gas settles, it is discharged through the first ash discharger. The CO in the flue gas is converted into carbon dioxide through the long process in the first and second high-temperature vertical downward and upward flue, achieving CO emission standards. Fifth, a low-temperature superheater and a high-temperature economizer are installed in the third high-temperature vertical downward flue. The flue gas temperature entering the third high-temperature vertical downward flue is 610℃-400℃, which avoids the corrosion of high-temperature heating surfaces caused by the condensation of gaseous alkali metal compounds in the flue gas into liquid. The flue gas velocity in the third high-temperature vertical downward flue is designed to be 10 m / s, and the flue gas flow direction is consistent with the direction of fly ash settling. After the fly ash in the flue gas settles again, it is discharged through the second ash discharger. Step 6: The flue gas enters the high-temperature metal cartridge dust collector from the outlet of the third high-temperature vertical downward flue for the third dust removal. The flow velocity of the flue gas in the high-temperature metal cartridge dust collector is designed to be 2-3 meters per second, and the heat dissipation temperature drop of the high-temperature metal cartridge dust collector is 20℃. Step 7: After the clean flue gas flows out of the outlet of the high-temperature metal cartridge dust collector, it enters the U-shaped steel plate flue. The flue gas velocity in the U-shaped steel plate flue is designed to be 7 meters per second. After the flue gas undergoes convective heat exchange with the low-temperature heating surfaces of the low-temperature economizer and air preheater, it flows out from the outlet of the U-shaped steel plate flue.

[0011] This invention optimizes the design of the boiler furnace structure, separator structure, tail flue, and heating surface arrangement, achieving stable combustion of municipal sludge fuel and complete combustion of organic matter, preventing high-temperature slagging corrosion and low-temperature acid corrosion of the tail heating surface. This invention explores an operating mechanism that separately feeds sludge fuel and biomass fuel into the furnace for co-firing, achieving efficient combustion of sludge and preventing corrosion and blockage of the heating surface. It is simple to operate, has low operating costs, and meets environmental protection requirements. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a diagram showing the relationship between fuel mixing points in the dense phase zone 14 of the furnace according to the present invention; Figure 3 This is a diagram showing the positional relationship of the fuel inlet in the dense phase zone 14 of the furnace according to the present invention. Detailed Implementation

[0013] The present invention will now be described in detail with reference to the accompanying drawings: A circulating fluidized bed boiler for sludge incineration with biomass fuel combustion includes a circulating fluidized bed boiler furnace 1, a high-temperature adiabatic cyclone separator 2, and a tail flue. A sludge fuel inlet 19 is provided on the front wall of the furnace inside, above the cyclone separator return port 17 of the high-temperature adiabatic cyclone separator 2. A sludge fuel feed conveyor 20 is connected to the sludge fuel inlet 19. A biomass fuel inlet 21 is provided on the front wall of the furnace inside, above the sludge fuel inlet 19. A biomass fuel feed conveyor 22 is connected to the biomass fuel inlet 21. A single row of two [unclear] ... At the secondary air inlet 23, sludge fuel, biomass fuel, and recycled ash are efficiently mixed and burned, achieving complete combustion of the sludge. The tail flue is a split-type design, consisting of a high-temperature section and a low-temperature section. A high-temperature metal cartridge dust collector 3 is installed between the high-temperature and low-temperature sections. Through staged dust removal, the flue gas from the low-temperature heating surface is kept clean. The high-temperature three-flue design lowers the flue gas temperature to below 610 degrees Celsius before exchanging heat with the high-temperature convective heating surface, effectively avoiding the condensation of gaseous alkali metal compounds in the flue gas into liquid and preventing corrosion of the high-temperature heating surface.

[0014] The high-temperature section flue consists of a first high-temperature vertical downward flue 4, a second high-temperature vertical upward flue 5, and a third high-temperature vertical downward flue 6, which are arranged side by side and connected end to end. The first high-temperature vertical downward flue 4, the second high-temperature vertical upward flue 5, and the third high-temperature vertical downward flue 6 are all water-cooled film-walled flues. The first high-temperature vertical downward flue 4 and the second high-temperature vertical upward flue 5 are water-cooled film-walled empty flues. A low-temperature superheater 7 and a high-temperature economizer 8 are installed in the third high-temperature vertical downward flue 6. The low-temperature section flue is a U-shaped steel plate flue 9, in which a low-temperature economizer 10 and an air preheater 11 are installed respectively.

[0015] A first dust collector 12 is installed at the connection between the lower end of the first high-temperature vertical downward flue 4 and the lower end of the second high-temperature vertical upward flue 5, and a second dust collector 13 is installed at the bottom of the third high-temperature vertical downward flue 6; by controlling and changing the flue gas velocity, effective dust removal of the three high-temperature flues is achieved.

[0016] A method for operating a biomass fuel-assisted sludge incineration circulating fluidized bed boiler, characterized by the following steps: Step 1: Lay the furnace bottom material 16 on the air distribution plate 15, heat the furnace bottom material 16 to the ignition temperature of the biomass fuel using an oil ignition burner, and input biomass fuel into the furnace through the biomass fuel feeder 22. After the furnace temperature continues to rise steadily, continuously input biomass fuel into the furnace through the biomass fuel feeder 22 to continue to raise the furnace temperature, and then stop using the oil ignition burner. The sludge fuel is sludge fuel with a moisture content of 40%-45% and in soil-like form. The biomass combustion aid is granular fuel with a particle size of less than 10 cm. The second step is to start the sludge fuel feeder 20 when the furnace temperature rises to 850℃, and continuously feed sludge fuel into the furnace. The sludge fuel has a moisture content of 40%-45% and is in soil-like form. The sludge falling into the sludge drop point 18 is heated by the high temperature furnace bottom material, the moisture evaporates, and after rising under the action of primary air, it merges with the biomass fuel that has just entered the furnace and is ignited, so as to realize the mixed combustion of sludge fuel and biomass fuel. The third step involves the return ash that has been separated by the high-temperature insulated cyclone separator 2 and returned to the furnace. The ash falls through the return port 17 of the cyclone separator into the sludge discharge point 18, thus continuously replenishing the high-temperature furnace bottom material in the lower part of the furnace. The return ash, sludge fuel and biomass fuel are disturbed and mixed in the dense phase zone 14 of the furnace to achieve complete combustion of the sludge. Step 4: The flue gas temperature entering the inlet of the first high-temperature vertical downward flue duct 4 from the outlet of the high-temperature adiabatic cyclone separator 2 is 910℃. This flue gas descends along the first high-temperature vertical downward flue duct 4, makes a 180-degree turn at its lower end, and then ascends along the second high-temperature vertical upward flue duct 5. At the 180-degree turn, the flue gas temperature is 700℃. When the flue gas ascends to the upper end of the second high-temperature vertical upward flue duct 5 and makes another 180-degree turn, it enters the third high-temperature vertical downward flue duct 6. At this point, the flue gas temperature is 610℃. The flow velocity of the flue gas in the first high-temperature vertical downward flue duct 4 and the second high-temperature vertical upward flue duct 5 is 7 m / s. After the fly ash in the flue gas settles, it is discharged through the first ash discharger 12. The CO in the flue gas is converted into carbon dioxide through the long process of the first high-temperature vertical downward flue duct 4 and the second high-temperature vertical upward flue duct 5, achieving CO emission standards. Fifth, a low-temperature superheater 7 and a high-temperature economizer 8 are installed in the third high-temperature vertical downward flue 6. The flue gas temperature entering the third high-temperature vertical downward flue 6 is 610℃-400℃, which avoids the corrosion of high-temperature heating surfaces caused by the condensation of gaseous alkali metal compounds in the flue gas into liquid. The flue gas velocity of the third high-temperature vertical downward flue 6 is designed to be 10 m / s, and the flue gas flow direction is consistent with the direction of fly ash settling. After the fly ash in the flue gas settles again, it is discharged through the second ash discharger 13. Step 6: The flue gas enters the high-temperature metal cartridge dust collector 3 from the outlet of the third high-temperature vertical downward flue 6 for the third dust removal. The flow velocity of the flue gas in the high-temperature metal cartridge dust collector 3 is designed to be 2-3 meters per second, and the heat dissipation temperature drop of the high-temperature metal cartridge dust collector 3 is 20℃. Step 7: After the clean flue gas flows out of the outlet of the high-temperature metal cartridge dust collector 3, it enters the U-shaped steel plate flue 9. The flue gas velocity in the U-shaped steel plate flue 9 is designed to be 7 meters per second. After the flue gas undergoes convective heat exchange with the low-temperature economizer 10 and the air preheater 11, it flows out from the outlet of the U-shaped steel plate flue 9. During this process, when the flue gas passes through the outer wall of the working fluid inlet end of the low-temperature heating surface, since the working fluid has not yet been heated and the temperature is low, a lot of dew will form on the pipe wall. However, since the fly ash concentration in the flue gas is low, it will not cause blockage of the low-temperature heating surface.

Claims

1. A biomass fuel combustion-supporting sludge incineration circulating fluidized bed boiler comprising a circulating fluidized bed boiler furnace (1), a high-temperature adiabatic cyclone (2), and a back pass, characterized in that, A sludge fuel inlet (19) is provided on the front wall of the furnace above the cyclone separator return port (17) of the high-temperature adiabatic cyclone separator (2). A sludge fuel feeder (20) is connected to the sludge fuel inlet (19). A biomass fuel inlet (21) is provided on the front wall of the furnace above the sludge fuel inlet (19). A biomass fuel feeder (22) is connected to the biomass fuel inlet (21). A single row of secondary air inlets (23) is provided on the front and rear walls of the furnace above the biomass fuel inlet (21). The tail flue is a split-type flue, that is, the tail flue is divided into a high-temperature section flue and a low-temperature section flue. A high-temperature metal cartridge dust collector (3) is provided between the high-temperature section flue and the low-temperature section flue.

2. The biomass fuel assisted sludge incineration circulating fluidized bed boiler according to claim 1, characterized in that, The high-temperature section flue consists of a first high-temperature vertical downward flue (4), a second high-temperature vertical upward flue (5), and a third high-temperature vertical downward flue (6) that are arranged side by side and connected end to end. The first high-temperature vertical downward flue (4), the second high-temperature vertical upward flue (5), and the third high-temperature vertical downward flue (6) are all water-cooled film wall flues. The first high-temperature vertical downward flue (4) and the second high-temperature vertical upward flue (5) are empty flues with water-cooled film walls. A low-temperature superheater (7) and a high-temperature economizer (8) are installed in the third high-temperature vertical downward flue (6). The low-temperature section flue is a U-shaped steel plate flue (9). A low-temperature economizer (10) and an air preheater (11) are installed in the U-shaped steel plate flue (9).

3. The biomass fuel assisted sludge incineration circulating fluidized bed boiler according to claim 2, characterized in that, A first ash remover (12) is provided at the connection between the lower end of the first high-temperature vertical downward flue (4) and the lower end of the second high-temperature vertical upward flue (5), and a second ash remover (13) is provided at the bottom of the third high-temperature vertical downward flue (6).

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