Circulating fluidized bed boiler for purely burning furfural residues
By adjusting the airflow ratio and fluidization velocity of the circulating fluidized bed boiler, combined with cyclone separator optimization, the problems of limited furfural residue combustion and easy slagging were solved, achieving efficient combustion and stable operation, and enhancing the boiler's durability and combustion efficiency.
Patent Information
- Application Number
- CN202422641592.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-31
- Publication Date
- 2026-01-09
- Estimated Expiration
- 2034-10-31
AI Technical Summary
Existing technologies are difficult to effectively process large quantities of furfural residue, resulting in limited combustion capacity, easy slagging in the furnace, backflow of smoke and fire. Furthermore, the boiler system design is not suitable for the characteristics of furfural residue, leading to low combustion efficiency and equipment corrosion problems.
A circulating fluidized bed boiler was designed. By adjusting the air ratio, fluidization velocity, and particle fluidization mode, combined with the optimization of the cyclone separator, efficient combustion of furfural residue and flue gas purification are achieved. High-temperature superheated screens and medium-temperature superheated screens are used to prevent slagging and corrosion. A coarse particle bottom material addition system is added to stabilize the bed pressure.
It achieves large-scale digestion and efficient combustion of furfural residue, reduces the amount of tail ash in flue gas, avoids high-temperature slagging and low-temperature corrosion, and improves the boiler's operational stability and combustion efficiency.
Smart Images
Figure CN223782839U_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a circulating fluidized bed boiler, and more particularly to a circulating fluidized bed boiler that burns only furfural residue. Background Technology
[0002] Furfural residue, a biomass material, is a biomass waste generated during furfural refining. It contains residual acid, sulfur and chlorine, and is rich in alkali metals, characterized by high moisture content and low calorific value. How to environmentally treat furfural residue is a pressing problem for relevant enterprises and environmental protection departments. Currently, small-capacity chain grate furnaces are used to burn furfural residue, but this method has the drawback of limited processing capacity, failing to meet the market's demand for processing large quantities of furfural residue. Furthermore, due to the characteristics of furfural residue, slagging easily occurs in the furnace during combustion. Developing a circulating fluidized bed boiler system suitable for burning only furfural residue, capable of processing 10-62 tons per hour (at 45% moisture content), using fluidized bed reconfiguration technology, to achieve large-scale utilization of furfural residue and transform waste into valuable resources for producing steam at pressures of 3.82-13.73 MPa, has become an urgent problem to be solved on-site.
[0003] Furfural residue has a small particle size and low specific gravity, resulting in a lack of large particles to stabilize the furnace bed temperature during combustion. The proportion of suspended combustion in the upper part of the furnace is relatively large. The conventional circulating particle flow velocity of 5 meters per second in a circulating fluidized bed furnace is completely unsuitable for the combustion and heat transfer of furfural residue fuel. The fuel has a high alkali metal content, with approximately 15% K₂O in the ash. The fuel ash has a low melting point, making it prone to adhesion within the furnace, leading to poor fuel circulation and fluidization. Conventional circulating fluidized bed boilers are designed with a primary air ratio of approximately 50-60%, the primary air's main function being to ensure the fluidization of combustion particles within the furnace, while the secondary air's role... The main focus is on enhancing the mixed combustion of fuels. However, for the circulating fluidization of furfural residue, due to its fine particle size and low specific gravity, with very few coarse particles at the bottom, the proportion of combustion in the upper part must be increased. How to adapt to the large proportion of combustion in the upper part of the furnace, and how to design the ratio of primary and secondary air to meet the characteristics of furfural residue combustion, all require exploration and experimentation. In addition, ensuring normal circulation and fluidization in the furnace during the process of transporting a large amount of furfural residue into the furnace, and minimizing the occurrence of backflow and crossfire when the lighter furfural residue enters the furnace, is another problem that needs to be solved on-site.
[0004] Furfural residue has a low calorific value (1400-2200 kcal / kg) and a high moisture content (40-60%), resulting in a large amount of flue gas production upon combustion. Furfural residue also has a high alkali metal content and contains residual acid, sulfur, and chlorine. This high alkali metal content leads to a low ash melting point, making the heated surfaces in the tail flue prone to slagging, ash accumulation, and corrosion, especially at the final air preheater stage, where moisture in the flue gas is more likely to condense, leading to low-temperature corrosion and even blockage by ash. Given these characteristics, the design and layout of the tail flue has become a challenging problem to solve on-site.
[0005] Circulating fluidized bed (CFB) boiler technology originated and developed under coal-fired fuel conditions, with the boiler system and fuel combustion flow pattern construction based on coal-fired fuel. Furfural residue fuel differs fundamentally from coal-fired fuel. How to reconstruct the flow pattern of furfural residue fuel within the furnace to accommodate the characteristics of large-volume furfural residue combustion has become a creative task in the design of pure furfural residue CFB boilers. Furfural residue has small particle size and low specific gravity; upon entering the furnace, most particles are suspended in the upper part of the furnace, especially after combustion. After flue gas and particulate matter in the flue gas enter the cyclone separator from the dilute phase zone of the furnace, they are very likely to escape from the exhaust port at the top of the cyclone separator. This results in a significant reduction in the number of particles entering the cyclone separator for separation, which directly deteriorates the boiler circulation state and affects the boiler's combustion and heat transfer. Therefore, how to design a reasonable flow velocity in the furnace cross section, how to enhance the capture capacity of the cyclone separator, and how to reconstruct the flue gas flow field and separation efficiency in the cyclone separator so that the entire boiler circulation system is matched with the fuel are also important aspects of the circulating fluidization reconstructing process for pure furfural residue combustion. Summary of the Invention
[0006] This invention provides a circulating fluidized bed boiler that burns furfural residue, exploring a new path for the efficient combustion and utilization of large quantities of low-quality furfural residue fuel resources. It creatively realizes the flow pattern reconstruction of furfural residue in circulating fluidized bed boilers, expanding the utilization pathways of biomass fuels.
[0007] The present invention solves the above technical problems through the following technical solutions:
[0008] A circulating fluidized bed boiler that burns only furfural residue includes a steel frame, on which a furnace, a cyclone separator, and a tail flue are respectively arranged. The furnace is connected to the upper cylinder of the cyclone separator through the upper outlet flue. The lower cone of the cyclone separator is connected to the lower end of the upper cylinder, and the lower end of the lower cone is connected to the furnace through a return material device. A central outlet cylinder of the separator is located at the top of the upper cylinder, and the other end of the central outlet cylinder is connected to the tail flue. A dust collector, an induced draft fan, and a chimney are connected in series at the outlet of the tail flue. The lower part of the furnace is a dense phase zone, and the upper part of the furnace is a dilute phase zone. A water-cooled air chamber is located at the lower end of the furnace, and an air distribution plate is located at the connection between the water-cooled air chamber and the furnace. A primary air box and an igniter are connected to the water-cooled air chamber. A lower secondary air annular wind box and an upper secondary air annular wind box are respectively installed on the outer wall of the furnace in the dense phase zone. The lower secondary air annular wind box and the upper secondary air annular wind box are parallel to each other and spaced apart. The lower secondary air annular wind box is connected to the dense phase zone through a lower secondary air branch duct, and the upper secondary air annular wind box is connected to the dense phase zone through an upper secondary air branch duct. The air distribution volume of the lower secondary air branch duct is equal to that of the upper secondary air annular wind box. The ratio of the secondary air distribution volume to the primary air distribution volume in the furnace is 55:45. The shrinkage ratio of the dense phase zone in the furnace is 40%. A furfural residue feed port is set on the outer wall of the furnace between the lower secondary air annular wind box and the upper secondary air annular wind box. By setting the induced draft fan, the pressure at the furfural residue feed port in the dense phase zone is 0.
[0009] The fluidization velocity of the circulating fluidized particles in the furnace is 3.6-4.2 meters per second. When the circulating fluidized particles enter the upper outlet flue of the furnace and flow out from the separator throat C in the upper cylinder, their fluidization velocity is 30 meters per second.
[0010] The distance H2 between the furfural residue feed inlet and the air distribution plate is 4.5 meters; the distance H1 between the outlet of the secondary air lower branch duct and the air distribution plate is 2.5 meters; the distance H3 between the outlet of the secondary air upper branch duct and the air distribution plate is 5.5-6 meters; the height of the dense phase zone is 9-11 meters.
[0011] A first flue is connected to the central outlet cylinder of the cyclone separator. The lower end of the first flue is connected to the second flue via a connecting flue. The first flue, the connecting flue, and the second flue are arranged in an N-shape. A bottom slag discharge cylinder for the first flue is provided at the lower end of the first flue, and a bottom slag discharge cylinder for the second flue is provided at the lower end of the second flue.
[0012] The furnace is equipped with a high-temperature superheater and a medium-temperature superheater. The first flue is equipped with a low-temperature superheater and a high-temperature economizer. The second flue is equipped with a low-temperature economizer and an air preheater.
[0013] A method for fluid regime reconstruction in a circulating fluidized bed boiler that burns only furfural residue includes the following steps:
[0014] Step 1: Set the induced draft fan power so that when the induced draft fan is working, the pressure at the furfural residue feed port in the dense phase zone of the furnace is 0.
[0015] The second step is to set the shrinkage ratio of the furnace in the dense phase zone to 40%; set the air inlet area of the secondary air upper branch duct to be equal to the air inlet area of the secondary air lower branch duct, and make the ratio of the secondary air distribution volume to the primary air distribution volume in the furnace 55:45.
[0016] The third step is to control the circulating particle fluidization velocity in the furnace to 3.6-4.2 meters per second, set the circulating particle fluidization velocity in the upper cylinder of the cyclone separator to 5 meters per second, and set the fluidization velocity of the circulating fluidized particles flowing out from the upper outlet flue of the furnace to the separator throat C at the upper cylinder of the cyclone separator to 30 meters per second, so that the cyclone separator can circulate and fluidize flue gas particles with a diameter greater than 50 micrometers.
[0017] Step 4: Set the temperature inside the furnace to 740-780℃, the flue gas temperature in the first flue to 500℃, and the flue gas temperature at the outlet of the second flue to 140℃; set the flue gas velocity in the first flue to 9 meters per second and the flue gas velocity in the second flue to 7 meters per second.
[0018] The fifth step involves installing a coarse-particle bottom material addition system in the dense phase zone of the furnace. The coarse-particle bottom material is added according to the furnace pressure to stabilize the furnace bed pressure.
[0019] This invention is based on existing circulating fluidized bed (CFB) boiler technology and addresses the challenges encountered when burning furfural residue as fuel in CFB boilers. Starting with fluidization remodeling, it aims to improve bed quality, increase ash concentration in the furnace, reduce tail-end ash in the flue gas, and prevent high-temperature slagging corrosion and low-temperature corrosion ash blockage on the heating surfaces. This has resulted in a CFB boiler combustion technology with a furnace characterized by low fluidization velocity, large cross-section, small bed surface, high upper combustion share, and high bed quality. The development of this product efficiently utilizes a large amount of idle, low-quality furfural residue resources, not only finding a way to dispose of furfural residue and achieving fuel substitution, but also expanding the utilization value of biomass fuels and achieving low-carbon, high-efficiency operation. Attached Figure Description
[0020] Figure 1 This is a schematic diagram of the structure of the present invention;
[0021] Figure 2 This is a schematic diagram of the structure of the present invention from a top view. Detailed Implementation
[0022] The present invention will now be described in detail with reference to the accompanying drawings:
[0023] A method for fluid regime reconfiguration in a circulating fluidized bed boiler that burns only furfural residue includes the following steps:
[0024] Step 1: Set the induced draft power of the induced draft fan 19. When the induced draft fan 19 is working, make the pressure at the furfural residue feed port 17 in the dense phase zone 11 of the furnace 2 0.
[0025] The second step is to set the shrinkage ratio of the furnace 2 in the dense phase zone 11 to 40%; set the air inlet area of the secondary air upper branch duct 16 and the air inlet area of the secondary air lower branch duct 15 to be equal, and make the ratio of the secondary air distribution volume to the primary air distribution volume in the furnace 55:45.
[0026] The third step is to control the circulating particle fluidization velocity in the furnace 2 at 3.6-4.2 meters per second, design the circulating particle fluidization velocity in the upper cylinder 3 of the cyclone separator to be 5 meters per second, and design the fluidization velocity of the circulating fluidized particles flowing out from the separator throat C at the upper cylinder 3 of the cyclone separator from the upper outlet flue 4 of the furnace to be 30 meters per second, so that the cyclone separator can achieve circulating fluidization of flue gas particles with a particle size greater than 50 micrometers.
[0027] Step 4: The temperature inside furnace 2 is designed to be 740-780℃, the flue gas temperature in the first flue 4 is designed to be 500℃, and the flue gas temperature at the outlet of the second flue 5 is designed to be 140℃; the flue gas velocity in the first flue 4 is designed to be 9 meters per second, and the flue gas velocity in the second flue 5 is designed to be 7 meters per second.
[0028] Step 5: Set up a coarse particle bottom material addition system in zone 11 of the dense phase zone 2 of the furnace chamber. Add coarse particle bottom material according to the pressure inside the furnace to stabilize the bed pressure.
[0029] A furfural residue feed port 17 is set at the front of the furnace 2. The furfural residue feeding system outside the furnace adopts a two-stage spiral conveying method to push and transport the furfural residue into the furnace. Since this type of furnace is for pure furfural residue combustion, the design of inert bed material addition should be considered to ensure that the boiler maintains normal bed pressure. An inert bed material addition system is reserved in the furnace. An inert bed material addition port can be reserved on the return pipe, or it can be added to the furnace front feeding system. For a boiler of 180 tons per hour of this invention, the furfural residue consumption is 50.87 tons per hour, and approximately 380,000 tons of furfural residue are consumed annually.
[0030] A circulating fluidized bed boiler that burns only furfural residue includes a steel frame 1. A furnace 2, a cyclone separator, and a tail flue are respectively arranged on the steel frame 1. The furnace 2 is connected to the upper cylinder 3 of the cyclone separator via an upper outlet flue 4. A lower cone 5 of the cyclone separator is connected to the lower end of the upper cylinder 3. The lower end of the lower cone 5 is connected to the furnace 2 via a return material device 6. A central outlet cylinder 18 of the separator is located at the top of the upper cylinder 3. The other end is connected to a tail flue, and a dust collector 31, an induced draft fan 19, and a chimney 32 are connected in series at the outlet of the tail flue; the lower part of the furnace 2 is a dense phase zone 11, and the upper part of the furnace 2 is a dilute phase zone 12; a water-cooled air chamber 7 is provided at the lower end of the furnace 2, and an air distribution plate 8 is provided at the connection between the water-cooled air chamber 7 and the furnace 2, and a primary air box 9 is connected to the water-cooled air chamber 7; a secondary air lower annular air box 13 and a secondary air upper annular air box are respectively provided on the outer wall of the furnace 2 at the dense phase zone 11. 14. The lower annular secondary air box 13 and the upper annular secondary air box 14 are parallel to each other and spaced apart. The lower annular secondary air box 13 is connected to the dense phase zone 11 through the lower secondary air branch duct 15, and the upper secondary air box 14 is connected to the dense phase zone 11 through the upper secondary air branch duct 16. The air distribution volume of the lower secondary air branch duct 15 is equal to that of the upper secondary air box 14. The ratio of the secondary air distribution volume to the primary air distribution volume in the furnace is 55:45. The shrinkage ratio in the dense phase zone 11 is 40%. A furfural residue feed port 17 is provided on the outer wall of the furnace 2 between the lower annular wind box 13 and the upper annular wind box 14 of the secondary air. By utilizing the induced draft capacity of the induced draft fan 19, the pressure at the furfural residue feed port 17 in the dense phase zone 11 of the furnace 2 is kept at 0, thus ensuring that the relatively light furfural residue does not experience backflow or flashback when entering the furnace. The furnace 2 is a membrane water-cooled furnace with a large furnace cross-section B2 and a fluidization velocity designed to be 3.6 rpm. -4.2 meters, ensuring sufficient residence time of fuel in the furnace for complete combustion; the lower dense phase zone is 9-11 meters high, all welded with dense pins and coated with wear-resistant plastic; the water-cooled bed section B1 is 40% of the upper section of the furnace; due to the fuel being rich in alkali metals and having a low ash melting point, the furnace temperature is designed to be controlled at 740-780℃ to prevent coking in the furnace; high-temperature superheaters and medium-temperature superheaters are installed in furnace 2, and the high-temperature superheaters and medium-temperature superheaters 16 are made of TP347H material, which ensures the heat absorption of the superheaters and avoids the high-temperature corrosion problem caused by placing them at the tail end; the secondary air inlet is arranged on the upper front and rear walls of the combustion chamber, and the inlet is square. The furfural residue feed port 17 has a double layer of secondary air arranged on the upper and lower sides. The secondary air inlet should have large momentum, low resistance, and strong penetration and disturbance effect, which improves the boiler combustion efficiency, controls CO production, and reduces the power of the secondary air fan.
[0031] The fluidization velocity of the circulating fluidized particles in the furnace 2 is 3.6-4.2 meters per second. The fluidization velocity of the circulating fluidized particles flowing out from the upper outlet flue 4 of the furnace into the separator throat C of the upper cylinder 3 of the cyclone separator is 30 meters per second. This invention adopts an adiabatic cyclone separator, which increases the cross-section QD of the upper cylinder 3 of the cyclone separator and reduces the cross-section of the separator throat C. The separator inlet, cone and central cylinder are all optimized. The separation efficiency reaches d99<50μm and d50<20μm, which greatly improves the separator's capture ability and increases the residence time of particles in the furnace, which is beneficial to the combustion of furfural residue fine fuel.
[0032] A first flue 22 is connected to the central outlet cylinder of the cyclone separator. The lower end of the first flue 22 is connected to the second flue 23 via a connecting flue 24. The first flue 22, the connecting flue 24, and the second flue 23 are arranged in an N-shape. A first flue bottom slag discharge cylinder 25 is provided at the lower end of the first flue 22, and a second flue bottom slag discharge cylinder 26 is provided at the lower end of the second flue 23, so that the slag in the flue can fall and be discharged in time.
[0033] A high-temperature superheater and a medium-temperature superheater 16 are installed in the furnace 2. A low-temperature superheater 27 and a high-temperature economizer 28 are installed in the first flue 22. A low-temperature economizer 29 and an air preheater 30 are installed in the second flue 23. The N-shaped flue not only reduces the introduction of large ash particles into the rear vertical shaft second flue 23, but also allows for a staggered arrangement of the low-temperature economizer 29, reducing steel consumption and controlling costs. Because the fuel is fine and light, the proportion of upper suspension combustion is high, and the primary and secondary air ratio is 45:55 to ensure complete fuel combustion. The transverse pitch of the tubes in the final stage of the air preheater 30 is increased to avoid ash blockage in the final stage. At the same time, the last two stages of tubes use enamel tubes with Q355GNH base material to avoid low-temperature corrosion and extend service life.
[0034] The distance H2 between the furfural residue feed inlet 17 and the air distribution plate 8 is 4.5 meters; the distance H1 between the outlet of the secondary air lower branch duct 15 on the furnace 2 and the air distribution plate 8 is 2.5 meters; the distance H3 between the outlet of the secondary air upper branch duct 16 on the furnace 2 and the air distribution plate 8 is 5.5-6 meters; the height of the dense phase zone 11 is 9-11 meters; the furfural residue is fed into the furnace by a screw conveyor. The design height of the furfural residue feed inlet 17 is 5-6 meters above the air distribution plate, which already provides a certain distance from the air distribution plate. Controlling the flue gas pressure at the feed inlet to zero pressure ensures that furfural residue can be smoothly and stably fed into the furnace, preventing backflow and flame spikes, thus effectively improving the stability and reliability of boiler operation. For existing circulating fluidized bed boilers, the furnace needs both fine particles for heat transfer and coarse particles for stabilizing bed pressure and temperature. However, when burning furfural residue, the fuel basically does not contain coarse particles. Therefore, a bottom material addition system is set up in the furnace to add coarser bottom material to the dense phase zone of the furnace to ensure stable and reliable boiler operation.
Claims
1. A circulating fluidized bed boiler for burning pure furfural residue, comprising a steel frame (1), on which a furnace (2), a cyclone separator and a tail flue are respectively arranged. The furnace (2) is connected to the upper cylinder (3) of the cyclone separator through the upper outlet flue (4). The lower cone (5) of the cyclone separator is connected to the lower end of the upper cylinder (3). The lower end of the lower cone (5) is connected to the furnace (2) through a return material device (6). The center outlet cylinder of the separator is provided at the top of the upper cylinder (3). (18), a tail flue is connected to the other end of the separator central outlet cylinder (18), and a dust collector (31), an induced draft fan (19) and a chimney (32) are connected in series at the outlet of the tail flue; the lower part of the furnace (2) is a dense phase zone (11), and the upper part of the furnace (2) is a dilute phase zone (12); a water-cooled air chamber (7) is provided at the lower end of the furnace (2), an air distribution plate (8) is provided at the connection between the water-cooled air chamber (7) and the furnace (2), and a primary air box (9) is connected to the water-cooled air chamber (7); characterized in that, A secondary air lower annular air box (13) and a secondary air upper annular air box (14) are respectively installed on the outer wall of the furnace (2) in the dense phase zone (11). The secondary air lower annular air box (13) and the secondary air upper annular air box (14) are parallel to each other and spaced apart. The secondary air lower annular air box (13) is connected to the dense phase zone (11) through the secondary air lower branch air pipe (15), and the secondary air upper annular air box (14) is connected to the dense phase zone (11) through the secondary air upper branch air pipe (16). The air distribution volume of the furnace is equal to that of the secondary air upper annular wind box (14); the ratio of the secondary air distribution volume to the primary air distribution volume in the furnace is 55:45; the shrinkage ratio of the furnace (2) in the dense phase zone (11) is 40%; a furfural residue feed port (17) is provided on the outer wall of the furnace (2) between the secondary air lower annular wind box (13) and the secondary air upper annular wind box (14); by setting the induced draft capacity of the induced draft fan (19), the pressure at the furfural residue feed port (17) in the dense phase zone (11) of the furnace (2) is 0.
2. A circulating fluidized bed boiler for burning pure furfural residue according to claim 1, characterized in that, The fluidization velocity of the circulating fluidized particles in the furnace (2) is 3.6-4.2 meters per second, and the fluidization velocity of the circulating fluidized particles when they flow out from the throat C of the separator is 30 meters per second.
3. A circulating fluidized bed boiler for burning pure furfural residue according to claim 1 or 2, characterized in that, The distance H2 between the furfural residue feed port (17) and the air distribution plate (8) is 4.5 meters; the distance H1 between the outlet of the secondary air lower branch pipe (15) and the air distribution plate (8) is 2.5 meters; the distance H3 between the outlet of the secondary air upper branch pipe (16) and the air distribution plate (8) is 5.5-6 meters; the height of the dense phase zone (11) is 9-11 meters.
4. A circulating fluidized bed boiler for burning pure furfural residue according to claim 1 or 2, characterized in that, A first flue (22) is connected to the central outlet cylinder of the cyclone separator. The lower end of the first flue (22) is connected to the second flue (23) through a connecting flue (24). The first flue (22), the connecting flue (24), and the second flue (23) are arranged in an N-shape. A first flue bottom slag discharge cylinder (25) is provided at the lower end of the first flue (22), and a second flue bottom slag discharge cylinder (26) is provided at the lower end of the second flue (23).
5. A circulating fluidized bed boiler for burning pure furfural residue according to claim 4, characterized in that, A high-temperature superheater and a medium-temperature superheater are installed in the furnace (2). A low-temperature superheater (27) and a high-temperature economizer (28) are installed in the first flue (22). A low-temperature economizer (29) and an air preheater (30) are installed in the second flue (23).