阅读说明：本技术 一种循环流化床锅炉及其使用方法 (Circulating fluidized bed boiler and use method thereof ) 是由 谭波 卢晓明 司硕 宋令坡 王传志 王海苗 刘忠攀 杨晓辉 于 2020-04-22 设计创作，主要内容包括：本发明提供了一种循环流化床锅炉及其使用方法,所述的循环流化床锅炉包括依次连接的炉膛、分离装置和尾部烟道,所述的分离装置通过返料管路与炉膛循环连接；所述的尾部烟道内设置有预热装置,所述的预热装置连接炉膛,一次风经预热装置预热后送入炉膛,所述的尾部烟道筒体上开设有出风口,所述的出风口经输送风机接入返料管路。本发明提供的循环流化床锅炉可以实现炉膛内800～850℃低温燃烧,有利于实现锅炉的超低排放。(The invention provides a circulating fluidized bed boiler and a using method thereof, wherein the circulating fluidized bed boiler comprises a hearth, a separating device and a tail flue which are sequentially connected, and the separating device is circularly connected with the hearth through a return pipeline; the preheating device is connected with the hearth, primary air is preheated by the preheating device and then sent into the hearth, an air outlet is formed in the barrel of the tail flue, and the air outlet is connected into a material returning pipeline through a conveying fan. The circulating fluidized bed boiler provided by the invention can realize low-temperature combustion at 800-850 ℃ in a hearth, and is beneficial to realizing ultralow emission of the boiler.)

1. A circulating fluidized bed boiler is characterized by comprising a hearth, a separation device and a tail flue which are sequentially connected, wherein the separation device is circularly connected with the hearth through a return pipeline;

the preheating device is connected with the hearth, primary air is preheated by the preheating device and then sent into the hearth, an air outlet is formed in the barrel of the tail flue, and the air outlet is connected into a material returning pipeline through a conveying fan.

2. The circulating fluidized bed boiler of claim 1, wherein the tail flue is internally provided with a heat exchange device and a preheating device in sequence along the flow direction of flue gas;

preferably, the air outlet is arranged on a tail flue cylinder between the heat exchange device and the preheating device;

preferably, the inside of the tail flue is provided with a high-temperature overheating device, a coal-saving device and a preheating device in sequence along the flow direction of the flue gas;

preferably, the air outlet is arranged on a tail flue cylinder between the high-temperature overheating device and the coal saving device;

preferably, a first-stage high-temperature overheating device, a second-stage high-temperature overheating device, a first-stage coal-saving device, a second-stage coal-saving device and a preheating device are sequentially arranged in the tail flue along the flow direction of flue gas;

preferably, the air outlet is arranged on the tail flue cylinder between the secondary high-temperature overheating device and the primary coal saving device.

3. The circulating fluidized bed boiler according to claim 1 or 2, wherein the furnace chamber is divided into a dense phase zone, a transition zone and a dilute phase zone from bottom to top;

preferably, the dense-phase zone shell and the dilute-phase zone shell are of vertical columnar structures, and the transition zone cylinder is of an inverted frustum-shaped structure for connecting the dense-phase zone and the dilute-phase zone;

preferably, the dense-phase zone shell is provided with a feeding port, a feed back port and a primary air inlet, and the discharge port of the separating device is connected with the feed back port through a feed back pipeline;

preferably, a secondary air inlet is formed in the transition area shell;

preferably, the diameter of the shell of the dense-phase zone is smaller than that of the shell of the dilute-phase zone;

preferably, the cross-sectional area of the dilute phase zone is 1.2-1.5 times of the cross-sectional area of the dense phase zone;

preferably, the height of the dilute phase zone shell is 20-30 m.

4. The circulating fluidized bed boiler of any one of claims 1 to 3, wherein the outlet end of the air outlet main pipe of the conveying fan is divided into two paths, one path is connected with the secondary air inlet, and the other path is connected to a material return pipeline.

5. The circulating fluidized bed boiler according to any one of claims 1 to 4, wherein the outlet of the preheating device is divided into two paths, one path is connected with the primary air inlet through a primary air inlet pipeline, and the other path is connected with the air outlet main pipe of the air delivery blower through a secondary air inlet pipeline;

preferably, the secondary air inlet pipeline is provided with a secondary fan.

6. A method of using the circulating fluidized bed boiler according to any one of claims 1 to 5, characterized in that the method of using specifically comprises:

feeding materials at the bottom of the hearth, feeding primary air into the hearth to participate in combustion after the primary air is preheated by the preheating device, separating and recycling fuel particles in flue gas generated by combustion through the separating device, and returning the fuel particles to the hearth through the material returning pipeline after the fuel particles are recycled; after entering the tail flue, the separated flue gas is sent into a return pipeline by an air outlet through a conveying fan to assist the backflow of fuel particles.

7. The use method according to claim 6, characterized in that the use method specifically comprises the following steps:

feeding raw materials into a hearth from a feeding port, preheating combustion-supporting air by a preheating device, and feeding the preheated combustion-supporting air into a dense-phase region of the hearth as primary air to participate in raw material combustion;

(II) discharging flue gas generated by raw material combustion from the top of the hearth into a separation device, separating and recovering fuel particles in the flue gas, and circulating and refluxing the recovered fuel particles to the bottom of the hearth through a return pipeline;

(III) the separated flue gas enters a tail flue to carry out heat recovery, part of the flue gas after heat recovery is divided into two parts by a conveying fan, and one part of the flue gas is used as conveying air and is conveyed into a return pipeline to assist fuel particles to flow back; the other part is used as secondary air and is introduced into a transition area of the hearth to support combustion.

8. The use method according to claim 7, wherein in the step (I), the temperature of the combustion-supporting air preheated by the preheating device is 180-210 ℃;

preferably, the feedstock comprises a fuel;

preferably, the particle size of the fuel is 0-1 mm;

preferably, the water content of the fuel is less than or equal to 10 wt%;

preferably, the raw material also comprises a desulfurizing agent;

preferably, the particle size of the desulfurizer is 0-800 μm;

preferably, the combustion temperature of the raw materials is 800-850 ℃;

preferably, step (i) further comprises: when the load of the circulating fluidized bed boiler is higher than 60%, a secondary fan is started, combustion-supporting air is divided into two parts after being preheated, one part is used as primary air and sent into a hearth dense-phase region to participate in raw material combustion, and the other part is used as secondary air and is introduced into a hearth transition region through the secondary fan to support combustion;

preferably, after the secondary air fan is started, the air intake ratio of the primary air to the secondary air is (2-4): (6-8), and further preferably, the air intake ratio of the primary air to the secondary air is 3: 7.

9. the use method of claim 7 or 8, wherein in the step (II), the temperature of flue gas generated by raw material combustion is 820-900 ℃;

preferably, the flow velocity of the flue gas generated by combustion in a dilute phase zone of the hearth is 5-8 m/s;

preferably, the separation device separates and recovers fuel particles with the particle size of more than or equal to 70 mu m in the flue gas.

10. The use method of any one of claims 7 to 9, wherein in the step (III), the air supply rate ratio of the air supply and the secondary air is (10-20): (80-90), and further preferably, the air inlet ratio of the conveying air to the secondary air is 15:85 parts by weight;

preferably, the heat recovery process specifically includes:

the separated flue gas sequentially passes through a primary overheating device and a secondary overheating device to recover heat, then part of the flue gas sequentially passes through a primary coal-saving device and a secondary coal-saving device to recover waste heat, enters a preheating device to contact combustion-supporting air to exchange heat, and the flue gas after heat exchange is discharged outside;

preferably, the temperature of the flue gas after heat recovery by the primary superheating device and the secondary superheating device is reduced to 400-500 ℃, and further preferably, the temperature of the flue gas is reduced to 450 ℃;

preferably, the temperature of combustion-supporting air after heat exchange is 180-210 ℃;

preferably, the temperature of the flue gas after heat exchange is 135-150 ℃.

Technical Field

The invention belongs to the technical field of combustion boilers, relates to a circulating fluidized bed boiler and a using method thereof, and particularly relates to a circulating fluidized bed boiler suitable for fine powder fuel particles with the particle size of 0-1 mm and a using method thereof.

Background

NO_xIs one of the important and powerful problems in environment, such as acid rain, haze and the like, and the main source of the environment is the combustion process of various fuels, particularly the emission from power stations and industrial boilers. Circulating fluidized bed combustion technology has become the best approach for clean combustion of fuels due to its superior performance in terms of fuel flexibility and low cost of emission control. Because of the characteristics of medium-temperature combustion (800-900 ℃), a large amount of reducing materials in a circulating fluidized bed (circulating fluidized bed) boiler and the like, original NO is generated under the condition of adopting graded air supply_xThe emission is low, and the environmental protection standard of most of the countries at present can be generally met. However, the achievement of the original ultra-low emissions presents a significant challenge and there is still a need to deeply mine the low nitrogen combustion potential of circulating fluidized bed technology.

CN104728834A discloses a reducing atmosphere combustion process of a circulating fluidized bed boiler, which comprises a circulating fluidized bed boiler, wherein a primary air chamber of the circulating fluidized bed boiler is communicated with a primary air pipeline, a combustion chamber of the circulating fluidized bed boiler is communicated with a secondary air pipeline, a flue gas recirculation pipe is arranged on a flue gas discharge pipeline of the circulating fluidized bed boiler and is communicated with the primary air chamber of the circulating fluidized bed boiler, and a flow control valve and a gas flow sensor are respectively arranged on the primary air pipeline, the secondary air pipeline and the flue gas recirculation pipe.

CN204554801U discloses a circulating fluidized bed boiler secondary air hierarchical arrangement system, which comprises a circulating fluidized bed boiler body, a primary air system is connected with the bottom of the circulating fluidized bed boiler body, the primary air system comprises a first fan, the first fan is connected with the circulating fluidized bed boiler body through an air pipe, the side wall of the lower part of the circulating fluidized bed boiler body is connected with a secondary air system, the secondary air system comprises a high-efficiency secondary air system and a lower secondary air system, the nozzle of the high-efficiency secondary air system is positioned above the nozzle of the lower secondary air system, the high-efficiency secondary air system comprises a second fan, the second fan is connected with the circulating fluidized bed boiler body through an air pipe, the lower secondary air system comprises a third fan, the third fan is connected with the circulating fluidized bed boiler body through an air pipe, and the output air of the first fan, the output air of the second fan and the output air of the third fan are heated through an air preheater.

CN207486788U discloses a gas-doped circulating fluidized bed boiler, which comprises a hearth, a primary air chamber, a cyclone separator, a dipleg, a material return valve and a tail flue; a coal feeding port and a secondary air port are arranged in the hearth; the tail flue comprises a superheater, an economizer and an air preheater; the circulating fluidized bed boiler also comprises a gas chamber, the gas chamber and the primary air chamber are arranged below the hearth, the gas chamber is arranged above the primary air chamber, and gas nozzles are uniformly arranged at the upper part of the gas chamber; the primary air chamber is connected with an air preheater through a gas pipeline.

The particle size of the conventional furnace-entering fuel is generally required to be within the range of 0-8 mm. For fine powder fuel, the circulating fluidized bed boiler mostly adopts a mode of adding water into the fuel, for example, when a byproduct generated in the coal washing process, namely coal slime adopts a circulating fluidized bed combustion technology, the water content of the coal slime can reach more than 28%. The vaporization of the extra water reduces the thermal efficiency of the boiler, and meanwhile, the thermal explosion characteristic of the fine powder fuel added with water in the combustion process increases the difficulty of controlling the emission of pollutants in the boiler, thereby increasing the ultralow emission cost of the boiler.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a circulating fluidized bed boiler, high ash content generated after fuel combustion is fluidized by additionally arranging a conveying fan to form circulating materials to return to a hearth, and a large amount of circulating materials increase the heat storage capacity of the hearth, so that low-temperature combustion at 800-850 ℃ in the hearth can be realized, ultralow emission of the boiler is favorably realized, feeding in a coal slurry mode is not needed, fine powder fuel particles with low water content can be directly conveyed into the hearth, the difficulty in controlling the emission of pollutants in the boiler due to the thermal explosion characteristic of the fine powder fuel particles after water is added in the combustion process is avoided, and the ultralow emission cost of the boiler is effectively reduced.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the invention provides a circulating fluidized bed boiler, which comprises a hearth, a separation device and a tail flue, wherein the hearth, the separation device and the tail flue are sequentially connected, and the separation device is circularly connected with the hearth through a material returning pipeline.

The preheating device is connected with the hearth, primary air is preheated by the preheating device and then sent into the hearth, an air outlet is formed in the barrel of the tail flue, and the air outlet is connected into a material returning pipeline through a conveying fan.

The circulating fluidized bed boiler provided by the invention is mainly used for carrying out structural improvement on the existing circulating fluidized bed boiler aiming at fine powder fuel particles with the particle size of 0-1 mm, high ash content generated after the fine powder fuel particles are combusted is fully fluidized by adding the conveying fan to form external circulating fuel which is separated and returned to the hearth through the separating device, the conveying fan is added to provide driving force for fluidization of the fine powder particles, the apparent gas velocity in the hearth of the boiler is designed at the terminal velocity of the fuel particles not lower than 700 mu m, the apparent gas velocity in the hearth can enable the fuel particles with the particle size of less than 700 mu m to pass through the hearth at one time, few fuel particles adhere to the wall to form internal circulating materials, most of the particle materials enter the separating device to form external circulation and return to the hearth, the heat storage capacity of the hearth is increased, and low-temperature combustion at 800-850 ℃ in the hearth can be, is beneficial to the realization of ultra-low emission of the boiler.

The circulating fluidized bed boiler provided by the invention can directly feed the fine powder fuel particles with low water content into the hearth without adopting a coal slime feeding mode, avoids the difficulty in controlling the discharge of pollutants in the boiler due to the thermal explosion characteristic of the fine powder fuel particles after water is added in the combustion process, and effectively reduces the ultralow discharge cost of the boiler.

As a preferable technical scheme of the invention, the heat exchange device and the preheating device are sequentially arranged in the tail flue along the flow direction of the flue gas.

Preferably, the air outlet is arranged on the tail flue cylinder between the heat exchange device and the preheating device.

Preferably, the heat exchange device comprises a high-temperature overheating device and a coal saving device which are sequentially arranged along the flow direction of the flue gas.

Preferably, the air outlet is arranged on the tail flue cylinder between the high-temperature overheating device and the coal saving device.

Preferably, a first-stage high-temperature overheating device, a second-stage high-temperature overheating device, a first-stage coal-saving device, a second-stage coal-saving device and a preheating device are sequentially arranged in the tail flue along the flow direction of flue gas.

Preferably, the air outlet is arranged on the tail flue cylinder between the secondary high-temperature overheating device and the primary coal saving device.

As a preferable technical scheme of the invention, the inner cavity of the hearth is divided into a dense-phase region, a transition region and a dilute-phase region from bottom to top.

Preferably, the dense phase zone shell and the dilute phase zone shell are of vertical columnar structures, and the transition zone cylinder is of an inverted frustum-shaped structure for connecting the dense phase zone and the dilute phase zone.

Preferably, the dense phase zone shell is provided with a feeding port, a feed back port and a primary air inlet, and the discharge port of the separating device is connected with the feed back port through a feed back pipeline.

Preferably, the transition area shell is provided with a secondary air inlet.

Preferably, the diameter of the shell in the dense phase zone is smaller than that of the shell in the dilute phase zone.

Preferably, the dilute phase zone has a cross-sectional area 1.2 to 1.5 times, for example, 1.2 times, 1.3 times, 1.4 times or 1.5 times, but not limited to the recited values, and other values not recited in the range of values are also applicable.

Preferably, the height of the dilute phase zone shell is 20-30 m, for example, 20m, 21m, 22m, 23m, 24m, 25m, 26m, 27m, 28m, 29m or 30m, but is not limited to the values listed, and other values not listed in the range of the values are also applicable.

In the invention, the height of the shell of the dilute phase zone is required to ensure that fuel particles with the particle size of less than 120 mu m are burnt out at one time in the hearth, and if the height of the dilute phase zone is insufficient, fine powder fuel particles can not be fully burnt out and attached to the inner wall of the hearth, thus affecting the combustion efficiency.

As a preferred technical scheme of the invention, the outlet end of the air outlet main pipe of the conveying fan is divided into two paths, one path is connected with the secondary air inlet, and the other path is connected with the material returning pipeline.

As a preferable technical scheme of the invention, the outlet of the preheating device is divided into two paths, one path is connected with a primary air inlet through a primary air inlet pipeline, and the other path is connected with an air outlet main pipe of the air delivery blower through a secondary air inlet pipeline.

Preferably, the secondary air inlet pipeline is provided with a secondary fan.

In a second aspect, the present invention provides a method for using the circulating fluidized bed boiler according to the first aspect, specifically comprising:

feeding materials at the bottom of the hearth, feeding primary air into the hearth to participate in combustion after the primary air is preheated by the preheating device, separating and recycling fuel particles in flue gas generated by combustion through the separating device, and returning the fuel particles to the hearth through the material returning pipeline after the fuel particles are recycled; after entering the tail flue, the separated flue gas is sent into a return pipeline by an air outlet through a conveying fan to assist the backflow of fuel particles.

As a preferred technical solution of the present invention, the using method specifically comprises the following steps:

feeding raw materials into a hearth from a feeding port, preheating combustion-supporting air by a preheating device, and feeding the preheated combustion-supporting air into a dense-phase region of the hearth as primary air to participate in raw material combustion;

(II) discharging flue gas generated by raw material combustion from the top of the hearth into a separation device, separating and recovering fuel particles in the flue gas, and circulating and refluxing the recovered fuel particles to the bottom of the hearth through a return pipeline;

(III) the separated flue gas enters a tail flue to carry out heat recovery, part of the flue gas after heat recovery is divided into two parts by a conveying fan, and one part of the flue gas is used as conveying air and is conveyed into a return pipeline to assist fuel particles to flow back; the other part is used as secondary air and is introduced into a transition area of the hearth to support combustion.

In a preferred embodiment of the present invention, in the step (I), the temperature of the combustion air preheated by the preheating device is 180 to 210 ℃, and may be, for example, 180 ℃, 182 ℃, 184 ℃, 186 ℃, 188 ℃, 190 ℃, 192 ℃, 194 ℃, 196 ℃, 198 ℃, 200 ℃, 202 ℃, 204 ℃, 206 ℃, 208 ℃ or 210 ℃, but is not limited to the above-mentioned values, and other values not listed in the above-mentioned range of values are also applicable.

Preferably, the feedstock comprises a fuel.

Preferably, the fuel has a particle size of 0 to 1mm, for example, 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm or 1.0mm, but is not limited to the recited values, and other values not recited in the numerical range are also applicable.

Preferably, the fuel has a water content of 10 wt.% or less, and may be, for example, 1 wt.%, 2 wt.%, 3 wt.%, 4 wt.%, 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.% or 10 wt.%, but is not limited to the recited values, and other values not recited within the range of values are equally applicable.

Preferably, the raw material also comprises a desulfurizing agent.

Preferably, the particle size of the desulfurizing agent is 0 to 800. mu.m, and may be, for example, 50 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm, 500 μm, 550 μm, 600 μm, 650 μm, 700 μm, 750 μm or 800 μm, but is not limited to the values listed, and other values not listed in the numerical range are also applicable.

Preferably, the raw material combustion temperature is 800 to 850 ℃, for example 800 ℃, 805 ℃, 810 ℃, 815 ℃, 820 ℃, 825 ℃, 830 ℃, 835 ℃, 840 ℃, 845 ℃ or 850 ℃, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, step (i) further comprises: when the load of the circulating fluidized bed boiler is higher than 60%, a secondary fan is started, combustion-supporting air is divided into two parts after being preheated, one part is used as primary air and sent into a hearth dense-phase region to participate in raw material combustion, and the other part is used as secondary air and is introduced into a hearth transition region through the secondary fan to support combustion.

Preferably, after the secondary air fan is started, the air intake ratio of the primary air to the secondary air is (2-4): (6 to 8) may be, for example, 2:6, 2:7, 2:8, 3:6, 3:7, 3:8, 4:6 or 4:7, but not limited to the above-mentioned values, and other values not shown in the above-mentioned range are also applicable, and it is further preferable that the ratio of the intake amount of the primary air and the intake amount of the secondary air is 3: 7.

In a preferred embodiment of the present invention, in the step (II), the temperature of the flue gas generated by the combustion of the raw material is 820 to 900 ℃, for example 820 ℃, 830 ℃, 840 ℃, 850 ℃, 860 ℃, 870 ℃, 880 ℃, 890 ℃ or 900 ℃, but is not limited to the above-mentioned values, and other values not shown in the above-mentioned range of values are also applicable.

Preferably, the flow velocity of the flue gas generated by combustion in the lean phase zone of the furnace is 5-8 m/s, such as 5m/s, 6m/s, 7m/s or 8m/s, but not limited to the values listed, and other values not listed in the range of the values are also applicable.

Preferably, the fuel particles with a particle size of 70 μm or more in the recovered flue gas are separated by the separation device, and may be 70 μm, 72 μm, 74 μm, 76 μm, 78 μm, 80 μm, 82 μm, 84 μm, 86 μm, 88 μm, 90 μm, 92 μm, 94 μm, 96 μm, 98 μm or 100 μm, for example, but not limited to the values listed, and other values not listed in the range of the values are also applicable.

In a preferred embodiment of the present invention, in the step (III), the temperature of the flue gas after separation is 820 to 900 ℃, for example 820 ℃, 830 ℃, 840 ℃, 850 ℃, 860 ℃, 870 ℃, 880 ℃, 890 ℃ or 900 ℃, but is not limited to the above-mentioned values, and other values not shown in the above-mentioned range of values are also applicable.

Preferably, the air inlet amount ratio of the conveying air to the secondary air is (10-20): (80-90), and further preferably, the air inlet ratio of the conveying air to the secondary air is 15: 85.

preferably, the temperature of the portion of the flue gas after heat recovery is 400 to 500 ℃, for example, 400 ℃, 410 ℃, 420 ℃, 430 ℃, 440 ℃, 450 ℃, 460 ℃, 470 ℃, 480 ℃, 490 ℃ or 500 ℃, but not limited to the recited values, and other values not recited within the range of the values are also applicable, and more preferably, the temperature of the flue gas after heat recovery is 450 ℃.

Preferably, the heat recovery process specifically includes:

the separated flue gas is heated to saturated steam through a primary superheating device and a secondary superheating device in sequence to obtain superheated steam, then part of the flue gas enters a preheating device after heat exchange through the primary coal saving device and the secondary coal saving device in sequence to contact with combustion-supporting air for heat exchange, and the flue gas after heat exchange is discharged outside.

Preferably, the temperature of the combustion air after heat exchange is 180 to 210 ℃, and may be, for example, 180 ℃, 182 ℃, 184 ℃, 186 ℃, 188 ℃, 190 ℃, 192 ℃, 194 ℃, 196 ℃, 198 ℃, 200 ℃, 202 ℃, 204 ℃, 206 ℃, 208 ℃ or 210 ℃, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, the exhaust gas temperature of the flue gas is 135 to 150 ℃, for example, 135 ℃, 136 ℃, 137 ℃, 138 ℃, 139 ℃, 140 ℃, 141 ℃, 142 ℃, 143 ℃, 144 ℃, 145 ℃, 146 ℃, 147 ℃, 148 ℃, 149 ℃ or 150 ℃, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.

Illustratively, the invention provides a using method of a circulating fluidized bed boiler, which specifically comprises the following steps:

(1) feeding fuel into a hearth from a feeding port by adopting a low-level storage bin pneumatic conveying mode, wherein the particle size of the fuel is 0-1 mm, the moisture content is less than or equal to 10 wt%, combustion-supporting air is preheated to 180-210 ℃ by a preheating device and then is fed into a dense-phase region of the hearth as primary air to participate in fuel combustion, and the combustion temperature of the fuel is 800-850 ℃;

optionally, when the load of the circulating fluidized bed boiler is higher than 60% or the oxygen content in the flue gas is lower, a secondary fan is started, combustion-supporting air is preheated to 180-210 ℃ by a preheating device and then divided into two parts, one part is used as primary air and sent into a hearth dense-phase region to participate in raw material combustion, the combustion temperature of fuel is 800-850 ℃, the other part is used as secondary air and sent into a hearth transition region through the secondary fan to support combustion, and the air intake ratio of the primary air and the secondary air is (2-4): (6-8);

(2) the temperature of flue gas generated by fuel combustion is 820-900 ℃, the flow velocity of the flue gas in a dilute phase zone of a hearth is 5-8 m/s, the flue gas is discharged from the top of the hearth and enters a separating device, the separating device separates and recovers fuel particles with the particle size of more than or equal to 70 mu m in the flue gas, and the recovered fuel particles circularly flow back to the bottom of the hearth through a return pipeline;

(3) the separated flue gas is discharged from the top of the separation device, enters a tail flue, sequentially passes through a primary high-temperature superheating device and a secondary high-temperature superheating device to contact and exchange heat with saturated steam, the temperature of the saturated steam is raised to form superheated steam, and the temperature of the flue gas is reduced to 400-500 ℃;

(4) and (2) dividing the cooled partial flue gas into two parts by a conveying fan, wherein one part is used as conveying air and sent into a return pipeline to assist fuel particles to flow back, the other part is used as secondary air and introduced into a hearth transition region to support combustion, and the air inlet ratio of the conveying air to the secondary air is (10-20): (80-90);

(5) and the rest of cooled flue gas enters a preheating device after waste heat is recovered by a primary coal saving device and a secondary coal saving device along a tail flue in sequence, the flue gas is contacted with combustion-supporting air in the preheating device for heat exchange, the temperature of the combustion-supporting air after heat exchange is 180-210 ℃, the temperature of the flue gas after heat exchange is 135-150 ℃, and the flue gas is discharged after heat exchange.

Compared with the prior art, the invention has the beneficial effects that:

(1) the circulating fluidized bed boiler provided by the invention is mainly used for carrying out structural improvement on the existing circulating fluidized bed boiler aiming at fine powder fuel particles with the particle size of 0-1 mm, high ash content generated after the fine powder fuel particles are combusted is fully fluidized by adding the conveying fan to form external circulating fuel which is separated and returned to the hearth through the separating device, the conveying fan is added to provide driving force for fluidization of the fine powder particles, the apparent gas velocity in the hearth of the boiler is designed at the terminal velocity of the fuel particles not lower than 700 mu m, the apparent gas velocity in the hearth can enable the fuel particles with the particle size of less than 700 mu m to pass through the hearth at one time, few fuel particles adhere to the wall to form internal circulating materials, most of the particle materials enter the separating device to form external circulation and return to the hearth, the heat storage capacity of the hearth is increased, and low-temperature combustion at 800-850 ℃ in the hearth can be, is beneficial to the realization of ultra-low emission of the boiler.

(2) The circulating fluidized bed boiler provided by the invention can directly feed the fine powder fuel particles with low water content into the hearth without adopting a coal slime feeding mode, avoids the difficulty in controlling the discharge of pollutants in the boiler due to the thermal explosion characteristic of the fine powder fuel particles after water is added in the combustion process, and effectively reduces the ultralow discharge cost of the boiler.

Drawings

Fig. 1 is a schematic structural view of a circulating fluidized bed boiler according to an embodiment of the present invention.

Wherein, 1-hearth; 2-a separation device; 3-tail flue; 4-first-stage high-temperature overheating device; 5-a second-stage high-temperature overheating device; 6-first-level coal saving device; 7-a secondary coal saving device; 8-a preheating device; 9-a material returning pipeline; 10-a conveying fan; 11-a secondary air fan; 12-secondary air inlet pipeline; 13-a feed port; 14-primary air inlet pipeline.

Detailed Description

It is to be understood that in the description of the present invention, the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate orientations or positional relationships based on those shown in the drawings, and are used only for convenience in describing the present invention and for simplicity in description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be taken as limiting the present invention. Furthermore, the terms "primary," "secondary," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "primary," "secondary," etc. may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless otherwise specified.

It should be noted that, in the description of the present invention, unless otherwise explicitly specified or limited, the terms "disposed," "connected" and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art through specific situations.

The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.

In one embodiment, the present invention provides a circulating fluidized bed boiler, as shown in fig. 1, comprising a furnace 1, a separation device 2 and a tail flue 3 connected in sequence, wherein the separation device 2 is connected with the furnace 1 in a circulating manner through a return pipe 9. A preheating device 8 is arranged in the tail flue 3, the preheating device 8 is connected with the hearth 1, primary air is preheated by the preheating device 8 and then sent into the hearth 1, an air outlet is formed in the barrel body of the tail flue 3, and the air outlet is connected into a material returning pipeline 9 through a conveying fan 10.

One of the optional devices is that a heat exchange device and a preheating device 8 are sequentially arranged in the tail flue 3 along the flow direction of flue gas, and an air outlet is formed in the barrel of the tail flue 3 between the heat exchange device and the preheating device 8. The second option is that the inside of the tail flue 3 is provided with a high-temperature overheating device, a coal-saving device and a preheating device 8 in sequence along the flow direction of the flue gas, and the air outlet is arranged on the barrel of the tail flue 3 between the high-temperature overheating device and the coal-saving device. Optionally, a first-stage high-temperature overheating device 4, a second-stage high-temperature overheating device 5, a first-stage coal saving device 6, a second-stage coal saving device 7 and a preheating device 8 are sequentially arranged in the tail flue 3 along the flow direction of flue gas, and an air outlet is formed in the barrel of the tail flue 3 between the second-stage high-temperature overheating device 5 and the first-stage coal saving device 6.

The inner cavity of the hearth 1 is divided into a dense-phase area, a transition area and a dilute-phase area from bottom to top; the dense-phase zone shell and the dilute-phase zone shell are of vertical columnar structures, and the transition zone cylinder is of an inverted frustum structure used for connecting the dense-phase zone and the dilute-phase zone. The dense phase area shell is provided with a feeding port 13, a feed back port and a primary air inlet, a discharge port of the separating device 2 is connected with the feed back port through a feed back pipeline 9, and the transition area shell is provided with a secondary air inlet. The sectional area of the dilute phase zone shell is smaller than that of the dense phase zone shell, and further the sectional area of the dilute phase zone shell is 1.2-1.5 times of that of the dense phase zone shell. The height of the shell in the dilute phase zone is 20-30 m.

The outlet end of the air outlet main pipe of the conveying fan 10 is divided into two paths, one path is connected with the secondary air inlet, and the other path is connected to the material returning pipeline 9. The outlet of the preheating device 8 is divided into two paths, one path is connected with a primary air inlet through a primary air inlet pipeline 14, the other path is connected with an air outlet main pipe of the conveying fan 10 through a secondary air inlet pipeline 12, and a secondary fan 11 is arranged on the secondary air inlet pipeline 12.