CN107940448B - Pulverized coal particle circulating fluidized bed combustion system and combustion method thereof - Google Patents

Abstract

The present invention discloses a pulverized coal particle circulating fluidized bed combustion system and a combustion method thereof, belonging to the field of clean coal technology. The system includes an ignition device, a slag discharge pipe, an air distribution device, a furnace, a coal feeding pipe, a return pipe, a secondary air duct, a cyclone separator, a return valve, a tail flue, a superheater, an economizer, an air preheater and a column crusher device in front of the furnace; the fine powder of the pulverized coal furnace is conducive to uniform flow and rapid combustion, and the lower bed temperature of the fluidized bed and the internal and external circulation of a large amount of materials are conducive to reducing pollutant emissions. The present invention has been deeply optimized on the basis of organically combining the two coal-fired technologies of the pulverized coal furnace and the circulating fluidized bed, and a combustion technology with ultra-high performance and ultra-low emissions is obtained.

Description

A pulverized coal particle circulating fluidized bed combustion system and combustion method thereof

Technical Field

The invention belongs to the technical field of clean coal, and in particular relates to a pulverized coal particle circulating fluidized bed combustion system and a combustion method thereof.

Background technique

Circulating fluidized bed coal-fired technology is a mature clean coal combustion technology, which has now entered the large-scale commercialization stage. However, with the increasingly stringent environmental protection policies, the pollutant control measures in the circulating fluidized bed boiler alone can no longer meet the existing environmental protection standards. At the same time, in order to take into account the environmental protection characteristics, the circulating fluidized bed boiler is forced to sacrifice some energy efficiency characteristics, such as reducing the furnace temperature and reducing the excess air coefficient. The most direct manifestation is that the carbon content of fly ash and bottom ash in the environmentally friendly circulating fluidized bed boiler is generally high. The pulverized coal furnace has an operating history of nearly two hundred years and is recognized as the coal-fired technology with the highest combustion efficiency. However, in order to achieve better environmental protection characteristics, the furnace must be equipped with expensive SCR denitrification systems, wet desulfurization and wet electrostatic precipitator systems, etc., which is a heavy burden for pulverized coal furnace users. Based on the above factors, a pulverized coal particle circulating fluidized bed (PC-CFB) combustion method and system are urgently needed to meet the market needs of efficient combustion and ultra-low emissions.

Summary of the invention

The object of the present invention is to provide a pulverized coal particle circulating fluidized bed combustion system and a combustion method thereof in view of the deficiencies in the prior art.

To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a pulverized coal particle circulating fluidized bed combustion system, which includes: an ignition device, a slag discharge pipe, an air distribution device, a furnace, a coal feeding pipe, a return pipe, a secondary air duct, a cyclone separator, a return valve, a tail flue, a superheater, an economizer, an air preheater and a column crusher device in front of the furnace; the ignition device is located at the rear end of the air distribution device and is suspended on the boiler beam by a spring hanger; the upper end of the slag discharge pipe is connected to the furnace through the air distribution device, and the lower end is connected to the slag cooler; there are 4 slag discharge pipes, the two outer ones are continuous slag discharge pipes, and the two inner ones are selective slag discharge pipes; the furnace is located above the air distribution device, and the outlet of the furnace is connected to the cyclone separator through a non-metallic expansion joint. connected; the coal feeding pipe is arranged on the lower side of the front wall of the furnace; the return pipe is arranged on the lower side of the rear wall of the furnace; the secondary air ducts are staggered at the front and rear walls of the furnace, and the number of secondary air outlets on the front wall is greater than that on the rear wall; the cyclone separator is located in the middle of the furnace and the tail flue, and the inlet of the cyclone separator is connected to the furnace through a non-metallic expansion joint, and the exhaust port of the cyclone separator is connected to the tail flue through a non-metallic expansion joint; the upper port of the return valve is connected to the lower riser of the cyclone separator, and the lower port of the return valve is connected to the return pipe through a metal expansion joint; the tail flue is located at the rear of the combustion system, and the superheater and economizer are supported in the tail flue in sequence; the air preheater is connected to the bottom of the economizer through an expansion joint.

In a further preferred embodiment, the furnace is divided into a bottom vertical section area, a transition section area and an upper vertical section area (4-3). The bottom vertical section area is located below the secondary air inlet, with a height of 3.8m. The width dimension of the bottom vertical section area is the same as that of the upper part of the furnace, and the depth dimension is 0.35 times the depth of the upper part of the furnace. The transition section area is an upper section of the secondary air inlet, which shrinks to 0.35 times the original depth from top to bottom. The upper vertical section area is the main space for heat transfer, with a height of 25m. In order to reduce the particle size of the circulating material, the apparent gas velocities of the bottom vertical section area and the upper vertical section area of the furnace are both selected to be 4m/s.

In a further preferred embodiment, the cyclone separator includes an inlet acceleration section, a cylinder, a cone, a riser and an exhaust pipe. The throat flow velocity at the tangent point between the acceleration section and the cylinder is designed to be 35 m/s, the cylinder height is 1.5 times the cylinder diameter, the cone height is 2 times the cylinder diameter, and the exhaust pipe adopts an "inverted cone" structure, and the insertion depth is 0.5 times the inlet height.

In a further preferred embodiment, the cross-sectional area of the air distribution device is 35% of the cross-sectional area of the furnace, and a small bell-shaped hood is used, the flow rate of the hood small hole is 40Nm/s, and the hood resistance is 2300Pa, so that the PC-CFB furnace can operate stably even under low load conditions.

In a further preferred embodiment, the secondary air outlets are arranged alternately on the front and rear walls of the single-layer, and the number of secondary air outlets on the front wall is greater than that on the rear wall. The flow rate of the secondary air outlets is 80 m/s, and the vertical distance from the air distribution device is 3.5 to 4.5 m. Under the premise of ensuring combustion, the environmental protection characteristics of the PC-CFB furnace are improved.

The present invention discloses a method for burning pulverized coal particles by utilizing the pulverized coal particle circulating fluidized bed combustion system, specifically, the raw coal particles are crushed into pulverized coal particles of 0 to 2 mm by a column crusher device in front of the furnace, the primary air accounting for 35% of the total air volume is preheated by an air preheater and enters the vertical section area at the bottom of the furnace through an air distribution device, the pulverized coal particles entering the bottom of the furnace through a coal feeding pipe and the circulating ash entering the bottom of the furnace through a return pipe are mostly transported to the transition section area of the furnace under the bubbling action of the primary air, the secondary air accounting for 65% of the total air volume is preheated by an air preheater and is replenished in time through a secondary air duct located at the lower end of the transition section area, the secondary air is easy to reach the center of the furnace, avoiding the oxygen-poor zone, and under the joint action of the primary and secondary air, the material is then sent to the upper vertical section area of the furnace, and then, the particle size is greater than 300 um particles adhere to the wall and reflux to form internal circulation materials. After the fine materials with a particle size of less than 300um enter the high-efficiency cyclone separator, 99.9% of the materials are captured to form external circulation materials. The remaining ultra-fine materials are carried by the flue gas into the tail flue in the form of fly ash. In order to avoid the deposition of fine ash in the tail flue, the tail flue gas flow rate is 3m/s higher than that of conventional boilers. The superficial gas velocities in the vertical section area at the bottom of the furnace and the upper vertical section area are both 4m/s. The pulverized coal particles complete the combustion process in this series of internal and external circulations. During operation, the furnace differential pressure is maintained at 8Kpa, the tail oxygen content is 2-3%, the bed temperature is maintained at 850℃, and the furnace differential pressure above the secondary air port is maintained at an average of 100Pa/m. While efficiently burning, it can better inhibit the generation of NOx and efficiently remove _SO2 . The column crusher device is a crusher system.

Compared with the existing coal combustion technology, the present invention has the following beneficial effects:

① High combustion efficiency, good desulfurization effect in the furnace, and effective suppression of NOx generation. When the calcium-sulfur ratio is less than 2, the desulfurization efficiency in the furnace is greater than 99%, and the original generation of NOx is less than 50mg/Nm3;

② The ash concentration in the furnace is high, the heat transfer coefficient in the furnace is high, the flue gas velocity at the tail is high, and the convection heat transfer coefficient at the tail is high, which reduces the heat exchange area and saves steel consumption.

③ The material in the furnace has fine particle size and low fluidizing wind speed, which completely eliminates the wear problem of CFB boiler.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural diagram of a pulverized coal particle circulating fluidized bed combustion system according to the present invention.

Detailed ways

As shown in Figure 1, a pulverized coal particle circulating fluidized bed combustion system described in this embodiment includes: an ignition device 1, a slag discharge pipe 2, an air distribution device 3, a furnace 4, a coal feeding pipe 5, a return pipe 6, a secondary air duct 7, a cyclone separator 8, a return valve 9, a tail flue 10, a superheater 11, an economizer 12, an air preheater 13 and a column crusher device in front of the furnace; the ignition device 1 is located at the rear end of the air distribution device 3 and is suspended on the boiler beam by a spring hanger; the upper end of the slag discharge pipe 2 passes through the air distribution device 3 and is connected to the furnace 4, and the lower end is connected to the slag cooler; there are 4 slag discharge pipes 2, the outer two are continuous slag discharge pipes, and the inner two are selective slag discharge pipes; the furnace 4 is located above the air distribution device 3, and the outlet of the furnace 4 is connected to the cyclone separator 8 through a non-metallic expansion joint; The tube 5 is arranged on the lower side of the front wall of the furnace 4; the return pipe 6 is arranged on the lower side of the rear wall of the furnace 4; the secondary air duct 7 is staggered at the front and rear walls of the furnace 4, and the number of secondary air ports on the front wall is greater than that on the rear wall; the cyclone separator 8 is located between the furnace 4 and the tail flue 10, and the inlet of the cyclone separator 8 is connected to the furnace 4 through a non-metallic expansion joint, and the exhaust port of the cyclone separator 8 is connected to the tail flue 10 through a non-metallic expansion joint; the upper port of the return valve 9 is connected to the lower riser of the cyclone separator 8, and the lower port of the return valve 9 is connected to the return pipe 6 through a metal expansion joint; the tail flue 10 is located at the rear of the combustion system, and the superheater 11 and the economizer 12 are supported in the tail flue 10 in sequence; the air preheater 13 is connected to the bottom of the economizer 12 through an expansion joint.

The furnace 4 described in this embodiment is divided into a bottom vertical section area 4-1, a transition section area 4-2 and an upper vertical section area 4-3. The bottom vertical section area 4-1 is located below the secondary air inlet 7, with a height of 3.8m. The width dimension of the bottom vertical section area is the same as that of the upper part of the furnace, and the depth dimension is 0.35 times the depth of the upper part of the furnace. The transition section area 4-2 is an upper section of the secondary air inlet, which shrinks to 0.35 times the original depth from top to bottom. The upper vertical section area 4-3 is the main space for heat transfer, with a height of 25m. In order to reduce the particle size of the circulating material, the apparent gas velocities of the bottom vertical section area 4-1 and the upper vertical section area 4-3 of the furnace are both selected to be 4m/s.

The cyclone separator 8 in this embodiment includes an inlet acceleration section 8-1, a cylinder 8-2, a cone 8-3, a riser 8-4 and an exhaust pipe 8-5. The throat flow velocity at the tangent point between the acceleration section 8-1 and the cylinder 8-2 is designed to be 35 m/s. The height of the cylinder 8-2 is 1.5 times the diameter of the cylinder, the height of the cone 8-3 is 2 times the diameter of the cylinder, and the exhaust pipe 8-5 adopts an "inverted cone" structure, and the insertion depth is 0.5 times the inlet height.

The cross-sectional area of the air distribution device 3 in this embodiment is 35% of the furnace cross-sectional area. At the same time, a small bell-shaped hood is used, the hood hole flow rate is 40Nm/s, and the hood resistance is 2300Pa, so that the PC-CFB furnace can also operate stably under low load conditions.

The secondary air outlets 7 described in this embodiment are arranged alternately on the front and rear walls of a single layer, and the number of secondary air outlets on the front wall is greater than that on the rear wall. The flow rate of the secondary air outlets is 80m/s, and the vertical distance from the air distribution device 3 is 3.5 to 4.5m. Under the premise of ensuring combustion, the environmental protection characteristics of the PC-CFB furnace are improved.

The present embodiment provides a method for burning pulverized coal particles by utilizing the pulverized coal particle circulating fluidized bed combustion system, specifically, the raw coal particles are crushed into pulverized coal particles of 0-2 mm by a column crusher device in front of the furnace, the primary air accounting for 35% of the total air volume is preheated by an air preheater 13 and enters the vertical section area 4-1 at the bottom of the furnace through an air distribution device 3, the pulverized coal particles entering the bottom of the furnace through a coal feeding pipe 5 and the circulating ash entering the bottom of the furnace through a return pipe 6 are mostly transported to the transition section area 4-2 of the furnace under the bubbling action of the primary air, the secondary air accounting for 65% of the total air volume is preheated by an air preheater 13 and replenished in time through a secondary air duct 7 located at the lower end of the transition section area, the secondary air can easily reach the center of the furnace to avoid the oxygen-poor zone, and under the joint action of the primary and secondary air, the material is then sent to the upper vertical section area 4-3 of the furnace, and then, the particles Particles with a diameter greater than 300um adhere to the wall and reflux to form internal circulation materials. After fine materials with a particle size less than 300um enter the high-efficiency cyclone separator 8, 99.9% of the materials are captured to form external circulation materials, and the remaining ultra-fine materials are carried by the flue gas into the tail flue 10 in the form of fly ash. In order to avoid the deposition of fine ash in the tail flue 10, the tail flue gas flow rate is 3m/s higher than that of conventional boilers, and the superficial gas velocities in the vertical section area at the bottom and the upper vertical section area of the furnace are both 4m/s. The pulverized coal particles complete the combustion process in this series of internal and external circulations; during operation, the furnace differential pressure is maintained at 8Kpa, the tail oxygen content is 2-3%, the bed temperature is maintained at 850℃, and the furnace differential pressure above the secondary air port is maintained at an average of 100Pa/m, while efficient combustion can be achieved, while the generation of NOx can be better suppressed and _SO2 can be efficiently removed; the column crusher device is a crusher system.

The return valve 9 is a self-balancing return device. The air chamber at the bottom of the return valve realizes "zoned air distribution and separate adjustment". The air volume on the discharge side is small, and the air volume on the return side is large.

The tail flue 10 is prone to adhesion and deposition of ultrafine ash, and the tail flue gas velocity needs to be increased. The tail flue gas velocity is selected to be 3 m/s higher than that of the CFB boiler.

The present invention provides a clean coal combustion technology that achieves both energy saving and emission reduction, so that the fine powder in the pulverized coal furnace is conducive to uniform flow and rapid combustion, and the lower bed temperature of the fluidized bed and the internal and external circulation of a large amount of materials are conducive to reducing pollutant emissions. The present invention conducts in-depth optimization based on the organic combination of the two coal-fired technologies of pulverized coal furnace and circulating fluidized bed, and obtains a combustion technology with ultra-high performance and ultra-low emissions.

Claims (4)

1. The method is applied to a pulverized coal particle circulating fluidized bed combustion system, and the combustion system comprises an ignition device (1), a slag discharging pipe (2), an air distribution device (3), a hearth (4), a coal feeding pipe (5), a return pipe (6), a secondary air pipe (7), a cyclone separator (8), a return valve (9), a tail flue (10), a superheater (11), an economizer (12), an air preheater (13) and a post crusher device in front of the furnace; the ignition device (1) is positioned at the rear end of the air distribution device (3) and is suspended on a boiler beam through a spring hanger; the upper end of the slag discharging pipe (2) passes through the air distribution device (3) to be communicated with the hearth (4), and the lower end of the slag discharging pipe is connected with a slag cooling machine; the number of the slag discharging pipes (2) is 4, two slag discharging pipes are continuous, and two slag discharging pipes are selective; the hearth (4) is positioned above the air distribution device (3), and an outlet of the hearth (4) is connected with the cyclone separator (8) through a nonmetal expansion joint; the coal feeding pipe (5) is arranged at the lower side of the front wall of the hearth (4); the return pipe (6) is arranged at the lower side of the rear wall of the hearth (4); the secondary air pipes (7) are arranged on the front wall and the rear wall of the hearth (4) in a staggered mode, and the number of secondary air ports of the front wall is larger than that of the rear wall; the cyclone separator (8) is positioned between the hearth (4) and the tail flue (10), the inlet of the cyclone separator (8) is connected with the hearth (4) through a nonmetallic expansion joint, and the exhaust port of the cyclone separator (8) is connected with the tail flue (10) through a nonmetallic expansion joint; the upper opening of the return valve (9) is connected with a lower vertical pipe of the cyclone separator (8), and the lower opening of the return valve (9) is connected with the return pipe (6) through a metal expansion joint; the tail flue (10) is positioned at the rear of the combustion system, and the superheater (11) and the economizer (12) are sequentially supported in the tail flue (10); the air preheater (13) is connected to the lower part of the economizer (12) through an expansion joint; the furnace chamber (4) is divided into a bottom vertical section area (4-1), a transition section area (4-2) and an upper vertical section area (4-3), the bottom vertical section area (4-1) is located below the secondary air port (7), the height is 3.8m, the width direction size of the bottom vertical section area is the same as that of the upper part of the furnace chamber, the depth direction size is 0.35 times of the depth of the upper part of the furnace chamber, the transition section area (4-2) is one section of the upper part of the secondary air port, the shrinkage of the transition section area in the depth direction from top to bottom is 0.35 times of the original, the upper vertical section area (4-3) is a main heat transfer space, and the height is 25m, and the furnace chamber is characterized in that: the combustion method comprises the following steps:

Crushing raw coal particles into 0-2 mm pulverized coal particles through a column crusher device in front of a furnace, preheating primary air accounting for 35% of total air quantity through an air preheater (13), enabling the primary air to enter a vertical section area (4-1) at the bottom of a furnace through an air distribution device (3), enabling the pulverized coal particles entering the bottom of the furnace through a coal feeding pipe (5) and circulating ash entering the bottom of the furnace through a return pipe (6) to be conveyed to a furnace transition section area (4-2) under the bubbling action of the primary air, enabling secondary air accounting for 65% of total air quantity to be preheated through the air preheater (13) and then timely fed into the center of the furnace through a secondary air pipe (7) positioned at the lower end of the transition section area, avoiding the secondary air from reaching an oxygen-deficient area, enabling the materials to be conveyed to the vertical section area (4-3) at the upper part of the furnace under the common action of the secondary air, enabling particles with particle diameters larger than 300um to adhere to the wall and flow back to form internal circulating materials, enabling 99.9% of the materials to be formed into external circulating materials after the fine materials with particle diameters smaller than 300um enter a high-efficient cyclone (8), enabling the rest of the fine materials to be carried into a tail part (10 m/10 in the form of fine coal circulating smoke and the tail part of the boiler to be in the vertical section area, and the tail part of the vertical section area (10 m) in the vertical section of the furnace, and the tail part of the tail part is formed in the high-speed smoke-stream cycle gas-stream cycle mode, and the tail end part is formed in the tail end part of the high-gas cycle gas is in the high-quality flue gas cycle gas and the high-quality flue gas flow cycle gas and the high quality; when the device runs, the differential pressure of the hearth is maintained to be 8Kpa, the oxygen amount at the tail part is 2-3%, the bed temperature is kept at 850 ℃, the differential pressure of the hearth above the secondary air port is kept at 100Pa/m on average, and the device can effectively inhibit the generation of NOx and effectively remove SO ₂ at the same time of high-efficiency combustion; the column crusher device is a crusher system.

2. A method of burning pulverized coal particles in a pulverized coal circulating fluidized bed combustion system as set forth in claim 1, wherein: the cyclone separator (8) comprises an inlet accelerating section (8-1), a cylinder body (8-2), a cone (8-3), a vertical pipe (8-4) and an exhaust pipe (8-5), wherein the throat flow speed at the tangential position of the accelerating section (8-1) and the cylinder body (8-2) is designed to be 35m/s, the height of the cylinder body (8-2) is 1.5 times of the diameter of the cylinder body, the height of the cone (8-3) is 2 times of the diameter of the cylinder body, the exhaust pipe (8-5) adopts an inverted cone structure, and the insertion depth is 0.5 times of the inlet height.

3. A method of burning pulverized coal particles in a pulverized coal circulating fluidized bed combustion system as set forth in claim 1, wherein: the sectional area of the air distribution device (3) is 35% of the sectional area of a hearth, and meanwhile, a small bell jar hood is adopted, the flow speed of a hood small hole is 40Nm/s, and the hood resistance is 2300Pa, so that the PC-CFB furnace can stably operate under a low load state.

4. A method of burning pulverized coal particles in a pulverized coal circulating fluidized bed combustion system as set forth in claim 1, wherein: the secondary air ports (7) are arranged in a staggered manner on the single-layer front wall and the single-layer rear wall, the number of the secondary air ports on the front wall is larger than that of the secondary air ports on the rear wall, the flow speed of the secondary air ports is 80m/s, and the vertical distance between the secondary air ports and the air distribution device (3) is 3.5-4.5 m.