A flue gas post combustion device comprising one or more flue gas vortex combustion chambers

Abstract

The invention is a flue gas post-combustion device comprising one or more flue gas vortex combustion chambers, which discloses a process engineering method for achieving clean combustion of straw and low CO emission in a circulating fluidized bed boiler (1). For this purpose, the invention proposes a flue gas post-combustion device (8) comprising one or more flue gas vortex combustion chambers, in which device, due to the small inner radius of the flue gas vortex combustion chamber, a large centrifugal force acts. The unburnt fuel carbon particles in the flue gas are broken up on the inner wall of the flue gas vortex combustion chamber (12) having a small inner radius and burn rapidly and completely. Therefore, the invention is particularly suitable for clean combustion of loose straw in a circulating fluidized bed boiler or a moving grate boiler.

Description

TECHNICAL FIELD

[0001] The present invention belongs to the field of biomass fuel combustion device, in particular, it is a flue gas afterburning device containing one or more flue gas vortex combustion chamber. BACKGROUND

[0002] In the process of burning loose straw in a moving grate boiler, especially in the fluidized bed boiler of a biomass power plant, a large amount of particulate matter will be entrained. These particulate matters include mineral impurities, incompletely combusted or insufficiently gasified carbon-containing particulate matters, which are mainly the residues of long carbon chain cellulose. These carbon-containing particulate matters are often relatively soft, porous and low in density.

[0003] This will result in a decrease in the thermal conductivity of these carbon-containing particulate matters, and a longer time is needed for gasification. However, these carbon-containing particulate matters stay in the high-temperature zone of the boiler for a short time, so they cannot achieve the time required for complete gasification and combustion. Since the circulating fluidized bed boiler was originally developed for coal combustion, the entrained coal particles have relatively high strength and density, so they are effectively separated from the gas flow by the centrifugal particle separator and returned to the fluidized bed.

[0004] However, when burning straw in a fluidized bed boiler, only heavy, mineral-containing and other component-containing large particles can be effectively separated in the centrifugal particle separator. Those lighter, porous carbon-containing particles are more likely to go up with the flue gas to the heat exchange surface and continue to release CO. However, as the flue gas temperature decreases, these late-released CO cannot be completely and sufficiently combusted, resulting in poor CO emission value.

[0005] To reduce the impact on flue gas emission value, these incompletely combusted CO and the like can be further combusted in one or more vortex afterburning devices connected in series, such as according to CN201811060841.6. However, due to the large size and large number of carbon-containing particles entrained in the fluidized bed and other combustion equipment, it is difficult to ensure complete combustion of all CO and the like using the above known vortex afterburning device and the like, and it is even more difficult for larger carbon-containing particles.

[0006] Unburned carbon including CO in hot flue gas during waste incineration makes it possible for dioxin to re-polymerize in hot flue gas, and since straw fuel also contains chloride ions, the process of utilizing the heat of straw will also face the problem of dioxin re-polymerization during the incineration of waste and the like.

[0007] Because the centrifugal particle separator can only separate the mineral-containing or relatively large mass particles within a limited range, the unburnt, non-mineral-containing and smaller carbon-containing particles that cannot be separated will descend and damage the downstream heat exchange surface, etc. Even if multiple centrifugal particle separators are used, it is still impossible to completely separate the particles in the flue gas, especially the unburnt carbon-containing particles, and the operation cost will not be worth the increase in power consumption of the induced draft fan, etc. SUMMARY

[0008] The purpose of the present application is to use a flue gas afterburning device containing one or more flue gas vortex combustion chambers to break the unburnt carbon-containing particles in the flue gas by mechanical force rather than relying on the increase of mechanical power devices, so that the combustion intensity of the unburnt carbon-containing particles after swirling is greatly enhanced and full combustion is achieved in a shorter time, and the emission of dust particles containing minerals and the like in the tail flue gas is effectively controlled without significantly increasing the power consumption of the fan.

[0009] The method of the present application is to make the flue gas containing many unburnt carbon-containing particles flow through one or more flue gas vortex combustion chambers arranged close to each other and in parallel, and the afterburning device containing one or more flue gas vortex combustion chambers also contains a larger volume and longer combustion time flue gas combustion chamber. The large volume of the larger volume and longer combustion time flue gas combustion chamber can make the flue gas burn for a longer combustion time, and the low flue gas flow rate in the larger volume and longer combustion time flue gas combustion chamber can make the larger mass particles in the flue gas sink downward and effectively separate from the flue gas through the slag discharge slot, ash discharge device and slag cooling air device at the bottom of the longer combustion time flue gas combustion chamber, etc.

[0010] One or more flue gas vortex combustion chambers arranged close to each other and in parallel and a larger volume and longer combustion time flue gas combustion chamber are surrounded by the same heat insulation layer. One or more flue gas vortex combustion chambers can be arranged in a circular, square, rectangular, oval or even other irregular shape according to actual needs and available site restrictions.

[0011] The flue gas containing many unburnt carbon-containing particles is designed to flow into one or more flue gas vortex afterburning chambers through flue gas inlet nozzles composed of movable refractory materials and the like. These flue gas inlet nozzles composed of movable refractory materials and the like can change the opening size of the flue gas inlet nozzle by changing the spacing of the components composed of movable refractory materials and the like according to the pressure requirement.

[0012] The centrifugal force acting on the particles in the vortex combustion chamber in the present application can be calculated by the following formula:

[0013]

[0014] The radius r of the vortex flow in the formula is halved, and the centrifugal force F is doubled. When the same flow of flue gas is distributed among more than one flue gas vortex combustion chamber, the radius of the vortex flow of the flue gas distributed among more than one flue gas vortex combustion chamber is reduced to a fraction of the radius of the vortex flow of the flue gas when there is only one flue gas vortex combustion chamber. This results in a multiplication of the centrifugal force of the flue gas in the more than one flue gas vortex combustion chamber, and the carbon-containing particles in the flue gas are thrown against the fire face of the hard flue gas vortex combustion chamber and collide and rub against it. The carbon-containing particles after the collision and rubbing are broken into smaller particles and obtain a larger surface area, thereby accelerating the combustion process.

[0015] At the same time, the flue gas velocity V increases in a fourth power relationship with the change in the centrifugal force and has an effect on the breaking of the particles in the flue gas, and the central area of the vortex flow has a negative pressure, the pressure gradually increases from the inside to the outside and increases the intensity of the oxidation process of the flue gas. At a temperature above 720°C, the large negative pressure in the central area of the vortex flow can also cause water molecules to split to produce extremely active hydrogen and oxygen ions and combine with free carbon radicals to form combustible components.

[0016] Due to the small inner diameter of the flue gas vortex combustion chamber in the device of the present application, the flue gas vortex rotates at high speed in the flue gas vortex combustion chamber, thereby enabling complete combustion of the flue gas and the carbon-containing particles in the flue gas, and it is even possible to make the CO emission value close to zero. The mechanism of this is currently not fully determined, but it is certain that the electric current and charge generated by dynamics and chemical reactions act on the chemical process itself and can strengthen these processes.

[0017] The fire face of each flue gas vortex combustion chamber is composed of a plurality of superimposed fireproof concrete rings, and these superimposed fireproof concrete rings make the cross-sectional area of the flue gas flow in the vortex combustion chamber not a constant value, thus causing the velocity and pressure of the flue gas flow to change constantly and produce pressure oscillation. Each flue gas vortex combustion chamber is supported by a support wall, and there is a flue gas discharge slot between each support wall. The bottom of the flue gas discharge slot is steeply inclined downward. This can reduce the deposition of particles in the flue gas discharge slot. In the downward flow direction of the flue gas, the cross-sectional area of the flue gas discharge slot expands constantly, thereby reducing the flue gas velocity and producing a certain negative pressure effect.

[0018] Each flue gas discharge slot leads to a longer flue gas combustion chamber, and the size of the longer flue gas combustion chamber should be large enough to allow the flue gas to have a residence time of more than one second. A blowing device is arranged at the upper part of the flue gas discharge slot and can periodically blow compressed air downward to clean possible dust accumulation.

[0019] An air blowing device is located at the top of the flue gas chute and can periodically blow compressed air downwards to remove any accumulated ash. At the bottom of the longer-burning-time flue gas combustion chamber is a narrow and high ash discharge chute, with an ash discharge device and a ash cooling air supply device at its bottom to cool large particles containing minerals and recover some heat. The flue gas flowing downwards along the bottom of the flue gas chute is vertically turbulent upwards at the bottom of the longer-burning-time flue gas combustion chamber. The combined effects of centrifugal force and gravity during this process cause large particles containing minerals to deposit downwards and be effectively separated from the flue gas through the ash discharge chute, ash discharge device, and ash cooling air supply device at the bottom of the longer-burning-time flue gas combustion chamber. The deposition of these large particles does not require additional force. Attached Figure Description

[0020] Figure 1 The diagram illustrates this embodiment, which includes a circulating fluidized bed boiler (1), a centrifugal particulate separator (3), and a flue gas afterburner (8) containing one or more flue gas vortex combustors. For ease of explanation, the flue gas vortex combustors (12) are shown here arranged side by side, while the actual arrangement of the flue gas vortex combustors (12) can be seen in the diagram. Figure 2 .

[0021] Figure 2 A top view is shown of a circulating fluidized bed burner (1), a centrifugal particulate separator (3), and a flue gas afterburner (8) designed to be approximately rectangular and containing one or more flue gas vortex combustion chambers.

[0022] Figure 3 Showing from Figure 3 A side cross-sectional view of the flue gas combustion chamber (20) with a longer combustion time in a flue gas afterburner (8) containing one or more flue gas vortex combustion chambers, looking toward the flue gas vortex combustion chamber (12).

[0023] Figure 4 The design of the flue gas inlet nozzle (26) at the top of the vortex combustion chamber (12) is shown.

[0024] Figure: 1 - circulating fluidized bed boiler, 2 - fuel feeder, 3 - centrifugal particle separator, 4 - flue gas discharge channel, 5 - return pipe, 6 - flue gas channel to the flue gas post-combustion device comprising one or more flue gas vortex combustion chambers, 7 - second heat exchange surface, 8 - flue gas post-combustion device comprising one or more flue gas vortex combustion chambers, 9 - secondary air, 10 - preheated tertiary air, 11 - flue gas channel to the second heat exchange surface, 12 - flue gas vortex combustion chamber, 13 - outer wall, 14 - thermal insulation, 15 - masonry lining, 16 - support wall, 17 - flue gas duct, 18 - flue gas duct bottom, 19 - ring of refractory concrete, 20 - flue gas combustion chamber with longer combustion time, 21 - slagging channel, 22 - slagging device, 23 - slag cooling air supply device, 24 - air blowing device, 25 - movable refractory element, 26 - flue gas inlet nozzle, 27 - flue gas vortex combustion chamber upper cover, 28 - tertiary air annular channel, 29 - flue gas cross-section reduction device, 30 - first heat exchange surface. DETAILED DESCRIPTION

[0025] The flue gas post-combustion device comprising one or more vortex combustion chambers of the present application will be described in more detail by means of one example. The purpose of the present example is to achieve the CO emission standard requirement by modifying the combustion process of a boiler of a thermal power plant with a thermal power of 45 MW, which uses crop straw as fuel.

[0026] Figure 1 It is shown that crop straw fuel according to the present application, which comprises one or more flue gas vortex combustion chambers, is fed into the circulating fluidized bed boiler (1) through the fuel feeder (2). The secondary air (9) is added above the furnace of the circulating fluidized bed boiler (1). The majority of the particles that fly upwards with the flue gas from the fluidized bed are separated in the centrifugal particle separator (3) and returned to the furnace through the return pipe (5). The flue gas containing particles with a smaller mass and carbon content or the like, which passes through the centrifugal particle separator (3), enters the flue gas discharge channel (4) and the flue gas channel (6) to the flue gas post-combustion device comprising one or more flue gas vortex combustion chambers, and enters the downstream flue gas post-combustion device comprising one or more flue gas vortex combustion chambers of the present application (8) and completes the final combustion process.

[0027] To ensure that the flue gas velocity of the flue gas passage (6) leading to the flue gas post-combustion device containing more than one flue gas vortex combustion chamber always remains at a relatively constant value, a flue gas cross-section reducing device (29) according to CN201811655101.7 is arranged in the flue gas passage (6) leading to the flue gas post-combustion device containing more than one flue gas vortex combustion chamber. The preheated tertiary air (10) enters the flue gas discharge passage (4) from the tertiary air annular passage (28) through many small openings. Due to the constant flue gas flow rate of not less than 100 m / s from the centrifugal particle separator (3), a certain negative pressure is formed on the preheated tertiary air (10), thereby achieving the sufficient mixing of the flue gas containing small mass carbon-containing particles from the flue gas discharge passage (4) and the preheated tertiary air (10). This will cause the flue gas containing small mass carbon-containing particles from the flue gas discharge passage (4) to accelerate combustion and increase temperature before entering the flue vortex combustion chamber (12) of the flue gas post-combustion device (8) containing more than one flue gas vortex combustion chamber. The number of flue gas vortex combustion chambers (12) in this embodiment is 24.

[0028] Each flue gas vortex combustion chamber (12) is supported by a support wall (16), and each support wall (16) has a flue gas discharge groove (17) between them. The bottom of the flue gas discharge groove (18) connected to the flue gas vortex combustion chamber (12) is steeply inclined downward to the longer combustion time flue gas combustion chamber (20). A blowing device (24) is installed at the top of each flue gas discharge groove (17) to blow off the ash particles that may deposit on the steep flue gas discharge groove bottom (18) if necessary. There are two points to note. First, because the residual unburned carbon in the vortex combustion chamber (12) is greatly reduced, the possibility of coking on the steep flue gas discharge groove bottom (18) is minimal. Second, the blowing device (24) will not cause significant temperature changes when it is running, because the total weight of the refractory concrete ring (19) is about 111 tons, which can completely stabilize the flue gas temperature.

[0029] After the flue gas reaches the steep flue gas discharge groove bottom (18), it turns upward in the vertical direction and enters the longer combustion time flue gas combustion chamber (20) for longer combustion, and then flows to the second heat transfer surface (7) through the flue gas passage (11) leading to the second heat transfer surface. The longer combustion time flue gas combustion chamber (20) can achieve complete combustion of the flue gas without the flame entering the second heat transfer surface (7), thereby avoiding the second heat transfer surface (7) receiving strong radiant heat and effectively reducing the high temperature corrosion of the surface of the second heat transfer surface (7).

[0030] A slagging chute (21) is arranged at the bottom of the longer combustion duration flue gas combustion chamber (20), and the slagging chute (21) is provided with a slagging device (22) and a slag cooling air feeding device (23) at the bottom. During the process of the flue gas turning back vertically upward through the steep flue gas chute bottom (18) into the longer combustion duration flue gas combustion chamber (20), the slightly larger particles containing minerals and other substances will be deposited downward to the slagging chute (21) under the action of centrifugal force and gravity, and effectively separated from the flue gas through the slagging device (22) and the slag cooling air feeding device (23).

[0031] Figure 2 The layout of the circulating fluidized bed boiler (1), the centrifugal particle separator (3) and the flue gas post-combustion device (8) designed as an approximate rectangle and containing 24 flue gas vortex combustion chambers is shown. The flue gas post-combustion device (8) containing 24 flue gas vortex combustion chambers needs a floor area of about 4.5 x 9 meters, and the heat insulation layer (14) of the flue gas post-combustion device (8) containing 24 flue gas vortex combustion chambers is at least 40 centimeters thick, so that no other technical measures are needed to cool the outer wall (13) of the flue gas post-combustion device (8) containing 24 flue gas vortex combustion chambers. The arrangement shape, diameter size and number of the flue gas vortex combustion chambers (12) can be adjusted according to actual needs.

[0032] Figure 3 The side sectional view of the longer combustion duration flue gas combustion chamber (20) of the flue gas post-combustion device (8) containing 24 flue gas vortex combustion chambers (12) from Figure 3 is shown. The flue gas vortex combustion chamber (12) is about 12 meters high, and the top of the flue gas vortex combustion chamber (12) is composed of a flue gas inlet nozzle (26) formed by two movable refractory material components (25) and a flue gas vortex combustion chamber upper cover (27). The fire-facing surface of each flue gas vortex combustion chamber (12) is composed of 35 refractory concrete rings (19) arranged in upper and lower rows. The refractory concrete rings (19) are arranged to cause pressure oscillation of the flowing flue gas by changing the internal cross section, thereby helping to break the particles in the flue gas. In this embodiment, the vertical flow velocity of the flue gas is about 30 meters / second, and the pressure oscillation frequency is about 90 hertz.

[0033] The refractory concrete rings (19) are made of heavy and hard refractory ceramics with an alumina content of more than 50%, so that the catalytic effect of the refractory concrete rings (19) is enhanced by wall friction and centrifugal force. The total internal surface area of the 24 flue gas vortex combustion chambers (12) arranged in this embodiment is about 480 m 2 , which is almost 5 times the internal surface area of a single vortex combustion chamber containing the same volume of flue gas and having the same residence time.

[0034] The smoke vortex combustion chamber (12) here is placed on a support wall (16) made of refractory bricks or the like, with a smoke exhaust channel (17) arranged between the support walls (16). The smoke from the smoke vortex combustion chamber (12) falls steeply along the bottom of the smoke exhaust channel (17) to the bottom of the longer combustion duration smoke combustion chamber (20) and then turns upward in the vertical direction to enter the longer combustion duration smoke combustion chamber (20) which is about 20 m high, without the need for additional thrust, and can accommodate the smoke to stay for more than one second.

[0035] When the smoke changes its flow direction slowly at the bottom of the longer combustion duration smoke combustion chamber (20), the mineral-containing particles that may remain in the smoke will precipitate under the dual action of gravity and centrifugal force, thereby further strengthening the protection of the second heat exchange surface (7).

[0036] Figure 4 The top structure of one vortex combustion chamber (12) of the smoke afterburning device (8) containing 24 smoke vortex combustion chambers is shown, in which the inner diameters of the refractory concrete rings (19) are 480 mm and 560 mm, respectively. When the temperature of the smoke in the circulating fluidized bed boiler (1) is up to 850°C, the temperature of the smoke in the smoke vortex combustion chamber (12) can reach 740°C. The total flow rate of the smoke through the smoke afterburning device (8) containing 24 smoke vortex combustion chambers is about 150 cubic meters per second, and the flow rate of the smoke through each smoke vortex combustion chamber (12) is about 6.25 cubic meters per second.

[0037] The smoke enters the smoke vortex combustion chamber (12) tangentially through two smoke inlet nozzles (26) composed of two movable refractory material members (25). The two movable refractory material members (25) can change and optimize the smoke flow rate by changing the offset distance. The smoke speed in this embodiment is 90 meters per second, and the width of the smoke inlet nozzle (26) at this time is 140 mm and the height is 500 mm.

[0038] The smoke vortex speed in the vortex combustion chamber (12) exceeds 3000 revolutions per minute, which is more than 3000 times the centrifugal force particle mass of the particles in various smokes according to A carbon particle with a mass of 0.1 grams is thrown to the fire surface lined with refractory concrete rings (19) of the smoke vortex combustion chamber (12) by a force of up to 3.52 Newtons (= 0.35 kilograms) and is broken there. The finer particles after breaking burn quickly and completely, and the smoke vortex combustion chamber (12) in this process becomes a grinding device for unburned carbon particles in the smoke.

[0039] The flue gas afterburning device (8) of the present application containing one or more flue gas vortex combustion chambers can burn the flue gas completely, and there is almost no unburned carbon in the flue gas, and the CO emission is far below 200 mg / m3 and tends to be zero. Even if the temperature of the hot gas reaching the second heat exchange surface (7) is reduced to 600℃ and may contain a small amount of chlorine compounds, the recombination of dioxin is effectively prevented because there is no unburned carbon in the flue gas.

[0040] Therefore, the flue gas afterburning device (8) of the present application containing one or more flue gas vortex combustion chambers can be more widely used in the future in the field of waste incineration power generation. In the field of waste power generation, the natural gas in waste power generation can be replaced by straw when the flue gas afterburning device (8) containing one or more flue gas vortex combustion chambers is used. Also, the heat stored in a large amount of refractory concrete can make up for the lack of heat source when the heat output is low. The coal-fired thermal system can also use the flue gas afterburning device (8) containing one or more flue gas vortex combustion chambers to modify the coal-fired thermal system, thereby avoiding the deterioration of the emission indicators of the coal-fired thermal system when the heat output is low.

Claims

1. A flue gas post-combustion device comprising one or more flue gas vortex combustion chambers, comprising one or more flue gas vortex combustion chambers (12) with an inner surface of refractory ceramic material with tangential flue gas inlet nozzles (26); characterized in that, More than one smoke vortex combustion chamber (12) is arranged in parallel next to each other, the inner diameter of the smoke vortex combustion chamber is small, the carbon-containing particles in the smoke will be thrown to the fire-facing surface of the hard smoke vortex combustion chamber and collide and rub with it, the carbon-containing particles after collision and rubbing will be broken into smaller particles to obtain larger surface area and thus accelerate the combustion process.

2. A flue gas post-combustion device comprising one or more flue gas vortex combustion chambers according to claim 1, characterized in that, The smoke post-combustion device (8) containing more than one smoke vortex combustion chamber is surrounded by a heat insulation layer (14).

3. A flue gas post-combustion device comprising one or more flue gas vortex combustion chambers according to claim 1, characterized in that, It also includes a smoke combustion chamber with longer combustion duration (20).

4. A flue gas post-combustion device comprising one or more flue gas vortex combustion chambers according to claim 1, characterized in that, The fire-facing surface of more than one smoke vortex combustion chamber (12) is composed of superimposed fireproof concrete rings (19), and the cross-sectional area of the smoke inside is not fixed.

5. A flue gas post-combustion device comprising one or more flue gas vortex combustion chambers according to claim 1, characterized in that, The smoke vortex combustion chamber (12) is arranged on the support wall (16), and there is a smoke exhaust channel (17) between the support walls.

6. A flue gas post-combustion device comprising one or more flue gas vortex combustion chambers according to claim 1, characterized in that, The smoke enters the smoke vortex combustion chamber (12) tangentially through the smoke inlet nozzle (26) composed of movable fireproof material components (25).

7. A flue gas post-combustion device comprising one or more flue gas vortex combustion chambers according to claim 5, characterized in that, The bottom of the smoke exhaust channel (18) is steeply inclined downward.

8. A flue gas post-combustion device comprising one or more flue gas vortex combustion chambers according to claim 5, characterized in that, The smoke discharged by the smoke exhaust channel (17) flows to the smoke combustion chamber with longer combustion duration (20).

9. A flue gas post-combustion device comprising one or more flue gas vortex combustion chambers according to claim 5, characterized in that, A blowing device (24) is arranged at the upper part of each smoke exhaust channel (17).

10. A flue gas post-combustion device comprising one or more flue gas vortex combustion chambers according to claim 3, characterized in that, A slag discharge channel (21) is arranged at the bottom of the smoke combustion chamber with longer combustion duration (20), and there is a slag discharge device (22) and a slag cooling air supply device (23) at the bottom of the slag discharge channel (21).

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