A three-stage separation fluidized bed boiler burning low calorific value coal gangue

Abstract

A three-stage separation fluidized bed boiler for pure combustion of low calorific value coal gangue, an isobaric wind chamber is provided below the furnace, the isobaric wind chamber is connected to the isobaric wind chamber through an air distribution plate, a high-position buried pipe is provided above the air distribution plate, a feed port is provided on one side of the lower part of the furnace, a return port is provided on the other side, a primary water-cooled trough separator and a secondary water-cooled trough separator are provided at the flue gas outlet of the upper part of the furnace in sequence, the secondary water-cooled trough separator is connected to the return port of the furnace through a primary U-shaped return device, a flue gas channel is provided at the flue gas outlet of the secondary water-cooled trough separator, a selective multi-tube separator is provided in the flue gas channel, and the first fly ash outlet of the selective multi-tube separator is connected to the return port of the furnace through a secondary U-shaped return device. The device of the present invention can realize pure combustion of 700-1600kcal / kg low calorific value fuel, with high combustion efficiency and a large adjustment range, and the fluidization in the bed is uniform and stable, the excess air coefficient is small, the furnace membrane wall is free of wear, NO X Low emission (<200mg / m 3 ), which makes it easier for SNCR and SCR to achieve ultra-low emissions.

Description

Technical Field

[0001] The invention relates to a fluidized bed boiler, in particular to a three-stage separation fluidized bed boiler purely burning low calorific value coal gangue. Background Art

[0002] Gangue is a waste product from coal mining, with a low calorific value. With the innovation and improvement of mining and washing technology, the calorific value of gangue produced by coal mines and coal washing plants is getting lower and lower, and the low calorific value is mostly below 1400kcal / kg; using boilers that burn low calorific value gangue fuel for heating and power generation (the large amount of ash produced is also the raw material of building materials in the cement industry) can generate huge economic and environmental benefits.

[0003] The calorific value of the gangue used in the rapid circulating fluidized bed boilers of the current gangue power plants is above 1800kcal / kg (actually the gangue is mixed with medium coal in a certain proportion), which is costly. The rapid circulating fluidized bed boilers that burn only low calorific value gangue have too much return material due to the high rate circulation, which often causes the main bed to shut down.

[0004] The use of low-speed bed can achieve pure combustion of low calorific value coal gangue fuel. Some users use double-bed staged combustion technology, but the structure and operation are complicated; some users have tried to use low furnace and cyclone separator. Because the furnace is low and the combustion time is short, only by increasing the number of cycles can the basic stable operation be achieved. However, due to the large amount of return material, it often causes the main bed temperature to be low or flameout. Taking a 40-ton boiler burning 1030kcal / kg coal gangue as an example, the fuel ash content reaches 71.986%, and the total amount of ash produced by combustion reaches 17.8 tons / hour. It is not feasible to increase the number of cycles to improve efficiency.

[0005] A small change in the calorific value of coal gangue can cause a large fluctuation. For example, from 900kcal / kg to 1400kcal / kg, a change of 500kcal / kg has a relative range of 55% (for the same boiler, the range of change when burning thermal coal fluctuates from 5000kcal / kg to 5500kcal / kg is only 10%). The operation of the designed boiler is difficult to adjust due to the change in the calorific value of the fuel.

[0006] Low-speed beds have large bed area and heavy bed materials, and high air volume operation causes the original emission of NO X At 400 mg / m 3 The above means that the flue gas meets ultra-low emission standards and the environmental protection operation costs remain high. Summary of the invention

[0007] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a novel combustion engine with high combustion efficiency and low NO XA three-stage separation fluidized bed boiler that burns pure low calorific value (700-1600kcal / kg) coal gangue to reduce emissions and environmental costs.

[0008] The technical solution adopted by the present invention to solve its technical problems is: a pure combustion low calorific value (700-1600kcal / kg) coal gangue three-stage separation fluidized bed boiler, including a furnace, an isobaric wind chamber is arranged below the furnace, the isobaric wind chamber is connected with the isobaric wind chamber through an air distribution plate, a high-position buried pipe is arranged above the air distribution plate, a feed port is arranged on one side of the lower part of the furnace, and a return port is arranged on the other side, a slag discharge pipe is arranged at the lower part of the furnace near the return port, a primary water-cooled trough separator and a secondary water-cooled trough separator are arranged at the flue gas outlet of the upper part of the furnace in sequence, the secondary water-cooled trough separator is connected with the return port of the furnace through a primary U-shaped return device, a flue gas channel is arranged at the flue gas outlet of the secondary water-cooled trough separator, a selective multi-tube separator is arranged in the flue gas channel, a first fly ash outlet of the selective multi-tube separator is connected with the return port of the furnace through a secondary U-shaped return device, and a second fly ash outlet of the selective multi-tube separator is connected to an ash bin.

[0009] Furthermore, the air distribution plate is provided with directional hoods in ten rows near the front wall, so as to facilitate the bed material to spread to the rear without accumulation. Furthermore, the diameter of the hoods on the air distribution plate is 30-50 mm, the diameter of the ventilation holes on the hoods is 4.5-5 mm, and the distance between adjacent hoods is 70-75 mm.

[0010] Furthermore, a high-temperature superheater, a low-temperature superheater, a high-temperature economizer, a medium-temperature economizer and an air preheater are sequentially arranged in the flue gas channel.

[0011] Furthermore, an intermediate ash storage bin and pneumatic conveying equipment are provided on the pipeline connecting the second fly ash outlet of the selective multi-tube separator and the ash bin.

[0012] Furthermore, a flow regulating valve is provided on the pipeline connecting the first fly ash outlet of the selective multi-tube separator and the secondary U-shaped returner. For different fuel calorific values, the return amount is adjusted through the flow regulating valve and the secondary U-shaped returner to meet the requirements of boiler combustion efficiency.

[0013] Furthermore, the first-stage water-cooled trough separator is a trough formed by the heating surface tube and the hook-shaped fins welded on the heating surface tube, and the wear-resistant flat steel is welded in the trough. The fly ash separated by the first-stage water-cooled trough separator flows down along the rear wall and returns to the lower part of the furnace. It belongs to the furnace circulation.

[0014] Furthermore, the secondary water-cooled trough-shaped separator is a heat-resistant alloy steel plate pressed into a trough shape.

[0015] Furthermore, the selective multi-tube separator is downwardly exhausted, and the spiral assembly in the selective multi-tube separator is a building block structure, in which the spiral blades can be taken out and replaced after the furnace is shut down. The selective multi-tube separator is arranged at about 500°C after the high-temperature economizer. When the calorific value of the fuel is greater than 1200kcal / kg or the carbon content of the fly ash is found to be greater than 4-5% by sampling, part or all of the material is returned to the furnace through the flow regulating valve and the secondary U-shaped return feeder. The separation efficiency of the selective multi-tube separator is as high as 95%, and the separation efficiency can be adjusted by replacing different spiral blades. The selective multi-tube separator is also equivalent to a dust collector in the furnace, reducing the wear of the rear heating surface and reducing the load of the rear bag.

[0016] Preferably, the furnace cross-section is small at the bottom and large at the top, the flue gas velocity is 2.5-4.0 m / s, the flue gas flow is 6-8 s, the full membrane wall structure is used, and the fire-facing surface of the furnace below the flue gas outlet is completely covered with fire-protection belts. The water-cooled wall does not produce wear due to the isolation of the fire-protection belts.

[0017] Preferably, the high-position buried pipe is located at a height of 650-800 mm in the furnace, and the lower edge of the feed port is located at a height of 1900-2200 mm in the furnace.

[0018] The furnace circulation combustion system of the present invention has high combustion efficiency for low calorific value coal gangue fuel and no wear on the water-cooled wall; the slag discharge pipe close to the return port is selected to increase the residence time of the coarse bed material during the combustion process and assist in adjusting the circulation volume of the boiler fly ash. It has the following advantages: First, the furnace process is extended by 6-8s, which is 50% higher than that of ordinary boilers, meeting the requirement that the fine ash that passes through the furnace once and is not separated and returned by the separator is basically burned out; second, the furnace circulation is strengthened: the efficiency of the first-level water-cooled trough separator is 40-60%, and the separated fly ash flows down along the rear wall and returns to the lower part of the furnace, which belongs to the furnace circulation; third, the furnace outer circulation ratio is reduced, the efficiency of the second-level water-cooled trough separator is 60-85%, and the furnace outer circulation ratio is relatively low; fourth, the temperature of the upper part of the furnace is 850-920℃, which is uniform and does not decrease.

[0019] Through the three-stage separation and return, the concentration of fine carbon ash in the upper part of the furnace is high, ensuring that the upper temperature is 850-1000℃ and does not decrease evenly; during operation, by adding 0-30% tail flue gas into the wind chamber, the fluidization in the bed is maintained uniform and stable, and the excess air coefficient is controlled. The lack of oxygen in the lower part and the uniform and stable combustion suppress NO X The high concentration of hot carbon particles in the upper part of the furnace forms NO X The strong reducing conditions and the extended height, the reduction reaction reduces NO X emission.

[0020] The device of the present invention can realize pure combustion of 700-1600kcal / kg low calorific value fuel, with high combustion efficiency, large adjustment range, uniform and stable fluidization in the bed, small excess air coefficient, no wear on the furnace membrane wall, NO X Low emission (<200mg / m 3 ), which makes it easier for SNCR and SCR to achieve ultra-low emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural schematic diagram of an embodiment of the present invention;

[0022] Figure 2 for Figure 1 Middle AA view;

[0023] Figure 3 for Figure 1 Middle BB view.

[0024] In the figure: 1. furnace, 2. isobaric wind chamber, 3. small hood air distribution plate, 4. slag discharge pipe, 5. directional hood, 6. high-position buried pipe, 7. feed inlet, 8. first-stage water-cooled trough separator, 9. second-stage water-cooled trough separator, 10. first-stage U-shaped return feeder, 11. anti-wear flat steel, 12. high-temperature superheater, 13. low-temperature superheater, 14. high-temperature economizer, 15. selective multi-tube separator, 1501. first fly ash outlet, 1502. second fly ash outlet, 16. spiral blade, 17. second-stage U-shaped return feeder, 18. flow control valve, 19. medium-temperature economizer, 20. low-temperature economizer, 21. air preheater, 22. intermediate ash storage bin and pneumatic conveying equipment. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] like Figure 1As shown, this embodiment includes a furnace 1, an isobaric wind chamber 2 is arranged below the furnace 1, and is connected to the isobaric wind chamber 2 through a small wind hood air distribution plate 3, and a high-position buried pipe 6 and a feed port 7 are arranged above it. The small wind hood air distribution plate 3 is arranged with a directional wind hood 5 in 10 rows near the front wall, and a slag discharge pipe 4 is arranged near the return port. A primary water-cooled trough separator 8 and a secondary trough separator 9 are sequentially arranged at the flue gas outlet of the furnace 1. The secondary trough separator 9 is connected to the furnace return port through a primary U-shaped returner 10. The flue gas outlet of the secondary trough separator 9 is sequentially connected to a high-temperature superheater 12, a low-temperature superheater 13, a high-temperature economizer 14, a selective multi-tube separator 15, a medium-temperature economizer 19, a low-temperature economizer 20, and an air preheater 21, and then the flue gas enters the tail environmental protection treatment equipment to meet the emission standards. The first fly ash outlet 1501 of the selective multi-tube separator 15 is connected to the return port 7 of the furnace 1 through the secondary U-shaped return device 17, and the second fly ash outlet 1502 of the selective multi-tube separator 15 sends the fly ash to the ash storage (not shown in the figure).

[0027] The cross-sectional dimensions of furnace 1 are small at the bottom and large at the top, with a flue gas velocity of 3m / s and a flue gas flow rate of 6-8s. Furnace 1 is a full membrane wall structure, and a fire-prevention belt is laid all the way from the flue gas outlet to the fire surface. The water-cooled wall of furnace 1 does not produce wear due to the isolation of the fire-prevention belt.

[0028] The diameter of the hood of the small hood air distribution plate 3 is 50mm, and its area is about 20% larger than that of the fuel burning 3000kcal / kg. The diameter of the ventilation hole on the hood is 5mm, and the distance between adjacent hoods is 70mm. The ten rows of small hood air distribution plates 3 near the front wall are directional hoods 5. A slag discharge pipe 4 is set near the return port of the small hood air distribution plate 3. The fluidizing air of the air distribution plate 3 is fresh air mixed with 20% tail flue gas.

[0029] The high-position buried pipe 6 is located at a height of 700 mm in the furnace 1. The lower edge of the feed port 7 is located at a height of 2000 mm in the furnace 1.

[0030] like Figure 2 As shown, the first-stage water-cooled trough separator 8 is composed of a heating surface tube and hook-shaped fins welded on the heating surface tube to form a trough shape, and an anti-wear flat steel 11 is welded in the trough.

[0031] like Figure 3 As shown, the secondary water-cooled trough-type separator 9 is a heat-resistant alloy steel plate pressed into a trough shape.

[0032] The selective multi-tube separator 5 is exhaust gas from the bottom. The spiral assembly in the selective multi-tube separator is a building block structure. The spiral blades 16 in the spiral assembly can be taken out and replaced after the furnace is shut down. Or different structures can be replaced according to the requirements of coal types, such as adjusting the number of blades, single spiral, double spiral, triple spiral and climbing angle.

[0033] The working process of the present invention is as follows:

[0034] 850-1400kcal / kg of coal gangue fuel is added to the dense phase area at the bottom of the furnace from the feed port, and the fresh air is mixed with 20% of the tail flue gas for fluidized boiling combustion, and coarse particles larger than 2mm are burned in the dense phase area. Fine particles are blown into the dilute phase area at the top of the furnace, and after 6-8s of combustion, they are discharged from the furnace 1. A part (40-60%) is intercepted by the first-level water-cooled trough separator and falls along the rear wall to the dense phase area for cyclic combustion. The coarser particles that are not intercepted are basically separated (60-85%) when passing through the second-level trough separator and fall, and are sent back to the furnace 1 for cyclic combustion through the return mechanism.

[0035] For fuels below 1200kcal / kg, due to the low carbon content and the burning time of 6-8s, the smaller particles can basically burn out and are not intercepted by the first and second level water-cooled trough separators, and enter the tail heating surface. For fuels above 1200kcal / kg, due to the high carbon content, although the burning time is 6-8s, the smaller particles may not be burned out and are not intercepted, and enter the tail heating surface. Because the selective multi-tube separator (separation efficiency up to 95%) is arranged at about 500℃ after the high-temperature economizer 14, when the sampling finds that the carbon content of the fly ash is greater than 4-5%, part or all of the material is returned to the furnace through the flow control valve and the second level U-shaped returner. The selective multi-tube separator 15 (the separation efficiency can be adjusted by replacing different spiral blades) is also equivalent to the dust collector in the furnace, reducing the wear of the tail heating surface and reducing the tail bag load.

[0036] By adding 20% ​​tail flue gas into the isobaric wind chamber 2, the fluidization in the bed is maintained uniform and stable, and the excess air coefficient is controlled. The lack of oxygen in the lower part and the uniform and stable combustion suppress the NO X The production of; through the three-stage separation return material, the upper part of the furnace contains a high concentration of fine carbon ash, and the laying of the fire protection belt ensures that the upper temperature is 850-920℃ evenly and does not decrease. The high concentration of hot carbon particles in the upper part of the furnace forms a NO X The strong reducing conditions and the extended height, the reduction reaction reduces NO X emission.

[0037] Application Example 1:

[0038] A 40-ton power generation boiler installed in a coal gangue power plant uses the above technology. When the actual operation of the coal gangue calorific value is 1000-1200kcal / kg, the selective multi-tube separator does not need to return the material; when the actual operation of the coal gangue calorific value is 1200-1400kcal / kg, the selective multi-tube separator partially returns the material (<50%). The boiler burns stably, and all parameters meet the design requirements. The bed temperature can be stabilized at 850℃-920℃, the carbon content of fly ash is 1-3%, the carbon content of slag is 0.5-2%, the exhaust temperature is 130-140℃, and the original emission of NO without flue gasification is 0. X At 250 mg / m3 Below, the original emission of NO with flue gasification X At 150 mg / m 3 the following.

[0039] Those skilled in the art may make various modifications and variations to the present invention. If these modifications and variations are within the scope of the claims of the present invention and their equivalents, then these modifications and variations are also within the protection scope of the present invention.

[0040] The contents not described in detail in the specification are prior art known to those skilled in the art.

Claims

1. A three-stage separation fluidized bed boiler for pure combustion of low calorific value coal gangue, comprising a furnace, an isobaric wind chamber is arranged below the furnace, and the furnace is connected to the isobaric wind chamber through an air distribution plate, characterized in that: A high-position buried pipe is provided above the air distribution plate, a feed port is provided on one side of the lower part of the furnace, and a return port is provided on the other side, a slag discharge pipe is provided at the lower part of the furnace near the return port, a primary water-cooled trough separator and a secondary water-cooled trough separator are provided at the flue gas outlet of the upper part of the furnace in sequence, the secondary water-cooled trough separator is connected to the return port of the furnace through a primary U-shaped return device, a flue gas channel is provided at the flue gas outlet of the secondary water-cooled trough separator, a selective multi-tube separator is provided in the flue gas channel, a first fly ash outlet of the selective multi-tube separator is connected to the return port of the furnace through a secondary U-shaped return device, and a second fly ash outlet of the selective multi-tube separator is connected to the ash bin; The flue gas channel is provided with a high-temperature superheater, a low-temperature superheater, a high-temperature economizer, a medium-temperature economizer and an air preheater in sequence; The first-stage water-cooled slot separator is composed of a heating surface tube and hook-shaped fins welded on the heating surface tube to form a slot, and anti-wear flat steel is welded in the slot; The secondary water-cooled trough-shaped separator is made of heat-resistant alloy steel plates pressed into a trough shape.

2. The three-stage separation fluidized bed boiler for pure combustion of low calorific value coal gangue according to claim 1 is characterized in that: The wind distribution plate is arranged with directional wind hoods in ten rows close to the front wall.

3. The three-stage separation fluidized bed boiler for pure combustion of low calorific value coal gangue according to claim 2 is characterized in that: The diameter of the hood on the air distribution plate is 30-50 mm, the diameter of the ventilation hole on the hood is 4.5-5 mm, and the distance between adjacent hoods is 70-75 mm.

4. The three-stage separation fluidized bed boiler for pure combustion of low calorific value coal gangue according to any one of claims 1 to 3, characterized in that: An intermediate ash storage bin and pneumatic conveying equipment are arranged on the pipeline connecting the second fly ash outlet of the selective multi-tube separator and the ash bin.

5. The three-stage separation fluidized bed boiler for pure combustion of low calorific value coal gangue according to claim 4 is characterized in that: A flow regulating valve is provided on the pipeline connecting the first fly ash outlet of the selective multi-tube separator and the secondary U-shaped return device.

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