A method for transforming a solid slagging coal-fired boiler into a liquid slagging boiler

Abstract

The present invention relates to a method for transforming a solid slag-discharging coal-fired boiler into a liquid slag-discharging boiler. While retaining the original combustion mode of the boiler, by means of moving the overall position of the burner downward, reducing the nozzle spacing of the burner, and setting a constricted furnace arch above the burner area, the flame center is transferred to the lower furnace, a strong recirculation zone of high-temperature flue gas is formed in the lower furnace, the pulverized coal particles and the combustion-supporting air are fully mixed, the stable combustion and complete combustion of the pulverized coal as well as the wall-throwing effect of the liquid slag droplets are strengthened, the residence time of the high-temperature flue gas in the lower furnace is increased, the temperature of the lower furnace is effectively increased, and a continuous and stable liquid slag film is formed on the inner wall surface of the lower furnace. At the same time, by laying refractory castables in the lower furnace, at the constricted opening of the furnace arch and at a certain distance above the furnace arch in the present invention, the heat absorption of the heating surface in the lower furnace can be reduced, the combustion temperature in the lower furnace can be further increased, the wear of the water-cooled wall in the lower furnace can be alleviated, and it is more beneficial to the full combustion of the pulverized coal and the continuous formation of the liquid slag.

Description

Technical Field

[0001] The present invention relates to a method for transforming a solid slagging coal-fired boiler into a liquid slagging boiler, belonging to the field of power station boiler combustion technology. Background Art

[0002] In Xinjiang, China, there are huge reserves of high-alkali coal. However, due to the high content of alkali metals such as Na and K and alkaline earth metals in the coal, serious slagging and fouling problems of the boiler have affected the long-term, safe and reliable operation of the boiler, thus restricting the development and utilization of high-alkali coal as power coal. The liquid slagging boiler combustion technology is a combustion technology with high combustion intensity, high slag capture rate and less dust content in flue gas. It can overcome the shortcomings of the solid slagging boiler, such as slagging on the furnace water wall and serious fouling / ash accumulation / slagging on the heating surface when burning coal types prone to slagging. It is particularly suitable for coal types with low volatile content, low ash melting point and moderate ash content. When using the liquid slagging boiler combustion technology to burn Xinjiang high-alkali coal, on the one hand, it can greatly improve the slag capture rate in the furnace and reduce the dust concentration in the flue gas at the furnace outlet; on the other hand, through the high-temperature combustion of coal in the cyclone burner, the low-melting minerals such as Na, K, Ca, and Fe in the coal ash are melted and discharged from the bottom of the boiler, thus greatly reducing the content of low-melting minerals in the fly ash of the flue gas entering the boiler tail heating surface. It is an effective way to solve the serious slagging and fouling problems of the heating surface of the boiler furnace when burning high-alkali coal in existing power station boilers.

[0003] At present, the coal-fired boilers put into operation in China are still mainly solid slagging. Building a new liquid slagging boiler for efficient combustion of high-alkali coal will face problems such as high investment and long construction period. Summary of the Invention

[0004] The object of the present invention is to propose a simple, reliable, economical and practical method for transforming a coal-fired boiler into a liquid slagging boiler based on the existing boiler.

[0005] In order to achieve the above object, the technical solution of the present invention provides a method for transforming a solid slagging coal-fired boiler into a liquid slagging boiler, which is characterized by including the following steps:

[0006] Add two symmetrically arranged furnace arches in the middle of the furnace with tangentially fired burners at the four corners or tangential swirl burners. The two furnace arches are respectively arranged on the opposite side walls of the furnace, and the space inside the furnace forms a constriction at the position where the furnace arches are located; divide the furnace into an upper furnace and a lower furnace through the furnace arches. Among them, the upper part above the horizontal middle plane of the furnace arch is the upper furnace, and the lower part below the horizontal middle plane of the furnace arch is the lower furnace, and the elevation of the top of the lower furnace is higher than the upper edge elevation of the nozzles of the tangentially fired burners at the four corners or the tangential swirl burners; if tangentially fired burners at the four corners are arranged in the furnace, reduce the spacing of the primary air nozzles of the tangentially fired burners at the four corners, and if tangential swirl burners are arranged in the furnace, reduce the distance between the centers of each tangential swirl burner; transfer the flame center to the lower furnace by reducing the spacing of the primary air nozzles of the tangentially fired burners at the four corners or reducing the distance between the centers of each tangential swirl burner, form a strong recirculation zone of high-temperature flue gas in the lower furnace, and the pulverized coal particles and combustion-supporting air are fully mixed in the strong recirculation zone, strengthening the stable combustion, burnout of pulverized coal and the wall-throwing effect of liquid slag droplets, increasing the residence time of high-temperature flue gas in the lower furnace, raising the temperature of the lower furnace, and forming a continuous and stable liquid slag film on the inner wall surface of the lower furnace.

[0007] Change the ash hopper at the bottom of the furnace to an approximate planar structure, so that the angle between the inclined plane on the side of the ash hopper and the horizontal plane does not exceed 15°, and set a liquid slag discharge port on the bottom surface of the ash hopper.

[0008] Preferably, the opposite side walls are the front wall and the rear wall of the furnace, or the left wall and the right wall of the furnace.

[0009] Preferably, the tangentially fired coal-fired boiler is a π-type boiler or a tower-type boiler.

[0010] Preferably, the furnace arch extends into the furnace in the horizontal direction, and the extension length is 1 / 8 to 1 / 4 of the distance between the opposite side walls.

[0011] Preferably, the vertical distance reduction between the uppermost and lowermost primary air nozzle centers of the tangentially fired burners at the four corners is not less than 10% of the vertical distance between the uppermost and lowermost primary air nozzle centers of the tangentially fired burners arranged in the original solid slag-discharging coal-fired boiler.

[0012] Preferably, the reduction of the distance between the centers of each tangential swirl burner is not less than 10% of the distance between the centers of each tangential swirl burner arranged in the original solid slag-discharging coal-fired boiler.

[0013] Preferably, the ash hopper at the bottom of the furnace and the furnace arch are composed of cooling pipes through which a medium passes and connecting components that connect the cooling pipes into a whole.

[0014] Preferably, refractory materials are laid in the lower furnace area except for the nozzles of the tangentially fired burners at the four corners, the liquid slag discharge port and the through holes for safety measures;

[0015] Refractory materials are laid at the lower part of the upper furnace area, and the height of the refractory materials laid in the upper furnace does not exceed 1 / 3 of the height of the upper furnace.

[0016] Preferably, the upper furnace is provided with burner staging air nozzles.

[0017] A method for transforming a solid slag-discharging coal-fired boiler into a liquid slag-discharging boiler according to the present invention retains the original combustion mode of the boiler. By moving the overall position of the burners downward, reducing the spacing of the primary air nozzles of the tangentially-fired burners at the four corners or the distance between the centers of each tangential combustion burner, and setting a constricted furnace arch above the burner area, the flame center is transferred to the lower furnace, forming a strong recirculation zone of high-temperature flue gas in the lower furnace, enabling the pulverized coal particles and the combustion-supporting air to be fully mixed, strengthening the stable combustion and complete combustion of the pulverized coal and the wall-throwing effect of the liquid slag droplets, increasing the residence time of the high-temperature flue gas in the lower furnace, effectively increasing the temperature of the lower furnace, and forming a continuous and stable liquid slag film on the inner wall surface of the lower furnace. At the same time, the present invention lays refractory castables in the lower furnace, at the constricted opening of the furnace arch and at a certain distance above the furnace arch, which can reduce the heat absorption of the heating surface in the lower furnace, further increase the combustion temperature in the lower furnace, reduce the wear of the water-cooled wall in the lower furnace, and be more conducive to the full combustion of pulverized coal and the continuous formation of liquid slag. The present invention can not only achieve the efficient utilization of high-alkali coal, but also minimize the renovation workload and investment, and improve the operation economy of the power plant. Description of the Drawings

[0018] Figure 1 It is a schematic diagram of the original tangentially-fired coal-fired boiler.

[0019] Figure 2 It is a schematic diagram of the boiler after being transformed by the method described in the present invention.

[0020] In the figure: 1 - Tangentially-fired burner (original boiler), 2 - SOFA air nozzle, 3 - Furnace arch, 4 - Tangentially-fired burner (after transformation), 5 - Upper furnace, 6 - Lower furnace, 7 - Liquid slag discharge port. Detailed Embodiments

[0021] The following further elaborates the present invention in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0022] On the basis of making the most of the original boiler system equipment, the present invention improves the combustion temperature in the burner area at the lower part of the furnace by changing the position of the original tangentially-fired burners and the structure of the furnace bottom ash hopper, adding a constricted furnace arch above the burner area, etc., realizes liquid slag discharge, reduces the renovation scope, and reduces the renovation investment.

[0023] Specifically, in combination with Figure 1 and Figure 2 , taking the original boiler as a π-shaped boiler as an example, a method for transforming a solid slagging coal-fired boiler into a liquid slagging boiler provided by the present invention will be described in detail as follows:

[0024] Two furnace arches 3 are newly added at a certain height in the middle of the furnace of the original boiler. The two furnace arches 3 are respectively arranged on the opposite side walls of the furnace. For example, they are respectively arranged on the front wall and the rear wall of the furnace, or respectively arranged on the left wall and the right wall of the furnace. The rear ends of the two furnace arches 3 are fixed on the furnace wall of the furnace, and the front ends extend horizontally into the furnace, and the extension length is 1 / 4 of the distance between the opposite side walls. The two furnace arches 3 are arranged symmetrically front and back or left and right on the opposite side walls.

[0025] The original furnace is divided into an upper furnace 5 and a lower furnace 6 by the two furnace arches 3. Among them, above the horizontal middle plane of the furnace arch 3 is the upper furnace 5, and below the horizontal middle plane of the furnace arch 3 is the lower furnace 6. And the top elevation of the lower furnace 6 is higher than the topmost elevation of the nozzles of the tangentially fired burners 4 at the four corners. At the same time, the vertical distance between the centers of the uppermost and lowermost primary air nozzles of the tangentially fired burners 4 at the four corners is reduced by 20%.

[0026] The ash hopper at the bottom of the furnace is changed from the Figure 1 shown shape to the Figure 2 shown approximate plane structure, so that the included angle between the inclined plane on the side of the furnace bottom and the horizontal plane is 5°. A liquid slagging port 7 is arranged on the bottom surface of the furnace bottom. After the transformation, the furnace bottom and the newly added furnace arches 3 are composed of cooling pipes through which a medium passes and their connecting components.

[0027] Refractory materials are laid in the lower furnace 6 area except for the nozzles of the tangentially fired burners 4 at the four corners, the liquid slagging port 7 and the necessary through holes for safety measures. Refractory materials are laid in the lower part of the upper furnace 5 area, and the height of the refractory materials laid in the upper furnace 5 is 1 / 5 of the height of the upper furnace 5.

[0028] SOFA air nozzles 2 are arranged in the upper furnace 5.

[0029] A method for transforming a solid slagging coal-fired boiler into a liquid slagging boiler according to this embodiment retains the tangential combustion mode of the original boiler at the four corners. By lowering the overall position of the burners, reducing the primary air nozzle spacing of the tangential burners at the four corners or the distance between the centers of each tangential burner, and setting a constricted furnace arch above the burner area, the flame center is transferred to the lower furnace, forming a strong recirculation zone of high-temperature flue gas in the lower furnace. The pulverized coal particles and the combustion-supporting air are fully mixed, strengthening the stable combustion and complete combustion of the pulverized coal and the wall-throwing effect of the liquid slag droplets, increasing the residence time of the high-temperature flue gas in the lower furnace, effectively increasing the temperature of the lower furnace, and forming a continuous and stable liquid slag film on the inner wall surface of the lower furnace. At the same time, laying refractory castables in the lower furnace, the furnace arch constriction and a certain distance above the furnace arch can reduce the heat absorption of the heating surface in the lower furnace, further increase the combustion temperature in the lower furnace, reduce the wear of the water-cooled wall in the lower furnace, and be more conducive to the full combustion of pulverized coal and the continuous formation of liquid slag.

[0030] A method for transforming a solid slagging coal-fired boiler into a liquid slagging boiler according to this embodiment utilizes the original boiler system equipment to the greatest extent to achieve the purpose of liquid slagging transformation. It can be implemented on common π-type boilers or tower boilers, has a wide application range, good transformation effect, can greatly reduce the transformation workload and investment, and improve the economy of the transformation implementation.

Claims

1. A method for transforming a solid slagging coal-fired boiler into a liquid slagging boiler, characterized in that It includes the following steps: Add two symmetrically arranged furnace arches in the middle of the furnace equipped with tangentially fired burners with corner-rounding or swirl burners. The two furnace arches are respectively arranged on the opposite side walls of the furnace, and the space inside the furnace forms a constriction at the position where the furnace arches are located. The furnace is divided into an upper furnace and a lower furnace by the furnace arches. The overall position of the burners is moved downward, and the burner area is located below the constriction furnace arches. Among them, the area above the horizontal middle plane of the furnace arch is the upper furnace, and the area below the horizontal middle plane of the furnace arch is the lower furnace. And the elevation of the top of the lower furnace is higher than the elevation of the uppermost edge of the burner nozzle. If tangentially fired burners with corner-rounding are installed in the furnace, the spacing of the primary air nozzles of the tangentially fired burners with corner-rounding is reduced. If swirl burners are installed in the furnace, the distance between the centers of each swirl burner is reduced. Transfer the flame center to the lower furnace by reducing the spacing of the primary air nozzles of the tangentially fired burners with corner-rounding or reducing the distance between the centers of each swirl burner, form a strong recirculation zone of high-temperature flue gas in the lower furnace, and fully mix the pulverized coal particles and combustion-supporting air in the strong recirculation zone to strengthen the stable combustion, burnout of the pulverized coal and the wall-throwing effect of the liquid slag droplets, increase the residence time of the high-temperature flue gas in the lower furnace, raise the temperature of the lower furnace, and form a continuous and stable liquid slag film on the inner wall surface of the lower furnace; Change the ash hopper at the bottom of the furnace to an approximate planar structure, so that the angle between the inclined plane on the side of the ash hopper and the horizontal plane does not exceed 15°, and set a liquid slag discharge port on the bottom surface of the ash hopper; SOFA air nozzles are arranged in the upper furnace.

2. The method for transforming a solid slagging coal-fired boiler into a liquid slagging boiler according to claim 1, characterized in that The opposite side walls are the front wall and the rear wall of the furnace, or the left wall and the right wall of the furnace.

3. The method for transforming a solid slagging coal-fired boiler into a liquid slagging boiler according to claim 1, characterized in that The coal-fired boiler including tangentially fired burners with corner-rounding is a π-type boiler or a tower-type boiler.

4. The method for transforming a solid slagging coal-fired boiler into a liquid slagging boiler according to claim 1, characterized in that The furnace arch extends horizontally into the furnace, and the extension length is 1 / 8 - 1 / 4 of the distance between the opposite side walls.

5. The method for transforming a solid slagging coal-fired boiler into a liquid slagging boiler according to claim 1, characterized in that The vertical distance between the centers of the uppermost and lowermost primary air nozzles of the tangentially fired burners with corner-rounding is reduced by no less than 10% of the vertical distance between the centers of the uppermost and lowermost primary air nozzles of the tangentially fired burners with corner-rounding arranged in the original solid slag-discharging coal-fired boiler.

6. The method for transforming a solid slagging coal-fired boiler into a liquid slagging boiler according to claim 1, characterized in that The distance between the centers of each swirl burner is reduced by no less than 10% of the distance between the centers of each swirl burner arranged in the original solid slag-discharging coal-fired boiler.

7. The method for transforming a solid slagging coal-fired boiler into a liquid slagging boiler according to claim 1, characterized in that The ash hopper at the bottom of the furnace and the furnace arch are composed of cooling pipes through which a medium passes and connecting components that connect the cooling pipes into a whole.

8. The method for transforming a solid slagging coal-fired boiler into a liquid slagging boiler according to claim 1, characterized in that Refractory materials are laid in the lower furnace area except for the nozzles of the tangentially fired burners with corner-rounding, the liquid slag discharge port and the safety measure through holes; Refractory materials are laid in the lower part of the upper furnace area, and the height of the refractory materials laid in the upper furnace does not exceed 1 / 3 of the height of the upper furnace.

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