A low-low temperature economizer for preventing ash accumulation at the bottom

Abstract

A low-low temperature economizer for preventing ash accumulation at the bottom, comprising a box body. Heat exchange tubes are arranged above the interior of the box body, and the heat exchange tubes are arranged in the horizontal flue between the air preheater and the dust collector of a coal-fired power station boiler. A porous partition is arranged below the interior of the box body, and an ash removal bin is arranged below the porous partition. The ash removal bin is used for collecting the fly ash that falls through the porous partition. A scraper that moves in a reciprocating manner is arranged in the ash removal bin. A ash hopper is arranged below the front side of the ash removal bin. The deposited ash is scraped into the ash hopper located at the front side of the ash removal bin by the scraper. A flue gas baffle with adjustable opening is arranged at the tail of the ash removal bin. During normal operation, the deposited ash in the flue falls into the ash removal bin through the porous partition. When a leakage occurs, the opening of the flue gas baffle is increased to increase the flue gas flow rate, and the adhered fly ash or slurry is brought into the ash removal bin, which can not only prevent ash blocking of the lower heat exchange tubes of the low-low temperature economizer, but also prevent ash blocking of the bottom heat exchange module caused by the leakage of the low-low temperature economizer.

Description

Technical Field

[0001] The invention belongs to the field of coal-fired power plant boilers, and particularly relates to a low-low temperature economizer for preventing bottom ash accumulation. Background Art

[0002] The low-low temperature economizer is arranged on the horizontal flue between the air preheater and the electrostatic precipitator of the coal-fired power plant boiler, used to heat condensate, return water of the heat supply network, etc., recover part of the heat of the flue gas at the outlet of the boiler air preheater, and at the same time reduce the water consumption of the desulfurization system, so as to achieve the purpose of energy saving and water saving. In recent years, with the extensive implementation of energy-saving transformation of coal-fired generating units, most of the existing coal-fired power plant boilers in China have been retrofitted with low-low temperature economizers, and flue gas coolers have been arranged at the beginning of the design of new power plants. The inlet flue gas temperature of the low-low temperature economizer is 120 - 150 °C, and the outlet flue gas temperature is 90 °C. The inlet water temperature of the cooling medium (condensate, return water of the heat supply network) is above 70 °C, and the outlet water temperature is above 95 °C. Due to the limited space between the air preheater and the electrostatic precipitator of most existing coal-fired power boilers, in order to enhance heat transfer, the following two methods are adopted in the design of the low-low temperature economizer:

[0003] (1) Set as a countercurrent heat exchange mode. Considering the small heat transfer temperature difference between the flue gas and the cooling medium (condensate, return water of the heat supply network), changing the flow pattern arrangement can increase the average temperature difference; (2) H-shaped fins are designed outside the heat exchange tubes of the low-low temperature economizer, which expands the heat transfer area and at the same time destroys the convective boundary layer, increases the fluid disturbance, and enhances the heat transfer effect. However, due to the compact arrangement of the heat exchange tubes of the low-low temperature economizer and the design of H-shaped fin heat exchange tubes, there will be no maintenance space for the low-low temperature economizer. If a leakage occurs in the low-low temperature economizer, only the elbow of the leaking tube can be cut and blocked for isolation.

[0004] The retrofitting position of the low-low temperature economizer in some power plants is limited, resulting in a low local flue gas velocity. After the flue gas passes through the low-low temperature economizer, some fly ash deposits in the bottom area of the low-low temperature economizer, causing ash blockage. Affected by factors such as uneven inlet flue gas flow field of some low-low temperature economizers, high ash and sulfur content of coal, and large ammonia escape in the denitration system, some low-low temperature economizers after being put into operation have problems such as wear, corrosion, and ash blockage, resulting in leakage. The leaked water and fly ash in the flue gas form mud, which deposits in the lower area of the low-low temperature economizer, causing serious blockage of the bottom heating surface of the low-low temperature economizer. The serious blockage reduces the flue gas flow area, increases the local flue gas velocity, and further exacerbates wear and leakage, forming a vicious cycle. According to statistics, in the past two years, due to leakage and ash blockage problems of the low-low temperature economizer, especially serious ash blockage of the bottom heat exchange tubes of the low-low temperature economizer, most power plants have isolated the bottom heat exchange modules of the low-low temperature economizer, and some power plants have been forced to carry out the retrofit work of the low-low temperature economizer again. Summary of the Invention

[0005] The object of the present invention is to provide a low-low temperature economizer that prevents bottom ash accumulation, aiming at the problems of ash blockage in the bottom heat exchange tubes of the existing low-low temperature economizer and heat exchange module isolation caused by leakage, which can not only prevent ash blockage in the lower heat exchange tubes of the low-low temperature economizer, but also prevent ash blockage in the bottom heat exchange module caused by leakage of the low-low temperature economizer.

[0006] To achieve the above object, the present invention has the following technical solutions:

[0007] A low-low temperature economizer that prevents bottom ash accumulation, including a box body. Heat exchange tubes are arranged above the interior of the box body, and the heat exchange tubes are arranged in the horizontal flue between the air preheater and the dust collector of a coal-fired power station boiler. A porous partition is arranged below the interior of the box body, and an ash removal bin is arranged below the porous partition. The ash removal bin is used to collect the fly ash that falls through the porous partition. A scraper that makes a reciprocating motion is arranged in the ash removal bin. A ash hopper is arranged below the front side of the ash removal bin. The deposited ash is scraped into the ash hopper located on the front side of the ash removal bin by the scraper. A flue gas baffle with adjustable opening is arranged at the tail of the ash removal bin.

[0008] Preferably, the heat exchange tubes adopt horizontally arranged H-shaped finned tubes and are connected to the header on the side of the box body; reinforcing ribs are arranged around the heat exchange tubes above the interior of the box body to meet the boiler explosion-proof requirements through the reinforcing ribs.

[0009] Preferably, ash removal bin pressure measuring points are respectively arranged at the front and rear parts of the ash removal bin along the horizontal flue to online monitor the pressure in the ash removal bin during operation through the ash removal bin pressure measuring points; a low-low temperature economizer inlet pressure measuring point is arranged between the heat exchange tubes and the outlet flue of the air preheater, and a low-low temperature economizer outlet pressure measuring point is arranged between the heat exchange tubes and the inlet flue of the dust collector. The differential pressure on the flue gas side of the low-low temperature economizer during operation is online monitored through the difference between the two pressure measuring points.

[0010] Preferably, a number of circular holes are evenly distributed on the porous partition, the diameter of a single circular hole is 80 mm to 100 mm, and the distance between the centers of adjacent circular holes is 120 mm to 150 mm; the porous partition is made of Q235 steel plate with a thickness of 4 mm to 6 mm.

[0011] Preferably, the height of the ash removal bin is 300 mm to 500 mm, and its bottom and surroundings are made of Q235 steel plate with a thickness of 4 mm to 6 mm.

[0012] Preferably, the scraper is driven by a chain arranged in the ash removal bin. A scraper is fixed on the chain every 300 mm, and the gap between the scraper and the bottom plate of the ash removal bin is 3 mm to 5 mm.

[0013] Preferably, chain guide grooves for installing chains are provided on both sides of the ash removal bin. The chains are driven by driving sprockets to move in a cyclic reciprocating motion. The ash scraped into the ash hopper is transported to the ash yard by pneumatic ash conveying; the chains are supported by cooperating guide sprockets, and a chain tensioning device for maintaining a constant tension is provided at the guide sprockets.

[0014] Preferably, a number of bin pumps are provided below the ash hopper. The bin pumps are connected to the pneumatic ash conveying pipeline. A ash discharge pipe is provided on the pipeline connecting each ash hopper and the bin pump, and the ash discharge pipe is detachably connected to a collection bottle.

[0015] Preferably, the collection bottle and the ash discharge pipe are connected by threads, and a heat preservation layer is laid outside the ash discharge pipe.

[0016] Preferably, the opening degree of the flue gas baffle is driven and adjusted by an electric actuator, and the outlet of the flue gas baffle is connected to the inlet flue of the dust collector.

[0017] Compared with the prior art, the present invention has the following beneficial effects: By arranging a porous partition in the low-low temperature economizer box body below the heat exchange tubes, when the low-low temperature economizer operates normally without leakage, the deposited ash in the low-low temperature economizer flue falls into the ash removal bin through the porous partition, and a scraper that moves in a cyclic reciprocating motion is arranged in the ash removal bin. Under the action of the scraper, the deposited ash is sent into the ash hopper to prevent ash blockage of the heat exchange tubes at the lower part of the low-low temperature economizer. When the low-low temperature economizer leaks, the relatively wet fly ash or slurry adheres to the heat exchange tubes of the lower module of the low-low temperature economizer, or falls into the ash removal bin through the porous partition. By increasing the opening degree of the flue gas baffle at the rear side of the ash removal bin, the flue gas flow rate at the lower module of the low-low temperature economizer is increased online, and the adhered fly ash or slurry is brought into the ash removal bin to prevent ash blockage of the lower heat exchange module of the low-low temperature economizer caused by the leakage of the low-low temperature economizer. When the differential pressure on the flue gas side of the low-low temperature economizer returns to the differential pressure value before leakage, the tail flue gas baffle is closed, thereby preventing the continuous increase of the flue gas flow rate from causing wear of the lower module of the low-low temperature economizer.

[0018] Furthermore, a bin pump is provided below the ash hopper of the present invention. The bin pump is connected to the pneumatic ash conveying pipeline. A ash discharge pipe is provided on the pipeline connecting each ash hopper and the bin pump, and the ash discharge pipe is detachably connected to a collection bottle. During the operation of the low-low temperature economizer, the viscosity of the deposited ash in the collection bottle is monitored regularly, and the leakage problem of the low-low temperature economizer can be detected in time. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Side view of the structure of the low-low temperature economizer of the present invention;

[0020] Figure 2 Front view of the structure of the low-low temperature economizer of the present invention;

[0021] Figure 3Schematic structural diagram of the porous separator of the present invention;

[0022] In the attached drawings: 1 - heat exchange tube; 2 - header; 3 - porous separator; 4 - ash removal bin; 5 - scraper; 6 - ash hopper; 7 - round hole; 8 - chain; 9 - bottom plate of ash removal bin; 10 - driving sprocket; 11 - chain guide groove; 12 - bin pump; 13 - pneumatic ash conveying pipeline; 14 - ash discharge pipe; 15 - collection bottle; 16 - guiding sprocket; 17 - flue gas baffle; 18 - pressure measuring point for ash removal bin. Specific embodiments

[0023] The present invention will be further described in detail below with reference to the attached drawings.

[0024] See Figures 1-3 , the low-low temperature economizer of the present invention is arranged in the horizontal flue between the air preheater and the dust collector of a coal-fired power plant boiler, and includes a box body. Above the interior of the box body, heat exchange tubes 1 are arranged. The heat exchange tubes 1 are H-shaped finned tubes arranged horizontally, and the heat exchange tubes 1 are connected to the header 2 on the side of the box body. Pressure measuring points are arranged between the heat exchange tubes 1 and the outlet flue of the air preheater, and between the heat exchange tubes 1 and the inlet flue of the dust collector. The differential pressure on the flue gas side of the low-low temperature economizer during operation is monitored online through the difference between the two pressure measuring points to judge whether there is ash blockage in the low-low temperature economizer.

[0025] Reinforcing ribs are arranged above the interior of the box body around the heat exchange tubes 1 to meet the boiler explosion-proof requirements. A porous separator 3 is arranged below the interior of the box body. The porous separator 3 is made of steel plate. A number of round holes 7 are evenly distributed on the porous separator 3. The diameter of a single round hole 7 is 80 mm to 100 mm, and the distance between the centers of adjacent round holes 7 is 120 mm to 150 mm; the porous separator 3 is made of Q235 steel plate with a thickness of 4 mm to 6 mm. An ash removal bin 4 is arranged below the porous separator 3. The ash removal bin 4 is used to collect the fly ash falling through the porous separator 3. A scraper 5 that moves in a reciprocating motion is arranged in the ash removal bin 4. An ash hopper 6 is arranged below the front side of the ash removal bin 4. The deposited ash is scraped into the ash hopper 6 located on the front side of the ash removal bin 4 by the scraper 5. The scraper 5 is driven by a chain 8 arranged in the ash removal bin 4. A scraper 5 is fixed to the chain 8 every 300 mm, and the gap between the scraper 5 and the bottom plate 9 of the ash removal bin is 3 mm to 5 mm.

[0026] A number of bin pumps 12 are arranged below the ash hopper 6. The bin pumps 12 are connected to the pneumatic ash conveying pipeline 13. An ash discharge pipe 14 is arranged on the pipeline connecting each ash hopper 6 and the bin pump 12. The ash discharge pipe 14 is detachably connected to the collection bottle 15.

[0027] The collection bottle 15 and the ash discharge pipe 14 are connected by threads, and the ash discharge pipe 14 is covered with a heat preservation layer on the outside.

[0028] On both sides of the ash removal bin chamber 4, chain guide grooves 11 for installing chains 8 are provided. The chains 8 are driven by a driving sprocket 10 to move in a cyclic reciprocating motion. The ash scraped into the ash hopper 6 is transported to the ash yard through pneumatic ash conveying; the chains 8 are supported by cooperating with guide sprockets 16, and a chain tensioning device for maintaining a constant tension force is provided at the guide sprocket 16.

[0029] At the tail of the ash removal bin chamber 4, a flue gas baffle 17 with adjustable opening is arranged, and the outlet of the flue gas baffle 17 is connected to the inlet flue of the dust collector. Pressure measuring points 18 for the ash removal bin chamber are respectively arranged at the front and rear parts of the ash removal bin chamber 4 along the horizontal flue, and the pressure inside the ash removal bin chamber 4 during operation is monitored online through the pressure measuring points 18 for the ash removal bin chamber. The height of the ash removal bin chamber 4 is 300 mm to 500 mm, and its bottom and surroundings are made of Q235 steel plates with a thickness of 4 mm to 6 mm.

[0030] The working process of the present invention is as follows:

[0031] During normal operation, the flue gas carrying fly ash at the outlet of the air preheater flows through the heat exchange tubes 1, and transfers heat to the cooling medium (condensate, return water of the heat supply network) inside the tubes through heat conduction and convective heat transfer. The flue gas carrying fly ash flows towards the dust collector behind the low-low temperature economizer. According to the pressure measured by the arranged pressure measuring points 18 for the ash removal bin chamber, the flue gas baffle 17 at the tail of the ash removal bin chamber 4 is in a closed state. Although the flue gas can enter the ash removal bin chamber 4 through the porous partition 3, due to the closed flue gas baffle 17, the flow resistance inside the ash removal bin chamber 4 is relatively large, so the flue gas will still flow out of the ash removal bin chamber 4 through the porous partition 3. When the flow field in the low-low temperature economizer flue is uneven and the pressure in the flue fluctuates, the local flue gas velocity is too low, which will cause fly ash deposition, and the deposited fly ash will fall into the ash removal bin chamber 4 through the porous partition 3. The scraper 5 running in a cyclic reciprocating motion inside the ash removal bin chamber 4 scrapes the deposited ash into the ash hoppers 6 on the left and right sides of the ash removal bin chamber 4. The deposited ash in the ash hoppers 6 is transported to the ash yard through pneumatic ash conveying.

[0032] A small amount of deposited ash in the ash hopper 6 falls into the collection bottle 15 through the ash discharge pipe 14. The deposited ash in the collection bottle 15 is taken out every day, and the viscosity of the ash is visually inspected and felt by hand. If there is water in the ash or the ash is relatively sticky, it should be checked whether the low-low temperature economizer leaks.

[0033] When a heat exchange tube 1 of the low-low temperature economizer leaks due to wear or corrosion, the cooling medium (condensate, return water of the heat supply network) sprays water around through the leak point. When the water meets the fly ash in the flue gas, sticky ash or slurry is formed, which falls to the lower part of the low-low temperature economizer under the action of gravity, or falls into the ash removal bin 4 through the porous partition 3. The reciprocating scraper 5 scrapes the sticky ash or slurry into the ash hopper 6. By monitoring the pressure in the ash removal bin 4 and observing the viscosity of the ash in the collection bottle 15, it is judged whether there is a leak in the low-low temperature economizer. At this time, the leaking heat exchange module should be isolated in time. Since there is no heat exchange tube 1 arranged in the ash removal bin 4, the flue gas resistance along the way in the ash removal bin 4 is small. At this time, the flue gas baffle 17 is opened, and the appropriate opening of the flue gas baffle 17 is adjusted to maintain a certain flue gas flow rate in the ash removal bin 4. By changing the pressure difference between the flue of the low-low temperature economizer and the ash removal bin 4, the wetter fly ash or slurry is guided to fall into the ash removal bin 4 through the porous partition 3. Although the wetter fly ash or slurry falls into the ash removal bin 4 through the porous partition 3, there is still some fly ash or slurry adhering to the lower module of the low-low temperature economizer. When it is found during operation that the differential pressure on the flue gas side of the low-low temperature economizer is relatively high, it can be judged that there is ash clogging in the low-low temperature economizer. By increasing the opening of the flue gas baffle 17, the flue gas volume flowing through the porous partition 3 is increased, and the fly ash or slurry adhering to the lower module of the low-low temperature economizer is brought into the ash removal bin 4 by appropriately increasing the flue gas flow rate. When the differential pressure on the flue gas side of the low-low temperature economizer returns to the differential pressure value before the leak, the tail flue gas baffle 17 is closed to prevent the continuous increase of the flue gas flow rate from causing wear of the lower module of the low-low temperature economizer.

[0034] A scraper ash removal device is arranged in the ash removal bin 4. The scraper 5 is connected to the chain 8, and a scraper 5 is arranged every 300 mm. Guide chain grooves 11 are arranged on both sides of the ash removal bin 4, and the chain 8 is placed in the guide chain grooves 11. Driven by the driving sprocket 10, the chain 8 drives the scraper 5 to make a reciprocating motion, scraping the deposited ash in the ash removal bin 4 into the ash hopper 6. The ash in the ash hopper 6 is transported to the ash yard by pneumatic ash conveying. To ensure the constant tension of the chain during operation and ensure that the chain 8 is in contact with and properly tensioned with the driving sprocket 10 and the guiding sprocket 16, a chain tensioning device is arranged at the guiding sprocket 16.

[0035] A porous partition plate 3, an ash removal bin 4, a scraper ash removal system and a flue gas baffle 17 are designed at the lower part of the low-low temperature economizer of the present invention. When the low-low temperature economizer of the present invention operates normally without leakage, the deposited ash in the flue of the low-low temperature economizer falls into the ash removal bin 4 through the porous partition plate 3 and is sent into the ash hopper 6 under the action of the scraper 5, preventing ash blockage of the heat exchange tubes at the lower part of the low-low temperature economizer. During operation, regularly monitor the viscosity of the deposited ash in the collection bottle 15 to timely detect the leakage problem of the low-low temperature economizer. When the low-low temperature economizer leaks, the wetter fly ash or slurry falls into the ash removal bin 4 through the porous partition plate 3. By increasing the opening degree of the flue gas baffle 17 at the rear side of the ash removal bin 4, the flue gas flow rate of the lower module of the low-low temperature economizer is increased online, and the adhered fly ash or slurry is brought into the ash removal bin 4, preventing ash blockage of the bottom heat exchange module caused by the leakage of the low-low temperature economizer.

[0036] The above are only the preferred embodiments of the present invention, and are not used to limit the technical solutions of the present invention. Those skilled in the art should understand that without departing from the spirit and principle of the present invention, the technical solutions can be subject to several simple modifications and substitutions, and these modifications and substitutions also fall within the protection scope covered by the claims.

Claims

1. A low-low temperature economizer for preventing ash accumulation at the bottom, characterized in that: It includes a box body. Above the interior of the box body, heat exchange tubes (1) are arranged in the horizontal flue between the air preheater and the dust collector of a coal-fired power station boiler. Below the interior of the box body, a porous partition plate (3) is provided. Below the porous partition plate (3), an ash removal bin chamber (4) is provided. The ash removal bin chamber (4) is used to collect the fly ash falling through the porous partition plate (3). In the ash removal bin chamber (4), a scraper (5) that makes a reciprocating motion is provided. Below the front side of the ash removal bin chamber (4), an ash hopper (6) is provided. The deposited ash is scraped into the ash hopper (6) located on the front side of the ash removal bin chamber (4) by the scraper (5). At the tail of the ash removal bin chamber (4), a flue gas baffle (17) with adjustable opening degree is arranged. Below the ash hopper (6), a number of bin pumps (12) are provided. The pneumatic ash conveying pipeline (13) is connected through the bin pumps (12). On the pipeline connecting each ash hopper (6) and the bin pump (12), a ash discharge pipe (14) is provided. The ash discharge pipe (14) is detachably connected to a collection bottle (15). The opening degree of the flue gas baffle (17) is driven and adjusted by an electric actuator. The outlet of the flue gas baffle (17) is connected to the inlet flue of the dust collector. On the front and rear parts of the ash removal bin chamber (4) along the horizontal flue, ash removal bin chamber pressure measuring points (18) are respectively provided. The pressure inside the ash removal bin chamber (4) during operation is monitored online through the ash removal bin chamber pressure measuring points (18). Between the heat exchange tubes (1) and the outlet flue of the air preheater, a low-low temperature economizer inlet pressure measuring point is provided. Between the heat exchange tubes (1) and the inlet flue of the dust collector, a low-low temperature economizer outlet pressure measuring point is provided. The differential pressure on the flue gas side of the low-low temperature economizer during operation is monitored online through the difference between the two pressure measuring points. Whether there is leakage in the low-low temperature economizer is judged by monitoring the pressure inside the ash removal bin chamber (4) and observing the viscosity of the ash in the collection bottle (15).

2. The low-low temperature economizer for preventing ash accumulation at the bottom according to claim 1, characterized in that: The heat exchange tubes (1) adopt horizontal H-shaped finned tubes arranged horizontally, and the heat exchange tubes (1) are connected to the header (2) on the side of the box body. Above the interior of the box body, reinforcement ribs are arranged around the heat exchange tubes (1) to meet the boiler explosion-proof requirements through the reinforcement ribs.

3. The low-low temperature economizer for preventing ash accumulation at the bottom according to claim 1, characterized in that: The porous partition plate (3) is evenly distributed with a number of round holes (7). The diameter of a single round hole (7) is 80 mm to 100 mm, and the distance between the centers of adjacent round holes (7) is 120 mm to 150 mm. The porous partition plate (3) is made of Q235 steel plate with a thickness of 4 mm to 6 mm.

4. The low-low temperature economizer for preventing ash accumulation at the bottom according to claim 1, wherein: The height of the ash removal bin chamber (4) is 300 mm to 500 mm, and its bottom and surrounding are made of Q235 steel plate with a thickness of 4 mm to 6 mm.

5. The low-low temperature economizer for preventing bottom ash accumulation according to claim 1, characterized in that: The scraper (5) is driven by a chain (8) arranged in the ash removal bin chamber (4). A scraper (5) is fixed every 300 mm on the chain (8). The gap between the scraper (5) and the bottom plate (9) of the ash removal bin chamber is 3 mm to 5 mm.

6. The low-low temperature economizer for preventing ash accumulation at the bottom according to claim 5, wherein: Guide chain grooves (11) for installing chains (8) are provided on both sides of the ash removal bin chamber (4). The chains (8) are driven by a driving sprocket (10) to move in a cyclic reciprocating motion. The ash scraped into the ash hopper (6) is transported to the ash yard through pneumatic ash conveying; the chains (8) are supported by cooperating with guide sprockets (16), and a chain tensioning device for maintaining a constant tension force is provided at the guide sprockets (16).

7. The low-low temperature economizer for preventing bottom ash accumulation according to claim 1, characterized in that: The collection bottle (15) is connected to the ash discharge pipe (14) by a threaded connection, and a heat insulation layer is laid outside the ash discharge pipe (14).

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