Air heating system capable of reducing corrosion and ash deposition of boiler air preheater

Abstract

The utility model discloses an air heating system capable of reducing corrosion and ash deposition of a boiler air preheater. The air heating system comprises an air feeder, the air preheater located in a boiler flue gas flow path and an air heater located outside the boiler flue gas flow path. The air heater comprises a tube pass part and a shell pass part, the tube pass part comprises an inlet header, an outlet header and a heat exchange tube, and the shell pass part comprises a shell pass barrel, a shell pass inlet tube and a shell pass outlet tube; the inlet header is arranged on the left side wall of the shell pass cylinder, the outlet header is arranged on the right side wall of the shell pass cylinder, the left ends of the heat exchange tubes are communicated with the inlet header, and the right ends of the heat exchange tubes are communicated with the outlet header. The air heater is arranged between the air feeder and the air preheater, normal-temperature air entering the air heater is heated through saturated steam of the boiler barrel, the temperature of the normal-temperature air is increased to be higher than the smoke acid dew point temperature, then the normal-temperature air is fed into the air preheater, the cold end air inlet temperature of the air preheater is increased, acid in smoke cannot be condensed, and the smoke is heated to the normal temperature. And the phenomena of blockage and low-temperature corrosion of the air pre-heater can be avoided.

Description

Technical Field

[0001] The utility model belongs to the technical field of boiler air preheaters, and particularly relates to an air heating system for reducing corrosion and ash accumulation of boiler air preheaters. Background Art

[0002] The air preheater is arranged at the end of the boiler convection flue, and uses the heat of the boiler tail flue gas to heat the air required for fuel combustion, thereby increasing the air temperature entering the furnace, improving the ignition and combustion conditions of the fuel, reducing the incomplete combustion heat loss, and further improving the combustion efficiency.

[0003] The boiler fuel contains a certain amount of sulfur, which will generate sulfur dioxide during combustion, and a part of it will be further oxidized to generate sulfur trioxide. Sulfur trioxide combines with the water vapor in the flue gas to form sulfuric acid vapor. When the wall temperature of the heating surface is lower than the sulfuric acid vapor dew point (the temperature at which the sulfuric acid vapor in the flue gas begins to condense, referred to as the acid dew point), the sulfuric acid vapor will condense into acid liquid on the wall surface and corrode the heating surface. Therefore, this kind of corrosion phenomenon will occur in the air preheater arranged at the end of the convection flue, especially at the cold end of the low-temperature stage air preheater with a lower flue gas temperature. At the same time, it adheres to the ash in the flue gas, causing low-temperature sticky ash accumulation. This kind of ash accumulation is integrated with the tube metal and is difficult to remove during the operation of the boiler, resulting in tube blockage. In severe cases, the boiler has to be stopped for ash cleaning, and even a large number of heating surfaces need to be replaced. Biomass fuels in our country have high moisture content and low calorific value, and boiler flue gas often contains a large amount of acid gases such as SO2, SO3 and chlorides that are easily soluble in water. Corrosion and ash accumulation and tube blockage of the air preheater have become the main reasons restricting the continuous operation of biomass boilers.

[0004] For this reason, in the prior art, by providing an air heater located outside the boiler flue gas flow path, the clean cold air for boiler combustion air supply is heated by boiler feed water to a temperature higher than the dew point temperature of water, and then sent to an air preheater heated by flue gas for further heating to increase the temperature, and then sent to the furnace combustion zone, so that the water vapor in the flue gas will not condense into water droplets on the tube wall of the air preheater located within the boiler flue gas flow path, and thus will not cause low-temperature corrosion and ash accumulation and blockage of the air preheater tubes. However, for the air heater in the prior art, each row of heat exchange tubes inside it needs to be first connected to a header (including a water outlet header and a water inlet header), and then the headers of each row of heat exchange tubes are merged into the overall water inlet header and water outlet header of the heater. The structure is complex and the cost is high. The heat source working medium of the air heater is hot water, and the heated working medium is clean air. The water inlet header and water outlet header of the air heater are respectively located at the upper and lower parts of the air heater housing. Multiple rows of heat exchange tubes are arranged in parallel inside the heater housing. The air to be heated flows through the shell side, into and out of the heater. The outlet end of the air passage of the air heater is connected to the inlet end of the air passage of the air preheater, and the inlet end of the air passage of the air heater is connected to a forced draft fan; the high-temperature boiler feed water flows through the heat exchange tubes, headers and other tube side parts, enters the water inlet header from the heater inlet pipe, then flows through all the heat exchange tubes, completes the heat exchange and then converges into the water outlet header, and flows out through the outlet pipe. Summary of the Invention

[0005] The purpose of the present utility model is to overcome the deficiencies of the prior art and provide an air heating system for reducing corrosion and ash accumulation of a boiler air preheater, so as to solve the problems existing in the background art.

[0006] The present utility model adopts the following technical solutions to achieve the above purpose:

[0007] An air heating system for reducing corrosion and ash accumulation in a boiler air preheater, comprising a forced draft fan, an air preheater located within the boiler flue gas flow path, and an air heater located outside the boiler flue gas flow path; a second clean air passage and a flue gas passage are provided within the air preheater, and the high-temperature flue gas within the boiler flue gas flow path can pass through the flue gas passage. The heat source working medium of the air preheater is flue gas, and the heated working medium is the clean air sent by the forced draft fan; a first clean air passage and a heat source working medium passage are provided within the air heater. The heated working medium of the air heater is clean air. The outlet end of the first clean air passage of the air heater is connected to the inlet end of the second clean air passage of the air preheater, and the inlet end of the first clean air passage of the air heater is connected to the forced draft fan. It is characterized in that: the heat source working medium of the air heater is saturated steam from the boiler drum; the air heater includes a tube side part and a shell side part. The tube side part includes an inlet header, an outlet header, and heat exchange tubes. The shell side part includes a shell side cylinder body, a shell side inlet pipe, and a shell side outlet pipe; the inlet header is arranged on the left side wall of the shell side cylinder body, the outlet header is arranged on the right side wall of the shell side cylinder body, the left end of the heat exchange tube is communicated with the inlet header, and the right end of the heat exchange tube is communicated with the outlet header.

[0008] By adopting the above technical solution, an air heater is arranged between the forced draft fan and the air preheater, and the saturated steam of the boiler drum is used to heat the normal temperature air (such as 20°C) entering the air heater, so that its temperature rises above the acid dew point temperature of the flue gas (such as 70°C), and then it is sent into the air preheater. In this way, the inlet air temperature at the cold end of the air preheater is increased, and the acid in the flue gas cannot condense, which can avoid the blockage and low-temperature corrosion of the air preheater. While improving the operating economy of the boiler, the safety of the air preheater is also improved.

[0009] In the above air heating system for reducing corrosion and ash accumulation in a boiler air preheater, the heat exchange tubes adopt spiral fin tubes.

[0010] By adopting the above technical solution, the spiral fin tubes can not only expand the heat transfer area but also increase the turbulence of the fluid, improving the heat exchange effect of the air heater and achieving the purpose of strengthening heat transfer.

[0011] In the above air heating system for reducing corrosion and ash accumulation in a boiler air preheater, a steam inlet is provided on the inlet header, and the steam inlet is connected to the boiler drum through a steam pipeline, and a regulating valve is provided on the steam pipeline.

[0012] By adopting the above technical solution, according to the needs of the boiler combustion situation, the steam flow rate entering the air heater can be adjusted through the regulating valve, thereby adjusting the outlet temperature of the clean air of the air heater.

[0013] In the above air heating system for reducing corrosion and ash accumulation of the boiler air preheater, a steam outlet is provided on the outlet header. The steam outlet is sequentially connected to a steam trap and a drain tank through pipelines. A bypass pipeline is further provided between the steam outlet and the drain tank, and a shut-off valve is provided in the bypass pipeline.

[0014] By adopting the above technical solution, a steam trap and a drain tank are connected to the steam outlet. The saturated steam introduced from the boiler drum is first sent to the air heater. In the air heater, the steam and the cold air perform indirect heat exchange, the temperature of the cold air is increased, and the temperature of the steam drops after releasing heat, and part of the steam condenses into condensate water and enters the drain tank through the steam trap.

[0015] In the above air heating system for reducing corrosion and ash accumulation of the boiler air preheater, the shell-side cylinder body is a cylinder body with a rectangular cross-section. The shell-side inlet pipe is connected to the front end of the cylinder body, and the shell-side outlet pipe is connected to the rear end of the cylinder body. The rear end face of the shell-side inlet pipe is rectangular and is connected to the front end of the cylinder body. The front end face of the shell-side inlet pipe is circular and is connected to the outlet of the air blower. The area of the rectangle is larger than the area of the circle.

[0016] By adopting the above technical solution, the shell-side cylinder body is a cylinder body with a rectangular cross-section, which is convenient for arranging heat exchange tubes. The rear end face of the shell-side inlet pipe is rectangular and is connected to the front end of the cylinder body. The front end face of the shell-side inlet pipe is circular and is connected to the outlet of the air blower. The area of the rectangle is larger than the area of the circle. The purpose of such a design is that after the clean air sent by the air blower enters the shell-side cylinder body, the speed slows down, which is beneficial to the full heat exchange between the clean air and the cold air in the air heater, improves the heat exchange efficiency, and achieves a better heat exchange effect. Beneficial effects

[0017] By setting an air heater outside the boiler flue gas flow path, the clean cold air for boiler combustion air supply is heated to a temperature higher than the dew point temperature of water by using the saturated steam of the boiler drum, sent to the air preheater heated by the flue gas for further heating to increase the temperature, and then sent to the furnace combustion area. Therefore, the water vapor in the flue gas will not condense on the tube wall of the air preheater located within the boiler flue gas flow path, avoiding low-temperature corrosion and ash accumulation blockage of the air preheater tubes, reducing the maintenance time, and extending the service life of the boiler. The shell-side cylinder body of the air heater is a cylinder body with a rectangular cross-section, which is convenient for arranging heat exchange tubes. The rear end face of the shell-side inlet pipe is rectangular and is connected to the front end of the cylinder body. The front end face of the shell-side inlet pipe is circular and is connected to the outlet of the air blower. The area of the rectangle is larger than the area of the circle. The purpose of such a design is that after the clean air sent by the air blower enters the shell-side cylinder body, the speed slows down, which is beneficial to the full heat exchange between the clean air and the cold air in the air heater, improves the heat exchange efficiency, and achieves a better heat exchange effect. Description of the drawings

[0018] Figure 1 This is a schematic diagram of the present utility model.

[0019] Figure 2 This is a schematic diagram of the air heater in the present utility model.

[0020] In the figure: 1 boiler drum, 2 steam pipeline, 3 regulating valve, 4 connecting ventilation pipe, 5 air preheater,

[0021] 6 air heater, 61 shell-side inlet pipe, 62 shell-side cylinder body, 63 shell-side outlet pipe, 64 steam inlet, 65 inlet header, 66 steam outlet, 67 outlet header, 68 heat exchange tube,

[0022] 7 drain pipeline, 8 drain valve, 9 shut-off valve, 10 drain tank, 11 forced draft fan, 12 forced draft duct. Specific embodiments

[0023] To clearly illustrate the technical features of the present utility model, the present utility model will be further described below through non-limiting embodiments in conjunction with the accompanying drawings.

[0024] The front, rear, left, and right directions described in the present utility model are based on the front, rear, left, and right directions shown in the accompanying drawings. For the convenience of description, only parts related to the embodiments of the present utility model are shown.

[0025] Please refer to Figure 1 、 Figure 2 , an air heating system for reducing corrosion and ash accumulation of the boiler air preheater 5, including a forced draft fan 11, an air preheater 5 located within the boiler flue gas flow, and an air heater 6 located outside the boiler flue gas flow;

[0026] A second clean air passage and a flue gas passage are provided in the air preheater 5. The high-temperature flue gas within the boiler flue gas flow can pass through the flue gas passage. It can also be understood that the inlet end of the flue gas passage is connected to the combustion chamber of the boiler, and the outlet end of the flue gas passage is connected to the chimney; the heat source working medium of the air preheater 5 is flue gas, and the heated working medium is the clean air sent by the forced draft fan 11;

[0027] The air heater 6 is provided with a first clean air passage and a heat source working medium passage. The heated working medium of the air heater 6 is clean air. The outlet end of the first clean air passage of the air heater 6 is connected to the inlet end of the second clean air passage of the air preheater 5. The inlet end of the first clean air passage of the air heater 6 is connected to the blower 11. The heat source working medium of the air heater 6 is the saturated steam from the boiler drum 1. The air heater 6 includes a tube side part and a shell side part. The shell side part further includes a shell side cylinder body 62, a shell side inlet pipe 61, and a shell side outlet pipe 63. Specifically, the shell side cylinder body 62 is a cylinder with a rectangular cross-section. The shell side inlet pipe 61 is connected to the front end of the cylinder body. The shell side outlet pipe 63 is connected to the rear end of the cylinder body. In this embodiment, the rear end face of the shell side inlet pipe 61 is rectangular and is connected to the front end of the cylinder body. The front end face of the shell side inlet pipe 61 is circular and is connected to the outlet of the blower 11 through an air delivery pipe 12. The area of the rectangle is larger than the area of the circle. The front end face of the shell side outlet pipe 63 is rectangular and is connected to the rear end of the cylinder body. The rear end face of the shell side outlet pipe 63 is circular and is connected to the inlet end of the air preheater 5 through a connecting air pipe 4.

[0028] The tube side part further includes an inlet header 65, an outlet header 67, and heat exchange tubes 68. The inlet header 65 is arranged on the left side wall of the shell side cylinder body 62, and the outlet header 67 is arranged on the right side wall of the shell side cylinder body 62. The left end of the heat exchange tube 68 is communicated with the inlet header 65, and the right end of the heat exchange tube 68 is communicated with the outlet header 67. In this embodiment, the heat exchange tubes 68 are spiral fin tubes.

[0029] A steam inlet 64 is provided on the inlet header 65. The steam inlet 64 is connected to the boiler drum 1 through a steam pipeline 2, and a regulating valve 3 is provided on the steam pipeline 2.

[0030] A steam outlet 66 is provided on the outlet header 67. The steam outlet 66 is sequentially connected with a steam trap 8 and a drain tank 10 through a drain pipeline 7. In this embodiment, a bypass pipeline is further provided between the steam outlet 66 and the drain tank 10, and a shut-off valve 9 is provided in the bypass pipeline.

[0031] In this embodiment, the air flow path is as follows:

[0032] The clean cold air is sent into the air heater 6 by the blower 11 through the air delivery pipe 12. The normal temperature air (such as 20°C) entering the air heater 6 is heated by the saturated steam introduced from the boiler drum 1, so that its temperature rises above the flue gas acid dew point temperature (such as 70°C), and then it is sent into the air preheater 5. In the air preheater 5, it is indirectly heated by the high-temperature flue gas discharged from the boiler to further increase its temperature and become hot air, which enters the furnace, increases the temperature of the furnace, and makes the fuel burn more fully. On the other hand, the heat in the high-temperature flue gas is recovered.

[0033] In the air heater 6, the clean cold air flows outside the spiral finned tubes (shell side), and the steam flows inside the spiral finned tubes of the air heater 6 (tube side).

[0034] In this embodiment, the flow path of the saturated steam introduced from the steam drum 1 is as follows:

[0035] The saturated steam introduced from the steam drum 1 enters the air heater 6 through the inlet header 65 of the air heater 6, heats the clean cold air sent by the air blower 11. After the steam releases heat, its temperature drops, and the steam condenses into condensate, which enters the condensate tank 10 through the steam trap 8. According to the needs of the boiler combustion conditions, the steam flow rate entering the air heater 6 can be adjusted through the regulating valve 3, thereby adjusting the clean air outlet temperature of the air heater 6.

[0036] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "left", "right", "front", "rear", "upper", "lower", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0037] Unless otherwise clearly defined and limited, the terms "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, a direct connection, or an indirect connection through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0038] Except for the technical features described in the specification, the rest are well-known technologies to those skilled in the art.

[0039] The above-listed embodiments are only for understanding the present invention and are not a limitation on the technical solutions described in the present invention. Those of ordinary skill in the relevant art can make various changes or deformations based on the technical solutions described in the claims, and all equivalent changes or deformations should be covered within the protection scope of the claims of the present invention.

Claims

1. An air heating system for reducing corrosion and dust accumulation of a boiler air preheater, comprising a blower, an air preheater located within the boiler flue gas flow path, and an air heater located outside the boiler flue gas flow path; The air preheater is provided with a second clean air channel and a flue gas channel. The high-temperature flue gas in the boiler flue gas process can pass through the flue gas channel. The heat source medium of the air preheater is flue gas, and the heated medium is the clean air sent in by the blower. The air heater is provided with a first clean air passage and a heat source medium passage, the heated medium of the air heater is clean air, the outlet end of the first clean air passage of the air heater is connected to the inlet end of the second clean air passage of the air preheater, and the inlet end of the first clean air passage of the air heater is connected to the blower, characterized in that: the heat source medium of the air heater is saturated steam from the boiler drum; the air heater comprises a tube side part and a shell side part, the tube side part comprises an inlet header, an outlet header and heat exchange tubes, the shell side part comprises a shell side cylinder, a shell side inlet tube and a shell side outlet tube; the inlet header is arranged on the left side wall of the shell side cylinder, the outlet header is arranged on the right side wall of the shell side cylinder, the left end of the heat exchange tube is connected to the inlet header, and the right end of the heat exchange tube is connected to the outlet header.

2. The air heating system for reducing corrosion and dust accumulation of boiler air preheater according to claim 1, characterized in that: The heat exchange tubes are spiral fin tubes.

3. The air heating system for reducing corrosion and dust accumulation of boiler air preheater according to claim 1, characterized in that: The inlet header is provided with a steam inlet, which is connected to the boiler drum through a steam pipeline, and a regulating valve is provided on the steam pipeline.

4. The air heating system for reducing corrosion and dust accumulation of boiler air preheater according to claim 1, characterized in that: The outlet header is provided with a steam outlet, which is connected to a steam trap and a steam trap box in sequence through pipelines; a bypass pipeline is also provided between the steam outlet and the steam trap box, and a shut-off valve is provided in the bypass pipeline.

5. The air heating system for reducing corrosion and dust accumulation of boiler air preheater according to claim 1, characterized in that: The shell-side cylinder is a cylinder with a rectangular cross-section, the shell-side inlet pipe is connected to the front end of the cylinder, and the shell-side outlet pipe is connected to the rear end of the cylinder; the rear end face of the shell-side inlet pipe is rectangular and connected to the front end of the cylinder, the front end face of the shell-side inlet pipe is circular and connected to the outlet of the blower, and the area of ​​the rectangle is larger than the area of ​​the circle.

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