Gravity assisted heat pipe type smoke air heater with enamel oval pipe

Abstract

The utility model discloses a gravity assisted heat pipe type flue gas air heater with an enamel oval pipe, which comprises a flue gas side casing, a flue gas inlet pipe, a flue gas outlet pipe, a flue gas inlet pipe, a flue gas outlet pipe, a flue gas outlet pipe, a flue gas outlet pipe, a flue gas inlet pipe and a flue gas outlet pipe, and is characterized in that the upper end of the flue gas side casing is fixed on the outlet side of an air pre-heater; the upper end of the air side shell is fixed to the inlet side of the air pre-heater, and an air channel for cooling primary air and cooling secondary air to flow from bottom to top is formed in the air side shell; the gravity assisted heat pipes are obliquely arranged in the smoke channel and the air channel, the pipe sections, located in the smoke channel and the air channel, of the gravity assisted heat pipes are evaporation sections and cooling sections correspondingly, and the cooling sections are higher than the evaporation sections; the gravity assisted heat pipe is an oval pipe filled with a working medium, the long axis direction of the gravity assisted heat pipe is arranged in the same direction as the flow direction of smoke, and the outer wall of an evaporation section of the gravity assisted heat pipe is plated with an enamel coating. Flue gas at an outlet of the air pre-heater is used for heating air pre-heater inlet cold primary air and air pre-heater inlet cold secondary air, so that the temperature of the cold end of the air pre-heater is increased, and the problems of air pre-heater blockage and low-temperature corrosion are solved.

Description

Technical Field

[0001] This utility model relates to the field of heat exchanger technology, and more specifically to a gravity heat pipe flue gas heater with an enamel elliptical tube. Background Technology

[0002] For coal-fired power units, the air preheater (hereinafter referred to as the air preheater) enhances combustion and improves boiler efficiency, making it an important component of the boiler system. When the flue gas temperature of the air preheater is low, because the coal burned in the boiler contains sulfur, nitrogen, and ash, some of the sulfur in the flue gas is converted into SO3. SO3 reacts with water vapor in the flue gas to generate sulfuric acid vapor. The presence of sulfuric acid vapor significantly increases the dew point of the flue gas. Due to the low temperature of the air in the air preheater, the flue gas temperature in the preheater section is not high, and the wall temperature is often lower than the flue gas dew point. As a result, sulfuric acid vapor condenses on the heating surfaces of the air preheater, causing low-temperature corrosion of the heat exchange elements. At the same time, SCR denitrification technology is now widely used in various coal-fired power plants, but SCR denitrification generally suffers from ammonia escape problems. The escaped NH3 reacts with SO3 to produce ABS (ammonium bisulfate crystals), which is currently the main cause of air preheater blockage. Low-temperature corrosion and blockage can reduce the heat exchange efficiency and service life of the air preheater's heat exchange elements, block the channels, and in severe cases, cause the air preheater's pressure differential to far exceed the design value, limiting boiler output or even forcing a shutdown.

[0003] To address the issues of low-temperature corrosion and blockage in air preheaters, current main methods include: hot air recirculation (CN203907656U-Boiler Hot Air Recirculation System), steam-heated air heaters (CN114263927B-Gravity Heat Pipe-Based Air Heater Device and Gravity Heat Pipe Bundle Configuration Method), and low-temperature economizer-heated medium water-heated air heater combined systems. However, each method has its own drawbacks. For example, hot air recirculation requires additional power consumption from the recirculation fan, and the recirculation air volume is difficult to meet the demand under low-temperature and low-load conditions in winter. Steam-heated air heaters require an additional steam supply, resulting in a significant waste of high-quality steam. The combined system of low-temperature economizer and heat transfer water heater requires heat transfer water as the heat exchange medium, which requires the addition of a heat transfer water circulation pump to achieve heat transfer water circulation. This will increase the power consumption of the heat transfer water circulation pump motor. In addition, this method is equivalent to transferring the problems of low-temperature corrosion and ABS (ammonium bisulfate crystals) to the low-temperature economizer. After leakage caused by wear and corrosion of traditional flue gas-water tube heat exchangers, a large amount of heat transfer water flows into the flue, causing dust collector caking and ash blockage, which affects the safe operation of the unit.

[0004] Therefore, how to provide a gravity heat pipe flue gas heater with enamel-lined elliptical tubes that utilizes the waste heat of flue gas at the air preheater outlet to heat the primary and secondary cold air (air) at the air preheater inlet, thereby increasing the overall temperature of the cold end of the air preheater and improving air preheater blockage and low-temperature corrosion, is a problem that urgently needs to be solved by those skilled in the art. Utility Model Content

[0005] In view of this, the present invention provides a gravity heat pipe flue gas heater with enamel elliptical tubes that utilizes the waste heat of flue gas at the air preheater outlet to heat the primary and secondary cold air (air) at the air preheater inlet, thereby increasing the overall temperature of the cold end of the air preheater and improving air preheater blockage and low-temperature corrosion.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A gravity heat pipe flue gas heater with an enamel-lined elliptical tube, comprising:

[0008] The flue gas side shell has its upper end fixed to the outlet side of the air preheater, and the flue gas side shell has a flue gas channel inside for flue gas to flow from top to bottom.

[0009] An air-side housing, the upper end of which is fixed to the inlet side of the air preheater, and the interior of which has an air passage for cooling primary and secondary air to flow from bottom to top;

[0010] A gravity heat pipe is inclinedly arranged in the flue gas channel and the air channel. The section of the gravity heat pipe in the flue gas channel and the section in the air channel are respectively an evaporation section and a cooling section. The height of the cooling section is higher than that of the evaporation section.

[0011] The gravity heat pipe is an elliptical tube filled with working fluid, and its major axis is arranged in the same direction as the flue gas flow. The outer wall of the evaporation section of the gravity heat pipe is coated with an enamel coating.

[0012] As can be seen from the above technical solution, compared with the prior art, this utility model discloses a gravity heat pipe type flue gas heater with an enamel-lined elliptical tube. Flue gas from the air preheater outlet flows through the evaporation section of the gravity heat pipe located in the flue gas channel. The working fluid inside the gravity heat pipe absorbs heat from the flue gas and undergoes a phase change, transforming into steam. The steam moves obliquely upwards to the cooling section of the gravity heat pipe located in the air channel. The steam in the cooling section exchanges heat with the upward-flowing primary and secondary cold air (i.e., air), heating the primary and secondary cold air. Meanwhile, the steam in the cooling section condenses into a liquid state. Driven by gravity, the liquid working fluid flows back to the evaporation section located in the flue gas channel to continue the next working fluid heat exchange cycle. Through this continuous working fluid circulation, the flue gas at the air preheater outlet is used to heat the primary and secondary cold air (i.e., air), thereby increasing the overall cold-end temperature of the air preheater and improving the problems of air preheater blockage and low-temperature corrosion. In addition, the flue gas flows along the long axis of the elliptical tube. Due to the streamlined shape of the elliptical tube, the tail vortex area can be reduced when the flue gas is turbulent, resulting in better heat transfer and resistance performance than the circular tube structure. At the same time, it can reduce the problems of dust accumulation and wear on the heated surface.

[0013] Furthermore, there are multiple gravity heat pipes arranged in multiple rows and columns, and the multiple gravity heat pipes are fixed together by support plates.

[0014] The beneficial effects of adopting the above technical solution are: multiple gravity heat pipes can increase the heat exchange area between flue gas and primary and secondary air, thereby improving heat exchange efficiency, which can greatly reduce the flue gas temperature at the flue gas outlet and increase the temperature of primary and secondary air at the air preheater inlet.

[0015] Furthermore, the support plate has a through hole, a limiting sleeve is inserted through the through hole, and the gravity heat pipe is inserted through the limiting sleeve.

[0016] The beneficial effects of adopting the above technical solution are: the limiting sleeve can limit and fix the gravity heat pipe, preventing the enamel coating from being damaged by vibration and collision during operation.

[0017] Furthermore, the two ends of the limiting sleeve have a first stop flange and a second stop flange, respectively, and the first stop flange and the second stop flange are respectively engaged on the two sides of the through hole.

[0018] The beneficial effects of adopting the above technical solution are: improving the stability of the limiting sleeve installed in the through hole and preventing the limiting sleeve from slipping off.

[0019] Furthermore, heat exchange fins are fixed on the wall of the evaporation section or / and cooling section of the gravity heat pipe.

[0020] The beneficial effects of adopting the above technical solution are: improving the heat exchange efficiency between the evaporation section and the flue gas, and improving the heat exchange efficiency between the cooling section and the primary and secondary air.

[0021] Furthermore, two vertically arranged partitions are fixed between the flue gas side shell and the air side shell. The two partitions, the flue gas side shell, and the air side shell enclose a heat insulation space. The heat insulation space is filled with heat insulation components, and the gravity heat pipe passes through the heat insulation components.

[0022] The beneficial effects of adopting the above technical solution are: the heat insulation component can isolate the flow of flue gas and the primary and secondary air and the transfer of heat. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0024] Figure 1 This utility model provides a structural schematic diagram of a gravity heat pipe flue gas heater with an enamel elliptical tube.

[0025] Figure 2 This is a side view of a gravity heat pipe.

[0026] Figure 3 This is a schematic diagram of the longitudinal section of a gravity heat pipe.

[0027] Figure 4 This is a schematic diagram of a gravity heat pipe fixed to a support plate by a limiting sleeve.

[0028] Figure 5 This is a schematic diagram of a gravity heat pipe with spiral heat exchange fins on its pipe wall.

[0029] Figure 6 This is a schematic diagram of a gravity heat pipe with H-shaped heat exchange fins on its pipe wall. Detailed Implementation

[0030] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0031] like Figures 1-6 This utility model discloses a gravity heat pipe type flue gas heater with an enamel elliptical tube, comprising:

[0032] The flue gas side housing 1 has its upper end fixed to the outlet side of the air preheater 100, and the flue gas side housing 1 has a flue gas passage 101 inside for flue gas to flow from top to bottom.

[0033] Air-side housing 2, the upper end of which is fixed to the inlet side of air preheater 100, and the interior of air-side housing 2 has an air passage 201 for supplying cooling primary and secondary air to flow from bottom to top;

[0034] Gravity heat pipe 3 is inclinedly arranged in flue gas channel 101 and air channel 201. The section of gravity heat pipe 3 located in flue gas channel 101 and the section located in air channel 201 are respectively evaporation section 31 and cooling section 32. The height of cooling section 32 is higher than that of evaporation section 31. That is, gravity heat pipe 3 is inclined downward from air side to flue gas side.

[0035] Gravity heat pipe 3 is an elliptical tube filled with working fluid. Its major axis is arranged in the same direction as the flue gas flow. Compared with the same circular tube arrangement, this can effectively reduce the deposition rate of flue gas particles on the surface of the gravity heat pipe, thus having lower resistance and higher heat transfer efficiency. At the same time, since the major axis of the elliptical tube is the heating surface of the hot air, its heating surface area is smaller than that of the minor axis, which can reduce the accumulation of dust and wear on the heating surface of the major axis of the elliptical tube.

[0036] The outer wall of the evaporation section 31 of the gravity heat pipe 3 is coated with an enamel coating 4 with a thickness of ≥180μm.

[0037] The thermal conductivity of enamel-coated gravity heat pipes is close to that of low-carbon steel, resulting in good heat transfer performance. The enamel glaze sintered on the gravity heat pipes has strong corrosion resistance to various acidic liquids that condense in the flue gas during cooling.

[0038] The enamel coating on gravity heat pipes has the following corrosion resistance characteristics:

[0039] ① Sulfuric acid resistance: 30% sulfuric acid, boiling for 18 hours, corrosion amount ≤2.0g / m³ 2 Reference standard ISO28706-2;

[0040] ② Adhesion: Grade 1 or above, reference standard: EN10209;

[0041] ③ Electrical spark resistance: Number of current points tested at 2000V ≤ 1 / 0.09m 2 ;

[0042] ④ Resistance to rapid heat change: No cracks were observed in water at 23±3℃ and 300℃. Reference standard: German DEZ-MB7.7.1;

[0043] ⑤ Hydrochloric acid resistance: 20% sulfuric acid, boiling for 6 hours, corrosion amount ≤3.5g / m³ 2 The test methods are based on the reference standard ISO28706-2 and the standard GB25025-2010 "Technical Conditions for Enameled Equipment".

[0044] In addition, the hardness of the enamel coating 4 is HV=652, which is about 4 times that of ND steel, and it has excellent wear resistance.

[0045] The interior of a gravity heat pipe is a sealed cavity with a slight negative pressure, also known as a slight vacuum (negative pressure relative to the external atmospheric pressure). The purpose of this is to lower the internal pressure of the heat pipe cavity, which reduces the boiling point (i.e., saturation temperature) of the working fluid inside the heat pipe. This allows the working fluid to undergo phase changes (evaporation and condensation) more easily, resulting in higher operating efficiency. Typically, the vacuum level inside a gravity heat pipe needs to reach 10⁻⁴ to 10⁻⁵ Torr.

[0046] Common working fluids for gravity heat pipes include water (distilled water), ethanol, FC-72, etc. Water is suitable as the working fluid for the working temperature range and working environment of this invention.

[0047] To improve the performance and service life of gravity heat pipe 3, the interior of the heat pipe cavity needs to be chemically cleaned and passivated, and a certain amount of anodic corrosion inhibitor needs to be added to the working fluid to reduce the generation of non-condensable gases. The reason is that during the operation of the heat pipe, the internal working fluid (water) undergoes a continuous evaporation-condensation phase change cycle. Over time, the working fluid reacts with the inner wall of the gravity heat pipe, gradually generating non-condensable gases. The generation of non-condensable gases reduces the working efficiency and service life of the gravity heat pipe. Therefore, acid pickling and passivation of the interior of the gravity heat pipe and the addition of corrosion inhibitors to the working fluid can reduce the generation of non-condensable gases and improve the lifespan of the heat pipe.

[0048] The flue gas side shell 1 is a cylindrical structure welded from a steel plate of about 6mm thickness and reinforcing ribs (set according to requirements). The flue gas from the air preheater outlet flows from top to bottom in the flue gas channel inside the flue gas side shell 1 and exchanges heat with the working fluid inside the evaporation section of the gravity heat pipe 3. After cooling down to about 90°C, it enters the dust collector. The working fluid inside the evaporation section is heated and turned into steam. The steam moves obliquely upward to the cooling section of the gravity heat pipe.

[0049] The air-side shell 2 is a cylindrical structure welded together with a thickness of about 4-6 mm and reinforcing ribs (as required). The primary and secondary air (i.e., air) flows from bottom to top in the air channel inside the air-side shell 2 and exchanges heat with the steam inside the cooling section of the gravity heat pipe 3. After being heated to about 50-75°C, it enters the air preheater. The steam inside the cooling section condenses into liquid. The liquid working fluid is driven by gravity to flow back to the evaporation section located in the flue gas channel to continue the next working fluid heat exchange cycle.

[0050] Therefore, this embodiment uses this continuous working fluid circulation to heat the primary and secondary cold air (i.e., air) with the flue gas at the air preheater outlet, thereby increasing the overall cold end temperature of the air preheater and improving the problems of air preheater blockage and low-temperature corrosion.

[0051] In some embodiments, such as Figures 1-2 As shown, there are multiple gravity heat pipes 3 arranged in multiple rows and columns. These gravity heat pipes 3 are fixed and positioned together by support plates 5. This positioning and support prevents vibration and collisions during operation from damaging the enamel coating. Specifically, as... Figure 4 As shown, the support plate 5 has a through hole 51, and a limiting sleeve 6 passes through the through hole 51. The gravity heat pipe 3 passes through the limiting sleeve 6. The two ends of the limiting sleeve 6 have a first stop flange 61 and a second stop flange 62, which are respectively engaged with the two sides of the through hole 51.

[0052] Of course, the support plate 5 can also be welded and fixed to the air-side shell and the flue gas-side shell by connecting rods, thereby providing more stable support for the gravity heat pipe.

[0053] In this embodiment, the limiting sleeve 6 can be made of polytetrafluoroethylene, which is heat-resistant, corrosion-resistant, and has a long service life.

[0054] Spiral heat exchange fins 7 are welded and fixed to the wall of the evaporation section 31 or / and cooling section 32 of the gravity heat pipe 3. Figure 5 ) or H-type heat exchange fins 7 ( Figure 6 This is to enhance the heat exchange effect of the evaporation section 31 or the cooling section 32.

[0055] Two vertically arranged partitions 8 are welded and fixed between the flue gas side shell 1 and the air side shell 2. The two partitions 8, the flue gas side shell 1 and the air side shell 2 enclose a heat insulation space 9. The heat insulation space 9 is filled with heat insulation cotton, castable material and other heat insulation components. Gravity heat pipes 3 are inserted into the heat insulation components to isolate the flue gas from the movement and heat transfer between the primary and secondary air (i.e., air).

[0056] The principle of this invention is as follows: Flue gas from the outlet of the air preheater 100 flows downwards through the flue gas passage 101. After passing through the evaporation section 31 of the gravity heat pipe 3, the working fluid inside the gravity heat pipe 3 absorbs heat from the flue gas and undergoes a phase change, transforming into steam. The steam moves obliquely upwards to the cooling section 32 located in the air passage 201. The steam in the cooling section 32 exchanges heat with the upward-flowing primary and secondary air. The steam in the cooling section 32 condenses into a liquid state. Driven by gravity, the liquid working fluid flows back to the evaporation section 31 on the flue gas side to continue the next working fluid heat exchange cycle. Through this continuous working fluid circulation, the flue gas at the air preheater outlet is used to heat the primary and secondary air, thereby increasing the overall cold-end temperature of the air preheater and improving the problems of air preheater blockage and low-temperature corrosion.

[0057] Therefore, this invention utilizes the flue gas at the air preheater outlet to heat the primary and secondary cold air (air) at the air preheater inlet, thereby increasing the temperature of the primary and secondary cold air (air) entering the air preheater from the original 20-25℃ to approximately 50-75℃. This raises the minimum operating metal wall temperature of the cold end of the air preheater's heat storage elements from 20-25℃ to 50-75℃. This temperature is higher than the flue gas water dew point temperature (typically around 40-45℃), preventing low-temperature corrosion and blockage caused by sulfuric acid vapor condensing on the heat exchange elements of the air preheater.

[0058] The advantages of this utility model compared with the prior art are as follows:

[0059] 1. This utility model's flue gas air heater is based on the phase change high-efficiency heat transfer mechanism of gravity heat pipes. It uses the flue gas at the air preheater outlet to heat the cold primary and secondary air (air) at the air preheater inlet, thereby increasing the overall temperature of the cold end of the air preheater and improving the problems of air preheater blockage and low-temperature corrosion. Compared with conventional hot air recirculation and steam air heaters, it has the advantages of simple system, low overall heat loss, and no need for additional high-quality steam consumption. Compared with the combined system of low-temperature economizer-heating medium water air heater, it does not require the addition of a large number of auxiliary equipment such as circulating water pumps, water pipelines, and valves. Moreover, since it uses the working principle of gravity heat pipes to achieve heat exchange between flue gas and cold primary and secondary air (air), it does not require heating medium water as an intermediate heat exchange medium. Therefore, it does not have the disadvantages of traditional tubular flue gas-water low-temperature economizers, such as ash accumulation and caking after leakage, which affect the safe operation of the unit.

[0060] 2. Using an elliptical tube as the base tube type for gravity heat pipes, the flue gas flows along the long axis of the elliptical tube. Its streamlined shape has lower resistance and higher heat transfer coefficient than that of a circular tube, while also reducing ash accumulation and wear on the heated surface.

[0061] 3. The outer wall of the gravity heat pipe in the evaporation section is enamel-coated. The enamel glaze sintered on the gravity heat pipe has strong corrosion resistance to various acidic liquids that condense in the flue gas, improving the corrosion resistance of the flue gas heater. Furthermore, the hardness of the enamel glaze on the enamel-coated pipe is approximately four times that of ND steel, offering higher wear resistance and a longer service life compared to ND steel and other materials used in conventional low-temperature economizers and other flue gas waste heat recovery devices.

[0062] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0063] The above description of the disclosed embodiments enables those skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A gravity heat pipe type flue gas heater with an enamel-lined elliptical tube, characterized in that, include: The flue gas side housing (1) has its upper end fixed on the outlet side of the air preheater (100), and the flue gas side housing (1) has a flue gas passage (101) inside for flue gas to flow from top to bottom. Air-side housing (2), the upper end of which is fixed on the inlet side of the air preheater (100), and the interior of the air-side housing (2) has an air passage (201) for supplying cooling primary and secondary air to flow from bottom to top; Gravity heat pipe (3), the gravity heat pipe (3) is inclinedly arranged in the flue gas channel (101) and the air channel (201), the pipe section of the gravity heat pipe (3) located in the flue gas channel (101) and the pipe section located in the air channel (201) are respectively the evaporation section (31) and the cooling section (32), the height of the cooling section (32) is higher than that of the evaporation section (31); The gravity heat pipe (3) is an elliptical tube filled with working fluid, and its major axis is arranged in the same direction as the flue gas flow. The outer wall of the evaporation section (31) of the gravity heat pipe (3) is coated with an enamel coating (4).

2. A gravity heat pipe flue gas heater with an enamel-lined elliptical tube according to claim 1, characterized in that, There are multiple gravity heat pipes (3), which are arranged in multiple rows and columns, and the multiple gravity heat pipes (3) are fixed together by a support plate (5).

3. A gravity heat pipe flue gas heater with an enamel-lined elliptical tube according to claim 2, characterized in that, The support plate (5) has a through hole (51), and a limiting sleeve (6) is inserted through the through hole (51). The gravity heat pipe (3) is inserted through the limiting sleeve (6).

4. A gravity heat pipe flue gas heater with an enamel-lined elliptical tube according to claim 3, characterized in that, The two ends of the limiting sleeve (6) have a first stop flange (61) and a second stop flange (62), respectively, and the first stop flange (61) and the second stop flange (62) are respectively engaged on the two sides of the through hole (51).

5. A gravity heat pipe flue gas heater with an enamel-lined elliptical tube according to any one of claims 1-4, characterized in that, Heat exchange fins (7) are fixed on the wall of the evaporation section (31) or / the cooling section (32) of the gravity heat pipe (3).

6. A gravity heat pipe flue gas heater with an enamel-lined elliptical tube according to any one of claims 1-4, characterized in that, Two vertically arranged partitions (8) are fixed between the flue gas side shell (1) and the air side shell (2). The two partitions (8), the flue gas side shell (1) and the air side shell (2) enclose a heat insulation space (9). The heat insulation space (9) is filled with heat insulation components, and the gravity heat pipe (3) passes through the heat insulation components.

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