Air preheating device utilizing low-grade waste heat

Abstract

The utility model relates to an air preheating device utilizing low-grade waste heat, which comprises a heat preservation air duct arranged at an air inlet of an air feeder, at least two groups of air preheating heat exchangers arranged in pairs are arranged in the heat preservation air duct, and the two groups of air preheating heat exchangers are arranged along the center line of the heat preservation air duct to form a V shape. An opening of the V shape faces an air inlet or an air outlet of the heat preservation air duct; the air preheating heat exchanger receives heat from condenser waste heat, heat supply network primary water return waste heat and desulfurized slurry or desulfurized saturated wet flue gas and preheats air before entering the air feeder. Various waste heat of 40-60 DEG C in a coal-fired boiler of a power plant is used as a heat source to preheat cold air entering an air feeder, such as waste heat of a condenser, waste heat of primary water return of a heat supply network, waste heat of desulfurization slurry and waste heat of saturated wet flue gas after desulfurization, the cold air can be heated to 25-40 DEG C, and then the cold air is fed into an air preheater by the air feeder to be secondarily heated; and the problems of freezing and blocking of a large amount of water vapor at the air duct opening are solved.

Description

Technical Field

[0001] This utility model relates to the field of energy engineering technology, specifically to an air preheating device that utilizes low-grade waste heat. Background Technology

[0002] The statements in this section are merely background information related to this utility model and do not necessarily constitute prior art.

[0003] In some extremely cold regions, such as those with temperatures below -20°C, to reduce the impact of cold air on the operation of coal-fired boilers, low-pressure steam is used to preheat the air after the forced draft fan before it enters the air preheater. This preheating method, due to the rapid cooling of the low-pressure steam, causes a large amount of water vapor to condense at the inlet of the forced draft fan duct, forming frost or even freezing. Simultaneously, because the forced draft fan is located in an outdoor environment, the condensing water vapor attracts dust from the environment, reducing the effective area of ​​the duct opening and even blocking it.

[0004] To address the aforementioned issues, manual cleaning is currently carried out on a scheduled or irregular basis, which wastes manpower, increases the air resistance of the blower, and increases power consumption, resulting in energy waste. Utility Model Content

[0005] To address the technical problems mentioned above, this invention provides an air preheating device utilizing low-grade waste heat. It uses waste heat from coal-fired power plants (40-60°C, such as condenser waste heat, primary water return heat from the heating network, desulfurization slurry, and saturated wet flue gas after desulfurization) to heat the cold air entering the blower through a heat exchanger. This heats the cold air to 25-40°C before the blower sends it to the air preheater for secondary heating. This method avoids the accumulation of large amounts of water vapor and blockage by debris at the air duct inlet; it also utilizes low-grade waste heat to heat the cold air, reducing or stopping steam heating at the blower's downstream end, thus improving energy efficiency.

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

[0007] This utility model provides an air preheating device utilizing low-grade waste heat, including an insulated air duct arranged at the air inlet of a blower. The insulated air duct is equipped with at least two sets of paired air preheating heat exchangers. The two sets of air preheating heat exchangers are arranged in a V-shape along the center line of the insulated air duct, with the opening of the V-shape facing the air inlet or outlet of the insulated air duct. The air preheating heat exchangers receive heat from the waste heat of the condenser, the waste heat of the primary return water of the heating network, the desulfurization slurry, or the saturated wet flue gas after desulfurization, and preheat the air before it enters the blower.

[0008] Furthermore, the air preheating heat exchanger is connected to the waste heat recovery heat exchanger through a pipeline, and the waste heat recovery heat exchanger transfers the waste heat from the condenser, desulfurization slurry, or saturated wet flue gas after desulfurization to the air preheating heat exchanger.

[0009] Furthermore, the air preheating heat exchanger is connected to the waste heat recovery heat exchanger through a pipeline. The waste heat recovery heat exchanger is placed in the desulfurization slurry and exchanges heat with the desulfurization slurry through the waste heat recovery heat exchanger, transferring the heat in the desulfurization slurry to the air preheating heat exchanger through the working medium.

[0010] Furthermore, the air preheating heat exchanger is connected to the waste heat recovery heat exchanger through a pipeline. The waste heat recovery heat exchanger is arranged in the flue and located in the saturated wet flue gas between the desulfurization tower and the demister. It exchanges heat with the saturated wet flue gas through the waste heat recovery heat exchanger, transferring the heat in the saturated wet flue gas to the air preheating heat exchanger through the working medium.

[0011] Furthermore, the air preheating heat exchanger is connected to the waste heat recovery heat exchanger through a pipeline. The waste heat recovery heat exchanger is arranged in the circulation loop of the desulfurization slurry. The waste heat recovery heat exchanger exchanges heat with the desulfurization slurry, transferring the heat in the desulfurization slurry to the air preheating heat exchanger through the working medium.

[0012] Furthermore, the desulfurization slurry circulation loop includes a slurry pump, a waste heat recovery heat exchanger, and a desulfurization tower connected by pipelines. The slurry pump drives the desulfurization slurry to circulate between the waste heat recovery heat exchanger and the desulfurization tower.

[0013] Furthermore, the desulfurization tower is connected to the flue gas duct, allowing the flue gas to flow through and the desulfurization slurry to absorb sulfur-containing substances in the flue gas.

[0014] Furthermore, the inlet pipe of the air preheating heat exchanger is connected to the inlet pipe of the condenser, and the outlet pipe of the air preheating heat exchanger is connected to the outlet pipe of the condenser.

[0015] Furthermore, an expansion tank is installed between the outlet pipe of the air preheating heat exchanger and the outlet pipe of the condenser.

[0016] Furthermore, the inlet pipes of the air preheating heat exchanger and the condenser receive the primary water return from the heating network. After the air preheating heat exchanger preheats the air, the resulting return water is returned to the condenser through pipelines.

[0017] Compared with existing technologies, one or more of the above technical solutions have the following beneficial effects:

[0018] 1. Utilize various types of waste heat (40-60℃) in the coal-fired boilers of power plants as heat sources to preheat the cold air entering the blower, such as condenser waste heat, primary water return waste heat of the heating network, desulfurization slurry and saturated wet flue gas after desulfurization. This can heat the cold air to 25-40℃, and then the blower will send it into the air preheater for secondary heating, avoiding the problem of large amounts of water vapor freezing and clogging at the air duct opening.

[0019] 2. The waste heat from the condenser, the waste heat from the primary return water of the heating network, the desulfurization slurry, and the saturated wet flue gas after desulfurization are all low-grade waste heat, which is easy to obtain. Using low-grade waste heat to heat cold air reduces or stops the steam heating at the back end of the blower, thereby improving energy utilization and indirectly reducing the energy consumption of coal-fired boilers. Attached Figure Description

[0020] The accompanying drawings, which form part of this specification, are used to provide a further understanding of this utility model. The illustrative embodiments of this utility model and their descriptions are used to explain this utility model and do not constitute an improper limitation of this utility model.

[0021] Figure 1 This is a schematic diagram of the principle of an air preheating device provided in one or more embodiments of this utility model;

[0022] Figure 2 This is a schematic diagram of the air preheating device provided in one or more embodiments of the present invention;

[0023] Figure 3 This is a schematic diagram of the structure of the waste heat recovery heat exchanger of the air preheating device provided in one or more embodiments of the present invention, placed in the desulfurization slurry;

[0024] Figure 4 This is a schematic diagram of the structure of the waste heat recovery heat exchanger of the air preheating device provided in one or more embodiments of the present invention, placed in saturated wet flue gas;

[0025] Figure 5 This is a schematic diagram of the waste heat recovery heat exchanger and desulfurization slurry pump circulation structure of the air preheating device provided in one or more embodiments of this utility model;

[0026] Figure 6 This is a schematic diagram of the air preheating device utilizing municipal heating return water provided in one or more embodiments of the present invention;

[0027] Figures 7-11 This is a schematic diagram of different arrangement methods of the air preheating heat exchanger provided in one or more embodiments of this utility model.

[0028] In the diagram: 1. Exhaust fan, 2. Insulated air duct, 3. Air preheating heat exchanger, 4. Chimney, 5. Demister, 6. Waste heat recovery heat exchanger; 7. Slurry pump, 8. Condenser, 9. Expansion tank. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0030] It should be noted that the following detailed description is exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0031] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this utility model. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0032] Example 1:

[0033] This embodiment utilizes the waste heat of 40-60°C from coal-fired power plants (such as condenser waste heat, primary return water waste heat from the heating network, desulfurization slurry, and saturated wet flue gas after desulfurization) to heat the cold air entering the blower through a heat exchanger. This heats the cold air to 25-40°C before it is sent to an air preheater for secondary heating. This avoids the accumulation of large amounts of water vapor and blockage by debris at the air duct inlets; it also utilizes low-grade waste heat to heat the cold air, reducing or stopping steam heating at the blower's downstream end, thus improving energy efficiency. The principle of waste heat utilization is as follows: Figure 1 As shown.

[0034] like Figure 2 As shown, the air preheating device utilizing low-grade waste heat includes an insulated air duct 2 arranged at the air inlet of the blower 1. Inside the insulated air duct 2, at least two sets of air preheating heat exchangers 3 are arranged in pairs. The two sets of air preheating heat exchangers 3 are arranged in pairs along the center line of the insulated air duct to form a V shape. The opening of the V shape faces the air inlet or outlet of the insulated air duct.

[0035] The insulated air duct has a rectangular structure with an air inlet and an air outlet at each end. The wall is covered with insulation material. The V-shaped air preheating heat exchangers 3, arranged in pairs, are confined in the insulated air duct. Outside cold air passes through the heat exchange surface of the air preheating heat exchanger 3, is preheated, and then enters the blower. The blower then pressurizes the air and sends it into the air preheater.

[0036] The insulation material can be aluminum silicate insulation material.

[0037] The air preheating heat exchanger 3 is connected to the waste heat recovery heat exchanger 6 through a pipeline. The waste heat recovery heat exchanger 6 transfers the waste heat from the condenser, the desulfurization slurry, and the saturated wet flue gas after desulfurization to the air preheating heat exchanger 3. The outside cold air is heated by exchanging heat with the air preheating heat exchanger 3.

[0038] The air preheating heat exchanger 3 can be a finned plate heat exchanger, a spiral plate heat exchanger, or an immersed coil heat exchanger. Considering corrosion and clogging issues, the heat exchange pipes can be made of composite materials with better thermal conductivity and excellent corrosion resistance, such as PTFE, carbon fiber composites, titanium alloys, or graphite.

[0039] Example 2:

[0040] In this embodiment, the waste heat recovery heat exchanger 6 is placed in the desulfurization slurry to realize the recovery of low-grade heat and transfer it to the air preheating heat exchanger 3.

[0041] Wet desulfurization process is used to remove sulfur-containing substances from flue gas of coal-fired boilers. The temperature of the desulfurization slurry is 20-50 ℃, and the low-grade waste heat contained therein can be used as heat required for air preheating.

[0042] like Figure 3 As shown, the waste heat recovery heat exchanger 6 is placed in the desulfurization slurry. By exchanging heat with the desulfurization slurry, the heat in the desulfurization slurry is transferred from the waste heat recovery heat exchanger 6 to the air preheating heat exchanger 3 through the working medium, and then the air is preheated by the air preheating heat exchanger 3.

[0043] After passing through the desulfurization slurry, the flue gas is transformed into saturated wet flue gas, which then passes through the demister 5 and enters the chimney 4 for discharge.

[0044] Since the waste heat recovery heat exchanger 6 is placed in the desulfurization slurry, the temperature of the entire desulfurization system is reduced, thereby making full use of the low-grade waste heat in the desulfurization slurry.

[0045] Meanwhile, the demister 5 filters out the condensate carried by the flue gas and returns it to the desulfurization system, thus eliminating whitening.

[0046] Example 3:

[0047] In this embodiment, the waste heat recovery heat exchanger 6 is placed in the saturated wet flue gas before the demister 5 in the wet desulfurization process to realize the recovery of low-grade heat and transfer it to the air preheating heat exchanger 3.

[0048] like Figure 4 As shown, after passing through the desulfurization slurry, the flue gas is transformed into saturated wet flue gas, which then passes through the demister 5 and enters the chimney 4 for discharge.

[0049] The waste heat recovery heat exchanger 6 is placed in the saturated wet flue gas before the demister 5. By exchanging heat with the saturated wet flue gas, the heat in the saturated wet flue gas is transferred from the waste heat recovery heat exchanger 6 to the air preheating heat exchanger 3 through the working medium, and then the air is preheated by the air preheating heat exchanger 3.

[0050] When this method is used to recover waste heat, the waste heat recovery heat exchanger 6 has a 3-5° angle, which makes it easier for the condensed water to flow into the condensate collector. The demister 5 filters the condensate from the moisture carried by the flue gas into the collector, recovering part of the moisture in the desulfurization system. At the same time, it helps to lower the temperature of the desulfurization slurry and facilitates the elimination of white spots.

[0051] Example 4:

[0052] In this embodiment, the waste heat recovery heat exchanger 6 is placed in the desulfurization slurry circulation loop of the desulfurization tower to realize the recovery of low-grade heat and transfer it to the air preheating heat exchanger 3.

[0053] like Figure 5 As shown, after passing through the desulfurization slurry, the flue gas is transformed into saturated wet flue gas, which then passes through the demister 5 and enters the chimney 4 for discharge.

[0054] The desulfurization slurry is located in the desulfurization tower. The slurry is circulated by the slurry pump 7, so that the desulfurization slurry continuously contacts the flue gas in the desulfurization tower, thereby removing sulfur-containing substances from the flue gas.

[0055] In this embodiment, the waste heat recovery heat exchanger 6 is placed in the desulfurization slurry circulation loop. The desulfurization slurry is pumped to the waste heat recovery heat exchanger 6 by the slurry pump 7 for heat exchange before returning to the desulfurization system. This method utilizes some of the low-grade waste heat in the desulfurization slurry to reduce its temperature. Similar to Embodiment 2, both methods use the desulfurization slurry itself for heat exchange. The difference lies in the specific material and structural type of the waste heat recovery heat exchanger 6. Here, a readily available and mature heat exchanger can be used as the waste heat recovery heat exchanger 6; no specific limitations are imposed in this embodiment. Since the desulfurization slurry contains chloride ions, which severely corrode stainless steel, the waste heat recovery heat exchanger 6 can be made of polytetrafluoroethylene (PTFE) as the material in contact with the desulfurization slurry.

[0056] Example 5:

[0057] In this embodiment, the air preheating device uses the preheating of municipal heating return water to preheat the boiler air. Instead of using the waste heat recovery heat exchanger 6, it takes advantage of the fact that the boiler main unit's condenser is idle in winter. Combined with the requirements of heating the intake air of the primary and secondary air fans, the unit's condenser is used as a carrier to fully utilize the waste heat at the cold end of the boiler main unit. Using circulating water as a medium, a portion of the heat is transferred to the air preheating heat exchanger 3 to heat the ambient air, thereby reducing the steam consumption of the original air preheating, achieving the energy-saving goal, and improving the reliability and economy of the system operation.

[0058] like Figure 6 As shown, the inlet pipe of the air preheating heat exchanger 3 is connected to the inlet pipe of the condenser 8, and the outlet pipe of the air preheating heat exchanger 3 is connected to the outlet pipe of the condenser 8 and the expansion tank 9. The primary return water of the heating network enters the condenser 8 and the air preheating heat exchanger 3 respectively. After the air preheating heat exchanger 3 preheats the air, the resulting return water returns to the condenser 8 through the pipe. The expansion tank 9 absorbs the pressure fluctuations generated during heat exchange. Since the primary return water of the heating network contains a small amount of flash steam, the heat released after this part of the flash steam condenses into liquid water, along with the heat contained in the liquid water itself, is transferred to the air by the air preheating heat exchanger 3 through heat exchange.

[0059] Due to environmental factors and heat exchange efficiency, the temperature of the primary heat exchanger return water is between 40℃ and 60℃, but this heat still has value. To fully absorb the heat from the heat exchanger return water and achieve complete utilization, an air preheating device as described in this solution can be installed at the inlet of the boiler blower and primary air blower to heat the air using the waste heat from the return water.

[0060] Example Analysis: The lowest outdoor ambient temperature during the heating season is -25℃. When the outdoor ambient temperature is -30℃, a 660MW single unit operating at full load requires 135GJ / h of heat to heat the primary and secondary air to 27℃. The primary return water temperature of the heating network is between 35℃ and 60℃. Assuming an outlet water temperature of 20℃ after heat exchange in the heating room, when the heating network returns water to the 660MW single unit at a supply rate of 1100t / h, the maximum released heat is 179GJ / h, which meets the requirements for safe operation of the unit under extremely cold weather conditions.

[0061] If calculated based on an average outdoor temperature of -30℃ in winter (average temperature during the heating season), when the unit is running at full load, if the primary return water of the heating network is used to replace the heaters, reducing or eliminating the use of heaters, the 660MW unit can reduce auxiliary steam consumption by 229,600 tons per year, save 627,400 gigajoules of heat, and save 23,200 tons of standard coal.

[0062] Example 6:

[0063] To maximize the contact time and area between the heat exchanger and the cold air, and to confine the heat exchanger within a defined rectangular space, arranging multiple V-shaped air preheating heat exchangers is the most scientifically sound approach. For recovering lower-grade waste heat or requiring higher air temperatures, it is advisable to consider arranging several rows of V-shaped air preheating heat exchangers.

[0064] For example Figures 7-11 As shown, two sets of air preheating heat exchangers arranged in a V-shape form a pair. Figure 7 In the middle, two pairs of air preheating heat exchangers are stacked along the air flow direction. Figure 8 and Figure 9 In the middle, two pairs of air preheating heat exchangers are arranged side by side in the insulated air duct, and Figure 8 and Figure 9 The V-shaped openings in the middle face opposite directions. Figure 10 and Figure 11 In the middle, four pairs of air preheating heat exchangers are arranged in a parallel and stacked manner.

[0065] The direction of the V-shaped opening depends on the actual site conditions and can be determined based on parameters such as air resistance, flow rate, and temperature at the inlet of the blower.

[0066] The above description is merely a preferred embodiment of this utility model and is not intended to limit the utility model. Various modifications and variations can be made to this utility model by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. An air preheating device utilizing low-grade waste heat, characterized in that, It includes an insulated air duct arranged at the air inlet of the blower. The insulated air duct is equipped with at least two sets of paired air preheating heat exchangers. The two sets of air preheating heat exchangers are arranged in a V-shape along the center line of the insulated air duct, and the opening of the V-shape faces the air inlet or outlet of the insulated air duct. The air preheating heat exchangers receive heat from the waste heat of the condenser, the waste heat of the primary water return water of the heating network, the desulfurization slurry, or the saturated wet flue gas after desulfurization, and preheat the air before it enters the blower.

2. The air preheating device utilizing low-grade waste heat as described in claim 1, characterized in that, The air preheating heat exchanger is connected to the waste heat recovery heat exchanger through a pipeline. The waste heat recovery heat exchanger transfers the waste heat from the condenser, desulfurization slurry, or saturated wet flue gas after desulfurization to the air preheating heat exchanger.

3. The air preheating device utilizing low-grade waste heat as described in claim 1, characterized in that, The air preheating heat exchanger is connected to the waste heat recovery heat exchanger through a pipeline. The waste heat recovery heat exchanger is placed in the desulfurization slurry and exchanges heat with the desulfurization slurry through the waste heat recovery heat exchanger, transferring the heat in the desulfurization slurry to the air preheating heat exchanger through the working medium.

4. The air preheating device utilizing low-grade waste heat as described in claim 1, characterized in that, The air preheating heat exchanger is connected to the waste heat recovery heat exchanger through a pipeline. The waste heat recovery heat exchanger is arranged in the flue and located in the saturated wet flue gas between the desulfurization tower and the demister. The waste heat recovery heat exchanger exchanges heat with the saturated wet flue gas, transferring the heat in the saturated wet flue gas to the air preheating heat exchanger through the working medium.

5. The air preheating device utilizing low-grade waste heat as described in claim 1, characterized in that, The air preheating heat exchanger is connected to the waste heat recovery heat exchanger through a pipeline. The waste heat recovery heat exchanger is arranged in the circulation loop of the desulfurization slurry. The waste heat recovery heat exchanger exchanges heat with the desulfurization slurry, and transfers the heat in the desulfurization slurry to the air preheating heat exchanger through the working medium.

6. The air preheating device utilizing low-grade waste heat as described in claim 5, characterized in that, The circulation loop of the desulfurization slurry includes a slurry pump, a waste heat recovery heat exchanger, and a desulfurization tower connected by pipelines. The slurry pump drives the desulfurization slurry to circulate between the waste heat recovery heat exchanger and the desulfurization tower.

7. The air preheating device utilizing low-grade waste heat as described in claim 6, characterized in that, The desulfurization tower is connected to the flue gas duct, through which flue gas flows and desulfurization slurry absorbs sulfur-containing substances in the flue gas.

8. The air preheating device utilizing low-grade waste heat as described in claim 1, characterized in that, The inlet pipe of the air preheating heat exchanger is connected to the inlet pipe of the condenser, and the outlet pipe of the air preheating heat exchanger is connected to the outlet pipe of the condenser.

9. The air preheating device utilizing low-grade waste heat as described in claim 8, characterized in that, An expansion tank is also provided between the water outlet pipe of the air preheating heat exchanger and the water outlet pipe of the condenser.

10. The air preheating device utilizing low-grade waste heat as described in claim 1, characterized in that, The air preheating heat exchanger and the condenser's inlet pipe receive primary water return from the heating network. After the air preheating heat exchanger preheats the air, the resulting return water is returned to the condenser through a pipeline.

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