Coal-fired boiler waste heat utilization device

Abstract

The utility model provides a coal-fired boiler waste heat utilization device. The coal-fired boiler waste heat utilization device comprises a boiler and an air pre-heater. The primary fan is connected with a primary air inlet of the boiler through the air pre-heater and the coal mill in sequence; the secondary fan is connected with a secondary air inlet of the boiler through the air pre-heater; the boiler is further sequentially connected with a turboset, a condenser and an economizer. The condenser is connected with the air cooling tower to form a loop; a heat exchanger group is arranged on the water return pipeline between the condenser and the air cooling tower; and the primary fan and the secondary fan are respectively connected with the heat exchanger group. According to the device, heat in return water of circulating cooling water of the condenser is recycled by arranging the heat exchanger set, primary air and secondary air of the boiler are heated, and an additional heating device is not needed; the negative phenomenon that the cold end of the air pre-heater is corroded when the primary air and the secondary air which are low in temperature enter the air pre-heater can be effectively avoided, and the defect that an existing device is high in energy consumption due to the fact that a heater is adopted to avoid the cold end corrosion of the air pre-heater is overcome.

Description

Technical Field

[0001] This application relates to the field of boiler energy-saving technology, and in particular to a waste heat utilization device for coal-fired boilers. Background Technology

[0002] my country's power supply is still mainly based on thermal power generation, and the main energy source for thermal power generation is coal. In the process of thermal power generation, fuel is burned in the furnace of a boiler, heating the water in the water-cooled walls of the furnace to generate steam, which converts the chemical energy of the fuel into heat energy. The steam pressure drives the turbine to rotate, converting the heat energy into mechanical energy. Then the turbine drives the generator to rotate, converting the mechanical energy into electrical energy to achieve the purpose of power generation.

[0003] During boiler operation, the primary and secondary air required for boiler combustion are usually drawn from outside the boiler room. In order to ensure the air inlet temperature of the air preheater and prevent cold-end corrosion of the air preheater, in seasons or regions with low temperatures, air heaters are usually installed, using steam or electricity as energy to heat the air inlet. Obviously, this heating method requires additional energy consumption. Utility Model Content

[0004] This application provides a waste heat utilization device for coal-fired boilers, which solves the problem of high energy consumption caused by the use of heaters in existing devices to avoid cold-end corrosion of the air preheater.

[0005] This application provides a waste heat utilization device for a coal-fired boiler, including a boiler and an air preheater;

[0006] The primary air fan is connected to the primary air inlet of the boiler in sequence through the air preheater and the coal mill;

[0007] The secondary air fan is connected to the secondary air inlet of the boiler via the air preheater;

[0008] The boiler is also connected in sequence to the steam turbine unit, condenser and economizer;

[0009] The condenser and the air-cooled tower are connected in a loop;

[0010] A heat exchanger assembly is installed on the return water pipeline between the condenser and the air-cooled tower. The primary air fan and the secondary air fan are both connected to the heat exchanger assembly.

[0011] Optionally, a heater is installed on the pipeline between the air preheater and the coal mill;

[0012] The air preheater and coal mill are connected to the tube side of the heater;

[0013] The shell side of the heater is connected in parallel between the condenser and the economizer.

[0014] Optionally, the heat exchanger group includes a first heat exchanger and a second heat exchanger connected in parallel, the first heat exchanger being connected to a primary air fan and the second heat exchanger being connected to a secondary air fan.

[0015] Optionally, the air preheater is also connected to a flue gas treatment unit;

[0016] The flue gas treatment device includes an evaporator, a dust collector, a desulfurization device, and a chimney connected in series.

[0017] The desulfurization unit is also connected in sequence to the desulfurization wastewater pool, the transfer pump, and the evaporation tower.

[0018] Optionally, the desulfurization unit includes a desulfurization tower and a sedimentation tank connected to the desulfurization tower, the sedimentation tank being connected to a desulfurization wastewater tank;

[0019] The sedimentation tank is also connected to a filter press, which is in turn connected to a gypsum storage silo and a desulfurization wastewater tank.

[0020] Optionally, the desulfurization wastewater pond is also connected to an alkali metering pump.

[0021] Optionally, the evaporation tower includes a tower body;

[0022] The bottom of the tower is connected to the flue gas output end of the air preheater via a pipe;

[0023] The bottom of the tower body is equipped with multiple guide plates parallel to the flue gas flow direction;

[0024] A liquid distribution pipe is installed inside the tower, which is located above and close to the guide plate.

[0025] The upper surface of the liquid distribution pipe is equipped with multiple nozzles with the spray direction facing upward;

[0026] The liquid distribution pipe passes through the side wall of the tower and connects to the desulfurization wastewater pool.

[0027] This application provides a waste heat recovery device for coal-fired boilers. By setting up a heat exchanger group, the heat in the return water of the circulating cooling water of the condenser is recovered and the primary and secondary air of the boiler is heated and increased in temperature without the need for additional heating devices. This can effectively solve the problem of cold-end corrosion of the air preheater caused by the low temperature of the primary and secondary air entering the air preheater. It also overcomes the drawback of high energy consumption caused by the use of heaters in existing devices to avoid cold-end corrosion of the air preheater. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of this application 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 some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 A schematic diagram of a waste heat recovery device for a coal-fired boiler provided in an embodiment of this application;

[0030] Figure 2 A schematic diagram of a waste heat recovery device for a coal-fired boiler provided in another embodiment of this application;

[0031] Figure 3 This is a schematic diagram of a flue gas treatment device provided in an embodiment of this application;

[0032] Figure 4 This is a schematic diagram of the structure of an evaporation tower provided in one embodiment of this application;

[0033] Figure 5 This is a top view of the nozzle arrangement provided in one embodiment of this application.

[0034] Explanation of reference numerals in the attached figures:

[0035] 1. Boiler; 2. Air preheater; 3. Coal mill; 4. Air-cooled tower; 5. Flue gas treatment device; 6. Steam turbine unit; 7. Condenser; 8. Heat exchanger group; 9. Heater; 11. Economizer; 21. Primary air fan; 22. Secondary air fan; 51. Evaporator; 52. Dust collector; 53. Desulfurization device; 54. Chimney; 55. Desulfurization wastewater pool; 81. First heat exchanger; 82. Second heat exchanger; 511. Tower body; 512. Baffle plate; 513. Liquid distribution pipe; 514. Nozzle; 530. Transfer pump; 531. Desulfurization tower; 532. Sedimentation tank; 533. Filter press; 534. Gypsum storage silo; 550. Alkali metering pump. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are also within the scope of protection of this application.

[0037] like Figure 1 As shown, this application provides a waste heat utilization device for a coal-fired boiler, including a boiler 1 and an air preheater 2;

[0038] The primary air fan 21 is connected to the primary air inlet of the boiler 1 in sequence through the air preheater 2 and the coal mill 3;

[0039] The secondary air fan 22 is connected to the secondary air inlet of the boiler 1 through the air preheater 2;

[0040] Boiler 1 is also connected in sequence to turbine unit 6, condenser 7 and economizer 11;

[0041] Condenser 7 is connected to air-cooled tower 4 in a loop;

[0042] A heat exchanger group 8 is installed on the return water pipeline between the condenser 7 and the air-cooled tower 4. The primary air fan 21 and the secondary air fan 22 are both connected to the heat exchanger group 8.

[0043] like Figure 1 As shown, during operation, the primary air fan 21 and the secondary air fan 22 are started, and the heat exchange return water of the condenser 7 flows into the heat exchanger group 8 to exchange heat and raise the temperature of the primary and secondary air, thereby reducing the cold end corrosion of the air preheater 2. The raised primary and secondary air are then transferred to the air preheater 2 by the corresponding fans for further heating. The raised secondary air enters the furnace of the boiler 1 from the secondary air input end of the boiler 1. The raised primary air is fed into the pulverizing system of the coal mill 3 and mixed with pulverized coal. After mixing, the primary air is fed into the furnace of the boiler 1 along with the pulverized coal for combustion.

[0044] Fuel (pulverized coal in this application) is burned in the furnace of boiler 1 to generate heat, which heats the water in the water-cooled wall of the furnace to produce high-temperature and high-pressure steam. This high-temperature and high-pressure steam is input into turbine unit 6 to drive the turbine to do work and generate electricity. The temperature and pressure of the steam after doing work are reduced, which is called exhaust steam. A portion of the exhaust steam is fed into a heater installed on the boiler return water pipe (this setting is common knowledge and therefore not shown in the figure. In production, the heater is installed on the pipe between condenser 7 and economizer 11) to heat the boiler condensate. The remaining steam is fed into condenser 7 and condensed by circulating cooling water supplied by air-cooled tower 4.

[0045] After the circulating cooling water cools the steam, it is output from the condenser 7 and then enters the heat exchanger group 8 to heat the primary air and secondary air. Finally, it is sent back to the air-cooled tower 4 for cooling.

[0046] The condensed steam water is heated by a heater in the boiler return water pipe and then returned to the economizer 11 for recycling in the boiler 1.

[0047] After the fuel is burned in the boiler 1, the high-temperature flue gas generated heats the water-cooled wall and is then output through the flue. After the economizer 11 absorbs the heat of the flue gas, it is denitrified and then enters the air preheater 2 to heat the primary and secondary air. The flue gas after heat exchange in the air preheater 2 is then fed into the flue gas treatment section for further processing.

[0048] This application provides a waste heat utilization device for a coal-fired boiler. By setting up a heat exchanger group 8, the heat in the return water of the circulating cooling water of the condenser 7 is recovered and the primary and secondary air of the boiler 1 is heated and increased in temperature without the need for an additional heating device. This can effectively solve the problem of cold end corrosion of the air preheater 2 caused by the low temperature of the primary and secondary air entering the air preheater 2. It also overcomes the drawback of high energy consumption caused by the use of heaters in existing devices to avoid cold end corrosion of the air preheater 2.

[0049] like Figure 2 As shown, optionally, a heater 9 is installed on the pipeline between the air preheater 2 and the coal mill 3;

[0050] Air preheater 2 and coal mill 3 are connected to the tube side of heater 9;

[0051] The shell side of the heater 9 is connected in parallel between the condenser 7 and the economizer 11.

[0052] In this application, to prevent the primary air from becoming too hot and causing spontaneous combustion of pulverized coal, the primary air is fed into the heater 9 to heat the condensate return water of the boiler 1, thereby reducing the temperature of the primary air to a suitable range for input into the coal mill 3. After the primary air and pulverized coal are mixed, they are fed into the furnace of the boiler 1 together with the pulverized coal for combustion.

[0053] After condensation, part of the steam condensate is heated by a heater in the boiler return water pipe, and the other part is fed into the heater 9 to exchange heat with the primary air. Then it is combined with the boiler return water pipe and heated by the heater (because the heater uses steam extracted from the steam turbine for heating, this can save some steam from the steam turbine, and the saved steam can be used for power generation). Finally, it is fed back to the economizer 11 and circulated in the boiler 1.

[0054] like Figure 2 As shown, optionally, the heat exchanger group 8 includes a first heat exchanger 81 and a second heat exchanger 82 connected in parallel. The first heat exchanger 81 is connected to the primary air fan 21, and the second heat exchanger 82 is connected to the secondary air fan 22.

[0055] When in use, the primary air fan 21 and the secondary air fan 22 are started. At the same time, the heat exchange return water of the condenser 7 flows into the heat exchange medium channel of the first heat exchanger 81 and the heat exchange medium channel of the second heat exchanger 82 respectively to exchange heat and raise the temperature of the primary air and the secondary air, so as to reduce the cold end corrosion of the air preheater 2.

[0056] After the circulating cooling water cools the steam, it is output from the condenser 7 and then enters the first heat exchanger 81 and the second heat exchanger 82 respectively to heat the primary air and secondary air. Finally, it is sent back to the air-cooled tower 4 for cooling.

[0057] like Figure 1 and Figure 2 As shown, optionally, the air preheater 2 is also connected to the flue gas treatment device 5;

[0058] The flue gas treatment device 5 includes an evaporator 51, a dust collector 52, a desulfurization device 53 and a chimney 54 connected in series.

[0059] The desulfurization unit 53 is also connected in sequence to the desulfurization wastewater pool 55, the liquid transfer pump 530 and the evaporation tower 51.

[0060] During operation, the high-temperature flue gas generated after the fuel is burned in the boiler 1 heats the water-cooled wall and is then output through the flue. After the economizer 11 absorbs the heat of the flue gas, it undergoes denitrification and then enters the air preheater 2 to heat the primary and secondary air. The flue gas after heat exchange in the air preheater 2 is then fed into the flue gas treatment device 5 for treatment.

[0061] The flue gas first enters the evaporation tower 51 to evaporate and dry the desulfurization wastewater injected into the tower, obtaining crystalline salt and water vapor. This water vapor and inorganic salt particles, mixed with the flue gas, enter the dust collector 52 (such as a bag filter or cyclone dust collector) to separate and collect the crystalline salt particles and dust from the flue gas. The separated flue gas is then drawn and pressurized by an induced draft fan and input into the desulfurization unit 53 for desulfurization. After passing inspection, it is discharged through the chimney 54. The desulfurization wastewater generated during the desulfurization process is transferred to the desulfurization wastewater pool 55 and then transported to the evaporation tower 51 by a transfer pump 530 for evaporation and drying using the preheated flue gas.

[0062] like Figure 3 As shown, optionally, the desulfurization device 53 includes a desulfurization tower 531 and a sedimentation tank 532 connected to the desulfurization tower 531, and the sedimentation tank 532 is connected to the desulfurization wastewater tank 55.

[0063] The sedimentation tank 532 is also connected to the filter press 533, which is connected to the gypsum storage silo 534 and the desulfurization wastewater tank 55 respectively.

[0064] When the flue gas is desulfurized in the desulfurization tower 531, an alkaline absorbent (lime slurry in this application) is used for circulating washing and desulfurization. When the absorbent is saturated, the saturated desulfurization liquid is fed into the sedimentation tank 532 for sedimentation. The supernatant obtained is transferred to the desulfurization wastewater tank 55. The sediment is then transported to the filter press 533 for dewatering. The resulting filter cake is transported to the gypsum storage silo 534 for storage. The filtrate is transferred to the desulfurization wastewater tank 55 and combined with the supernatant. It is then transported to the evaporation tower 51 for evaporation and drying using the preheating of the flue gas.

[0065] like Figure 3 As shown, optionally, the desulfurization wastewater tank 55 is also connected to the alkali metering pump 550.

[0066] In this application, an alkali metering pump 550 is installed to add inorganic alkali to the desulfurization wastewater, adjusting the desulfurization wastewater to alkalinity (e.g., 10~11). When the wastewater is evaporated in the evaporation tower 51, the alkaline desulfurization wastewater can absorb some of the sulfur dioxide in the flue gas, thereby reducing the treatment load of the desulfurization unit.

[0067] like Figure 4 and Figure 5 As shown, optionally, the evaporation tower 51 includes a tower body 511;

[0068] The bottom of tower body 511 is connected to the flue gas output end of air preheater 2 via a pipe;

[0069] Multiple guide plates 512 parallel to the flue gas flow direction are installed at the bottom of the tower body 511.

[0070] A liquid distribution pipe 513 is installed inside the tower body 511. The liquid distribution pipe 513 is located above and close to the guide plate 512.

[0071] The upper surface of the liquid distribution pipe 513 is provided with multiple nozzles 514 with the spray direction facing upward;

[0072] The liquid distribution pipe 513 passes through the side wall of the tower body 511 and connects to the desulfurization wastewater pool 55.

[0073] In operation, flue gas first enters evaporation tower 51 to evaporate and dry the desulfurization wastewater injected into the tower, yielding crystalline salt and water vapor. Specifically, high-temperature flue gas discharged from air preheater 2 enters from the bottom of evaporation tower 51, is evenly distributed by guide plate 512, and continues to rise. Simultaneously, desulfurization wastewater from desulfurization wastewater pool 55 enters evaporation tower 51 and then flows into distribution pipe 513, which distributes it to nozzles 514, where it is sprayed out in a mist. Because the spray direction is upward, the pressure drop of flue gas within evaporation tower 51 is reduced. Furthermore, since the desulfurization wastewater has undergone alkalization, it can absorb some of the sulfur dioxide in the flue gas, thereby reducing the processing load on the desulfurization unit.

[0074] The desulfurization wastewater (essentially a high-concentration inorganic salt solution) is sprayed into a mist and comes into contact with the rising high-temperature flue gas, causing it to heat up. The mist-like desulfurization wastewater heats up and evaporates the water, producing water vapor and inorganic salt particles, thus drying the desulfurization wastewater.

[0075] In this application, the portion of the liquid distribution pipe 513 inside the evaporation tower 51 is composed of multiple concentric circles connected by an intermediate connecting pipe, and the nozzles are arranged on the upper surface of these concentric circular liquid distribution pipes 513.

[0076] A waste heat recovery device for coal-fired boilers operates as follows:

[0077] During operation, the primary air fan 21 and the secondary air fan 22 are started. Simultaneously, the heat exchange return water from the condenser 7 flows into the heat exchange medium channels of the first heat exchanger 81 and the second heat exchanger 82, respectively, to heat and raise the temperature of the primary and secondary air, thereby reducing cold-end corrosion of the air preheater 2. The heated primary and secondary air are then transferred to the air preheater 2 by the corresponding fans for further heating. The heated secondary air enters the furnace of the boiler 1 from the secondary air inlet. To prevent the heated primary air from becoming too hot and causing spontaneous combustion of pulverized coal, it needs to be fed into the heater 9 to heat the condensate return water of the boiler 1, reducing the temperature of the primary air to a suitable range for input into the coal mill 3. The primary air is then fed into the pulverizing system of the coal mill 3 and mixed with pulverized coal before being fed into the furnace of the boiler 1 for combustion.

[0078] Fuel (pulverized coal in this application) is burned in the furnace of boiler 1 to generate heat, which heats the water in the water-cooled wall of the furnace to produce high-temperature and high-pressure steam. This high-temperature and high-pressure steam is input into turbine unit 6 to drive the turbine to do work and generate electricity. The temperature and pressure of the steam after doing work are reduced, which is called exhaust steam. A portion of the exhaust steam is fed into a heater installed on the boiler return water pipe (this setting is common knowledge and therefore not shown in the figure. In production, the heater is installed on the pipe between condenser 7 and economizer 11) to heat the boiler condensate. The remaining steam is fed into condenser 7 and condensed by circulating cooling water supplied by air-cooled tower 4.

[0079] After the circulating cooling water cools the steam, it is output from the condenser 7 and then enters the first heat exchanger 81 and the second heat exchanger 82 respectively to heat the primary air and secondary air. Finally, it is sent back to the air-cooled tower 4 for cooling.

[0080] The condensed steam water is partially heated by a heater in the boiler return water pipe, and the other part is fed into the heater 9 to exchange heat with the primary air. Then it is combined with the boiler return water pipe and heated by the heater (because the heater uses steam extracted from the steam turbine for heating, this can save some steam from the steam turbine, and the saved steam can be used for power generation). Finally, it is fed back to the economizer 11 and circulated in the boiler 1.

[0081] After the fuel is burned in the boiler 1, the high-temperature flue gas generated heats the water-cooled wall and is then output through the flue. After the economizer 11 absorbs the heat of the flue gas, it is denitrified and then enters the air preheater 2 to heat the primary and secondary air. The flue gas after heat exchange in the air preheater 2 is then fed into the flue gas treatment device 5 for treatment.

[0082] The flue gas first enters the evaporation tower 51 to evaporate and dry the desulfurization wastewater injected into the tower, yielding crystalline salt and water vapor. Specifically, the high-temperature flue gas discharged from the air preheater 2 enters the bottom of the evaporation tower 51, is evenly distributed by the guide plate 512, and continues to rise. Simultaneously, the desulfurization wastewater from the desulfurization wastewater pool 55 enters the distribution pipe 513, and is then distributed to the nozzles 514, where it is sprayed out in a mist. Because the spray direction is upward, the pressure drop of the flue gas within the evaporation tower 51 is reduced. Furthermore, since the desulfurization wastewater has undergone alkalization, it can absorb some of the sulfur dioxide in the flue gas, thereby reducing the processing load on the desulfurization unit.

[0083] The desulfurization wastewater (essentially a high-concentration inorganic salt solution) is sprayed into a mist and comes into contact with the rising high-temperature flue gas, causing it to heat up. The heated desulfurization wastewater evaporates the water, producing water vapor and inorganic salt particles, thus drying the desulfurization wastewater. These water vapor and inorganic salt particles, along with the flue gas, enter the dust collector 52 (such as a bag filter or cyclone dust collector) to separate and collect the crystalline salt particles and dust in the flue gas. The separated flue gas is then drawn and pressurized by an induced draft fan and fed into the desulfurization tower 531 for desulfurization. After passing the test, it is discharged through the chimney 54.

[0084] When the flue gas is desulfurized in the desulfurization tower 531, an alkaline absorbent (lime slurry in this application) is used for circulating washing and desulfurization. When the absorbent is saturated, the saturated desulfurization liquid is fed into the sedimentation tank 532 for sedimentation. The supernatant obtained is transferred to the desulfurization wastewater tank 55. The sediment is then transported to the filter press 533 for dewatering. The resulting filter cake is transported to the gypsum storage silo 534 for storage. The filtrate is transferred to the desulfurization wastewater tank 55 and combined with the supernatant. The pH is then adjusted to alkaline (e.g., 10-11) by the alkali metering pump 550, and then transported to the evaporation tower 51 by the transfer pump 530 for evaporation and drying using the preheating of the flue gas.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A waste heat recovery device for a coal-fired boiler, characterized in that, Includes a boiler (1) and an air preheater (2); The primary air fan (21) is connected to the primary air inlet of the boiler (1) in sequence through the air preheater (2) and the coal mill (3); The secondary air fan (22) is connected to the secondary air inlet of the boiler (1) through the air preheater (2); The boiler (1) is also connected in sequence to the steam turbine unit (6), the condenser (7) and the economizer (11); The condenser (7) and the air-cooled tower (4) are connected in a loop; A heat exchanger assembly (8) is installed on the return water pipeline between the condenser (7) and the air-cooled tower (4), and the primary air fan (21) and the secondary air fan (22) are respectively connected to the heat exchanger assembly (8).

2. The waste heat utilization device for coal-fired boilers according to claim 1, characterized in that, A heater (9) is installed on the pipeline between the air preheater (2) and the coal mill (3); The air preheater (2) and the coal mill (3) are connected to the tube side of the heater (9); The shell side of the heater (9) is connected in parallel between the condenser (7) and the economizer (11).

3. The waste heat utilization device for coal-fired boilers according to claim 1, characterized in that, The heat exchanger group (8) includes a first heat exchanger (81) and a second heat exchanger (82) connected in parallel. The first heat exchanger (81) is connected to a primary air fan (21), and the second heat exchanger (82) is connected to a secondary air fan (22).

4. The waste heat recovery device for coal-fired boilers according to any one of claims 1-3, characterized in that, The air preheater (2) is also connected to the flue gas treatment device (5); The flue gas treatment device (5) includes an evaporator (51), a dust collector (52), a desulfurization device (53), and a chimney (54) connected in series. The desulfurization device (53) is also connected in sequence to the desulfurization wastewater pool (55), the liquid transfer pump (530), and the evaporation tower (51).

5. The waste heat utilization device for a coal-fired boiler according to claim 4, characterized in that, The desulfurization device (53) includes a desulfurization tower (531) and a sedimentation tank (532) connected to the desulfurization tower (531), and the sedimentation tank (532) is connected to the desulfurization wastewater tank (55); The sedimentation tank (532) is also connected to a filter press (533), which is connected to a gypsum storage silo (534) and a desulfurization wastewater tank (55).

6. The waste heat utilization device for a coal-fired boiler according to claim 4, characterized in that, The desulfurization wastewater pool (55) is also connected to an alkali metering pump (550).

7. The waste heat utilization device for a coal-fired boiler according to claim 4, characterized in that, The evaporation tower (51) includes a tower body (511); The bottom of the tower body (511) is connected to the flue gas output end of the air preheater (2) via a pipe; The bottom of the tower body (511) is provided with multiple guide plates (512) that are parallel to the flue gas flow direction. The tower body (511) is provided with a liquid distribution pipe (513), which is located above the guide plate (512) and close to the guide plate (512). The upper surface of the liquid distribution pipe (513) is provided with multiple nozzles (514) with the spray direction facing upward. The liquid distribution pipe (513) passes through the side wall of the tower body (511) and is connected to the desulfurization wastewater pool (55).

Images