Boiler waste heat recovery system

Abstract

The utility model provides a boiler waste heat recovery system. The boiler waste heat recovery system comprises a first heat exchanger, a second heat exchanger, a deaerator, a blowdown flash tank and a water supply device. Waste heat recovery water is contained in the water supply device, the water supply device is connected with the first heat exchanger and the second heat exchanger, the first heat exchanger and the second heat exchanger are connected in parallel, and the water supply device provides the waste heat recovery water for the first heat exchanger and the second heat exchanger; dead steam is discharged from the deaerator, the deaerator is connected with the first heat exchanger and provides the dead steam for the first heat exchanger, and the dead steam heats waste heat recovery water flowing through the first heat exchanger; high-temperature boiler water is contained in the blowdown flash tank, the blowdown flash tank is connected with the second heat exchanger and provides the high-temperature boiler water for the second heat exchanger, and the high-temperature boiler water heats waste heat recovery water flowing through the second heat exchanger. Waste heat recovery water flows through the first heat exchanger and the second heat exchanger and is heated, the temperature difference between a heat source and the waste heat recovery water is large, the heat transfer effect is better, and more waste heat can be recovered.

Description

Technical Field

[0001] The present application relates to the field of heat recovery technology, and in particular to a boiler waste heat recovery system. Background Art

[0002] At present, it is often necessary to discharge impurities in the boiler during operation. Generally, in the process of generating steam in the boiler, high-temperature boiler water on the surface of the drum is discharged to remove surface impurities. The high-temperature boiler water flows into the blowdown expansion tank. The usual method is to use the blowdown expansion tank to reduce the steam blowdown pressure and expand the capacity of the boiler. The blowdown water is adiabatically expanded in the blowdown expansion tank to separate into secondary steam and high-temperature boiler water, and then discharged.

[0003] At the same time, in order to prevent the oxygen in the steam from corroding the steam supply equipment and pipelines, the boiler system often needs to use a deaerator for deoxygenation. The working principle of the deaerator is to heat the feed water and condensate entering the deaerator through steam heating to the saturation temperature corresponding to the internal pressure of the deaerator, so that the oxygen dissolved in the water is precipitated from the water and discharged to the external space. The discharged gas is exhaust steam, which contains some waste heat.

[0004] The discharged high-temperature boiler water and exhaust steam have high temperatures, resulting in a large amount of heat loss and waste. The prior art discloses a system for utilizing waste heat from a boiler fixed-discharge expansion tank and a deaerator. The system sequentially provides a medium to a first heat exchanger and a second heat exchanger, and simultaneously provides exhaust steam and high-temperature boiler water to the first heat exchanger and the second heat exchanger, respectively, so that the exhaust steam and the high-temperature boiler water sequentially heat the medium, thereby partially recovering the heat energy. During the heat transfer process, when other conditions remain unchanged, the greater the temperature difference between two objects, the greater the heat energy transferred between the objects. Therefore, when the exhaust steam and the high-temperature boiler water continuously and sequentially recover heat from the medium, at least one of the exhaust steam and the high-temperature boiler water has a poor heat exchange effect with the medium, thereby insufficiently recovering the waste heat of the boiler. Utility Model Content

[0005] Based on this, the present application provides a boiler waste heat recovery system to improve the problem of insufficient waste heat recovery and utilization of the boiler system in the prior art.

[0006] The boiler waste heat recovery system provided in the present application includes a first heat exchanger, a second heat exchanger, a deaerator, a blowdown expansion tank and a water supply device;

[0007] The water supply device contains waste heat recovery water, the water supply device is connected to both the first heat exchanger and the second heat exchanger, the first heat exchanger and the second heat exchanger are connected in parallel, and the water supply device provides waste heat recovery water to the first heat exchanger and the second heat exchanger respectively;

[0008] Exhaust steam is discharged from the deaerator, the deaerator is connected to the first heat exchanger, and provides the exhaust steam to the first heat exchanger, and the exhaust steam heats the waste heat recovery water flowing through the first heat exchanger;

[0009] The blowdown expansion tank is filled with high-temperature boiler water, and the blowdown expansion tank is connected to the second heat exchanger and provides the high-temperature boiler water to the second heat exchanger. The high-temperature boiler water heats the waste heat recovery water flowing through the second heat exchanger.

[0010] In one of the embodiments, the water supply device includes a low-temperature water tank, and the number of the low-temperature water tanks is at least one. The first heat exchanger and the second heat exchanger are respectively connected to at least one of the low-temperature water tanks.

[0011] In one embodiment, the waste heat recovery water is soft water.

[0012] In one embodiment, the boiler waste heat recovery system also includes a high-temperature water tank, and the high-temperature water tank is provided as at least one. The first heat exchanger and the second heat exchanger are respectively connected to at least one of the high-temperature water tanks, and the high-temperature water tank is used to store the heated waste heat recovery water.

[0013] In one of the embodiments, the high temperature water tank is connected to the second heat exchanger, and the high temperature water tank provides the heated waste heat recovery water to the second heat exchanger.

[0014] In one embodiment, the blowdown expansion tank is also filled with flash steam, the blowdown expansion tank is connected to the deaerator, and provides the flash steam to the deaerator, the flash steam is mixed with the exhaust steam in the deaerator, and the deaerator also provides the flash steam to the first heat exchanger, and the flash steam also heats the waste heat recovery water flowing through the first heat exchanger.

[0015] In one embodiment, a return air pipe is further provided between the first heat exchanger and the deaerator, and the deaerator is provided with a waste gas discharge port. The exhaust steam heats the waste heat recovery water flowing through the first heat exchanger, and is then transported to the deaerator through the return air pipe, and is discharged from the deaerator through the waste gas discharge port.

[0016] In one of the embodiments, a liquid level sensor is provided on the sewage expansion tank, the second heat exchanger is provided with a high-temperature boiler water drain outlet, and a control valve is provided at the high-temperature boiler water drain outlet. When the liquid level sensor measures that the high-temperature boiler water level in the sewage expansion tank exceeds the safe liquid level, the control valve automatically opens to increase the discharge flow rate of the high-temperature boiler water.

[0017] In one embodiment, the first heat exchanger is a condenser.

[0018] In one embodiment, the second heat exchanger is a plate heat exchanger.

[0019] The boiler waste heat recovery system provided by the present application is provided with a first heat exchanger and a second heat exchanger connected in parallel with a water supply device, and the deaerator is connected to the first heat exchanger and the exhaust steam is transported to the heat exchanger as the first heat source, and the blowdown expansion tank is connected to the second heat exchanger and the high-temperature boiler water is used as the second heat source, so that the exhaust steam and the high-temperature boiler water can be respectively exchanged with the waste heat recovery water provided by the water supply device in the first heat exchanger and the second heat exchanger to realize the recovery and utilization of the boiler waste heat. Compared with the design in which the waste heat recovery water first flows through the first heat exchanger and then flows through the second heat exchanger, under the condition that other conditions remain unchanged, since the water is not heated twice, the present application can make the temperature difference between the water and the heat source in the heat exchanger larger, thereby making the heat transfer effect better and improving the heat energy recovery rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the structure of a boiler waste heat recovery system in one embodiment.

[0021] In the figure: 1. Deaerator; 2. Sewage expansion tank; 3. Low-temperature water tank; 4. High-temperature water tank; 5. Second heat exchanger; 6. First heat exchanger; 7. Control gate valve; 8. Water pump; 9. Control valve; 10. Cooling water pool; 11-Liquid level sensor. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0023] It should be noted that the illustrations provided in this embodiment are only used to schematically illustrate the basic concept of the present invention. Therefore, the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0024] The structures, proportions, sizes, etc. illustrated in the drawings in this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with the technology. They are not used to limit the conditions under which the present invention can be implemented, and therefore have no substantive technical significance. Any structural modification, change in proportion or adjustment of size shall still fall within the scope of the technical contents disclosed in the present invention without affecting the effects and purposes that can be achieved by the present invention.

[0025] The directions or positional relationships indicated by the terms "upper", "lower", "left", "right", "middle", "longitudinal", "lateral", "horizontal", "inner", "outer", "radial", "circumferential" and the like in this specification are based on the directions or positional relationships shown in the drawings and are only for the convenience of simplifying the description. They do not indicate or imply that the devices or elements referred to must have a specific direction, be constructed and operate in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0026] An embodiment of the present application provides a boiler waste heat recovery system, including a first heat exchanger 6, a second heat exchanger 5, a deaerator 1, a blowdown expansion tank 2 and a water supply device; the water supply device is filled with waste heat recovery water, the water supply device is connected to both the first heat exchanger 6 and the second heat exchanger 5, the first heat exchanger 6 and the second heat exchanger 5 are connected in parallel, and the water supply device provides waste heat recovery water to the first heat exchanger 6 and the second heat exchanger 5 respectively; exhaust steam is discharged from the deaerator 1, the deaerator 1 is connected to the first heat exchanger 6, and the exhaust steam is provided to the first heat exchanger 6, and the exhaust steam heats the waste heat recovery water flowing through the first heat exchanger 6; the blowdown expansion tank 2 is filled with high-temperature boiler water, the blowdown expansion tank 2 is connected to the second heat exchanger 5, and the high-temperature boiler water is provided to the second heat exchanger 5, and the high-temperature boiler water heats the waste heat recovery water flowing through the second heat exchanger 5.

[0027] The principle of thermal deoxygenation is to heat water to boiling point, so that the solubility of oxygen decreases and escapes, and then remove the oxygen generated on the water surface. Figure 1 As shown, steam needs to be introduced into the deaerator 1 to heat the water in the deaerator 1. In addition, in order to remove impurities on the surface of the boiler, the boiler will discharge part of the sewage, and the high-temperature boiler water of the boiler will flow to the sewage expansion tank 2 through the pipeline. Therefore, under normal circumstances, the sewage expansion tank 2 is connected to the sewage outlet of the boiler, and the boiler sewage flows into the expansion tank 2, and expands and separates into flash steam and high-temperature boiler water in the sewage expansion tank 2.

[0028] like Figure 1 As shown, in this embodiment, it is exemplified that the emissions from the boiler system may include exhaust steam in the deaerator 1 and high-temperature boiler water in the blowdown expansion tank 2. Since both the exhaust steam and the high-temperature boiler water have relatively high heat, their heat can be recovered through the first heat exchanger 6 and the second heat exchanger 5.

[0029] The deaerator 1 can be connected to the first heat exchanger 6, and the exhaust steam in the deaerator 1 can be used as a heat source for heating in the first heat exchanger 6. The blowdown expansion tank 2 can be connected to the second heat exchanger 5, and the high-temperature boiler water in the blowdown expansion tank 2 can be used as a heat source for heating in the second heat exchanger 5. The heat sources in the first heat exchanger 6 and the second heat exchanger 5 can be used to heat the waste heat recovery water in the first heat exchanger 6 and the second heat exchanger 5, respectively. The waste heat recovery water in the first heat exchanger 6 and the second heat exchanger 5 can be provided by the water supply device, respectively, and the flow path of the waste heat recovery water provided by the water supply device to the first heat exchanger 6 and the second heat exchanger 5 constitutes a parallel connection mode. When the waste heat recovery water provided by the water supply device flows through the first heat exchanger 6, the exhaust steam can heat the waste heat recovery water in the first heat exchanger 6; and when the waste heat recovery water provided by the water supply device flows through the second heat exchanger 5, the high-temperature boiler water can heat the waste heat recovery water in the second heat exchanger 5. By rationally using waste heat recovery water, the waste heat of the boiler system can be recovered and utilized.

[0030] It is not difficult to understand that the boiler waste heat recovery system of the present application is provided with a first heat exchanger 6 and a second heat exchanger 5 connected in parallel with the water supply device, the deaerator 1 is connected to the first heat exchanger 6, and the exhaust steam is transported to the first heat exchanger 6 as the first heat source; at the same time, the blowdown expansion tank 2 is connected to the second heat exchanger 5, and the high-temperature boiler water is used as the second heat source, so that the exhaust steam in the first heat exchanger 6 and the high-temperature boiler water in the second heat exchanger 5 are respectively exchanged with the waste heat recovery water provided by the water supply device to realize the recovery and utilization of the boiler waste heat. Compared with the design in which the waste heat recovery water first flows through the first heat exchanger and then flows through the second heat exchanger, under the condition that other conditions remain unchanged, since the water is not heated twice, the present application can make the temperature difference between the waste heat recovery water and the heat sources in the first heat exchanger 6 and the second heat exchanger 5 larger, thereby making the heat transfer effect better and increasing the amount of heat energy recovery.

[0031] Optionally, the water supply device includes at least one low-temperature water tank 3, and the water in the low-temperature water tank 3 flows to the first heat exchanger 6 and the second heat exchanger 5 through pipelines.

[0032] In this embodiment, it is exemplified that the water supply device may include a low-temperature water tank 3, and the waste heat recovery water may be arranged in the low-temperature water tank 3. At least one low-temperature water tank 3 is provided. When only one low-temperature water tank 3 is provided, the first heat exchanger 6 and the second heat exchanger 5 are both connected to the low-temperature water tank 3, and the low-temperature water tank 3 may provide waste heat recovery water for the first heat exchanger 6 and the second heat exchanger 5 at the same time. Of course, in some embodiments, the low-temperature water tank 3 may also be provided in multiple numbers, such as two, three or four, and any one of the first heat exchanger 6 and the second heat exchanger 5 is connected to at least one low-temperature water tank 3; in other words, the first heat exchanger 6 and the second heat exchanger 5 may be provided with waste heat recovery water by one or more low-temperature water tanks 3.

[0033] In this embodiment, the water supply device may further include a water pump 8, which may be provided on the low-temperature water tank 3. The water pump 8 is used to pump the waste heat recovery water from the low-temperature water tank 3 to the first heat exchanger 6 or the second heat exchanger 5 to improve the water supply efficiency, or to realize the automatic pumping and stopping of the waste heat recovery water. Of course, in some embodiments, the low-temperature water tank 3 may also be set at a high place to provide the waste heat recovery water to the first heat exchanger 6 and the second heat exchanger 5 by using the pressure difference.

[0034] Optionally, the waste heat recovery water is soft water.

[0035] In this embodiment, the water in the low-temperature water tank 3 can be soft water. Soft water is water with a low content of hardness salts such as calcium and magnesium. Soft water can reduce the scaling rate of the boiler system and reduce the risk of the boiler system.

[0036] Optionally, the boiler waste heat recovery system also includes a high-temperature water tank 4, which is provided with at least one high-temperature water tank 4. The first heat exchanger 6 and the second heat exchanger 5 are respectively connected to at least one high-temperature water tank 4, and the high-temperature water tank 4 is used to store heated waste heat recovery water.

[0037] In this embodiment, it is exemplified that the heated waste heat recovery water is high temperature water, and the boiler waste heat recovery system may include a high temperature water tank 4 for storing high temperature water, and the high temperature water tank 4 is provided with at least one. When the high temperature water tank 4 is provided with only one, the first heat exchanger 6 and the second heat exchanger 5 are both connected to the high temperature water tank 4, and the high temperature water tank 4 can simultaneously collect and store the waste heat recovery water heated by the first heat exchanger 6 and the second heat exchanger 5. Of course, in some embodiments, the high temperature water tank 4 may also be provided with multiple, such as two, three or four, and any one of the first heat exchanger 6 and the second heat exchanger 5 is connected with at least one high temperature water tank 4; in other words, the waste heat recovery water heated in the first heat exchanger 6 and the second heat exchanger 5 can be collected and stored by one or more high temperature water tanks 4.

[0038] Since multiple low-temperature water tanks 3 and high-temperature water tanks 4 can be provided, in some embodiments, the low-temperature water tank can provide different waste heat recovery water, and the first heat exchanger 6 and the second heat exchanger 5 respectively heat different waste heat recovery water, and finally flow into different high-temperature water tanks 4 respectively. This design enables the boiler waste heat recovery system of the present application to heat different types of water, thereby improving the adaptability of the boiler waste heat recovery system to different media to be heated.

[0039] Optionally, the high-temperature water tank 4 is connected to the second heat exchanger 5 , and the high-temperature water tank 4 provides the heated waste heat recovery water to the second heat exchanger 5 .

[0040] In this embodiment, it is exemplified that the water supply device is connected to the high-temperature water tank 4. Specifically, the water outlet of the high-temperature water tank 4 is connected to the water supply pipe of the water supply device. Since the second heat exchanger 5 is also connected to the water supply pipe, the heated waste heat recovery water in the high-temperature water tank 4 flows through the water supply pipe to the second heat exchanger 5 for heat exchange. Since the heated waste heat recovery water can be heated again and flow back to the high-temperature water tank 4, the water in the high-temperature water tank can achieve the effect of maintaining high temperature. In some embodiments, a plurality of valves and water pumps can be provided on the water supply pipe of the water supply device. The valves and water pumps cooperate to control the type and flow of water flowing into the second heat exchanger 5. In some embodiments, one of the valves is opened near the water outlet of the high-temperature water tank to control the flow of the heated waste heat recovery water provided by the high-temperature water tank 4 to the second heat exchanger 5.

[0041] Optionally, the blowdown expansion tank 2 is also filled with flash steam, and the blowdown expansion tank 2 is connected to the deaerator 1 and provides flash steam to the deaerator 1. The flash steam is mixed with the exhaust steam in the deaerator 1. The deaerator 1 also provides flash steam to the first heat exchanger 6, and the flash steam also heats the waste heat recovery water flowing through the first heat exchanger 6.

[0042] In this embodiment, in some embodiments, the flash steam in the blowdown expansion tank 2 is transported to the deaerator 1 through a pipeline, so that the flash steam and the exhaust steam are mixed in the deaerator 1, and then enter the first heat exchanger 6 for heat exchange. Therefore, the heat discharged by the boiler is recovered in both the flash steam and the high-temperature boiler water, realizing efficient recovery of the waste heat of the boiler.

[0043] Optionally, a return air pipe is further provided between the first heat exchanger 6 and the deaerator 1, and the deaerator 1 is provided with a waste gas discharge port. The exhaust steam heats the waste heat recovery water flowing through the first heat exchanger 6, and is then transported to the deaerator 1 through the return air pipe, and is discharged from the deaerator 1 through the waste gas discharge port.

[0044] In this embodiment, it is exemplified that the exhaust steam sent to the first heat exchanger 6 in the deaerator 1 completes heat transfer and then flows back to the deaerator 1 through the return air pipeline. The deaerator 1 is provided with a waste gas discharge port, and the utilized exhaust steam flowing back to the deaerator 1 is discharged from the deaerator 1 through the waste gas discharge port.

[0045] Optionally, a liquid level sensor 11 is provided on the sewage expansion tank 2, the second heat exchanger 5 is provided with a high-temperature boiler water drain outlet, and a control valve 9 is provided at the high-temperature boiler water drain outlet. When the liquid level sensor 11 measures that the high-temperature boiler water level in the sewage expansion tank 2 exceeds the safe liquid level, the control valve 9 automatically opens to increase the discharge flow of the high-temperature boiler water.

[0046] In this embodiment, it is explained by way of example that since the high-temperature boiler water level in the sewage expansion tank 2 should not be too high, otherwise it will affect the safety of sewage expansion, a liquid level sensor 11 is provided to monitor the liquid level of the high-temperature boiler water in the sewage expansion tank 2 in real time, and a control gate valve 7 is provided between the pipeline connecting the sewage expansion tank 2 and the second heat exchanger 5. The second heat exchanger 5 is provided with a high-temperature boiler water drain port. Generally, the high-temperature boiler water is discharged from the high-temperature boiler water drain port after completing heat exchange in the second heat exchanger 5. The high-temperature boiler water drain port is provided with a control valve 9. When the liquid level sensor 11 measures that the high-temperature boiler water level in the sewage expansion tank 2 exceeds the safe liquid level, the control valve 9 and the control gate valve 7 can automatically increase the flow rate to increase the high-temperature boiler water discharge flow rate so that the liquid level drops back to the safe liquid level range. When the high-temperature boiler water level drops back to the safe range, the flow rates of the control valve 9 and the control gate valve 7 are reduced to the permanent state.

[0047] Optionally, the first heat exchanger 6 is a condenser.

[0048] In this embodiment, the exhaust steam is used as a heat source, and the condenser transfers heat energy to the waste heat recovery water flowing through the first heat exchanger 6, so that the waste heat recovery water is heated. Optionally, the first heat exchanger 6 is a flue gas condenser. Furthermore, since the exhaust steam contains corrosive gases such as oxygen, in order to reduce the corrosion of oxygen to the equipment, the first heat exchanger 6 can be a flue gas condenser made of anti-corrosion materials or with a corrosion-resistant coating on the surface.

[0049] Optionally, the second heat exchanger 5 is a plate heat exchanger.

[0050] In this embodiment, it is exemplified that the plate heat exchanger includes a detachable plate heat exchanger, a welded plate heat exchanger, a spiral plate heat exchanger, a plate coil heat exchanger, etc., and high-temperature boiler water is used as a heat source. The heat energy of the plate heat exchanger is transferred to the waste heat recovery water flowing therethrough, so that the waste heat recovery water is heated.

[0051] The blowdown expansion tank 2 in this embodiment may include one or more of a continuous blowdown expansion tank and a periodic blowdown expansion tank. The boiler waste heat recovery system in this embodiment also includes a cooling water pool 10, which is used to collect condensed water generated by condensation of exhaust steam in the first heat exchanger 6 and high-temperature boiler water after heat exchange in the second heat exchanger 5.

[0052] The implementation principle of a boiler waste heat recovery system provided in the embodiment of the present application is:

[0053] When recovering waste heat, the low temperature water tank provides waste heat recovery water to the first heat exchanger 6, and the deaerator 1 provides exhaust steam to the first heat exchanger 6; at the same time, the low temperature water tank 3 provides waste heat recovery water to the second heat exchanger 5, and the blowdown expansion tank 2 provides high temperature boiler water to the second heat exchanger 5. The boiler waste heat recovery system is provided with a first heat exchanger 6 and a second heat exchanger 5 connected in parallel with a water supply device, the deaerator 1 is connected to the first heat exchanger 6 and the exhaust steam is transported to the first heat exchanger 6 as the first heat source, and the blowdown expansion tank 2 is connected to the second heat exchanger 5 and the high temperature boiler water is used as the second heat source, so that the exhaust steam and the high temperature boiler water can be respectively exchanged with the waste heat recovery water provided by the water supply device in the first heat exchanger 6 and the second heat exchanger 5, so as to realize the recovery and utilization of the boiler waste heat. Compared with the design in which the waste heat recovery water first flows through the first heat exchanger 6 and then flows through the second heat exchanger 5, when other conditions remain unchanged, since the water is not heated twice, the present application can make the temperature difference between the water and the heat source larger, thereby making the heat transfer effect better and increasing the heat energy recovery rate.

[0054] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0055] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the utility model patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A boiler waste heat recovery system, characterized in that: The boiler waste heat recovery system comprises a first heat exchanger (6), a second heat exchanger (5), a deaerator (1), a blowdown expansion tank (2) and a water supply device; The water supply device contains waste heat recovery water, the water supply device is connected to both the first heat exchanger (6) and the second heat exchanger (5), the first heat exchanger (6) and the second heat exchanger (5) are connected in parallel, and the water supply device provides waste heat recovery water to the first heat exchanger (6) and the second heat exchanger (5) respectively; Exhaust steam is discharged from the deaerator (1), the deaerator (1) is connected to the first heat exchanger (6), and provides the exhaust steam to the first heat exchanger (6), and the exhaust steam heats the waste heat recovery water flowing through the first heat exchanger (6); The blowdown expansion tank (2) is filled with high-temperature boiler water. The blowdown expansion tank (2) is connected to the second heat exchanger (5) and provides the high-temperature boiler water to the second heat exchanger (5). The high-temperature boiler water heats the waste heat recovery water flowing through the second heat exchanger (5).

2. The boiler waste heat recovery system according to claim 1, characterized in that: The water supply device comprises a low-temperature water tank (3), wherein at least one low-temperature water tank (3) is provided, and the first heat exchanger (6) and the second heat exchanger (5) are respectively connected to at least one of the low-temperature water tanks (3).

3. The boiler waste heat recovery system according to claim 1, characterized in that: The waste heat recovery water is soft water.

4. The boiler waste heat recovery system according to claim 1, characterized in that: The boiler waste heat recovery system further comprises a high-temperature water tank (4), wherein at least one high-temperature water tank (4) is provided, and the first heat exchanger (6) and the second heat exchanger (5) are respectively connected to at least one of the high-temperature water tanks (4), and the high-temperature water tank (4) is used to store the heated waste heat recovery water.

5. The boiler waste heat recovery system according to claim 4, characterized in that: The high-temperature water tank (4) is connected to the second heat exchanger (5), and the high-temperature water tank (4) provides the heated waste heat recovery water to the second heat exchanger (5).

6. The boiler waste heat recovery system according to claim 1, characterized in that: The blowdown expansion tank (2) is also filled with flash steam. The blowdown expansion tank (2) is connected to the deaerator (1) and provides the flash steam to the deaerator (1). The flash steam is mixed with the exhaust steam in the deaerator (1). The deaerator (1) also provides the flash steam to the first heat exchanger (6). The flash steam also heats the waste heat recovery water flowing through the first heat exchanger (6).

7. The boiler waste heat recovery system according to claim 1, characterized in that: A return air pipeline is also provided between the first heat exchanger (6) and the deaerator (1), and the deaerator (1) is provided with a waste gas discharge port. After the exhaust steam heats the waste heat recovery water flowing through the first heat exchanger (6), it is transported to the deaerator (1) through the return air pipeline and discharged from the deaerator (1) through the waste gas discharge port.

8. The boiler waste heat recovery system according to any one of claims 1 to 7, characterized in that: The blowdown expansion tank (2) is provided with a liquid level sensor (11), the second heat exchanger (5) is provided with a high-temperature boiler water outlet, and the high-temperature boiler water outlet is provided with a control valve (9). When the liquid level sensor (11) measures that the high-temperature boiler water level in the blowdown expansion tank (2) exceeds a safe liquid level, the control valve (9) automatically opens to increase the discharge flow of the high-temperature boiler water.

9. The boiler waste heat recovery system according to claim 1, characterized in that: The first heat exchanger (6) is a condenser.

10. The boiler waste heat recovery system according to claim 1, characterized in that: The second heat exchanger (5) is a plate heat exchanger.

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