System for waste heat recovery using combined air heater and method of using the same

Abstract

The present invention relates to a system for recovering waste heat using a combined air heater and a method for using the system. The system includes a boiler, a low-temperature economizer, a vortex-tube air preheater, and a combined air heater. The combined air heater includes a first heat medium inlet, a first heat medium outlet, a second heat medium inlet, and a second heat medium outlet. The first heat medium outlet is connected to the water inlet of the boiler via a third pipeline. An outlet valve is installed on the third pipeline near the first heat medium outlet. A flow channel is formed before the inlet of the outlet valve and between the first heat medium outlet and the second heat medium inlet. The flow channel is provided with a flow channel valve. The second heat medium outlet is connected to the water inlet of the low-temperature economizer via a fourth pipeline. The vortex-tube air preheater, the low-temperature economizer, and the combined air heater in the system of the present invention are interconnected to reduce the consumption of low-pressure steam in the boiler, thereby solving the problem of low efficiency of the entire boiler caused by high exhaust temperature and high flue gas temperature. The system structure is simple.

Description

Technical Field

[0001] The present invention belongs to the technical field of boiler waste heat recovery, and in particular relates to a system for recovering waste heat by using a combined air heater and a method for using the system. Background Art

[0002] Heat loss from flue gas in thermal power plants is the largest of all boiler heat losses, typically ranging from 5% to 8% and accounting for 80% or more of the boiler's total heat loss. The primary factor influencing this heat loss is the boiler's flue gas temperature. Generally, for every 10°C increase in flue gas temperature, heat loss increases by 0.6% to 1.0%. Boiler flue gas temperatures in currently operating thermal power units generally range from 125°C to 150°C, sometimes reaching 160°C. High flue gas temperatures are common.

[0003] A boiler air heater is a heat exchanger that uses low-pressure steam extracted from the steam turbine to heat the air entering the air preheater. Installed between the blower outlet and the air preheater inlet, it is also called a pre-mounted air preheater. Installing a heater increases the air temperature entering the air preheater, raising the wall temperature of the air preheater and thus preventing low-temperature corrosion. The use of a heater reduces the heat transfer temperature difference in the air preheater, increasing the boiler exhaust temperature and reducing boiler thermal efficiency, which is more significant than with hot air recirculation. However, a heater uses low-pressure steam extracted from the steam turbine as its heat source. The increase in low-pressure steam extraction improves the turbine cycle efficiency. Whether the decrease in boiler thermal efficiency offsets the increase in turbine efficiency depends on the air heating temperature and the steam extraction pressure used. Generally, the increase in turbine efficiency does not offset the decrease in boiler thermal efficiency, resulting in a decrease in overall power plant efficiency.

[0004] In addition, existing power plants either use steam heaters or water-heated heaters. For example, patent CN114459016A adopts a low-temperature economizer combined with heater full-operating condition adjustment system, including a low-temperature economizer, a heater, a steam heater, a condensate heater, a circulating water pump and an expansion water tank. Although the low-temperature economizer is combined with the heater for full-operating condition adjustment in this technical solution, the heater adopts a water-heated heater. In order to ensure that the low-energy recovered heat can meet the heating air temperature of the heater in winter and low-load conditions, a steam heater is added. The whole system will appear redundant, the structure will become complicated, the energy-saving effect will be greatly reduced, and the boiler efficiency will be greatly reduced. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the prior art, the technical problem to be solved by the present invention is to provide a system and a method for using the combined air heater to realize waste heat recovery, so as to avoid the problems of excessive heat loss, complex structure and insufficient energy saving of the existing boiler exhaust.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A system for waste heat recovery using a combined air heater comprises a boiler and a low-temperature economizer, wherein a circulating water pump is provided before the water inlet of the low-temperature economizer; a vortex tube air preheater and a combined air heater;

[0008] The combined air heater includes a first heat medium inlet, a first heat medium outlet, a second heat medium inlet, and a second heat medium outlet; the steam outlet of the boiler is connected to the first heat medium inlet via a first pipeline, and the water outlet of the low-temperature economizer is connected to the first heat medium inlet via a second pipeline; the first heat medium outlet is connected to the boiler via a third pipeline, and an outlet valve is installed on the third pipeline near the first heat medium outlet. The first heat medium outlet is also connected to the second heat medium inlet through a flow channel, and a flow channel valve is provided on the flow channel; the second heat medium outlet is connected to the water inlet of the low-temperature economizer via a fourth pipeline;

[0009] The air duct outlet of the combined air heater is connected to the air inlet of the vortex tube air preheater; the air outlet of the vortex tube air preheater is connected to the boiler, the flue gas outlet of the boiler is connected to the flue gas inlet of the vortex tube air preheater, and the flue gas outlet of the vortex tube air preheater is connected to the low-temperature economizer.

[0010] To further improve the above technical solution, the combined air heater includes a shell, which is open at both vertical ends; a combined heat exchange area is provided in the shell, and a plurality of rows of horizontal heat exchange tubes are arranged vertically at intervals in the combined heat exchange area, and the combined heat exchange area includes an upper half area and a lower half area located below the upper half area;

[0011] The heat exchange tube at the top of the upper half extends out of the shell and forms the first heat medium inlet, and the heat exchange tube at the bottom of the upper half extends out of the shell and forms the first heat medium outlet. The first heat medium inlet and the first heat medium outlet are connected through the heat exchange tube in the upper half; the heat exchange tube at the top of the lower half extends out of the shell and forms the second heat medium inlet, and the heat exchange tube at the bottom of the lower half extends out of the shell and forms the second heat medium outlet. The second heat medium inlet and the second heat medium outlet are connected through the heat exchange tube in the lower half;

[0012] The bottom end of the shell is open and serves as the air duct inlet of the combined air heater and is connected to a fan. The top end of the shell is open and forms the air duct outlet of the combined air heater. An air channel is formed between the air duct inlet and the air duct outlet of the combined air heater, and the flow direction of the air channel is perpendicular to the length direction of the heat exchange tube.

[0013] Furthermore, the heat exchange tubes in the upper half have a downward inclination along the flow direction of the heat medium, and the heat exchange tubes in the lower half are placed horizontally.

[0014] Furthermore, the multiple rows of transverse heat exchange tubes are in the form of serpentine tube panels connected in sequence, and the bending parts of the serpentine tube panels are located at the left and right parts thereof respectively;

[0015] Tube sheets parallel to the air passage are provided on the outer side of the shell at positions corresponding to the bent portions on both sides of the serpentine tube panel. Holes are provided on the tube sheets at positions corresponding to the bent portions for the bent portions to extend out of the tube sheets, and the area of the holes is larger than the cross-sectional area of the bent portions.

[0016] Furthermore, the first heat medium inlet, the first heat medium outlet, the second heat medium inlet, the second heat medium outlet and the flow channel are all arranged on the same side;

[0017] The bent portion close to the flow channel is welded to the tube plate; a cover shell is arranged outside the bent portion away from the flow channel, and the cover shell is welded to the tube plate to cover the bent portion inside.

[0018] Furthermore, inlet valves are provided on the first pipeline and the second pipeline near the first heat medium inlet. The inlet valve on the first pipeline is externally connected to the boiler to control the entry of steam into the combined air heater, and the inlet valve on the second pipeline is externally connected to the low-temperature economizer to control the entry of circulating water into the combined air heater.

[0019] Furthermore, the outlet valve includes a gate valve and an electric valve that are arranged adjacent to each other, and the gate valve is arranged on a side close to the flow channel;

[0020] The inlet valve includes a gate valve and an electric valve which are arranged adjacent to each other, and the gate valve is arranged on a side close to the first heat medium inlet.

[0021] Furthermore, a hot water point is provided on the second pipeline near the low-temperature economizer for domestic hot water.

[0022] Furthermore, the heat exchange tubes of the combined air heater and the low-temperature economizer adopt composite reinforced heat exchange tubes with inner micro-ribs and cells having a plurality of spherical concavities on the outer surface of the tube wall;

[0023] The heat exchange tube of the vortex tube type air preheater adopts a vortex-enhanced heat exchange tube with a plurality of spherical protrusions on the inner wall.

[0024] The present invention also relates to a method for using the system for recovering waste heat using the combined air heater as described above, specifically comprising:

[0025] The flue gas discharged from the vortex tube air preheater heats the circulating water in the low-temperature economizer;

[0026] When the combined air heater uses steam from the boiler to heat the air, the outlet valve is opened, the flow channel valve is closed, and the steam enters from the first heat medium inlet and is discharged from the first heat medium outlet;

[0027] When the combined air heater uses the circulating water from the low-temperature economizer to heat the air, the flow channel valve is opened, the outlet valve is closed, and the circulating water enters from the first heat medium inlet until it is discharged from the second heat medium outlet;

[0028] The air heated by the combined air heater passes through the vortex tube air preheater and then flows to the boiler.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. The present invention relates to a system and method for using a combined air heater to recover waste heat. The system comprises a vortex-tube air preheater, a low-temperature economizer, and a combined air heater, all of which are interconnected. The combined air heater can heat the air using either steam from the boiler or circulating water from the low-temperature economizer. A valve controls whether steam flows through the upper half of the combined air heater or circulating water flows through the entire combined heat exchange zone. This addresses the shortcomings of traditional steam or water heaters, which rely on a single heating medium, and can meet the required heating temperature for the air heater in both summer and winter. It also reduces the consumption of low-pressure steam in the boiler, resolving the issue of low boiler efficiency caused by high exhaust and flue gas temperatures. The combined air heater has a simple structure and reduces the redundancy of the entire system.

[0031] 2. The system of the present invention uses a combined air heater to realize waste heat recovery and its use method. When there is no need for heating or domestic hot water in summer, the entire combined heat exchange area uses circulating water to heat the air, and the outlet valve is closed and the flow valve is opened to allow hot water from the low-temperature economizer to enter from the first heat medium inlet and be discharged from the second heat medium outlet; when hot water heating is needed in winter, the upper half area uses steam to heat the air, and the flow valve is closed and the outlet valve is opened to allow steam from the boiler to enter through the first heat medium inlet and be discharged from the first heat medium outlet; the combination of steam heating and circulating water heating is realized, and the medium in the heat exchange tube can be adjusted according to user needs, thereby reducing the consumption of low-pressure steam extraction from the boiler. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the structure of a system for recovering waste heat using a combined air heater according to an embodiment;

[0033] Figure 2 Schematic diagram of the structure of the combined air heater in the embodiment;

[0034] Among them, there are boiler 1, low-temperature economizer 2, vortex tube air preheater 3, combined air heater 4, outer shell 41, upper zone 42, lower zone 43, air duct inlet 44, air duct outlet 45, bending part 46, tube sheet 47, cover 48, outlet valve 49, circulating water pump 5, first pipeline 6, second pipeline 7, hot water point 71, third pipeline 8, flow channel 9, flow channel valve 91, fourth pipeline 10, fan 11, first heat medium inlet A, first heat medium outlet B, second heat medium inlet C, second heat medium outlet D, SCR reactor 12, dust collector 13, desulfurization tower 14, chimney 15. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0036] It should be noted that similar reference numerals and letters denote similar items in the following figures. Therefore, once an item is defined in one figure, it does not require further definition or explanation in subsequent figures. In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the figures, or the orientations or positional relationships in which the inventive product is typically placed when in use. These terms are intended solely to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation, and are therefore not to be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third," etc., are used solely to distinguish descriptions and are not to be construed as indicating or implying relative importance. Furthermore, terms such as "horizontal" and "vertical" do not imply that a component must be absolutely horizontal or overhanging, but rather may be slightly tilted. For example, "horizontal" simply refers to a direction that is more horizontal than "vertical," and does not imply that the structure must be completely horizontal, but rather may be slightly tilted. In the description of the present invention, it should also be noted that, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to mechanical connections or electrical connections; they may refer to direct connections or indirect connections through an intermediate medium; and they may refer to internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0037] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0038] See Figure 1-Figure 2 , a system for realizing waste heat recovery by using a combined air heater in a specific embodiment comprises a boiler 1 and a low-temperature economizer 2, a circulating water pump 5 being provided before the water inlet of the low-temperature economizer 2; further comprising a vortex tube air preheater 3 and a combined air heater 4; the combined air heater comprises a first heat medium inlet A, a first heat medium outlet B, a second heat medium inlet C and a second heat medium outlet D; the steam outlet of the boiler is connected to the first heat medium inlet A via a first pipeline 6, and the water outlet of the low-temperature economizer 2 is connected to the first heat medium inlet A via a second pipeline 7; the first heat medium outlet B is connected to the boiler via a third pipeline 8, an outlet valve 49 is installed on the third pipeline 8 near the first heat medium outlet B, a flow channel 9 is provided before the inlet of the outlet valve 49, the first heat medium outlet B and the second heat medium inlet C are connected, and a flow channel valve 91 is provided on the flow channel 9; the second heat medium outlet D is connected to the water inlet of the low-temperature economizer 2 via a fourth pipeline 10;

[0039] The air duct outlet of the combined air heater 4 is connected to the air inlet of the vortex tube air preheater 3; the air outlet of the vortex tube air preheater 3 is connected to the boiler 1, the flue gas outlet of the boiler 1 is connected to the flue gas inlet of the vortex tube air preheater 3, and the flue gas outlet of the vortex tube air preheater 3 is connected to the low-temperature economizer 2.

[0040] In the embodiment, a system employing a combined air heater for waste heat recovery is described. The system comprises a vortex-tube air preheater 3, a low-temperature economizer 2, and a combined air heater 4, which are interconnected. The combined air heater 4 can heat the air using either steam from the boiler 1 or circulating water from the low-temperature economizer 2. A valve controls whether steam is passed through a portion of the combined air heater 4 or circulating water is passed through the entire combined air heater 4. This solves the shortcomings of conventional steam or water heaters, which rely on a single heating medium, and can meet the heating air temperature requirements of the heater in both summer and winter. It also reduces the consumption of low-pressure steam in the boiler, resolving the problem of low boiler efficiency caused by high exhaust and flue gas temperatures. The combined air heater 4 has a simple structure, reducing the redundancy of the entire system.

[0041] Please continue to see Figure 1-Figure 2 The combined air heater 4 includes a shell 41, which is open at both ends vertically; a combined heat exchange area is provided in the shell 41, and a plurality of rows of horizontal heat exchange tubes are arranged vertically at intervals in the combined heat exchange area. The combined heat exchange area includes an upper half area 42 and a lower half area 43 located below the upper half area;

[0042] The heat exchange tube at the top of the upper section 42 extends out of the shell 41 and forms the first heat medium inlet A. The heat exchange tube at the bottom of the upper section 42 extends out of the shell 41 and forms the first heat medium outlet B. The first heat medium inlet A and the first heat medium outlet B are connected through the heat exchange tube in the upper section 42. The heat exchange tube at the top of the lower section 43 extends out of the shell 41 and forms the second heat medium inlet C. The heat exchange tube at the bottom of the lower section 43 extends out of the shell 41 and forms the second heat medium outlet D. The second heat medium inlet C and the second heat medium outlet D are connected through the heat exchange tube in the lower section 43.

[0043] The bottom end of the shell 41 is open as the air duct inlet 44 of the combined air heater and is connected to a fan 11. The top end of the shell is open and forms the air duct outlet 45 of the combined air heater. There is an air channel between the air duct inlet 44 and the air duct outlet 45 of the combined air heater, and the flow direction of the air channel is perpendicular to the length direction of the heat exchange tube.

[0044] In this way, when there is no need for heating or domestic hot water in the summer, the entire combined heat exchange area uses circulating water to heat the air, and the outlet valve 49 is closed and the flow channel valve 91 is opened to allow hot water to enter from the first heat medium inlet A and then be discharged from the second heat medium outlet D; when hot water heating is needed in the winter, the upper half area 42 uses steam to heat the air, and the flow channel valve 91 is closed and the outlet valve 49 is opened to allow steam to enter through the first heat medium inlet A and then be discharged from the first heat medium outlet B; this realizes the combination of steam heating and circulating water heating, and at the same time, the medium in the heat exchange tube can be adjusted according to user needs, thereby reducing the consumption of low-pressure steam extraction from the boiler.

[0045] The heat exchange tubes in the upper zone 42 have a downward inclination along the flow direction of the heat medium, and the heat exchange tubes in the lower zone 43 are placed horizontally.

[0046] Since steam heating is performed only in the upper section 42, and condensate will flow out during steam heating, if condensate remains in the heat exchange tubes, it will affect heat exchange efficiency. Therefore, the heat exchange tubes passing steam are set at a certain angle to facilitate condensate drainage. When circulating water is used to heat the air, this issue does not need to be considered, so the heat exchange tubes in the lower section 43 can be arranged horizontally. In practice, the heat exchange tubes in the upper section 42 adopt an inclination of 5:1000.

[0047] The multiple rows of transverse heat exchange tubes are in the form of serpentine tube panels connected in sequence, and the bending portions 46 of the serpentine tube panels are located at the left and right portions thereof respectively;

[0048] On the outside of the shell 41, corresponding to the positions of the bent portions 46 on both sides of the serpentine tube panel, tube sheets 47 parallel to the air channel are provided. The positions of the tube sheets 47 corresponding to the bent portions 46 are provided with holes for the bent portions 46 to extend out of the tube sheets 47. The area of the holes is larger than the cross-sectional area of the bent portions 46.

[0049] In this way, the area of the opening on the tube sheet 47 is larger than the cross-sectional area of the bent portion 46, which facilitates the expansion of the heat exchange tube due to heat.

[0050] The first heat medium inlet A, the first heat medium outlet B, the second heat medium inlet C, the second heat medium outlet D and the flow channel 9 are all arranged on the same side;

[0051] The bent portion 46 close to the flow channel 9 is welded to the tube sheet 47; a cover 48 is provided outside the bent portion 46 away from the flow channel 9, and the cover 48 is welded to the tube sheet 47 to cover the bent portion 46 inside.

[0052] In this way, the bent portion 46 on one side is welded to the tube sheet 47, while the bent portion 46 on the other side is not welded to the tube sheet 47, so that the heat exchange tube expands toward the designated side due to heat, and a cover 48 is provided outside the bent portion 46 that is not welded to the tube sheet 47 for sealing to prevent heat loss.

[0053] It will be appreciated that, in practice, multiple serpentine tube panels are provided in both the upper and lower sections 42, 43. In the upper section, the multiple serpentine tube panels are arranged parallel to each other and laterally spaced apart. The heat exchange tubes at the top of each serpentine tube panel extend from the outer casing to form a heat medium inlet. These multiple heat medium inlets are combined through a header to form the first heat medium inlet A. Similarly, the heat exchange tubes at the bottom of each serpentine tube panel extend from the outer casing 41 and are combined through a header to form the first heat medium outlet B. In the lower section, the heat exchange tubes at the top of each serpentine tube panel extend from the outer casing 41 and are combined through a header to form the second heat medium inlet C. The heat exchange tubes at the bottom of each serpentine tube panel extend from the outer casing 41 and are combined through a header to form the second heat medium outlet D.

[0054] Among them, inlet valves are provided on the first pipeline 6 and the second pipeline 7 near the first heat medium inlet A. The inlet valve on the first pipeline 6 is externally connected to the boiler 1 for controlling the steam entering the combined air heater 4, and the inlet valve on the second pipeline 7 is externally connected to the low-temperature economizer 2 for controlling the circulating water entering the combined air heater 4.

[0055] In this way, after the fan 11 is started, when steam is used to heat the air, the inlet valve and the outlet valve 49 for controlling the steam are opened at the same time, and the flow channel valve 91 and the inlet valve for controlling the circulating water are closed; when circulating water is used to heat the air, the circulating water pump 5, the inlet valve and the flow channel valve 91 for controlling the circulating water are opened at the same time, and the inlet valve and the outlet valve 49 for controlling the steam are closed; thereby realizing the switching of the heating medium in the combined air heater.

[0056] During implementation, the flow channel valve 91 is a butterfly valve so as to quickly open and close the valve plate.

[0057] The outlet valve 49 includes a gate valve and an electric valve that are adjacent to each other, and the gate valve is located on a side close to the flow channel 9; the inlet valve includes a gate valve and an electric valve that are adjacent to each other, and the gate valve is located on a side close to the first heat medium inlet A.

[0058] In this way, an electric valve is used to adjust the flow of the medium in the pipeline, and a gate valve is set to play a protective role. When the electric valve loses control, the gate valve can be used to fully open or close the medium.

[0059] During implementation, the electric valve driving device is a reversible electric motor, which drives the valve core to control the valve of the electric valve by rotating the motor for a certain period of time. It adopts AI analog signal control to adjust the flow of pipeline medium, and can also use digital signal control in specific pipeline environments.

[0060] A hot water point 71 for domestic hot water is provided on the second pipeline 7 near the low-temperature economizer 2 .

[0061] The heat exchange tubes of the combined air heater 4 and the low-temperature economizer 2 are composite reinforced heat exchange tubes with inner micro-ribs and cells and a plurality of spherical concavities on the outer surface of the tube wall;

[0062] The heat exchange tubes of the vortex-tube air preheater 3 are vortex-enhanced heat exchange tubes with multiple spherical protrusions on the inner wall.

[0063] In this way, compared with ordinary bare tubes, internal micro-ribbed cellular composite reinforced heat exchange tubes (please refer to CN110081763A for details) and vortex segment reinforced heat exchange tubes (please refer to CN210108115U for details) help to improve the heat exchange efficiency of air preheaters, low-temperature economizers and combined air heaters, effectively reduce dust accumulation and even blockage in the tubes, reduce the space required for heat exchange tubes (the number of heat exchange tubes under the same heat exchange effect), and extend the service life of equipment in the system.

[0064] Please continue to see Figure 1 and Figure 2 The present invention also provides a method for using the system for recovering waste heat using the combined air heater, which specifically includes:

[0065] The flue gas discharged from the vortex tube air preheater 3 heats the circulating water in the low-temperature economizer 2;

[0066] When the combined air heater 4 uses the steam from the boiler 1 to heat the air, the outlet valve 49 is opened and the flow channel valve 91 is closed, and the steam enters from the first heat medium inlet A and is discharged from the first heat medium outlet B;

[0067] When the combined air heater 4 uses the circulating water from the low-temperature economizer 2 to heat the air, the flow channel valve 91 is opened and the outlet valve 49 is closed, and the circulating water enters from the first heat medium inlet A until it is discharged from the second heat medium outlet D;

[0068] The air heated by the combined air heater 4 passes through the vortex tube air preheater 3 and then flows into the boiler 1.

[0069] In this embodiment, the flue gas outlet of boiler 1 is connected to the flue gas inlet of a vortex-tube air preheater 3 via an SCR reactor 12. Because the air preheater utilizes vortex-enhanced heat exchange tubes, the flue gas temperature can be reduced to 160°C, heating the air through heat exchange. The low-temperature economizer 2 utilizes internal micro-ribbed butyl cell composite-enhanced heat exchange tubes, further reducing the flue gas temperature to 140°C. This increases the water temperature within the low-temperature economizer 2 tubes from 50°C to 80°C. The hot water heated by the low-temperature economizer 2 is fed into a combined air heater 4, which heats the primary and secondary air temperatures (air temperatures) at the air inlet of the vortex-tube air preheater 3 to 30°C. After passing through the vortex-tube air preheater 3, the primary air temperature is raised to 360°C and the secondary air temperature to 320°C before entering the boiler. This effectively utilizes the entire system's temperature, saving energy and reducing emissions. The low-temperature economizer 2 is connected to a dust collector 13 and a desulfurization tower 14, through which the flue gas flows in sequence before being discharged through a chimney 15.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A system for waste heat recovery using a combined air heater, comprising a boiler and a low-temperature economizer, wherein a circulating water pump is provided before the water inlet of the low-temperature economizer; characterized in that: It also includes a vortex tube air preheater and a combined air heater; The combined air heater includes a first heat medium inlet, a first heat medium outlet, a second heat medium inlet, and a second heat medium outlet; the steam outlet of the boiler is connected to the first heat medium inlet via a first pipeline, and the water outlet of the low-temperature economizer is connected to the first heat medium inlet via a second pipeline; the first heat medium outlet is connected to the boiler via a third pipeline, and an outlet valve is installed on the third pipeline near the first heat medium outlet. Before the inlet of the outlet valve, the first heat medium outlet and the second heat medium inlet are connected by a flow channel, and the flow channel is provided with a flow channel valve; the second heat medium outlet is connected to the water inlet of the low-temperature economizer via a fourth pipeline; The air duct outlet of the combined air heater is connected to the air inlet of the vortex tube air preheater; the air outlet of the vortex tube air preheater is connected to the boiler, the flue gas outlet of the boiler is connected to the flue gas inlet of the vortex tube air preheater, and the flue gas outlet of the vortex tube air preheater is connected to the low-temperature economizer; The combined air heater includes a shell, which is open at both vertical ends; a combined heat exchange area is provided in the shell, wherein a plurality of rows of transverse heat exchange tubes are arranged vertically at intervals in the combined heat exchange area, and the combined heat exchange area includes an upper half area and a lower half area located below the upper half area; The heat exchange tube at the top of the upper half extends out of the shell and forms the first heat medium inlet, and the heat exchange tube at the bottom of the upper half extends out of the shell and forms the first heat medium outlet. The first heat medium inlet and the first heat medium outlet are connected through the heat exchange tube in the upper half; the heat exchange tube at the top of the lower half extends out of the shell and forms the second heat medium inlet, and the heat exchange tube at the bottom of the lower half extends out of the shell and forms the second heat medium outlet. The second heat medium inlet and the second heat medium outlet are connected through the heat exchange tube in the lower half; The bottom end of the housing is open and forms an air duct inlet of the combined air heater and is connected to a fan. The top end of the housing is open and forms an air duct outlet of the combined air heater. An air channel is formed between the air duct inlet and the air duct outlet of the combined air heater. The flow direction of the air channel is perpendicular to the length direction of the heat exchange tube. The heat exchange tubes in the upper half are inclined downward along the direction of heat medium flow, while the heat exchange tubes in the lower half are placed horizontally; The multiple rows of transverse heat exchange tubes are in the form of serpentine tube panels connected in sequence, and the bending parts of the serpentine tube panels are respectively located on the left and right parts thereof; Tube sheets parallel to the air passage are provided on the outer side of the shell at positions corresponding to the bent portions on both sides of the serpentine tube panel. Holes are provided on the tube sheets at positions corresponding to the bent portions for the bent portions to extend out of the tube sheets, and the area of the holes is larger than the cross-sectional area of the bent portions.

2. The system for waste heat recovery using a combined air heater according to claim 1, characterized in that: The first heat medium inlet, the first heat medium outlet, the second heat medium inlet, the second heat medium outlet and the flow channel are all arranged on the same side; The bent portion close to the flow channel is welded to the tube plate; a cover shell is arranged outside the bent portion away from the flow channel, and the cover shell is welded to the tube plate to cover the bent portion inside.

3. The system for waste heat recovery using a combined air heater according to claim 1, characterized in that: Inlet valves are provided on the first pipeline and the second pipeline near the first heat medium inlet. The inlet valve on the first pipeline is used to control the steam to enter the combined air heater, and the inlet valve on the second pipeline is used to control the circulating water to enter the combined air heater.

4. The system for waste heat recovery using a combined air heater according to claim 3, characterized in that: The outlet valve includes a gate valve and an electric valve arranged in series, and the gate valve is arranged on a side close to the flow channel; The inlet valve includes a gate valve and an electric valve arranged in series, and the gate valve is arranged on a side close to the first heat medium inlet.

5. The system for waste heat recovery using a combined air heater according to claim 1, characterized in that: A hot water point is also provided on the second pipeline near the low-temperature economizer for domestic hot water.

6. The system for waste heat recovery using a combined air heater according to any one of claims 1 to 5, characterized in that: The heat exchange tubes of the combined air heater and the low-temperature economizer are composite reinforced heat exchange tubes with inner micro-ribs and cells and a plurality of spherical concavities on the outer surface of the tube wall; The heat exchange tube of the vortex tube type air preheater adopts a vortex-enhanced heat exchange tube with a plurality of spherical protrusions on the inner wall.

7. The method for using the system for recovering waste heat using a combined air heater as claimed in claim 1, characterized in that: include: The flue gas discharged from the vortex tube air preheater heats the circulating water in the low-temperature economizer; When the combined air heater uses steam from the boiler to heat the air, the outlet valve is opened, the flow channel valve is closed, and the steam enters from the first heat medium inlet and is discharged from the first heat medium outlet; When the combined air heater uses the circulating water from the low-temperature economizer to heat the air, the flow channel valve is opened, the outlet valve is closed, and the circulating water enters from the first heat medium inlet until it is discharged from the second heat medium outlet; The air heated by the combined air heater passes through the vortex tube air preheater and then flows to the boiler.

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