CN217635583U - System for realizing waste heat recovery by adopting combined air heater - Google Patents

Abstract

The utility model relates to a system for realizing waste heat recovery by adopting a combined air heater, which comprises a boiler, a low-low temperature economizer, a vortex tube type air preheater and the combined air heater; the combined air heater comprises a first heating medium inlet, a first heating medium outlet, a second heating medium inlet and a second heating medium outlet; the first heat medium outlet is connected with the water inlet of the boiler through a third pipeline, an outlet valve is arranged on the third pipeline close to the first heat medium outlet, a flow channel is formed by the communication between the first heat medium outlet and the second heat medium inlet before the inlet of the outlet valve, and a flow channel valve is arranged on the flow channel; the second heating medium outlet is connected with the water inlet of the low-temperature economizer through a fourth pipeline. The vortex tube type air preheater, the low-temperature economizer and the combined air heater in the system are linked mutually, so that the consumption of low-pressure steam of the boiler is reduced, and the problem of low efficiency of the whole boiler caused by high exhaust gas temperature and high flue gas temperature of the boiler is solved; and the system structure is simple.

Description

System for realizing waste heat recovery by adopting combined air heater

Technical Field

The utility model belongs to the technical field of boiler waste heat recovery, concretely relates to system for adopt combined air heater to realize waste heat recovery.

Background

The heat loss of the exhaust smoke of the thermal power plant is the largest one of various heat losses of a power station boiler, generally ranges from 5% to 8%, and accounts for 80% or more of the total heat loss of the boiler. The main factor influencing the heat loss of the exhaust smoke is the exhaust smoke temperature of the boiler, and generally, the heat loss of the exhaust smoke is increased by 0.6 to 1.0 percent when the exhaust smoke temperature is increased by 10 ℃. The boiler exhaust gas temperature in the active thermal power generating unit is generally maintained at about 125-150 ℃, even reaches 160 ℃, and the exhaust gas temperature is high, which is a common phenomenon.

Wherein, the boiler air heater is a heat exchanger which utilizes low-pressure steam extraction of a steam turbine to heat inlet air of the air preheater. The boiler air heater is installed between the outlet of the blower and the inlet of the air preheater, so the boiler air heater is also called a front-mounted air preheater. The air heater is additionally arranged, so that the temperature of air entering the air preheater is increased, and the wall temperature of the air preheater is increased, thereby preventing low-temperature corrosion. After the air heater is adopted, the heat transfer temperature difference of the air preheater is reduced, the exhaust gas temperature of the boiler is also increased, the thermal efficiency of the boiler is reduced, and the heat transfer temperature difference is more obvious than that of the boiler adopting hot air recirculation. However, the low-pressure extraction steam of the steam turbine is used as a heating source of the air heater, and the low-pressure extraction steam quantity is increased, so that the cycle efficiency of the steam turbine is improved. The heat efficiency of the boiler is reduced, the efficiency of the steam turbine is improved, and whether the efficiency of the boiler and the efficiency of the steam turbine can compensate each other needs to be determined according to the difference between the heating temperature of air and the extraction pressure. Generally, the increase in turbine efficiency does not offset the decrease in boiler thermal efficiency and, as a result, the plant-wide efficiency of the power plant decreases.

In addition, the existing power plant adopts either a steam air heater or a water heating air heater, for example, in patent CN114459016a, a low-temperature economizer combined air heater full-working-condition adjusting system is adopted, which comprises a low-temperature economizer, an air heater, a steam heater, a condensed water heater, a circulating water pump and an expansion water tank.

Disclosure of Invention

The above-mentioned not enough to prior art, the to-be-solved technical problem of the utility model is to provide an adopt system that joint fan heater realized waste heat recovery, avoid current boiler exhaust heat loss too high, the structure is complicated and not enough energy-conserving problem.

In order to solve the technical problem, the utility model adopts the following technical scheme:

a system for realizing waste heat recovery by adopting a combined air heater comprises a boiler and a low-temperature economizer, wherein a circulating water pump is arranged in front of a water inlet of the low-temperature economizer; the air preheater also comprises a vortex tube type air preheater and a combined air heater;

the combined air heater comprises a first heating medium inlet, a first heating medium outlet, a second heating medium inlet and a second heating medium outlet; a steam outlet of the boiler is connected with a first heat medium inlet through a first pipeline, and a water outlet of the low-temperature economizer is connected with the first heat medium inlet through a second pipeline; the first heat medium outlet is connected with the boiler through a third pipeline, an outlet valve is arranged on the third pipeline close to the first heat medium outlet, the first heat medium outlet is also communicated with a second heat medium inlet through a flow channel, and the flow channel is provided with a flow channel valve; the second heating medium outlet is connected with the water inlet of the low-temperature economizer through a fourth pipeline;

an air duct outlet of the combined air heater is connected with an air inlet of the vortex tube type air preheater; the air outlet of the vortex tube type air preheater is connected with the boiler, the smoke outlet of the boiler is connected with the smoke inlet of the vortex tube type air preheater, and the smoke outlet of the vortex tube type air preheater is connected with the low-temperature economizer.

Further perfecting the technical scheme, the combined air heater comprises a shell, wherein two ends of the shell are opened along the vertical direction; a combined heat exchange area is arranged in the shell, a plurality of rows of transverse heat exchange tubes are vertically arranged in the combined heat exchange area at intervals, and the combined heat exchange area comprises an upper half area and a lower half area positioned below the upper half area;

the heat exchange tube at the top of the upper half area extends out of the shell and forms the first heat medium inlet, the heat exchange tube at the bottom of the upper half area extends out of the shell and forms the first heat medium outlet, and the first heat medium inlet and the first heat medium outlet are communicated through the heat exchange tube in the upper half area; the heat exchange tube at the top of the lower half area extends out of the shell and forms a second heat medium inlet, the heat exchange tube at the bottom of the lower half area extends out of the shell and forms a second heat medium outlet, and the second heat medium inlet and the second heat medium outlet are communicated through the heat exchange tube in the lower half area;

the bottom end of the shell is open and is an air duct inlet of the combined air heater and is connected with a fan, the top end of the shell is open and is formed into an air duct outlet of the combined air heater, an air channel is arranged between the air duct inlet and the air duct outlet of the combined air heater, and the overflowing direction of the air channel is perpendicular to the length direction of the heat exchange tube.

Further, the heat exchange tubes of the upper half have a downward inclination in the flow direction of the heating medium, and the heat exchange tubes of the lower half are horizontally disposed.

Furthermore, the plurality of rows of transverse heat exchange tubes are sequentially connected to form a serpentine tube panel, and the bending parts of the serpentine tube panel are respectively positioned at the left part and the right part of the serpentine tube panel;

the position that the outside of shell corresponds snakelike tube panel both sides portion of bending all is equipped with the tube sheet that parallels with air passage, the hole that supplies the portion of bending to stretch out outside the tube sheet is seted up to the position that corresponds the portion of bending on the tube sheet, and the area of trompil is greater than the cross-sectional area of the portion of bending.

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 arranged on the same side;

the bending part close to the flow channel is welded with the tube plate; and an encloser is arranged outside the bending part far away from the flow channel, and the encloser is welded with the tube plate so as to cover the bending part in the duct.

Furthermore, the first pipeline and the second pipeline are provided with inlet valves close to the first heating medium inlet, the inlet valves on the first pipeline are externally connected with a boiler to control steam to enter the combined air heater, and the inlet valves on the second pipeline are externally connected with a low-temperature economizer to control circulating water to enter the combined air heater.

Furthermore, the outlet valve comprises a gate valve and an electric valve which are arranged adjacent to each other, and the gate valve is arranged on one side close to the flow channel;

the inlet valve comprises a gate valve and an electric valve which are arranged in close proximity, and the gate valve is arranged on one side close to the first heating medium inlet.

Furthermore, a hot water taking point is further arranged on the second pipeline close to the low-temperature economizer and used as domestic hot water.

Furthermore, the heat exchange tube of the combined air heater and the low-temperature economizer adopts a plurality of spherical concave inner micro-rib dimpled composite reinforced heat exchange tubes arranged on the outer surface of the tube wall;

the heat exchange tube of the vortex node tube type air preheater adopts a vortex node reinforced heat exchange tube with a plurality of spherical bulges on the inner wall.

Compared with the prior art, the utility model discloses following beneficial effect has:

1. the utility model discloses an adopt system that joint air heater realized waste heat recovery, vortex festival tubular air preheater, low temperature economizer and the mutual linkage of joint air heater three in the system, joint air heater lies in both can adopting the steam heating air who comes from the boiler, also can adopt the circulating water heating air who comes from low temperature economizer, and leads to steam or whole joint heat transfer district through the first district of valve control joint air heater and lead to the circulating water. Therefore, the defects caused by single heating medium of the traditional steam air heater or water heating air heater can be overcome, and the requirement of the air heater for heating the air temperature can be met in summer or winter; the consumption of low-pressure steam of the boiler can be reduced, and the problem of low efficiency of the whole boiler caused by high exhaust gas temperature and high exhaust gas temperature of the boiler is solved; the combined air heater is simple in structure, and the redundancy of the whole system is reduced.

2. The utility model discloses an adopt system that joint air heater realized waste heat recovery, when summer does not need to heat or life hot water, whole joint heat transfer district adopts the circulating water heating air, just closes outlet valve among them, opens the runner valve, lets the hot water from the economizer of low temperature enter from the first heat medium import until discharging from the second heat medium export; when hot water is needed for heating in winter, the upper half area adopts steam to heat air, the flow channel valve is closed, the outlet valve is opened, and steam from the boiler enters through the first heat medium inlet and is discharged from the first heat medium outlet; the combination of steam heating and circulating water heating is realized, the medium in the heat exchange pipe can be adjusted according to the requirements of users, and the consumption of low-pressure steam extraction of the boiler is reduced.

Drawings

FIG. 1 is a schematic structural diagram of a system for implementing waste heat recovery by using a combined air heater according to an embodiment;

FIG. 2 is a schematic structural diagram of a combined air heater in an embodiment;

the system comprises a boiler 1, a low-temperature economizer 2, a vortex tube type air preheater 3, a combined air heater 4, a shell 41, an upper half 42, a lower half 43, an air duct inlet 44, an air duct outlet 45, a bent part 46, a tube plate 47, a housing 48, an outlet valve 49, a circulating water pump 5, a first pipeline 6, a second pipeline 7, a hot water taking point 71, a third pipeline 8, a flow channel 9, a flow channel valve 91, a fourth pipeline 10, a fan 11, a first heat medium inlet A, a first heat medium outlet B, a second heat medium inlet C, a second heat medium outlet D, an SCR reactor 12, a dust remover 13, a desulfurizing tower 14 and a chimney 15.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the drawings in the embodiments of the present invention are combined below to clearly and completely describe the technical solutions in the embodiments of the present invention. It is to be understood that the embodiments described are only some of the embodiments of the present invention, and not all of them. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the invention, as presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative efforts belong to the protection scope of the present invention.

It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained 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", "outer", and the like indicate the position or positional relationship based on the position or positional relationship shown in the drawings, or the position or positional relationship which is usually placed when the product of the present invention is used, and are only for convenience of description and simplification of the description, but do not indicate or imply that the device or element referred to must have a specific position, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," "third," and the like are used solely to distinguish one from another, and are not to be construed as indicating or implying relative importance. Furthermore, the terms "horizontal", "vertical" and the like do not imply that the components are required to be absolutely horizontal or pendant, but rather may be slightly inclined. For example, "horizontal" merely means that the direction is more horizontal than "vertical" and does not mean that the structure must be perfectly horizontal, but may be slightly inclined. In the description of the present invention, it should also be noted that, unless otherwise explicitly specified or limited, the terms "disposed," "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in the present invention can be understood in specific cases to those skilled in the art.

The following describes the embodiments of the present invention in further detail with reference to the attached drawings.

Referring to fig. 1-2, a system for realizing waste heat recovery by using a combined air heater according to an embodiment includes a boiler 1 and a low-temperature economizer 2, wherein a water circulating pump 5 is arranged before a water inlet of the low-temperature economizer 2; the air preheater also comprises a vortex joint pipe type air preheater 3 and a combined air heater 4; the combined air heater comprises a first heating medium inlet A, a first heating medium outlet B, a second heating medium inlet C and a second heating medium outlet D; the steam outlet of the boiler is connected with a first heat medium inlet A through a first pipeline 6, and the water outlet of the low-low temperature economizer 2 is connected with the first heat medium inlet A through a second pipeline 7; the first heat medium outlet B is connected with the boiler through a third pipeline 8, an outlet valve 49 is arranged on the third pipeline 8 and close to the first heat medium outlet B, the front part of an inlet of the outlet valve 49, the first heat medium outlet B and the second heat medium inlet C are communicated through a flow channel 9, and a flow channel valve 91 is arranged on the flow channel 9; the second heating medium outlet D is connected with the water inlet of the low-temperature economizer 2 through a fourth pipeline 10;

an air duct outlet of the combined air heater 4 is connected with an air inlet of the vortex tube type air preheater 3; an air outlet of the vortex joint pipe type air preheater 3 is connected with the boiler 1, a smoke outlet of the boiler 1 is connected with a smoke inlet of the vortex joint pipe type air preheater 3, and a smoke outlet of the vortex joint pipe type air preheater 3 is connected with the low-low temperature economizer 2.

According to the system for realizing waste heat recovery by adopting the combined air heater, the vortex tube type air preheater 3, the low-temperature economizer 2 and the combined air heater 4 in the system are linked with each other, the combined air heater 4 can heat air by adopting steam from the boiler 1 or circulating water from the low-temperature economizer 2, and a part of the combined air heater 4 or the whole combined air heater 4 is controlled to be communicated with the circulating water by a valve. Therefore, the defects caused by single heating medium of the traditional steam air heater or water heating air heater can be overcome, and the requirement of the air heater for heating the air temperature can be met in summer or winter; the consumption of low-pressure steam of the boiler can be reduced, and the problem of low efficiency of the whole boiler caused by high exhaust gas temperature and high exhaust gas temperature of the boiler is solved; the combined air heater 4 has a simple structure, and the redundancy of the whole system is reduced.

With continued reference to fig. 1-2, the combined air heater 4 includes a housing 41, and the housing 41 is open at two vertical ends; a combined heat exchange area is arranged in the shell 41, a plurality of rows of transverse heat exchange tubes are vertically arranged in the combined heat exchange area at intervals, and the combined heat exchange area comprises an upper half area 42 and a lower half area 43 positioned below the upper half area;

the heat exchange pipe at the top of the upper half 42 protrudes out of the case 41 and forms the first heating medium inlet a, the heat exchange pipe at the bottom of the upper half 42 protrudes out of the case 41 and forms the first heating medium outlet B, and the first heating medium inlet a and the first heating medium outlet B are communicated through the heat exchange pipe in the upper half 42; the heat exchange pipe at the top of the lower half 43 protrudes out of the case 41 and is formed as the second heating medium inlet C, the heat exchange pipe at the bottom of the lower half 43 protrudes out of the case 41 and is formed as the second heating medium outlet D, and the second heating medium inlet C and the second heating medium outlet D are communicated through the heat exchange pipe in the lower half 43;

the bottom end of the shell 41 is open and is an air channel inlet 44 of the combined air heater and is connected with a fan 11, the top end of the shell is open and is formed into an air channel outlet 45 of the combined air heater, an air channel is arranged between the air channel inlet 44 and the air channel outlet 45 of the combined air heater, and the overflowing direction of the air channel is perpendicular to the length direction of the heat exchange tube.

Therefore, when heating or domestic hot water is not needed in summer, the whole combined heat exchange area heats air by using circulating water, the outlet valve 49 in the combined heat exchange area is closed, the flow channel valve 91 is opened, and hot water enters from the first heat medium inlet A until is discharged from the second heat medium outlet D; when hot water is needed for heating in winter, the upper half area 42 adopts steam to heat air, the flow channel valve 91 is closed, the outlet valve 49 is opened, and the steam enters through the first heat medium inlet A and then is discharged from the first heat medium outlet B; the combination of steam heating and circulating water heating is realized, the medium in the heat exchange pipe can be adjusted according to the requirements of users, and the consumption of low-pressure steam extraction of the boiler is reduced.

Wherein the heat exchange tubes of the upper half 42 have a downward inclination in the flow direction of the heating medium, and the heat exchange tubes of the lower half 43 are horizontally disposed.

Because, only carry out steam heating at first half district 42, and steam heating can have the comdenstion water to flow out, if the comdenstion water stays in the heat exchange tube, can influence heat exchange efficiency, the event will lead to the heat exchange tube of steam and set up certain gradient to the discharge comdenstion water, and when adopting circulating water heating air, then need not to consider this problem, the event heat exchange tube level of second half district 43 arrange can. In practice, the heat exchange tubes of the upper half zone 42 adopt a structure of 5: a gradient of 1000 deg.

The transverse heat exchange tubes are sequentially connected serpentine tube panels, and the bending parts 46 of the serpentine tube panels are respectively positioned at the left part and the right part of the serpentine tube panels;

the outside of shell 41 corresponds snakelike tube panel both sides position of bending 46 and all is equipped with the tube sheet 47 that parallels with air duct, the hole that supplies bending 46 to stretch out outside tube sheet 47 is seted up to the position that corresponds bending 46 on the tube sheet 47, and the area of trompil is greater than the cross-sectional area of bending 46.

Thus, the area of the opening on the tube plate 47 is larger than the cross-sectional area of the bending part 46, so that the heat exchange tube can be conveniently expanded by heating.

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 arranged on the same side;

the bending part 46 close to the flow channel 9 is welded with a tube plate 47; a cover 48 is arranged outside the bending part 46 far away from the flow channel 9, and the cover 48 is welded with the tube plate 47 to cover the bending part 46 inside.

Thus, the bending part 46 on one side is welded with the tube plate 47, the bending part 46 on the other side is not welded with the tube plate 47, so that the heat exchange tube is expanded towards the designated side by heating, and a cover shell 48 is arranged outside the bending part 46 which is not welded with the tube plate 47 for sealing, thereby avoiding heat loss.

It will be appreciated that in practice, there are a plurality of serpentine tube panels in both the upper half 42 and the lower half 43. In last half, a plurality of snakelike tube panels are parallel to each other, horizontal interval arrangement, and the heat exchange tube at every snakelike tube panel top stretches out the shell and forms the heat medium import, and a plurality of heat medium imports through the collection case and collects and form first heat medium import A, equally, the heat exchange tube of every snakelike tube panel bottom stretches out shell 41 and collects through the collection case and forms first heat medium export B. In the lower half, the heat exchange tubes at the top of each serpentine tube panel extend out of the housing 41 and are collected by the header to form the second heat medium inlet C, and the heat exchange tubes at the bottom of each serpentine tube panel extend out of the housing 41 and are collected by the header to form the second heat medium outlet D.

Wherein, the first pipeline 6 and the second pipeline 7 are all equipped with the inlet valve near first heat medium import A department, and the external boiler 1 of inlet valve on the first pipeline 6 is in order to be used for controlling steam and get into combined air heater 4, and the external low-temperature economizer 2 of inlet valve on the second pipeline 7 is in order to be used for controlling the circulating water and get into combined air heater 4.

Thus, after the fan 11 is started, when the air is heated by steam, the inlet valve for controlling steam and the outlet valve 49 are opened at the same time, and the flow channel valve 91 and the inlet valve for controlling circulating water are closed; when the circulating water is adopted to heat air, the circulating water pump 5, the inlet valve for controlling the circulating water and the flow channel valve 91 are opened at the same time, and the inlet valve for controlling the steam and the outlet valve 49 are closed; thereby realizing the switching of the heating medium in the combined air heater.

In practice, the flow path valve 91 is a butterfly valve to rapidly open and close the valve plate.

Wherein, the outlet valve 49 comprises a gate valve and an electric valve which are arranged adjacently, and the gate valve is arranged at one side close to the flow passage 9; the inlet valve comprises a gate valve and an electric valve which are arranged in close proximity, and the gate valve is arranged on one side close to the first heating medium inlet A.

In this way, the electric valve is used for realizing the flow regulation of the medium in the pipeline, the gate valve is arranged for protecting, and when the electric valve is out of control, the electric valve can be fully opened or fully closed.

When the electric valve driving device is implemented, the electric valve driving device is a reversible electric motor, the valve of the valve core control electric valve is driven by the rotation of the motor for a certain time, the AI analog signal control is adopted, the flow of the pipeline medium can be regulated, and the digital signal control can be used instead in a specific pipeline environment.

Wherein, a hot water taking point 71 is further arranged on the second pipeline 7 near the low-temperature economizer 2 and is used as domestic hot water.

The heat exchange tubes of the combined air heater 4 and the low-temperature economizer 2 adopt a plurality of spherical concave inner micro-rib dimpled composite reinforced heat exchange tubes arranged on the outer surface of the tube wall;

the heat exchange tube of the vortex tube type air preheater 3 adopts a vortex reinforced heat exchange tube with a plurality of spherical bulges on the inner wall.

Therefore, compared with the common light pipe, the inner micro-rib dimpled composite reinforced heat exchange pipe (particularly CN 110081763A) and the vortex reinforced heat exchange pipe (particularly CN 210108115U) are beneficial to improving the heat exchange efficiency of the air preheater, the low-temperature economizer and the combined air heater, effectively reducing the phenomenon of dust accumulation and even blockage in the pipes, reducing the occupied space of the heat exchange pipes (the number of the heat exchange pipes under the same heat exchange effect), and prolonging the service life of equipment in the system.

In the embodiment, the flue gas outlet of the boiler 1 is connected with the flue gas inlet of the vortex tube type air preheater 3 through the SCR reactor 12, and the adopted air preheater adopts a vortex reinforced heat exchange tube, so that the temperature of the flue gas can be reduced to 160 ℃, and air is heated through heat exchange; the low-temperature economizer 2 adopts an inner micro-ribbed dimpled composite reinforced heat exchange tube, the temperature of the flue gas can be further reduced to 140 ℃, and the temperature of the water in the tube of the low-temperature economizer 2 is increased from 50 ℃ to 80 ℃; the hot water heated by the low-temperature economizer 2 is used for a combined air heater 4, the combined air heater 4 heats the air to ensure that the temperature of the secondary air (air temperature) at the air inlet I of the vortex joint pipe type air preheater 3 is up to 30 ℃, the temperature of the primary air is increased to 360 ℃ after the secondary air passes through the vortex joint pipe type air preheater 3, and the temperature of the secondary air is up to 320 ℃ and enters a boiler; and finally, the effective utilization of the temperature of the whole system is realized, and the effects of energy conservation and emission reduction are achieved. The low-temperature economizer 2 is connected with a dust remover 13 and a desulfurizing tower 14, and the flue gas flows through a chimney 15 in sequence and then is discharged.

Finally, although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the present invention can be modified or replaced by other means without departing from the spirit and scope of the present invention, which should be construed as limited only by the appended claims.

Claims (9)

1. A system for realizing waste heat recovery by adopting a combined air heater comprises a boiler and a low-temperature economizer, wherein a circulating water pump is arranged in front of a water inlet of the low-temperature economizer; the method is characterized in that: the air preheater also comprises a vortex tube type air preheater and a combined air heater;

the combined air heater comprises a first heating medium inlet, a first heating medium outlet, a second heating medium inlet and a second heating medium outlet; a steam outlet of the boiler is connected with a first heating medium inlet through a first pipeline, and a water outlet of the low-low temperature economizer is connected with the first heating medium inlet through a second pipeline; the first heat medium outlet is connected with the boiler through a third pipeline, an outlet valve is arranged on the third pipeline close to the first heat medium outlet, the front of an inlet of the outlet valve, the first heat medium outlet and the second heat medium inlet are communicated through a flow channel, and a flow channel valve is arranged on the flow channel; the second heating medium outlet is connected with the water inlet of the low-temperature economizer through a fourth pipeline;

the air duct outlet of the combined air heater is connected with the air inlet of the vortex tube type air preheater; the air outlet of the vortex tube type air preheater is connected with the boiler, the smoke outlet of the boiler is connected with the smoke inlet of the vortex tube type air preheater, and the smoke outlet of the vortex tube type air preheater is connected with the low-temperature economizer.

2. The system for realizing waste heat recovery by adopting the combined air heater as claimed in claim 1, characterized in that: the combined air heater comprises a shell, wherein two ends of the shell are opened along the vertical direction; a combined heat exchange area is arranged in the shell, a plurality of rows of transverse heat exchange tubes are vertically arranged in the combined heat exchange area at intervals, and the combined heat exchange area comprises an upper half area and a lower half area positioned below the upper half area;

the heat exchange tube at the top of the upper half area extends out of the shell and forms the first heat medium inlet, the heat exchange tube at the bottom of the upper half area extends out of the shell and forms the first heat medium outlet, and the first heat medium inlet and the first heat medium outlet are communicated through the heat exchange tube in the upper half area; the heat exchange tube at the top of the lower half zone extends out of the shell and forms a second heat medium inlet, the heat exchange tube at the bottom of the lower half zone extends out of the shell and forms a second heat medium outlet, and the second heat medium inlet and the second heat medium outlet are communicated through the heat exchange tube in the lower half zone;

the bottom end opening of the shell is an air channel inlet of the combined air heater and is connected with a fan, the top end opening of the shell is formed into an air channel outlet of the combined air heater, an air channel is arranged between the air channel inlet and the air channel outlet of the combined air heater, and the overflowing direction of the air channel is perpendicular to the length direction of the heat exchange tube.

3. The system for realizing waste heat recovery by adopting the combined air heater as claimed in claim 2, is characterized in that: the heat exchange pipes in the upper half area have downward inclination along the flow direction of the heat medium, and the heat exchange pipes in the lower half area are horizontally arranged.

4. The system for realizing waste heat recovery by adopting the combined air heater as claimed in claim 2, characterized in that: the plurality of rows of transverse heat exchange tubes are sequentially connected into a serpentine tube panel, and the bending parts of the serpentine tube panel are respectively positioned at the left part and the right part of the serpentine tube panel;

the position that the outside of shell corresponds snakelike tube panel both sides portion of bending all is equipped with the tube sheet that parallels with air duct, the hole that supplies the portion of bending to stretch out outside the tube sheet is seted up to the position that corresponds the portion of bending on the tube sheet, and the area of trompil is greater than the cross-sectional area of the portion of bending.

5. The system for realizing waste heat recovery by adopting the combined air heater as claimed in claim 4, is characterized in that: the first heating medium inlet, the first heating medium outlet, the second heating medium inlet, the second heating medium outlet and the flow channel are arranged on the same side;

the bending part close to the flow channel is welded with the tube plate; and a housing is arranged outside the bending part far away from the flow channel, and the housing is welded with the tube plate so as to cover the bending part in the tube plate.

6. The system for realizing waste heat recovery by adopting the combined air heater as claimed in claim 1, is characterized in that: and inlet valves are arranged on the first pipeline and the second pipeline and close to a first heat medium inlet, the inlet valve on the first pipeline is used for controlling steam to enter the combined air heater, and the inlet valve on the second pipeline is used for controlling circulating water to enter the combined air heater.

7. The system for realizing waste heat recovery by adopting the combined air heater as claimed in claim 6, is characterized in that: the outlet valve comprises a gate valve and an electric valve which are arranged in series, and the gate valve is arranged on one side close to the flow channel;

the inlet valve comprises a gate valve and an electric valve which are arranged in series, and the gate valve is arranged on one side close to the first heating medium inlet.

8. The system for realizing waste heat recovery by adopting the combined air heater as claimed in claim 1, characterized in that: and a hot water taking point is also arranged on the second pipeline close to the low-temperature economizer and used as domestic hot water.

9. The system for realizing waste heat recovery by adopting the combined air heater according to any one of claims 1-8, characterized in that: the heat exchange tube of the combined air heater and the low-temperature economizer adopts a plurality of spherical concave inner micro-rib dimpled composite reinforced heat exchange tubes arranged on the outer surface of the tube wall;

the heat exchange tube of the vortex node tube type air preheater adopts a vortex node reinforced heat exchange tube with a plurality of spherical bulges on the inner wall.

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