Two-stage anti-freezing energy-saving air heater system

Abstract

The utility model relates to a two-stage anti-freezing energy-saving air heater system which comprises an air heater heat exchange device, a smoke waste heat utilization device, a steam exhaust waste heat heat exchange device, a steam exhaust waste heat utilization device and an intermediate heat exchanger. The air heater heat exchange device comprises a primary air heater and a secondary air heater, the primary air heater and the secondary air heater are arranged in parallel, and the air heater heat exchange device is used for correspondingly adjusting the primary air heater and the secondary air heater to enter matched heat exchange modes according to the external temperature, the heat exchange mode comprises countercurrent heat exchange and downstream heat exchange; the flue gas waste heat utilization device is connected with the air heater heat exchange device; the dead steam waste heat exchange device is connected with the dead steam waste heat utilization device; the air heater heat exchange device is connected with the dead steam waste heat utilization device through the intermediate heat exchanger; and high-quality steam is replaced by exhaust waste heat of the steam turbine, so that the energy efficiency of the unit is improved.

Description

Technical Field

[0001] The utility model relates to the field of power station boilers, in particular to a double-stage antifreeze energy-saving air heater system. Background Art

[0002] In the extremely cold regions of northern my country, the operating temperature difference of the heater system is large in winter, resulting in a large thermal expansion between the heat exchange tubes, which is difficult to absorb in the structure and easily causes leakage accidents; at the same time, the water in the heater drain pipe is easy to freeze in low temperature environments, causing the heater tube bundle to freeze and crack, threatening the safe operation of the unit. At present, heaters mostly use auxiliary steam sources or other extraction steam for heating, using high-temperature, high-pressure, high-quality energy to supply low-grade heat, resulting in high-grade energy loss of the unit and problems such as reduced unit efficiency.

[0003] In order to prevent or reduce low-temperature corrosion and ash blockage of the air preheater, it is necessary to install a heater to increase the air temperature at the air preheater inlet. The conventional steam heater is replaced by an air-water heat exchange heater, and circulating water is used as the heat medium to release the heat absorbed on the flue gas side to the primary and secondary cold air, preheating the cold air before entering the air preheater, thereby realizing the recovery of flue gas heat and reducing the auxiliary steam source consumption of conventional steam heaters. However, there are still some problems in the current application of heaters.

[0004] When used in the extremely cold northern regions, the heater tubes are prone to freezing and cracking. There are generally two locations for freezing and cracking: one is the elbow of the heater heat exchange tube, and the other is the bottom rows of heat exchange tubes in the bottom module of the heater. There are two reasons for the freezing and cracking: (1) When the heater header is arranged in a bottom-in-top-out manner, water is easily stored outside the elbow of the lower header. Most heaters use serpentine tubes and the heat exchange tubes are arranged horizontally. When the heater is shut down, the water in the heat exchange tube cannot be effectively drained. When the ambient temperature is low, the heater heat exchange tube freezes and cracks; at the same time, when the ambient temperature is low and the load is low, the flow rate in the heat exchange tube is small, which is also easy to cause the heat exchange tube to freeze and crack. (2) The heater heat exchange tube is generally arranged horizontally, with countercurrent heat exchange. At this time, the cold and hot fluids have the largest average temperature difference and the heat exchange performance is the best. At this time, the temperature of the water is low after the heat is released, and the heater is prone to freezing.

[0005] Using flue gas waste heat to provide heat for the heater can effectively recover waste heat and improve unit efficiency. However, it is easy to have low return water temperature and flue gas condensation. In addition, for the joint design system of low-temperature economizer and heater, when the flue gas recovery heat temperature is high and absorbed by the heater, if it directly enters the low-pressure heating system, it needs to be supplemented with heat again, causing the low-pressure heater to extract more steam for heating, and not utilizing low-grade heat.

[0006] In order to solve the problem of heater antifreeze, Xi'an Thermal Engineering Research Institute Co., Ltd. proposed a two-stage antifreeze heater system. The system's primary air heater and secondary air heater are both set up in two stages, namely conventional heater and antifreeze heater, to achieve step-by-step heating of primary and secondary air. The heat source of the antifreeze heater comes from the condensed water between the No. 4 low-pressure heater and the No. 5 low-pressure heater, and the heat is transferred to the primary and secondary air through the circulating antifreeze liquid. The system adopts a two-stage heat exchange method to reduce the temperature rise of each stage of the heater, reduce the operating temperature difference of the heater, and reduce the thermal expansion amplitude between the rows of heater tubes to avoid leakage accidents. However, an antifreeze heater is set before the conventional heater to heat the primary and secondary air in stages. Both stages of the heater adopt countercurrent heat exchange, which has better heat exchange performance, but the cold air and cold water appear at the same end, and the heater may still freeze under low flow conditions.

[0007] Regarding the energy-saving design of the heater system, Guo Xingjun proposed an antifreeze and energy-saving power station heater system that uses exhaust steam waste heat to provide heat for the heater. This system uses the exhaust heat of the turbine to save high-grade energy of the unit and solve the problem of reduced efficiency of the unit. Chu Xiaoliang and others proposed an efficient and energy-saving antifreeze heater system that uses high-temperature cold water at the outlet of the turbine condenser to heat the cold air at the outlet of the boiler fan. The heat of the high-temperature cooling water is completely waste heat. The use of this part of heat can greatly improve the economy of the entire plant and has a huge energy-saving effect. This scheme takes into account the recovery of the turbine exhaust heat and the high-temperature cold water at the outlet of the condenser, but when this part of the heat cannot meet the temperature increase requirements of the primary and secondary air, more high-quality steam is still required to provide heat.

[0008] Li Nan and others proposed a heater antifreeze technology that changes the heater's co-current or countercurrent heat exchange mode for different low-temperature environments, reducing the risk of heater freezing and cracking through operation control. Although this solution can change the heat exchange mode of the primary air heater and the secondary air heater according to the ambient temperature, the temperature rise of the heater will be large when the single-stage heater is running, which will increase the thermal expansion amplitude between the heater tube rows and cause leakage accidents.

[0009] It can be seen that how to solve the problems of leakage accidents easily caused by large temperature difference in the operation of the heater system, freezing and cracking of the heater tube bundle easily caused by low temperature environment, and energy loss and reduced unit efficiency caused by using high temperature and high pressure high-quality energy to supply low-grade heat, has become a technical problem that technical personnel in this field need to solve urgently. Utility Model Content

[0010] The utility model provides a two-stage antifreeze energy-saving heater system to solve the technical problems of leakage accidents easily caused when the temperature difference of the heater system is large, freezing and cracking of the heater tube bundle easily caused in a low temperature environment, and energy loss and reduced unit efficiency caused by using high-temperature and high-pressure high-quality energy to supply low-grade heat.

[0011] In order to solve the above technical problems, the utility model provides a two-stage antifreeze energy-saving heater system, which includes a heater heat exchange device, a flue gas waste heat utilization device, an exhaust steam waste heat heat exchange device, an exhaust steam waste heat utilization device and an intermediate heat exchanger;

[0012] The heater heat exchange device comprises a primary air heater and a secondary air heater, the primary air heater and the secondary air heater are arranged in parallel, and the heater heat exchange device is used to adjust the primary air heater and the secondary air heater to enter a matching heat exchange mode according to the external temperature, wherein the heat exchange mode includes countercurrent heat exchange and cocurrent heat exchange;

[0013] The flue gas waste heat utilization device is connected to the air heater heat exchange device;

[0014] The exhaust steam waste heat heat exchange device is connected to the exhaust steam waste heat utilization device;

[0015] The air heater heat exchange device is connected to the exhaust steam waste heat utilization device through the intermediate heat exchanger.

[0016] Furthermore, the heater heat exchange device also includes a heater bypass pipe and a plurality of first control valves;

[0017] The primary air heater comprises a primary air level one heater and a primary air level two heater, and the secondary air heater comprises a secondary air level one heater and a secondary air level two heater; the working medium inlet and outlet pipes of the primary air level one heater, the working medium inlet and outlet pipes of the primary air level two heater, the connecting pipe between the primary air level one heater and the primary air level two heater, the working medium inlet and outlet pipes of the secondary air level one heater, the working medium inlet and outlet pipes of the secondary air level two heater, the connecting pipe between the secondary air level one heater and the secondary air level two heater, and the heater bypass pipe are all provided with the corresponding first control valve;

[0018] The inlet and outlet of the primary air heater are connected to the inlet and outlet of the secondary air heater through the heater bypass pipe.

[0019] Furthermore, the flue gas waste heat utilization device includes a flue gas water heat exchanger, a flue gas heat source and a plurality of second control valves;

[0020] The flue gas heat source is connected to the heat absorption side inlet of the smoke-water heat exchanger, the primary air two-stage heater and the secondary air two-stage heater are connected to the heat release side outlet of the smoke-water heat exchanger, and the working medium inlet and outlet pipe of the smoke-water heat exchanger is provided with the corresponding second control valve.

[0021] Furthermore, the exhaust steam waste heat heat exchange device comprises an exhaust steam waste heat exchanger, an exhaust steam input pipeline and an exhaust steam heat source;

[0022] The exhaust steam heat source is connected to the exhaust steam waste heat exchanger through the exhaust steam input pipeline.

[0023] Furthermore, the exhaust steam waste heat exchange device also includes an auxiliary steam source, an auxiliary steam source input pipeline and a steam ejector;

[0024] The auxiliary steam source is connected to the steam ejector through the auxiliary steam source input pipeline, and the steam ejector is connected to the exhaust steam waste heat exchanger.

[0025] Furthermore, the exhaust steam waste heat exchange device also includes a drain pipe, a drain tank, a drain pump and a vacuum pump;

[0026] The drain tank and the drain pump are both arranged on the drain pipe, and the drain pipe is connected to the exhaust steam waste heat exchanger;

[0027] The vacuum pump is connected to the exhaust steam waste heat exchanger.

[0028] Furthermore, the exhaust steam waste heat exchange device also includes a plurality of third control valves;

[0029] The exhaust steam input pipeline, the auxiliary steam source input pipeline and the drain pipeline are all provided with corresponding third control valves.

[0030] Furthermore, the exhaust steam waste heat utilization device includes a pressure stabilizing tank, a variable frequency pump, a circulating medium input pipeline and a circulating medium output pipeline; wherein,

[0031] One end of the pressure stabilizing tank is connected to one end of the variable frequency pump, the other end of the variable frequency pump is connected to one end of the circulating medium input pipeline, the other end of the circulating medium input pipeline is connected to one end of the exhaust steam waste heat exchanger, the other end of the exhaust steam waste heat exchanger is connected to one end of the circulating medium output pipeline, the other end of the circulating medium output pipeline is connected to one end of the intermediate heat exchanger, and the other end of the intermediate heat exchanger is connected to the other end of the pressure stabilizing tank.

[0032] Furthermore, the exhaust steam waste heat utilization device also includes a heat exchange bypass pipeline and a plurality of fourth control valves;

[0033] One end of the intermediate heat exchanger is connected to the other end of the intermediate heat exchanger through the heat exchange bypass pipeline;

[0034] The heat exchange bypass pipeline, the circulating medium input pipeline and the circulating medium output pipeline are all provided with corresponding fourth control valves.

[0035] Furthermore, the system further comprises a system isolation pipeline and a plurality of fifth control valves, the flue gas waste heat utilization device further comprises a flue gas waste heat utilization bypass pipeline, and the exhaust steam waste heat utilization device further comprises an exhaust steam waste heat utilization bypass pipeline;

[0036] The flue gas waste heat utilization bypass pipeline, the exhaust steam waste heat utilization bypass pipeline, the system isolation pipeline and the heater bypass pipeline form a pipeline loop, and a circulating water pump is provided on the pipeline loop;

[0037] The system isolation pipeline, the flue gas waste heat utilization bypass pipeline and the exhaust steam waste heat utilization bypass pipeline are all provided with corresponding fifth control valves.

[0038] Compared with the prior art, the beneficial effects of the embodiments of the present invention are at least one of the following:

[0039] (1) According to different operating conditions, the flow mode of the working fluid is changed by controlling the valve opening and closing, reducing the operating temperature difference to achieve the purpose of anti-freezing, thereby improving the operating safety of the heater;

[0040] (2) By designing a flue gas waste heat utilization device and an exhaust steam waste heat heat exchange device, the flue gas waste temperature is ensured to meet the requirements, and then the turbine exhaust steam waste heat is fully utilized to replace the use of high-quality steam, thereby improving the unit energy efficiency. The flue gas waste heat and turbine exhaust steam heat are also used to heat the air, achieving energy saving goals through waste heat recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a block diagram of a two-stage antifreeze and energy-saving heater system provided by an embodiment of the utility model;

[0042] Figure 2 It is a structural schematic diagram of a two-stage antifreeze energy-saving heater system provided by an embodiment of the utility model;

[0043] Figure 3 It is a schematic structural diagram of a two-stage antifreeze energy-saving heater system in summer working condition provided by an embodiment of the utility model;

[0044] Figure 4 It is a schematic diagram of the structure of a two-stage antifreeze energy-saving heater system in winter working conditions provided by an embodiment of the utility model;

[0045] Description of the drawings: 100, heater heat exchange device; 101, primary air heater; 1011, primary air level 1 heater; 1012, primary air level 2 heater; 102, secondary air heater; 1021, secondary air level 1 heater; 1022, secondary air level 2 heater; 103-119, first control valve; 120, 127 and 128 fifth control valves; 121, flue gas waste heat utilization bypass pipeline; 122, system isolation pipeline; 123, exhaust steam waste heat utilization bypass pipeline; 124-125, pipeline drain valve; 126, circulating water pump; 200, flue gas waste heat utilization device; 201, flue gas water heat exchanger; 202-203, The second control valve; 300, exhaust steam waste heat heat exchange device; 301, exhaust steam waste heat heat exchanger; 302, auxiliary steam source input pipeline; 303, exhaust steam input pipeline; 304, drain pipeline; 305, auxiliary steam source; 306, exhaust steam heat source; 307, steam ejector; 308, vacuum pump; 309, drain tank; 310, drain pump; 311-315, the third control valve; 400, exhaust steam waste heat utilization device; 401, pressure regulating tank; 402, frequency conversion pump; 403, circulating medium input pipeline; 404, heat exchange bypass pipeline; 405, circulating medium output pipeline; 406-408, the fourth control valve; 500, intermediate heat exchanger. DETAILED DESCRIPTION

[0046] The following is a detailed explanation of the implementation mode of the present invention in conjunction with the accompanying drawings. The embodiments are provided for illustrative purposes only and cannot be understood as limitations on the present invention. The accompanying drawings are provided for reference and illustration only and do not constitute limitations on the scope of patent protection of the present invention, because many changes can be made to the present invention without departing from the spirit and scope of the present invention.

[0047] In the description of the present invention, it should be understood that the terms "upper", "lower", "left", "right", "top", "middle", "bottom", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0048] refer to Figure 1 The utility model embodiment provides a two-stage antifreeze energy-saving heater system, such as Figure 1 As shown, the system includes a heater heat exchange device 100, a flue gas waste heat utilization device 200, an exhaust steam waste heat heat exchange device 300, an exhaust steam waste heat utilization device 400 and an intermediate heat exchanger 500;

[0049] The heater heat exchange device 100 includes a primary air heater 101 and a secondary air heater 102, the primary air heater 101 and the secondary air heater 102 are arranged in parallel, and the heater heat exchange device 100 is used to adjust the primary air heater 101 and the secondary air heater 102 to enter a matching heat exchange mode according to the external temperature, wherein the heat exchange mode includes countercurrent heat exchange and cocurrent heat exchange;

[0050] The flue gas waste heat utilization device 200 is connected to the heater heat exchange device 100;

[0051] The exhaust steam waste heat heat exchange device 300 is connected to the exhaust steam waste heat utilization device 400;

[0052] The air heater heat exchange device 100 is connected to the exhaust steam waste heat utilization device 400 through the intermediate heat exchanger 500 .

[0053] The present application adopts a double air heater and adjusts the heat exchange mode of the double air heater according to the external temperature to reduce the operating temperature difference of the heater system, and designs a flue gas waste heat utilization device 200 and an exhaust steam waste heat heat exchange device 300 to ensure that the flue gas waste temperature meets the conditions, fully utilize the turbine exhaust waste heat, replace the use of high-quality steam, improve the unit energy efficiency, and effectively improve the unit efficiency.

[0054] In one specific embodiment, see Figure 2 , the heater heat exchange device 100 also includes a heater bypass pipe and a plurality of first control valves;

[0055] The primary air heater 101 includes a primary air level 1 heater 1011 and a primary air level 2 heater 1012, and the secondary air heater 102 includes a secondary air level 1 heater 1021 and a secondary air level 2 heater 1022; the working medium inlet and outlet pipes of the primary air level 1 heater 1011, the working medium inlet and outlet pipes of the primary air level 2 heater 1012, the connecting pipe between the primary air level 1 heater 1011 and the primary air level 2 heater 1012, the working medium inlet and outlet pipes of the secondary air level 1 heater 1021, the working medium inlet and outlet pipes of the secondary air level 2 heater 1022, the connecting pipe between the secondary air level 1 heater 1021 and the secondary air level 2 heater 1022, and the heater bypass pipe are all provided with the corresponding first control valve;

[0056] The inlet and outlet of the primary air heater 101 are connected to the inlet and outlet of the secondary air heater 102 through the heater bypass pipe.

[0057] The two air heaters in the present application are arranged in parallel, so that the circulating medium 1 flowing therein can be connected to the inlets of the two primary air heaters after being split by the fifth control valve 120, and the outlets of the two secondary air heaters are connected to the exhaust steam waste heat utilization device 400 and the flue gas waste heat utilization device 200 after passing through the pipeline. In addition, the outlets of the two secondary air heaters are also provided with pipeline drain valves 124 and 125 to drain the water in the pipeline.

[0058] When the unit is running under different working conditions, the flow pattern of the heater changes. Figure 3 At this time, the ambient temperature is relatively high and the antifreeze requirement is low. In order to improve the heat exchange effect, the two-stage heat exchange mode of the primary air heater 101 and the secondary air heater 102 is countercurrent heat exchange. For the primary air heater 101, the first control valve 107 is opened and the first control valve 108 is closed to realize the two-stage countercurrent heat exchange of the primary air heater 101; for the secondary air heater 102, the first control valve 113 is opened and the first control valve 114 is closed to realize the two-stage countercurrent heat exchange of the secondary air heater 102.

[0059] Winter operating conditions of the unit Figure 4 , since the ambient temperature is relatively low in winter, antifreeze protection of the heater needs to be considered. For the primary air heater 101, the circulating working medium flows through the primary air secondary heater 1012 for countercurrent heat exchange, the first control valve 108 is opened, the first valve 107 is closed, and the primary air first heater 1011 is downstream heat exchange; for the secondary air heater 102, the circulating working medium flows through the secondary air secondary heater 1022 for countercurrent heat exchange, the first control valve 114 is opened, and the first control valve 113 is closed, so that the secondary air first heater 1021 is downstream heat exchange; the downstream heat exchange method can reduce the average temperature difference of the circulating working medium in the cold primary air, cold secondary air and heater, and realize the antifreeze of the heater. The two-stage adjustable heat exchange method adopted in this application can reduce the temperature rise of each stage of the heater and thus reduce the operating temperature difference of the heater.

[0060] In a specific embodiment, the flue gas waste heat utilization device 200 includes a flue gas water heat exchanger 201, a flue gas heat source and a plurality of second control valves;

[0061] The flue gas heat source is connected to the heat absorption side inlet of the smoke-water heat exchanger 201, the primary air two-stage heater 1012 and the secondary air two-stage heater 1022 are connected to the heat release side outlet of the smoke-water heat exchanger 201, and the working medium inlet and outlet pipes of the smoke-water heat exchanger 201 are provided with the corresponding second control valve.

[0062] Specifically, the smoke-water heat exchanger 201 in the present application is connected to two secondary air heaters, so that the smoke-water heat exchanger 201 can release the waste heat in the smoke to the circulating medium 1, and then transfer the heat to the primary air and the secondary air; and the second control valves 202 and 203 are used to control the inlet and outlet of the smoke.

[0063] In a specific embodiment, the exhaust steam waste heat exchange device 300 includes an exhaust steam waste heat exchanger 301, an exhaust steam input pipeline 303 and an exhaust steam heat source 306;

[0064] The exhaust steam heat source 306 is connected to the exhaust steam waste heat exchanger 301 through the exhaust steam input pipeline 303 .

[0065] The exhaust steam waste heat exchange device 300 further includes an auxiliary steam source 305, an auxiliary steam source input pipeline 302 and a steam ejector 307;

[0066] The auxiliary steam source 305 is connected to the steam ejector 307 via the auxiliary steam source input pipeline 302 , and the steam ejector 307 is connected to the exhaust steam waste heat exchanger 301 .

[0067] The exhaust steam waste heat exchange device 300 further includes a drain pipe 304, a drain tank 309, a drain pump 310 and a vacuum pump 308;

[0068] The drain tank 309 and the drain pump 310 are both disposed on the drain pipe 304, and the drain pipe 304 is connected to the exhaust steam waste heat exchanger 301;

[0069] The vacuum pump 308 is connected to the exhaust steam waste heat exchanger 301 .

[0070] The exhaust steam waste heat exchange device 300 also includes a plurality of third control valves;

[0071] The exhaust steam input pipeline 303 , the auxiliary steam source input pipeline 302 and the drain pipeline 304 are all provided with corresponding third control valves.

[0072] The exhaust steam input pipeline 303 in the exhaust steam waste heat exchange device 300 is connected to the inlet of the exhaust steam waste heat exchanger 301, and the outlet of the exhaust steam waste heat exchanger 301 is connected to the drain pipeline 304, so that the exhaust steam enters the exhaust steam waste heat exchanger 301 through the exhaust steam input pipeline 303, releases heat to the circulating medium 2, and is discharged through the drain pipeline 304 after being converted into water. Among them, a steam source bypass pipeline is also arranged between the auxiliary steam source input pipeline 302 and the exhaust steam input pipeline 303, and a third control valve 315 is also arranged on the steam source bypass pipeline. A third control valve 314 is also arranged on the pipeline where the vacuum pump 308 is located. The third control valves 311-315 in the exhaust steam waste heat exchange device 300 are all used to control the flow rate of the flowing working medium in the pipeline where they are located.

[0073] In a specific embodiment, the exhaust steam waste heat utilization device 400 includes a pressure stabilizing tank 401, a variable frequency pump 402, a circulating medium input pipeline 403 and a circulating medium output pipeline 405;

[0074] One end of the pressure stabilizing tank 401 is connected to one end of the variable frequency pump 402, the other end of the variable frequency pump 402 is connected to one end of the circulating medium input pipeline 403, the other end of the circulating medium input pipeline 403 is connected to one end of the exhaust steam waste heat exchanger 301, the other end of the exhaust steam waste heat exchanger 301 is connected to one end of the circulating medium output pipeline 405, the other end of the circulating medium output pipeline 405 is connected to one end of the intermediate heat exchanger 500, and the other end of the intermediate heat exchanger 500 is connected to the other end of the pressure stabilizing tank 401.

[0075] The exhaust steam waste heat utilization device 400 further includes a heat exchange bypass pipeline 404 and a plurality of fourth control valves;

[0076] One end of the intermediate heat exchanger 500 is connected to the other end of the intermediate heat exchanger 500 through the heat exchange bypass pipe 404;

[0077] The heat exchange bypass pipeline 404 , the circulating medium input pipeline 403 , and the circulating medium output pipeline 405 are all provided with corresponding fourth control valves.

[0078] The pressure stabilizing tank 401, the variable frequency pump 402, the circulating medium input pipeline 403, the circulating medium output pipeline 405 and the intermediate heat exchanger 500 in the exhaust steam waste heat utilization device 400 form a closed circulation loop, so that the circulating medium 2 enters the exhaust steam waste heat exchanger 301 from the inlet of the exhaust steam waste heat exchanger 301 to absorb the exhaust steam heat, and then flows through the intermediate heat exchanger 500 to release the heat to the circulating medium 1, and then returns to the heat absorption side inlet of the exhaust steam waste heat exchanger 301 through the circulating medium input pipeline 403; wherein, the circulating medium 2 flows in the circulating medium input pipeline 403 and the circulating medium output pipeline 405; the fourth control valves 406-408 in the exhaust steam waste heat utilization device 400 are also used to control the flow rate of the flowing working medium in the pipeline in which they are located.

[0079] The heat source of the utility model includes flue gas exhaust at the tail end of the boiler and exhaust steam exhaust from the turbine; wherein the flue gas waste heat is transferred to the circulating medium 1 through the flue gas water heat exchanger 201; the exhaust steam waste heat is transferred to the circulating medium 2 through the exhaust steam waste heat heat exchanger 301, and the circulating medium 2 flows through the intermediate heat exchanger 500 to release heat to the circulating medium 1; after absorbing the waste heat, the circulating medium 1 releases heat in the primary air heater 101 and the secondary air heater 102 to achieve heating of the primary air and the secondary air. wherein the flue gas waste heat utilization device 200 and the heater heat exchange device 100 form a two-stage heat exchange system, the first stage heat exchange is the heat exchange between the flue gas heat and the circulating medium 1, and the second stage heat exchange is the heat exchange between the circulating medium 1 and the primary air and the secondary air in the heater. The exhaust steam waste heat heat exchange device 300, the exhaust steam waste heat utilization device 400 and the heater heat exchange device 100 are a three-stage heat exchange system, the first stage heat exchange is the heat exchange between the exhaust steam waste heat and the circulating medium 2, the second stage heat exchange is the heat exchange between the circulating medium 2 and the circulating medium 1, and the third stage heat exchange is the heat exchange between the circulating medium 1 and the air.

[0080] Furthermore, the system further includes a system isolation pipeline 122 and a plurality of fifth control valves, the flue gas waste heat utilization device 200 further includes a flue gas waste heat utilization bypass pipeline 121, and the exhaust steam waste heat utilization device 400 further includes an exhaust steam waste heat utilization bypass pipeline 123;

[0081] The flue gas waste heat utilization bypass pipeline 121, the exhaust steam waste heat utilization bypass pipeline 123, the system isolation pipeline 122 and the heater bypass pipeline form a pipeline loop, and a circulating water pump 126 is provided on the pipeline loop;

[0082] The system isolation pipeline 122 , the flue gas waste heat utilization bypass pipeline 121 and the exhaust steam waste heat utilization bypass pipeline 123 are all provided with corresponding fifth control valves.

[0083] For the generator set, exhaust gas loss and exhaust steam loss are important heat losses of the unit, and effective utilization is very important. The utility model proposes to use the flue gas waste heat and turbine exhaust steam waste heat in stages to heat the primary and secondary air of the heater, effectively reducing the use of high-temperature, high-pressure and high-quality energy; the effective utilization of waste heat can reduce the energy consumption of the unit, while reducing carbon dioxide emissions, bringing certain economic benefits.

[0084] For the flue gas waste heat utilization device 200, the return water temperature is low after the circulating medium 1 releases heat, which is easy to cause flue gas condensation. Therefore, the flue gas waste heat is reasonably released and the flue gas temperature cannot drop too low. At this time, the circulating working medium 1 can be partially heated up; then the exhaust steam waste heat utilization device 400 is used in series to continue heating the circulating working medium 1 using the exhaust steam waste heat. The flue gas waste heat utilization device 200 is provided with a flue gas waste heat utilization bypass pipe 121, and a second control valve is arranged on the pipe. The exhaust steam waste heat utilization device 400 is provided with an exhaust steam waste heat utilization bypass pipe 123, and a fourth control valve is also arranged on the pipe. A system isolation pipe 122 is arranged between the two bypass pipes. When a system in the flue gas waste heat utilization device 200 and the exhaust steam waste heat utilization device 400 fails, it can be effectively isolated without affecting the normal operation of the other system. When the two systems are operated in series, closing the control valves in the flue gas waste heat utilization bypass pipe 121, the system isolation pipe 122 and the exhaust steam waste heat utilization bypass pipe 123 can achieve step-by-step heating of the circulating medium 1.

[0085] See also Figure 3 When the unit is operated in summer, the ambient temperature is high and the heat required to heat the air is low. At this time, the flue gas waste heat utilization bypass pipe 121 is closed, the fifth control valve 127 is opened, the fifth control valve 128 is closed, the system isolation pipe 122 and the exhaust steam waste heat utilization bypass pipe 123 are opened, that is, only the flue gas waste heat is used to heat the air; please refer to Figure 4 When the unit is operated in winter conditions, the ambient temperature is low and more heat is required to heat the air. At this time, the flue gas waste heat utilization bypass pipeline 121, the system isolation pipeline 122 and the exhaust steam waste heat utilization bypass pipeline 123 are closed at the same time, and the fifth control valves 127 and 128 are opened to use the flue gas waste heat and the exhaust steam waste heat to step-heat the circulating medium 1, and then release the heat to the low-temperature air.

[0086] When the ambient temperature is too low (such as in the extremely cold northern regions), and the flue gas waste heat and exhaust steam waste heat cannot meet the air heating requirements, a steam ejector 307 is added to the exhaust steam inlet to introduce an auxiliary steam source to raise the temperature and quality of the exhaust steam, further meeting the requirements of heating the primary air or secondary air. Although some high-quality heat sources are used at this time, most of the heat still comes from waste heat. When the unit is running at low load or shutting down, the auxiliary steam source is introduced through the auxiliary steam source input pipeline 302 to heat the circulating medium 1 in the exhaust steam waste heat heat exchanger 301; the circulating medium 2 exchanges heat with the circulating medium 1 in the intermediate heat exchanger 500 to obtain heat to prevent the circulating medium 1 from freezing in the pipeline when shutting down.

[0087] The primary air heater 101 and the secondary air heater 102 are now mostly partition-type or vacuum tube-type. The circulating medium 1 flows through the heater to release heat to the primary air or secondary air in the air duct, thereby completing the heating function; after releasing the heat, the circulating medium 1 returns to the flue gas waste heat utilization device 200 and the exhaust steam waste heat utilization device 400 to form a closed cycle. The flue gas water heat exchanger 201, the exhaust steam waste heat exchanger 301 and the intermediate heat exchanger 500 are mostly partition-type heat exchangers. In the flue gas water heat exchanger 201, the flue gas exchanges heat with the circulating medium 1, the flue gas cools down, and the circulating medium 1 heats up; in the exhaust steam waste heat exchanger 301, the exhaust steam exchanges heat with the circulating medium 1, and the exhaust steam releases heat to become drain and flows into the drain tank 309; in the intermediate heat exchanger 500, the circulating medium 2 exchanges heat with the circulating medium 1 to heat the circulating medium 1.

[0088] Considering the antifreeze requirements of air heaters in extremely cold areas, the antifreeze characteristics of the circulating medium are very important. For temperatures below 0 degrees in northern winter, the circulating medium 1 in the air heater heat exchange device 100 must use antifreeze as the medium. Antifreeze is used as the working medium, and the appropriate operating mode of the air heater is determined to avoid ice formation in the air heater drain pipe and excessive operating temperature difference, and to prevent the heater tube bundle from freezing and cracking. The circulating medium 2 of the exhaust steam waste heat utilization device 400 can be water, freezing liquid or other media, which can effectively prevent the exhaust steam and other heat sources from freezing after heat release, adjust the outlet temperature after the heat source releases heat, and return to the hot well at a suitable temperature.

[0089] The exhaust steam waste heat utilization device 400 sets a heat exchange bypass pipeline 404 for the intermediate heat exchanger 500 and is equipped with a fourth control valve to control the flow of the circulating medium 2 flowing into the intermediate heat exchanger 500; at the same time, when the intermediate heat exchanger 500 fails, the heat exchange bypass pipeline 404 can also be used to take emergency isolation measures.

[0090] The heater heat exchange device 100 is provided with a heater bypass pipe between the inlet and outlet of the circulating medium, and is equipped with a first control valve 119 for adjusting the flow of the circulating medium entering the heater. At the same time, when the primary air heater 101 and the secondary air heater 102 fail or are disabled, opening one or more of the first control valves 103-119 and the fifth control valve 120 can form a loop and cut off the heater.

[0091] With flue gas waste heat and exhaust steam as the main heat source and auxiliary steam source as the auxiliary, the working process of the above two-stage antifreeze heater system is as follows:

[0092] The exhaust steam flows through the exhaust steam heat source 306 input pipeline through the steam ejector 307 and enters the exhaust steam waste heat exchanger 301, releasing the exhaust steam waste heat to the circulating medium 2; when the waste heat is insufficient, the exhaust steam in the exhaust steam heat source 306 and the steam in the auxiliary steam source 306 enter the steam ejector 307 through the exhaust steam input pipeline 303 and the auxiliary steam source input pipeline 302 respectively, generating a mixed steam source with increased temperature and quality, and flows into the exhaust steam waste heat exchanger 301; the exhaust steam after heat release is discharged into the drain device through the drain pipeline 304; for the exhaust steam waste heat utilization device 400, the circulating medium 2 in the pressure stabilizing tank 401 flows into the inlet of the exhaust steam waste heat exchanger 301 through the variable frequency pump 402, and after absorbing the exhaust steam waste heat, flows into the medium through the circulating medium output pipeline 405 The intermediate heat exchanger 500 releases heat, and the circulating medium 2 after releasing heat absorbs the exhaust steam heat to complete the working medium cycle; for the flue gas waste heat utilization device 200, the flue gas flows into the flue gas water heat exchanger 201, releases heat and then flows out; for the heater heat exchange device 100, the circulating medium 1 first passes through the flue gas water heat exchanger 201 to absorb the flue gas waste heat, then flows through the intermediate heat exchanger 500 to absorb the exhaust steam waste heat, passes through the circulating water pump 126, and then passes through the control valve 120 to be divided into the primary air heater 101 and the secondary air heater 102, releases heat in the heater to heat the air in the air duct, and the circulating medium 1 after releasing heat returns to the flue gas waste heat utilization device 200 and the exhaust steam waste heat utilization device 400 to absorb heat again, completing the cycle of heat absorption and heat release.

[0093] It should be noted that the utility model adopts a heater system that can change the flow direction, in which the primary air heater and the secondary air heater are both set in two stages. When anti-freezing measures are taken, the first-stage heater adopts a co-current heat exchange method, and the inlet air temperature is -25°C for the primary air temperature and -18°C for the secondary air temperature, and the outlet air temperature is 0°C. The second-stage heater adopts a countercurrent heat exchange method, and the inlet air temperature is 0°C and the outlet air temperature is 55°C.

[0094] The utility model relates to the field of power station boilers, and in particular to a two-stage antifreeze and energy-saving air heater system, the system comprising an air heater heat exchange device, a flue gas waste heat utilization device, an exhaust steam waste heat heat exchange device, an exhaust steam waste heat utilization device and an intermediate heat exchanger; wherein the air heater heat exchange device comprises a primary air heater and a secondary air heater, the primary air heater and the secondary air heater are arranged in parallel, and the air heater heat exchange device is used to adjust the primary air heater and the secondary air heater to enter a matching heat exchange mode according to the external temperature, wherein the heat exchange mode includes countercurrent heat exchange and downstream heat exchange; the flue gas waste heat utilization device is connected to the air heater heat exchange device; the exhaust steam waste heat heat exchange device is connected to the exhaust steam waste heat utilization device; the air heater heat exchange device is connected to the exhaust steam waste heat utilization device through the intermediate heat exchanger. The utility model reduces the operating temperature difference of the heater by using a double heater, designs a flue gas waste heat utilization device and an exhaust steam waste heat heat exchange device, ensures that the flue gas waste temperature meets the conditions, and then fully utilizes the turbine exhaust steam waste heat to replace the use of high-quality steam, thereby improving the energy efficiency of the unit.

[0095] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principle of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A two-stage antifreeze energy-saving heater system, characterized in that: The system comprises a heater heat exchange device, a flue gas waste heat utilization device, an exhaust steam waste heat heat exchange device, an exhaust steam waste heat utilization device and an intermediate heat exchanger; The heater heat exchange device comprises a primary air heater and a secondary air heater, the primary air heater and the secondary air heater are arranged in parallel, and the heater heat exchange device is used to adjust the primary air heater and the secondary air heater to enter a matching heat exchange mode according to the external temperature, wherein the heat exchange mode includes countercurrent heat exchange and cocurrent heat exchange; The flue gas waste heat utilization device is connected to the air heater heat exchange device; The exhaust steam waste heat heat exchange device is connected to the exhaust steam waste heat utilization device; The air heater heat exchange device is connected to the exhaust steam waste heat utilization device through the intermediate heat exchanger.

2. A two-stage antifreeze energy-saving heater system according to claim 1, characterized in that: The heater heat exchange device also includes a heater bypass pipe and a plurality of first control valves; The primary air heater comprises a primary air level one heater and a primary air level two heater, and the secondary air heater comprises a secondary air level one heater and a secondary air level two heater; the working medium inlet and outlet pipes of the primary air level one heater, the working medium inlet and outlet pipes of the primary air level two heater, the connecting pipe between the primary air level one heater and the primary air level two heater, the working medium inlet and outlet pipes of the secondary air level one heater, the working medium inlet and outlet pipes of the secondary air level two heater, the connecting pipe between the secondary air level one heater and the secondary air level two heater, and the heater bypass pipe are all provided with the corresponding first control valve; The inlet and outlet of the primary air heater are connected to the inlet and outlet of the secondary air heater through the heater bypass pipe.

3. A two-stage antifreeze energy-saving heater system according to claim 2, characterized in that: The flue gas waste heat utilization device includes a flue gas water heat exchanger, a flue gas heat source and a plurality of second control valves; The flue gas heat source is connected to the heat absorption side inlet of the smoke-water heat exchanger, the primary air two-stage heater and the secondary air two-stage heater are connected to the heat release side outlet of the smoke-water heat exchanger, and the working medium inlet and outlet pipe of the smoke-water heat exchanger is provided with the corresponding second control valve.

4. A two-stage antifreeze energy-saving heater system according to claim 2, characterized in that: The exhaust steam waste heat exchange device comprises an exhaust steam waste heat exchanger, an exhaust steam input pipeline and an exhaust steam heat source; The exhaust steam heat source is connected to the exhaust steam waste heat exchanger through the exhaust steam input pipeline.

5. A two-stage antifreeze energy-saving heater system according to claim 4, characterized in that: The exhaust steam waste heat exchange device also includes an auxiliary steam source, an auxiliary steam source input pipeline and a steam ejector; The auxiliary steam source is connected to the steam ejector through the auxiliary steam source input pipeline, and the steam ejector is connected to the exhaust steam waste heat exchanger.

6. A two-stage antifreeze energy-saving heater system according to claim 5, characterized in that: The exhaust steam waste heat exchange device also includes a drain pipe, a drain tank, a drain pump and a vacuum pump; The drain tank and the drain pump are both arranged on the drain pipe, and the drain pipe is connected to the exhaust steam waste heat exchanger; The vacuum pump is connected to the exhaust steam waste heat exchanger.

7. A two-stage antifreeze energy-saving air heater system according to claim 6, characterized in that: The exhaust steam waste heat exchange device also includes a plurality of third control valves; The exhaust steam input pipeline, the auxiliary steam source input pipeline and the drain pipeline are all provided with corresponding third control valves.

8. A two-stage antifreeze energy-saving heater system according to claim 4, characterized in that: The exhaust steam waste heat utilization device comprises a pressure stabilizing tank, a frequency conversion pump, a circulating medium input pipeline and a circulating medium output pipeline; One end of the pressure stabilizing tank is connected to one end of the variable frequency pump, the other end of the variable frequency pump is connected to one end of the circulating medium input pipeline, the other end of the circulating medium input pipeline is connected to one end of the exhaust steam waste heat exchanger, the other end of the exhaust steam waste heat exchanger is connected to one end of the circulating medium output pipeline, the other end of the circulating medium output pipeline is connected to one end of the intermediate heat exchanger, and the other end of the intermediate heat exchanger is connected to the other end of the pressure stabilizing tank.

9. A two-stage antifreeze energy-saving heater system according to claim 8, characterized in that: The exhaust steam waste heat utilization device also includes a heat exchange bypass pipeline and a plurality of fourth control valves; One end of the intermediate heat exchanger is connected to the other end of the intermediate heat exchanger through the heat exchange bypass pipeline; The heat exchange bypass pipeline, the circulating medium input pipeline and the circulating medium output pipeline are all provided with corresponding fourth control valves.

10. A two-stage antifreeze energy-saving heater system according to claim 2, characterized in that: The system further comprises a system isolation pipeline and a plurality of fifth control valves, the flue gas waste heat utilization device further comprises a flue gas waste heat utilization bypass pipeline, and the exhaust steam waste heat utilization device further comprises an exhaust steam waste heat utilization bypass pipeline; The flue gas waste heat utilization bypass pipeline, the exhaust steam waste heat utilization bypass pipeline, the system isolation pipeline and the heater bypass pipeline form a pipeline loop, and a circulating water pump is provided on the pipeline loop; The system isolation pipeline, the flue gas waste heat utilization bypass pipeline and the exhaust steam waste heat utilization bypass pipeline are all provided with corresponding fifth control valves.

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