Power plant \ heat source plant flue gas - waste heat recovery of steam heat supply system and method of large temperature difference

Abstract

The application discloses a flue gas-waste steam residual heat recovery large-temperature-difference heat supply system and method for power plants and heat source plants, solves the problem of low energy utilization efficiency in the prior art, has the beneficial effects of saving water and electricity and realizing full utilization of energy, and specifically has the following arrangement: the flue gas-waste steam residual heat recovery large-temperature-difference heat supply system for power plants and heat source plants comprises a flue gas residual heat recovery unit, a condenser, and a heat supply boiler; the flue gas residual heat recovery unit comprises a first heat exchanger, and treated flue gas enters the flue gas residual heat recovery unit for residual heat recovery; the waste steam residual heat recovery unit comprises the condenser; the condenser is connected with the heat supply boiler; the flue gas residual heat recovery unit is connected in series with the heat supply boiler; the heat supply unit comprises a first water supply pipeline, the heat supply boiler and the waste steam residual heat recovery unit are connected in series with the first water supply pipeline, a first branch of a second water return pipeline is heat-exchanged with the first water supply pipeline through a second heat exchanger, and the second heat exchanger is provided with the first water return pipeline and a second water supply pipeline.

Description

Large Temperature Difference Heating System and Method for Waste Heat Recovery from Flue Gas and Exhaust Steam in Power Plants / Heat Source Plants Technical Field

[0001] This invention relates to the field of power plants, and in particular to a large temperature difference heating system and method for recovering waste heat from flue gas and exhaust steam in power plants / heat source plants. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] For a considerable period, heating in northern regions will still rely on high-temperature heat sources such as large boiler rooms and combined heat and power (CHP) to supply heat to users through heating network systems. However, this method directly uses fossil fuels or high-grade heat (steam, high-temperature water at 120 / 130℃, etc.) to meet the low-grade (30℃) heating demand, resulting in a mismatch in energy quality and unreasonable application, leading to low energy utilization efficiency.

[0004] In recent years, numerous waste incineration power plants and biomass power plants have rapidly developed around cities. The inventors discovered that existing power plants and heat source plants of this type have low energy efficiency and high economic costs. One important reason for this is the significant energy loss, mainly due to the direct emission of low-temperature waste heat from flue gas and waste steam from power generation into the atmosphere, thus preventing the efficient utilization of energy. Summary of the Invention

[0005] In view of the shortcomings of existing technologies, the purpose of this invention is to provide a large temperature difference heating system for recovering waste heat from flue gas and exhaust steam in power plants / heat source plants, which realizes the recovery and utilization of low-grade waste heat from power plants, making the heating system more low-carbon and environmentally friendly.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] Large temperature difference heating system for flue gas-exhaust steam waste heat recovery in power plants / heat source plants, including:

[0008] Flue gas waste heat recovery unit: includes a first heat exchanger, and the treated flue gas enters the flue gas waste heat recovery unit for waste heat recovery.

[0009] Waste steam heat recovery unit: includes a condenser, with a first heat exchanger connected to the condenser, and waste steam generated by the waste incineration boiler enters the condenser;

[0010] The heating boiler has a condenser connected to it, and the flue gas waste heat recovery unit and the exhaust steam waste heat recovery unit are connected in series with the heating boiler.

[0011] The heating unit includes a primary water supply pipeline, a heating boiler, and a waste heat recovery unit connected in series with the primary water supply pipeline. The first branch of the secondary return water pipeline exchanges heat with the primary water supply pipeline through a second heat exchanger. The second heat exchanger is equipped with the primary return water pipeline and the secondary water supply pipeline. The heating boiler is connected in parallel to the second heat exchanger, and the pipeline is equipped with a control switch. The second heat exchanger is connected in series with a heat pump, which is located between the primary return water pipeline and the secondary return water pipeline.

[0012] As described above, in the power plant / heat source plant flue gas-exhaust steam waste heat recovery large temperature difference heating system, the primary return water pipeline is connected to the first heat exchanger after passing through the heat pump, and the second branch of the secondary return water pipeline is connected to the secondary supply water pipeline after passing through the heat pump.

[0013] The heating boiler is a peak-shaving boiler, which plays a role in peak shaving, increasing water supply temperature, and emergency backup, greatly improving the stability of the heating system.

[0014] The heat pump is an electric heat pump.

[0015] The large temperature difference heating system for flue gas-exhaust steam waste heat recovery in the power plant / heat source plant as described above, wherein the flue gas waste heat recovery unit includes a flue gas spray tower, which is connected to the chimney.

[0016] The first heat exchanger is connected to the bottom and top of the flue gas spray tower respectively to achieve heat exchange between the flue gas spray liquid and the water in the first network return water pipeline, thereby increasing the temperature of the water entering the condenser.

[0017] In the power plant / heat source plant flue gas-exhaust steam waste heat recovery large temperature difference heating system as described above, a first switch is provided between the heating boiler and the second heat exchanger, and the control switch is the second switch.

[0018] The second return water pipeline is connected to the second heat exchanger, and a third switch is installed on the pipeline connecting the second return water pipeline and the second heat exchanger.

[0019] The heat pump is equipped with a fourth switch.

[0020] As described above, in the power plant / heat source plant flue gas-exhaust steam waste heat recovery large temperature difference heating system, the heat pump includes an evaporator, the evaporator is connected to a compressor, and the compressor is connected to a condenser.

[0021] The second heat exchanger is connected to the evaporator in the heat pump, and the second branch of the second network return water pipe is connected to the condenser.

[0022] As described above, in the power plant / heat source plant flue gas-exhaust steam waste heat recovery large temperature difference heating system, there are several condensers. The number of condensers corresponds one-to-one with the number of steam turbines, and all condensers are connected in series.

[0023] The condenser is connected to the heating boiler to supply water to the boiler.

[0024] In the power plant / heat source plant flue gas-exhaust steam waste heat recovery large temperature difference heating system described above, the pipeline connecting the primary return water pipeline to the first heat exchanger is the first pipeline, the pipeline connecting the condenser to the heating boiler is the second pipeline, a heat storage tank is installed between the first pipeline and the second pipeline, a circulation pump and a second valve are connected in parallel between the heat storage tank and the first pipeline, and a circulation pump and a first valve are connected in parallel between the heat storage tank and the second pipeline.

[0025] As described above, in the power plant / heat source plant flue gas-exhaust steam waste heat recovery large temperature difference heating system, the second pipeline is equipped with a third valve;

[0026] A fourth valve is connected in parallel to the first pipeline and the second pipeline on one side of the heat storage tank, and a fifth valve is installed on the first pipeline.

[0027] Secondly, the present invention also provides a method for large temperature difference heating through flue gas-exhaust steam waste heat recovery in power plants / heat source plants, employing the aforementioned large temperature difference heating system for flue gas-exhaust steam recovery in power plants / heat source plants, including the following:

[0028] The treated flue gas enters the flue gas waste heat recovery unit for heat recovery, and the flue gas after waste heat recovery enters the chimney.

[0029] After the exhaust steam enters the condenser, it then enters the heating boiler.

[0030] The water at the first temperature generated by the heating boiler enters the first network water supply pipeline. After the water at the first temperature is heated by the second heat exchanger, it becomes water at the second temperature. After the water at the second temperature enters the heat pump, it becomes water at the third temperature. The water at the third temperature returns to the first heat exchanger.

[0031] Water at the fourth temperature in part of the secondary network return water pipeline is heated by the second heat exchanger to produce water at the fifth temperature. Water at the fourth temperature in another part of the secondary network return water pipeline is heated by the heat pump to produce water at the sixth temperature. Water at the fifth temperature and water at the sixth temperature are mixed in the secondary network supply water pipeline to form water at the seventh temperature.

[0032] As described above, in the large temperature difference heating method for recovering waste heat from flue gas and exhaust steam in a power plant, the first temperature is higher than the fifth temperature, the second temperature is higher than the third temperature, and the fifth temperature is higher than the sixth temperature.

[0033] Water at the third temperature is heated by the first heat exchanger to form water at the eighth temperature. Water at the eighth temperature enters the condenser to produce water at the ninth temperature.

[0034] The beneficial effects of the present invention are as follows:

[0035] 1) The heating system of this invention connects the heating boiler, flue gas waste heat recovery unit, exhaust steam waste heat recovery unit and heating unit into one unit. Through the setting of heat exchangers and heat pumps, the waste heat of flue gas and exhaust steam can be reasonably recovered and utilized. The heat pump cools the primary network return water and heats the secondary network return water. The primary heat exchanger performs a first heating of the primary network return water after cooling. The condenser enables the exhaust steam to perform a second heating of the primary network return water. Under the premise of ensuring the safe operation of the turbine unit, the system achieves large temperature difference heating of the primary network circulating water, making full use of the thermal energy of the power plant or heat source plant, thereby saving energy and improving energy utilization efficiency.

[0036] 2) In this invention, the heating boiler is connected in parallel with the pipeline on the side of the second heat exchanger. Under emergency conditions, the heating boiler undertakes 40% of the heating load, the flow rate of the heating system remains unchanged, and the temperature of the primary network water supply drops to a level comparable to that of the secondary network water supply. At this time, the parallel pipeline is activated, and the secondary heat exchanger is disconnected, which reduces the system friction resistance caused by the secondary heat exchanger and can save electricity. At the same time, it helps to realize the large temperature difference heating of the heating system and increases the heat transfer capacity of the heating unit.

[0037] 3) The heating boiler of this invention is connected in series with the heating unit, which can improve the water temperature of the primary network, reduce the proportion of heat load provided by fossil fuel combustion, and reduce the initial investment in heating pipelines; the heating boiler is selected as a peak-shaving boiler, which can play the role of peak shaving and emergency backup, greatly improving the stability of the system.

[0038] 4) By setting up a heat pump, the temperature of the return water from the first network is reduced to a sufficiently low level after passing through the heat pump. After heat exchange in the first heat exchanger, it is then sent to the condenser, which increases the temperature of the water entering the condenser and reduces the temperature of the liquid circulating into the flue gas spray tower. This helps to further reduce the temperature of the flue gas, so that the temperature of the flue gas after waste heat recovery is low enough to achieve the effect of eliminating white spots in the flue gas.

[0039] 5) This invention utilizes the waste heat of steam turbine exhaust steam. During the heating season, cooling circulating water no longer enters the cooling tower for cooling and temperature reduction, reducing the evaporation of this part of the water in the tower, which can save water.

[0040] 6) By setting up multiple heat exchangers and heat pumps, this invention can recover and utilize waste heat in different temperature ranges according to the principle of temperature matching and tiered utilization of waste heat. It can be used for centralized heating in urban areas, which can not only achieve efficient energy utilization and alleviate the problem of insufficient urban heat sources, but also play a role in energy conservation and emission reduction.

[0041] 7) The heating system of the present invention integrates "source-network-load-storage" into one system, realizing the coordinated operation of the heat source side, heat network side, load side, and energy storage side. It can be used in power plants or heat source plants to utilize waste steam energy and recover and utilize the originally wasted waste heat resources, realizing "turning waste into treasure". It can improve the energy utilization efficiency of power plants and heat source plants; it can provide residential heating for towns and cities, alleviating the problem of insufficient heat sources in towns and cities; it can reduce gas emissions from power plants and heat source plants, realize the elimination of white smoke in flue gas, and has good environmental benefits. Attached Figure Description

[0042] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0043] Figure 1 is a schematic diagram of a large temperature difference heating system for recovering waste heat from flue gas and exhaust steam in a power plant / heat source plant according to one or more embodiments of the present invention.

[0044] Figure 2 is a schematic diagram of a large temperature difference heating system for recovering waste heat from flue gas and exhaust steam in a power plant / heat source plant according to one or more embodiments of the present invention.

[0045] The diagram exaggerates the spacing or dimensions between parts to show their positions; the diagram is for illustrative purposes only.

[0046] The components are: 1. Flue gas treatment equipment, 2. Flue gas spray tower, 3. Chimney, 4. Waste incineration boiler, 5. Steam turbine, 6. Condenser, 7. Heat storage tank, 8. Peak-shaving boiler, 9. End user, 10. Second circulation pump, 11. First valve, 12. Third valve, 13. First solenoid valve, 14. Second solenoid valve, 15. Second heat exchanger, 16. Third solenoid valve, 17. Evaporator, 18. Compressor, 19. Condenser, 20. Fourth solenoid valve, 21. Fourth valve, 22. Second valve, 23. Third circulation pump, 24. Fifth valve, 25. Fourth circulation pump, 26. First circulation pump, 27. Primary water supply pipeline, 28. Secondary water supply pipeline, 29. Secondary return water pipeline, 30. Primary return water pipeline, 31. First heat exchanger. Detailed Implementation

[0047] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0048] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, unless otherwise expressly indicated by the invention, the singular form is also intended to include the plural form. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0049] For ease of description, the words "up," "down," "left," and "right" appearing in this invention only indicate that they are consistent with the up, down, left, and right directions of the accompanying drawings themselves, and do not limit the structure. They are merely for the purpose of facilitating the description of this invention and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0050] Terminology Explanation: The terms "installation," "connection," "linking," and "fixing" in this invention should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components or the interaction relationship between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0051] As described in the background section, existing technologies suffer from low energy utilization efficiency in power plants or heat source plants. To address these technical issues, this invention proposes a large temperature difference heating system for recovering waste heat from flue gas and exhaust steam in power plants / heat source plants.

[0052] Example 1

[0053] In a typical embodiment of the present invention, referring to Figures 1 and 2, a large temperature difference heating system for recovering waste heat from flue gas and exhaust steam in power plants / heat source plants includes:

[0054] Flue gas waste heat recovery unit: includes a first heat exchanger 31, and the flue gas after being treated by the flue gas treatment equipment 1 enters the flue gas waste heat recovery unit for waste heat recovery.

[0055] Waste heat recovery unit: includes condenser 6, first heat exchanger connected to condenser, first heat exchanger connected to flue gas waste heat recovery unit, waste steam generated by waste incineration boiler 4 enters condenser 6.

[0056] The heating boiler is connected to the condenser 6, and the flue gas waste heat recovery unit and the exhaust steam waste heat recovery unit are connected in series with the heating boiler.

[0057] The heating unit includes a primary water supply pipeline 27, a heating boiler, a flue gas waste heat recovery unit, and a waste steam waste heat recovery unit, all connected in series with the primary water supply pipeline 27. The first branch of the secondary return water pipeline exchanges heat with the primary water supply pipeline through a second heat exchanger 15. The second heat exchanger 15 is equipped with a primary return water pipeline 30 and a secondary water supply pipeline 28. The heating boiler is connected in parallel to the second heat exchanger, and a control switch is installed on the pipeline. The second heat exchanger 15 is connected in series with a heat pump. The heat pump reduces the temperature of the primary return water to 20°C or even lower, thereby achieving heating with a large temperature difference in the primary circulating water. The heat pump is located between the primary return water pipeline 30 and the secondary return water pipeline 29.

[0058] Understandably, during waste heat recovery, the primary water supply needs to maintain a constant flow rate. To ensure full recovery of flue gas waste heat, the turbine exhaust pressure is increased (around 45 kPa). This pressure range meets the safe operating pressure range of the turbine unit, eliminating the need for structural modifications. Because of the utilization of the turbine exhaust heat, cooling circulating water no longer enters the cooling tower for cooling during the heating season, reducing evaporation of this water and thus saving water.

[0059] In addition, the heating boiler is connected in parallel to the second heat exchanger via a pipeline. The pipeline is equipped with a control switch, which controls the use of the second heat exchanger 15. When the heating system is in an emergency, the standard requires that the load be no less than 40% of the total heating load. In the emergency, the heating load is entirely provided by the heating boiler. In the emergency, the water supply temperature is similar to that of the secondary network. The control switch of the second heat exchanger is turned off, and the control switch of the parallel pipeline is turned on. The second heat exchanger is disconnected, and the primary network water supply transfers heat to the secondary network through a heat pump. This reduces the friction resistance during the circulation of the primary network water, thus achieving the effect of saving electricity.

[0060] In this embodiment, the heat pump is an electric heat pump. Specifically, the heat pump includes an evaporator 17, which is connected to a compressor 18, and the compressor 18 is connected to a condenser 19. The evaporator, compressor, and condenser are all existing technologies.

[0061] The second heat exchanger 15 is connected to the evaporator 17 in the heat pump, and the second branch of the second network return water pipe is connected to the condenser 19.

[0062] The primary return water pipeline is connected to the first heat exchanger 31 after passing through the heat pump, and the second branch of the secondary return water pipeline is connected to the secondary supply water pipeline after passing through the heat pump.

[0063] Among them, the heating boiler is a peak-shaving boiler 8. The peak-shaving boiler plays the role of peak shaving, increasing water supply temperature, and emergency backup, which greatly improves the stability of the heating system. The peak-shaving boiler is connected in series with the main water supply pipeline. Compared with the existing absorption heat pump and the existing mixing system, there is no need to increase the diameter of the heating pipe, which reduces investment. Moreover, the peak-shaving boiler load accounts for about 40% of the total heating load. At this time, it is extremely cold weather. When the outdoor temperature is high (outdoor temperature is greater than 8-12℃), the peak-shaving boiler can be completely shut down.

[0064] It should be noted that in this embodiment, the flue gas waste heat recovery unit includes a flue gas spray tower 2, which is connected to a chimney 3. The flue gas spray tower, chimney, and steam turbine are all existing technologies.

[0065] The first heat exchanger is connected to the bottom and top of the flue gas spray tower 2 respectively to achieve heat exchange between the flue gas spray liquid and the water in the primary return water pipeline, thereby increasing the temperature of the water entering the condenser. A first circulation pump 26 is installed between the first heat exchanger and the bottom of the flue gas spray tower. Driven by the first circulation pump, the circulating cooling water in the flue gas spray tower completes heat and mass exchange with the flue gas in the flue gas spray tower. After the circulating cooling water is heated, it heats the primary return water through the first heat exchanger.

[0066] In this embodiment, both the first heat exchanger and the second heat exchanger are plate heat exchangers.

[0067] It should be added that a first switch is installed between the heating boiler and the second heat exchanger, and the control switch is the second switch. The first switch and the second heat exchanger are connected in parallel with the second switch.

[0068] The return water pipeline of the second network is connected to the second heat exchanger, and a third switch is installed on the pipeline connecting the return water pipeline of the second network to the second heat exchanger; a fourth switch is installed on the heat pump, and the fourth switch is located on the pipeline connecting the heat pump evaporator and condenser.

[0069] Specifically, the first, second, third, and fourth switches are all solenoid valves. Under normal operating conditions, the second solenoid valve 14 is closed, while the first solenoid valve 13, the third solenoid valve 16, and the fourth solenoid valve 20 are open. At this time, the second heat exchanger and the electric heat pump operate simultaneously. Under emergency conditions, the second solenoid valve 14 and the fourth solenoid valve 20 are open, while the first solenoid valve 13 and the third solenoid valve 16 are closed. At this time, the second heat exchanger will be disconnected from the electric heat pump, and only the electric heat pump will operate, reducing the friction loss of the heating system and saving the power consumption of the circulating pump on the main network side.

[0070] The steam turbine 5 is connected to the waste incineration boiler 4. The steam turbine generates exhaust steam, which, combined with flue gas, heats the primary network return water on the heat source side using flue gas and exhaust steam. The heated primary network supply water temperature is relatively low, which can meet the regional heating water supply temperature. By connecting the peak-shaving boiler in series, the primary network supply water temperature can be further increased, and it can also play a peak-shaving role. The fourth valve 21 is located in the pipeline, and the peak-shaving boiler can play a backup role in case of emergency.

[0071] The waste heat recovery unit, flue gas waste heat recovery unit, and heating unit are connected in series. The primary return water, heated by the flue gas, enters the waste heat recovery unit. Adhering to the principle of "temperature matching and cascaded utilization," and minimizing the impact on power generation, a high back pressure retrofit is adopted for some turbine units in the power plant. After the high back pressure retrofit, the turbines not only produce waste steam but also high back pressure waste steam. First, the waste heat from the waste steam is recovered to reheat the primary return water. Then, the high back pressure waste steam reheats the primary return water a third time. The principle of the high back pressure retrofit is to ensure the safe operation of the power plant's turbine units.

[0072] Understandably, there are several condensers, and the number of condensers corresponds one-to-one with the number of steam turbines. All condensers are connected in series. The condensers are connected to the heating boiler to feed water to the boiler. The condensers are located between the first heat exchanger and the peak-shaving boiler. In this embodiment, two sets of condensers are set up. The exhaust pressures of the two sets of condensers are different. One set of steam turbines produces exhaust steam at 40-45°C, and the other set, after being modified to have high back pressure, produces exhaust steam at 55-60°C. After the steam turbines do work to generate electricity, the exhaust steam enters the condensers.

[0073] The pipeline connecting the return water pipeline 30 to the first heat exchanger 31 is the first pipeline, and the pipeline connecting the condenser to the heating boiler is the second pipeline. A heat storage tank 7 is installed between the first pipeline and the second pipeline. The heat storage tank 7 is connected in parallel with the heating unit. The heat storage tank 7 stores excess heat during the day and releases the stored heat to the heating system when the heating load increases at night to achieve "thermal-electric synergy". A third circulation pump 23 and a second valve 22 are installed in parallel between the heat storage tank and the first pipeline, and a second circulation pump 10 and a first valve 11 are installed in parallel between the heat storage tank and the second pipeline.

[0074] The second pipeline is equipped with a third valve 12; a fourth valve 21 is connected in parallel between the first pipeline and the second pipeline on one side of the heat storage tank; the first pipeline is equipped with a fifth valve 24 and a fourth circulation pump 25.

[0075] Under heat storage conditions, the first valve 11 is opened, the second valve 22 is closed, and the third circulation pump 23 is started to transport the cold water in the heat storage tank to the primary return water pipeline 30. The primary water supply (high temperature water) enters the heat storage tank 7 through the first valve 11. The heat storage process is completed when the heat storage pipe is filled with high temperature water.

[0076] Under heat release conditions, the first valve 11 is closed and the second valve 22 is opened, the second circulation pump 10 is started, and the high-temperature water in the heat storage tank is transported to the primary water supply pipeline 27 to provide heat to the end user 9. At the same time, the primary return water enters the heat storage tank through the second valve. Once the heat storage pipe is filled with low-temperature water, the heat release process is completed.

[0077] When the boiler raises the water supply temperature, the third valve 12 and the fifth valve 24 are open, and the fourth valve 21 is closed. At this time, the boiler plays the role of peak regulation and temperature increase. When the power plant's heat source side cannot provide heat, the third valve 12 and the fifth valve 24 are closed, and the fourth valve 21 is opened. At this time, the boiler plays the role of emergency backup.

[0078] Example 2

[0079] This embodiment provides a method for large temperature difference heating through flue gas-exhaust steam waste heat recovery from power plants / heat source plants, employing the large temperature difference heating system for flue gas-exhaust steam waste heat recovery from power plants / heat source plants described in Embodiment 1, including the following:

[0080] The treated flue gas enters the flue gas waste heat recovery unit for heat recovery, and the flue gas after waste heat recovery enters the chimney.

[0081] After the exhaust steam enters the condenser, it then enters the heating boiler.

[0082] Water at a first temperature (75-85℃) generated by the heating boiler enters the first network water supply pipeline. After heat exchange in the second heat exchanger, the water at the first temperature becomes water at a second temperature (30-40℃). After entering the heat pump, the water at the second temperature becomes water at a third temperature (7-25℃). The water at the third temperature returns to the first heat exchanger.

[0083] Water at the fourth temperature (30-38℃) in part of the secondary network return water pipeline is heated by the second heat exchanger to produce water at the fifth temperature (45-55℃). Water at the fourth temperature in another part of the secondary network return water pipeline is heated by the heat pump to produce water at the sixth temperature (35-45℃). Water at the fifth temperature and water at the sixth temperature are mixed in the secondary network supply water pipeline to form water at the seventh temperature (42-48℃).

[0084] It can be understood that the first temperature is higher than the fifth temperature, the second temperature is higher than the third temperature, and the fifth temperature is higher than the sixth temperature.

[0085] Water at the third temperature is heated by the first heat exchanger to form water at the eighth temperature (22-30℃). Water at the eighth temperature enters the condenser to produce water at the ninth temperature (50-60℃).

[0086] For example, the flue gas temperature after desulfurization and denitrification in a waste incineration power plant boiler is 140℃, and the flue gas volume is 236499 Nm³.3 / h; The waste incineration power plant has two 12MW steam turbines with a steam turbine exhaust pressure of 0.008Mpa and a single steam turbine exhaust capacity of 39.18t / h. After the steam turbine is modified, the upper pressure limit is 0.042Mpa.

[0087] Based on the actual operating parameters of the waste-to-energy power plant and the saturation characteristics of water, it can be determined that the turbine exhaust pressure can heat the primary network return water to a maximum of 40℃. After modifying the turbine to a high back pressure, at a pressure of 0.042 MPa, the primary network return water can be heated to a maximum of 75℃. To achieve the whitening effect in the flue gas, the flue gas temperature is set at 30℃. Considering the heat exchange temperature difference of the cooling circulating water in the flue gas scrubbing tower, the supply and return water temperatures of the scrubbing tower are set at 22℃ and 27℃, respectively. Considering the heat exchange temperature difference of the plate heat exchanger, the supply and return water temperatures of the plate heat exchanger on the primary network return water side are set at 20℃ and 25℃, respectively. Therefore, the evaporator outlet temperature of the terminal electric heat pump is determined to be 20℃.

[0088] Adhering to the principle of "temperature matching and tiered utilization," the return water from the evaporator outlet of the terminal electric heat pump, with a temperature of 20℃, first undergoes primary heating in the flue gas waste heat recovery unit to 25℃. Then, it enters the unmodified exhaust steam waste heat recovery unit for secondary heating to 40℃. This second-heated return water then enters the modified exhaust steam waste heat recovery unit for a third heating, reaching 75℃. At this temperature, the high-temperature water can be directly used for heating. Based on these operating parameters, the circulation flow rate of the high-temperature water is calculated. Under the condition of complete recovery of flue gas and exhaust steam waste heat, the required circulation flow rates for flue gas waste heat, conventional exhaust steam waste heat, and exhaust steam waste heat after high back pressure modification are 1738.9 t / h, 1494 t / h, and 617 t / h, respectively.

[0089] Because the flue gas waste heat recovery unit and the exhaust steam waste heat recovery unit of this invention are connected in series, the calculated primary network circulating water flow rate is mismatched. In order to match the primary network circulating water flow rate and maximize the recovery of flue gas and exhaust steam waste heat, it was finally determined to modify the turbine back pressure to 0.018 MPa and heat the primary network return water temperature to 55°C. It was calculated that the primary network circulating water flow rate at this time is 1494 t / h, the flue gas waste heat recovery rate is 90%, the exhaust steam waste heat recovery rate is 100%, and the impact of the high back pressure modification on power generation is 1.3%.

[0090] A water supply temperature of 55℃ can meet the heating needs of the regional direct supply system. However, the waste incineration power plant is 10km away from the heat load area. Therefore, the peak-shaving boiler will further heat the supplied water. Based on the actual site conditions, a gas-fired boiler was selected for peak-shaving boiler 8. Considering the end-user energy consumption, the water supply temperature was ultimately determined to be heated to 80℃. Since the peak-shaving boiler simultaneously serves the functions of temperature increase, peak regulation, and emergency backup, its heating load should be selected based on the maximum value of the three calculated values. When the gas-fired boiler is used for peak regulation, it should account for 30% of the total heating load; when it is used for emergency backup, it should account for 40% of the total heating load. The calculated heating load of the gas-fired boiler is 42.88MW.

[0091] The heat storage tank primarily stores 55°C high-temperature water, storing excess heat during the day. This heat is then released into the heating network for heating when nighttime heating demand increases. The initial purpose of this invention is to achieve "thermal-power synergy." Since this invention is used in waste-to-energy power plants, which are unaffected by peak-valley electricity generation, their turbines can operate continuously at rated conditions. Therefore, their heating load is almost unaffected by changes in the plant's operating conditions. However, due to variations in the calorific value of waste, the heating load of waste-to-energy power plants fluctuates. Therefore, in this example, the heat storage tank primarily mitigates these load fluctuations. Assuming the daily 8-15 hour heat load is 75% of the heat load during other time periods, storing this excess heat in the heat storage tank, the calculated heat requirement is 120 MWh, which can meet 8.3% of the load fluctuation, thus satisfying the heat load shortfall caused by the calorific value fluctuations in waste-to-energy power plants.

[0092] The supply and return water temperatures on the first network side are 80℃ and 20℃, respectively. The supply and return water temperatures on the second network side are 45℃ and 35℃, respectively. Calculations show that the high-temperature water outlet temperature on the first network side of the plate heat exchanger is 35℃, the circulating water flow rate entering the second heat exchanger on the second network side is 5145t / h, and the circulating water flow rate entering the heat pump is 3996t / h.

[0093] This invention is used in a waste incineration power plant. The heat load composition of each subsystem is calculated and shown in Table 1 below.

[0094] Table 1. Composition of Heat Load in Flue Gas-Exhaust Steam Waste Heat Recovery Large Temperature Difference Heating System

[0095]

[0096] Based on the qualitative and quantitative analysis of each subsystem of the flue gas-exhaust steam waste heat recovery large temperature difference heating system above, the parameters of each device can be obtained. The specific operating parameters are shown in Table 2.

[0097] Table 2. Overview of Equipment Parameters for Flue Gas-Exhaust Steam Combined Waste Heat Recovery Heating System

[0098]

[0099]

[0100] The flue gas-exhaust steam waste heat recovery system with a large temperature difference was applied to this waste incineration power plant. Compared with the conventional coal-fired cogeneration heating system, the calculated reduction in carbon and other pollutant emissions by this system is shown in Table 3 below:

[0101] Table 3. Reduction of CO2, SO2, and NO by various flue gas-exhaust steam waste heat recovery large temperature difference heating systems. x Emissions

[0102]

[0103] Meanwhile, due to the recovery of waste heat from the power plant's exhaust steam, the evaporation of water caused by the cooling circulating water entering the cooling tower is reduced. It is calculated that 219,500 tons of water can be saved in one heating season.

[0104] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A large temperature difference heating system for recovering waste heat from flue gas and exhaust steam in power plants / heat source plants, characterized in that: include: The system includes: a flue gas waste heat recovery unit (comprising a first heat exchanger, where treated flue gas enters for waste heat recovery); a waste steam waste heat recovery unit (comprising a condenser, with the first heat exchanger connected to the condenser, and waste steam from the waste incineration boiler entering the condenser); a heating boiler, with the condenser connected to the heating boiler, and the flue gas waste heat recovery unit and waste steam waste heat recovery unit connected in series with the heating boiler); and a heating unit, including a primary water supply pipeline, with the heating boiler and waste steam waste heat recovery unit connected in series with the primary water supply pipeline, and the first branch of the secondary return water pipeline exchanging heat with the primary water supply pipeline through a second heat exchanger. The heat exchanger is equipped with a primary return water pipeline and a secondary supply water pipeline. The heating boiler has a pipeline connected in parallel to the second heat exchanger. The pipeline is equipped with a control switch. The second heat exchanger is connected in series with a heat pump, which is located between the primary and secondary return water pipelines. The primary return water pipeline connects to the first heat exchanger after passing through the heat pump. A second branch of the secondary return water pipeline connects to the secondary supply water pipeline after passing through the heat pump. The heat pump includes an evaporator, which is connected to a compressor, and the compressor is connected to a condenser. The second heat exchanger is connected to the evaporator in the heat pump, and the second branch of the secondary return water pipeline is connected to the condenser.

2. The large temperature difference heating system for flue gas-exhaust steam waste heat recovery in power plants / heat source plants according to claim 1, characterized in that, The heating boiler is a peak-shaving boiler; the heat pump is an electric heat pump.

3. The large temperature difference heating system for flue gas-exhaust steam waste heat recovery in power plants / heat source plants according to claim 1, characterized in that, The flue gas waste heat recovery unit includes a flue gas spray tower connected to a chimney; a first heat exchanger is connected to the bottom and top of the flue gas spray tower respectively.

4. The large temperature difference heating system for flue gas-exhaust steam waste heat recovery in power plants / heat source plants according to claim 1, characterized in that, A first switch is provided between the heating boiler and the second heat exchanger, and the control switch is a second switch; a third switch is provided on the pipeline where the second network return water pipeline is connected to the second heat exchanger and the pipeline where the second network return water pipeline is connected to the second heat exchanger; and a fourth switch is provided on the heat pump.

5. The large temperature difference heating system for flue gas-exhaust steam waste heat recovery in power plants / heat source plants according to claim 1, characterized in that, The condenser is provided in several units, and the number of condensers corresponds one-to-one with the number of steam turbines. All condensers are connected in series. The condenser is connected to the heating boiler to feed water to the boiler.

6. The large temperature difference heating system for flue gas-exhaust steam waste heat recovery in power plants / heat source plants according to claim 1, characterized in that, The pipeline connecting the return water pipeline to the first heat exchanger is the first pipeline, and the pipeline connecting the condenser to the heating boiler is the second pipeline. A heat storage tank is installed between the first pipeline and the second pipeline. A circulation pump and a second valve are connected in parallel between the heat storage tank and the first pipeline. A circulation pump and a first valve are also connected in parallel between the heat storage tank and the second pipeline.

7. The large temperature difference heating system for flue gas-exhaust steam waste heat recovery in power plants / heat source plants according to claim 6, characterized in that, The second pipeline is equipped with a third valve; a fourth valve is connected in parallel between the first pipeline and the second pipeline on one side of the heat storage tank, and a fifth valve is installed on the first pipeline.

8. A method for large temperature difference heating through flue gas-exhaust steam waste heat recovery in power plants, characterized in that, The power plant / heat source plant flue gas-exhaust steam waste heat recovery large temperature difference heating system according to any one of claims 1-7 includes the following: the treated flue gas enters the flue gas waste heat recovery unit for heat recovery, and the flue gas after waste heat recovery enters the chimney; the exhaust steam enters the condenser and then enters the heating boiler; the water at a first temperature generated by the heating boiler enters the primary network water supply pipeline, the water at the first temperature is transformed into water at a second temperature after heat exchange in the second heat exchanger, the water at the second temperature enters the heat pump and transforms into water at a third temperature, and the water at the third temperature returns to the first heat exchanger; a portion of the water at a fourth temperature in the secondary network return water pipeline is transformed into water at a fifth temperature after heat exchange in the second heat exchanger, and another portion of the water at a fourth temperature in the secondary network return water pipeline is transformed into water at a sixth temperature after heat pump; the water at the fifth temperature and the water at the sixth temperature are mixed in the secondary network water supply pipeline to form water at a seventh temperature.

9. A method for large temperature difference heating through flue gas-exhaust steam waste heat recovery in power plants according to claim 8, characterized in that, The first temperature is higher than the fifth temperature, the second temperature is higher than the third temperature, and the fifth temperature is higher than the sixth temperature; the water at the third temperature becomes water at the eighth temperature after heat exchange in the first heat exchanger, and the water at the eighth temperature enters the condenser to produce water at the ninth temperature.

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