Flue gas waste heat coupled condensation water-return heating system

Abstract

Provided in the present invention is a flue gas waste heat coupled condensation water-return heating system. The heating system can be divided into a garbage incineration flue gas emission system, a condensed water heating system and a closed circulating water system according to the circulation of different media. A boiler, a dust collector, a flue gas–steam heat exchanger, an SCR denitrification apparatus, a low-temperature economizer and an induced draft fan are sequentially connected by means of a flue. A steam turbine, a condenser, a low-pressure heater, a water-water heat exchanger, a deaerator and a boiler water-supply pump are sequentially connected by means of a condensed water channel. The deaerator, a circulating water pump, the water-water heat exchanger and the low-temperature economizer are sequentially connected by means of a circulating water pipe. A path of circulating water is led from low-pressure water supply of the deaerator to the water-water heat exchanger so as to heat condensed water from an outlet of the low-temperature heater; and cooled circulating water is fed to the low-temperature economizer, and returns to the deaerator again after being subjected to heat exchange with flue gas, thereby forming an independent closed circulating water system. By utilizing the characteristic of the constant water temperature of the outlet of the deaerator, the influence of parameter fluctuation of the condensed water can be effectively overcome, thereby ensuring that the low-temperature economizer has no low-temperature corrosion.

Description

A flue gas waste heat coupled condensation return water heating system

[0001] This invention claims priority to the Chinese patent application filed with the Patent Office of China on May 31, 2023, with application number 202310634633.7 and invention name “A Flue Gas Waste Heat Coupled Condensation Return Water Heating System”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The invention belongs to the technical field of waste incineration, and in particular relates to a flue gas waste heat coupled condensation return water heating system. Background Art

[0003] The exhaust temperature of waste incineration boiler systems is typically around 150°C, but can reach over 180°C with SCR (Selective Catalytic Reduction) systems. Excessively high exhaust temperatures result in a significant amount of energy in the flue gas being released into the atmosphere without being utilized. Therefore, further reducing exhaust temperatures has become an inevitable choice for developing energy-saving and emission-reduction technologies for power plant boilers, both for energy conservation and emission reduction, and for economic reasons.

[0004] Currently, the low-temperature economizer system can recover flue gas waste heat, improve the economic efficiency of unit operation, and has significant economic benefits. The most common solution is to directly lead the condensate to the low-temperature economizer, exchange heat with the flue gas, and then return it to the condensate system. In waste incineration plants, fluctuations in the amount and calorific value of garbage cause changes in the steam turbine load, resulting in changes in the extraction parameters of the low-pressure heater, and thus large fluctuations in the temperature of the heated condensate. If condensate is directly used to enter the low-temperature economizer to recover flue gas waste heat, when the steam turbine load is low, the condensate temperature sent to the low-temperature economizer will be low, which can easily lead to low-temperature corrosion of the low-temperature economizer, making it difficult to ensure long-term stable operation. In addition, the low exhaust temperature will cause severe corrosion to the chimney and pipelines, which brings difficulties to the comprehensive utilization of flue gas waste heat.

[0005] Therefore, how to overcome the influence of condensate parameter fluctuations and ensure that low-temperature economizers do not suffer from low-temperature corrosion is an urgent problem to be solved by those skilled in the art.

[0006] Summary of the Invention

[0007] The purpose of the present invention is to provide a flue gas waste heat coupled condensate return water heating system, which can effectively overcome the influence of condensate parameter fluctuations and ensure that low-temperature economizers do not suffer from low-temperature corrosion.

[0008] In order to solve the above technical problems, the present invention provides a flue gas waste heat coupled condensation return water heating system, comprising a boiler, a dust collector, a flue gas-steam heat exchanger, an SCR denitrification device, a low-temperature economizer, an induced draft fan, a steam turbine, a condenser, a low-pressure heater, a water-to-water heat exchanger, a deaerator, a boiler feed water pump, and a circulating water pump;

[0009] The flue gas outlet of the boiler is sequentially connected to the dust collector, the flue gas-steam heat exchanger, the SCR denitrification equipment and the flue gas duct in the induced draft fan; the steam drum outlet of the boiler is connected to the steam inlet of the steam turbine; the steam outlet of the steam turbine is sequentially connected to the condenser, the low-pressure heater and the condensate channel of the water-to-water heat exchanger;

[0010] The first inlet of the deaerator is connected to the condensate outlet of the water-to-water heat exchanger, the second inlet is connected to the circulating water outlet of the low-temperature economizer, the first outlet is connected to the water inlet of the boiler, and the second outlet is connected to the circulating water inlet of the low-temperature economizer through the circulating water channel of the water-to-water heat exchanger.

[0011] Optionally, in the above-mentioned flue gas waste heat coupled condensation return water heating system, the second inlet of the deaerator is connected to one end of the first circulation return water main pipe, the circulating water outlet of the low-temperature economizer is connected to one end of the first branch pipe, the second circulation return water main pipe between the circulating water inlet of the low-temperature economizer and the circulating water outlet of the water-to-water heat exchanger is connected to one end of the second branch pipe, and the other end of the second branch pipe is respectively connected to the other end of the first branch pipe and the other end of the first circulation return water main pipe;

[0012] The first circulating water return main pipe is connected in series with a circulating water return main pipe electric regulating valve, and the second branch pipe is connected in series with a low-temperature economizer bypass electric regulating valve.

[0013] Optionally, the flue gas waste heat coupled condensation return water heating system further includes a first temperature sensor and a first pressure sensor for measuring the water temperature and water pressure of the first circulating return water main pipe, and a second temperature sensor for measuring the water temperature of the first branch pipe;

[0014] The low-temperature economizer bypass electric regulating valve is used to control the opening according to the value of the first temperature sensor, and the circulating return pipe electric regulating valve is used to control the opening according to the values ​​of the second temperature sensor and the first pressure sensor.

[0015] Optionally, in the above flue gas waste heat coupled condensation return water heating system, a third branch pipe is provided between the circulating water inlet and the circulating water outlet of the water-to-water heat exchanger, and a water-to-water heat exchanger bypass electric regulating valve is connected in series to the third branch pipe.

[0016] Optionally, the above-mentioned flue gas waste heat coupled condensation return water heating system also includes a third temperature sensor for measuring the water temperature of the second circulating return water main pipe between the circulating water inlet of the low-temperature economizer and the circulating water outlet of the water-to-water heat exchanger, and the water-to-water heat exchanger bypass electric regulating valve is used to control the opening according to the value of the third temperature sensor.

[0017] Optionally, in the above flue gas waste heat coupled condensation return water heating system, a boiler feed water pump is connected in series between the first outlet of the deaerator and the water inlet of the boiler.

[0018] Optionally, in the above flue gas waste heat coupled condensation return water heating system, a circulating water pump is provided between the second outlet of the deaerator and the circulating water inlet of the water-to-water heat exchanger.

[0019] Optionally, in the above flue gas waste heat coupled condensate return water heating system, a fourth temperature sensor is provided between the flue gas outlet of the low-temperature economizer and the induced draft fan for monitoring the flue gas temperature;

[0020] The circulating water pump is used to control the power of the circulating water pump according to the value of the fourth temperature sensor.

[0021] Optionally, in the above-mentioned flue gas waste heat coupled condensation return water heating system, the water-to-water heat exchanger is a plate heat exchanger.

[0022] Optionally, in the above-mentioned flue gas waste heat coupled condensation return water heating system, the low-temperature economizer is a double H-type fin-tube economizer.

[0023] The present invention provides a flue gas waste heat coupled condensation return water heating system, which has the following beneficial effects:

[0024] Based on the flow of different media, the system can be specifically divided into the waste incineration flue gas emission system, the condensate heating system, and the closed circulating water system. The waste incineration flue gas emission system includes, along the flue gas flow path, a boiler, a dust collector, a flue gas-steam heat exchanger, an SCR denitrification system, a low-temperature economizer, and an induced draft fan, all connected in sequence through the flue. The condensate heating system, along the steam-water flow path, includes a steam turbine, a condenser, a low-pressure heater, a water-to-water heat exchanger, a deaerator, and a boiler feed water pump. The closed circulating water system, along the water flow path, includes a deaerator, a circulating water pump, a water-to-water heat exchanger, and a low-temperature economizer, all connected in sequence through the circulating water pipe.

[0025] This solution utilizes a circulating water system that draws circulating water from the deaerator's low-pressure feedwater to a water-to-water heat exchanger, where it is used to heat condensate from the low-temperature heater outlet. The cooled circulating water is then fed to the low-temperature economizer, where it exchanges heat with the flue gas and then returns to the deaerator, forming an independent closed-loop circulating water system. By leveraging the constant water temperature at the deaerator outlet, the system effectively mitigates the effects of fluctuating condensate parameters under varying operating conditions, ensuring low-temperature corrosion of the low-temperature economizer. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0027] FIG1 is a schematic diagram of a flue gas waste heat coupled condensation return water heating system provided by an embodiment of the present invention.

[0028] In the figure above: 1- boiler; 2- dust collector; 3- flue gas-steam heat exchanger; 4- SCR denitrification equipment; 5- low-temperature economizer; 6- induced draft fan; 7- steam turbine; 8- condenser; 9- low-pressure heater; 10- water-to-water heat exchanger; 11- deaerator; 12- boiler feed water pump; 13- circulating water pump; 14- water-to-water heat exchanger bypass electric regulating valve; 15- low-temperature economizer bypass electric regulating valve; 16- circulating return water main pipe electric regulating valve; T1- first temperature sensor; T2- second temperature sensor; T3- third temperature sensor; T4- fourth temperature sensor; P1- first pressure sensor. DETAILED DESCRIPTION

[0029] The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention.

[0030] The core of the present invention is to provide a flue gas waste heat coupled condensate return water heating system, which can effectively overcome the influence of condensate parameter fluctuations and ensure that the low-temperature economizer does not suffer from low-temperature corrosion.

[0031] In order to enable those skilled in the art to better understand the technical solutions provided by the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] Specifically, please refer to Figure 1. The present invention provides a flue gas waste heat coupled condensation return water heating system, including: a boiler 1, a dust collector 2, a flue gas-steam heat exchanger 3, an SCR denitrification device 4, a low-temperature economizer 5, an induced draft fan 6, a steam turbine 7, a condenser 8, a low-pressure heater 9, a water-to-water heat exchanger 10, a deaerator 11, a boiler feed water pump 12 and a circulating water pump 13.

[0033] The flue gas outlet of the boiler 1 is connected in sequence to the flue gas ducts in the dust collector 2, the flue gas-steam heat exchanger 3, the SCR denitrification equipment 4, and the induced draft fan 6; the steam drum outlet of the boiler 1 is connected to the steam inlet of the steam turbine 7; the steam outlet of the steam turbine 7 is connected in sequence to the condenser 8, the low-pressure heater 9, and the condensate channel of the water-to-water heat exchanger 10;

[0034] The first inlet of the deaerator 11 is connected to the condensate outlet of the water-to-water heat exchanger 10, the second inlet is connected to the circulating water outlet of the low-temperature economizer 5, the first outlet is connected to the water inlet of the boiler 1, and the second outlet is connected to the circulating water inlet of the low-temperature economizer 5 through the circulating water channel of the water-to-water heat exchanger 10.

[0035] It should be noted that the deaerator 11 uses the thermal deoxidation principle and adopts a medium-pressure rotary film structure. The steam turbine 7 is used to extract steam to heat the condensate, provide the condensate temperature and deoxidize it, and then send it to the boiler 1. The outlet water temperature of the deaerator 11 is usually designed to be a conventional parameter (such as 130°C / 150°C). The working pressure of the deaerator 11 of the waste incineration plant is constant, and the feed water temperature is also a constant value, which does not fluctuate with load changes. A low-pressure feed water from the deaerator 11 is drawn as circulating water and sent to the water-to-water heat exchanger 10.

[0036] The SCR denitration device 4 is a device that performs denitration using a selective catalytic reduction method.

[0037] The flue gas waste heat coupled condensate return water heating system provided in this solution can be specifically divided into a waste incineration flue gas emission system, a condensate heating system, and a closed circulating water system according to the circulation of different media. The waste incineration flue gas emission system includes a boiler 1, a dust collector 2, a flue gas-steam heat exchanger 3, an SCR denitrification device 4, a low-temperature economizer 5, and an induced draft fan 6, which are connected in sequence through the flue gas flow. The condensate heating system includes a steam turbine 7, a condenser 8, a low-pressure heater 9, a water-to-water heat exchanger 10, a deaerator 11, and a boiler feed water pump 12, along the steam-water flow. The closed circulating water system includes a deaerator 11, a circulating water pump 13, a water-to-water heat exchanger 10, and a low-temperature economizer 5, which are connected in sequence through a circulating water pipe, along the water flow.

[0038] In this solution, circulating water is routed from the low-pressure feedwater of deaerator 11 to water-to-water heat exchanger 10, where it is used to heat condensate from the outlet of the low-temperature heater. The cooled circulating water is then fed to low-temperature economizer 5, where it exchanges heat with the flue gas and then returns to deaerator 11, forming an independent closed-loop circulating water system. By leveraging the constant outlet water temperature of deaerator 11, the effects of fluctuating condensate parameters under varying operating conditions can be effectively mitigated, ensuring that low-temperature economizer 5 does not suffer from low-temperature corrosion.

[0039] In a specific embodiment, the second inlet of the deaerator 11 is connected to one end of the first circulating return water main pipe, the circulating water outlet of the low-temperature economizer 5 is connected to one end of the first branch pipe, the second circulating return water main pipe between the circulating water inlet of the low-temperature economizer 5 and the circulating water outlet of the water-to-water heat exchanger 10 is connected to one end of the second branch pipe, and the other end of the second branch pipe is respectively connected to the other end of the first branch pipe and the other end of the first circulating return water main pipe.

[0040] A main electric regulating valve 16 is connected in series to the first return pipe. This valve controls the valve opening on the main pipe. A low-temperature economizer bypass electric regulating valve 15 is connected in series to the second branch pipe. This valve controls the valve opening on the second branch pipe.

[0041] The present invention also includes a first temperature sensor T1 and a first pressure sensor P1 for measuring the water temperature and water pressure of the first circulating water return pipe, and a second temperature sensor T2 for measuring the water temperature of the first branch pipe.

[0042] The low-temperature economizer bypass electric regulating valve 15 is used to control the opening according to the value of the first temperature sensor T1, and the circulating return pipe electric regulating valve 16 is used to control the opening according to the values ​​of the second temperature sensor T2 and the first pressure sensor P1.

[0043] When the temperature value of the first temperature sensor T1 exceeds a first preset value, the low-temperature economizer bypass electric regulating valve 15 opens, reducing the temperature value of the first temperature sensor T1 below the first preset value. When the temperature value of the second temperature sensor T2 exceeds a second preset value, the valve opening of the circulating return water main pipe electric regulating valve 16 is reduced, ensuring that the pressure value of the first pressure sensor P1 does not fall below a third preset value.

[0044] In a specific embodiment, a third branch pipe is provided between the circulating water inlet and the circulating water outlet of the water-to-water heat exchanger 10, and a water-to-water heat exchanger bypass electric regulating valve 14 is connected in series to the third branch pipe. The water-to-water heat exchanger bypass electric regulating valve 14 is used to control the valve opening of the third branch pipe.

[0045] This case also includes a third temperature sensor T3 for measuring the water temperature of the second circulating return water main pipe between the circulating water inlet of the low-temperature economizer 5 and the circulating water outlet of the water-to-water heat exchanger 10. The water-to-water heat exchanger bypass electric regulating valve 14 is used to control the opening according to the value of the third temperature sensor T3.

[0046] When the temperature value of the third temperature sensor T3 is lower than the fourth preset value, the water-to-water heat exchanger bypass electric regulating valve 14 is opened to ensure that the temperature value of the third temperature sensor T3 is not lower than the fourth preset value.

[0047] In order to improve fluid dynamics, a boiler feed water pump 12 is connected in series between the first outlet of the deaerator 11 and the water inlet of the boiler 1 .

[0048] In a specific embodiment, a circulating water pump 13 is provided between the second outlet of the deaerator 11 and the circulating water inlet of the water-to-water heat exchanger 10. The circulating water pump 13 is a variable frequency pump.

[0049] A fourth temperature sensor T4 is provided between the flue gas outlet of the low-temperature economizer 5 and the induced draft fan 6 for monitoring the flue gas temperature.

[0050] The circulating water pump 13 is used to control the power of the circulating water pump 13 according to the value of the fourth temperature sensor T4.

[0051] When the temperature value of the fourth temperature sensor T4 is lower than the fifth preset value, the power of the circulating water pump 13 is increased, the circulating water flow rate is increased, and the exhaust gas temperature is increased to be above the fifth preset value.

[0052] It should be noted that the first preset value, the second preset value, the third preset value, the fourth preset value and the fifth preset value can be adaptively selected according to actual needs and will not be elaborated here.

[0053] The above arrangement can comprehensively utilize the flue gas waste heat recovered by the low-temperature economizer 5, achieve system stability under different working conditions, overcome the influence of fluctuations in different condensate parameters, and accurately and flexibly adjust system performance parameters.

[0054] In one specific embodiment, the water-to-water heat exchanger 10 is a plate-type heat exchanger, offering high heat exchange efficiency and compact size. Low-pressure feedwater from the deaerator 11 is delivered to the water-to-water heat exchanger 10 via a circulating water pump 13, serving as the hot end of the water-to-water heat exchanger 10. The cold end of the water-to-water heat exchanger 10 receives condensate from the outlet of the low-pressure heater 9. The heated condensate is returned to the deaerator 11, reducing the amount of steam extraction required for heating and improving power generation efficiency. The condensed circulating water is then fed to the low-temperature economizer 5.

[0055] In another specific embodiment, the low-temperature economizer 5 is a double H-shaped fin-tube economizer made of ND steel, with low equipment investment cost, large pitch, and not easy to be blocked by ash. This equipment is arranged between the SCR denitrification equipment 4 and the induced draft fan 6, and the inlet flue gas temperature is constant at 180°C. The inlet circulating water temperature of the low-temperature economizer 5 is required to be no less than 100°C, and the outlet flue gas temperature is required to be no less than 120°C. If it is lower than this value, the low-temperature economizer 5 is at great risk of low-temperature corrosion, causing equipment damage, which is not conducive to long-term operation. The circulating water outlet of the low-temperature economizer 5 is sent to the deaerator 11. The temperature of the circulating return water main pipe shall not exceed the saturation temperature under the working pressure of the deaerator 11. The purpose is to prevent the deaerator 11 from boiling due to excessive temperature and affecting the operation of the equipment.

[0056] Taking the design of a 1x500t / d waste incineration plant as an example, the main steam parameters of waste heat boiler 1 are 6.4MPa / 450℃, the low-pressure feed water temperature of deaerator 11 under design load is 130℃, the outlet flue gas temperature of SCR denitrification equipment 4 is 180℃, and the flue gas volume is 113000Nm 3 / h, the condensate temperature at the outlet of low-pressure heater 9 is 82℃, and the condensate volume is 45t / h.

[0057] The flue gas waste heat recovery system is a closed-loop circulating water system. The low-temperature economizer bypass electric regulating valve 15 is interlocked with the first temperature sensor T1 of the first circulating return water main pipe. The circulating return water main pipe electric regulating valve 16 is interlocked with the second temperature sensor T2 on the first branch pipe at the circulating water outlet of the low-temperature economizer 5 and the first pressure sensor P1 on the first circulating return water main pipe. The water-to-water heat exchanger bypass electric regulating valve 14 is interlocked with the third temperature sensor T3 on the second circulating return water main pipe at the circulating water inlet of the low-temperature economizer 5. The circulating water pump 13 is interlocked with the fourth temperature sensor T4. When the circulating water pump 13 is operating normally, the water-to-water heat exchanger bypass electric regulating valve 14 and the low-temperature economizer bypass electric regulating valve 15 are closed, and the circulating return water main pipe electric regulating valve 16 is fully open. The first step is to monitor the temperature of the first temperature sensor T1. When the temperature of the first temperature sensor T1 exceeds 130°C, the low-temperature economizer bypass electric regulating valve 15 opens to control the temperature of the first temperature sensor T1 within 130°C. The temperature of the second temperature sensor T2 is then monitored. When the temperature of the second temperature sensor T2 exceeds 150°C, the opening of the circulating return main pipe electric regulating valve 16 is reduced to ensure that the pressure value of the first pressure sensor P1 is not less than 0.6MPa. The second step is to monitor the water temperature at the circulating water inlet of the low-temperature economizer 5 (i.e., the temperature of the third temperature sensor T3). When the temperature of the third temperature sensor T3 is less than 100°C, the water-to-water heat exchanger bypass electric regulating valve 14 opens to ensure that the temperature of the third temperature sensor T3 is not less than 100°C. The third step is to monitor the exhaust gas temperature of the fourth temperature sensor T4. When the exhaust gas temperature is less than 120°C, the power of the circulating water pump 13 is increased, the circulating water flow rate is increased, and the exhaust gas temperature is raised above 120°C.

[0058] The condensate system utilizes waste heat from flue gas to heat the condensate. When the circulating water pump 13 is running at a flow rate of 64 t / h, the circulating water outlet temperature of the water-to-water heat exchanger 10 is 100°C, and the condensate outlet temperature is 124°C. The circulating water inlet temperature of the low-temperature economizer 5 is 100°C. After exchanging heat with the 180°C flue gas, the circulating water temperature rises to 129°C. The circulating water then returns to the deaerator 11, reducing the exhaust gas temperature to 130°C. This improves the overall power generation efficiency of the plant by 1%.

[0059] The present invention provides a flue gas waste heat coupled condensation return water heating system, which has at least the following beneficial effects or advantages:

[0060] This case features a closed-loop circulating water system with a fully enclosed internal circulation system, which avoids water pollution, reduces scaling and corrosion of heat exchange equipment, and improves heat transfer efficiency and lifespan. Using circulating water as the intermediate medium, the low-temperature economizer 5 recovers flue gas waste heat to directly heat condensate. Furthermore, the system can be switched with a conventional thermal system, ensuring stable operation when this system is shut down for maintenance.

[0061] 2. The outlet water temperature of the deaerator 11 is constant. By using the bypass valve opening of the water-to-water heat exchanger 10, the outlet water temperature can be easily controlled under variable operating conditions, overcoming the influence of fluctuations in parameters under different operating conditions and ensuring that the low-temperature economizer 5 does not suffer from low-temperature corrosion.

[0062] 3. The waste heat recovery system is equipped with a control system that precisely adjusts the exhaust temperature. This reduces exhaust temperature, improves overall plant power generation efficiency, and achieves significant energy savings, emissions, and carbon reduction. The visual appearance of white smoke is adjusted by varying the exhaust temperature of Boiler 1's chimney.

[0063] As used in this application and the claims, unless the context clearly indicates an exception, the terms "a," "an," "an," and / or "the" are not intended to refer to the singular and may include the plural, unless the context clearly indicates otherwise. Generally speaking, the terms "comprises" and "include" only indicate the inclusion of the steps and elements specifically identified, and these steps and elements do not constitute an exclusive list. A method or apparatus may also include other steps or elements. The phrase "comprises a..." does not preclude the presence of additional identical elements in the process, method, product, or apparatus that includes the elements.

[0064] In the description of this application, unless otherwise clearly defined, terms such as setting, installing, and connecting should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in this application based on the specific content of the technical solution.

[0065] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0066] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. It should be noted that those skilled in the art can make various improvements and modifications to the present invention without departing from the principles of the present invention, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A flue gas waste heat coupled condensation return water heating system, characterized in that: Including boiler, dust collector, flue gas-steam heat exchanger, SCR denitrification equipment, low-temperature economizer, induced draft fan, steam turbine, condenser, low-pressure heater, water-to-water heat exchanger, deaerator, boiler feed pump and circulating water pump; The flue gas outlet of the boiler is sequentially connected to the dust collector, the flue gas-steam heat exchanger, the SCR denitration equipment and the flue gas pipeline in the induced draft fan, the drum outlet of the boiler is connected to the steam inlet of the steam turbine, and the steam outlet of the steam turbine is sequentially connected to the condenser, the low-pressure heater and the condensate channel of the water-to-water heat exchanger; The first inlet of the deaerator is connected to the condensate outlet of the water-to-water heat exchanger, the second inlet is connected to the circulating water outlet of the low-temperature economizer, the first outlet is connected to the water inlet of the boiler, and the second outlet is connected to the circulating water inlet of the low-temperature economizer through the circulating water channel of the water-to-water heat exchanger.

2. The flue gas waste heat coupled condensation return water heating system according to claim 1 is characterized in that: The second inlet of the deaerator is connected to one end of the first circulating water return mother pipe, the circulating water outlet of the low-temperature economizer is connected to one end of the first branch pipe, the second circulating water return mother pipe between the circulating water inlet of the low-temperature economizer and the circulating water outlet of the water-to-water heat exchanger is connected to one end of the second branch pipe, and the other end of the second branch pipe is respectively connected to the other end of the first branch pipe and the other end of the first circulating water return mother pipe; The first circulating water return main pipe is connected in series with a circulating water return main pipe electric regulating valve, and the second branch pipe is connected in series with a low-temperature economizer bypass electric regulating valve.

3. The flue gas waste heat coupled condensation return water heating system according to claim 2 is characterized in that: It also includes a first temperature sensor and a first pressure sensor for measuring the water temperature and water pressure of the first circulating water return pipe, and a second temperature sensor for measuring the water temperature of the first branch pipe; The low-temperature economizer bypass electric regulating valve is used to control the opening according to the value of the first temperature sensor, and the circulating return water main pipe electric regulating valve is used to control the opening according to the values ​​of the second temperature sensor and the first pressure sensor.

4. The flue gas waste heat coupled condensation return water heating system according to claim 1 is characterized in that: A third branch pipe is arranged between the circulating water inlet and the circulating water outlet of the water-to-water heat exchanger, and a bypass electric regulating valve of the water-to-water heat exchanger is connected in series to the third branch pipe.

5. The flue gas waste heat coupled condensation return water heating system according to claim 4 is characterized in that: It also includes a third temperature sensor for measuring the water temperature of the second circulating water return pipe between the circulating water inlet of the low-temperature economizer and the circulating water outlet of the water-to-water heat exchanger. The water-to-water heat exchanger bypass electric regulating valve is used to control the opening according to the value of the third temperature sensor.

6. The flue gas waste heat coupled condensation return water heating system according to claim 1 is characterized in that: A boiler feed water pump is connected in series between the first outlet of the deaerator and the water inlet of the boiler.

7. The flue gas waste heat coupled condensation return water heating system according to claim 1 is characterized in that: A circulating water pump is arranged between the second outlet of the deaerator and the circulating water inlet of the water-to-water heat exchanger.

8. The flue gas waste heat coupled condensation return water heating system according to claim 7 is characterized in that: A fourth temperature sensor is provided between the flue gas outlet of the low-temperature economizer and the induced draft fan for monitoring the flue gas temperature; The circulating water pump is used to control the power of the circulating water pump according to the value of the fourth temperature sensor.

9. The flue gas waste heat coupled condensation return water heating system according to claim 1 is characterized in that: The water-to-water heat exchanger is a plate-type heat exchanger.

10. The flue gas waste heat coupled condensation return water heating system according to claim 1, characterized in that: The low-temperature economizer is a double H-shaped fin-tube economizer.

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