Fuel gas heating system and variable working condition adjusting method

Abstract

The invention discloses a gas heating system and a variable working condition adjusting method, and relates to the technical field of gas power generation. The first heat exchanger comprises a first heat exchanger, a first fuel gas inlet is communicated with a fuel gas inlet pipeline through a first double-shut-off valve, and a first fuel gas outlet is communicated with a fuel gas outlet pipeline through a fourth double-shut-off valve; the second gas inlet of the second heat exchanger is communicated with the first gas outlet through a third double-shut-off valve, and the second gas outlet of the second heat exchanger is communicated with the gas outlet pipeline through a fifth double-shut-off valve; the working conditions comprise the simultaneous operation condition of the first heat exchanger and the second heat exchanger, the independent operation condition of the first heat exchanger and the independent operation condition of the second heat exchanger, and each working condition comprises hot water circulation adjustment and fuel gas circulation adjustment. The problem that the whole heating system is forced to be scrapped due to leakage or damage of a single heat exchanger in the prior art is solved, and the problem that effective adjustment is difficult due to the fact that the temperature of a fuel gas outlet is too high in the prior art is effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of gas power generation, and in particular to a gas heating system and a variable operating condition regulation method. Background Art

[0002] Gas turbines in gas-fired power plants generally use natural gas, a mixture of natural gas and hydrogen, or pure hydrogen as fuel to generate heat energy through combustion. The front module plays a vital role in this process. It is cleverly placed between the power plant's pressure regulating station and the gas turbine. Its main function is to increase the temperature of the gas and efficiently transport the heated gas to the gas turbine to ensure that the gas turbine can start smoothly, accelerate, and operate stably under load. At present, the front modules of most gas-fired power plants use a two-stage temperature heating system consisting of two heat exchangers in series. This design aims to significantly increase the temperature of the gas by heating it step by step.

[0003] However, this series heat exchanger system has two defects that cannot be ignored: first, once any of the heat exchangers leaks or is damaged and loses its working ability, the entire heating system will be paralyzed and unable to continue to provide gas turbines with gas at a suitable temperature. In this case, the entire heating system will be scrapped and new equipment will need to be purchased, which will undoubtedly bring huge economic burdens and time costs; second, when the gas outlet temperature is too high, due to the lack of effective adjustment methods, the gas temperature cannot be accurately controlled to meet the operating requirements of the gas turbine. Summary of the invention

[0004] The object of the present invention is to provide a gas heating system and a variable operating condition adjustment method, which can freely switch to a two-heat exchanger series operation mode or a single heat exchanger independent operation mode.

[0005] To achieve the above purpose, the technical solution of the present application is: a gas heating system, comprising:

[0006] A first heat exchanger having a first heat exchange tube therein, wherein a first gas inlet of the first heat exchanger is connected to a gas inlet pipeline via a first double-blocking valve, and a first gas outlet of the first heat exchanger is connected to a gas outlet pipeline via a fourth double-blocking valve;

[0007] The second heat exchanger has a second heat exchange tube built in. The second gas inlet of the second heat exchanger is connected to the first gas outlet through the third double-blocking valve, and the second gas outlet of the second heat exchanger is connected to the gas outlet pipeline through the fifth double-blocking valve.

[0008] As a preferred solution of the present invention, the second hot water inlet of the second heat exchanger is connected to the hot water inlet pipeline through the fifth ball valve and the second control valve, and the second hot water outlet of the second heat exchanger is connected to the hot water outlet pipeline through the first ball valve and the first control valve.

[0009] As a preferred solution of the present invention, the first hot water inlet of the first heat exchanger is connected to the second hot water outlet through the fourth ball valve, and the first hot water outlet of the first heat exchanger is connected to the hot water outlet pipeline through the second ball valve and the first control valve.

[0010] As a preferred solution of the present invention, the first hot water inlet of the first heat exchanger is connected to the hot water inlet pipeline through the third ball valve and the second control valve.

[0011] As a preferred solution of the present invention, the second gas inlet of the second heat exchanger is connected to the gas inlet pipeline through a second double-blocking valve.

[0012] As a preferred solution of the present invention, the tube-side fluid of the first heat exchanger and the second heat exchanger is hot water, and the shell-side fluid is fuel gas.

[0013] The present invention also provides a variable operating condition regulation method for a gas heating system, including a first heat exchanger and a second heat exchanger operating simultaneously, a first heat exchanger operating independently, and a second heat exchanger operating independently, each operating condition including hot water circulation regulation and gas circulation regulation.

[0014] As a preferred solution of the present invention, a hot water circulation regulation method for the simultaneous operation of the first heat exchanger and the second heat exchanger is as follows: the second control valve is opened, the third ball valve is closed, the fifth ball valve is opened, the hot water flows through the hot water inlet pipeline through the fifth ball valve and enters the second hot water inlet of the second heat exchanger, then flows through the inside of the second heat exchange tube and flows out from the second hot water outlet, the first ball valve is closed, the fourth ball valve is opened, the hot water flows through the pipeline through the fourth ball valve and enters the first hot water inlet of the first heat exchanger, then flows through the inside of the first heat exchange tube and flows out from the first hot water outlet, the second ball valve is opened, the first control valve is opened, and the hot water flows through the pipeline through the second ball valve and the first control valve to reach the hot water outlet pipeline;

[0015] The gas circulation regulation method for the simultaneous operation condition of the first heat exchanger and the second heat exchanger is: the second double-blocking valve is closed, the first double-blocking valve is opened, the gas flows through the gas inlet pipeline through the first double-blocking valve and then enters the first gas inlet of the first heat exchanger, and then flows through the outside of the first heat exchange tube and flows out from the first gas outlet, the third double-blocking valve is opened, the gas enters the second gas inlet of the second heat exchanger through the pipeline and flows through the third double-blocking valve, and then flows through the outside of the second heat exchange tube and flows out from the second gas outlet, the fourth double-blocking valve is closed, the fifth double-blocking valve is opened, and the gas flows through the fifth double-blocking valve to reach the gas outlet pipeline.

[0016] As a preferred solution of the present invention, the hot water circulation regulation mode of the independent operation condition of the first heat exchanger is: the second control valve is opened, the third ball valve is opened, the fifth ball valve is closed, the fourth ball valve is closed, the hot water flows through the hot water inlet pipeline through the third ball valve into the first hot water inlet of the first heat exchanger, and then flows through the inside of the first heat exchange tube and flows out from the first hot water outlet, the first ball valve is closed, the second ball valve is opened, the first control valve is opened, and the hot water flows through the pipeline through the second ball valve and the first control valve to reach the hot water outlet pipeline;

[0017] The gas circulation regulation method for the independent operation condition of the first heat exchanger is: the second double-blocking valve is closed, the first double-blocking valve is opened, the gas enters the first gas inlet of the first heat exchanger through the gas inlet pipeline and the first double-blocking valve, and then flows through the outside of the first heat exchange tube and flows out from the first gas outlet, the third double-blocking valve is closed, the fifth double-blocking valve is closed, the fourth double-blocking valve is opened, and the gas flows through the pipeline through the fourth double-blocking valve to reach the gas outlet pipeline.

[0018] As a preferred solution of the present invention, the hot water circulation regulation mode of the second heat exchanger in the independent operation condition is: the second control valve is opened, the third ball valve is closed, the fifth ball valve is opened, the hot water passes through the hot water inlet pipeline and flows through the fifth ball valve to enter the second hot water inlet of the second heat exchanger, and then flows through the inside of the second heat exchange tube and flows out from the second hot water outlet, the fourth ball valve is closed, the second ball valve is closed, the first ball valve is opened, the first control valve is opened, and the hot water flows through the pipeline through the first ball valve and the first control valve to reach the hot water outlet pipeline;

[0019] The gas circulation regulation method for the independent operation condition of the second heat exchanger is: the first double-blocking valve is closed, the third double-blocking valve is closed, the second double-blocking valve is opened, the gas flows through the gas inlet pipeline through the second double-blocking valve and enters the second gas inlet of the second heat exchanger, and then flows through the outside of the second heat exchange tube and flows out from the second gas outlet, the fourth double-blocking valve is closed, the fifth double-blocking valve is opened, the gas passes through the pipeline and flows through the fifth double-blocking valve to reach the gas outlet pipeline.

[0020] Due to the adoption of the above technical solution, the present invention can achieve the following technical effects: a bypass system is set on the pipeline connecting the two heat exchangers, and the bypass system includes various valves; by operating the opening or closing state of these valves, it is possible to switch freely between two operating modes: one is to allow the two heat exchangers to work together in series, and the other is to select one of the heat exchangers to operate independently. Such a design solves the thorny problem that the entire heating system is forced to be scrapped due to leakage or damage of a single heat exchanger, and greatly improves the economy and operating efficiency of the system. At the same time, it also effectively solves the problem that it is difficult to effectively adjust the gas outlet temperature due to excessively high gas outlet temperature, thereby meeting the actual needs under different working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 It is a structural principle diagram of the working condition of the first heat exchanger and the second heat exchanger operating simultaneously;

[0023] Figure 2 This is the structural principle diagram of the first heat exchanger under independent operation;

[0024] Figure 3 This is the structural principle diagram of the second heat exchanger under independent operation;

[0025] Explanation of the serial numbers in the figure: 1. first heat exchanger; 2. second heat exchanger; 3. first ball valve; 4. first control valve; 5. second ball valve; 6. third ball valve; 7. second control valve; 8. first double-blocking valve; 9. second double-blocking valve; 10. third double-blocking valve; 11. fourth ball valve; 12. fourth double-blocking valve; 13. fifth double-blocking valve; 14. fifth ball valve; 15. second heat exchange tube; 16. first heat exchange tube; 17. second hot water inlet; 18. second gas outlet; 19. second gas inlet; 20. second hot water outlet; 21. first hot water inlet; 22. first gas outlet; 23. first gas inlet; 24. first hot water outlet. DETAILED DESCRIPTION

[0026] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0027] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0028] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, "multiple" means two or more, unless otherwise clearly and specifically defined. "Several" means one or more, unless otherwise clearly and specifically defined.

[0029] In the description of the present application, it should be understood that the terms "center", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply 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 application.

[0030] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0031] Example 1

[0032] This embodiment provides a gas heating system, including:

[0033] The first heat exchanger has a first heat exchange tube built therein; the first gas inlet of the first heat exchanger is connected to the gas inlet pipeline through the first double-blocking valve, and the first gas outlet of the first heat exchanger is connected to the gas outlet pipeline through the fourth double-blocking valve; the first hot water inlet of the first heat exchanger is connected to the second hot water outlet through the fourth ball valve, and the first hot water outlet of the first heat exchanger is connected to the hot water outlet pipeline through the second ball valve and the first control valve; the first hot water inlet of the first heat exchanger is also connected to the hot water inlet pipeline through the third ball valve and the second control valve.

[0034] The second heat exchanger has a second heat exchange tube built in. The second gas inlet of the second heat exchanger is connected to the first gas outlet through the third double-blocking valve, and the second gas outlet of the second heat exchanger is connected to the gas outlet pipeline through the fifth double-blocking valve; the second hot water inlet of the second heat exchanger is connected to the hot water inlet pipeline through the fifth ball valve and the second control valve, and the second hot water outlet of the second heat exchanger is connected to the hot water outlet pipeline through the first ball valve and the first control valve; the second gas inlet of the second heat exchanger is also connected to the gas inlet pipeline through the second double-blocking valve.

[0035] It should be noted that the first heat exchanger 1 and the second heat exchanger 2 are both fixed tube sheet structures. The tube-side fluid of the first heat exchanger 1 and the second heat exchanger 2 is hot water, and the shell-side fluid is gas. After the gas passes through the outer wall of the first heat exchange tube 16 of the first heat exchanger 1 and the second heat exchange tube 15 of the second heat exchanger 2, the hot water flowing through the inside of the first heat exchange tube 16 and the second heat exchange tube 15 heats the gas through heat transfer, thereby increasing the gas temperature.

[0036] Example 2

[0037] This embodiment provides a variable operating condition adjustment method for a gas heating system, including a first heat exchanger and a second heat exchanger operating simultaneously, a first heat exchanger operating independently, and a second heat exchanger operating independently;

[0038] like Figure 1 As shown, the hot water circulation regulation mode of the first heat exchanger and the second heat exchanger operating simultaneously is: the second control valve 7 is opened, the third ball valve 6 is closed, the fifth ball valve 14 is opened, the hot water flows through the hot water inlet pipeline through the fifth ball valve 14 and then enters the second hot water inlet 17 of the second heat exchanger 2, the hot water flows through the inside of the second heat exchange tube 15 and flows out from the second hot water outlet 20, the first ball valve 3 is closed, the fourth ball valve 11 is opened, the hot water flows through the pipeline through the fourth ball valve 11 and then enters the first hot water inlet 21, the hot water flows through the inside of the first heat exchange tube 16 and flows out from the first hot water outlet 24, the second ball valve 5 is opened, the first control valve 4 is opened, the hot water flows through the pipeline through the second ball valve 5 and the first control valve 4 to reach the hot water outlet pipeline for the next cycle;

[0039] The gas circulation regulation mode of the working condition in which the first heat exchanger and the second heat exchanger are operated simultaneously is as follows: the second double-blocking valve 9 is closed, the first double-blocking valve 8 is opened, the gas enters the first gas inlet 23 of the first heat exchanger 1 through the gas outlet pipeline and the first double-blocking valve 8, the gas flows through the outside of the first heat exchange tube 16 and flows out from the first gas outlet 22, the third double-blocking valve 10 is opened, the gas enters the second gas inlet 19 of the second heat exchanger 2 through the pipeline and the third double-blocking valve 10, the gas flows through the outside of the second heat exchange tube 15 and flows out from the second gas outlet 18, the fourth double-blocking valve 12 is closed, the fifth double-blocking valve 13 is opened, the gas flows through the pipeline through the fifth double-blocking valve 13 to reach the gas outlet pipeline for the next cycle.

[0040] Through the above adjustments, both the gas and hot water are respectively passed through the first heat exchanger 1 and the second heat exchanger 2 for gas circulation heating.

[0041] like Figure 2 As shown, the hot water circulation regulation mode of the independent operation condition of the first heat exchanger is: the second control valve 7 is opened, the third ball valve 6 is opened, the fifth ball valve 14 is closed, and the fourth ball valve 11 is closed. The hot water enters the first hot water inlet 21 of the first heat exchanger 1 through the hot water inlet pipeline and flows through the second control valve 7 and the third ball valve 6. The hot water flows through the inside of the first heat exchange tube 16 and flows out from the first hot water outlet 24. The first ball valve 3 is closed, the second ball valve 5 is opened, and the first control valve 4 is opened. The hot water flows through the pipeline through the second ball valve 5 and the first control valve 4 to reach the hot water outlet pipeline for the next cycle.

[0042] The gas circulation regulation mode of the independent operation condition of the first heat exchanger is: the second double-blocking valve 9 is closed, the first double-blocking valve 8 is opened, the gas enters the first gas inlet 23 of the first heat exchanger 1 through the gas inlet pipeline and the first double-blocking valve 8, the gas flows through the outside of the first heat exchange tube 16 and flows out from the first gas outlet 22, the third double-blocking valve 10 is closed, the fifth double-blocking valve 13 is closed, the fourth double-blocking valve 12 is opened, and the gas flows through the pipeline through the fourth double-blocking valve 12 to reach the gas outlet pipeline for the next cycle.

[0043] Through the above adjustment, both gas and hot water are separately heated by gas circulation through the first heat exchanger 1, which is suitable for the situation where the second heat exchanger 2 leaks or is damaged and cannot work, or the total gas outlet temperature is too high and the outlet temperature needs to be adjusted and the second heat exchanger 2 needs to be shut down.

[0044] like Figure 3As shown, the hot water circulation regulation mode of the second heat exchanger in the independent operation condition is: the second control valve 7 is opened, the third ball valve 6 is closed, the fifth ball valve 14 is opened, the hot water passes through the hot water outlet pipeline and flows through the second control valve 7 and the fifth ball valve 14 to enter the second hot water inlet 17 of the second heat exchanger 2, the hot water flows through the inside of the second heat exchange tube 15 and flows out from the second hot water outlet 20, the fourth ball valve 11 is closed, the second ball valve 5 is closed, the first ball valve 3 is opened, the first control valve 4 is opened, and the hot water flows through the pipeline through the first ball valve 3 and the first control valve 4 to reach the hot water outlet pipeline for the next cycle;

[0045] The gas circulation regulation mode of the second heat exchanger under independent operation condition is as follows: the first double-blocking valve 8 is closed, the third double-blocking valve 10 is closed, the second double-blocking valve 9 is opened, the gas passes through the gas inlet pipeline and flows through the second double-blocking valve 9 to enter the second gas inlet 19 of the second heat exchanger 2, the gas flows through the outside of the second heat exchange tube 15 and flows out from the second gas outlet 18, the fourth double-blocking valve 12 is closed, the fifth double-blocking valve 13 is opened, the gas passes through the pipeline and flows through the fifth double-blocking valve 13 to reach the gas outlet pipeline for the next cycle.

[0046] Through the above adjustment, both gas and hot water are separately heated by gas circulation through the second heat exchanger 2, which is suitable for situations where the first heat exchanger 1 leaks or is damaged and cannot work, or the total gas outlet temperature is too high and the outlet temperature needs to be adjusted and the first heat exchanger 1 needs to be shut down.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A gas heating system, characterized in that: include: A first heat exchanger having a first heat exchange tube therein, wherein a first gas inlet of the first heat exchanger is connected to a gas inlet pipeline via a first double-blocking valve, and a first gas outlet of the first heat exchanger is connected to a gas outlet pipeline via a fourth double-blocking valve; The second heat exchanger has a second heat exchange tube built in. The second gas inlet of the second heat exchanger is connected to the first gas outlet through the third double-blocking valve, and the second gas outlet of the second heat exchanger is connected to the gas outlet pipeline through the fifth double-blocking valve.

2. A gas heating system according to claim 1, characterized in that: The second hot water inlet of the second heat exchanger is connected to the hot water inlet pipeline through the fifth ball valve and the second control valve, and the second hot water outlet of the second heat exchanger is connected to the hot water outlet pipeline through the first ball valve and the first control valve.

3. A gas heating system according to claim 2, characterized in that: The first hot water inlet of the first heat exchanger is connected to the second hot water outlet through the fourth ball valve, and the first hot water outlet of the first heat exchanger is connected to the hot water outlet pipeline through the second ball valve and the first control valve.

4. A gas heating system according to claim 1, characterized in that: The first hot water inlet of the first heat exchanger is connected to the hot water inlet pipeline through the third ball valve and the second control valve.

5. A gas heating system according to claim 1, characterized in that: The second gas inlet of the second heat exchanger is connected to the gas inlet pipeline through a second double-blocking valve.

6. A gas heating system according to claim 1, characterized in that: The tube-side fluid of the first heat exchanger and the second heat exchanger is hot water, and the shell-side fluid is fuel gas.

7. A variable operating condition adjustment method for a gas heating system, implemented in any system of claims 1-6, characterized in that: It includes the working conditions of the first heat exchanger and the second heat exchanger operating simultaneously, the working condition of the first heat exchanger operating independently and the working condition of the second heat exchanger operating independently, and each working condition includes hot water circulation regulation and gas circulation regulation.

8. A variable operating condition adjustment method for a gas heating system according to claim 7, characterized in that: The hot water circulation regulation mode of the working condition where the first heat exchanger and the second heat exchanger are operated simultaneously is as follows: the second control valve is opened, the third ball valve is closed, the fifth ball valve is opened, the hot water flows through the hot water inlet pipeline through the fifth ball valve and enters the second hot water inlet of the second heat exchanger, then flows through the inside of the second heat exchange tube and flows out from the second hot water outlet, the first ball valve is closed, the fourth ball valve is opened, the hot water flows through the pipeline through the fourth ball valve and enters the first hot water inlet of the first heat exchanger, then flows through the inside of the first heat exchange tube and flows out from the first hot water outlet, the second ball valve is opened, the first control valve is opened, the hot water flows through the pipeline through the second ball valve and the first control valve to reach the hot water outlet pipeline; The gas circulation regulation method for the simultaneous operation condition of the first heat exchanger and the second heat exchanger is: the second double-blocking valve is closed, the first double-blocking valve is opened, the gas flows through the gas inlet pipeline through the first double-blocking valve and then enters the first gas inlet of the first heat exchanger, and then flows through the outside of the first heat exchange tube and flows out from the first gas outlet, the third double-blocking valve is opened, the gas enters the second gas inlet of the second heat exchanger through the pipeline and flows through the third double-blocking valve, and then flows through the outside of the second heat exchange tube and flows out from the second gas outlet, the fourth double-blocking valve is closed, the fifth double-blocking valve is opened, and the gas flows through the fifth double-blocking valve to reach the gas outlet pipeline.

9. The variable operating condition adjustment method of a gas heating system according to claim 7, characterized in that: The hot water circulation regulation mode of the independent operation condition of the first heat exchanger is: the second control valve is opened, the third ball valve is opened, the fifth ball valve is closed, the fourth ball valve is closed, the hot water flows through the hot water inlet pipeline through the second control valve and the third ball valve and enters the first hot water inlet of the first heat exchanger, and then flows through the inside of the first heat exchange tube and flows out from the first hot water outlet, the first ball valve is closed, the second ball valve is opened, the first control valve is opened, and the hot water flows through the pipeline through the second ball valve and the first control valve to reach the hot water outlet pipeline; The gas circulation regulation method for the independent operation condition of the first heat exchanger is: the second double-blocking valve is closed, the first double-blocking valve is opened, the gas enters the first gas inlet of the first heat exchanger through the gas inlet pipeline and the first double-blocking valve, and then flows through the outside of the first heat exchange tube and flows out from the first gas outlet, the third double-blocking valve is closed, the fifth double-blocking valve is closed, the fourth double-blocking valve is opened, and the gas flows through the pipeline through the fourth double-blocking valve to reach the gas outlet pipeline.

10. The variable operating condition adjustment method of a gas heating system according to claim 7, characterized in that: The hot water circulation regulation mode of the second heat exchanger under independent operation condition is: the second control valve is opened, the third ball valve is closed, the fifth ball valve is opened, the hot water passes through the hot water inlet pipeline and flows through the second control valve and the fifth ball valve to enter the second hot water inlet of the second heat exchanger, and then flows through the inside of the second heat exchange tube and flows out from the second hot water outlet, the fourth ball valve is closed, the second ball valve is closed, the first ball valve is opened, the first control valve is opened, and the hot water flows through the pipeline through the first ball valve and the first control valve to reach the hot water outlet pipeline; The gas circulation regulation method for the independent operation condition of the second heat exchanger is: the first double-blocking valve is closed, the third double-blocking valve is closed, the second double-blocking valve is opened, the gas flows through the gas inlet pipeline through the second double-blocking valve and enters the second gas inlet of the second heat exchanger, and then flows through the outside of the second heat exchange tube and flows out from the second gas outlet, the fourth double-blocking valve is closed, the fifth double-blocking valve is opened, the gas passes through the pipeline and flows through the fifth double-blocking valve to reach the gas outlet pipeline.

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