A modular heat exchange combined energy-saving system and method for a steam boiler

Abstract

A modular heat exchange combined energy-saving system for a steam boiler is provided with a connecting pipeline between the low-temperature end of the low-temperature water tank and the water inlet of the condenser, a connecting pipeline between the water outlet of the condenser and the water inlet of the air preheater, a connecting pipeline between the water outlet of the air preheater and the high-temperature end of the low-temperature water tank, a pipeline is connected between the high-temperature end of the low-temperature water tank and the water inlet of the economizer, and a connecting pipeline is provided between the water outlet of the economizer and the water inlet of the boiler; there is a connecting pipeline between the water outlet of the economizer and the low-temperature end of the low-temperature water tank. A modular heat exchange combined energy-saving method forms different paths according to the amount and temperature of the condensed water. After the condensed water and the makeup water of the low-temperature water tank enter the low-temperature water tank, the temperature of the entire low-temperature water tank is calculated by the control system to be lower than 60°C and higher than 60°C. The present invention improves the operating efficiency of the boiler.

Description

Technical Field

[0001] The present invention relates to an energy-saving integrated condensing boiler, and particularly to a modular heat exchange combined energy-saving system and method for an integrated condensing boiler, belonging to the technical field of boilers. Background Art

[0002] Since a large amount of heat is contained in the condensate of a steam boiler, the recovery of the steam boiler condensate for boiler make-up water will significantly improve the efficiency of the entire thermal system, save electricity, fuel, water and pollution treatment costs, and play a significant role in the energy conservation and consumption reduction of factories and the improvement of economic benefits. The factory-designed condensing boilers produced by boiler manufacturers are designed according to a feed water temperature of 20 degrees. Under such conditions, the steam system of the boiler is stable and the flue gas temperature is normal. The behavior of users to recover steam condensate changes the product design feed water temperature condition of the boiler factory from the traditional single feed water of 20 degrees to the combination of high-temperature recovered water and normal-temperature water. Moreover, the recovery amount, recovery temperature and their proportion of condensate vary in different industrial users, and even for the same user, these data will be different at different times. Therefore, the complex feed water conditions in the case of condensate recovery make the flue gas temperature of the product difficult to control due to its association with condensate. In practical use, it is found that using condensate as make-up water will bring the following problems to the steam boiler: 1. Affect the stability of the steam system; 2. The return water volume does not match the boiler make-up water, which is prone to cause make-up water accidents; 3. If the recovered condensate temperature is high and the volume is large, if the flue gas at the tail of the boiler is directly heat-exchanged with the high-temperature water and then discharged, the flue gas temperature will increase due to the increase in the inlet water temperature, and the heat exchange components such as economizers are prone to water vaporization, resulting in a poor heat exchange effect, damage to the heat exchange components, and reduction of the overall thermal efficiency of the boiler. Summary of the Invention

[0003] The purpose of the present invention is to overcome the above problems existing in the current steam boiler in the use of condensate return water, and to provide a modular heat exchange combined energy-saving system and method.

[0004] To achieve the object of the present invention, the following technical solutions are adopted: A modular heat exchange combined energy-saving system for a steam boiler, including a low-temperature water tank, a condenser, an economizer, an air preheater, a condensate recovery machine, and a control system. A flow meter and a water temperature detection device are provided on the outlet water of the condensate recovery machine. The lower part of the low-temperature water tank is the low-temperature end for water inlet, and the upper part is the high-temperature end for water outlet. The combustion-supporting air of the steam boiler is drawn from a fan into the air preheater for heat exchange and temperature rise, and then enters the burner. The flue gas formed after the burner burns exchanges heat in the furnace body of the boiler and then enters the economizer and the condenser in sequence for heat exchange. The flue gas is discharged through the condenser. A connecting pipeline is provided between the low-temperature end of the low-temperature water tank and the water inlet of the condenser. A connecting pipeline is provided between the water outlet of the condenser and the water inlet of the air preheater. A connecting pipeline is provided between the water outlet of the air preheater and the high-temperature end of the low-temperature water tank. A pipeline is connected between the high-temperature end of the low-temperature water tank and the water inlet of the economizer. A connecting pipeline is provided between the water outlet of the economizer and the water inlet of the boiler; There is a connecting pipeline between the water outlet of the economizer and the low-temperature end of the low-temperature water tank;

[0005] The energy-saving system further includes a high-temperature water tank. There is a connecting pipeline between the low-temperature end of the low-temperature water tank and the water inlet of the condenser. There is a connecting pipeline between the water outlet of the condenser and the high-temperature end of the low-temperature water tank. There is a connecting pipeline between the low-temperature water tank and the water inlet of the high-temperature water tank. The outlet pipeline of the condensate recovery machine is connected to the connecting pipeline between the low-temperature water tank and the water inlet of the high-temperature water tank. There is a connecting pipeline between the water outlet of the high-temperature water tank and the water inlet of the air preheater. There is a connecting pipeline between the water outlet of the air preheater and the water inlet of the boiler; There is a connecting pipeline between the water outlet of the economizer and the high-temperature end of the low-temperature water tank;

[0006] Electric control valves are provided on the above pipelines, and each electric control valve is connected to the control system of the boiler.

[0007] Further; The energy-saving system further includes a thermal deaerator. There is a connecting pipeline between the high-temperature end of the low-temperature water tank and the water inlet of the thermal deaerator. There is a connecting pipeline between the water outlet of the thermal deaerator and the water inlet of the air preheater. There is a connecting pipeline between the water outlet of the air preheater and the water inlet of the economizer. There is a connecting pipeline between the water outlet of the economizer and the water inlet of the boiler. There is a connecting pipeline between the water outlet of the high-temperature water tank and the water inlet of the thermal deaerator. There is a connecting pipeline between the water outlet of the thermal deaerator and the water inlet of the air preheater. Electric control valves are provided on the above pipelines, and each electric control valve is connected to the control system of the boiler.

[0008] A modular heat exchange combined energy-saving method adopts the above-mentioned modular heat exchange combined energy-saving system for a steam boiler. The method is as follows: When there is no thermal deaerator in the system,

[0009] A: Based on the amount and temperature of the condensed water, when the control system calculates that the temperature of the entire low-temperature water tank is lower than 60°C after the condensed water and the make-up water of the low-temperature water tank enter the low-temperature water tank, the control system realizes the following process A1 by controlling the opening and closing of the electric control valves on the relevant pipelines: The make-up water and condensed water of the low-temperature water tank enter the low-temperature end of the low-temperature water tank. The water at the low-temperature end of the low-temperature water tank flows into the inlet of the condenser through the connecting pipeline. The outlet water of the condenser flows into the inlet of the air preheater through the connecting pipeline. The outlet water of the air preheater flows into the high-temperature end of the low-temperature water tank through the connecting pipeline. The outlet water at the high-temperature end of the low-temperature water tank flows into the inlet of the economizer through the connecting pipeline. The outlet water of the economizer enters the boiler or the low-temperature water tank according to the make-up water signal of the boiler.

[0010] B: Based on the amount and temperature of the condensed water, when the control system calculates that the temperature of the entire low-temperature water tank is higher than 60°C after the condensed water and the make-up water of the low-temperature water tank enter the low-temperature water tank, the control system realizes the following process B1 by controlling the opening and closing of the electric control valves on the relevant pipelines: The make-up water of the low-temperature water tank enters the low-temperature end of the water tank. The outlet water at the low-temperature end of the low-temperature water tank flows into the inlet of the condenser through the connecting pipeline. The outlet water of the condenser flows into the high-temperature end of the low-temperature water tank through the connecting pipeline. The outlet water at the high-temperature end of the low-temperature water tank is mixed with the condensed water and then flows into the inlet of the high-temperature water tank. The outlet water of the high-temperature water tank flows to the inlet of the air preheater through the connecting pipeline. The outlet water of the air preheater enters the inlet of the economizer through the connecting pipeline. The outlet water of the economizer enters the boiler or the low-temperature water tank according to the make-up water signal of the boiler.

[0011] A modular heat exchange combined energy-saving method is as follows: When there is a thermal deaerator in the system, the following A1 or B1 is adopted.

[0012] A1: Based on the amount and temperature of the condensed water, when the control system calculates that the temperature of the entire low-temperature water tank is lower than 60°C after the condensed water and the make-up water of the low-temperature water tank enter the low-temperature water tank, the control system realizes the following process A2 by controlling the opening and closing of the electric control valves on the relevant pipelines: The make-up water and condensed water of the low-temperature water tank enter the low-temperature end of the low-temperature water tank. The water at the low-temperature end of the low-temperature water tank flows into the inlet of the condenser through the connecting pipeline. The outlet water of the condenser flows into the high-temperature end of the low-temperature water tank through the connecting pipeline. The outlet water at the high-temperature end of the low-temperature water tank flows into the inlet of the thermal deaerator through the connecting pipeline. The outlet water of the thermal deaerator enters the inlet of the air preheater through the connecting pipeline. The outlet water of the air preheater enters the inlet of the economizer through the connecting pipeline. The outlet water of the economizer enters the boiler or the low-temperature water tank according to the make-up water signal of the boiler.

[0013] According to the amount and temperature of the condensed water, when the control system calculates that the temperature of the entire low-temperature water tank is higher than 60°C after the condensed water and the makeup water of the low-temperature water tank enter the low-temperature water tank, the control system realizes the following process B2 by controlling the opening and closing of the electric control valves on the relevant pipelines: The makeup water of the low-temperature water tank enters the low-temperature end of the water tank, the water discharged from the low-temperature end of the low-temperature water tank flows into the inlet of the condenser through the connecting pipeline, the water discharged from the condenser flows into the high-temperature end of the low-temperature water tank through the connecting pipeline, the water discharged from the high-temperature end of the low-temperature water tank is mixed with the condensed water and then flows into the inlet of the high-temperature water tank, the water discharged from the high-temperature water tank flows through the connecting pipeline to the inlet of the thermal deaerator, the water discharged from the thermal deaerator flows through the connecting pipeline to the inlet of the air preheater, the water discharged from the air preheater flows through the connecting pipeline into the inlet of the economizer, and the water discharged from the economizer enters the boiler or the low-temperature water tank according to the makeup water signal of the boiler.

[0014] The positive and beneficial technical effects of the present invention are as follows: The modular heat exchange combined energy-saving system of the modular steam boiler sets different heat exchange paths according to the overall influence of the recovery amount of the condensed water and the return water temperature on the water temperature in the water tank, which can make the boiler operate stably, the steam supply is stable, maintain a relatively low and stable flue gas temperature, avoid damage to the economizer and condenser due to excessive temperature, and at the same time effectively utilize the heat of the recovered condensed water, improving the operation efficiency of the boiler. Brief Description of the Drawings

[0015] Figure 1 It is a schematic diagram of the A1 scheme of the present invention.

[0016] Figure 2 It is a schematic diagram of the A2 scheme of the present invention.

[0017] Figure 3 It is a schematic diagram of the B1 scheme of the present invention. Detailed Embodiments

[0018] To more fully explain the implementation of the present invention, embodiments of the present invention are provided. These embodiments are only an elaboration of the present invention and do not limit the scope of the present invention.

[0019] The present invention is further explained in detail in conjunction with the accompanying drawings. The marks in the drawings are as follows: 1: furnace body; 2: economizer; 3: condenser; 4: condensed water recovery machine; 5: low-temperature water tank; 6: air preheater; 7: fan, 8: burner; 9: thermal deaerator; 10: high-temperature water tank. In each figure, the arrow from the fan to the air preheater and then to the burner is the air flow path, and the other arrows shown are all water flow paths.

[0020] As shown in the attached drawings, a modular heat exchange combined energy-saving system for a steam boiler includes a low-temperature water tank 5, a condenser 3, an economizer 2, an air preheater 6, a condensate recovery machine 4, and a control system. A flow meter and a water temperature detection device are provided on the water outlet of the condensate recovery machine. The lower part of the low-temperature water tank is the low-temperature end for water inlet, and the upper part is the high-temperature end for water outlet. The combustion-supporting air of the steam boiler is drawn from a blower 7 into the air preheater 6 for heat exchange and temperature rise, and then enters the burner. The flue gas formed after the burner burns exchanges heat in the furnace body 1 of the boiler and then enters the economizer and the condenser in sequence for heat exchange, and the flue gas is discharged from the condenser. The above are all existing configurations on the current steam boiler. A connecting pipeline is provided between the low-temperature end of the low-temperature water tank and the water inlet of the condenser. A connecting pipeline is provided between the water outlet of the condenser and the water inlet of the air preheater. A connecting pipeline is provided between the water outlet of the air preheater and the high-temperature end of the low-temperature water tank. A pipeline is connected between the high-temperature end of the low-temperature water tank and the water inlet of the economizer. A connecting pipeline is provided between the water outlet of the economizer and the water inlet of the boiler. There is a connecting pipeline between the water outlet of the economizer and the high-temperature end of the low-temperature water tank. The connecting pipeline between the water outlet of the economizer and the high-temperature end of the low-temperature water tank is used for the circulation between the economizer and the water tank. Because in actual use, the water supply at the user's place is not in an ideal continuous state. If the boiler requires too little makeup water or no makeup water, it will cause the water in the economizer to stagnate in the economizer tube bank and be heated and vaporized by the flue gas. At this time, an electric three-way valve needs to be added at the outlet of the economizer and connected to the low-temperature water tank. According to the boiler makeup water signal, it is judged whether the water outlet of the economizer enters the boiler or the low-temperature water tank. In each of the attached drawings, in order to avoid intersection, the process of the boiler's water outlet from the economizer entering the high-temperature end of the low-temperature water tank is not shown.

[0021] The energy-saving system further includes a high-temperature water tank 10. There is a connecting pipeline between the low-temperature end of the low-temperature water tank and the water inlet of the condenser. There is a connecting pipeline between the water outlet of the condenser and the high-temperature end of the low-temperature water tank. There is a connecting pipeline between the low-temperature water tank and the water inlet of the high-temperature water tank. The outlet pipeline of the condensate recovery machine is connected to the connecting pipeline between the low-temperature water tank and the water inlet of the high-temperature water tank. There is a connecting pipeline between the water outlet of the high-temperature water tank and the water inlet of the air preheater. There is a connecting pipeline between the water outlet of the air preheater and the water inlet of the boiler; electric control valves are provided on the above pipelines, and each electric control valve is connected to the control system of the boiler. Connecting the electric control valve to the control system is a commonly used technical solution on the boiler.

[0022] Some boilers are equipped with a thermal deaerator. In this case, the energy-saving system may further include a thermal deaerator 9. There is a connecting pipeline between the high-temperature end of the low-temperature water tank and the inlet of the thermal deaerator, a connecting pipeline between the outlet of the thermal deaerator and the inlet of the air preheater, a connecting pipeline between the outlet of the air preheater and the inlet of the economizer, a connecting pipeline between the outlet of the economizer and the inlet of the boiler, a connecting pipeline between the outlet of the high-temperature water tank and the inlet of the thermal deaerator, and a connecting pipeline between the outlet of the thermal deaerator and the inlet of the air preheater. Electric control valves are provided on each of the above pipelines, and each electric control valve is connected to the control system of the boiler.

[0023] A modular heat exchange combined energy-saving method uses the above-mentioned steam boiler modular heat exchange combined energy-saving system. The method is as follows: When there is no thermal deaerator in the system,

[0024] A1: According to the amount and temperature of the condensed water, after calculation by the control system, when the temperature of the entire low-temperature water tank is lower than 60 °C after the condensed water and the makeup water of the low-temperature water tank enter the low-temperature water tank, the control system controls the opening and closing of the electric control valves on the relevant pipelines to implement the following process A1: The makeup water of the low-temperature water tank and the condensed water enter the low-temperature end of the low-temperature water tank. The water at the low-temperature end of the low-temperature water tank flows into the inlet of the condenser through the connecting pipeline. The outlet water of the condenser flows into the inlet of the air preheater through the connecting pipeline. The outlet water of the air preheater flows into the high-temperature end of the low-temperature water tank through the connecting pipeline. The outlet water at the high-temperature end of the low-temperature water tank flows into the inlet of the economizer through the connecting pipeline. The outlet water of the economizer enters the boiler or the low-temperature water tank according to the makeup water signal of the boiler. Figure 1 Figure 8 is a schematic diagram of Process A1. In this case, the return water volume of the condensed water is small or the return water temperature is low, and the temperature after mixing the low-temperature makeup water and the condensed water is low. Due to the low feed water temperature, the condenser and the air preheater are used in series, so that the temperature of the low-temperature water tank will not be too high, and at the same time, the flue gas temperature is low, which is beneficial to energy saving.

[0025] B1: According to the amount and temperature of the condensed water, after calculation by the control system, when the temperature of the entire low-temperature water tank is higher than 60 °C after the condensed water and the makeup water of the low-temperature water tank enter the low-temperature water tank, the control system controls the opening and closing of the electric control valves on the relevant pipelines to implement the following process B1: The makeup water of the low-temperature water tank enters the low-temperature end of the water tank. The outlet water at the low-temperature end of the low-temperature water tank flows into the inlet of the condenser through the connecting pipeline. The outlet water of the condenser flows into the high-temperature end of the low-temperature water tank through the connecting pipeline. The outlet water at the high-temperature end of the low-temperature water tank is mixed with the condensed water and then flows into the inlet of the high-temperature water tank. The outlet water of the high-temperature water tank flows to the inlet of the air preheater through the connecting pipeline. The outlet water of the air preheater enters the inlet of the economizer through the connecting pipeline. The outlet water of the economizer enters the boiler or the low-temperature water tank according to the makeup water signal of the boiler. Figure 3It is a solution under condition B1. The temperature in the low-temperature water tank is relatively low. After passing through the condenser, the flue gas temperature is lowered, and the overall operating efficiency is high. Then, the water discharged from the high-temperature end of the low-temperature water tank is mixed with the condensed water and enters the high-temperature water tank. After heat exchange in the air preheater, the combustion-supporting air is heated up. The cooled water then enters the economizer to absorb heat, thereby reducing the inlet water temperature and flue gas temperature of the economizer, making the economizer operate more efficiently. The heated combustion-supporting air is mixed with the flue gas and then enters the burner, which also solves the condensation problem caused by the mixing of low-temperature air and flue gas. The combustion is FGR flue gas recirculation combustion, and part of the flue gas needs to be extracted, mixed with the combustion-supporting air, and then returned to the combustion for re-combustion.

[0026] A modular heat exchange combined energy-saving method. When there is a thermal deaerator in the system, the method is as follows:

[0027] A2: According to the amount and temperature of the condensed water, after calculation by the control system, when the temperature of the entire low-temperature water tank is lower than 60°C after the condensed water and the makeup water of the low-temperature water tank enter the low-temperature water tank, the control system controls the opening and closing of the electric control valves on the relevant pipelines to achieve the following process A2: The makeup water and condensed water of the low-temperature water tank enter the low-temperature end of the low-temperature water tank. The water at the low-temperature end of the low-temperature water tank flows into the inlet of the condenser through the connecting pipeline. The outlet water of the condenser flows into the high-temperature end of the low-temperature water tank through the connecting pipeline. The water discharged from the high-temperature end of the low-temperature water tank flows into the inlet of the thermal deaerator through the connecting pipeline. The outlet water of the thermal deaerator enters the inlet of the air preheater through the connecting pipeline. The outlet water of the air preheater enters the inlet of the economizer through the connecting pipeline. The economizer enters the boiler or the low-temperature water tank according to the makeup water signal of the boiler. Figure 2 It is a schematic diagram of solution A2. In this case, the amount of condensed water is small or the temperature is low. After entering the low-temperature water tank, the overall feed water temperature will not be too high. Since the economizer has been heat-exchanged by the relatively low-temperature water flowing out of the air heat exchanger, the inlet flue gas temperature of the condenser is not high. After coming out of the condenser and entering the high-temperature end of the low-temperature water tank, it will not cause the water temperature of the low-temperature water tank to be too high. At the same time, the flue gas temperature of the condenser is also low, which is beneficial to improving the efficiency, and the overall operating efficiency is relatively high. The high-temperature water preheats the low-temperature air after passing through the thermal deaerator and the air preheater, thereby reducing the inlet water temperature and flue gas temperature of the economizer, making the economizer operate more efficiently. The heated combustion-supporting air is mixed with the flue gas and then enters the burner, which also solves the condensation problem caused by the mixing of low-temperature air and flue gas.

[0028] B2: According to the amount and temperature of the condensed water, when the control system calculates that the temperature of the entire low-temperature water tank is higher than 60°C after the condensed water and the make-up water of the low-temperature water tank enter the low-temperature water tank, the control system realizes the following process B2 by controlling the opening and closing of the electric control valves on the relevant pipelines: The make-up water of the low-temperature water tank enters the low-temperature end of the water tank, the water discharged from the low-temperature end of the low-temperature water tank flows into the inlet of the condenser through the connecting pipeline, the water discharged from the condenser flows into the high-temperature end of the low-temperature water tank through the connecting pipeline, the water discharged from the high-temperature end of the low-temperature water tank is mixed with the condensed water and then flows into the inlet of the high-temperature water tank, the water discharged from the high-temperature water tank flows through the connecting pipeline to the inlet of the thermal deaerator, the water discharged from the thermal deaerator flows through the connecting pipeline to the inlet of the air preheater, the water discharged from the air preheater flows through the connecting pipeline into the inlet of the economizer, and the water discharged from the economizer enters the boiler or the low-temperature water tank B2 according to the make-up water signal of the boiler. The solution of B2 is to add a thermal deaerator between the high-temperature water tank and the air preheater on the basis of B1, and the others remain unchanged. The advantages of this situation are the same as those of the B1 solution.

[0029] Regarding whether the temperature of the entire low-temperature water tank is lower or higher than 60°C when the condensed water and the make-up water of the low-temperature water tank enter the low-temperature water tank, because there are a liquid level gauge and a temperature detection device configured in the low-temperature water tank, the condensed water has a flow rate and a temperature, and there is a total make-up water volume, so the low-temperature make-up water has a flow rate and a temperature. According to these parameters, the control system can calculate whether the temperature of the entire low-temperature water tank is lower or higher than 60°C when the condensed water and the make-up water of the low-temperature water tank enter the low-temperature water tank.

[0030] After the embodiments of the present invention are described in detail, those skilled in the art can clearly understand that various changes and modifications can be made without departing from the scope and spirit of the above-mentioned patent application. Any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention all belong to the scope of the technical solution of the present invention, and the present invention is not limited to the implementation manners of the examples given in the specification.

Claims

1. A modular heat exchange combined energy-saving system for a steam boiler, comprising a low-temperature water tank, a condenser, an economizer, an air preheater, a condensate recovery machine, and a control system. A flow meter and a water temperature detection device are provided on the water outlet of the condensate recovery machine. The lower part of the low-temperature water tank is the low-temperature end for water inlet, and the upper part is the high-temperature end for water outlet. The combustion-supporting air of the steam boiler is drawn from a blower into the air preheater for heat exchange and temperature rise, and then enters the burner. The flue gas formed after the burner burns exchanges heat in the furnace body of the boiler and then enters the economizer and the condenser in sequence for heat exchange, and the flue gas is discharged through the condenser. It is characterized in that: A connecting pipe is provided between the low-temperature end of the low-temperature water tank and the water inlet of the condenser. A connecting pipe is provided between the water outlet of the condenser and the water inlet of the air preheater. A connecting pipe is provided between the water outlet of the air preheater and the high-temperature end of the low-temperature water tank. A pipe is connected between the high-temperature end of the low-temperature water tank and the water inlet of the economizer. A connecting pipe is provided between the water outlet of the economizer and the water inlet of the boiler; there is a connecting pipe between the water outlet of the economizer and the high-temperature end of the low-temperature water tank; The energy-saving system further includes a high-temperature water tank. There is a connecting pipe between the water outlet of the condenser and the high-temperature end of the low-temperature water tank. There is a connecting pipe between the low-temperature water tank and the water inlet of the high-temperature water tank. The outlet pipe of the condensate recovery machine is connected to the connecting pipe between the low-temperature water tank and the water inlet of the high-temperature water tank. There is a connecting pipe between the water outlet of the high-temperature water tank and the water inlet of the air preheater. There is a connecting pipe between the water outlet of the air preheater and the water inlet of the boiler; Electric control valves are provided on the above-mentioned pipes, and each electric control valve is connected to the control system of the boiler.

2. A modular heat exchange combined energy-saving method, which adopts a steam boiler modular heat exchange combined energy-saving system as described in claim 1, and is characterized in that The method is as follows: There is no thermal deaerator in the system; A1: According to the amount and temperature of the condensate, after the control system calculates that when the condensate and the make-up water of the low-temperature water tank enter the low-temperature water tank and the temperature of the entire low-temperature water tank is lower than 60°C, the control system controls the opening and closing of the electric control valves on the relevant pipes to achieve the following process A1: The make-up water of the low-temperature water tank and the condensate enter the low-temperature end of the low-temperature water tank. The water at the low-temperature end of the low-temperature water tank flows into the water inlet of the condenser through the connecting pipe. The water outlet of the condenser flows into the water inlet of the air preheater through the connecting pipe; The water outlet of the air preheater flows into the high-temperature end of the low-temperature water tank through the connecting pipe. The water outlet of the high-temperature end of the low-temperature water tank flows into the water inlet of the economizer through the connecting pipe. The water outlet of the economizer enters the boiler or the low-temperature water tank according to the water make-up signal of the boiler. B1: According to the amount and temperature of the condensate, after the control system calculates that when the condensate and the make-up water of the low-temperature water tank enter the low-temperature water tank and the temperature of the entire low-temperature water tank is higher than 60°C, the control system controls the opening and closing of the electric control valves on the relevant pipes to achieve the following process B1: The make-up water of the low-temperature water tank enters the low-temperature end of the water tank. The water outlet of the low-temperature end of the low-temperature water tank flows into the water inlet of the condenser through the connecting pipe. The water outlet of the condenser flows into the high-temperature end of the low-temperature water tank through the connecting pipe. The water outlet of the high-temperature end of the low-temperature water tank is mixed with the condensate and then flows into the water inlet of the high-temperature water tank. The water outlet of the high-temperature water tank flows through the connecting pipe to the water inlet of the air preheater. The water outlet of the air preheater enters the water inlet of the economizer through the connecting pipe. The water outlet of the economizer enters the boiler or the low-temperature water tank according to the water make-up signal of the boiler.

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