Efficient flue gas waste heat recovery device based on water vapor recirculation

Abstract

The utility model discloses an efficient flue gas waste heat recovery device based on water vapor recirculation, which relates to the technical field of boiler flue gas waste heat recovery, and comprises a gas-fired boiler, a superheater, an enthalpy increasing device, a flue gas heat exchanger and a hot water circulation pipeline, the smoke heat exchanger is arranged on a smoke exhaust pipeline of the gas-fired boiler; the hot water circulating pipeline is sequentially communicated with the superheater, the enthalpy increasing device and the flue gas heat exchanger; a condensate water collecting bin of the flue gas heat exchanger is communicated with a water storage bin of the enthalpy increasing device through a condensate water return pipeline, the water storage bin is communicated with a spraying mechanism in the enthalpy increasing device, and the spraying mechanism is used for spraying gas in a gas inlet pipeline in the enthalpy increasing device; therefore, the utilization efficiency of high-temperature return water heat and the recovery efficiency of flue gas heat are improved, and meanwhile, the energy loss of the gas-fired boiler is reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of boiler flue gas waste heat recovery, in particular to a high-efficiency flue gas waste heat recovery device based on water vapor recirculation. Background Art

[0002] Traditional gas boiler flue gas waste heat recovery devices usually use heating water to directly exchange heat with flue gas. When the heating water temperature is high, the temperature difference between it and the flue gas is small, making it difficult to cool down the flue gas temperature to obtain the condensation heat in the flue gas, and the heat recovery effect is poor. At present, for gas boiler rooms with high heating water temperatures, lithium bromide heat pumps or electric compression heat pumps are used to cool down the flue gas temperature and extract the heat in the flue gas for heating. However, the use of heat pumps requires high investment, occupies a large area, and is complex, so a large number of boilers cannot implement heat pump solutions.

[0003] In view of the above problems, a high-efficiency flue gas waste heat recovery device based on water vapor recirculation is specially developed, which is suitable for working conditions with high heating water temperature. It can perform good heat exchange on the flue gas, so as to recover the flue gas condensation heat and reduce energy consumption. Utility Model Content

[0004] The purpose of the utility model is to provide a high-efficiency flue gas waste heat recovery device based on water vapor recirculation to solve the problems existing in the prior art, improve the utilization efficiency of high-temperature return water heat and the flue gas heat recovery efficiency, and at the same time reduce the energy loss of gas boilers.

[0005] To achieve the above purpose, the utility model provides the following solutions:

[0006] The utility model provides a high-efficiency flue gas waste heat recovery device based on water vapor recirculation, comprising a gas boiler, a superheater, an enthalpy increaser, a flue gas heat exchanger and a hot water circulation pipeline, the enthalpy increaser and the superheater are arranged in sequence on the air supply pipeline of the gas boiler along the air intake direction, and the flue gas heat exchanger is arranged on the smoke exhaust pipeline of the gas boiler; the hot water circulation pipeline is connected with the superheater, the enthalpy increaser and the flue gas heat exchanger in sequence; the condensate collection bin of the flue gas heat exchanger is connected with the water storage bin of the enthalpy increaser through a condensate reflux pipeline, the water storage bin is connected with a spray mechanism in the enthalpy increaser, and the spray mechanism is used to spray the gas in the air intake pipeline of the enthalpy increaser.

[0007] Preferably, the enthalpy increaser, the superheater and the flue gas heat exchanger all include plate heat exchangers, and the plate heat exchanger includes a plurality of vertically arranged parallel plates, liquid flow pipelines are provided in the parallel plates, and flow gaps for gas flow are provided between adjacent parallel plates; in the enthalpy increaser, the spray mechanism is provided above the plate heat exchanger; in the flue gas heat exchanger, the condensate collection bin is provided below the plate heat exchanger.

[0008] Preferably, the enthalpy increaser comprises a closed tower body, in which the spray mechanism, the plate heat exchanger and the water storage tank are arranged.

[0009] Preferably, a lifting pump is provided between the water storage tank and the spray mechanism.

[0010] Preferably, on the air supply pipeline, an air supply fan is also provided between the superheater and the gas boiler.

[0011] Preferably, an online alkali adder is provided on the condensate return pipeline between the condensate collection tank and the water storage tank.

[0012] Preferably, a circulating water pump is provided on the hot water circulation pipeline.

[0013] Preferably, the end of the smoke exhaust pipeline is connected to the chimney.

[0014] Compared with the prior art, the utility model has achieved the following technical effects:

[0015] 1. The utility model cools the return water twice by passing the high-temperature return water in the hot water circulation pipeline into the superheater and the enthalpy increaser in sequence, thereby reducing the return water temperature, increasing the temperature difference with the flue gas, improving the heat exchange efficiency with the flue gas, and being able to reduce the flue gas temperature to a lower level;

[0016] 2. The high-temperature return water in the utility model is used for heat exchange with the make-up air, which increases the temperature of the make-up air, thereby increasing the intake air temperature of the gas boiler and reducing the heat and energy loss required for boiler intake combustion;

[0017] 3. After the utility model utilizes the spray mechanism to humidify the supplementary air, the humidity of the flue gas is also increased accordingly, and the water vapor in the flue gas is easier to condense. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0019] Figure 1 It is a schematic diagram of the overall structure of a high-efficiency flue gas waste heat recovery device based on water vapor recirculation in the utility model;

[0020] Figure 2 It is a curve diagram of the ratio of flue gas heat to flue gas low-level heat;

[0021] Among them, 1. gas boiler; 2. flue gas heat exchanger; 3. enthalpy increaser; 4. superheater; 5. air supply fan; 6. circulating water pump; 7. chimney; 8. online alkali doser; 9. lifting pump; 10. water storage tank; 11. condensate return pipeline. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0023] The purpose of the utility model is to provide a high-efficiency flue gas waste heat recovery device based on water vapor recirculation to solve the problems existing in the prior art, improve the utilization efficiency of high-temperature return water heat and the flue gas heat recovery efficiency, and at the same time reduce the energy loss of gas boilers.

[0024] In order to make the above-mentioned objectives, features and advantages of this embodiment more obvious and easy to understand, this embodiment is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0025] like Figure 1 As shown, this embodiment provides a high-efficiency flue gas waste heat recovery device based on water vapor recycling, including a gas boiler 1, a superheater 4, an enthalpy increaser 3, a flue gas heat exchanger 2 and a hot water circulation pipeline. The enthalpy increaser 3 and the superheater 4 are arranged in sequence on the air supply pipeline of the gas boiler 1 along the air intake direction, and the flue gas heat exchanger 2 is arranged on the exhaust pipeline of the gas boiler 1; the hot water circulation pipeline is connected with the superheater 4, the enthalpy increaser 3 and the flue gas heat exchanger 2 in sequence; the condensate collection tank of the flue gas heat exchanger 2 is connected with the water storage tank 10 of the enthalpy increaser 3 through the condensate return pipeline 11, and the water storage tank 10 is connected with the spray mechanism in the enthalpy increaser 3, and the spray mechanism is used to spray the gas in the air intake pipeline of the enthalpy increaser 3.

[0026] In this embodiment, the hot water flowing into the superheater 4, the enthalpy increaser 3 and the flue gas heat exchanger 2 in the hot water circulation pipeline is called return water, and the hot water flowing out of the flue gas heat exchanger 2 and completing the heat exchange is called supply water.

[0027] When in use, the low-temperature make-up air first enters the enthalpy increaser 3 to exchange heat with the return water in the return water circulation pipeline, and the temperature of the make-up air is increased; at the same time, the spray mechanism sprays the make-up air to increase the humidity of the make-up air, so that the make-up air is heated and humidified, and the make-up air enthalpy is increased; the make-up air after enthalpy increase enters the superheater 4. Since the return water first passes through the superheater 4 and then passes through the enthalpy increaser 3, the return water temperature in the superheater 4 is higher than the return water flowing into the enthalpy increaser 3, which is equivalent to the superheater 4 forming the superheating section of the make-up air, which can effectively prevent the moisture in the make-up air from condensing into water droplets and then entering the burner of the gas boiler 1, causing damage to the burner. The make-up air that passes through the superheater 4 is mixed with the fuel and enters the gas boiler 1 for reaction, and the reaction gas generated by the combustion is discharged into the smoke exhaust pipe. In terms of hot water circulation, the return water enters the flue gas heat exchanger 2 after passing through the enthalpy increaser 3, exchanges heat with the flue gas heat exchanger 2 to reduce the flue gas temperature, and the moisture in the flue gas condenses and is collected by the condensate collection bin. After treatment, the condensate flows back to the water storage bin 10 in the enthalpy increaser 3 to be used for humidifying the make-up air in the enthalpy increaser 3; the heated supply water flowing out of the flue gas heat exchanger 2 flows into other areas for heat exchange, such as into residential areas for heating.

[0028] Therefore, this embodiment cools the return water twice by passing the high-temperature return water in the hot water circulation pipeline into the superheater 4 and the enthalpy increaser 3 in sequence, thereby reducing the return water temperature, increasing the temperature difference with the flue gas, and improving the heat exchange efficiency with the flue gas, and can reduce the flue gas temperature to a lower level; and the high-temperature return water is used for heat exchange with the make-up air, which increases the temperature of the make-up air, thereby increasing the intake air temperature of the gas boiler 1, and reducing the heat and energy loss required for the boiler intake combustion. Therefore, this embodiment improves the overall utilization efficiency of the high-temperature return water heat and the flue gas heat recovery efficiency, and also reduces the energy loss of the gas boiler 1; in addition, after the make-up air is humidified by the spray mechanism, the humidity of the flue gas is also increased accordingly, and the water vapor in the flue gas is easier to condense.

[0029] Specifically, in this embodiment, the enthalpy increaser 3, the superheater 4 and the flue gas heat exchanger 2 all include plate heat exchangers, which include a plurality of vertically arranged parallel plates usually made of stainless steel, and a liquid circulation pipeline is arranged in the parallel plates for hot water circulation, and the liquid circulation pipelines in the plurality of parallel plates are connected. A circulation gap for gas circulation is arranged between adjacent parallel plates; in the enthalpy increaser 3, the air supply gas flows from bottom to top in the circulation gap, and the return water flows in the liquid circulation pipeline, preferably, the return water flows from top to bottom, and the heat exchange between the air supply gas and the return water is enhanced by convection. A spray mechanism is provided above the plate heat exchanger, which sprays from top to bottom. The spray water falls from the circulation gap or adheres to the outer surface of the parallel plates to increase the humidity of the air supply gas. The falling spray water is collected by the water storage tank 10. In the flue gas heat exchanger 2 and the reheater, the heat exchange method between the flue gas and the return water is similar to the heat exchange method in the enthalpy increaser 3, and the condensed water in the flue gas adheres to the outer surface of the parallel plates. In the flue gas heat exchanger 2, a condensed water collection tank is provided below the plate heat exchanger to collect the condensed water dripping from the outer surface of the parallel plates. The setting of the plate heat exchanger in this embodiment makes the airflow and water distribution more uniform, which can improve the enthalpy increase and heat exchange effects.

[0030] The plate heat exchanger is a common heat exchange device in the art, and those skilled in the art are familiar with its structure and usage, so this embodiment does not elaborate on it. Furthermore, the reheater and the flue gas heat exchanger 2 both use asymmetric plate heat exchangers, which can reduce the heat exchange end difference, improve the heat exchange effect, and reduce the exhaust resistance.

[0031] In this embodiment, the enthalpy increaser 3 includes a closed tower body, in which a spray mechanism, a plate heat exchanger and a water storage tank 10 are arranged. The structure of the closed tower body ensures that the internal circulating water is not polluted, and at the same time, reduces heat loss and ensures heat exchange efficiency.

[0032] Furthermore, in this embodiment, an online alkali doser 8 is provided between the condensate collection bin and the water storage bin 10 on the condensate return line 11 to control the condensate to be weakly alkaline. The online alkali doser 8 is an existing device, which generally includes an alkali material barrel, a metering pump, a pH meter, a controller and other structures. The alkali material barrel is used to store alkaline substances, such as sodium hydroxide or calcium hydroxide; the metering pump is used to accurately control the amount of alkaline substances added to ensure that the pH value of the condensate in the condensate return line 11 reaches a predetermined target; the pH meter is used to monitor the pH value in the condensate return line 11 in real time, so as to adjust the amount of alkali added in time; the controller is used to connect with the metering pump and the pH meter to control the entire alkali addition process.

[0033] Furthermore, in this embodiment, a lifting pump 9 is provided between the water storage tank 10 and the spraying mechanism to provide spray lifting power.

[0034] Furthermore, in this embodiment, an air supply fan 5 is provided between the superheater 4 and the gas boiler 1 on the air supply pipeline to provide air supply power.

[0035] Furthermore, in this embodiment, a circulating water pump 6 is provided on the hot water circulation pipeline to provide power for hot water circulation.

[0036] Furthermore, in this embodiment, the end of the smoke exhaust pipeline is connected to the chimney 7 and is discharged into the atmosphere through the chimney 7.

[0037] Specific calculation example:

[0038] 1) General natural gas properties

[0039]

[0040]

[0041] 2) Make-up air components

[0042]

[0043] 3) Flue gas components

[0044]

[0045] 4) Flue gas waste heat

[0046] To ensure the complete combustion of natural gas, a larger excess air coefficient is required to ensure full combustion because the specific gravity of water vapor increases after humidification. Calculated based on an excess air coefficient of 1.30, the volume fraction of water vapor in the flue gas is 22.3%, and the corresponding dew point temperature is 63°C, which is 5°C higher than the dew point temperature of traditional boiler flue gas. Due to the increase in water vapor content, the condensation heat of the flue gas accounts for a larger proportion, which is more conducive to the recovery of flue gas waste heat.

[0047]

[0048] 5) Calculation of air supply enthalpy increase

[0049] Enthalpy increaser 3 heats and humidifies the boiler air supply air uniformly and efficiently to increase enthalpy. Calculated based on the boiler air excess coefficient of 1.3, 1Nm 3 Natural gas combustion consumes 16kg of air. The temperature of the make-up air increases from 5℃, 50% humidity, 11.8kJ / kg to 45℃, 95% humidity, 204.8kJ / kg. The enthalpy increaser 3 increases the heat of the make-up air by 3088kJ, accounting for 8.6% of the calorific value of the gas.

[0050] After the enthalpy is increased, the make-up air enters the reheater, and the make-up air temperature is increased to 47°C, the moisture content is 85.8%, and the enthalpy value is 207.1 kJ / kg. The superheat of the make-up air is increased to prevent water droplets from entering the burner.

[0051] 6) Waste heat recovery calculation

[0052] The flue gas heat exchanger 2 uses 30°C circulating water to cool the flue gas from 80°C to 38°C, and the flue gas recovered heat accounts for 17.3% of the calorific value of the fuel gas.

[0053] Therefore, this embodiment can achieve a final exhaust gas temperature of below 40°C when the heating return water temperature is 50°C.

[0054] Adaptive changes made according to actual needs are all within the protection scope of this embodiment.

[0055] It should be noted that it is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any reference numerals in the claims should not be regarded as limiting the claims involved.

[0056] In this embodiment, specific examples are used to illustrate the principle and implementation of this embodiment. The above description of the embodiment is only used to help understand the method and core idea of ​​this embodiment; at the same time, for those skilled in the art, according to the idea of ​​this embodiment, there will be changes in the specific implementation and application scope. In summary, the content of this specification should not be understood as limiting this embodiment.

Claims

1. A high-efficiency flue gas waste heat recovery device based on water vapor recirculation, characterized in that: It includes a gas boiler, a superheater, an enthalpy increaser, a flue gas heat exchanger and a hot water circulation pipeline. The enthalpy increaser and the superheater are arranged in sequence on the air supply pipeline of the gas boiler along the air intake direction, and the flue gas heat exchanger is arranged on the smoke exhaust pipeline of the gas boiler; the hot water circulation pipeline is connected with the superheater, the enthalpy increaser and the flue gas heat exchanger in sequence; the condensate collection tank of the flue gas heat exchanger is connected with the water storage tank of the enthalpy increaser through a condensate return pipeline, and the water storage tank is connected with the spray mechanism in the enthalpy increaser, and the spray mechanism is used to spray the gas in the air intake pipeline of the enthalpy increaser.

2. The high-efficiency flue gas waste heat recovery device based on water vapor recirculation according to claim 1 is characterized in that: The enthalpy increaser, superheater and flue gas heat exchanger all include plate heat exchangers, and the plate heat exchanger includes a plurality of vertically arranged parallel plates, liquid circulation pipelines are arranged in the parallel plates, and circulation gaps for gas circulation are arranged between adjacent parallel plates; in the enthalpy increaser, the spray mechanism is arranged above the plate heat exchanger; in the flue gas heat exchanger, the condensate collection bin is arranged below the plate heat exchanger.

3. The high-efficiency flue gas waste heat recovery device based on water vapor recirculation according to claim 2 is characterized in that: The enthalpy increaser comprises a closed tower body, in which the spray mechanism, the plate heat exchanger and the water storage tank are arranged.

4. The high-efficiency flue gas waste heat recovery device based on water vapor recirculation according to claim 2 is characterized in that: A lifting pump is arranged between the water storage tank and the spraying mechanism.

5. The high-efficiency flue gas waste heat recovery device based on water vapor recirculation according to claim 1 is characterized in that: On the air supply pipeline, an air supply fan is also arranged between the superheater and the gas boiler.

6. The high-efficiency flue gas waste heat recovery device based on water vapor recirculation according to claim 1 is characterized in that: On the condensate return pipeline, an online alkali adder is arranged between the condensate collection bin and the water storage bin.

7. The high-efficiency flue gas waste heat recovery device based on water vapor recirculation according to claim 1 is characterized in that: The hot water circulation pipeline is provided with a circulating water pump.

8. The high-efficiency flue gas waste heat recovery device based on water vapor recirculation according to claim 1 is characterized in that: The end of the smoke exhaust pipeline is communicated with the chimney.

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