Heat recovery device

Abstract

The amount of waste heat recovered is increased without increasing the heat transfer area of ​​the latent heat recovery heat exchanger. [Solution] The HO gas (water vapor) contained in the combustion exhaust gas generated by combustion is recovered as drain (moisture) generated by heat exchange at the outlet of the latent heat recovery heat exchanger (latent heat recovery device) 14. This drain (moisture) is injected into the high-temperature exhaust gas section on the primary side of the latent heat recovery heat exchanger (latent heat recovery device) 14 and the exhaust heat recovery device 12, and on the secondary side of the heat source equipment (combustion device) 10 such as a boiler, and vaporized. This process is repeated multiple times, and the recovered drain (moisture) generated by the latent heat recovery heat exchanger (latent heat recovery device) 14 is circulated within the combustion exhaust gas system, making it possible to increase the amount of HO gas (water vapor) in the exhaust gas supplied to the latent heat recovery heat exchanger (latent heat recovery device) 14 to the amount that maximizes the latent heat recovery.

Description

Technical Field

[0001] The present invention relates to a heat recovery device that recovers water vapor condensate in exhaust gas, re-evaporates it in high-temperature exhaust gas, and then recovers and circulates it again as condensate to increase the latent heat recovery amount.

Background Art

[0002] In recent years, in fuel combustion type heat source equipment such as hot water generators, hot water boilers, and steam boilers, latent heat recovery type high-efficiency heat source equipment equipped with a latent heat recovery heat exchanger has become the mainstream in order to achieve high efficiency from the perspective of energy conservation. A latent heat recovery heat exchanger generally performs further heat recovery from combustion exhaust gas that has been discharged from an exhaust heat recovery device attached to the heat source equipment and has cooled to a low temperature near the combustion exhaust gas dew point temperature. It is added to the secondary side of the exhaust gas system of the exhaust heat recovery device, or the heat transfer area of the exhaust heat recovery device is increased to also serve as a latent heat recovery heat exchanger, thereby performing latent heat recovery and improving the exhaust heat recovery rate.

[0003] Further, Patent Document 1 below discloses a configuration for efficiently recovering water vapor in exhaust gas using a latent heat recovery liquid. Patent Document 1 directly contacts the latent heat recovery liquid with the combustion exhaust gas, and due to the vapor pressure drop in the combustion exhaust gas, it promotes the condensation of the vapor in the combustion exhaust gas not only by the temperature difference but also by the concentration difference. After recovering the latent heat + sensible heat of the waste heat with the latent heat recovery liquid, the latent heat recovery liquid after exhaust heat recovery is used to perform exhaust heat recovery as a sensible heat change by a heat exchanger in the liquid phase state. Patent Document 1 uses a latent heat recovery liquid to cope with the case where the dew point temperature of the combustion exhaust gas is low.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Latent heat recovery heat exchangers recover waste heat from combustion exhaust gas that has cooled to near the dew point temperature. Therefore, it is not possible to have a large temperature difference between the heated fluid (feedwater side) and the heat exchange fluid (combustion exhaust gas side). In order to achieve the required amount of waste heat recovery while meeting various allowable design conditions such as exhaust gas pressure loss conditions, the heat transfer area of ​​the heat exchanger must be increased. Furthermore, there is a demand for even higher efficiency of latent heat exchangers. Meeting the demand for higher efficiency requires larger latent heat recovery heat exchangers (increased heat transfer area), which necessitates the use of a large amount of additional heat transfer tube material and presents the challenge of the device size increasing, making it impossible to fit into the planned installation space.

[0006] Furthermore, in latent heat recovery heat exchangers, H in the combustion exhaust gas generated from the heat source equipment 2 In order to recover the latent heat when O gas (water vapor) condenses through heat exchange, H in the combustion exhaust gas is used. 2 It is known that the more oxygen gas (water vapor) there is, the greater the amount of latent heat recovered. However, in the current system, the fuel is burned in a combustion device built into the heat source equipment, and the H2O gas in the combustion exhaust gas generated therefrom is recovered. 2 The amount of oxygen (water vapor) in the combustion exhaust gas depends on the fuel components and the combustion air supplied to the combustion device, therefore, H2O gas is present in the combustion exhaust gas. 2 To increase the amount of O gas (water vapor), one could use a fuel with a high proportion of hydrogen atoms or add moisture to the combustion air or combustion chamber. However, using a fuel with a high proportion of hydrogen atoms (e.g., hydrogen) requires modifications to the combustion system, and adding moisture to the combustion air or combustion chamber negatively affects fuel combustion in the combustion system. Therefore, the H gas in the combustion exhaust gas originating from the addition of moisture to the fuel, combustion air, or combustion chamber is a concern. 2 There is an increase limit to the amount of O gas (water vapor), and H in the combustion exhaust gas. 2 The amount of O gas (water vapor) is increased by adding water to the combustion exhaust gas from outside the system in the form of fuel or additive water in order to increase the amount of latent heat recovered, and the amount of H contained in the combustion exhaust gas is reduced. 2 It is difficult to arbitrarily increase the amount of oxygen gas (water vapor).

[0007] Furthermore, if more exhaust heat is recovered from the combustion exhaust gas using a latent heat recovery heat exchanger, and the heat recovery device and the latent heat recovery heat exchanger are installed in series, the temperature of the heated fluid (feedwater side) at the outlet of the latent heat recovery heat exchanger will rise. As a result, the temperature of the heated fluid (feedwater side) at the inlet of the heat recovery device, which is installed on the primary side of the exhaust gas system of the latent heat recovery heat exchanger to which the heated feedwater is supplied, will rise, reducing the amount of heat exchanged in the heat recovery device. Consequently, the temperature of the exhaust gas outlet, which is the heated fluid on the heating side of the heat recovery device, will rise. As a result, the temperature of the combustion exhaust gas supplied to the latent heat recovery heat exchanger will rise, and the combustion exhaust gas will be supplied to the heat recovery heat exchanger at a temperature higher than the dew point temperature of the combustion exhaust gas suitable for latent heat recovery. This presents a problem in that the heat transfer area, which was originally planned to contribute to latent heat exchange in the latent heat recovery heat exchanger, is used for sensible heat exchange by the amount of the increased supply exhaust gas temperature, thus hindering latent heat recovery.

[0008] As described above, Patent Document 1 directly contacts the latent heat recovery liquid with the combustion exhaust gas, promoting condensation of vapor in the combustion exhaust gas not only due to the temperature difference but also the concentration difference, thereby recovering latent heat + sensible heat as waste heat in the latent heat recovery liquid. After the waste heat recovery, the latent heat recovery liquid is in the liquid phase and then used in a heat exchanger to recover waste heat as a sensible heat change. Patent Document 1 does not increase the amount of waste heat recovered in the latent heat region by lowering the temperature of the high-temperature exhaust gas through the heat of vaporization when the sprayed water evaporates, or by forcibly increasing the amount of water vapor (moisture) in the combustion exhaust gas supplied to the latent heat recovery heat exchanger up to the saturation moisture region to raise the dew point temperature of the combustion exhaust gas. Furthermore, Patent Document 1 uses the latent heat recovery liquid to deal with the case when the dew point temperature of the combustion exhaust gas is low, and does not raise the dew point temperature of the combustion exhaust gas to solve the problem without using an additional medium such as the latent heat recovery liquid. Thus, increasing the amount of latent heat recovered by vaporizing and condensing the drain water generated during latent heat recovery in the combustion exhaust gas is neither disclosed nor suggested in Patent Document 1.

[0009] To solve the above problems, the present invention relates to H contained in the combustion exhaust gas generated by combustion. 2O gas (water vapor) is recovered as condensate (moisture) generated by heat exchange at the outlet of the latent heat recovery heat exchanger. This condensate (moisture) is injected into the high-temperature exhaust gas section on the primary side of the latent heat recovery heat exchanger and the exhaust heat recovery device, and on the secondary side of the combustion device, and vaporized. This process is repeated multiple times, and the recovered condensate (moisture) generated by the latent heat recovery heat exchange is circulated within the combustion exhaust gas system, thereby increasing the H content in the exhaust gas supplied to the latent heat recovery heat exchanger. 2 This invention provides a heat recovery device that can increase the amount of O gas (water vapor) to the amount that maximizes the latent heat recovery. [Means for solving the problem]

[0010] The heat recovery device of the present invention is a heat recovery device that recovers waste heat from combustion exhaust gas discharged from a heat source device, and has a latent heat recovery heat exchanger installed on the secondary side (downstream side) of the exhaust gas system of the waste heat recovery device, and recovers latent heat from low temperature combustion exhaust gas using this latent heat recovery heat exchanger, or a heat recovery device in which the heat transfer area of ​​the waste heat recovery device is enlarged and also serves as a latent heat recovery heat exchanger, and a drain pipe is installed at the outlet of the latent heat recovery heat exchanger to recover drain (moisture) generated by heat exchange, and this drain pipe is connected to the exhaust gas duct on the primary side (upstream side) of the latent heat recovery heat exchanger and the waste heat recovery device and on the secondary side (downstream side) of the heat source device, and H contained in the combustion exhaust gas 2 This system is characterized by recovering O gas (water vapor) as condensate (moisture) generated by heat exchange in a latent heat recovery heat exchanger, and circulating at least a portion of this condensate (moisture) within the combustion exhaust gas system.

[0011] In the above-described apparatus, a pressure-boosting means such as a pump can be provided in the drain piping. In this case, a temperature measuring means for measuring the temperature of the heated fluid inlet and outlet of the latent heat recovery heat exchanger can be provided, and a calculation means can be connected between this temperature measuring means and the pressure-boosting means to control the flow rate of the pressure-boosting means and adjust the circulating drain flow rate so that the amount of latent heat recovered in the latent heat recovery heat exchanger is maximized.

[0012] Furthermore, in the above-described apparatus, it is also possible to install a latent heat recovery heat exchanger above the exhaust gas duct, and to configure the apparatus so that the drain (moisture) generated by heat exchange in the latent heat recovery heat exchanger is dispersed into the exhaust gas duct installed below by gravity.

[0013] These devices may also be equipped with a spraying device in the exhaust gas duct that atomizes the drain from the drain piping into fine particles and sprays them. Furthermore, a heat exchange promoting plate may be installed in the exhaust gas duct to improve the contact efficiency between the combustion exhaust gas and the drain. [Effects of the Invention]

[0014] In this invention, without adding water from outside the system in the form of fuel or additive water, the H contained in the combustion exhaust gas generated by combustion is eliminated. 2 The process of "drain recovery" → "vaporization" is repeated multiple times, recovering the condensate (moisture) generated by heat exchange at the outlet of the latent heat recovery heat exchanger, and injecting it into the high-temperature exhaust gas section on the primary side of the latent heat recovery heat exchanger and the exhaust heat recovery device, as well as the secondary side of the combustion device, to vaporize the H gas supplied to the latent heat recovery heat exchanger. 2 It becomes possible to increase the amount of O gas (water vapor) to the amount that maximizes latent heat recovery. Also, H in the combustion exhaust gas 2 By increasing the amount of oxygen gas (water vapor), the amount of latent heat recovered can be increased through condensation heat transfer, which has a high heat transfer coefficient. This makes it possible to increase the amount of waste heat recovered without increasing the heat transfer area of ​​the latent heat recovery heat exchanger.

[0015] By injecting combustion exhaust gas drain (moisture) into high-temperature combustion exhaust gas and vaporizing it, the H content in the combustion exhaust gas is reduced without adversely affecting the combustion of the combustion device. 2The amount of O gas (water vapor) can be significantly increased from the latent heat recovery amount that can be recovered by a conventional latent heat recovery heat exchanger. Also, in high-temperature combustion exhaust gas, since the amount of saturated water vapor in the gas is larger compared to normal-temperature air, by injecting and vaporizing combustion exhaust gas drain (moisture), more H 2 O gas (water vapor) can be contained in the exhaust gas.

[0016] By injecting and vaporizing combustion exhaust gas drain (moisture) into the high-temperature exhaust gas on the primary side of the latent heat recovery heat exchanger and the exhaust heat recovery device and on the secondary side of the combustion device, in addition to the temperature of the high-temperature combustion exhaust gas decreasing due to the heat of vaporization, the amount of H 2 O gas (water vapor) in the combustion exhaust gas increases, and thus the exhaust gas dew point temperature also rises. As a result, there is a margin in the heat recovery amount in the exhaust heat recovery device, and the combustion exhaust gas temperature at the inlet of the latent heat recovery heat exchanger can be lowered close to the exhaust gas dew point temperature, making it possible to generate combustion exhaust gas suitable for the latent heat recovery heat exchanger.

Brief Description of the Drawings

[0017] [Figure 1] FIG. 1 is an explanatory diagram showing an example of the schematic configuration of the heat recovery device of the present invention. [Figure 2] FIG. 2 is an explanatory diagram showing another example of the schematic configuration of the heat recovery device of the present invention. [Figure 3] FIG. 3 is an enlarged cross-sectional explanatory diagram showing an example of the exhaust gas duct in the heat recovery device of the present invention. [Figure 4] FIG. 4 is an explanatory diagram showing yet another example of the schematic configuration of the heat recovery device of the present invention.

Modes for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described based on the drawings. However, the present invention is not limited to the following embodiments and can be implemented with appropriate modifications.

[0019] The embodiment shown in Figure 1 involves collecting exhaust gas drain generated by the latent heat recovery heat exchanger (latent heat recovery device) 14 into the duct through which the high-temperature exhaust gas passes on the primary side (upstream side) of the latent heat recovery heat exchanger (latent heat recovery device) 14, spraying it, and vaporizing it to lower the exhaust gas temperature in the high-temperature range. The sprayed water is circulated by repeating the process of collecting and vaporizing the exhaust gas drain generated by the latent heat recovery heat exchanger (latent heat recovery device) 14 multiple times. Note that H in the combustion exhaust gas 2 Since the amount of O gas (water vapor) is continuously supplied by fuel combustion during the operation of heat source equipment 10 such as a boiler, it is possible to arbitrarily increase the amount of drain sprayed into the exhaust gas in a circulation process that repeats the process of recovering and vaporizing exhaust gas drain multiple times. To spray the recovered exhaust gas drain into the exhaust gas duct at the outlet of the heat source equipment 10, a pump 16 or the like is used to increase the pressure, and then the drain is sprayed using a spray nozzle (not shown).

[0020] In Figure 1, fuel-combustion type heat source equipment 10, such as hot water generators, hot water boilers, and steam boilers, are equipped with latent heat recovery heat exchangers (latent heat recovery devices) 14 to achieve high efficiency from an energy-saving perspective. The latent heat recovery heat exchanger (latent heat recovery device) 14 is generally added to the exhaust gas system secondary side (downstream side) of the exhaust heat recovery device 12 attached to the heat source equipment 10 to recover further heat from the combustion exhaust gas, which has been cooled to near the dew point temperature of the combustion exhaust gas. Alternatively, the heat transfer area of ​​the exhaust heat recovery device 12 can be increased and the latent heat recovery heat exchanger (latent heat recovery device) 14 can be used in conjunction to recover latent heat and improve the exhaust heat recovery rate. 22 is the inlet of the fluid to be heated, and 24 is the outlet of the fluid to be heated.

[0021] The apparatus shown in Figure 1 is configured to recover latent heat from low-temperature combustion exhaust gas by installing a latent heat recovery heat exchanger (latent heat recovery device) 14 on the secondary side (downstream side) of the exhaust gas system of a heat recovery device 12 that recovers waste heat from combustion exhaust gas discharged from heat source equipment 10 such as a boiler. A drain pipe 18 is provided at the outlet of the latent heat recovery heat exchanger (latent heat recovery device) 14 to recover condensate (moisture) generated by the heat exchange. This drain pipe 18 is connected to the exhaust gas duct (not shown) on the primary side (upstream side) of the heat recovery device 12 and the secondary side (downstream side) of the heat source equipment 10, and H contained in the combustion exhaust gas. 2 In this embodiment, O gas (water vapor) is recovered as condensate (moisture) generated by heat exchange in a latent heat recovery heat exchanger (latent heat recovery device) 14, and at least a portion of this condensate (moisture) is circulated within the combustion exhaust gas system. Within the combustion exhaust gas system, the condensate (moisture) is circulated as steam. Excess condensate (moisture) is discharged outside the system. In this embodiment, a pump 16 is installed in the drain piping 18 to transfer and circulate the recovered condensate (moisture).

[0022] The embodiment shown in Figure 2 is a pumpless configuration in which, when spraying recovered exhaust gas drain into the exhaust gas duct at the outlet of a heat source equipment 10 such as a boiler, the recovered exhaust gas drain is sprayed by gravity into the exhaust gas duct installed below by installing a latent heat recovery heat exchanger (latent heat recovery device) 20 such as a latent heat recovery economizer above the exhaust gas outlet connection of the heat source equipment 10 such as a boiler, rather than using a pump to increase the pressure and then spraying it with a spray nozzle.

[0023] The apparatus shown in Figure 2 has a latent heat recovery heat exchanger (latent heat recovery device) 20 installed above the exhaust gas duct (not shown), and the drain (moisture) generated by heat exchange in the latent heat recovery heat exchanger (latent heat recovery device) 20 is dispersed by gravity into the exhaust gas duct installed below. 46 is the drain piping. Other configurations and operations are the same as those of the embodiment shown in Figure 1.

[0024] Furthermore, as shown in Figure 3, in order to efficiently vaporize the moisture sprayed inside the exhaust gas duct 26, a spraying device 28 is installed to atomize the drain into fine particles and spray them, and a heat exchange promoting plate 30 is installed inside the exhaust gas duct 26 to improve the contact efficiency with the exhaust gas, thereby efficiently vaporizing H in the combustion exhaust gas. 2 This makes it possible to increase the amount of O gas (water vapor). Such a configuration can be applied to all embodiments.

[0025] The embodiment shown in Figure 4 involves a process in which exhaust gas condensate generated in the latent heat recovery heat exchanger (latent heat recovery device) 32 is recovered, injected, vaporized, and then used again in the latent heat recovery heat exchanger (latent heat recovery device) 32 to recover latent heat, while circulating a portion of the exhaust gas condensate. The amount of circulated exhaust gas condensate is adjusted by measuring the temperature of the heated fluid, such as water, at the inlet and outlet of the latent heat recovery heat exchanger (latent heat recovery device) 32 and controlling the flow rate of the spray pump so that the amount of latent heat recovered in the latent heat recovery heat exchanger (latent heat recovery device) 32 is maximized. This control makes it possible to achieve a maximum latent heat recovery amount that matches the heat transfer area of ​​the latent heat recovery heat exchanger (latent heat recovery device) 32. In addition, any condensate water exceeding the maximum latent heat recovery amount is discharged outside the system as excess condensate (excess amount).

[0026] The apparatus shown in Figure 4 is equipped with temperature measuring devices 38 and 40 at the heated fluid inlet 34 and heated fluid outlet 36 of the latent heat recovery heat exchanger (latent heat recovery device) 32, respectively. A calculation device 44 is connected between these temperature measuring devices 38 and 40 and the pump 42 to control the flow rate of the pump 42 and adjust the circulating drain flow rate so that the latent heat recovery amount in the latent heat recovery heat exchanger (latent heat recovery device) 32 is maximized. With this configuration, the amount of circulating drain (water) can be increased to the amount at which the latent heat recovery amount is maximized. 48 is a drain pipe. Other configurations and operations are the same as those of the embodiment shown in Figure 1. [Explanation of symbols]

[0027] 10 Heat source equipment 12. Heat recovery system 14, 20, 32 Latent heat recovery heat exchanger (latent heat recovery device) 16, 42 pumps 18, 46, 48 Drain piping 22, 34 Heated fluid inlet 24, 36 Heated fluid outlet 26 Exhaust duct 28 Spraying device 30 Heat exchange promotion plate 38, 40 Temperature measuring device 44 Arithmetic unit

Claims

1. A heat recovery device that recovers waste heat from combustion exhaust gas discharged from a heat source equipment, wherein a latent heat recovery heat exchanger is provided on the secondary side of the exhaust gas system of the waste heat recovery device, and latent heat is recovered from low-temperature combustion exhaust gas using this latent heat recovery heat exchanger, or a heat recovery device in which the heat transfer area of ​​the waste heat recovery device is enlarged and also serves as a latent heat recovery heat exchanger, wherein a drain pipe is provided at the outlet of the latent heat recovery heat exchanger to recover the drain generated by heat exchange, and this drain pipe is connected to the exhaust gas duct on the primary side of the latent heat recovery heat exchanger and the waste heat recovery device and on the secondary side of the heat source equipment, and HO gas contained in the combustion exhaust gas is recovered as drain generated by heat exchange in the latent heat recovery heat exchanger, and at least a portion of this drain is circulated within the combustion exhaust gas system.

2. The heat recovery apparatus according to claim 1, wherein a pressure boosting means is provided in the drain piping.

3. The heat recovery apparatus according to claim 2, wherein a temperature measuring means is provided at the inlet and outlet of the heated fluid of the latent heat recovery heat exchanger to measure the respective temperatures, and a calculation means is connected between the temperature measuring means and the pressure boosting means to control the flow rate of the pressure boosting means and adjust the circulating drain flow rate so that the amount of latent heat recovered in the latent heat recovery heat exchanger is maximized.

4. The heat recovery apparatus according to claim 1, wherein a latent heat recovery heat exchanger is installed above the exhaust gas duct, and the drain generated by heat exchange in the latent heat recovery heat exchanger is dispersed into the exhaust gas duct installed below by gravity.

5. The heat recovery apparatus according to any one of claims 1 to 4, wherein a spraying device is installed in the exhaust gas duct for atomizing the drain from the drain pipe into fine particles and spraying them.

6. The heat recovery device according to any one of claims 1 to 5, wherein a heat exchange promoting plate is installed in the exhaust gas duct to improve the contact efficiency between combustion exhaust gas and drain.

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