Exhaust heat recovery device

Abstract

To provide an exhaust heat recovery device that has high heat recovery efficiency for recovering exhaust heat between liquids and has a simple structure, thereby reducing an introduction cost and a maintenance cost.SOLUTION: A winding shape of a heat exchange coil (heat exchange unit) 2-2, which can make maximum use of natural convection in a waste liquid tank 1 filled with warm waste liquid IN6, and a heat insulating effect of a heat insulating pipe (connection structure) 3-1 form a highly efficient counterflow heat exchanger, and used liquid IN7 is output as heated used liquid OUT8. Further, each component can be disassembled, which makes cleaning and component replacement easy, thereby making it highly maintainable.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a device (hereinafter referred to as an "exhaust heat recovery device") that recovers heat from degreasing cleaning wastewater in industrial applications, warm wastewater (hereinafter referred to as warm wastewater) discharged from commercial dishwashers, warm wastewater from hot spring facilities, etc. [Background technology]

[0002] Currently, the government is leading the way in implementing the "Global Warming Countermeasures Plan." In this "Global Warming Countermeasures Plan," Japan announced in April 2021 that it aims to "reduce greenhouse gas emissions by 46% (compared to fiscal 2013) by fiscal 2030, and continue to strive for an even higher 50%." A major cause of greenhouse gas emissions is the generation of electricity and heat through the combustion of fossil fuels, so reducing the use of electricity or heat is essential. Greenhouse gas emissions must be reduced by implementing energy conservation measures. Summary of the Invention [Problem to be solved by the invention]

[0003] One approach to solving the problem of reducing greenhouse gas emissions is the development of heat recovery systems for wastewater containing heat (see JP 2003-42539 A). Instead of simply disposing of high-temperature domestic or industrial wastewater, these systems utilize the heat recovery system, which is installed in the flow path from a water supply or other liquid source. By supplying high-temperature industrial or domestic wastewater to the heat recovery system, the liquid supplied from the liquid source can be heated without external energy input. While heat recovery systems such as shell-and-tube heat exchangers and plate heat exchangers exist, they are both large and expensive, making them difficult to install in terms of both installation and maintenance costs. Furthermore, performance declines due to contamination of parts that come into contact with the wastewater, and their structural design makes them difficult to clean and maintain. These obstacles limit their widespread adoption and hinder progress toward energy conservation. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-42539 [Patent Document 2] Japanese Patent Publication No. 2022-158672 [Patent Document 3] Japanese Patent Publication No. 2022-151995

[0005] Therefore, an object of the present invention is to provide a structure for an exhaust heat recovery device that can be miniaturized for recovering heat from hot waste liquid, can be introduced efficiently and at low cost, and has high maintainability.

[0006] In order to achieve the above object, a liquid-liquid waste heat recovery device for raising the temperature of a liquid to be used includes: a waste liquid tank 1; Liquid used The present invention provides a liquid-liquid waste heat recovery device that includes an inlet pipe 2-1, a heat exchange coil 2-2, a thermal insulation pipe 3-1, a height-adjustable stand 4, and an upright drain pipe 5.

[0007] The heat exchange coil installed in the waste liquid tank is always immersed in the waste liquid, and by utilizing the insulating effect of the insulated pipe and thermal convection within the waste liquid tank, a continuous, highly thermally efficient countercurrent heat exchange can be carried out between the liquid to be heated (hereinafter referred to as the used liquid) that passes through the heat exchange coil and the warm waste liquid that enters the waste liquid tank and is then discharged from the rising pipe, thereby making it possible to highly efficiently heat the used liquid.

[0008] According to the present invention, a structure can be easily manufactured using standardized commercially available materials without the need for a specially designed product, making it easy to achieve a compact and low-cost device. The wastewater tank, heat exchange coil, thermal insulation pipe, stand, and rising wastewater piping can all be disassembled, making them easy to clean and maintain, and the component parts are easily available, making it possible to provide a waste heat recovery device with low installation barriers.

[0009] Furthermore, for the heat exchange coil, by using, for example, a commercially available bellows-shaped stainless steel flexible pipe for water supply, the contact area between the passing liquid and the warm waste liquid filled in the waste liquid tank can be increased by approximately 30% compared to a straight pipe of the same length and nominal diameter, thereby improving heat recovery efficiency and making it possible to clean the heat exchange coil using acid or alkali cleaning. [Brief explanation of the drawings]

[0010] [Figure 1-1] FIG. 1-1 is a schematic diagram of an exhaust heat recovery device according to the present invention. [Figure 1-2] FIG. 1-2 is a side view of the exhaust heat recovery device of the present invention. [Figure 2-1] Figure 2-1 is a connection diagram of a conventional cleaning process. [Figure 2-2] FIG. 2-2 is a connection diagram of the cleaning process to which the present invention has been added. [Figure 3] FIG. 3 is a cross-sectional view of the exhaust heat recovery device of the present invention. [Figure 4] FIG. 4 is a graph showing the temperature distribution at various points in the exhaust heat recovery device of the present invention. [Figure 5-1] FIG. 5-1 is an external view of the liquid inlet pipe and the heat exchange coil (heat exchange section) of the exhaust heat recovery device of the present invention. [Figure 5-2] FIG. 5-2 is an external view of the heat insulating pipe (connection structure) of the exhaust heat recovery device of the present invention. [Figure 5-3] FIG. 5-3 is a side view of the heat insulating pipe (connection structure) of the exhaust heat recovery device of the present invention. [Figure 6-1] FIG. 6-1 is an external view of a heat exchange coil (single structure) as an embodiment of the exhaust heat recovery device of the present invention. [Figure 6-2] FIG. 6-2 is an external view of a thermal insulation pipe (notched structure) according to an embodiment of the exhaust heat recovery device of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention (hereinafter referred to as the present embodiment) will be described with reference to the drawings. Note that the embodiment described does not limit the present invention to the specific configuration described below, and it is preferable to appropriately adopt a specific configuration according to the embodiment when implementing the present invention.

[0012] The exhaust heat recovery system using the exhaust heat recovery device of the present invention is a system that recovers exhaust heat from warm waste liquid discharged from various facilities and uses the recovered heat to heat the liquid used, and can be widely implemented and applied to various facilities under conditions where warm waste liquid is present and the liquid used that needs to be heated is present nearby.

[0013] 1-1 and 1-2 are a schematic diagram and a side view of the waste heat recovery device of the present invention. Warm waste liquid (hereinafter referred to as warm waste liquid IN6) is supplied to the inside of the waste liquid tank 1 and the outside of the thermal insulation pipe (connection structure) 3-1. The warm waste liquid IN6 gradually fills the waste liquid tank 1 and the riser piping 5. After the liquid level of the warm waste liquid IN6 in the waste liquid tank 1 reaches a height that exceeds the internal height of the riser piping 5, the warm waste liquid is discharged from the riser piping 5 as warm waste liquid OUT9. The liquid to be used is supplied to the inlet pipe 2-1 connected to the insulated pipe (connection structure) 3-1 via the inlet pipe connection port 3-4 (hereinafter referred to as the liquid to be used IN7), and flows toward the heat exchange coil (heat exchange section) 2-2 connected to the insulated pipe (connection structure) 3-1 via the heat exchange coil (heat exchange section) connection port 3-5. As the heat exchange coil (heat exchange section) 2-2 passes through the area of the waste liquid tank 1 where it is immersed in the warm waste liquid, heat recovery is performed and the liquid is output as heated liquid to be used OUT8.

[0014] The wastewater tank 1 is made of, for example, a stainless steel tank or pot with a hole drilled in the bottom and a metal fitting for removing the tank, and by wrapping a heat-retaining material such as sponge tape around the outside of the stainless steel tank as an insulating treatment, it is possible to prevent the heat of the hot wastewater from escaping to the outside of the tank, thereby improving heat recovery efficiency and reducing manufacturing costs.In addition, other methods of insulating the tank include applying insulating paint, applying urethane foam resin, or attaching a resin material.

[0015] The heat exchange coil (heat exchange section) 2-2 is made of, for example, a stainless steel flexible pipe for water supply, and has a shape as shown in Figure 5-1. It is connected to the heat exchange coil (heat exchange section) connection port 3-5 of the thermal insulation pipe (connection structure) 3-1, Cut off The outer surface of the heat pipe (connection structure) 3-1 is wound multiple times toward the outer periphery of the wastewater tank 1, then rises one level, and wound multiple times toward the outer periphery of the wastewater tank 1, repeating this process. Figure 5-1 shows an example of a two-turn winding. The number of turns and stages can be determined appropriately depending on the size of the wastewater tank 1, the size of the heat insulating pipe (connection structure) 3-1, and the length of the heat exchange coil (heat exchange section) 2-2 used. However, since the longer the heat exchange coil, the higher the heat recovery efficiency, it is preferable to set it at the maximum possible length. Furthermore, when stainless steel flexible water pipe is used as the heat exchange coil (heat exchange section) 2-2, the bellows-shaped pipe surface allows for a surface area approximately 30% larger than that of a simple pipe made by bending it, thereby increasing the heat transfer area and improving heat exchange efficiency. Furthermore, the pipe is resistant to acids, alkalis, and chemicals, making it suitable for use with any type of liquid or hot wastewater.

[0016] The heat exchange coil 2-2 can be coated on its surface with a radiant paint, thereby making effective use of radiant heat and achieving high heat exchange efficiency.

[0017] The thermal insulation pipe (connection structure) 3-1 is used body It is installed for the purpose of insulation from the used liquid IN7 of the IN pipe 2-1 to the used liquid IN pipe connection port 3-4, and has the shape shown in Figures 5-2 and 5-3. The initially cold used liquid IN7 does not float in the hot waste liquid, and prevents heat exchange with the hot hot waste liquid in the waste liquid tank 1 in the used liquid IN pipe 2-1 section, and when the used liquid reaches the heat exchange coil (heat exchange section) connection port 3-5, heat exchange begins due to the temperature difference between the hot waste liquid and the used liquid, and as it proceeds to the top of the waste liquid tank 1, the temperature distribution of the hot waste liquid inside the waste liquid tank 1 is such that the hot waste liquid at the top of the waste liquid tank 1 is higher, and as it proceeds to the bottom of the waste liquid tank 1, the hot waste liquid becomes lower in temperature due to heat exchange with the used liquid. At the same time, the used liquid proceeds inside the heat exchange coil (heat exchange section 2-2) and is heated up. OUTThe temperature is gradually increased until it reaches 8. This series of conditions is effective in constantly increasing the temperature difference between the hot waste liquid and the liquid being used, thereby achieving a countercurrent heat exchange with high heat exchange efficiency.

[0018] The size of the stand 4 is determined by the installation location and position, and it is sufficient if it has a structure that can hold the drainage tank 1, the thermal insulation pipe 3, and the riser piping 5, and adjust the height of the drainage tank 1, the thermal insulation pipe 3, and the riser piping 5, and it can be constructed, for example, from a commercially available aluminum frame material with a 40 mm square, a group of connecting parts, and fastening bolts.

[0019] The riser pipe 5 is installed to keep the heat exchange coil 2-2 in the wastewater tank 1 constantly immersed in the hot wastewater IN6 inside the tank 1. For example, it may be connected to the wastewater tank 1, led to the outside of the tank 1, and then raised up to discharge the hot wastewater OUT9 downward. By providing a riser flow path within the riser pipe 5, the hot wastewater IN6 is not directly discharged from the wastewater tank 1 but fills the tank 1 and the riser pipe 5. After the liquid level of the hot wastewater IN6 in the wastewater tank 1 reaches a height that exceeds the internal height of the riser pipe 5, the hot wastewater is discharged from the riser pipe 5 as the hot wastewater OUT9. This keeps the level of the hot wastewater in the wastewater tank 1 constant, and the heat exchange coil 2-2 is constantly immersed in the hot wastewater, enabling efficient heat recovery.

[0020] The rising pipe 5 may be configured so that drain valves and service holes for cleaning are provided at each bend so that cleaning can be performed without disassembly.

[0021] Figures 2-1 and 2-2 show an example of the connection of the waste heat recovery device of the present invention in the waste heat recovery system according to this embodiment. Take the degreasing and cleaning process of neutral oils and greases in an industrial application as an example. In the conventional cleaning process shown in Figure 2-1, the liquid IN7 is supplied, heated to the desired temperature by an electric heater 10, and then cleaned in a cleaning device 15 using the liquid. After cleaning, the liquid is discharged as hot waste liquid OUT9. In contrast, in Figure 2-2, in the cleaning system with the added waste heat recovery device of the present invention, the liquid IN7 is supplied, passes through a three-way valve 13 that controls the ON / OFF of heat recovery, and is supplied to the waste heat recovery device 11 of the present invention. The heated liquid OUT8 is then heated by the electric heater 10 to the desired temperature. Cleaning is performed in the cleaning device 15 using the liquid. After cleaning, the heated liquid IN6 is supplied to the waste heat recovery device of the present invention, and after heat recovery, is discharged as hot waste liquid OUT9. The reason for using the three-way valve 13 and check valve 12 is that when considering maintenance such as replacing or cleaning the heat exchange coil 2 of the exhaust heat recovery device of the present invention, maintenance can be performed without stopping the operation of the cleaning device 15.

[0022] 3 is a cross-sectional view of the waste heat recovery device according to this embodiment. Hot waste liquid IN6 is supplied to the area between the waste liquid tank 1 and the thermal insulation pipe 3, filling the waste liquid tank 1 and the riser piping 5. Continuing to supply hot waste liquid IN6 causes hot waste liquid OUT9 to be discharged from the riser piping 5, maintaining a constant liquid level in the waste heat recovery device 11 of the present invention and ensuring that the heat exchange coil 2-2 is always immersed in the hot waste liquid. Here, the use liquid IN7 is supplied to the heat exchange coil 2-2 via the use liquid IN piping 2-1, the use liquid IN piping connection port 3-4, and the heat exchange coil (heat exchange unit) connection unit 3-5. Heat exchange occurs between the use liquid IN7 and the hot waste liquid as it passes through the heat exchange coil 2-2, and the use liquid is output as heated use liquid OUT8.

[0023] 3, the temperature distribution of the hot effluent flows from the position of hot effluent IN6 toward the bottom of the wastewater tank 1, where it is cooled in the heat exchange coil (heat exchange section) 2-2 while heat exchange takes place, and the cooled hot effluent settles more quickly to the bottom of the wastewater tank 1 due to its change in density, and hot effluent that does not come into sufficient contact with the heat exchange coil (heat exchange section) 2-2 and is not cooled enough moves to the upper part of the wastewater tank 1 due to its density difference, so that the hot effluent generally has a heat distribution where the temperature is higher at the top of the wastewater tank 1 and lower at the bottom of the wastewater tank 1. Also, the working liquid IN7 supplied to the heat exchange coil (heat exchange section) 2-2 begins heat exchange with the hot effluent from the heat exchange coil (heat exchange section) connection port 3-5 at the bottom of the wastewater tank, and heat exchange is carried out while the working liquid moves from the bottom of the wastewater tank 1 to the top of the wastewater tank 1 due to the shape of the heat exchange coil (heat exchange section) 2-2 mentioned above.

[0024] Figure 4 shows the heat change as the hot waste liquid IN6 moves to the hot waste liquid OUT9, and the temperature distribution as the working liquid IN7 changes to the heated working liquid OUT8 at the connection port 3-5 of the heat exchange coil (heat exchange section). This temperature distribution takes the form of a counterflow heat exchange in the logarithmic mean temperature difference (LMTD), which is an approximation of the average temperature difference between two fluids in the heat exchanger, and shows the high heat recovery efficiency, with the heated working liquid 8 being at a higher temperature than the hot waste liquid OUT9.

[0025] In order to further reduce the introduction cost, the exhaust heat recovery device 11 of the present invention may be configured using a heat exchange coil (single structure) 2-3 and a thermal insulation pipe (notched structure) 3-2 as shown in Figs. 6-1 and 6-2. The thermal insulation pipe (with cutout structure) 3-2 has a shape as shown in Figure 6-2, and has a cutout 3-3 at the bottom end through which a heat exchange coil can be passed. By using HT pipe as the material for the thermal insulation pipe (with cutout structure) 3-2 itself, the thermal conductivity is 0.16 (W / (m K)) and the density is 1.65 (g / cm 3), which prevents heat exchange between the descending portion of the heat exchange coil 3 and the high-temperature warm waste liquid in the waste liquid tank 1 without floating in the warm waste liquid, thereby achieving a highly efficient counterflow type heat exchange. Also, the heat exchange coil (single structure) 2-3 uses a single flexible water pipe up to the aforementioned used liquid IN piping 2-1, and in this case, the used liquid IN7 supplied to the heat exchange coil (single structure) 2-3 cools the warm waste liquid inside the thermal insulation pipe (cutout structure) 3-2, but the insulating effect of the thermal insulation pipe (cutout structure) 3-2 prevents heat transfer from the warm waste liquid side outside the thermal insulation pipe (cutout structure) 3-2, so the warm waste liquid inside the thermal insulation pipe (cutout structure) 3-2 always remains at a temperature similar to that of the bottom of the waste liquid tank 1. The heat exchange coil 2 begins to come into contact with the warm waste liquid from the cutout in the thermal insulation pipe at the bottom of the waste liquid tank 1, and with a shape similar to the heat exchange coil (heat exchange section) 2-2 described above, heat exchange is carried out while moving the used liquid from the bottom of the waste liquid tank 1 to the top of the waste liquid tank 1. However, the heat recovery efficiency is slightly lower than that of a thermal insulation pipe (connection structure). It is preferable to use different methods depending on the situation.

[0026] Regarding the exhaust heat recovery device 11 of the present invention, for example, when the used liquid IN7 is connected to a water supply, in an exhaust heat recovery system using the exhaust heat recovery device of the present invention, by devising a positional relationship with the waste liquid discharge equipment, it becomes possible to operate the system without requiring additional power such as pump power from the outside for the path from the hot waste liquid IN6 to the hot waste liquid OUT8, resulting in a very ecological form that does not require additional power.

[0027] The heat exchange efficiency of the heat exchange coil (heat exchange section) 2-2 decreases as contaminants contained in the hot waste liquid IN6 supplied to the waste liquid tank 1 and the used liquid IN7 adhere to and accumulate on its surface. However, the waste heat recovery device 11 of the present invention is disassembled and has a structure intended for cleaning and replacement, and therefore is superior in terms of maintainability and maintenance costs compared to heat exchangers that exchange heat between other liquids, such as shell-and-tube heat exchangers and plate heat exchangers.

[0028] The exhaust heat recovery device 11 of the present invention can be manufactured simply by combining commonly available materials, and this configuration can be reproduced even in remote areas of the world, thereby contributing to CO2 reduction in a broad sense.

[0029] The results of using the exhaust heat recovery device 11 of the present invention in a degreasing and cleaning process for neutral oils and grease in an industrial application are as follows.

[0030] The liquid used was supplied from a public water supply at a rate of 4 liters per minute per second, heated to 60°C using a commercially available electric heater, and used to wash the parts to be washed. The warm wastewater after washing was connected to the waste heat recovery device of the present invention. The specifications for the waste heat recovery device of the present invention were a waste water tank capacity of 20 liters, a heat exchange coil nominal diameter of 20 mm, and a coil length of 10 m. As a result, the installation cost of the waste heat recovery device of the present invention was 1 / 30 of that of a commercially available waste heat recovery device, and the power consumption of the electric heater used to heat the city water supplied to the washing process was reduced by 54%. [Explanation of symbols]

[0031] 1 drain tank, 2-1 Liquid used IN piping, 2-2 heat exchange coil (heat exchange section), 2-3 heat exchange coil (single structure), 3-1 thermal insulation pipe (connection structure), 3-2 thermal insulation pipe (notch structure), 3-3 thermal insulation pipe notch, 3-4 Liquid used IN piping connection port, 3-5 heat exchange coil (heat exchange section) connection port, 4 stand, 5 rising piping, 6 hot waste liquid IN, 7 used liquid IN, 8 heated used liquid OUT, 9 hot waste liquid OUT, 10 electric heater, 11 waste heat recovery device of the present invention, 12 check valve, 13 three-way valve, 14 pump, 15 cleaning device

Claims

1. The liquid-liquid waste heat recovery device includes a waste liquid tank (1), a hot waste liquid IN pipe (2-1), a heat exchange coil (2-2), a thermal insulation pipe (3-1), a height-adjustable stand (4), and a rising waste liquid pipe (5).

2. 2. The waste heat recovery system according to claim 1, wherein the waste liquid tank is made of stainless steel and is heat-insulated.

3. The exhaust heat recovery device according to claim 1 or 2, characterized in that the heat exchange coil 2-2 is formed of a stainless steel flexible pipe, is connected to a heat exchange coil (heat exchange section) connection port 3-5 of a thermal insulation pipe (connection structure) 3-1 on the lower side of the waste liquid tank 1, and is wound upward from here in a spiral shape multiple times, and the thermal insulation pipe 3-1 isolates the hot waste liquid in-pipe 2-1 from the waste liquid tank 1.

4. The exhaust heat recovery device according to claim 3, characterized in that the thermal insulation pipe (connection structure) 3-1 is made of a material with high thermal insulation properties, and the waste liquid tank 1 is provided with a hot waste liquid IN piping connection port 3-4 and a heat exchange coil (heat exchange section) connection port 3-5.

5. The exhaust heat recovery device according to claim 1 or 2, characterized in that the height-adjustable stand 4 holds the drainage tank 1 and the rising drainage piping 5, and has a structure that enables adjustment of the height of the insulated drainage tank 1 and the rising drainage piping 5.

Images