Heat exchange device and waste treatment system having the same

Abstract

The present invention discloses a heat exchange device and a garbage treatment system having the same. The heat exchange device includes: a first medium layer having a first medium inlet and a first medium outlet after heat exchange; a first heat exchange wall located inside the first medium layer, with the outer wall of the first heat exchange wall connected to the first medium layer; a liquid metal layer located inside the first heat exchange wall, connected to the inner wall of the first heat exchange wall, having a liquid metal inlet and a liquid metal outlet after heat exchange; a second heat exchange wall located inside the liquid metal layer, with the outer wall of the second heat exchange wall connected to the liquid metal layer; and a second medium layer located inside the second heat exchange wall, connected to the inner wall of the second heat exchange wall, having a second medium inlet and a second medium outlet after heat exchange. This heat exchange device can avoid a significant increase in the wall temperature of the heat exchange wall in contact with the high-temperature medium while increasing the temperature of the low-temperature medium, and solves the problem of corrosion of the wall surface of the heat exchange wall in contact with the high-temperature medium caused by increasing the parameters of the low-temperature medium in the prior art.

Description

Technical Field

[0001] The present invention belongs to the technical field of heat damage prevention, and more specifically, the present invention relates to a heat exchange device and a garbage treatment system having the same. Background Art

[0002] With the acceleration of the urbanization process in China, there is a large gap in the demand for domestic garbage treatment. By 2020, the urbanization rate of the permanent population in the Mainland is to reach 60%, and the urbanization rate of the household registered population is to reach about 45%. The scale of garbage incineration will reach approximately 620,000 tons per day, and at least a new garbage incineration power generation scale of more than 300,000 tons per day is required, which is equivalent to building 300 garbage incineration power plants with a capacity of 1,000 tons per day.

[0003] Currently, the medium-temperature and medium-pressure steam parameters (400°C, 4 MPa) are generally adopted in the domestic garbage incineration power generation system. With the progress of technology and the change of industry support policies, the garbage incineration power generation operators gradually attempt to increase the power generation and the overall economic efficiency of the plant by increasing the steam parameters.

[0004] The components of domestic garbage are complex. The chlorine and alkali metal elements contained therein enter the flue gas or form fly ash after combustion, causing metal corrosion of the boiler heating surface. The corrosion rate is closely related to the tube wall temperature. When the steam parameters are 400°C and 4 MPa, the corrosion of the heating surface using high-alloy steel is not obvious; when the steam temperature is increased from 400°C to 500°C, the corresponding tube wall temperature range is 450°C to 550°C, which has entered the region where the corrosion rate rapidly increases. The operation practice of adopting medium-temperature and sub-high-pressure steam parameters (450°C, 6.5 MPa) in China shows that under such steam parameter conditions, the heating surface burst pipe occurred only after 100 days of operation, and the boiler had to be shut down for maintenance, affecting the normal production. Therefore, to increase the steam temperature, the corrosion problem of the heat exchange tubes of the heating surface must be solved.

[0005] In the prior art, there is a process of applying a double-layer alloy coating resistant to chlorine corrosion on the heating surface of a waste incinerator. The double-layer structure includes a chlorine-resistant bottom layer and a solid particle erosion-resistant surface layer. The chlorine-resistant bottom layer in the double-layer structure is prepared by an active combustion high-speed gas spraying process, and the solid particle erosion-resistant surface layer in the double-layer structure is prepared by a supersonic flame spraying process, so as to solve the problems of thinning of the pipe wall and pipe bursting caused by high-temperature chlorine corrosion and solid particle erosion on the heating surface of the waste incinerator. This technology manufactures a high-alloy coating on the water-cooled wall and superheater surface of the waste incineration waste heat boiler through surface modification methods such as surfacing, laser cladding, and thermal spraying to enhance the corrosion resistance of the pipe wall. It has good use effects in European and American countries, but there are still few projects operating at high parameters or sub-high parameters in China, and the operating time is short. The anti-corrosion effect of using the metal surface modification method remains to be observed. At the same time, due to the different compositions of waste fuels from those in Europe and America, the corrosion components in the flue gas are different. Coupled with factors such as uneven coating manufacturing process levels and anti-corrosion metal contents, the actual use effects of some projects are not ideal.

[0006] There is also a process of arranging dense pins and laying refractory castables in the high-temperature section. By controlling heat transfer, the steam outlet parameters of the waste incineration waste heat boiler are increased to high temperature and high pressure, thereby reducing the corrosion and pipe bursting of the water-cooled wall and high-temperature superheater. By increasing pins and laying refractory castables, the heat exchange tubes can be effectively protected from corrosion. However, the heat transfer coefficient of the castable is lower than that of metal, resulting in a lower heat exchange efficiency between the flue gas and the working medium, a higher flue gas outlet temperature in the flue, and a lower thermal efficiency of the power generation system.

[0007] Therefore, the heat damage prevention technology in the existing domestic waste incineration power generation system needs to be further improved. Summary of the Invention

[0008] The present invention aims to solve at least one of the technical problems in the related art to some extent. To this end, an object of the present invention is to provide a heat exchange device and a waste treatment system having the same. By using the heat exchange device of the present application, while increasing the temperature of the low-temperature medium, the wall temperature of the heat exchange wall in contact with the high-temperature medium can be prevented from rising significantly, solving the problem of corrosion of the heat exchange wall in contact with the high-temperature medium caused by increasing the parameters of the low-temperature medium in the prior art. At the same time, the heat exchange wall in contact with the high-temperature medium does not need to use expensive high-alloy corrosion-resistant steel, which helps to save the device cost.

[0009] In one aspect of the present invention, the present invention provides a heat exchange device. According to an embodiment of the present invention, the heat exchange device includes:

[0010] A first medium layer having a first medium inlet and a first medium outlet after heat exchange;

[0011] The first heat exchange wall, the first heat exchange wall is located inside the periphery of the first medium layer, and the outer wall of the first heat exchange wall is connected to the first medium layer;

[0012] The liquid metal layer, the liquid metal layer is located inside the periphery of the first heat exchange wall and is connected to the inner wall of the first heat exchange wall. The liquid metal layer has a liquid metal inlet and an outlet for the heat-exchanged liquid metal;

[0013] The second heat exchange wall, the second heat exchange wall is located inside the periphery of the liquid metal layer, and the outer wall of the second heat exchange wall is connected to the liquid metal layer;

[0014] The second medium layer, the second medium layer is located inside the periphery of the second heat exchange wall, and the second medium layer is connected to the inner wall of the second heat exchange wall. The second medium layer has a second medium inlet and an outlet for the heat-exchanged second medium.

[0015] According to the heat exchange device of the embodiment of the present invention, by adding a liquid metal layer between the first medium layer and the second medium layer, and combining the first heat exchange wall and the second heat exchange wall, because the liquid metal layer has relatively high heat exchange capacity, the heat transfer thermal resistance between the high-temperature medium and the low-temperature medium can be significantly reduced, that is, the heat of the medium with a higher temperature in the first medium layer and the second medium layer can be quickly transferred to the medium with a lower temperature. Compared with the existing heat exchange method in which there is only one heat exchange wall between the first medium layer and the second medium layer, in the existing heat exchange device, the thermal resistance of the high-temperature medium and the low-temperature medium is large, and the heat transfer coefficient between the high-temperature medium and the heat exchange wall is small. After the heat of the high-temperature medium is transferred to the heat exchange wall, the low-temperature medium cannot take away the heat of the heat exchange wall in time, resulting in the temperature of the heat exchange wall being in the region with a relatively large corrosion rate, which is likely to cause problems such as thinning and tube explosion; while the heat exchange device in the present application can significantly reduce the heat exchange temperature difference between the low-temperature medium and the heat exchange wall, and between the heat exchange wall and the high-temperature medium. And when the wall temperature of the heat exchange wall in contact with the high-temperature medium is the same, using the heat exchange device in the present application can make the temperature of the low-temperature medium higher; and when the temperature of the low-temperature medium is the same, using the heat exchange device in the present application can make the wall temperature of the heat exchange wall in contact with the high-temperature medium lower, and the corrosion rate is smaller. That is, using the heat exchange device of the present application can avoid the obvious increase in the wall temperature of the heat exchange wall in contact with the high-temperature medium while increasing the temperature of the low-temperature medium, solve the problem of the wall corrosion of the heat exchange wall in contact with the high-temperature medium caused by the existing increase in the parameters of the low-temperature medium, and at the same time, the heat exchange wall in contact with the high-temperature medium does not need to use expensive high-alloy corrosion-resistant steel, which helps to save the device cost.

[0016] In addition, the heat exchange device according to the above embodiment of the present invention may further have the following additional technical features:

[0017] In some embodiments of the present invention, the boiling point of the liquid metal in the liquid metal layer is not less than 1000 °C.

[0018] In some embodiments of the present invention, the liquid metal is at least one selected from gallium, indium, tin, bismuth, zinc and their alloys.

[0019] In some embodiments of the present invention, the inner periphery of the first medium layer includes a plurality of the first heat exchange walls, and the inner periphery of each of the first heat exchange walls includes, from outside to inside, the liquid metal layer, the second heat exchange wall, and the second medium layer.

[0020] In some embodiments of the present invention, the inner periphery of the liquid metal layer includes a plurality of the second heat exchange walls, and the second medium layer is provided on the inner periphery of each of the second heat exchange walls.

[0021] In some embodiments of the present invention, the thicknesses of the first heat exchange wall and the second heat exchange wall are independently 3-7 mm.

[0022] In some embodiments of the present invention, the thermal conductivities of the first heat exchange wall and the second heat exchange wall are independently 30-54 W / (m·K).

[0023] In some embodiments of the present invention, the temperature of the first medium layer is 600-750 °C, and the temperature of the second medium layer is 20-500 °C; or the temperature of the first medium layer is 20-500 °C, and the temperature of the second medium layer is 600-750 °C.

[0024] In some embodiments of the present invention, the shape of the second medium layer is cylindrical and / or cuboid.

[0025] In some embodiments of the present invention, the materials of the first heat exchange wall and the second heat exchange wall are independently selected from at least one of the boiler steels 20G, 12Cr1MoVG, and 15CrMoG.

[0026] In yet another aspect of the present invention, the present invention provides a waste treatment system. According to an embodiment of the present invention, the system includes an incinerator, a heat exchange device, and a power generation unit that are connected in sequence. The heat exchange device is the above-mentioned heat exchange device. In the waste treatment system according to the embodiment of the present invention, a large amount of flue gas is generated when waste is incinerated in the incinerator. This flue gas, as a high-temperature medium, is introduced into the heat exchange device to exchange heat with the low-temperature medium water. After the water absorbs the heat of the flue gas, it becomes high-temperature steam. This high-temperature steam can be sent to the power generation unit for power generation, thereby improving the economic benefits of the system. Since this heat exchange device can increase the temperature of the low-temperature medium steam while preventing the wall temperature of the heat exchange wall in contact with the high-temperature medium flue gas from rising significantly, it solves the problem of corrosion of the heat exchange wall in contact with the high-temperature medium flue gas caused by increasing the steam parameters of the low-temperature medium in the prior art. Increasing the temperature of the low-temperature medium steam helps to increase the power generation of the power generation unit, thereby improving the economic benefits of the power generation unit and the entire system. Further, this heat exchange device enables the heat exchange wall in contact with the high-temperature medium not to use expensive high-alloy corrosion-resistant steel, which helps to save costs and thus reduce the system cost.

[0027] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The above and / or additional aspects and advantages of the present invention will become apparent and be readily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0029] Figure 1 is a schematic structural diagram of a heat exchange device according to an embodiment of the present invention;

[0030] Figure 2 is a partial structural diagram of the heat exchange device in an embodiment of the present invention;

[0031] Figure 3 is a partial structural diagram of the heat exchange device in the comparative example of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] Embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0033] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention.

[0034] In addition, the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise specifically and clearly defined.

[0035] In the present invention, unless otherwise clearly specified and limited, the terms "mounted", "connected", "coupled", "fixed", etc. shall be construed in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements or the interaction relationship between two elements, unless otherwise clearly limited. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0036] In one aspect of the present invention, the present invention provides a heat exchange device. According to an embodiment of the present invention, with reference to Figure 1 , the heat exchange device includes: a first medium layer 100, a first heat exchange wall 200, a liquid metal layer 300, a second heat exchange wall 400, and a second medium layer 500.

[0037] According to an embodiment of the present invention, the first medium layer 100 has a first medium inlet 101 and a first medium outlet 102 after heat exchange, and is adapted to provide heat to the liquid metal layer or absorb heat from the liquid metal layer. The inventors have found that through the first medium in the first medium layer, the first medium can exchange heat with the liquid metal in the liquid metal layer, and then obtain the first medium after heat exchange. It should be noted that the specific type, temperature, and flow rate of the first medium in the first medium layer are not particularly limited, and those skilled in the art can select according to actual needs. For example, when the first medium is a high-temperature medium, the first medium can be flue gas, such as at least one selected from flue gas generated by municipal solid waste incineration, flue gas generated by biomass combustion, flue gas generated by high-alkali coal combustion, high-temperature flue gas generated in industries such as metallurgy, glass, and cement; the temperature can be 600 - 750 °C. Another example is when the first medium is a low-temperature medium, the first medium can be selected from at least one of superheated steam and saturated steam, liquid water, superheated steam, steam-water mixture, solutions or vapors of low-boiling refrigerants (such as R245fa, R123), solutions or vapors of low-boiling combustible hydrocarbons (such as isopentane, n-pentane), etc., and the temperature can be 20 - 500 °C. The flow rate of the first medium is related to whether it is a high-temperature medium or a low-temperature medium. When it is a high-temperature medium, those skilled in the art can determine it according to the cross-sectional area of the first medium layer, the flow velocity of the first medium, etc. For example, the common value of the flue gas flow rate in the flue gas channel of the heat exchange device connected to the waste incinerator is 80,000 Nm 3 / h, and the flue gas flow velocity is 3 m / s; when it is a low-temperature medium, those skilled in the art can determine it according to the cross-sectional area of the first medium layer, the flow velocity and type of the first medium, etc. For example, when the first medium layer is formed by the inner wall of an 89*10 boiler tube and the outer wall of a 57*5 boiler tube, and the first medium is superheated steam with a pressure of 6.5 MPa, a temperature of 450 °C, and a density of 21 kg / m 3 , its flow velocity is 30 m / s and the flow rate is 1.5 kg / s; the first medium is superheated steam with a pressure of 6.5 MPa, a temperature of 80 °C, and a density of 970 kg / m 3When the flowing velocity of the liquid water is 2 m / s and the flow rate is 4.6 kg / s. The inventor found that if the first medium in the first medium layer is a high-temperature medium, if the flow rate of the high-temperature medium is too low, the content of the corrosive components therein is less, so the corrosion to the metal is limited and is not within the scope of discussion of the present invention; if the flow rate of the high-temperature medium is high, the content of the corrosive components therein is also more, and it has a strong corrosiveness to the first heat exchange wall. Further, in the current common industrial background (such as waste incineration flue gas, non-ferrous smelting flue gas, etc.), the higher the temperature of the high-temperature medium, the stronger the corrosiveness of the corrosive medium therein. By using the heat exchange device of the present invention and adding a liquid metal layer, the convective heat transfer coefficient between the liquid metal in the liquid metal layer and the first medium can be enhanced, thereby enhancing heat exchange, enabling the heat of the first medium to be quickly transferred to the liquid metal and the second medium, and then rapidly reducing the temperature of the high-temperature medium to a temperature region where the corrosion rate to the first heat exchange wall is relatively low, so as to reduce the corrosion of the corrosive medium to the first heat exchange wall. If the first medium in the first medium layer is a low-temperature medium, the temperature of the low-temperature medium should be lower than the temperatures of the liquid metal and the high-temperature medium. If the flow rate of the low-temperature medium is too low, the heat transfer coefficient between it and the liquid metal layer will be reduced.

[0038] According to an embodiment of the present invention, the first heat exchange wall 200 is located inside the first medium layer 100, and the outer wall of the first heat exchange wall 200 is connected to the first medium layer 100 and is adapted to transfer the heat of the first medium layer to the liquid metal layer or transfer the heat of the liquid metal layer to the first medium layer. The inventors found that, as a heat transfer medium between the first medium layer and the liquid metal layer, the first heat exchange wall has a fast heat transfer rate from the first medium layer to the liquid metal layer or from the liquid metal layer to the first medium layer due to the good heat transfer performance of the liquid metal in the liquid metal layer, avoiding the problem of increased corrosion rate of the first heat exchange wall caused by untimely heat transfer. Thus, it is not necessary to use expensive high-alloy anti-corrosion materials for the first heat exchange wall, which helps to reduce costs. It should be noted that the specific material, thickness, and thermal conductivity of the first heat exchange wall are not particularly limited, and those skilled in the art can select according to actual needs. For example, the material of the first heat exchange wall can be selected from at least one of 20G, 12Cr1MoVG, and 15CrMoG boiler steels, the thickness can be 3 - 7 mm, and the thermal conductivity can be 30 - 54 W / (m·K). The inventors found that the heat transfer mode of the first heat exchange wall during the entire heat exchange process is conduction. The larger the wall thickness and the smaller the thermal conductivity of the material, the greater the corresponding heat transfer resistance, that is, the worse the heat transfer effect. The smaller the wall thickness and the larger the thermal conductivity of the material, the smaller the corresponding heat transfer resistance, that is, the better the heat transfer effect. Under the conditions of common wall thickness and material thermal conductivity, the heat transfer resistance of the first heat exchange wall itself is much lower than the heat transfer resistance between the high-temperature flue gas and the metal wall surface (the first heat exchange wall or the second heat exchange wall). Therefore, regardless of whether the outside of the first heat exchange wall is a high-temperature medium or a low-temperature medium, and regardless of the material selected, its impact on the heat exchange effect of the device from the perspective of heat transfer is limited. On the premise of meeting safety requirements, pipes with a smaller wall thickness should be used, and materials with relatively low prices should be selected. Further, when the first medium is a low-temperature medium and the temperature of the outer wall surface of the first heat exchange wall exceeds 400 °C, the liquid-phase corrosion and gas-phase corrosion rates increase. When it exceeds 500 °C, the corrosion rate increases significantly. If the temperature of the first medium is to be increased, the temperature of the wall surface of the first heat exchange wall in contact with the first medium will increase accordingly, entering the region with a larger corrosion rate.

[0039] Further, it should be noted that the number of the first heat exchange walls in the inner periphery of the first medium layer is not particularly limited, and those skilled in the art can select according to actual needs. For example, the inner periphery of the first medium layer 100 includes a plurality of first heat exchange walls 200, and the inner periphery of each first heat exchange wall 200 includes a liquid metal layer 300, a second heat exchange wall 400, and a second medium layer 500 from outside to inside. Also, the flow direction of the first medium in the first medium layer is not particularly limited. For example, it can be the same as, opposite to, or perpendicular to the liquid metal in the liquid metal layer.

[0040] According to an embodiment of the present invention, the liquid metal layer 300 is located inside the first heat exchange wall 200 and is connected to the inner wall of the first heat exchange wall 200. The liquid metal layer 300 has a liquid metal inlet 301 and an outlet 302 for the liquid metal after heat exchange, and is adapted to improve the heat transfer rate between the high-temperature medium and the low-temperature medium, thereby avoiding the corrosion problem of the heat exchange wall in contact with the high-temperature medium caused by the heat not being conducted in time. The inventors have found that the liquid metal layer has good heat transfer performance. When it is in contact with the first heat exchange wall and the second heat exchange wall at the same time, it can improve the rate of transferring the temperature of the high-temperature medium to the liquid metal and then transferring the heat of the liquid metal to the low-temperature medium. Therefore, it is possible to avoid the phenomenon that the corrosion of the heat exchange wall in contact with the high-temperature medium is accelerated due to the heat not being conducted in time. Furthermore, under the condition of increasing the temperature of the low-temperature medium, the heat exchange wall in contact with the high-temperature medium can still have a long service life. It should be noted that the specific type and boiling point of the liquid metal in the liquid metal layer are not particularly limited, and those skilled in the art can select according to actual needs. For example, the liquid metal can be selected from at least one of gallium, indium, tin, bismuth, zinc and their alloys. Here, the alloy refers to an alloy composed of at least two of gallium, indium, tin, bismuth and zinc. Further, the boiling point of the liquid metal can be not less than 1000 °C. The inventors have found that when the boiling point of the liquid metal is too low, there is a risk of being heated into a gas state. At this time, not only does it change the heat transfer mechanism between the liquid metal layer and the first heat exchange wall and the second heat exchange wall (from convective heat transfer to boiling heat transfer), making the heat transfer coefficient in this link uncontrollable, but also the high-pressure liquid metal vapor may affect the safe operation of the components. Therefore, it is necessary to ensure that the liquid metal is always in a liquid state during the operation of the device. Further, it should be noted that the number of the second heat exchange walls inside the liquid metal layer is not particularly limited, and those skilled in the art can select according to actual needs. For example, the inside of the liquid metal layer 300 can include a plurality of second heat exchange walls 400, and a second medium layer 500 is provided inside each second heat exchange wall 400. Moreover, the flow direction of the liquid metal in the liquid metal layer and the flow direction of the second medium in the second medium layer are not particularly limited, and they can be the same or opposite, for example.

[0041] According to an embodiment of the present invention, the second heat exchange wall 400 is located inside the liquid metal layer 300, and the outer wall of the second heat exchange wall 400 is connected to the liquid metal layer 300 and is adapted to transfer the heat of the liquid metal layer to the second medium layer or transfer the heat of the second medium layer to the liquid metal layer. The inventor found that, as the heat transfer medium between the second medium layer and the liquid metal layer, the second heat exchange wall has a fast heat transfer rate from the second medium layer to the liquid metal layer or from the liquid metal layer to the second medium layer due to the good heat transfer performance of the liquid metal in the liquid metal layer, avoiding the problem of increased corrosion rate of the second heat exchange wall caused by untimely heat transfer. Thus, it is not necessary to use expensive high-alloy corrosion-resistant materials for the second heat exchange wall, which helps to reduce costs. It should be noted that the specific material, thickness, and thermal conductivity of the second heat exchange wall are not particularly limited, and those skilled in the art can select according to actual needs. For example, the material of the second heat exchange wall can be selected from at least one of the boiler steels 20G, 12Cr1MoVG, and 15CrMoG, the thickness can be 3 - 7 mm, and the thermal conductivity can be 30 - 54 W / (m·K). The inventor found that the heat transfer mode of the second heat exchange wall during the entire heat exchange process is conduction. The larger the wall thickness and the smaller the thermal conductivity of the material, the greater the corresponding heat transfer resistance, that is, the worse the heat transfer effect. The smaller the wall thickness and the larger the thermal conductivity of the material, the smaller the corresponding heat transfer resistance, that is, the better the heat transfer effect. Under the common wall thickness and material thermal conductivity, the heat transfer resistance of the second heat exchange wall itself is much lower than the heat transfer resistance between the high-temperature flue gas and the metal wall surface (the first heat exchange wall or the second heat exchange wall). Therefore, regardless of whether the medium inside the second heat exchange wall is a high-temperature medium or a low-temperature medium, and regardless of the material selected, its impact on the heat exchange effect of this device from the perspective of heat transfer is limited. Furthermore, on the premise of meeting safety requirements, materials with a smaller wall thickness and relatively lower prices should be used. Further, when the second medium is a low-temperature medium, when the temperature of the inner wall surface of the second heat exchange wall exceeds 400°C, the liquid-phase corrosion and gas-phase corrosion rates increase. When it exceeds 500°C, the corrosion rate increases significantly. If the temperature of the second medium is to be increased, the temperature of the wall surface of the second heat exchange wall in contact with the second medium will increase accordingly, entering the region with a larger corrosion rate.

[0042] According to an embodiment of the present invention, the second medium layer 500 is located inside the second heat exchange wall 400, and the second medium layer 500 is connected to the inner wall of the second heat exchange wall 400. The second medium layer 500 has a second medium inlet 501 and a second medium outlet 502 after heat exchange, and is adapted to provide heat to the liquid metal layer or absorb heat from the liquid metal layer. The inventor found that by delivering the second medium to the second medium layer, heat exchange between the second medium and the liquid metal in the liquid metal layer can be achieved, and thus the second medium after heat exchange can be obtained. It should be noted that the shape of the second medium layer is not particularly limited, such as it can be cylindrical, cuboid-shaped, etc. The specific type, temperature, and flow rate of the second medium in the second medium layer are not particularly limited, and those skilled in the art can select according to actual needs. For example, when the first medium is a low-temperature medium, the second medium is a high-temperature medium, and the second medium can be flue gas, such as at least one selected from flue gas generated by municipal solid waste incineration, flue gas generated by biomass combustion, flue gas generated by high-alkali coal combustion, high-temperature flue gas generated in industries such as metallurgy, glass, and cement; the temperature can be 600 - 750 °C. Another example is when the first medium is a high-temperature medium, the second medium is a low-temperature medium, and the second medium can be selected from at least one of superheated steam and saturated steam, liquid water, superheated steam, steam-water mixture, solution or steam of low-boiling refrigerants (such as R245fa, R123), solution or steam of low-boiling combustible hydrocarbons (such as isopentane, n-pentane), etc., and the temperature can be 20 - 500 °C. The flow rate of the second medium is related to whether it is a high-temperature medium or a low-temperature medium. When it is a high-temperature medium, those skilled in the art can determine it according to the cross-sectional area of the second medium layer, the flow velocity of the second medium, etc. For example, when the second medium layer is a cylindrical shape with a pipe diameter of 42 * 3, the flow velocity of the high-temperature medium can be 3 m / s, and the flow rate can be 0.005 kg / s; when it is a low-temperature medium, those skilled in the art can determine it according to the cross-sectional area of the first medium layer, the flow velocity and type of the first medium, etc. For example, when the second medium layer is formed by a boiler tube of 42 * 6, and the second medium is superheated steam with a pressure of 6.5 MPa, a temperature of 450 °C, and a density of 21 kg / m 3 ³, its flow velocity can be 30 m / s, and the flow rate can be 0.6 kg / s; when the first medium is superheated steam with a pressure of 6.5 MPa, a temperature of 80 °C, and a density of 970 kg / m 3When the second medium is liquid water, its flow rate can be 2 m / s and the flow rate can be 2 kg / s. The inventor found that if the second medium in the second medium layer is a high-temperature medium, if the flow rate of the high-temperature medium is too low, the content of corrosive components in it is less, so the corrosiveness to metals is limited and is not within the scope of discussion of the present invention; if the flow rate of the high-temperature medium is high, the content of corrosive components in it is also more, and it has strong corrosiveness to the second heat exchange wall. Further, in the current common industrial background (such as waste incineration flue gas, non-ferrous smelting flue gas, etc.), the higher the temperature of the high-temperature medium, the stronger the corrosiveness of the corrosive medium in it. By using the heat exchange device of the present invention and adding a liquid metal layer, the convective heat transfer coefficient between the liquid metal in the liquid metal layer and the second medium can be enhanced, thereby enhancing heat exchange, enabling the heat of the second medium to be quickly transferred to the liquid metal and the first medium, and then quickly reducing the temperature of the high-temperature medium to a temperature region where the corrosion rate of the second heat exchange wall is relatively low, thereby reducing the corrosion of the corrosive medium on the second heat exchange wall. If the second medium in the second medium layer is a low-temperature medium, the temperature of the low-temperature medium should be lower than the temperature of the liquid metal and the high-temperature medium. If the flow rate of the low-temperature medium is too low, the heat transfer coefficient between it and the liquid metal layer will be reduced.

[0043] According to the heat exchange device of the embodiment of the present invention, by adding a liquid metal layer between the first medium layer and the second medium layer and combining the first heat exchange wall and the second heat exchange wall, because the liquid metal layer has relatively high heat exchange capacity, the heat transfer thermal resistance between the high-temperature medium and the low-temperature medium can be significantly reduced, that is, the heat of the medium with a higher temperature in the first medium layer and the second medium layer can be quickly transferred to the medium with a lower temperature. Compared with the existing heat exchange method with only one heat exchange wall between the first medium layer and the second medium layer, in the existing heat exchange device, the thermal resistance between the high-temperature medium and the low-temperature medium is large, and the heat transfer coefficient between the high-temperature medium and the heat exchange wall is small. After the heat of the high-temperature medium is transferred to the heat exchange wall, the low-temperature medium cannot quickly take away the heat of the heat exchange wall, resulting in the temperature of the heat exchange wall being in a region with a relatively large corrosion rate, which is likely to cause problems such as thinning and pipe explosion; while the heat exchange device in the present application can significantly reduce the heat exchange temperature difference between the low-temperature medium and the heat exchange wall and between the heat exchange wall and the high-temperature medium. And when the wall temperature of the heat exchange wall in contact with the high-temperature medium is the same, using the heat exchange device in the present application can make the temperature of the low-temperature medium higher; and when the temperature of the low-temperature medium is the same, using the heat exchange device in the present application can make the wall temperature of the heat exchange wall in contact with the high-temperature medium lower and the corrosion rate smaller. That is, using the heat exchange device of the present application can avoid a significant increase in the wall temperature of the heat exchange wall in contact with the high-temperature medium while increasing the temperature of the low-temperature medium, solve the problem of wall corrosion of the heat exchange wall in contact with the high-temperature medium caused by increasing the parameters of the low-temperature medium in the prior art, and at the same time, the heat exchange wall in contact with the high-temperature medium does not need to use expensive high-alloy corrosion-resistant steel, which helps to save the device cost.

[0044] In another aspect of the present invention, the present invention provides a waste treatment system. According to an embodiment of the present invention, the system includes an incinerator, a heat exchange device, and a power generation unit connected in sequence, and the heat exchange device is the above-mentioned heat exchange device. In the waste treatment system according to the embodiment of the present invention, a large amount of flue gas is generated when waste is incinerated in the incinerator. This flue gas, as a high-temperature medium, is introduced into the heat exchange device to exchange heat with the low-temperature medium water. After the water absorbs the heat of the flue gas, it becomes high-temperature steam, and this high-temperature steam can be sent to the power generation unit for power generation, thereby improving the economic benefits of the system. Since this heat exchange device can avoid a significant increase in the wall temperature of the heat exchange wall in contact with the high-temperature medium flue gas while increasing the temperature of the low-temperature medium steam, it solves the problem of corrosion of the heat exchange wall in contact with the high-temperature medium flue gas caused by increasing the steam parameters of the low-temperature medium in the prior art. And increasing the temperature of the low-temperature medium steam helps to increase the power generation of the power generation unit, thereby improving the economic benefits of the power generation unit and the entire system. Further, this heat exchange device enables the heat exchange wall in contact with the high-temperature medium not to use expensive high-alloy corrosion-resistant steel, which helps to save costs and thus reduce the system cost.

[0045] The following describes the present invention with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0046] Embodiment

[0047] A tube-in-tube heat exchange device, a partial structural schematic diagram of which is as Figure 2 shown, includes:

[0048] The first medium layer 100 has a first medium inlet 101 and a first medium outlet 102 after heat exchange. The first medium in the first medium layer 100 is the flue gas from the incinerator, and its flow rate is 80,000 Nm 3 / h;

[0049] Twenty first heat exchange walls 200. The 20 first heat exchange walls 200 are all located inside the first medium layer 100, and the outer walls of the first heat exchange walls 200 are connected to the first medium layer 100. The material of the first heat exchange walls 200 is boiler steel 20G, the outer diameter d o2 = 57 mm, the inner diameter d i2 = 49 mm, the thermal conductivity λ 2 = 40 W / (m·K), the convective heat transfer coefficient h between the flue gas in the first medium layer and the first heat exchange wall o = 200 W / (m 2 ·K), and the length l = 1 m;

[0050] Twenty liquid metal layers 300, each liquid metal layer 300 is located inside the perimeter of a first heat exchange wall 200 and is connected to the inner wall of a first heat exchange wall 200. The liquid metal layer 300 has a liquid metal inlet 301 and an outlet 302 for the liquid metal after heat exchange. The liquid metal in the liquid metal layer 300 is a gallium-indium-tin alloy Galinsta with a boiling point of 2300 °C. The flow direction of the liquid metal in the liquid metal layer is perpendicular to the flow direction of the flue gas in the first medium layer;

[0051] Twenty second heat exchange walls 400, each second heat exchange wall 400 is located inside the perimeter of a liquid metal layer 300, and the outer wall of each second heat exchange wall 400 is connected to a liquid metal layer 300. The material of the second heat exchange wall 400 is boiler steel 20G, with an outer diameter d o1 = 42 mm and an inner diameter d i1 = 37 mm, and a thermal conductivity λ 1 = 40 W / (m·K). The convective heat transfer coefficient h between the liquid metal and the second heat exchange wall fi2 = 20000 W / (m 2 ·K), and the length l = 1 m;

[0052] Twenty second medium layers 500, the shapes of the second medium layers are all cylindrical. Each second medium layer 500 is located inside the perimeter of a second heat exchange wall 400, and each second medium layer 500 is connected to the inner wall of a second heat exchange wall 400. The second medium layer 500 has a second medium inlet 501 and an outlet 502 for the second medium after heat exchange. The second medium in the second medium layer 500 is steam, with a flow rate of 0.67 kg / s. The convective heat transfer coefficient h between the second medium layer and the second heat exchange wall fi1 = 1500 W / (m 2 ·K). The flow direction of the second medium is perpendicular to the flow direction of the first medium and opposite to the flow direction of the liquid metal.

[0053] Let the temperature of the flue gas be t fo , the temperature of the wall surface of the first heat exchange wall in contact with the flue gas be t wo2 , the temperature of the wall surface of the first heat exchange wall in contact with the liquid metal be t wi2 , the temperature of the liquid metal be t fi2 , the temperature of the wall surface of the second heat exchange wall in contact with the liquid metal be t wo1 , the temperature of the wall surface of the second heat exchange wall in contact with the steam be t wi1 , and the temperature of the steam be t fi1 . The heat exchange process between the flue gas and the steam is as follows:

[0054]

[0055]

[0056]

[0057]

[0058]

[0059]

[0060] From equations (1)-(6), the temperature difference between the flue gas temperature and the steam temperature can be obtained as follows:

[0061]

[0062] By changing the temperatures of the flue gas and the steam, the temperature t of the first heat exchange wall in contact with the flue gas wo2 As shown in Table 1.

[0063] Table 1 Temperatures of the wall surface of the first heat exchange wall in contact with the flue gas at different flue gas temperatures and steam temperatures

[0064]

[0065]

[0066] Comparative example

[0067] A heat exchange device, a partial structural schematic diagram of which is as Figure 3 shown, includes:

[0068] The first medium layer 100 has a first medium inlet 101 and a first medium outlet 102 after heat exchange. The first medium in the first medium layer 100 is the flue gas from the incinerator, and its flow rate is 80,000 Nm 3 / h;

[0069] Twenty second heat exchange walls 400, each second heat exchange wall 400 is located inside a first medium layer 100, and the outer wall of each second heat exchange wall 400 is connected to a first medium layer 100. The material of the second heat exchange wall 400 is boiler steel 20G, the outer diameter d o1 = 42 mm, the inner diameter d i1 = 37 mm, the thermal conductivity λ 1 = 40 W / (m·K), the convective heat transfer coefficient h between the flue gas in the first medium layer and the first heat exchange wall o = 200 W / (m 2 ·K), and the length l = 1 m;

[0070] Twenty second medium layers 500, the shapes of the second medium layers are all cylindrical, each second medium layer 500 is located inside the perimeter of a second heat exchange wall 400, and each second medium layer 500 is connected to the inner wall of a second heat exchange wall 400. The second medium layer 500 has a second medium inlet 501 and a second medium outlet 502 after heat exchange. The second medium in the second medium layer 500 is steam, and its flow rate is 0.67 kg / s. The convective heat transfer coefficient h fi1 = 1500 W / (m 2 ·K) between the second medium layer and the second heat exchange wall. The flow direction of the second medium is perpendicular to the flow direction of the first medium.

[0071] Let the temperature of the flue gas be t fo , the temperature of the wall surface of the second heat exchange wall in contact with the flue gas be t wo1 , the temperature of the wall surface of the second heat exchange wall in contact with the steam be t wi1 , and the temperature of the steam be t fi1 . The heat exchange process between the flue gas and the steam is as follows:

[0072]

[0073]

[0074]

[0075] From equations (8)-(10), the temperature difference between the flue gas temperature and the steam temperature can be obtained as:

[0076]

[0077] By changing the temperatures of the flue gas and the steam, the temperature t wo1 of the second heat exchange wall in contact with the flue gas is shown in Table 2.

[0078] Table 2 Temperatures of the wall surface of the second heat exchange wall in contact with the flue gas at different flue gas temperatures and steam temperatures

[0079]

[0080] By comparing Table 1 and Table 2, it can be found that if the temperature of the heat exchange wall surface in contact with the flue gas is controlled not to exceed 500°C, when using the heat exchange device in the comparative example, the flue gas temperature cannot exceed 650°C, and at the same time the steam temperature cannot exceed 410°C. When using the heat exchange device in the embodiment, when the flue gas temperature is 650 - 675°C, the steam temperature can reach 450°C. Even when the flue gas temperature reaches 750°C, the steam temperature can still reach 430°C. That is, using the heat exchange device in the embodiment can increase the steam parameters without increasing the metal corrosion rate.

[0081] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0082] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A heat exchange device, characterized in that, comprising: A first medium layer having a first medium inlet and a first medium outlet after heat exchange; A first heat exchange wall located inside the first medium layer, and the outer wall of the first heat exchange wall is connected to the first medium layer; A liquid metal layer located inside the first heat exchange wall and connected to the inner wall of the first heat exchange wall. The liquid metal layer has a liquid metal inlet and a liquid metal outlet after heat exchange; A second heat exchange wall located inside the liquid metal layer, and the outer wall of the second heat exchange wall is connected to the liquid metal layer; A second medium layer located inside the second heat exchange wall, and the second medium layer is connected to the inner wall of the second heat exchange wall. The second medium layer has a second medium inlet and a second medium outlet after heat exchange; The boiling point of the liquid metal in the liquid metal layer is not less than 1000 °C; the liquid metal is at least one selected from gallium, indium, tin, bismuth, zinc and their alloys; The shape of the second medium layer is cylindrical or cuboid.

2. The heat exchange device according to claim 1, characterized in that, The inside of the first medium layer includes a plurality of the first heat exchange walls, and the inside of each first heat exchange wall from the outside to the inside includes the liquid metal layer, the second heat exchange wall, and the second medium layer.

3. The heat exchange device according to claim 1 or 2, characterized in that, The inside of the liquid metal layer includes a plurality of the second heat exchange walls, and the second medium layer is provided inside each second heat exchange wall.

4. The heat exchange device according to claim 1, characterized in that, The thicknesses of the first heat exchange wall and the second heat exchange wall are independently 3-7 mm respectively.

5. The heat exchange device according to claim 1, characterized in that, The thermal conductivities of the first heat exchange wall and the second heat exchange wall are independently 30-54 W / (m·K) respectively.

6. The heat exchange device according to claim 1, characterized in that, The temperature of the first medium layer is 600-750 °C, and the temperature of the second medium layer is 20-500 °C; or the temperature of the first medium layer is 20-500 °C, and the temperature of the second medium layer is 600-750 °C.

7. The heat exchange device according to claim 1, characterized in that, The materials of the first heat exchange wall and the second heat exchange wall are independently selected from at least one of boiler steels 20G, 12Cr1MoVG, and 15CrMoG.

8. A waste treatment system, characterized in that, comprising an incinerator, a heat exchange device and a power generation unit connected in sequence, and the heat exchange device includes the heat exchange device according to any one of claims 1-7.

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