Waste heat recovery system and waste heat recovery method

Abstract

This system provides a waste heat recovery system that allows for adjustment of the amount of recovered water and heat according to the situation, without bypassing the exhaust gas. [Solution] The waste heat recovery system 1 of the present invention comprises a cooling tower that reduces the temperature of exhaust gas discharged from a waste incinerator by spraying cooling water onto it, a water vapor separation membrane that separates water vapor from the exhaust gas after it has passed through the cooling tower, a condensate tank that recovers the water vapor separated by the water vapor separation membrane as condensate, and a control means that controls the amount of recovered heat recovered in the condensate process by adjusting the condensate temperature.

Description

Technical Field

[0001] The present invention relates to an exhaust heat recovery system and an exhaust heat recovery method, and particularly to a technology for recovering moisture contained in combustion exhaust gas discharged from a waste incinerator and realizing efficient exhaust heat recovery.

Background Art

[0002] When cooling the combustion exhaust gas generated from a waste incinerator, a desuperheating tower is provided for spraying cooling water to cool it. When spraying cooling water into the combustion exhaust gas, the moisture concentration in the combustion exhaust gas increases. Therefore, when the exhaust gas is discharged from the chimney, the moisture in the exhaust gas condenses and white smoke is generated, which is undesirable. Therefore, in order to reduce the moisture concentration in the exhaust gas, there is a technology for separating water vapor with a water vapor separation membrane (Patent Document 1). However, simply separating water vapor using a water vapor separation membrane only increases the treatment cost because there is no technical idea of utilizing the separated high-temperature water vapor.

[0003] Therefore, as a technology that can reduce the exhaust gas treatment cost while preventing white smoke from the chimney, a technology has been developed in which the water vapor recovered by the water vapor separation membrane is returned to water by a condenser and used as the cooling water for the exhaust gas cooling device (Patent Document 2).

[0004] According to the technology described in Patent Document 2, the moisture in the exhaust gas is separated by a water vapor separation membrane, and the separated water vapor is cooled by a heat exchanger to become condensate and stored in a condensate tank. The stored condensate is reused as cooling water for blowing into the waste incinerator or plant water. Also, the warm water after cooling the water vapor is used as a heat source for a binary generator.

[0005] By doing so, it is possible to increase the thermal efficiency of the entire plant while suppressing the generation of white smoke without wasting the heat possessed by the separated water vapor.

[0006] Incidentally, in the technology described in Patent Document 2, a steam separation membrane for separating and recovering moisture from exhaust gas is provided with an exhaust gas bypass passage. By adjusting the amount of exhaust gas passing through the steam separation membrane and the amount of exhaust gas passing through the bypass passage with a damper, the amount of steam separated and recovered is controlled, and as a result, the amount of water recovered and the amount of heat recovered are controlled.

[0007] As described in Patent Document 2, controlling the amount of water vapor recovered by the amount of exhaust gas passing through the water vapor separation membrane requires ducts and dampers, and also requires control of the condensate in addition to the amount of exhaust gas passing through the water vapor separation membrane. This makes the mechanism complex and, as a result, leads to increased costs, which is undesirable. In particular, ducts and dampers for exhaust gas are prone to fouling and corrosion, which easily leads to increased costs. Furthermore, if the amount of exhaust gas bypassed increases, the water concentration in the exhaust gas discharged from the chimney increases, which may cause white smoke to be generated. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent No. 4074826 [Patent Document 2] Patent No. 6915873 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] This invention has been made in view of these problems, and aims to provide a waste heat recovery system that can adjust the amount of recovered water and recovered heat according to the situation without bypassing the exhaust gas. [Means for solving the problem]

[0010] The inventors of this invention discovered that by adjusting the temperature during the condensation of separated and recovered steam into condensate, the vapor pressure on the recovery side of the steam separation membrane can be adjusted, and as a result, the amount of recovered water and the amount of recovered heat can be controlled, leading to the present invention.

[0011] The present invention provides the following solutions.

[0012] The first feature of the waste heat recovery system comprises a cooling tower that reduces the temperature of exhaust gas discharged from a waste incinerator by spraying cooling water onto it, a steam separation membrane that separates steam from the exhaust gas after it has passed through the cooling tower, a condensate tank that recovers the steam separated by the steam separation membrane as condensate, and a control means that controls the amount of heat recovered during the condensation process by adjusting the condensate temperature.

[0013] According to the invention relating to the first feature, since a steam separation membrane is provided to separate steam from the exhaust gas after it has passed through the cooling tower, the generation of white smoke from the chimney can be suppressed. The steam separated and recovered using the steam separation membrane is saturated when it flows into the condensate tank as condensate, so when the condensate temperature, which is the temperature at which it flows into the condensate tank, is determined, the saturated vapor pressure at that time becomes the steam pressure. In other words, by adjusting the condensate temperature, the vapor pressure on the recovery side of the steam separation membrane can be adjusted. Furthermore, in a steam separation membrane, the amount of recovered water changes depending on the pressure difference between the vapor pressure on the inlet side and the vapor pressure on the recovery side, so adjusting the condensate temperature leads to adjusting the pressure difference between the inlet side and the recovery side of the steam separation membrane, and as a result, the amount of recovered heat and the amount of recovered water when recovering steam as condensate can be controlled.

[0014] The waste heat recovery system relating to the second feature is a waste heat recovery system relating to the first feature, comprising a heat exchanger between the steam separation membrane and the condensate tank for cooling the steam separated by the steam separation membrane, and adjusting the amount of heat exchanged in the heat exchanger to adjust the condensate temperature.

[0015] According to the invention relating to the second feature, a heat exchanger is provided between the steam separation membrane and the condensate tank to cool the steam separated by the steam separation membrane. By adjusting the amount of heat exchanged in the heat exchanger, the condensate temperature can be adjusted. Therefore, by simply adjusting the amount of heat exchanged in the heat exchanger, the steam pressure on the recovery side of the steam separation membrane can be adjusted, and as a result, the amount of heat recovered and the amount of water recovered when recovered as condensate can be controlled.

[0016] The third feature of the waste heat recovery system is a waste heat recovery system according to the second feature, comprising a bypass circuit that bypasses the heat exchanger from the steam separation membrane to the condensate tank, and a damper that adjusts the flow rate of steam passing through the bypass circuit, and the amount of heat exchange is adjusted by adjusting the opening of the damper.

[0017] According to the invention relating to the third feature, the invention includes a bypass circuit that bypasses the heat exchanger from the steam separation membrane to the condensate tank, and a damper that adjusts the flow rate of steam passing through the bypass circuit. By adjusting the opening degree of the damper, the amount of heat exchange is adjusted. Therefore, by adjusting the opening degree of the damper in the steam flow path, the steam pressure on the recovery side of the steam separation membrane can be adjusted, and as a result, the amount of heat and water recovered when recovered as condensate can be controlled. Since there is no need to use a large bypass circuit or damper in the combustion exhaust gas flow path, the amount of water and heat recovered can be controlled with a small-scale and inexpensive configuration. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide a waste heat recovery system that allows for adjustment of the amount of recovered water and the amount of recovered heat according to the situation, without bypassing the exhaust gas. [Brief explanation of the drawing]

[0019] [Figure 1] Figure 1 is a schematic diagram showing the waste heat recovery system 1 according to this embodiment. [Figure 2] Figure 2 is a flowchart showing the procedure for the waste heat recovery method using the waste heat recovery system 1 according to this embodiment.

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. Note that this is merely an example, and the technical scope of the present invention is not limited thereto.

[0021] [Overall Configuration of Exhaust Heat Recovery System 1] The overall configuration of the exhaust heat recovery system 1 according to the present embodiment will be described with reference to FIG. 1.

[0022] As shown in FIG. 1, the exhaust heat recovery system 1 of the present embodiment is composed of a waste incinerator 10, an exhaust heat recovery boiler 20, a desuperheating tower 30, a bag filter 40, an induced draft fan 50, a water vapor separation membrane 60, a condensate recovery device 70, a chimney 80, and a control device (not shown).

[0023] The waste incinerator 10 incinerates wastes such as amorphous general wastes, industrial wastes, and infectious medical wastes packed in packages having a predetermined shape. Any type of incinerator such as a stoker type, a fluidized bed type, or a vertical type can be used.

[0024] The exhaust heat recovery boiler 20 generates steam by recovering exhaust heat from high-temperature combustion exhaust gas generated when wastes are incinerated in the waste incinerator 10 and heating boiler feed water. The exhaust heat recovery boiler 20 is composed of a steam drum that separates steam generated by heating the boiler feed water in a heat transfer tube through which the boiler feed water flows, a superheater that further superheats the steam, and an evaporation amount detection means that detects the evaporation amount of the steam generated from the exhaust heat recovery boiler 20, but the form is not limited thereto.

[0025] The desuperheating tower 30 is for further cooling the combustion exhaust gas cooled in the exhaust heat recovery boiler 20 by spraying cooling water. By spraying cooling water on the combustion exhaust gas in the desuperheating tower 30, while the temperature of the combustion exhaust gas decreases, the moisture concentration in the combustion exhaust gas increases.

[0026] The bag filter 40 removes soot and harmful components contained in the combustion exhaust gas by filtering the reduced-temperature combustion exhaust gas, and is equipped with a filter cloth for removing soot and harmful components. A chemical supply device (not shown) for blowing chemicals into the bag filter 40 is provided in the exhaust gas flue at the inlet of the bag filter 40. The alkaline chemical supplied from the chemical supply device undergoes a neutralization reaction with acidic components in the combustion exhaust gas on the filter cloth of the bag filter 40, thereby purifying the combustion exhaust gas. In this embodiment, a sodium-based chemical is used as the alkaline chemical supplied from the chemical supply device.

[0027] The induced draft fan 50 is a fan installed downstream of the bag filter 40, and its purpose is to draw in the exhaust gas purified by the bag filter 40 and release the exhaust gas into the atmosphere from the chimney 80. In this embodiment, there are two induced draft fans 50: one installed in the path that passes through the water vapor separation membrane 60, and another installed in the path that bypasses the water vapor separation membrane 60. The path that bypasses the water vapor separation membrane 60 is used for maintenance and replacement of the water vapor separation membrane 60, and is not used to control the amount of heat recovered by the water vapor.

[0028] The water vapor separation membrane 60 selectively separates and recovers water vapor from the combustion exhaust gas purified by the bag filter 40, utilizing the difference in vapor pressure between the inlet side and the recovery side across the membrane to separate the water vapor. In the water vapor separation membrane 60, the larger the difference in vapor pressure between the inlet side and the recovery side across the membrane, the more water vapor can be recovered, and the smaller the difference, the less water vapor can be recovered. The temperature of the water vapor separated and recovered by the water vapor separation membrane 60 is approximately 200°C.

[0029] The condenser 70 cools steam back into water and includes a first heat exchanger 71, a second heat exchanger 72, a bypass circuit 73, a damper 74, a condensate tank 75, and a cooling tower 76.

[0030] The first heat exchanger 71 is a heat exchanger for recovering heat from the approximately 200°C water vapor separated and recovered by the water vapor separation membrane 60. Since the heat recovered by the first heat exchanger 71 is relatively high temperature, it can be used, for example, as a heat source for regenerating the absorbent in an absorption chiller, or for other heat utilization purposes.

[0031] The second heat exchanger 72 is installed in the path from the first heat exchanger 71 to the condensate tank 75. It is a heat exchanger that further cools and condenses the water vapor cooled in the first heat exchanger 71 to form condensate, and can also recover latent heat at the condensate pressure. In this embodiment, cooling water supplied from the cooling tower 76 is used as the refrigerant for the second heat exchanger 72, but it is not limited to this; any refrigerant that can cool and condense water vapor is acceptable.

[0032] The bypass circuit 73 is a path that bypasses the second heat exchanger 72 in the route from the first heat exchanger 71 to the condensate tank 75, and supplies condensate to the condensate tank 75 without cooling it.

[0033] The damper 74 is installed in the bypass circuit 73 and is used to adjust the amount of steam passing through the bypass circuit 73 and the amount of steam flowing into the second heat exchanger 72. The flow rate is adjusted by changing the opening of the damper. The damper 74 may also be installed in two locations: the bypass circuit 73 and the inlet of the second heat exchanger 72.

[0034] The condensate tank 75 is a tank for storing condensate that has been cooled and condensed in the second heat exchanger 72 and / or the first heat exchanger 71. In this invention, the condensate temperature refers to the temperature at which the condensate that has been cooled and condensed in the second heat exchanger 72 and / or the first heat exchanger 71 flows into the condensate tank 75. The condensate stored in the condensate tank 75 is then used as feedwater for various plant water systems, as cooling water in the cooling tower 30, or as makeup water for the cooling tower 76.

[0035] The cooling tower 76 sends condensate supplied as makeup water from the condensate tank 75 to the second heat exchanger 72 as cooling water, and also cools the high-temperature cooling water returning from the second heat exchanger 72 with air.

[0036] A control device (not shown) controls the amount of heat and water recovered by adjusting the opening of the damper 74 as needed. The control device also controls various parts of the system based on physical quantities measured by various measuring instruments (not shown).

[0037] [Waste heat recovery method in waste heat recovery system 1] Next, the flow of the waste heat recovery method using the waste heat recovery system 1 according to this embodiment will be explained using Figure 2. Figure 2 is a flowchart showing the waste heat recovery method using the waste heat recovery system 1 according to this embodiment. It is assumed that the waste incinerator 10 has already been heated to a temperature sufficient for incinerating waste and is in a steady-state operation state.

[0038] [Step S110: Waste heat recovery (steam generation)] In the waste incinerator 10, high-temperature combustion exhaust gas is generated by incinerating waste. Heat is recovered from the high-temperature combustion exhaust gas generated in the waste incinerator 10 in the waste heat recovery boiler 20, which heats the boiler feedwater and generates steam (step S110).

[0039] [Step S120: Reducing the temperature of combustion exhaust gases] In step S110, the combustion exhaust gas, after the heat has been recovered in the heat recovery boiler 20, is cooled in the cooling tower 30 by spraying it with cooling water until it reaches a temperature of 200°C or lower (step S120).

[0040] [Step S130: Purification of combustion exhaust gases] In step S120, the combustion exhaust gas, which has been cooled to below 200°C in the cooling tower 30, is purified by the bag filter 40 (step S130).

[0041] In this embodiment, a pre-coated bag filter is employed as the bag filter 40, in which a sodium-based chemical (for example, finely ground sodium bicarbonate or porous sodium carbonate) is supplied for a predetermined time to form a reaction layer of the sodium-based chemical on the surface of the filter cloth. By using a sodium-based chemical as a neutralizing agent, acidic gases such as hydrogen chloride and sulfur oxides can be efficiently neutralized even in the relatively high exhaust gas temperature range of 200°C.

[0042] Furthermore, by using a pre-coated bag filter as the bag filter 40, acidic gases contained in the combustion exhaust gas are neutralized by the pre-coated reaction layer, and the resulting salt is captured by the filter cloth. Similarly, soot contained in the combustion exhaust gas is also captured by the filter cloth. By using a pre-coated bag filter, the reaction rate between the chemical and the acidic components can be improved, so a sufficient reaction can be obtained with a small amount of chemical, and the amount of dust discharged from the bag filter after the filter cloth has been cleaned can be reduced.

[0043] Furthermore, the type of bag filter 40 is not limited to a pre-coated bag filter. It may also be a type in which a sodium-based agent is blown into the inlet of the bag filter 40.

[0044] In this way, by purifying the exhaust gas using a bag filter with sodium-based chemicals, the concentrations of hydrogen chloride and sulfur oxides are reduced to 10 ppm or less.

[0045] [Step S140: Separation of water vapor] In step S130, the purified combustion exhaust gas flows downstream by the induced draft fan 50 and passes through the water vapor separation membrane 60, where water vapor is selectively separated from the combustion exhaust gas (step S140). At this time, the combustion exhaust gas passes through the water vapor separation membrane 60 without separation, and almost the entire amount of combustion exhaust gas is separated from the water vapor contained in almost the entire amount of combustion exhaust gas. The amount of water vapor separated by the water vapor separation membrane 60 is determined by the condensate temperature, as will be described later.

[0046] Here, the combustion exhaust gas passing through the water vapor separation membrane 60 has had particulate matter removed and acidic gases neutralized by the bag filter 40, and its moisture concentration has been increased, so water vapor can be efficiently separated and recovered. Furthermore, since the water vapor has been separated from the combustion exhaust gas after passing through the water vapor separation membrane 60, it is discharged from the chimney 80 while preventing white smoke.

[0047] [Step S150: Condensation of water vapor] The steam separated from the combustion exhaust gas after passing through the steam separation membrane 60 flows into the first heat exchanger 71 and the second heat exchanger 72, where it is cooled by heat exchange with the refrigerant. The cooled steam condenses and flows into the condensate tank 75 (step S150).

[0048] The steam, which has a temperature of approximately 200°C and is separated from the combustion exhaust gas by the steam separation membrane 60, is first cooled in the first heat exchanger 71 to become steam at about 100-120°C. The refrigerant, which has undergone heat exchange with the high-temperature steam in the first heat exchanger 71, has a higher temperature and is therefore used as a heat source for the absorption chiller or for other heat utilization purposes.

[0049] The steam cooled in the first heat exchanger 71 to a temperature of approximately 100-120°C is further cooled and condensed in the second heat exchanger 72. Here, a control device (not shown) adjusts the opening of the damper 74 to balance the flow rate of steam flowing into the second heat exchanger 72 with the flow rate of steam bypassing the second heat exchanger 72, thereby controlling the temperature of the condensate flowing into the condensate tank 75. By controlling the temperature of the condensate flowing into the condensate tank 75, the steam pressure on the recovery side of the steam separation membrane can be adjusted, and as a result, the amount of water and heat recovered when recovered as condensate can be controlled.

[0050] In other words, to increase the amount of recovered water, the condensate temperature is lowered to about 60°C, and the steam pressure on the outlet side (i.e., the recovery side) of the steam separation membrane 60 is lowered to increase the pressure difference with the inlet side and increase the amount of recovered water. To this end, a control device (not shown) adjusts the damper 74 to increase the flow rate of steam flowing into the second heat exchanger 72, thereby increasing the amount of heat exchanged. In this way, the amount of heat recovered from steam in the second heat exchanger 72 can be increased, and a larger amount of condensate at a lower temperature can be obtained.

[0051] On the other hand, if high-temperature condensate is desired, for example, the condensate temperature can be raised to 80°C or higher, increasing the vapor pressure of the steam separation membrane 60 to reduce the pressure difference with the inlet side, thereby reducing the amount of recovered water and obtaining a small amount of high-temperature condensate. To achieve this, the control device adjusts the damper 74 to reduce the flow rate of steam flowing into the second heat exchanger 72 and increases the flow rate of steam bypassing the second heat exchanger 72, thereby reducing the amount of heat exchanged. In this way, the amount of heat recovered from steam in the second heat exchanger 72 can be reduced, and a small amount of higher-temperature condensate can be obtained. If the condensate temperature is raised to 80°C or higher, although the amount of recovered water will decrease, it will be possible to obtain cold energy suitable for binary power generation or ice making.

[0052] Furthermore, by ensuring a membrane area in the steam separation membrane 60 that is sufficient to secure the required amount of water for use in the plant while maintaining a condensate temperature of 80°C or higher, the condensate temperature can be lowered in the event of a disaster, and the increased amount of condensate can be supplied to the outside as domestic water. At this time, the control device increases the flow rate of steam flowing into the second heat exchanger 72 by adjusting the damper 74, thereby further increasing the amount of heat exchange. In this way, a large amount of condensate at a relatively low temperature can be obtained.

[0053] In this way, by simply adjusting the temperature at which the steam separated from the combustion exhaust gas by the steam separation membrane 60 is recovered into the condensate tank 75, the vapor pressure on the recovery side of the steam separation membrane 60 can be adjusted, and as a result, the amount of heat recovered and the amount of water recovered when the steam is recovered as condensate can be controlled. That is, since the steam separated and recovered using the steam separation membrane is saturated when it flows into the condensate tank as condensate, once the condensate temperature, which is the temperature at which it flows into the condensate tank, is determined, the saturated vapor pressure at that time becomes the steam pressure. In other words, by adjusting the condensate temperature, the vapor pressure on the recovery side of the steam separation membrane can be adjusted. Furthermore, in a steam separation membrane, the amount of water recovered changes depending on the pressure difference between the vapor pressure on the inflow side and the vapor pressure on the recovery side, so adjusting the condensate temperature leads to adjusting the pressure difference between the inflow side and the recovery side of the steam separation membrane, and as a result, the amount of heat recovered and the amount of water recovered when the steam is recovered as condensate can be controlled.

[0054] Furthermore, a second heat exchanger 72 is provided between the steam separation membrane 60 and the condensate tank 75 to cool the steam separated by the steam separation membrane 60. By adjusting the amount of heat exchanged in the second heat exchanger 72, the condensate temperature can be adjusted. Therefore, by simply adjusting the amount of heat exchanged in the second heat exchanger 72, the steam pressure on the recovery side of the steam separation membrane 60 can be adjusted, and as a result, the amount of heat and water recovered when recovered as condensate can be controlled.

[0055] Furthermore, the system includes a bypass circuit 73 that bypasses the second heat exchanger 72 from the steam separation membrane 60 to the condensate tank 75, and a damper 74 that adjusts the flow rate of steam passing through the bypass circuit 73. By adjusting the opening of the damper 74, the amount of heat exchange can be adjusted. Therefore, by simply adjusting the opening of the damper 74 in the steam flow path, the steam pressure on the recovery side of the steam separation membrane 60 can be adjusted, and as a result, the amount of heat and water recovered when recovered as condensate can be controlled. Since there is no need to use a large bypass circuit or damper in the combustion exhaust gas flow path, the amount of water and heat recovered can be controlled with a small-scale and inexpensive configuration.

[0056] In the above, the amount of heat exchanged in the heat exchanger was used as a means of adjusting the condensate temperature, but this is not the only means. For example, any means that can adjust the temperature of the condensate when it flows into the condensate tank 75 is acceptable, such as mixing water or steam with the condensate to adjust the condensate temperature.

[0057] Although embodiments of the present invention have been described above, the present invention is not limited to these embodiments. Furthermore, the effects described in the embodiments of the present invention are merely a list of the most preferred effects arising from the present invention, and the effects of the present invention are not limited to those described in the embodiments.

[0058] Furthermore, the embodiments described above are explained in detail for the purpose of clearly illustrating the present invention, and are not necessarily limited to those comprising all the configurations described. [Industrial applicability]

[0059] The waste heat recovery system of this invention can be applied to all types of waste incineration facilities that incinerate various types of waste. [Explanation of Symbols]

[0060] 1. Waste heat recovery system 10. Waste Incinerator 20 Waste heat recovery boiler 30 De-temperature towers 40 Bug Filter 50 Induced Driving Ventilation Fan 60 Water vapor separation membrane 70 Condenser 71 First heat exchanger 72 Second heat exchanger 73 Bypass Circuit 74 Damper 75 Condensate Tank 76 Cooling Tower 80 Chimney

Claims

1. A cooling tower that reduces the temperature of combustion exhaust gas discharged from a waste incinerator by spraying it with cooling water, A water vapor separation membrane that selectively separates water vapor from the combustion exhaust gas after it has passed through the aforementioned cooling tower, A condensate tank for recovering the steam separated by the steam separation membrane as condensate, A control means for controlling the amount of heat recovered in the condensation process by adjusting the condensate temperature, A waste heat recovery system equipped with this system.

2. A heat exchanger is provided between the steam separation membrane and the condensate tank to cool the steam separated by the steam separation membrane. The condensate temperature is adjusted by adjusting the amount of heat exchanged in the heat exchanger. The waste heat recovery system according to claim 1.

3. A bypass circuit that bypasses the heat exchanger from the steam separation membrane to the condensate tank, The circuit includes a damper that adjusts the flow rate of water vapor passing through the bypass circuit, The amount of heat exchange is adjusted by adjusting the opening degree of the damper. The waste heat recovery system according to claim 2.

4. The steps include reducing the temperature of the exhaust gas discharged from the waste incinerator by spraying it with cooling water, The steps include separating water vapor from the exhaust gas after it has been cooled, The steps include recovering the separated water vapor as condensate, The steps include controlling the amount of heat recovered during the condensation process by adjusting the condensate temperature, A heat recovery method that includes the following features.

Images