Exhaust gas boiler system
The exhaust gas boiler system with multiple evaporators and a steam compressor enhances heat recovery from low-temperature exhaust gas by boosting low-pressure steam, addressing inefficiencies and emissions in conventional systems.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- MIURA CO LTD
- Filing Date
- 2022-05-30
- Publication Date
- 2026-05-11
AI Technical Summary
Existing exhaust gas boilers struggle to effectively recover heat from low-temperature exhaust gas due to reduced steam generation, leading to inefficiencies and unstable steam pressure, especially when using ejectors.
An exhaust gas boiler system with multiple evaporators and a steam compressor, including an economizer to preheat makeup water, and a steam compressor to boost low-pressure steam to desired pressures, ensuring stable and efficient heat recovery.
The system effectively and stably increases the amount of heat recovered from low-temperature exhaust gas, reducing carbon dioxide emissions and equipment costs while maintaining efficient steam generation.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to an exhaust gas boiler system.
Background Art
[0002] For example, since high-temperature exhaust gas is discharged from a gas engine or the like that drives a generator, an exhaust gas boiler that recovers heat from the exhaust gas to generate steam is used. In order to increase the amount of heat that can be recovered from the exhaust gas, an exhaust gas boiler including a plurality of evaporators (cylinder bodies) arranged side by side from the upstream side to the downstream side of the exhaust gas flow path is also known. In such an exhaust gas boiler, steam with a higher pressure can be obtained on the upstream side. If the pressure of the steam is too low, the generated steam cannot be effectively utilized, so it is necessary to generate steam having a pressure of a certain level or higher even in an exhaust gas boiler.
[0003] For example, Patent Document 1 proposes obtaining steam with an available pressure by mixing high-pressure steam generated in an upstream evaporator and low-pressure steam generated in a downstream evaporator using an ejector.
Prior Art Documents
Patent Documents
[0004]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0005] In recent years, reducing carbon dioxide emissions has become an urgent issue, and in gas engines and other applications, the temperature of exhaust gas is decreasing as thermal efficiency improves. In exhaust gas boilers with a single-stage evaporator, the amount of steam generated decreases, which can lead to boiling due to a reduction in the flow rate of the feedwater heater. On the other hand, when heat is recovered from low-temperature exhaust gas using an exhaust gas boiler with multiple stages, the amount of high-pressure steam generated is relatively small. For this reason, in systems that utilize an ejector, such as in Patent Document 1, it may not be possible to pressurize the mixed steam to a usable pressure.
[0006] Therefore, the present invention aims to provide an exhaust gas boiler system that can effectively and stably increase the amount of heat recovered from relatively low-temperature exhaust gas. [Means for solving the problem]
[0007] An exhaust gas boiler system according to one aspect of the present invention comprises: a first evaporator that evaporates makeup water by heat exchange with exhaust gas; a second evaporator that evaporates makeup water by heat exchange with the exhaust gas that has passed through the first evaporator; an economizer that heats the makeup water supplied to the first and second evaporators by heat exchange with the exhaust gas that has passed through the second evaporator; a steam compressor that compresses the steam generated in the second evaporator; and a steam header into which the steam generated in the first evaporator and the steam compressed by the steam compressor are introduced.
[0008] In the exhaust gas boiler system described above, the temperature of the exhaust gas may be 250°C or more and 320°C or less, the vapor pressure of the first evaporator may be 0.5 MPa or more and 1.0 MPa or less, and the vapor pressure of the second evaporator may be 0.05 MPa or more and 0.2 MPa or less.
[0009] In the exhaust gas boiler system described above, the steam compressor may be a water-injection type steam compressor equipped with a water supply means for injecting water into the space in which the steam is compressed. [Effects of the Invention]
[0010] According to the present invention, the amount of heat recovered from relatively low-temperature exhaust gas can be increased effectively and stably. [Brief explanation of the drawing]
[0011] [Figure 1] This is a schematic diagram showing the configuration of an exhaust gas boiler system according to one embodiment of the present invention. [Modes for carrying out the invention]
[0012] Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is a schematic diagram showing the configuration of an exhaust gas boiler system 1 according to one embodiment of the present invention.
[0013] The exhaust gas boiler system 1 recovers heat from exhaust gas emitted by a gas engine (not shown) and generates steam. The exhaust gas boiler system 1 includes an exhaust gas chamber 10 for guiding the exhaust gas, a first evaporator 20, a second evaporator 30, and an economizer 40 arranged in order from the upstream side within the exhaust gas chamber 10, a steam compressor 50 for compressing the steam generated in the second evaporator 30, and a steam header 60 into which the steam generated in the first evaporator 20 and the steam compressed by the steam compressor 50 are introduced.
[0014] The exhaust gas chamber 10 guides the exhaust gas so that it passes through the first evaporator 20, the second evaporator 30, and the economizer 40 in that order before being discharged to the outside through a chimney (not shown).
[0015] The lower limit of the temperature of the exhaust gas introduced into the exhaust gas chamber 10 is preferably 250°C, and more preferably 270°C. On the other hand, the upper limit of the temperature of the exhaust gas introduced into the exhaust gas chamber 10 is preferably 320°C, and more preferably 300°C. If the temperature of the exhaust gas introduced into the exhaust gas chamber 10 is above the lower limit, heat can be effectively recovered by generating steam from the exhaust gas. Furthermore, if the temperature of the exhaust gas introduced into the exhaust gas chamber 10 is below the upper limit, a higher heat recovery rate can be achieved compared to conventional single-stage exhaust gas boilers, where the decrease in heat recovery rate is significant with decreasing exhaust gas temperature. In other words, the above temperature range is a range in which the exhaust gas boiler system 1 is particularly advantageous compared to conventional exhaust gas boilers.
[0016] The first evaporator 20 evaporates makeup water by exchanging heat with exhaust gas. The first evaporator 20 can be a once-through boiler comprising a lower header 21 for storing makeup water, a plurality of water tubes 22 extending from the lower header 21 and heated by exhaust gas to evaporate the makeup water inside, an upper header 23 for collecting steam generated in the water tubes 22, a steam-water separator 24 for separating water droplets contained in the steam flowing out from the upper header 23, and a feed valve 25 for adjusting the amount of makeup water supplied to the lower header 21 so as to maintain the water level in the water tubes 22 within a certain range.
[0017] The lower limit of the vapor pressure (gauge pressure) of the first evaporator 20 is preferably 0.5 MPa, and more preferably 0.6 MPa. On the other hand, the upper limit of the vapor pressure of the first evaporator 20 is preferably 1.0 MPa, and more preferably 0.9 MPa. By setting the vapor pressure of the first evaporator 20 to be above the lower limit, the steam generated in the first evaporator 20 can be used in general demand facilities. In addition, by setting the vapor pressure of the first evaporator 20 to be above the lower limit, it is possible to prevent the exhaust gas temperature in the first evaporator 20 from becoming too low, allowing for efficient heat recovery in the second evaporator 30 and improving the overall thermal efficiency of the exhaust gas boiler system 1. Furthermore, by setting the vapor pressure of the first evaporator 20 to be below the upper limit, it is possible to secure the amount of heat recovered in the first evaporator 20 and prevent unnecessary increases in equipment costs.
[0018] The second evaporator 30 evaporates the makeup water by exchanging heat with the exhaust gas that has passed through the first evaporator 20. The second evaporator 30 can be a once-through boiler having a lower header 31 for storing makeup water, a plurality of water tubes 32 extending from the lower header 31 and heated by the exhaust gas to evaporate the makeup water inside, an upper header 33 for collecting the steam generated in the water tubes 32, a steam-water separator 34 for separating water droplets contained in the steam flowing out from the upper header 33, and a feed valve 35 for adjusting the amount of makeup water supplied to the lower header 31 so as to maintain the water level in the water tubes 32 within a certain range.
[0019] The lower limit of the vapor pressure of the second evaporator 30 is preferably 0.05 MPa, and more preferably 0.06 MPa. On the other hand, the upper limit of the vapor pressure of the second evaporator 30 is preferably 0.20 MPa, and more preferably 0.15 MPa. By setting the vapor pressure of the second evaporator 30 to or above the lower limit, the load on the steam compressor 50, i.e., power consumption and the resulting carbon dioxide emissions, can be suppressed, thereby effectively and stably increasing the amount of heat recovered, and preventing unnecessary increases in equipment costs due to the enlargement of the steam compressor 50. Furthermore, by setting the vapor pressure of the second evaporator 30 to or below the upper limit, the amount of heat that can be recovered from the exhaust gas can be sufficiently increased.
[0020] The economizer 40 heats the makeup water supplied to the first evaporator 20 and the second evaporator 30 by exchanging heat with the exhaust gas that has passed through the second evaporator 30. In other words, the makeup water heated in the economizer 40 is distributed to the first evaporator 20 and the second evaporator 30, and the economizer 40 is supplied with makeup water by the feedwater pump 41 at a pressure equal to or greater than the vapor pressure of the first evaporator 20. For example, if the vapor pressure of the first evaporator is 0.8 MPa, the economizer is pressurized to 0.8 MPa or higher, while the temperature of the exhaust gas flowing into the economizer after passing through the second evaporator drops to 135°C. As a result, the water temperature in the economizer never exceeds the saturation temperature, enabling stable heat recovery without steaming.
[0021] The vapor compressor 50 compresses the vapor generated in the second evaporator 30 until it reaches the same pressure as the vapor generated in the first evaporator 20. As the vapor compressor 50, for example, a screw compressor can be used. Further, the vapor compressor 50 preferably includes, for example, a pump or the like, and is a water injection type vapor compressor provided with a water supply means 51 for injecting water into the space for compressing the vapor. By injecting water into the space for compressing the vapor of the vapor compressor 50, it is possible to prevent the vapor from becoming superheated vapor, and to increase the amount of discharged vapor by evaporating the injected water. Further, the vapor compressor 50 having the water supply means 51 can operate stably even if the amount of vapor generated in the second evaporator 30 fluctuates due to fluctuations in the exhaust gas temperature, so that maximum heat recovery can always be performed.
[0022] The steam header 60 is a buffer for primarily storing the steam generated in the first evaporator 20 and the steam compressed by the steam compressor 50, and for stably supplying steam to the demand facility. The capacity of the steam header 60 is appropriately set in consideration of fluctuations in the air volume and temperature of the exhaust gas supplied to the exhaust gas boiler system 1, load fluctuations of the demand facility, and the like. Steam may also be supplied to the steam header 60 from a normal boiler such as a fuel-fired boiler. Thereby, even when the amount of exhaust gas supplied to the exhaust gas boiler system 1 and the steam usage amount of the demand facility are not interlocked, the amount of steam required by the demand facility can be stably supplied.
[0023] As described above, the exhaust gas boiler system 1 recovers heat from the exhaust gas in the first evaporator 20 to generate steam at a desired pressure, and then further recovers heat from the exhaust gas in the second evaporator 30 to generate low-pressure steam, and boosts this low-pressure steam to the desired pressure by the steam compressor 50. Therefore, the exhaust gas boiler system 1 can recover more heat energy as available steam energy, so that even when the temperature of the exhaust gas is low and the amount of heat that can be recovered by a conventional exhaust gas boiler system is small, heat can be effectively and stably recovered from the exhaust gas.
[0024] As described above, the embodiments of the present invention have been explained. However, the present invention is not limited to the above-described embodiments, and various changes and modifications are possible. For example, in the exhaust gas boiler system according to the present invention, the first evaporator and the second evaporator are not limited to the through-flow boiler, and may have a configuration such as a water tube boiler that evaporates water in a steam drum, for example.
Example
[0025] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to the following examples.
[0026] A simulation was conducted on the amount of steam generated in an example of an exhaust gas boiler system having the configuration of FIG. 1 and a conventional exhaust gas boiler system having a single-stage evaporator and an economizer. The temperature of the exhaust gas supplied to the exhaust gas boiler system was 300°C, the flow rate of the exhaust gas was 37000 Nm3 / h, and the temperature of the makeup water was 25°C.
[0027] In the exhaust gas boiler system of the example, when the steam pressure of the first evaporator and the discharge pressure of the steam compressor were set to 0.78 MPa and the steam pressure of the second evaporator was set to 0.10 MPa, the steam generation amount of the first evaporator was 2397 kg / h, the steam generation amount of the second evaporator was 1182 kg / h, the power consumption of the steam compressor was 170 kW, and the water injection amount in the steam compressor was 117 kg / h (the discharge steam amount of the steam compressor was 1300 kg / h), and a total of 3698 kg / h of steam was obtained in the steam header. The temperature of the exhaust gas passing through the exhaust gas boiler system of the example was 109°C. On the other hand, in the exhaust gas boiler system of the comparative example, the steam generation amount was 2363 kg / h, and the temperature of the exhaust gas passing through the exhaust gas boiler system was 168°C.
[0028] The difference in steam generation between the exhaust gas system in the example and the comparative example is 1335 kg / h. If this amount of steam were obtained using a boiler fueled by city gas (13A), 57 m3 N / h of fuel would be required, resulting in carbon dioxide emissions of 172 kg / h. In contrast, the carbon dioxide emissions from the steam compressor in the example's exhaust gas system, calculated by multiplying the power consumed by the steam compressor by the power company's carbon dioxide emission factor, are 83 kg / h. Therefore, the exhaust gas system in the example can reduce carbon dioxide emissions by 52% compared to the comparative example.
[0029] Table 1 shows the results of a simulation conducted when the vapor pressure of the second evaporator was changed in the exhaust gas boiler system of the example. The table shows the exhaust gas temperature at the outlet of the second evaporator, the exhaust gas temperature at the outlet of the economizer, the total steam volume (sum of the evaporation volume of the first evaporator and the steam volume discharged from the steam compressor), and the power consumption of the steam compressor, each as a percentage of the case when the vapor pressure of the second evaporator is 0.10 MPa. The evaporation volume of the first evaporator and the steam volume discharged from the steam compressor are shown as a breakdown of the total steam volume (percentage).
[0030] [Table 1]
[0031] Lowering the vapor pressure of the second evaporator reduces the exhaust gas temperature at the outlet of the second evaporator, the water temperature at the outlet of the economizer, and the evaporation rate of the first evaporator. On the other hand, in the second evaporator, as the vapor pressure decreases, the temperature difference between the exhaust gas inlet and outlet increases, and the amount of steam in the second evaporator increases. Therefore, lowering the vapor pressure of the second evaporator increases the evaporation rate of the second evaporator, thus increasing the overall evaporation rate of the system. For this reason, the vapor pressure of the second evaporator is preferably 0.2 MPa or less, which ensures sufficient heat recovery from the second evaporator. In this case, the exhaust gas temperature at the outlet of the second evaporator is 150°C or less, and even if the water flow to the economizer is stopped, the feedwater temperature will not exceed the saturated vapor pressure, and boiling will not occur, allowing for a stable supply of steam. In addition, since boiling does not need to be considered, there is no increase in pressure loss in the pipes, no erosion, etc., and there is more margin in the design of the heat transfer surface of the economizer. Furthermore, the lower limit of the vapor pressure in the second evaporator is preferably 0.05 MPa, which does not excessively increase the load on the steam compressor and thus does not excessively increase carbon dioxide emissions and equipment costs associated with the power consumption of the steam compressor. [Explanation of Symbols]
[0032] 1. Exhaust gas boiler system 10 Exhaust gas chamber 20. First evaporator 30. Second evaporator 40 Economizer 50 Steam compressor 60 Steam Header 21 Bottom Header 22 Water pipe 23 Top Header 24 Steam water separator 25 Water supply valve 31 Bottom Header 32 Water pipe 33 Top Header 34 Steam water separator 35 Water supply valve 41 Water supply pump 51 Water supply means
Claims
1. A first evaporator that evaporates the makeup water by exchanging heat with the exhaust gas, A second evaporator exchanges heat with the exhaust gas that has passed through the first evaporator to evaporate the makeup water, An economizer that heats the makeup water supplied to the first and second evaporators by exchanging heat with the exhaust gas that has passed through the second evaporator, A steam compressor, powered by electricity, compresses the steam generated in the second evaporator, A steam header into which the steam generated in the first evaporator and the steam compressed in the steam compressor are introduced, Equipped with, The vapor pressure of the second evaporator is between 0.05 MPa and 0.2 MPa. Exhaust gas boiler system.
2. The exhaust gas temperature is between 250°C and 320°C. The vapor pressure of the first evaporator is between 0.5 MPa and 1.0 MPa. The exhaust gas boiler system according to claim 1.
3. The exhaust gas boiler system according to claim 1 or 2, wherein the steam compressor is a water injection type steam compressor equipped with a water supply means for injecting water into the space in which steam is compressed.