JP2023175102A - Exhaust gas boiler system - Google Patents

Abstract

To provide an exhaust gas boiler system for enabling heat recovery from exhaust gas having a relatively low temperature.SOLUTION: An exhaust gas boiler system 1 according to one aspect of the invention includes a first vaporizer 20 to be heat-exchanged with exhaust gas to vaporize makeup water, a second vaporizer 30 to be heat-exchanged with the exhaust gas passing through the first vaporizer 20 to vaporize the makeup water, an economizer 40 to be heat-exchanged with the exhaust gas passing through the second vaporizer 30 to heat the makeup water to be supplied to the first vaporizer 20 and the second vaporizer 30, a vapor compressor 50 for compressing vapor generated in the second vaporizer 30, and a vapor header 60 into which the vapor generated in the first vaporizer 20 and the vapor compressed by the vapor compressor 50 are introduced.SELECTED DRAWING: Figure 1

Description

The present invention relates to an exhaust gas boiler system.

For example, since high-temperature exhaust gas is discharged from a gas engine that drives a generator, an exhaust gas boiler is used that recovers heat from the exhaust gas and generates steam. In order to increase the amount of heat that can be recovered from exhaust gas, exhaust gas boilers are also known that include a plurality of evaporators (can bodies) arranged in line from the upstream side to the downstream side of the exhaust gas flow path. In such an exhaust gas boiler, steam can be obtained at a higher pressure on the upstream side. If the steam pressure is too low, the generated steam cannot be used effectively, so it is necessary to generate steam having a pressure above a certain level in the exhaust gas boiler as well.

For example, Patent Document 1 discloses that high-pressure steam generated in an upstream evaporator and low-pressure steam generated in a downstream evaporator are mixed using an ejector to obtain steam at a usable pressure. It is proposed that.

Patent No. 5359540

In recent years, it has become urgent to reduce carbon dioxide emissions, and the temperature of exhaust gas in gas engines and the like is decreasing as thermal efficiency improves. In an exhaust gas boiler having a single-stage evaporator, the amount of steam generated is small, and the amount of water flowing through the feed water heater is reduced, which may cause boiling. On the other hand, when heat is recovered from low-temperature exhaust gas using an exhaust gas boiler having a multi-stage evaporator, the amount of high-pressure steam generated becomes relatively small. For this reason, in a system using an ejector as in Patent Document 1, it may not be possible to increase the pressure of mixed steam to a usable pressure.

Therefore, an object of the present invention is to provide an exhaust gas boiler system that can effectively and stably increase the amount of heat recovered from relatively low-temperature exhaust gas.

An exhaust gas boiler system according to one aspect of the present invention includes a first evaporator that evaporates make-up water by exchanging heat with exhaust gas, and a second evaporator that evaporates make-up water by exchanging heat with the exhaust gas that has passed through the first evaporator. an economizer that heats make-up water supplied to the first evaporator and the second evaporator by exchanging heat with the exhaust gas that has passed through the second evaporator; It includes a vapor compressor that compresses vapor, and a vapor header into which the vapor generated in the first evaporator and the vapor compressed by the vapor compressor are introduced.

In the above-mentioned exhaust gas boiler system, the temperature of the exhaust gas is 250° C. or more and 320° C. or less, the vapor pressure of the first evaporator is 0.5 MPa or more and 1.0 MPa or less, and the vapor pressure of the second evaporator is It may be 0.05 MPa or more and 0.2 MPa or less.

In the above-mentioned exhaust gas boiler system, the vapor compressor may be a water injection type vapor compressor including a water supply means for injecting water into the space in which the vapor is compressed.

According to the present invention, the amount of heat recovered from relatively low-temperature exhaust gas can be effectively and stably increased.

1 is a schematic diagram showing the configuration of an exhaust gas boiler system according to an embodiment of the present invention.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of an exhaust gas boiler system 1 according to an embodiment of the present invention.

The exhaust gas boiler system 1 generates steam by recovering heat from exhaust gas discharged by a gas engine (not shown) or the like. The exhaust gas boiler system 1 includes an exhaust gas chamber 10 that guides exhaust gas, a first evaporator 20, a second evaporator 30, an economizer 40, and a second evaporator arranged in order from the upstream side in the exhaust gas chamber 10. The vapor compressor 50 compresses the vapor generated in the first evaporator 30, and a vapor header 60 into which the vapor generated in the first evaporator 20 and the vapor compressed by the vapor compressor 50 are introduced.

The exhaust gas chamber 10 guides the exhaust gas so that the exhaust gas passes through a first evaporator 20, a second evaporator 30, and an economizer 40 in this order, and then is exhausted to the outside through a chimney (not shown) or the like.

The lower limit of the temperature of the exhaust gas introduced into the exhaust gas chamber 10 is preferably 250°C, 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, more preferably 300°C. If the temperature of the exhaust gas introduced into the exhaust gas chamber 10 is equal to or higher than 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, the heat recovery rate is higher than that of a conventional single-stage exhaust gas boiler, in which the heat recovery rate decreases significantly as the exhaust gas temperature decreases. can be achieved. That is, the temperature range is a range in which the exhaust gas boiler system 1 is particularly advantageous compared to conventional exhaust gas boilers.

The first evaporator 20 evaporates makeup water by exchanging heat with exhaust gas. The first evaporator 20 includes a lower header 21 that stores make-up water, a plurality of water pipes 22 extending from the lower header 21 and heated by exhaust gas to evaporate the make-up water inside, and collecting steam generated in the water pipes 22. An upper header 23, a steam-water separator 24 that separates water droplets contained in steam flowing out from the upper header 23, and a replenisher supplied to the lower header 21 so as to maintain the water surface height in the water pipe 22 within a certain range. The boiler may be a once-through boiler including a water supply valve 25 that adjusts the amount of water.

The lower limit of the vapor pressure (gauge pressure) of the first evaporator 20 is preferably 0.5 MPa, 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, more preferably 0.9 MPa. By setting the vapor pressure of the first evaporator 20 to be equal to or higher than the lower limit, the steam generated in the first evaporator 20 can be used in general demand equipment. In addition, by setting the vapor pressure of the first evaporator 20 at or above the lower limit, the temperature of the exhaust gas in the first evaporator 20 is prevented from becoming too low, and heat is efficiently recovered in the second evaporator 30. Therefore, the thermal efficiency of the exhaust gas boiler system 1 as a whole can be improved. Further, by setting the vapor pressure of the first evaporator 20 to be equal to or lower than the upper limit, the amount of heat recovered in the first evaporator 20 can be ensured, and the equipment cost can be prevented from increasing unnecessarily.

The second evaporator 30 exchanges heat with the exhaust gas that has passed through the first evaporator 20 to evaporate makeup water. The second evaporator 30 includes a lower header 31 that stores make-up water, a plurality of water pipes 32 extending from the lower header 31 and heated by exhaust gas to evaporate the make-up water inside, and collecting steam generated in the water pipes 32. An upper header 33, a steam-water separator 34 that separates water droplets contained in steam flowing out from the upper header 33, and a replenisher supplied to the lower header 31 so as to maintain the water surface height in the water pipe 32 within a certain range. The boiler may be a once-through boiler including a water supply valve 35 that adjusts the amount of water.

The lower limit of the vapor pressure of the second evaporator 30 is preferably 0.05 MPa, 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, more preferably 0.15 MPa. By setting the vapor pressure of the second evaporator 30 at or above the lower limit, it is possible to suppress the load on the vapor compressor 50, that is, the power consumption and the associated carbon dioxide emissions, and effectively and stably increase the amount of heat recovery. It is possible to prevent equipment costs from increasing unnecessarily due to enlargement of the vapor compressor 50. Further, by setting the vapor pressure of the second evaporator 30 to be below the upper limit, the amount of heat that can be recovered from the exhaust gas can be sufficiently increased.

The economizer 40 heats 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 by the economizer 40 is distributed to the first evaporator 20 and the second evaporator 30, and the makeup water is supplied to the economizer 40 at a pressure higher than the vapor pressure of the first evaporator 20 by the water supply pump 41. is supplied. For example, when the vapor pressure of the first evaporator is 0.8 MPa, the economizer is pressurized to 0.8 MPa or more, and on the other hand, the exhaust gas temperature passing through the second evaporator and flowing into the economizer is 135°C. descend. Therefore, the water temperature of the economizer does not exceed the saturation temperature, and stable heat recovery without steaming can be performed.

The vapor compressor 50 compresses the vapor generated in the second evaporator 30 to a pressure equal to that of 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 is preferably a water injection type vapor compressor that includes, for example, a pump and includes a water supply means 51 that injects water into a space where vapor is compressed. By injecting water into the space in which steam is compressed in the vapor compressor 50, it is possible to prevent the steam from becoming overheated steam, and also to increase the amount of steam to be discharged by evaporating the injected water. Furthermore, the vapor compressor 50 having the water supply means 51 can operate stably even if the amount of steam generated in the second evaporator 30 fluctuates due to fluctuating exhaust gas temperature, so it always recovers the maximum amount of heat. be able to.

The steam header 60 is a buffer that temporarily stores the steam generated in the first evaporator 20 and the steam compressed by the vapor compressor 50, and stably supplies steam to demand equipment. 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 demand equipment, and the like. The steam header 60 may also be supplied with steam from a normal boiler, such as a fuel-fired boiler. Thereby, even if the amount of exhaust gas supplied to the exhaust gas boiler system 1 and the amount of steam used by the demand facility are not linked, the amount of steam required by the demand facility can be stably supplied.

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 recovers heat from the exhaust gas in the second evaporator 30 to generate steam at a low pressure. Steam is generated, and the low pressure steam is boosted to a desired pressure by a vapor compressor 50. Therefore, the exhaust gas boiler system 1 can recover more thermal energy as usable steam energy, so even if the temperature of the exhaust gas is low and the amount of heat that can be recovered with the conventional exhaust gas boiler system is small, Heat can be recovered effectively and stably.

Although the embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various changes and modifications can be made. For example, in the exhaust gas boiler system according to the present invention, the first evaporator and the second evaporator are not limited to once-through boilers, but may have a configuration such as a water tube boiler that evaporates water within a steam drum.

EXAMPLES Hereinafter, the present invention will be specifically explained based on Examples, but the present invention is not limited to the following Examples.

A simulation was conducted regarding the amount of steam generated for the embodiment of the exhaust gas boiler system having the configuration shown in FIG. 1 and a conventional exhaust gas boiler system having a single-stage evaporator and 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 make-up water was 25°C.

In the exhaust gas boiler system of the example, when the vapor pressure of the first evaporator and the discharge pressure of the vapor compressor are set to 0.78 MPa, and the vapor pressure of the second evaporator is set to 0.10 MPa, the steam generation of the first evaporator is The amount of steam generated by the second evaporator is 1182 kg/h, the power consumption of the vapor compressor is 170 kW, the amount of water injection in the vapor compressor is 117 kg/h (the amount of steam discharged from the vapor compressor is 1300 kg/h) h), and a total of 3,698 kg/h of steam was obtained at the steam header. In addition, the temperature of the exhaust gas that passed 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 amount of steam generated was 2363 kg/h, and the temperature of the exhaust gas that passed through the exhaust gas boiler system was 168 ° C. It became ℃.

The difference in the amount of steam generated between the exhaust gas system of the example and the comparative example is 1335 kg/h, but if this amount of steam is obtained by a boiler using city gas (13A) as fuel, 57 m3N/h of fuel is required. Carbon dioxide emissions will be 172 kg/h. On the other hand, in the exhaust gas system of the example, the amount of carbon dioxide emitted by the vapor compressor, which is calculated by multiplying the electric power consumed by the vapor compressor by the carbon dioxide emission coefficient of the electric power company, is 83 kg/h. Therefore, the exhaust gas system of the example can reduce carbon dioxide emissions by 52% compared to the comparative example.

Table 1 below shows the results of a simulation in which 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 economizer outlet, the total steam amount (the sum of the first evaporator evaporation amount and the vapor compressor discharge amount), and the vapor compressor power consumption, respectively. It is expressed as a percentage of the case where the vapor pressure of the evaporator is 0.10 MPa. Further, the first evaporator evaporation amount and the vapor compressor discharge vapor amount indicate the breakdown of the total vapor amount (percentage).

When the vapor pressure of the second evaporator is lowered, the vapor pressure of the second evaporator is reduced, thereby reducing the exhaust gas temperature at the outlet of the second evaporator, the water temperature at the outlet of the economizer, and the amount of evaporation from the first evaporator. On the other hand, in the second evaporator, as the vapor pressure decreases, the exhaust gas temperature difference between the inlet and the outlet increases, and the amount of vapor in the second evaporator increases. Therefore, when the vapor pressure of the second evaporator is lowered, the amount of evaporation of the second evaporator increases, and therefore the amount of evaporation of the entire system increases. Therefore, the vapor pressure of the second evaporator is preferably 0.2 MPa or less to ensure a sufficient amount of heat recovery in the second evaporator. At this time, the exhaust gas temperature at the outlet of the second evaporator becomes 150°C or lower, and even if the water flow to the ecomizer stops, the feed water temperature does not exceed the saturated vapor pressure and boiling does not occur, so steam is stably supplied. can. In addition, since there is no need to take boiling into account, there is no increase in pressure drop in the pipe, no erosion, etc., and there is more leeway in designing the heat transfer surface of the economizer. In addition, the lower limit of the vapor pressure of the second evaporator is preferably 0.05 MPa, which does not excessively increase the load on the vapor compressor and thereby avoid excessively increasing carbon dioxide generation and equipment costs due to power consumption of the vapor compressor. .

1 Exhaust gas boiler system 10 Exhaust gas chamber 20 First evaporator 30 Second evaporator 40 Economizer 50 Vapor compressor 60 Steam header 21 Lower header 22 Water pipe 23 Upper header 24 Steam water separator 25 Water supply valve 31 Lower header 32 Water pipe 33 Upper header 34 Steam water separator 35 Water supply valve 41 Water supply pump 51 Water supply means

Claims (3)

a first evaporator that evaporates make-up water by exchanging heat with exhaust gas;
a second evaporator that evaporates makeup water by exchanging heat with the exhaust gas that has passed through the first evaporator;
an economizer that heats make-up water supplied to the first evaporator and the second evaporator by exchanging heat with the exhaust gas that has passed through the second evaporator;
a vapor compressor that compresses the vapor generated in the second evaporator;
a steam header into which the steam generated in the first evaporator and the steam compressed by the vapor compressor are introduced;
Exhaust gas boiler system. The temperature of the exhaust gas is 250°C or more and 320°C or less,
The vapor pressure of the first evaporator is 0.5 MPa or more and 1.0 MPa or less,
The vapor pressure of the second evaporator is 0.05 MPa or more and 0.20 MPa or less,
The exhaust gas boiler system according to claim 1. The exhaust gas boiler system according to claim 1 or 2, wherein the vapor compressor is a water injection type vapor compressor equipped with water supply means for injecting water into a space for compressing vapor.

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