Boiler system

Abstract

To provide a boiler system capable of enhancing a CO2 concentration of exhaust gas from a small boiler and having improved energy efficiency.SOLUTION: A boiler system 100 includes: a boiler 10 that heats feed water W1; a gas cooler 14 that cools exhaust gas GE from the boiler by using cooling water W2; an exhaust line 16 for discharging the exhaust gas; a circulation gas line 20 branched from the exhaust line, the circulation gas line 20 having an oxygen supply line 30 and an atmospheric air supply line 26 connected thereto and supplying the exhaust gas to the boiler together with oxygen gas as a combustion supporting gas GS; a combustion supporting gas heating device 42 for heating the combustion supporting gas in the circulation gas line; and a water-cooled type heat pump 40 that is interposed between the gas cooler and the combustion supporting gas heating device and uses heat absorbed from the exhaust gas by the cooling water of the gas cooler as a heat source to heat the combustion supporting gas in the combustion supporting gas heating device.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a boiler system, and more particularly to a boiler system capable of increasing the CO2 concentration in exhaust gas.

Background Art

[0002] In recent years, there has been a demand for a significant reduction in the emissions of CO2 (carbon dioxide) gas, which is a cause of global warming. For this purpose, various systems for separating and recovering CO2 in exhaust gas discharged from combustion devices such as boilers by chemical adsorption methods, solid absorption methods, etc. have been developed. However, since the CO2 concentration in exhaust gas is usually as low as about 10%, there is a problem that the recovery efficiency of the CO2 separation and recovery device is low.

[0003] On the other hand, in a coal-fired power plant, a method has been proposed to increase the CO2 concentration in exhaust gas by performing oxygen combustion instead of conventional air combustion, and a demonstration test of CCS (Carbon dioxide Capture and Storage) using oxygen combustion has also been carried out. Oxygen combustion is a method of burning fuel by supplying oxygen gas instead of air as an oxidant or a supporting combustion gas, and the main component of the exhaust gas can be made into CO2 gas.

[0004] However, when using high-concentration oxygen gas, since the flame temperature becomes too high, there is a risk of damaging the burner and the boiler. For this reason, a technique is known in which a part of the exhaust gas is used to mix the produced oxygen and the recycled exhaust gas (mainly CO2 gas) to supply a supporting combustion gas with a lower oxygen concentration to the boiler.

[0005] In addition, Patent Document 1 discloses a boiler plant for coal-fired power generation that switches between oxygen combustion and air combustion. In this boiler plant, during boiler startup before shifting to oxygen combustion, air combustion can be performed by supplying air instead of oxygen gas and recycled exhaust gas. After it becomes possible to produce oxygen gas using the power obtained by air combustion, the air supply system is closed, and oxygen gas and recycled exhaust gas are supplied to the boiler, enabling an easy shift to oxygen combustion of coal.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] As described above, by performing oxygen combustion while recirculating a part of the exhaust gas, it is possible to increase the CO2 concentration in the exhaust gas while preventing damage to equipment, and efficiently recover and store CO2. However, in order to recirculate dry exhaust gas, it is preferable that the exhaust gas be cooled to, for example, 50°C or lower by a gas cooler or the like, and the contained water vapor be discharged as drain. The cooling water of the gas cooler used for such cooling of the exhaust gas is supplied from, for example, a cooling tower or the like, and the heat absorbed by the cooling water is released into the atmosphere. Therefore, there is room for improving energy efficiency in existing boiler systems.

[0008] The present invention has been made to solve the above problems, and an object thereof is to provide a boiler system that can improve the CO2 concentration in exhaust gas and improve energy efficiency even when using a small boiler.

Means for Solving the Problems

[0009] A boiler system according to an embodiment of the present invention includes a boiler that heats feed water by burning fuel gas, a gas cooler configured to cool exhaust gas from the boiler using cooling water, an exhaust line that exhausts the exhaust gas from the boiler, and a circulation gas line that branches from the exhaust line and to which an oxygen supply line and an air supply line are connected, and that supplies the exhaust gas as a supporting combustion gas to the boiler together with at least one of air and oxygen gas, a supporting combustion gas heating device configured to heat the supporting combustion gas passing through the circulation gas line, and a water-cooled heat pump interposed between the gas cooler and the supporting combustion gas heating device, the water-cooled heat pump being configured to heat the supporting combustion gas in the supporting combustion gas heating device provided as a heating load using heat absorbed by the cooling water of the gas cooler from the exhaust gas as a heat source.

[0010] In one embodiment, the boiler system is configured to control the cooling temperature of the exhaust gas in the gas cooler within a set range, while not controlling the heating temperature of the supporting combustion gas in the supporting combustion gas heating device.

[0011] In one embodiment, the water-cooled heat pump is configured to warm circulating hot water using the heat absorbed by the cooling water, and the hot water warmed in the water-cooled heat pump is sent to the supporting combustion gas heating device to heat the supporting combustion gas, and is configured to return to the water-cooled heat pump after heating the supporting combustion gas.

[0012] In one embodiment, the boiler system further includes an additional heating load provided separately from the supporting combustion gas heating device, connected to the water-cooled heat pump, and configured to heat a medium externally used by heat absorbed by the cooling water from the exhaust gas.

[0013] In one embodiment, the boiler system further includes an economizer that preheats the feed water to the boiler by the heat of the exhaust gas from the boiler, and the gas cooler is arranged to cool the exhaust gas on the downstream side of the economizer.

[0014] In one embodiment, the boiler system further includes an air preheater interposed between the economizer and the gas cooler, and the air preheater is configured to heat the combustible gas passing through the circulation gas line by the exhaust gas from the economizer.

[0015] In one embodiment, the fuel gas is either city gas or LP gas, and the boiler is either a once-through boiler or a hot water boiler.

Advantages of the Invention

[0016] According to the boiler system according to the embodiment of the present invention, it can be applied even when a small boiler is used, the CO2 concentration in the exhaust gas can be increased, and the energy efficiency can be improved.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0018] The applicant of the present application disclosed a boiler system in International Patent Application PCT / JP2023 / 26068 (International filing date: July 14, 2023) that can increase the CO2 concentration in the exhaust gas even in relatively small once-through boilers and hot water boilers in order to reduce CO2 emissions.

[0019] The above boiler system is configured to stably perform oxygen combustion and air combustion even in small boilers, and can stably perform oxygen combustion even in small boilers with large output fluctuations. The supply amount of oxygen as a combustion-supporting gas can be controlled precisely and with high responsiveness. In this boiler system, the supply of oxygen is carried out using a main line provided with an on-off valve and a sub-line provided with a valve with adjustable opening degree, and a desired flow rate can be supplied at high speed and with high precision.

[0020] Also, in the above boiler system, the exhaust gas from the boiler is cooled by a gas cooler to dry exhaust gas, mixed with oxygen gas and included in the combustion-supporting gas, and after reducing the oxygen concentration, it is supplied to the boiler. In the gas cooler, for example, the exhaust gas is cooled so that the outlet temperature is about 30 to 50 °C, and the steam contained in the exhaust gas is drained and discharged. Thereby, dry exhaust gas suitable for mixing with the combustion-supporting gas can be obtained, and good oxygen combustion can be performed.

[0021] FIG. 1 shows the cooling system of the gas cooler in a comparative example boiler system having the above configuration. In the comparative example, the cooling water W2 used in the gas cooler 90 is provided using a cooling water circulation line including a cooling tower 92, which is provided in a system separate from the supply system of the boiler feed water.

[0022] In the gas cooler 90, the exhaust gas GE discharged from a boiler (not shown) flows in and is cooled. The cooling water W2 used for cooling in the gas cooler 90 is returned to the cooling tower 92 by the pump 94. In the cooling tower 92, the temperature of the cooling water W2 is lowered by releasing the heat absorbed by the cooling water W2 to the atmosphere. The cooling tower 92 is configured to lower the cooling water temperature, for example, by spraying the cooling water W2 and bringing it into contact with the outside air flow.

[0023] The exhaust gas GE cooled by the cooling water W2 in the gas cooler 90 has water vapor condensed and is recovered as drain in the neutralization device 96. In this way, by passing through the gas cooler 90, a drier exhaust gas GE' can be obtained. The outlet temperature T1 of the exhaust gas GE' is set to, for example, 30°C to 50°C.

[0024] However, in the boiler system of the comparative example shown in FIG. 1, since the cooling water W2 that has absorbed heat from the exhaust gas GE is radiated heat in the cooling tower 92 and the heat is discarded to the outside, there is room for improving the energy efficiency. Therefore, in the embodiment of the present invention described below, the boiler system is configured so that the heat absorbed by the cooling water of the gas cooler can be utilized in the system. Hereinafter, specific embodiments will be described.

[0025] FIG. 2 shows a boiler system 100 according to Embodiment 1 of the present invention. The boiler system 100 includes a combustion boiler 10 having a burner 11 that burns fuel gas GF, an economizer (fuel-saving device) 12 through which the exhaust gas GE from the boiler 10 passes, a gas cooler 14 for cooling the exhaust gas GE that has passed through the economizer 12, and an exhaust line 16 for exhausting the exhaust gas GE cooled by the gas cooler 14. In the figure, the gas flow path is indicated by a broken line, and the path of the cooling water W2 (the part other than the heat exchanger) is indicated by a thick solid line.

[0026] The boiler 10 used in this embodiment is a relatively small-scale once-through boiler or hot-water boiler, for example, and the fuel gas GF used is, for example, city gas (or gas mainly composed of methane) or LP gas (or gas mainly composed of propane or butane). The boiler system 100 is configured to be able to generate and supply steam or hot water using the relatively small-scale boiler 10.

[0027] The boiler 10 can heat the feed water W1 to the boiler 10 by burning the fuel gas GF with the burner 11, and generate hot water or steam. The economizer 12 can preheat the feed water W1 before supplying it to the boiler 10 by utilizing the heat of the exhaust gas GE from the boiler 10, and can save the consumption amount of the fuel gas GF.

[0028] The gas cooler 14 is configured to cool the exhaust gas GE by performing heat exchange with the supplied cooling water W2 using various heat exchangers (for example, plate heat exchangers or tube heat exchangers). The gas cooler 14 is configured to be able to cool until the outlet temperature T1 of the cooled exhaust gas GE' becomes, for example, about 30 to 50°C, particularly about 40°C. Thereby, the steam contained in the exhaust gas GE can be drained and discharged, and a dry exhaust gas GE' can be obtained.

[0029] In particular, in the case of the relatively small-scale boiler 10 using city gas or LP gas as the fuel gas, although water vapor is generated by combustion, since the exhaust gas GE does not contain corrosive gases such as sulfur components, even if it is cooled to near room temperature, no major problems occur. Therefore, by cooling with the gas cooler 14, a dry exhaust gas with an increased CO2 concentration can be obtained without any particular problems. And in the boiler system 100, since dry exhaust gas is mixed with the support combustion gas for combustion in oxygen combustion, the adverse effect on the burner combustion due to the moisture in the recirculation gas can be avoided. In this embodiment, although a system for utilizing the heat absorbed by the cooling water W2 is connected to the gas cooler 14, this aspect will be described later.

[0030] The blowdown water from the boiler 10, the drain (wastewater) from the economizer 12, and the drain from the gas cooler 14 are sent to the neutralization device 18. The neutralization device 18 neutralizes the wastewater by various methods, adjusts it to a pH value conforming to the industrial wastewater standards, and then discharges it.

[0031] In the gas cooler 14, a large amount of drain is generated during the exhaust gas cooling. In order to efficiently move and drip this drain to the bottom of the gas cooler 14, it is preferable that the exhaust gas GE flows downward from the upper part to the bottom of the gas cooler 14. On the other hand, the cooling water W2 preferably flows upward to prevent the generation of air pockets. Further, since the drain absorbs CO2 and the like in the exhaust gas and becomes acidic, it is preferable that the gas cooler 14 is configured using an acid-resistant material. In addition, the gas cooler 14 is preferably configured using a material having a suitable heat-resistant temperature in consideration of the inlet exhaust gas temperature when the economizer 12 is operated in bypass.

[0032] In the boiler system 100 of the present embodiment, the exhaust line 16 is provided to discharge the exhaust gas GE' cooled by the gas cooler 14 from the flue 16A to the atmosphere or transfer it to the CO2 recovery facility via the CO2 recovery line 16B.

[0033] Further, a branched circulating gas line 20 is connected to the exhaust line 16. The circulating gas line 20 is configured to be able to circulate the exhaust gas GE' cooled by the gas cooler 14 to the boiler 10 as the supporting combustion gas GS using the push-in fan (supporting combustion gas fan) 22 provided near the boiler. A motor-driven damper 24 for drawing in the circulating gas is provided in the circulating gas line 20, and by adjusting the opening degree of the damper 24 for drawing in the circulating gas, the exhaust gas GE can be supplied to the boiler 10 at an arbitrary flow rate.

[0034] The circulation gas line 20 is connected to the air supply line 26 and the oxygen supply line 30. The boiler 10 can supply the air AIR, oxygen gas O2 and / or the exhaust gas GE' drawn from the exhaust line 16 as the supporting combustion gas GS. In this configuration, the boiler 10 can perform both air combustion and oxygen combustion. Note that the oxygen supply line 30 may be connected to the upstream side of the air supply line 26, or the oxygen supply line 30 and the air supply line 26 may be connected to the circulation gas line 20 using a common line.

[0035] In this way, air with controllable flow rate can be supplied to the boiler 10 as the supporting combustion gas GS via the circulation gas line 20. Therefore, when it is difficult to stably perform oxygen combustion, such as during boiler startup, the boiler can be operated by air combustion. Also, after the boiler starts up and combustion becomes stable and the stable circulation supply of the exhaust gas GE becomes possible, the combustion can be switched to oxygen combustion to improve the CO2 concentration in the exhaust gas.

[0036] Here, the oxygen supply line 30 is composed of a main line 30A and a sub-line 30B connected in parallel. In the illustrated embodiment, the main line 30A and the sub-line 30B are connected to the same oxygen supply source, but they may be connected to different oxygen supply sources. As the oxygen supply source, for example, oxygen gas generated from air by the pressure swing adsorption method (PSA) can be used.

[0037] An on-off valve 32 is provided in the main line 30A of the oxygen supply line 30. On the other hand, a valve with adjustable opening (typically a proportional valve) 34 is provided in the sub-line 30B. In this embodiment, the on-off valve 32 is composed of a solenoid valve (solenoid valve S), and the valve with adjustable opening 34 is composed of an electric valve driven by a motor M.

[0038] The on-off valve 32 may be constituted by, for example, an air-operated valve (AOV). The main line 30A may be constituted by a plurality of parallel lines each provided with an on-off valve 32. In this case, by controlling the opening and closing of the on-off valves 32 of the parallel lines, a flow rate control with a high step response can be realized. Further, in the sub-line 30B, a manual valve 38 may be provided on at least one of the primary side or the secondary side of the variable-opening valve 34. The manually-operated valve 38 arranged in this way can be used to adjust the maximum control flow rate in the sub-line 30B.

[0039] From the main line 30A, it is possible to supply, for example, 80 to 90% of the oxygen required for combustion that matches the components and flow rate of the fuel gas GF. From the sub-line 30B, it is possible to supply, for example, 0 to 50% of the oxygen required for theoretical combustion. The flow rate control of the oxygen gas in each line is performed so that this can be achieved. The oxygen gas supplied from the oxygen supply line 30 is mixed with the exhaust gas GE introduced by opening the circulation gas intake damper 24, and is supplied to the boiler 10 as a combustion-supporting gas GS with an adjusted oxygen concentration.

[0040] In the main line 30A, each solenoid valve constituting the on-off valve 32 has a sufficiently high responsiveness compared to an electric valve driven by a motor (variable-opening valve 34). Therefore, in order to match the combustion pattern, the opening control of each solenoid valve can be performed at high speed, and thereby oxygen gas can be supplied at a flow rate that can prevent the occurrence of combustion failure. Further, since the on-off valves 32 are provided in a plurality of lines and the flow rate is controlled by controlling their opening and closing, it is relatively easy to realize an instantaneous switching to a large flow rate or a small flow rate.

[0041] In particular, the output adjustment of a small boiler often needs to be switched in a very short time according to the requirements on the heat demand side. Also, since combustion is carried out with a high-output burner in a narrow combustion chamber, the amount of oxygen required for fuel combustion changes in a short time with each output switch. If the oxygen supply is delayed, it will lead to incomplete combustion, vibration combustion, and even misfire. In contrast, by supplying oxygen from the main line 30A with high responsiveness, it is possible to reliably supply the minimum amount of oxygen that does not lead to combustion failure in advance. Furthermore, by using the sub-line 30B having the freely adjustable valve 34, the oxygen concentration in the support combustion gas GS formed by the mixed gas of the oxygen gas O2 from the oxygen supply line 30, the exhaust gas from the exhaust line 16, and the GE can be adjusted more accurately by the total flow rate of the oxygen gas. The oxygen concentration of the support combustion gas GS is stably maintained, for example, at a ratio of about 21% (e.g., 20 - 22%) equivalent to the oxygen concentration in the atmosphere.

[0042] Moreover, the boiler system 100 of the present embodiment includes an oxygen sensor 36a for measuring the oxygen concentration of the support combustion gas GS. As the oxygen sensor 36a, for example, a galvanic cell type sensor is preferably used, but various types of sensors can be used as long as they can measure the oxygen concentration. Also, an oxygen concentration control circuit 36b is connected to the oxygen sensor 36a. The oxygen concentration control circuit 36b is configured to be able to perform feedback control on the freely adjustable valve 34 provided in the sub-line 30B of the oxygen supply line 30 based on the output of the oxygen sensor 36a. In this configuration, by using the oxygen concentration control circuit 36b to perform feedback control on the freely adjustable valve 34 so that the difference between the set concentration and the measured concentration approaches 0, it is possible to continuously supply the support combustion gas GS having a desired set oxygen concentration to the burner 11.

[0043] In this way, the boiler system 100 can supply the combustible gas GS, which is a mixture of oxygen gas and exhaust gas (mainly CO2), to the boiler 10 through the circulation gas line 20, so that oxygen combustion can be stably carried out. During the period of oxygen combustion, while the exhaust gas mixed with oxygen gas is supplied to the boiler 10 as the combustible gas GS, usually, the damper 28 for atmospheric intake is closed and the atmospheric supply line 26 is maintained in a closed state. When switching from air combustion to oxygen combustion, in synchronization with the closing operation of the damper 28 for atmospheric intake, the opening operation of the damper 24 for drawing in the circulation gas and the on-off valve 32 in the main line 30A is carried out. At the same time, the operation of adjusting the oxygen concentration by adjusting the opening degree of the variable-opening valve 34 in the sub-line 30B is also started. The boiler system 100 closes the damper 28 of the atmospheric supply line 26 and controls the opening and closing of the on-off valve 32 and the opening degree of the variable-opening valve 34 of the oxygen supply line 30, so as to adjust the oxygen concentration in the mixed gas of oxygen gas O2 and exhaust gas GE from the oxygen supply line, and then supply this as the combustible gas GS to the boiler 10 to carry out oxygen combustion.

[0044] Therefore, in the boiler system 100, it is possible to smoothly shift from air combustion to oxygen combustion at the time of boiler startup, and also to quickly switch the oxygen supply amount so as to conform to the output change characteristics of the small boiler after the oxygen combustion switch, preventing the occurrence of combustion failures such as incomplete combustion and misfire, and discharging exhaust gas with a high CO2 concentration.

[0045] Note that the configuration of the combustion system in the boiler system 100 described above is substantially the same as the configuration disclosed in the international patent application PCT / JP2023 / 26068 by the applicant of the present application. However, in the boiler system 100 of the present embodiment, a configuration for improving the energy efficiency by utilizing the heat absorbed by the cooling water W2 used in the gas cooler 14 is added. This will be specifically described below.

[0046] As shown in FIG. 2, the cooling water W2 used in the gas cooler 14 is not cooled using a cooling tower 92 as in the comparative example (see FIG. 1), but is configured to be cooled using a water-cooled (or water heat source) heat pump (WHP) 40. The water-cooled heat pump 40 is configured to absorb heat from the inflowing cooling water W2, cool it, and circulate it to the gas cooler 14. The circulation of the cooling water W2 between the gas cooler 14 and the water-cooled heat pump 40 is performed by a pump 44.

[0047] In addition, a supplementary fuel gas heating device 42 to which hot water HW2 is supplied is connected to the water-cooled heat pump 40. The supplementary fuel gas heating device 42 is provided in the circulation gas line 20 and is used to raise the temperature of the supplementary fuel gas GS passing therethrough. The circulation of the hot water HW2 between the water-cooled heat pump 40 and the supplementary fuel gas heating device 42 is performed by a pump 46. The supplementary fuel gas heating device 42 is constituted by a heat exchanger of any mode for raising the temperature of the supplementary fuel gas GS.

[0048] FIG. 3 is an exemplary configuration diagram of a refrigerant circuit included in the water-cooled heat pump 40. In this refrigerant circuit, a compressor 40a and an expansion valve 40b are provided. Further, a heat exchanger with the cooling water W2 functioning as an evaporator 40c is provided in the middle of the path from the expansion valve 40b to the compressor 40a, and a heat exchanger with the hot water HW2 functioning as a condenser 40d is provided in the middle of the path from the compressor 40a to the expansion valve 40b.

[0049] The water-cooled heat pump 40 is configured to heat the hot water HW2 using the cooling water W2 heated by the exhaust gas GE in the gas cooler 14 as a heat source. More specifically, the refrigerant flowing through the circuit absorbs heat from the cooling water W2 (cools the cooling water W2) in the evaporator 40c and rises in temperature, typically vaporizing. From the evaporator 40c, the refrigerant gas RG flows into the compressor 40a, where it is compressed into a high-temperature and high-pressure refrigerant gas RG'.

[0050] Also, the high-temperature and high-pressure refrigerant gas RG' transfers heat to the warm water HW2 (heating the warm water HW2) in the condenser 40d, causing its temperature to drop, and typically condenses to be converted into high-pressure liquid refrigerant RL or low-temperature refrigerant gas. The high-pressure liquid refrigerant RL is decompressed by the expansion valve 40b and converted into low-temperature and low-pressure refrigerant liquid RL'. Also, the low-temperature and low-pressure refrigerant liquid RL' is used for cooling the cooling water W2 in the evaporator 40c. By repeating such a cycle, the water-cooled heat pump 40 can dissipate heat in the condenser 40d by an amount equal to the electric power used to operate the compressor 40a for heat absorption in the evaporator 40c, and can efficiently cool the cooling water W2 and heat the warm water HW2.

[0051] Note that, for the sake of simplicity in the above description, it has been described that the refrigerant vaporizes in the evaporator 40c and condenses in the condenser 40d. However, depending on the temperature, phase transitions may not necessarily occur in the evaporator 40c and the condenser 40d.

[0052] Referring again to FIG. 2, by using the water-cooled heat pump 40 as described above, the cooling water W2 from the gas cooler 14 can be cooled, and the warm water HW2 can be generated by utilizing the heat absorbed from the cooling water W2. Also, the warm water HW2 is sent to the support combustion gas heating device 42 that forms a heating load and can be used to heat the support combustion gas GS. Thereby, the temperature of the support combustion gas GS can be raised in advance, so that the combustion efficiency in the boiler 10 can be improved and the overall energy efficiency of the boiler system 100 can be improved.

[0053] Note that in the circulation gas line 20, the cooled exhaust gas GE' is mixed with the support combustion gas GS, but its flow rate is adjusted by a damper or the like, and the mixing ratio with the oxygen gas also changes by control, and the temperature of the support combustion gas GS also fluctuates accordingly. And the support combustion gas GS is preheated in the support combustion gas heating device 42, but it is only secondarily heated to improve the combustion efficiency, and the heating temperature of the support combustion gas can be left to chance.

[0054] On the other hand, in the gas cooler 14, since it is required to obtain dry gas, the most important purpose in the system is to cool the exhaust gas GE in the gas cooler 14. Therefore, rather than aiming for sufficient heating in the auxiliary fuel gas heating device 42, it is preferable that the cooling system of the cooling water W2 is designed so that the cooling of the gas cooler 14 by the cooling water W2 is carried out sufficiently and appropriately.

[0055] From this, in the present embodiment, the boiler system 100 controls the cooling temperature (outlet temperature T1) of the exhaust gas GE in the gas cooler 14 within a set range such as, for example, 30°C to 50°C (particularly 40°C), while on the other hand, it is configured not to control the heating temperature of the auxiliary fuel gas.

[0056] FIG. 4 shows the cooling system of the cooling water W2 in another aspect of the boiler system 101. Note that since the configuration related to the combustion system is the same as that of the embodiment shown in FIG. 2, these configurations (the boiler, the oxygen supply line and the air supply line in the circulation gas line 20, etc.) are omitted in FIG. 4.

[0057] In the present embodiment, an additional heating load 50 is connected to the circulation path of the hot water HW2 heated by the water-cooled heat pump 40. The additional heating load 50 includes, in the illustrated aspect, a heat exchanger 52 and a hot water storage tank 54. The heat exchanger 52 is arranged so that the hot water HW2 flows when the valve 58 is closed, and can give heat to the water and hot water (media used externally) stored in the hot water storage tank 54 by the hot water HW2 and heat it.

[0058] The hot water storage tank 54 is supplied with the feed water W3 to be heated as needed, and the water HW3 heated in the hot water storage tank 54 is sent to external using devices as needed. The using devices are, for example, hot water supply facilities and boiler makeup water tanks. Also, the circulation of water between the hot water storage tank 54 and the heat exchanger is carried out by a pump 56. In this way, by providing the additional heating load 50, the heat obtained from the cooling water W2 as a heat source can be more reliably consumed on the heating load side.

[0059] Here, in the heat pump, the heating-side heat quantity corresponds to the heat absorption quantity from the cooling water W2 plus the electric power (input energy) for driving the compressor 40a. Therefore, when the heating load is small, heat cannot be fully consumed, the heat absorption quantity in the heat pump also decreases, and there is a possibility that the cooling water W2 cannot be sufficiently cooled.

[0060] On the other hand, by providing the additional heating load 50 as described above and using the additional heating load 50 as needed, the heat absorption of the cooling water W2 in the water-cooled heat pump 40 can be sufficiently performed, the cooling performance of the cooling water W2 can be ensured, and the outlet temperature of the exhaust gas GE' discharged from the gas cooler 14 can be more stably decreased to a desired temperature. Also, not only the heating of the combustion-supporting gas but also the stored water heated in the hot water storage tank 54 can be utilized externally.

[0061] FIG. 5 is a diagram for explaining the path of the exhaust gas GE in the boiler system 102 in yet another embodiment. In the boiler system 102 as well, similar to the embodiment shown in FIG. 1, the circulation gas line 20 is provided with an air supply line 26, an oxygen supply line 30, etc., but these are omitted in FIG. 5 for simplification.

[0062] The difference between the boiler system 102 and the boiler system 100 shown in FIG. 1 is that the exhaust gas GE discharged from the economizer 12 is sent to the air preheater 60 and used for heating the combustion-supporting gas GS, and then sent to the gas cooler 14. In this way, by using the heat of the exhaust gas GE for heating the combustion-supporting gas GS before cooling in the gas cooler 14, the cooling load is reduced, so that the facility (such as the water-cooled heat pump 40) for cooling the gas cooler 14 or the cooling water W2 of the gas cooler 14 can be miniaturized.

[0063] As described above, various boiler systems according to embodiments of the present invention have been explained, but various modifications are possible. For example, in the boiler system shown in FIG. 1, the economizer 12 does not necessarily have to be provided. Further, the boiler system 101 shown in FIG. 4 and the boiler system 102 shown in FIG. 5 may be combined to include an air preheater 60 on the circulation gas line 20 for introducing exhaust gas from the boiler 10 or the economizer 12, and an additional heating load 50 may be provided in the cooling system of the cooling water W2.

Industrial Applicability

[0064] The boiler system according to the embodiment of the present invention is suitably used, for example, in a small steam boiler or a hot water heater to increase the CO2 concentration in the exhaust gas while continuing stable combustion.

Explanation of Signs

[0065] 10 Boiler 12 Economizer 14 Gas cooler 16 Exhaust line 18 Neutralization device 20 Circulation gas line 22 Push-in fan (support combustion gas fan) 24 Damper for drawing in circulation gas 26 Atmosphere supply line 28 Damper for sucking in atmosphere 30 Oxygen supply line 30A Main line 30B Sub-line 32 On-off valve (solenoid valve) 34 Valve with adjustable opening (motorized valve) 36a Oxygen sensor 36b Oxygen concentration control circuit 38 Manual valve 40 Water-cooled heat pump (WHP) 42 Support combustion gas heating device 50 Additional heating load 52 Heat exchanger 54 Hot water storage tank 60 Air preheater 100 Boiler System GE Exhaust Gas GF Fuel Gas GS Support Combustible Gas W1 Feed Water W2 Cooling Water HW2 Warm Water

Claims

1. A boiler that heats feed water by burning fuel gas, A gas cooler configured to cool the exhaust gas from the boiler using cooling water, An exhaust line for exhausting the exhaust gas from the boiler, A circulation gas line branched from the exhaust line, to which an oxygen supply line and an air supply line are connected, and configured to supply the exhaust gas to the boiler as auxiliary combustion gas together with at least one of air and oxygen gas, An auxiliary combustion gas heating device configured to heat the auxiliary combustion gas passing through the circulation gas line, A water-cooled heat pump interposed between the gas cooler and the auxiliary combustion gas heating device, configured to heat the auxiliary combustion gas in the auxiliary combustion gas heating device provided as a heating load, using the heat absorbed by the cooling water of the gas cooler from the exhaust gas as a heat source, A boiler system comprising the above.

2. The boiler system according to claim 1, wherein the cooling temperature of the exhaust gas in the gas cooler is controlled within a set range, while the heating temperature of the auxiliary combustion gas in the auxiliary combustion gas heating device is not controlled.

3. The water-cooled heat pump is configured to warm the circulating hot water using the heat absorbed by the cooling water, The boiler system according to claim 1 or 2, wherein the hot water warmed in the water-cooled heat pump is sent to the auxiliary combustion gas heating device to heat the auxiliary combustion gas, and is configured to return to the water-cooled heat pump after heating the auxiliary combustion gas.

4. The boiler system according to claim 1 or 2, further comprising an additional heating load provided separately from the auxiliary combustion gas heating device, connected to the water-cooled heat pump, and configured to heat a medium used externally by the heat absorbed by the cooling water from the exhaust gas.

5. The boiler system according to claim 1 or 2, further comprising an economizer configured to preheat the feed water to the boiler by the heat of the exhaust gas from the boiler, and the gas cooler is arranged to cool the exhaust gas on the downstream side of the economizer.

6. An air preheater interposed between the economizer and the gas cooler, further comprising an air preheater configured to heat the combustible gas passing through the circulation gas line with exhaust gas from the economizer, the boiler system according to claim 5.

7. The fuel gas is either city gas or LP gas, and the boiler is either a once-through boiler or a hot water boiler, the boiler system according to claim 1 or 2.

Images