JP2014059104A - Oxyfuel combustion boiler system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxyfuel combustion boiler system capable of stable operation by preventing water condensation of exhaust gas in an exhaust gas circulation system to eliminate problems caused by condensed water.SOLUTION: An oxyfuel combustion boiler system comprises: a dust collecting apparatus 5 that collects dust and soot in exhaust gas discharged from a boiler 1; a wet desulfurization apparatus 7 that removes sulphur oxide in exhaust gas discharged from the dust collecting apparatus; an exhaust gas circulation system that receives exhaust gas from an exhaust gas intake port 20 disposed on an exhaust gas duct on the outlet side of the dust collecting apparatus or the wet desulfurization apparatus, and circulates the exhaust gas as a part of gas for combustion in the boiler; an air separation apparatus 30 that supplies oxygen-rich gas. In the oxyfuel combustion boiler system, the gas for combustion is generated by mixing the exhaust gas circulated by the exhaust gas circulation system with the oxygen-rich gas supplied from the air separation apparatus. An exhaust gas cooling apparatus 22, which cools at least the exhaust gas received in the exhaust gas circulation system by gas-liquid contact, is included in the oxyfuel combustion boiler system.

Description

  The present invention relates to an oxyfuel boiler system, and more specifically to a technique for avoiding adverse effects such as moisture concentrated by recirculation of exhaust gas mixed with oxygen-rich gas.

  An oxyfuel boiler is a combustion system that uses oxygen instead of air as the combustion gas used for fuel combustion. However, if the oxygen concentration of the combustion gas is high, the combustion temperature becomes too high. A combustion gas is used that is partially circulated and mixed with an oxygen-rich gas containing oxygen as a main component to adjust the oxygen concentration to a low level (for example, Patent Document 1 and Patent Document 2). As in the case of the air combustion type, the combustion gas is referred to as an after-gas port or an overgas port for primary combustion, secondary and tertiary combustion, for example, for pulverized coal supplied to a boiler burner. Used as a gas to be blown downstream of the combustion flame.

In the oxyfuel boiler system, most of the exhaust gas generated by combustion is H ₂ O and CO ₂ , and after exhaust gas purification such as denitration, dedusting and desulfurization is performed, the exhaust gas is compressed, for example, by a CO ₂ recovery facility. After being condensed and recovered, CO ₂ can be liquefied by further compression and recovered efficiently. Therefore, the feature is that CO ₂ emission to the environment can be prevented. In addition, it is also known that the CO ₂ recovery equipment recovers by absorbing CO _{2 in} an absorption liquid instead of the compression method.

However, in the oxyfuel boiler system, the water concentration and the SO ₃ concentration become higher than those of a normal air combustion boiler by recirculating the exhaust gas. For example, even when high-concentration sulfur coal is used as the fuel, the moisture concentration of the exhaust gas is about 10 wt% and the SO ₃ concentration is about 50 ppm at the highest in the air combustion boiler. On the other hand, in the oxyfuel boiler, although depending on the exhaust gas recirculation ratio, the moisture concentration of the exhaust gas is about 30 wt% and the SO ₃ concentration is about 60 to 300 ppm, which is concentrated about three times that of the air combustion type. there is a possibility.

As described above, since the dew point of water increases as the water concentration increases, the water easily condenses in the exhaust gas circulation system that circulates the exhaust gas. For example, even if the exhaust gas has the same temperature of 170 ° C., the water dew point is 50 ° C. when the water content is 10 wt%, but the water dew point is 77 ° C. when the water content is 30 wt%. Water condensation will occur at higher temperatures. When moisture condenses, SO ₂ in the circulating exhaust gas dissolves in the condensed water to become an acidic solution, and SO ₃ mists to cause acid corrosion of the exhaust gas circulation equipment and the like, for example, pulverization to pulverize coal There is a risk of clogging the device. Similarly, in the exhaust gas treatment system from the boiler to the wet desulfurization apparatus, when SO ₃ is misted along with the condensation of moisture, the gas-gas heat exchanger (GGH) of the exhaust gas treatment system is clogged, or the equipment is There is a risk of corrosion.

Therefore, in Patent Documents 1 and 2, exhaust gas from which dust has been removed through a dry dust collector is passed through a wet desulfurizer to remove SO ₂ , and further, exhaust gas from which SO ₃ that could not be removed by the wet desulfurizer has been removed through the wet dust collector. Has been proposed to condense and remove moisture in the exhaust gas through a cooling dehydration tower and recirculate a part of the exhaust gas (FIG. 4 of Patent Document 1 and FIG. 2 of Patent Document 2). Thereby, the water concentration in circulating exhaust gas can be reduced rather than the case of an air combustion type.

  Further, in Patent Document 2, an exhaust gas inlet for an exhaust gas circulation system is provided in an exhaust gas duct between a dry dust collector and a wet desulfurizer, and exhaust gas taken from the downstream side of the dry dust collector is passed through a cooling dehydration tower. It has been proposed to dehydrate and mix the dehydrated circulating exhaust gas and oxygen-rich gas and use them as combustion gases such as primary to tertiary.

  In addition, the cooling and dewatering towers described in Patent Documents 1 and 2 have a configuration in which a heat transfer tube through which a refrigerant is circulated is provided in a tower through which exhaust gas is circulated, but the refrigerant is discarded from a cryogenic separation type air separation device. The nitrogen gas used can be used.

JP 2009-270753 A JP 2010-107129 A

By the way, in the oxyfuel boiler system described in Patent Documents 1 and 2, a cooling dehydration tower is provided on the downstream side of the wet desulfurization apparatus and the wet dust collector, and the circulation exhaust gas is taken in from the downstream side. Can be reduced to about 5 wt%, and the concentration of SO ₂ and SO ₃ in the circulating exhaust gas can be reduced. However, since the total exhaust gas amount including the circulating exhaust gas amount flows through the wet desulfurization device, the wet dust collecting device, and the cooling and dehydration tower, it is not considered that the devices are enlarged.

On the other hand, Patent Documents 1 and 2 describe a method in which circulating exhaust gas is taken from an exhaust gas duct between a dust collector and a wet desulfurization device. According to this, the wet desulfurization device, the wet dust collector and the cooling dehydration tower can be prevented from becoming large, and the water concentration of the circulating exhaust gas is reduced to 5 wt% by cooling and dehydrating the incorporated circulating exhaust gas in the cooling dehydration tower. According to this, the moisture concentration of the exhaust gas from the boiler to the wet desulfurization apparatus can be reduced. Furthermore, according to the system in which the temperature of the cooled and dehydrated circulating exhaust gas is raised by the gas-gas heat exchanger with the exhaust gas upstream of the dust collector, the water dew point of the circulating exhaust gas is increased and the generation of condensed water is suppressed. As a result, even if SO ₂ is present in the circulating exhaust gas, the generation of the SO ₂ solution is suppressed, so that acid corrosion of the exhaust gas circulating system can be suppressed.

However, the cooling and dewatering towers described in Patent Documents 1 and 2 are heat exchangers that distribute the refrigerant to the heat transfer tubes arranged in the tower through which the exhaust gas flows, so there is room for improving the exhaust gas cooling performance and reducing the size. There is. Furthermore, according to the method of taking in the circulating exhaust gas from the exhaust gas duct between the dust collector and the wet desulfurization device, the SO ₂ concentration in the exhaust gas circulation is high, so the SO ₃ concentration generated according to the SO ₂ concentration is high. Therefore, there is room for improving acid corrosion in the exhaust gas circulation system.

  The problem to be solved by the present invention is to provide an oxyfuel boiler system that can avoid moisture condensation of the exhaust gas in the exhaust gas circulation system and that can stably operate without problems caused by the condensed water.

  In order to solve the above problems, the present invention provides a boiler that generates steam by burning fuel, a dust collector that collects soot in exhaust gas discharged from the boiler, and a dust collector that is discharged from the dust collector. A wet desulfurization device that removes sulfur oxides in the exhaust gas, and an exhaust gas from an exhaust gas inlet provided in an exhaust gas duct on the outlet side of the dust collector or the wet desulfurization device. An exhaust gas circulation system that circulates as a part and an oxygen production device that supplies oxygen-rich gas, and the exhaust gas that is circulated by the exhaust gas circulation system is mixed with the oxygen-rich gas supplied from the oxygen production device and used for the combustion An oxyfuel boiler system that generates gas is characterized in that an exhaust gas cooling device that cools at least exhaust gas taken into the exhaust gas circulation system by gas-liquid contact is provided.

According to the present invention, since at least the exhaust gas taken into the exhaust gas circulation system is cooled by gas-liquid contact, the exhaust gas can be effectively and uniformly cooled by the latent heat of vaporization of the coolant. As a result, the exhaust gas cooling device can be reduced in size, and the moisture concentration of the exhaust gas of the circulating exhaust gas system can be sufficiently reduced, so that moisture condensation of the exhaust gas of the circulating exhaust gas system can be avoided, resulting from the condensed water Stable operation can be ensured by eliminating adverse effects. That is, for example, in the case of a boiler that uses pulverized coal as fuel, it is possible to eliminate adverse effects such as clogging of the pulverized coal pulverizer due to condensed water in the circulating exhaust gas or clogging of the pulverized coal supply piping system to the burner. it can. Further, when the SO ₂ concentration in the circulating exhaust gas is high, SO ₂ may be dissolved in the condensed water, which may cause acid corrosion of the exhaust gas circulation piping and equipment. Acid corrosion can be suppressed. Furthermore, since the moisture concentration of the exhaust gas in the exhaust gas treatment system from the boiler to the dust collector or wet desulfurization device can be reduced, adverse effects due to moisture condensation in the exhaust gas treatment system can be eliminated.

The exhaust gas recirculation system includes a gas-gas heat exchanger (GGH) that heats the exhaust gas that has been cooled and dehydrated by the exhaust gas cooling device by exchanging heat with the exhaust gas that flows in the exhaust gas duct upstream of the dust collector. Is preferably provided. According to this, the bad influence resulting from the moisture condensation in the circulation exhaust gas in an exhaust gas recirculation system can be further eliminated. Further, by adjusting the temperature of the exhaust gas flowing into the dust collector by GGH to be lower than the acid dew point, the SO ₃ contained in the exhaust gas is condensed and attached to the dust, so that the SO ₃ is removed together with the dust in the dust collector. be able to. As a result, since it is not necessary to provide a wet dedusting device for collecting SO ₃ that passes through the wet desulfurization device, the configuration of the exhaust gas treatment system can be simplified.

  In the present invention, the exhaust gas inlet to the exhaust gas circulation system is provided in the exhaust gas duct between the dust collector and the wet desulfurization device, and the exhaust gas cooling device is connected to the exhaust gas intake pipe of the exhaust gas circulation system connected to the exhaust gas inlet. Can be provided. Alternatively, an exhaust gas cooling device can be provided in the exhaust gas duct between the dust collector and the exhaust gas intake. Furthermore, in the present invention, the exhaust gas inlet to the exhaust gas circulation system may be provided in the exhaust gas duct on the outlet side of the wet desulfurization device, and the exhaust gas cooling device may be provided in the exhaust gas duct between the wet desulfurization device and the exhaust gas inlet. it can.

  According to the present invention, it is possible to provide an oxyfuel boiler system that can avoid moisture condensation of exhaust gas in the exhaust gas circulation system and that can stably operate without problems caused by condensed water.

It is a system configuration | structure figure of Example 1 of the oxyfuel boiler system of this invention. It is a detailed block diagram of an example of the exhaust gas cooling device which is the characteristic part of this invention. It is a system | strain block diagram of Example 2 of the oxyfuel boiler system of this invention. It is a system | strain block diagram of Example 3 of the oxyfuel boiler system of this invention. It is a figure which compares and shows the verification test done using Examples 1-3.

  Hereinafter, the oxyfuel boiler system of the present invention will be described based on examples.

In FIG. 1, the system | strain block diagram of Example 1 of an oxyfuel boiler system is shown. As shown in the figure, the present embodiment includes a boiler 1 that burns pulverized coal as fuel to generate steam, a denitration device 2 that removes NOx in the exhaust gas discharged from the boiler 1, and a denitrated exhaust gas. A combustion gas preheater 3 and a dust collector 5 for collecting dust in the exhaust gas are provided through a heat recovery device 4a of a gas-gas heater (GGH) 4. A dry electric dust collector can be applied to the dust collector 5. A wet desulfurization device 7 is provided on the downstream side of the dust collector 5 to remove sulfur oxides in the exhaust gas via an induction fan 6. A CO ₂ recovery device 14 that separates and recovers moisture and CO ₂ in the exhaust gas is provided on the downstream side of the wet desulfurization device 7. The exhaust gas from which moisture and CO ₂ have been separated by the CO ₂ recovery device 14 is discharged as off-gas from a chimney (not shown) to the atmosphere.

The wet desulfurization apparatus 7 has a known configuration. That is, an absorption liquid containing a calcium-based desulfurization agent is sprayed from a spray nozzle 7b provided on the upper portion of the absorption tower 7a, and the absorption liquid that has absorbed SO ₂ in the exhaust gas is discharged from the bottom of the absorption tower 7a to the absorption liquid tank 7c. It is designed to flow down. The absorption liquid in the absorption liquid tank 7c is circulated to the spray nozzle 7b by an absorption liquid circulation pump (not shown).

The CO ₂ recovery device 14 includes a first drain recovery tank 8, a compressor 9, a second drain recovery tank 10, a dehumidifier 11, a condenser 12, and a liquefied CO ₂ tank 13. The off-gas is discharged from the liquefied CO ₂ tank 13 into the atmosphere via a chimney by a booster (BUF) (not shown). Further, coal 15 as fuel is supplied to a pulverizer 16 and is finely pulverized, and is conveyed to a burner 18 of the boiler 1 through a fuel conveyance pipe 17.

  An exhaust gas circulation system exhaust gas inlet 20 is provided in the exhaust gas duct between the dust collector 5 and the induction fan 6. The exhaust gas circulation system is composed of gas flow paths and equipment from the exhaust gas inlet 20 to the burner 18 and the after gas port 26 of the boiler 1. The exhaust gas cooling device 22, which is a characteristic part of the present embodiment, is provided in a circulating exhaust gas pipe 21 connected to the exhaust gas inlet 20. The exhaust gas circulation fan 23 connected to the exhaust gas cooling device 22 introduces the exhaust gas into the exhaust gas circulation system. The circulating exhaust gas discharged from the exhaust gas circulation fan 23 is circulated through the reheater 4b of the GGH 4 and the combustion gas preheater 3 to be heated. The reheater 4b is connected to the heat recovery unit 4a and a circulating heat transfer pipe 4c of the heat medium, recovers the heat of the exhaust gas by the heat recovery unit 4a, and heats the circulating exhaust gas by the reheater 4b by the circulating heat medium. It is like that. The circulating exhaust gas heated by the reheater 4b is further heated by the combustion gas preheater 3 and mixed with the oxygen-rich gas described later via the primary combustion gas fan 24 to obtain a predetermined oxygen concentration (air-fuel ratio). The combustion gas is adjusted. Combustion gas adjusted to a predetermined oxygen concentration is supplied to the fuel transfer pipe 17, and the pulverized coal supplied from the pulverizer 16 is transferred to the burner 18. Further, a part of the circulating exhaust gas heated by the combustion gas preheater 3 is supplied to the after gas port 26 of the boiler 1 through the adjustment valve 25. In this way, the exhaust gas circulation system takes in the exhaust gas from the exhaust gas inlet 20 provided in the exhaust gas duct, cools and dehydrates it by gas-liquid contact by the exhaust gas cooling device 22, and then increases the temperature so that the burner 18 and the after of the boiler 1 are heated. The gas is returned to the gas port 26 and recirculated.

As shown in FIG. 1, an air separation device 30, which is an example of an oxygen production device, takes in ambient air 31 through an air filter 32, removes dust and compresses it with a compressor 33, and then cools by a water cooling method or the like. The column 35 is cooled to about 10 ° C. and the drain 35 is separated. Thereafter, pressure is alternately applied to a plurality (two in the illustrated example) of the adsorbent packed towers 36a and 36b, and the switching valve group 37a and the switching valve group 37b are opened and closed to switch the flow path, while alternately adsorbing and desorbing. It is supposed to repeat. In this manner, CO ₂ and H ₂ O contained in a minute amount in the ambient air 31 are adsorbed to and desorbed from the adsorbents in the adsorbent packed towers 36a and 36b, and exhausted from the exhaust pipe 38. Here, as the adsorbent, for example, an adsorbent mainly composed of molecular sieve and zeolite can be used. The mixed gas mainly composed of oxygen and nitrogen after the removal of CO ₂ and H ₂ O is finally introduced into the rectification column 40 as liquefied air of about −200 ° C. through the heat exchanger 39. Here, since the boiling point of oxygen is −183 ° C. and the boiling point of nitrogen is −195.8 degrees, nitrogen having a low boiling point evaporates first from the liquefied air, and cryogenic nitrogen is removed from the top of the rectifying column 40. Nitrogen-rich gas 41 as a main component is discharged. The nitrogen-rich gas 41 passes through the heat exchanger 39 to release cold heat for liquefying the mixed gas flowing out from the adsorbent packed towers 36a and 36b, and is heated to, for example, about −10 ° C. Note that the rectifying column 40 has multiple stages, and oxygen can be separated into a plurality of stages and rectified to a 99.99% level oxygen-rich gas mainly composed of oxygen. The oxygen-rich gas 42 thus cryogenically separated is circulated after passing through the heat exchanger 39 to release cold heat for liquefying the mixed gas, and further releasing cold heat as a cold heat source for the cooling tower 34. It is mixed with exhaust gas and supplied as combustion gas.

  In FIG. 2, the detailed structure of the exhaust gas cooling device 22 which is the characteristic part of the present Example 1 is shown. As shown in the figure, the exhaust gas cooling device 22 is formed with a cylindrical container 44, and a plurality of spray nozzles 45 for spraying an absorption liquid containing a calcium-based desulfurization agent as a cooling liquid are provided on the top of the container 44. It has been. Further, below the plurality of spray nozzles 45 in the container 44, a heat transfer pipe 47 constituting an absorption liquid heat exchanger through which the refrigerant flows is disposed, and the absorption liquid sprayed by the refrigerant flowing through the heat transfer pipe 47. Is supposed to cool. Further, an absorption liquid storage section 48 is formed at the bottom of the container 44. Then, the circulating exhaust gas taken from the exhaust gas inlet 20 is introduced into the top of the container 44, and the circulating exhaust gas is sucked by the exhaust gas circulation fan 23 from a position higher than the absorbing liquid storage part 48 on the side surface of the container 44. ing.

  The absorbent in the absorbent reservoir 48 is transferred to the top of the absorbent tank 7c provided in the wet desulfurization device 7 by the first absorbent circulating pump 49 through the flow rate adjusting valve 50. . In the absorption liquid tank 7c, a heat transfer tube 52 constituting an absorption liquid heat exchanger through which the refrigerant flows is immersed in the absorption liquid, and the absorption in the absorption liquid tank 7c is absorbed by the refrigerant flowing through the heat transfer pipe 52. The liquid is cooled. The absorption liquid in the absorption liquid tank 7 c is extracted by the second absorption liquid circulation pump 53, supplied to the spray nozzle 45 through the heat exchanger 54 provided in the absorption liquid supply pipe 46, and stored in the container 44. It is supposed to be sprayed on. A heat transfer tube 54 a through which a refrigerant is circulated is provided in the heat exchanger 54, and the absorption liquid supplied to the absorption liquid supply pipe 46 is cooled. Further, a bypass line 55 that connects the discharge line of the first absorption liquid circulation pump 49 and the discharge line of the second absorption liquid circulation pump 53 is provided, and a flow rate adjustment valve 56 is interposed in the bypass line 55. . Thereby, a part of the absorption liquid of the exhaust gas cooling device 22 can be circulated to the spray nozzle 45 without the absorption liquid tank 7c by the first absorption liquid circulation pump 49 as necessary.

  In the present embodiment, nitrogen-rich gas 41 discarded from the air separation device 30 is circulated as a refrigerant that circulates through the heat transfer tube 47, the heat transfer tube 52, and the heat transfer tube 54a. Instead of the nitrogen-rich gas 41, the oxygen-rich gas generated by the air separation device 30 can be circulated through the heat transfer tube 47, the heat transfer tube 52, and the heat transfer tube 54a. In FIG. 2, the bypass line 55 may be omitted, and the heat exchanger 54 may be omitted. In addition, the heat transfer tube 47 and the heat transfer tube 52 of the present embodiment are configured to have the refrigerant inlet and outlet in the container 44 and the bottom plate of the absorbent tank 7c, respectively, but the present invention is not limited to this. In addition, a refrigerant inlet and outlet may be provided on the side wall of the absorbent tank 7c. Furthermore, although the heat transfer tube 47 and the heat transfer tube 52 of the present embodiment have been shown to be bent in a U shape, the present invention is not limited to this, and can be formed in a coil shape.

The operation of the oxyfuel boiler system of this embodiment configured as described above will be described below. Coal 15 is finely pulverized by a pulverizer 16 and fed into a fuel conveyance line 17. The pulverized coal charged into the fuel transfer line 17 is air-flowed by the combustion gas adjusted to a predetermined oxygen concentration and supplied to the burner 18. The exhaust gas generated by burning in the burner 18 is introduced from the boiler 1 to the denitration device 2 to remove nitrogen oxides (NOx) contained in the exhaust gas. In addition, since NOx contained in the exhaust gas of the oxyfuel boiler 1 of this embodiment is only fuel-derived nitrogen oxide (fuel NOx), the fuel NOx can be ignored by the combustion management of the boiler 1 or the like. If possible, the denitration device 2 can be omitted. The exhaust gas discharged from the denitration device 2 is introduced into the combustion gas preheater 3, and the circulating exhaust gas is preheated as will be described later. The exhaust gas that has passed through the combustion gas preheater 3 is introduced into the dust collector 5 through the heat recovery device 4a of the GGH 4. The heat recovery unit 4a is connected to the reheater 4b through the heat medium pipe 4c so as to be capable of transferring heat. Thereby, the heat | fever of the waste gas collect | recovered with the heat recovery device 4a heats the circulation waste gas which distribute | circulates the reheater 4b via the heat-medium conduit 4c. At this time, by reducing the temperature of the exhaust gas heat recovered by the heat recovery device 4a below the acid dew point, SO ₃ contained in the exhaust gas can be condensed and attached to the dust in the exhaust gas.

In the dust collector 5, soot in the exhaust gas is removed, and SO ₃ adsorbed on the soot when passing through the heat recovery device 4 a of the GGH 4 is removed together with soot. The exhaust gas that has passed through the dust collector 5 is introduced into the wet desulfurizer 7 through the induction fan 6. In the exhaust gas introduced into the wet desulfurization apparatus 7, SO _{2 in} the exhaust gas is absorbed by the absorption liquid. The exhaust gas from which nitrogen oxides, soot and sulfur oxides have been removed in this way is introduced into the CO ₂ recovery device 14. Since the SO ₃ concentration in the exhaust gas flowing into the CO ₂ recovery device 14 is lowered, it is useful for preventing corrosion of the components of the CO ₂ recovery device 14.

The moisture (saturated water vapor) in the exhaust gas introduced into the CO ₂ recovery device 14 is condensed in the drain recovery tank 8 and recovered as drain 8a. The exhaust gas that has passed through the drain recovery tank 8 is compressed by the compressor 9 and introduced into the drain recovery tank 10, and the moisture in the exhaust gas is recovered as the drain 10a. Next, moisture is removed by the dehumidifier 11, and finally the exhaust gas is cooled and compressed by the condenser 12, and the CO ₂ is liquefied and recovered in the liquefied CO ₂ tank 13 through the CO ₂ recovery line and remains. The gas is emitted from the chimney as off-gas. The exhaust gas is compressed in the CO ₂ recovery device, and NOx, SOx and the like are dissolved together with moisture in the exhaust gas in the compression process, and separated and recovered into drains 8a and 10a.

Next, the operation of the exhaust gas cooling device 22 and the exhaust gas circulation system, which are the features of this embodiment, will be described. The circulating exhaust gas sucked by the exhaust gas circulation fan 23 from the exhaust gas inlet 20 provided in the exhaust gas duct between the dust collector 5 and the induction fan 6 is circulated to the exhaust gas cooling device 22. Absorption liquid is sprayed from the spray nozzle 45 to the exhaust gas cooling device 22 by the second absorption liquid circulation pump 53. The circulating exhaust gas introduced into the exhaust gas cooling device 22 comes into gas-liquid contact with the absorbing liquid sprayed from the spray nozzle 45 and is effectively cooled by the latent heat of vaporization of the absorbing liquid. Further, SO ₂ contained in the circulating exhaust gas in gas-liquid contact with the absorption liquid is absorbed by the absorption liquid, reacts with the calcium component in the absorption liquid to generate gypsum, and is stored in the absorption liquid storage section 48 together with the remaining absorption liquid. Is done. The absorption liquid sprayed from the spray nozzle 45 and the absorption liquid in the absorption liquid storage section 48 are cooled by exchanging heat with the nitrogen-rich gas 41 circulated in the heat transfer tube 47.

The absorbent in the absorbent reservoir 48 is transferred to the absorbent tank 7c by the second absorbent circulation pump 49. The absorbing liquid containing gypsum in the absorbing liquid tank 7c is appropriately extracted to collect the gypsum, and the water that is the solution is purified. In this manner, the circulating exhaust gas that has been cooled and dehydrated by the exhaust gas cooling device 22 and from which SO ₂ has been removed is sucked by the exhaust gas circulation fan 23 from the side wall of the gas phase portion of the container 44 of the exhaust gas cooling device 22 and reheated. It is circulated through the vessel 4b and heated.

  The circulating exhaust gas heated by the reheater 4b is further heated by the heat of the exhaust gas by the combustion gas preheater 3, sucked by the primary combustion gas fan 24, and supplied from the air separation device 30. 42, is adjusted to a combustion gas having a predetermined oxygen concentration, and is supplied to the burner 18 as a primary to tertiary combustion gas together with the pulverized coal through the fuel conveyance line 17. The ratio of the circulating exhaust gas in the combustion gas supplied to the burner 18 is adjusted by a regulating valve (not shown). The boiler 1 burns the pulverized coal supplied from the pulverizer 16 via the pulverized coal conveyance line 27 together with the combustion gas. Note that the amount of primary to tertiary air supplied to the burner 18 is adjusted to form a combustion region of a reducing atmosphere inside the boiler 1, and the rate at which the nitrogen content in the pulverized coal is converted to NOx (fuel NOx) is reduced. Further, a combustion region of an oxidizing atmosphere is formed in the upper part of the boiler 1 by oxygen contained in the combustion gas supplied from the after gas port 26. Further, gas mixing in the boiler is promoted by a jet flow from the after gas port 13 to reduce the unburned portion remaining in the exhaust gas of the boiler.

  On the other hand, a part of the heated circulating exhaust gas discharged from the combustion gas preheater 3 is mixed with the oxygen-rich gas 42 supplied from the air separation device 30 through the regulating valve 25, and the after gas is used as the combustion gas. Supplied to port 26. The ratio of the circulated exhaust gas of the combustion gas supplied to the after gas port 26 is adjusted by the adjustment valve 25. It should be noted that the ratio of the circulated exhaust gas of the combustion gas supplied to the burner 18 and the after gas port 26 is the heat load of the burner 18, the boiler 1, the oxygen concentration in the exhaust gas, the required gas amount of the pulverizer 16, and the air separation device. It can be changed according to 30 abilities.

By the way, in FIG. 1, when circulating exhaust gas is taken in from the exhaust gas duct between the dust collector 5 and the wet desulfurization device 7, the exhaust gas before the SO ₂ concentration is reduced is circulated to the boiler 1. The water concentration and SO ₂ concentration are concentrated. In addition, the SO ₃ concentration generated at a constant rate with respect to SO ₂ also increases. Here, SO ₃ acid dew point is the temperature at which SO ₃ is atomized _is, SO 3 = 20 ppm, which is 140 ° C. in an air-fired water 10 wt%. In contrast, in the oxyfuel combustion type, for example, when SO ₃ = 60 ppm and the concentration rises to a concentration near 30 wt%, the acid dew point increases to 180 degrees. Therefore, when the exhaust gas cooling device 22 is not provided, acid corrosion can occur because SO ₃ is misted even in the temperature range of the exhaust gas circulation system in which the exhaust gas temperature decreases. Therefore, similarly to the air combustion method, in order to maintain the moisture concentration of the exhaust gas at the outlet of the boiler 1 at 10 wt%, it is sufficient to remove approximately 50 wt% of water and reduce the moisture concentration in the circulating exhaust gas to 5 wt% or less. .

  In this regard, according to the present embodiment, the exhaust gas cooling device 22 is provided, the coolant is sprayed, and the circulating exhaust gas is cooled by gas-liquid contact. Therefore, the moisture concentration of the circulating exhaust gas can be sufficiently reduced. . That is, when calculated from the water dew point, a sufficient moisture reduction effect can be obtained when the temperature of the circulating exhaust gas is cooled to 35 ° C. or less, for example. Further, the exhaust gas temperature flowing into the dust collector 5 is cooled to, for example, 90 ° C. in advance by the heat recovery device 4a of the GGH 4. Therefore, the exhaust gas temperature flowing out from the dust collector 5 can be easily cooled from 90 ° C. to 35 ° C. with the absorbing liquid by the exhaust gas cooling device 22, and the moisture concentration of the circulating exhaust gas can be reduced to 5 wt% or less. it can. Moreover, since reheating is performed by the reheater 4b (for example, close to 80 ° C.), moisture condensation in the exhaust gas recirculation system can be reliably prevented.

Further, in this embodiment, an absorption liquid containing a desulfurizing agent is used as the cooling liquid used in the exhaust gas cooling device 22, and the absorption liquid is actively cooled with nitrogen-rich gas and sprayed into the circulating exhaust gas. In addition to the water removal effect, the absorption effect of SO ₂ in the circulating exhaust gas can be enhanced. Further, the absorbing liquid containing SO ₂ and condensed water is collected in the absorbing liquid tank 7c of the wet desulfurization apparatus 7, and is processed by an absorption liquid processing facility (not shown) that is normally provided in the wet desulfurization apparatus 7. Therefore, it is not necessary to provide a separate processing facility in order to process the absorption liquid of the exhaust gas cooling device 22.

As a result, according to this embodiment, condensation of moisture in the exhaust gas circulation system, absorption of SO ₂ into the condensed water and mist formation of SO ₃ can be prevented, so that acid corrosion of the exhaust gas circulation system piping and equipment can be prevented. It is possible to suppress the clogging of pulverized coal and the like and to stably operate.

  Further, as in the present embodiment, a heat exchanger composed of the heat transfer pipe 52 is disposed in the absorption liquid tank 7c, and the entire absorption liquid is cooled with nitrogen-rich gas (or oxygen-rich gas). In the wet desulfurization apparatus 7, the exhaust gas is cooled, and the desulfurization rate and mercury (Hg) removal rate are improved. Further, a heat exchanger 54 is provided in the absorption liquid supply pipe 46, and the absorption liquid supplied from the first or second absorption liquid circulation pumps 49, 53 to the spray nozzle 45 is cooled by the nitrogen-rich gas 41 (for example, 35 ° C. or less). However, the heat exchanger 54 may be omitted. Further, the heat exchanger 54 may be provided on the suction side of the second absorbing liquid circulation pump 53. Moreover, when supplying a part of absorption liquid of the absorption liquid storage part 48 of the exhaust gas cooling device 22 from the discharge side of the 1st absorption liquid circulation pump 49 to the spray nozzle 45 via the bypass line 55, it is a heat exchanger. 54 is preferably provided at the position shown in FIG.

Furthermore, according to the present embodiment, the heat recovery device 4a of GGH4 is arranged upstream of the dust collector 5, and the circulating exhaust gas discharged from the exhaust gas cooling device 22 is reheated with the recovered heat. The exhaust gas temperature at the inlet of the device 5 can be cooled to, for example, about 90 ° C. (at least 80 to 120 ° C.), and SO ₃ in the exhaust gas can be condensed and attached to the dust and removed by the dust collector 5. As a result, acid corrosion due to SO _{3 in the} exhaust gas treatment system and exhaust gas circulation system on the downstream side of the dust collector 5 can be reduced.

In Example 1, an absorbing liquid containing a desulfurizing agent was used as the cooling liquid of the exhaust gas cooling device 22, but water can be used as the cooling liquid. In this case, the concentration of the moisture concentration of the exhaust gas in the exhaust gas circulation system and the exhaust gas treatment system can be suppressed, but the concentration of SO ₂ concentration in the exhaust gas cannot be suppressed. However, if the moisture concentration in the exhaust gas can be suppressed as compared with the conventional air combustion type, condensation of moisture in the circulating exhaust gas can be avoided, so that acid corrosion due to dissolution of SO ₂ in the condensed water is suppressed. Can do.

  Further, in the first embodiment, the absorption liquid that is the cooling liquid of the exhaust gas cooling device 22 is cooled by the heat transfer tube 47 disposed in the container 44. However, the present invention is not limited to this. In short, since the cooling liquid or the absorption liquid only needs to be cooled, for example, the cooling liquid or the absorption liquid can be cooled along a pipe or the like through which the refrigerant flows around the outer periphery of the container 44.

  In FIG. 3, the system configuration | structure figure of Example 2 of the oxyfuel boiler system of this invention is shown. Basically, in the present invention, if a certain amount of moisture in the circulating exhaust gas at the exhaust gas inlet 20 is removed, the problem caused by moisture condensation in the circulating exhaust gas can be solved. As shown in FIG. 3, the present embodiment is different from the first embodiment in that an exhaust gas cooling device 22 is provided in an exhaust gas duct between the dust collector 5 and the induction fan 6, and the exhaust gas inlet 20 is provided in the exhaust gas cooling device. 22 and the induction fan 6. Since the other points are the same as those of the first embodiment, the same reference numerals are assigned to the same devices and the description thereof is omitted.

According to the present embodiment, not only the circulating exhaust gas but also the total exhaust gas amount flows through the exhaust gas cooling device 22. Therefore, since the exhaust gas cooling device 22 supplements the function of the wet desulfurization device 7, in addition to the effect of the first embodiment, there is an effect that the SO ₂ concentration in the exhaust gas discharged from the wet desulfurization device 7 can be reduced. is there. However, since the amount of the processing gas in the exhaust gas cooling device 22 increases, the exhaust gas cooling device 22 is about 30% larger than the first embodiment, for example.

In FIG. 4, the system | strain block diagram of Example 3 of the oxyfuel boiler system of this invention is shown. The difference between the present embodiment and the first or second embodiment is that the exhaust gas cooling device 22 is provided in the exhaust gas duct between the wet desulfurization device 7 and the CO ₂ recovery device 14, and between the exhaust gas cooling device 22 and the CO ₂ recovery device 14. The exhaust gas intake 20 is provided in the exhaust gas duct. Since the other points are the same as those in the first or second embodiment, the same reference numerals are assigned to the same devices and the description thereof is omitted.

In the present embodiment, since desulfurization is performed by the wet desulfurization apparatus 7, the exhaust gas after most of the SO ₂ is removed is circulated to the exhaust gas cooling apparatus 22. Therefore, according to the present embodiment, the total amount of exhaust gas is desulfurized by the wet desulfurization device 7 and the exhaust gas cooling device 22, so that both devices are large. However, compared to Examples 1 and 2, the concentration of moisture, SO ₂ and SO _{3 in} the exhaust gas circulation system can be sufficiently lowered, so that acid corrosion of the exhaust gas circulation system can be prevented. Moreover, since the SO ₂ concentration in the exhaust gas flowing into the CO ₂ recovery device 14 is further reduced, acid corrosion of the equipment constituting the CO ₂ recovery device 14 can be further prevented.

(Verification test)
The result of having conducted the verification test using the oxyfuel boiler system of each of Examples 1 to 3 will be described below. The test equipment includes a boiler 1, a denitration device 2, a combustion gas preheater 3, a heat recovery device 4 a and a reheater 4 b of GGH 4, a dry dust collector 5, an induction fan 6, a wet desulfurization device 7, and the first embodiment. Was provided with a booster (BUF) (not shown) and the exhaust gas circulation system of each example. As the boiler 1, a combustion furnace with an exhaust gas amount of 900 m ³ / h is used, and the sulfur content (S) concentration in the coal is 0.77 wt%, the coal combustion amount is 110 kg / h, and the combustion gas is circulated at oxygen of 200 m ³ / h. An exhaust gas amount of 630 m ³ / h was mixed and produced.

(Demonstration test of Example 1)
In the oxyfuel boiler system of the first embodiment, as shown in FIG. 2, the absorption liquid supply pipe 46 is provided with a heat exchanger 54, and the wet desulfurization device 7 is built in while indirectly cooling 0 ° C. air as a simulated refrigerant. The absorption liquid is sprayed from the absorption liquid tank 7c into the container 44 of the exhaust gas cooling device 22 at a ratio of liquid gas ratio (L / G) = 5 L / m ³ N, in other words, the amount of the absorption liquid is 3.1 m ³ / h. did. The sprayed absorption liquid was temporarily stored in the absorption liquid storage section 48 of the container 44 and returned to the absorption liquid tank 7 c by the first absorption liquid circulation pump 49.

Here, the amount of exhaust gas flowing through the wet desulfurization apparatus 7 is 900−630 = 270 m ³ N / h obtained by subtracting the amount of circulating exhaust gas from the total gas amount. Therefore, even if L / G = 30 L / m ³ N in practice. The amount of the absorption liquid is 8.1 m ³ / h. Moreover, since the residual SO ₂ flowing into the CO ₂ recovery device 14 is sulfated in the compression process and causes corrosion of the device, the SO ₂ concentration at the outlet of the wet desulfurization device 7 is preferably as low as possible. For example, it is desirable to reduce to about 1 to several ppm. In Example 1, the desulfurization rate in the wet desulfurization apparatus 7 was 97% (L / G = 40). Moreover, the desulfurization rate in the exhaust gas cooling device 22 was 50% (L / G = 5). The respective concentrations of SO ₃ , SO ₂ , and H ₂ O in the exhaust gas of Example 1 performed under such test conditions were as shown in FIG.

(Demonstration test of Example 2)
In the oxyfuel boiler system of the second embodiment shown in FIG. 3, the second embodiment is configured so that the absorption liquid becomes L / G = 5 L / m ³ N in the exhaust gas cooling device 22 under the same conditions as in the first embodiment. I put it in. In Example 2, the amount of absorption liquid actually sprayed to the exhaust gas cooling device 22 is 4.5 m ³ / h. Moreover, since the amount of exhaust gas circulated through the wet desulfurization apparatus 7 is 900−630 = 270 m ³ N / h obtained by subtracting the amount of circulating gas from the total gas amount, it is actually absorbed even at L / G = 40 L / m ³ N. The liquid amount is 10.8 m ³ / h, which is the same as in Test Example 1. Each concentration of SO ₃ , SO ₂ , and H ₂ O in the exhaust gas of Example 2 performed under such test conditions was as shown in FIG.

(Demonstration test of Example 3)
In the oxyfuel boiler system of the third embodiment shown in FIG. 4, the third embodiment uses L / G = 5 L / m ³ N as the absorption liquid in the exhaust gas cooling device 22 under the same conditions as in the first and second embodiments. It was thrown to become. In Example 3, the amount of absorbed liquid actually sprayed to the exhaust gas cooling device 22 is 36 m ³ / h when L / G = 40 L / m ³ N because the total exhaust gas amount is distributed. Each concentration of SO ₃ , SO ₂ , and H ₂ O in the exhaust gas of Test Example 1 performed under such test conditions was as shown in FIG.

As the test results shown in FIG. 5, and SO ₂ concentration in the wet desulfurization system (FGD) outlet of Examples 1 and 2, when comparing the outlet SO ₂ concentration in the exhaust gas cooling system of Example 3, Example 1> In Example 2> The relationship of Example 3 was established, but in any Example, the SO ₂ concentration in the circulating exhaust gas can be reduced to 10 ppm or less.

  Moreover, the water concentration in the exhaust gas at the boiler outlet of each of Examples 1, 2, and 3 is about 12 wt%. This is because the same level of pulverized coal is the same as in the case of the air combustion type, so there is almost no increase in water dew point, and water condensation on the surface of the heat medium pipe 4c of the heat recovery device 4a of GGH4 is suppressed, This will prevent ash adhesion, blockage and corrosion.

Furthermore, the SO ₃ concentration in the exhaust gas in the exhaust gas treatment system is in a concentration range (<1 ppm) that hardly causes a corrosion problem at the outlet of the dust collector 5 in any of the embodiments. Acid corrosion can be prevented.

In Examples 1 and 2, although SO ₂ tends to concentrate by exhaust gas circulation, it can be seen that SO ₂ is removed to some extent by the exhaust gas cooling device 22. On the other hand, in Example 3, since the exhaust gas from which SO ₂ was removed by the wet desulfurization device 7 and the exhaust gas cooling device 22 is taken in as the circulating exhaust gas, the SO ₂ concentration is almost the same as that of a normal air combustion boiler. I think that.

  As mentioned above, although Examples 1-3 of the oxyfuel boiler system of the present invention were explained, the present invention is not limited to these Examples. In short, by providing the following requirements alone or in combination, appropriate technical effects can be obtained.

  (1) Since the exhaust gas cooling device that cools at least the exhaust gas circulating in the exhaust gas by gas-liquid contact with the cooling liquid and dehydrates it is provided, moisture in the circulating exhaust gas can be effectively removed. As a result, moisture condensation in the exhaust gas circulation system can be avoided, and clogging and corrosion due to moisture condensation can be prevented. In addition, although moisture removal can be performed by lowering the exhaust gas temperature in the exhaust gas cooling device, it is desirable to keep the temperature at a certain temperature or more because if it is too low, the thermal efficiency of the boiler system will be reduced.

  (2) It is preferable that the exhaust gas cooling device includes a coolant heat exchanger including a heat transfer tube that cools a coolant used for gas-liquid contact with a refrigerant. In this case, the oxygen production apparatus uses an air separation apparatus that cools the air into an oxygen-rich gas mainly containing oxygen and a nitrogen-rich gas mainly containing nitrogen, and the coolant heat exchanger is cooled deeply. At least one of oxygen-rich gas and nitrogen-rich gas discharged from the separator can be used as the refrigerant. According to this, the waste cooling heat of the oxygen-rich gas and nitrogen-rich gas separated by cryogenic cooling can be used as the cooling heat of the exhaust gas cooling device, and the thermal efficiency of the entire system can be improved.

  (3) The exhaust gas cooling device preferably cools the exhaust gas taken from the downstream side of the dust collector or wet desulfurization device. According to this, it is possible to prevent problems such as clogging due to the dust in the exhaust gas adhering to the exhaust gas cooling device by gas-liquid contact.

  (4) According to what provided GGH which heats the circulation exhaust gas dehydrated with the exhaust gas cooling device by the heat of the exhaust gas on the entrance side of the dust collector, moisture condensation in the exhaust gas circulation system can be surely avoided, Clogging and corrosion due to moisture condensation can be prevented.

(5) In the case of (4) above, SO ₃ can be made mist in the GGH heat recovery device, adsorbed to the dust, and removed by the dust collector, thus reducing acid corrosion caused by SO ₃ in the exhaust gas circulation system. can do. Furthermore, since there is no need to provide a wet dust collector that removes SO ₃ passing through the wet desulfurization apparatus, not only can the system configuration be simplified, but also acid corrosion of the CO ₂ recovery apparatus can be reduced.

(6) The exhaust gas cooling apparatus uses the same absorption liquid as the wet desulfurization apparatus as the cooling liquid, spray nozzles sprayed on the exhaust gas, an absorption liquid storage section that stores the absorption liquid that has absorbed sulfur oxide in the exhaust gas, It is desirable to supply the absorbent in the absorbent reservoir to the spray nozzle. According to this, since at least a certain amount of SO ₂ in the exhaust gas circulating in the exhaust gas can be removed, it is possible to reduce the concentration of SO ₂ due to the exhaust gas circulation, and SO ₃ generated according to the SO ₂ concentration is reduced. It is possible to reduce acid corrosion in the exhaust gas circulation system caused by mist formation. In this case, if an exhaust gas circulation system that circulates the exhaust gas from between the dust collector and the wet desulfurization apparatus is configured, the processing load of the downstream wet desulfurization apparatus can be reduced. can do. In addition, if an exhaust gas circulation system that circulates by taking in circulating exhaust gas from the downstream side of the wet desulfurization device is configured, SO ₂ can be removed to a higher degree by the exhaust gas cooling device, thereby preventing acid corrosion of the CO ₂ recovery device. Can do. However, since the total amount of exhaust gas passes through the wet desulfurization apparatus, the heat efficiency of the exhaust gas is deprived by the evaporation heat of the absorption liquid used in the desulfurization apparatus, and the thermal efficiency is higher than in Examples 1 and 2 that are recirculated upstream of the wet desulfurization apparatus. It tends to be low.

  (7) Further, there is provided a transfer means for sending the absorption liquid in the absorption liquid storage part of the exhaust gas cooling device to the absorption liquid tank of the wet desulfurization device, and the absorption liquid in the absorption liquid tank is supplied to the spray nozzle of the exhaust gas cooling device. can do. According to this, the waste water of the exhaust gas cooling device is returned to the absorption liquid tank provided inside or separately from the wet desulfurization device, so that it is not necessary to provide a separate waste water treatment facility for the exhaust gas cooling device, thereby simplifying the system configuration. it can. In addition, a part of the waste water of the exhaust gas cooling device is supplemented with the evaporated portion of the absorption liquid, so that the water that is normally used can be saved.

1 boiler 2 denitration apparatus 3 for combustion gas preheater 4 gas - gas heater 4a heat recovery unit 4b reheater 5 dust collector 7 wet desulfurization system 7b spray nozzle 7c absorption liquid tank 14 CO ₂ recovery device 20 the exhaust gas inlet port 21 circulates the exhaust gas Pipe line 22 Exhaust gas cooling device 23 Exhaust gas circulation fan 30 Air separation device 45 Spray nozzle 46 Absorption liquid supply pipe 47 Heat transfer pipe 48 Absorption liquid storage part 49 First absorption liquid circulation pump 53 Second absorption liquid circulation pump 54 Heat exchanger

Claims (10)

A boiler that generates steam by burning fuel, a dust collector that collects dust in the exhaust gas discharged from the boiler, and a wet desulfurization that removes sulfur oxides in the exhaust gas discharged from the dust collector An exhaust gas circulation system that takes in exhaust gas from an exhaust gas inlet provided in an exhaust gas duct on the outlet side of the dust collector or the wet desulfurization device and circulates it as a part of combustion gas of the boiler, oxygen-rich gas In an oxygen combustion boiler system for generating the combustion gas by mixing exhaust gas circulated by the exhaust gas circulation system with oxygen-rich gas supplied from the oxygen production device,
An oxyfuel boiler system comprising an exhaust gas cooling device that cools at least exhaust gas taken in by the exhaust gas circulation system by gas-liquid contact. The exhaust gas inlet is provided in an exhaust gas duct on the outlet side of the dust collector,
2. The oxyfuel boiler system according to claim 1, wherein the exhaust gas cooling device is provided in an exhaust gas intake pipe connected to the circulating exhaust gas intake.   The oxyfuel boiler system according to claim 2, wherein the exhaust gas cooling device is provided in an exhaust gas duct between the exhaust gas inlet and the dust collector. The exhaust gas intake is provided in an exhaust gas duct on the outlet side of the wet desulfurization device,
The oxyfuel boiler system according to claim 1, wherein the exhaust gas cooling device is provided in an exhaust gas duct between the wet desulfurization device and the exhaust gas intake.   The oxyfuel boiler according to any one of claims 1 to 4, wherein the exhaust gas cooling device includes a coolant heat exchanger that cools a coolant used for the gas-liquid contact with a refrigerant. system. The oxygen production device is an air separation device that separates the oxygen-rich gas mainly containing oxygen and the nitrogen-rich gas mainly containing nitrogen by deeply cooling air.
6. The oxyfuel combustion type according to claim 5, wherein the coolant heat exchanger uses at least one of the oxygen-rich gas and the nitrogen-rich gas discharged from the cryogenic separator as the refrigerant. Boiler system. The wet desulfurization apparatus includes a first spray nozzle that sprays an absorption liquid containing a calcium-based desulfurization agent onto exhaust gas, an absorption liquid tank that stores an absorption liquid that has absorbed sulfur oxide in the exhaust gas, and the absorption liquid tank. And a first circulation pump that circulates and supplies the absorption liquid to the first spray nozzle,
The exhaust gas cooling device includes: a second spray nozzle that sprays an exhaust liquid containing a calcium-based desulfurization agent as the liquid onto the exhaust gas; an absorbent storage part that stores the absorbent that has absorbed sulfur oxide in the exhaust gas; The oxyfuel boiler according to any one of claims 1 to 4, further comprising a second circulation pump that supplies the absorption liquid in the absorption liquid storage section to the second spray nozzle. system. A transfer means is provided for sending the absorbent in the absorbent reservoir to the absorbent tank of the wet desulfurization device,
8. The oxyfuel boiler system according to claim 7, wherein the second circulation pump supplies the absorption liquid in the absorption liquid tank to the second spray nozzle. The oxygen production device is an air separation device that separates the oxygen-rich gas mainly containing oxygen and the nitrogen-rich gas mainly containing nitrogen by deeply cooling air.
An absorption liquid heat exchanger is provided that cools the absorption liquid in the absorption liquid tank and the absorption liquid storage section with at least one of the oxygen-rich gas and the nitrogen-rich gas discharged from the cryogenic separator. The oxyfuel boiler system according to claim 7, wherein   The exhaust gas recirculation system includes a gas-gas heat exchanger on the downstream side of the exhaust gas cooling device for exchanging heat with the exhaust gas flowing in the exhaust gas duct on the upstream side of the dust collector to heat the circulating exhaust gas. The oxyfuel boiler system according to any one of claims 1 to 9, wherein the oxyfuel boiler system is provided.

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