JP5728956B2 - Oxy-combustion boiler system - Google Patents

Description

  The present invention relates to an oxyfuel boiler system.

In recent years, global warming has been widely taken up as a global environmental problem, and it has been clarified that the increase in the concentration of carbon dioxide (CO ₂ ) in the atmosphere is one of the main causes of global warming. Boiler facilities in thermal power plants and the like are attracting attention as a fixed emission source of these substances, but oil, natural gas, and coal are mainly used as boiler fuel.

  In particular, coal has a higher carbon content than natural gas and petroleum, and other components such as hydrogen, nitrogen, and sulfur, and inorganic ash. Is mostly nitrogen (about 70%), and also contains carbon dioxide, sulfur oxide (SOx), nitrogen oxide (NOx), and dust and oxygen (about 4%) consisting of ash and unburned coal particles. It will be.

  For this reason, in the case of the boiler equipment, the flue gas is subjected to flue gas treatment such as denitrification, desulfurization, and dust removal, and NOx, SOx, and fine particles are discharged from the chimney into the atmosphere so that they are below the environmental emission standard value. ing.

  The NOx generated in the combustion exhaust gas includes thermal NOx produced by oxidizing nitrogen in the air with oxygen and fuel NOx produced by oxidizing nitrogen in the fuel. Conventionally, for reducing thermal NOx, A combustion method for reducing the flame temperature has been adopted, and a fuel method for reducing fuel NOx has been adopted in which a fuel-excess region for reducing NOx is formed in the combustor.

  On the other hand, as a method of recovering carbon dioxide in the combustion exhaust gas, a method of absorbing in an absorbing solution such as amine, an adsorption method of adsorbing on a solid adsorbent, or a membrane separation method has been studied. Both have low conversion efficiency and have not yet been put into practical use.

  Therefore, as an effective method for simultaneously achieving the problem of separation of carbon dioxide in the combustion exhaust gas and suppression of thermal NOx, a method of burning fuel with oxygen instead of air has been proposed. Combustion with oxygen eliminates the generation of thermal NOx, and most of the combustion exhaust gas becomes carbon dioxide. In addition, since the gas contains fuel NOx and SOx, the carbon dioxide is cooled by cooling the combustion exhaust gas. It is relatively easy to liquefy and separate.

  However, when the fuel such as coal is burned with oxygen, the flame temperature becomes high, and there is a technical problem that it is necessary to improve the heat resistance and life of the material constituting the boiler body. As a measure to solve this problem, a part of the flue gas discharged from the boiler body and smoke-treated is branched, and the branched flue gas is mixed with air or oxygen or other combustion gas supplied to the boiler body. So-called exhaust gas recirculation is known.

  FIG. 7 shows an example of a conventional oxyfuel boiler system, in which 1 is a boiler body, 2 is a combustion gas supply line for supplying a combustion gas such as air or oxygen to the boiler body 1, and 3 is for combustion. An air suction port provided at the upstream end of the gas supply line 2, 4 is a forced air blower provided in the combustion gas supply line 2, 5 is an exhaust gas line through which combustion exhaust gas discharged from the boiler body 1 flows, and 6 is A flue gas treatment device that is provided in the exhaust gas line 5 and performs denitration, desulfurization, and dust removal of combustion exhaust gas, 7 is an induction fan provided in the exhaust gas line 5, and 8 is an exhaust gas line 5 on the suction side of the induction fan 7 An exhaust gas recirculation line connecting the combustion gas supply line 2 on the suction side of the forced air ventilator 4, and first switching to the combustion gas supply line 2 upstream from the junction of the exhaust gas recirculation line 8 Provided with a damper D1, it is the second switching damper D2 provided in the exhaust gas recirculation line 8.

In the oxyfuel boiler system shown in FIG. 7, at startup, as shown in FIG. 8, with the first switching damper D1 fully opened and the second switching damper D2 fully closed, the forced draft fan 4 and the induced draft The machine 7 is driven, and air is introduced into the boiler body 1 from the air inlet 3 at the upstream end of the combustion gas supply line 2 to burn the fuel in the air, and is discharged from the boiler body 1 in the same manner as a normal boiler. that flue gas after denitration, desulfurization and dedusting in flue gas treating device 6, released into the atmosphere through a stack (not shown), after start-up completion, as shown in FIG. 8, from t ₁ to t ₂ In the meantime, the first switching damper D1 is squeezed from the fully open position to be fully closed, and the second switching damper D2 is fully opened from the fully closed position to the fully open position. The boiler body 1 is supplied with oxygen from the combustion gas supply line 2. From boiler body 1 while introducing A part of the combustion exhaust gas is recirculated to the combustion gas supply line 2 through the exhaust gas recirculation line 8 to oxidize the fuel, thereby increasing the concentration of carbon dioxide in the combustion exhaust gas. As described above, the exhaust gas discharged from the exhaust gas is subjected to denitration, desulfurization, and dust removal by the smoke treatment device 6 and then carbon dioxide in a CO ₂ recovery facility (not shown) provided downstream of the induction fan 7. The combustion exhaust gas from which the carbon dioxide has been recovered is discharged into the atmosphere from the chimney.

  For example, Patent Document 1 shows a general technical level related to the oxyfuel boiler system as described above.

Japanese Patent No. 4161515

  By the way, in the oxyfuel boiler system shown in FIG. 7, when the opening control of the first switching damper D1 and the second switching damper D2 is performed as shown in FIG. The pressure at the junction of the exhaust gas recirculation line 8 to the combustion gas supply line 2 is prevented from becoming a positive pressure or a pressure close to zero, and the combustion exhaust gas to be recirculated even during a transient fluctuation is supplied to the air inlet 3. There is no worry of going backwards.

  However, in the oxyfuel boiler system shown in FIG. 7, as described above, the exhaust gas recirculation line 8 is branched from the exhaust gas line 5 on the suction side of the induction fan 7, so that the combustion is changed from air combustion to oxyfuel combustion. In this case, the flow rate of the flue gas flowing through the induction fan 7 is greatly reduced to about 20 to 30% during air combustion, and it becomes difficult to turn down the induction fan 7, and inverter control and fan characteristics are reviewed. It had the disadvantage of need.

  In view of such circumstances, the present invention can reliably recirculate combustion exhaust gas without backflowing to the air intake port during the transition from air combustion to oxyfuel combustion, and avoids the problem of turndown of the induction fan It is an object of the present invention to provide an oxyfuel boiler system that can be used.

The present invention introduces air from a combustion gas supply line to a boiler body at the time of startup to perform air combustion of fuel, and after completion of startup, the boiler is introduced while introducing oxygen from the combustion gas supply line to the boiler body. In an oxyfuel boiler system that recycles part of the flue gas discharged from the main body and oxyfuels the fuel,
Exhaust gas recirculation means for guiding a part of the combustion exhaust gas from the exhaust gas line on the discharge side of the induction fan to the combustion gas supply line ;
The exhaust gas recirculation means includes
An exhaust gas recirculation line branched from the exhaust gas line on the discharge side of the induction fan and joined to the combustion gas supply line on the suction side of the forced air fan;
Provided in the combustion gas supply line upstream from the confluence connection point of the exhaust gas recirculation line and downstream from the air suction port, and the opening degree is controlled from fully open to fully closed when shifting from air combustion to oxyfuel combustion. A first switching damper;
A second switching damper that is provided in the exhaust gas recirculation line, and whose opening degree is controlled stepwise from fully closed to a set opening degree when shifting from air combustion to oxyfuel combustion;
A third switching damper which is provided in the exhaust gas line downstream from the branch point of the exhaust gas recirculation line and whose opening degree is controlled from fully open to a set opening degree when shifting from air combustion to oxyfuel combustion;
With
The first switching damper is configured to hold the pressure at the junction point of the exhaust gas recirculation line at a negative pressure while controlling the opening degree from fully open to fully closed at the time of transition from air combustion to oxyfuel combustion. It relates to an oxyfuel boiler system.

  According to the above means, the following operation can be obtained.

  When configured as described above, it is possible to prevent the combustion exhaust gas to be recirculated from flowing back to the air intake port by the exhaust gas recirculation means at the time of transition from air combustion to oxyfuel combustion. Part of the combustion exhaust gas is led from the exhaust gas line on the discharge side of the induction fan to the combustion gas supply line, so when shifting from air combustion to oxyfuel combustion, the flow rate of the combustion exhaust gas flowing through the induction fan is different from that during air combustion. There is no significant drop in comparison, and the same amount of combustion exhaust gas flows through the induction fan during air combustion and oxyfuel combustion, so there is no concern that it will be difficult to turn down the induction fan. In addition, it is not necessary to review inverter control and fan characteristics.

In addition, the present invention introduces air from the combustion gas supply line to the boiler body at the time of startup to perform air combustion of the fuel, and after completion of startup, introduces oxygen from the combustion gas supply line to the boiler body. In an oxyfuel boiler system that recirculates part of the combustion exhaust gas discharged from the boiler body and performs oxyfuel combustion of the fuel,
Exhaust gas recirculation means for guiding a part of the combustion exhaust gas from the exhaust gas line on the discharge side of the induction fan to the combustion gas supply line;
The exhaust gas recirculation means includes
An exhaust gas recirculation line branched from the exhaust gas line on the discharge side of the induction fan and joined to the combustion gas supply line on the discharge side of the forced air fan;
Provided in the combustion gas supply line upstream from the confluence connection point of the exhaust gas recirculation line and on the discharge side of the forced air blower, the opening degree is controlled from fully open to fully closed at the time of transition from air combustion to oxyfuel combustion. A first switching damper
A first flow rate adjustment damper that is provided in a combustion gas supply line on the suction side of the forced air blower, and that is controlled to be fully closed from a set opening degree at the time of transition from air combustion to oxyfuel combustion;
A second switching damper provided in the exhaust gas recirculation line, the opening of which is controlled from fully closed to a set opening degree when shifting from air combustion to oxyfuel combustion;
A third switching damper which is provided in the exhaust gas line downstream from the branch point of the exhaust gas recirculation line and whose opening degree is controlled from the fully open to the set opening degree when shifting from air combustion to oxyfuel combustion,
The first flow rate control damper after opening control completed fully closed from set opening when moving to oxyfuel combustion from the air combustion, by being configured to opening control to fully closed the first switching damper from the fully opened The characteristic oxyfuel boiler system .

Furthermore, the present invention introduces air from the combustion gas supply line to the boiler body at the time of startup to perform fuel air combustion, and introduces oxygen from the combustion gas supply line to the boiler body after the startup is completed. In an oxyfuel boiler system that performs oxygen combustion of fuel by recirculating part of the combustion exhaust gas discharged from the boiler body,
Exhaust gas recirculation means for guiding a part of the combustion exhaust gas from the exhaust gas line on the discharge side of the induction fan to the combustion gas supply line;
The exhaust gas recirculation means includes
An exhaust gas recirculation line branched from the exhaust gas line on the discharge side of the induction fan and joined to the combustion gas supply line on the discharge side of the forced air fan;
Provided in the combustion gas supply line upstream from the confluence connection point of the exhaust gas recirculation line and on the discharge side of the forced air blower, the opening degree is controlled from fully open to fully closed at the time of transition from air combustion to oxyfuel combustion. A first switching damper
A first flow rate adjustment damper that is provided in a combustion gas supply line on the suction side of the forced air blower, and that is controlled to be fully closed from a set opening degree at the time of transition from air combustion to oxyfuel combustion;
An exhaust gas recirculation fan provided in the exhaust gas recirculation line and driven and controlled from a stopped state to a set flow rate discharge state at the time of transition from air combustion to oxyfuel combustion;
A second switching damper which is provided in the exhaust gas recirculation line on the discharge side of the exhaust gas recirculation fan and whose opening degree is controlled from a fully closed state to a set opening degree at the time of transition from air combustion to oxyfuel combustion;
A second flow rate adjustment damper that is provided in the exhaust gas recirculation line on the suction side of the exhaust gas recirculation fan and is controlled to open from a fully closed position to a set opening degree when shifting from air combustion to oxyfuel combustion. Branch of the exhaust gas recirculation line A third switching damper that is provided in the exhaust gas line downstream from the point and that is controlled to open from a fully open position to a set opening degree when shifting from air combustion to oxyfuel combustion,
The first flow rate control damper after opening control completed fully closed from set opening when moving to oxyfuel combustion from the air combustion, by being configured to opening control to fully closed the first switching damper from the fully opened The characteristic oxyfuel boiler system .

  According to the oxyfuel boiler system of the present invention, it is possible to reliably recirculate the combustion exhaust gas without flowing back to the air suction port when shifting from air combustion to oxyfuel combustion, and to solve the problem of turndown of the induction fan. An excellent effect that it can be avoided can be achieved.

1 is an overall schematic configuration diagram showing a first embodiment of an oxyfuel boiler system of the present invention. It is a diagram which shows each damper opening degree and merging connection point pressure in the 1st Example of the oxyfuel boiler system of this invention. It is a whole schematic block diagram which shows the 2nd Example of the oxyfuel boiler system of this invention. It is a diagram which shows each damper opening degree in the 2nd Example of the oxyfuel boiler system of this invention. It is a whole schematic block diagram which shows the 3rd Example of the oxyfuel boiler system of this invention. It is a diagram which shows each damper opening degree and exhaust gas recirculation fan flow volume in the 3rd Example of the oxyfuel boiler system of this invention. It is a whole schematic block diagram which shows an example of the conventional oxyfuel boiler system. It is a diagram which shows each damper opening degree in an example of the conventional oxyfuel boiler system.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  1 and 2 show a first embodiment of an oxyfuel boiler system according to the present invention. In the figure, the same reference numerals as those in FIGS. Is the same as the conventional one shown in FIGS. 7 and 8, but the feature of the first embodiment is that a part of the combustion exhaust gas is discharged from the induction fan 7 as shown in FIGS. The exhaust gas recirculation means 9 that leads from the exhaust gas line 5 to the combustion gas supply line 2 on the side is provided.

In the case of the first embodiment, the exhaust gas recirculation means 9 branches the exhaust gas recirculation line 8 from the exhaust gas line 5 on the discharge side of the induction fan 7 and the combustion gas on the suction side of the forced air fan 4. When the transition from air combustion to oxyfuel combustion is made, the combustion gas supply line 2 is joined and connected to the supply line 2 and is upstream of the joining point of the exhaust gas recirculation line 8 and downstream of the air suction port 3. The first switching damper D1 whose opening degree is controlled from fully open to fully closed between t ₁ and t ₂ shown in FIG. 2 is provided, and the exhaust gas recirculation line 8 is shown in FIG. 2 when shifting from air combustion to oxyfuel combustion. the second switching damper D2 which is stepwise opening control towards the set opening x from the fully closed provided at between t ₁ of t _2, the exhaust gas line 5 on the downstream side of the branching point of the exhaust gas recirculation line 8 Oxyfuel from air combustion A third switching damper D3 is opening control from full open between t ₂ from t ₁ shown in FIG. 2 when moving the set opening y to provided, of the first switching damper D1 to oxyfuel combustion from the air combustion During the transition, the pressure at the merging connection point with respect to the combustion gas supply line 2 of the exhaust gas recirculation line 8 is maintained at a negative pressure while the opening degree is controlled from fully open to fully closed between t ₁ and t ₂ shown in FIG. It is configured as follows.

  Next, the operation of the first embodiment will be described.

When configured as described above, during the transition from the air-fuel combustion to the oxyfuel combustion, at between t ₁ shown in FIG. 2 t _2, the first switching damper D1 of the exhaust gas recirculating means 9 is opening control fully closed from the fully opened The opening degree of the second switching damper D2 is gradually controlled from the fully closed position toward the set opening degree x, and the opening degree of the third switching damper D3 is controlled from the fully open position to the set opening degree y. A part of the combustion exhaust gas discharged from the boiler body 1 while oxygen is introduced from the combustion gas supply line 2 is recirculated to the combustion gas supply line 2 via the exhaust gas recirculation line 8 to perform oxygen combustion of the fuel. However, while the opening degree of the first switching damper D1 is controlled from fully open to fully closed, the pressure at the junction point of the exhaust gas recirculation line 8 with respect to the combustion gas supply line 2 is as shown in FIG. Open from the fully closed position of the two-switching damper D2. By the stepwise opening degree control toward the degree x, it becomes a shape that is fluctuated in a zigzag shape but kept at a negative pressure, and the exhaust gas recirculation means 9 causes the combustion exhaust gas to be recirculated to flow back to the air inlet 3 It becomes possible not to do.

  Moreover, the exhaust gas recirculation line 8 of the exhaust gas recirculation means 9 is branched from the exhaust gas line 5 on the discharge side of the induction fan 7 and joined to the combustion gas supply line 2 on the suction side of the forced air fan 4. Since a part of the combustion exhaust gas is led from the exhaust gas line 5 on the discharge side of the induction fan 7 to the combustion gas supply line 2, the combustion flowing through the induction fan 7 when shifting from air combustion to oxyfuel combustion The flow rate of the exhaust gas is not significantly reduced as compared with air combustion, and the same amount of combustion exhaust gas flows through the induction fan 7 during air combustion and during oxygen combustion. There is no worry that it will be difficult to turn down the inverter, and it is not necessary to review the inverter control and fan characteristics.

  In this way, it is possible to reliably recirculate the combustion exhaust gas without flowing back to the air suction port 3 during the transition from air combustion to oxyfuel combustion, and avoid the problem of turndown of the induction fan 7.

3 and 4 show a second embodiment of the oxyfuel boiler system according to the present invention. In the figure, the same reference numerals as those in FIGS. Is the same as that of the first embodiment shown in FIGS. 1 and 2, but the second embodiment is characterized by an exhaust gas line on the discharge side of the induction fan 7 as shown in FIGS. The exhaust gas recirculation line 8 branched from 5 is joined and connected to the combustion gas supply line 2 on the discharge side of the forced draft fan 4, and upstream of the merged connection point of the exhaust gas recirculation line 8 and the forced ventilator 4. The first switching damper D1 is provided in the combustion gas supply line 2 on the discharge side, and the combustion gas supply line 2 on the suction side of the forced air blower 4 is changed to the combustion gas supply line 2 in FIG. from set opening x'at between t ₁ shown in t ₂ A first flow rate control damper c1 which is opening control in the closed provided on the exhaust gas recirculation line 8, between the t ₁ shown in FIG. 4 at the transition from air combustion to oxyfuel combustion of t ₂ open setting from the fully closed A second switching damper D2 whose degree of opening is controlled to a degree x is provided, and the exhaust gas line 5 downstream from the branch point of the exhaust gas recirculation line 8 is connected to the exhaust gas line 5 from t ₁ shown in FIG. by providing the third switching damper D3 is opening control to set opening y from the fully open between t _2, constitute the exhaust gas recirculating means 9, oxyfuel said first flow rate control damper c1 from air combustion after opening control completed fully closed from set opening x'between t ₂ from t ₁ shown in FIG. 4 when moving to, configured to opening control fully closed from the fully open said first switching damper D1 It is in the point.

  Next, the operation of the second embodiment will be described.

When configured as described above, during the transition from air combustion to oxyfuel combustion, the first flow rate adjustment damper is maintained with the first switching damper D1 of the exhaust gas recirculation means 9 fully opened between t ₁ and t ₂ shown in FIG. c1 is opened from the set opening x 'to fully closed, the second switching damper D2 is controlled from fully closed to the set opening x, and the third switching damper D3 is opened from the fully opened to the set opening y. Thus, a part of the combustion exhaust gas discharged from the boiler body 1 while oxygen is introduced into the boiler body 1 from the combustion gas supply line 2 is transferred to the combustion gas supply line 2 via the exhaust gas recirculation line 8. Oxygen combustion of the fuel is performed by recirculation, but the exhaust gas recirculation line 8 branched from the exhaust gas line 5 on the discharge side of the induction fan 7 is replaced with a combustion gas supply line 2 on the discharge side of the forced air fan 4. For connecting together , By the exhaust gas recirculating means 9, the combustion exhaust gas to be recirculated it becomes possible to prevent backflow to the air inlet 3.

  Moreover, the exhaust gas recirculation line 8 of the exhaust gas recirculation means 9 is branched from the exhaust gas line 5 on the discharge side of the induction fan 7 and joined to the combustion gas supply line 2 on the discharge side of the forced air fan 4. Since a part of the combustion exhaust gas is led from the exhaust gas line 5 on the discharge side of the induction fan 7 to the combustion gas supply line 2, the combustion exhaust gas flowing through the induction fan 7 when moving from air combustion to oxyfuel combustion The flow rate is not significantly reduced compared with air combustion, and the same amount of combustion exhaust gas flows through the induction fan 7 during air combustion and during oxyfuel combustion. There is no worry that turning down will be difficult, and there is no need to perform inverter control or review of fan characteristics.

Further, the first flow rate control damper c1 is opening control completed fully closed from set opening x', after the air flow is throttled, the first switching damper D1 from the time of t ₂ of FIG. 4 from the fully opened Since the opening degree is controlled to be fully closed, the physical impact on the first switching damper D1 can be reduced.

  Thus, in the second embodiment shown in FIGS. 3 and 4 as well, as in the first embodiment shown in FIGS. 1 and 2, the combustion exhaust gas is caused to flow backward to the air intake port 3 during the transition from air combustion to oxyfuel combustion. Can be reliably recirculated, and the problem of turndown of the induction fan 7 can be avoided.

FIGS. 5 and 6 show a third embodiment of the oxyfuel boiler system of the present invention. In the figure, the same reference numerals as those in FIGS. 3 and 4 is the same as that of the second embodiment shown in FIGS. 3 and 4, but the feature of the third embodiment is that, as shown in FIGS. A second switching damper D2 whose opening is controlled from fully closed to a set opening x between t ₁ and t ₁ ′ shown in FIG. 6 at the time of transition to oxyfuel combustion is provided upstream of the second switching damper D2. The exhaust gas recirculation line 8 is provided with an exhaust gas recirculation fan 10 that is driven and controlled from a stop state to a set flow rate z discharge state between t ₁ ′ and t ₂ shown in FIG. 6 when shifting from air combustion to oxyfuel combustion. In the exhaust gas recirculation line 8 on the suction side of the exhaust gas recirculation fan 10, The second flow rate control damper c2 are opening control from the fully closed to the set opening x between t ₂ from t ₁ 'shown in FIG. 6 when moving to the oxyfuel combustion from the combustion is provided, the first flow rate control damper c1 After the opening control is completed from the set opening x ′ to the fully closed state between t ₁ ′ and t ₂ shown in FIG. 6 during the transition from air combustion to oxyfuel combustion, the first switching damper D1 is fully opened to fully closed. It is in the point comprised so that opening degree control might be carried out.

In the case of the third embodiment, the third switching damper D3 provided in the exhaust gas line 5 on the downstream side of the branch point of the exhaust gas recirculation line 8 is t ₁ ′ shown in FIG. 6 when shifting from air combustion to oxyfuel combustion. To t ₂ , the opening degree is controlled from the fully open to the set opening degree y.

The second switching damper D2 can start to open from t ₁ ′ as shown by the phantom line in FIG. 6 when shifting from air combustion to oxyfuel combustion.

  Next, the operation of the third embodiment will be described.

With the configuration as described above, at the time of transition from air combustion to oxyfuel combustion, the first switching damper D1 of the exhaust gas recirculation means 9 is fully opened between t ₁ and t ₂ shown in FIG. The opening of the damper D2 is controlled from fully closed to the set opening x between t ₁ and t ₁ ′ shown in FIG. 6, and then the first flow rate adjustment between t ₁ ′ and t ₂ shown in FIG. 6. The damper c1 is fully controlled from the set opening x ′ to the fully closed position, the second flow rate adjusting damper c2 is controlled from fully closed to the set opening x, and the exhaust gas recirculation fan 10 is discharged from the stopped state to the set flow rate z. The third switching damper D3 is controlled to the set opening degree y from the fully open state, so that oxygen is introduced into the boiler body 1 from the combustion gas supply line 2 and discharged from the boiler body 1. A part of the combustion exhaust gas is discharged through the exhaust gas recirculation line 8. 10 is recirculated to the combustion gas supply line 2 by the drive of the fuel 10, and the oxyfuel combustion of the fuel is carried out. Therefore, the exhaust gas recirculation means 9 can prevent the combustion exhaust gas to be recirculated from flowing back to the air suction port 3 because the exhaust gas recirculation means 9 is connected to the combustion gas supply line 2 on the discharge side.

  Moreover, the exhaust gas recirculation line 8 of the exhaust gas recirculation means 9 is branched from the exhaust gas line 5 on the discharge side of the induction fan 7 in the same manner as in the second embodiment shown in FIGS. Since a part of the combustion exhaust gas is led from the exhaust gas line 5 on the discharge side of the induction fan 7 to the combustion gas supply line 2, the combustion exhaust gas is oxygenated In the case of shifting to combustion, the flow rate of the flue gas flowing through the induction fan 7 is not significantly reduced as compared with air combustion, and the induction fan 7 has the same amount during air combustion and oxyfuel combustion. Since combustion exhaust gas circulates, there is no concern that it will be difficult to turn down the induction fan 7, and it is not necessary to perform inverter control or review of fan characteristics.

Further, the first flow rate control damper c1 is opening control completed fully closed from set opening x', after the air flow is throttled, the first switching damper D1 from the time of t ₂ in FIG. 6 from the fully opened Since the opening degree is controlled to be fully closed, the physical impact on the first switching damper D1 can be reduced.

  Thus, in the third embodiment shown in FIGS. 5 and 6 as well, as in the second embodiment shown in FIGS. 3 and 4, the combustion exhaust gas is caused to flow backward to the air intake port 3 during the transition from air combustion to oxyfuel combustion. Can be reliably recirculated, and the problem of turndown of the induction fan 7 can be avoided.

  Note that the oxyfuel boiler system of the present invention is not limited to the above-described embodiments, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 Boiler body 2 Combustion gas supply line 3 Air inlet 4 Push-in ventilator 5 Exhaust gas line 7 Induction fan 8 Exhaust gas recirculation line 9 Exhaust gas recirculation means 10 Exhaust gas recirculation fan D1 First switching damper D2 Second switching damper D3 3rd switching damper c1 1st flow adjustment damper c2 2nd flow adjustment damper x setting opening x 'setting opening y setting opening z setting flow

Claims (3)

At startup, air is introduced into the boiler body from the combustion gas supply line to perform air combustion of the fuel, and after startup is complete, oxygen is introduced into the boiler body from the combustion gas supply line and discharged from the boiler body. In an oxyfuel boiler system that recycles part of the combustion exhaust gas that oxyfuels the fuel,
Exhaust gas recirculation means for guiding a part of the combustion exhaust gas from the exhaust gas line on the discharge side of the induction fan to the combustion gas supply line ;
The exhaust gas recirculation means includes
An exhaust gas recirculation line branched from the exhaust gas line on the discharge side of the induction fan and joined to the combustion gas supply line on the suction side of the forced air fan;
Provided in the combustion gas supply line upstream from the confluence connection point of the exhaust gas recirculation line and downstream from the air suction port, and the opening degree is controlled from fully open to fully closed when shifting from air combustion to oxyfuel combustion. A first switching damper;
A second switching damper that is provided in the exhaust gas recirculation line, and whose opening degree is controlled stepwise from fully closed to a set opening degree when shifting from air combustion to oxyfuel combustion;
A third switching damper which is provided in the exhaust gas line downstream from the branch point of the exhaust gas recirculation line and whose opening degree is controlled from fully open to a set opening degree when shifting from air combustion to oxyfuel combustion;
With
The first switching damper is configured to hold the pressure at the junction point of the exhaust gas recirculation line at a negative pressure while controlling the opening degree from fully open to fully closed at the time of transition from air combustion to oxyfuel combustion. Oxy-combustion boiler system. At startup, air is introduced into the boiler body from the combustion gas supply line to perform air combustion of the fuel, and after startup is complete, oxygen is introduced into the boiler body from the combustion gas supply line and discharged from the boiler body. In an oxyfuel boiler system that recycles part of the combustion exhaust gas that oxyfuels the fuel,
Exhaust gas recirculation means for guiding a part of the combustion exhaust gas from the exhaust gas line on the discharge side of the induction fan to the combustion gas supply line;
The exhaust gas recirculation means includes
An exhaust gas recirculation line branched from the exhaust gas line on the discharge side of the induction fan and joined to the combustion gas supply line on the discharge side of the forced air fan;
Provided in the combustion gas supply line upstream from the confluence connection point of the exhaust gas recirculation line and on the discharge side of the forced air blower, the opening degree is controlled from fully open to fully closed at the time of transition from air combustion to oxyfuel combustion. A first switching damper
A first flow rate adjustment damper that is provided in a combustion gas supply line on the suction side of the forced air blower, and that is controlled to be fully closed from a set opening degree at the time of transition from air combustion to oxyfuel combustion;
A second switching damper provided in the exhaust gas recirculation line, the opening of which is controlled from fully closed to a set opening degree when shifting from air combustion to oxyfuel combustion;
A third switching damper which is provided in the exhaust gas line downstream from the branch point of the exhaust gas recirculation line and whose opening degree is controlled from the fully open to the set opening degree when shifting from air combustion to oxyfuel combustion,
The first flow rate control damper after opening control completed fully closed from set opening when moving to oxyfuel combustion from the air combustion, by being configured to opening control to fully closed the first switching damper from the fully opened A featured oxyfuel boiler system. At startup, air is introduced into the boiler body from the combustion gas supply line to perform air combustion of the fuel, and after startup is complete, oxygen is introduced into the boiler body from the combustion gas supply line and discharged from the boiler body. In an oxyfuel boiler system that recycles part of the combustion exhaust gas that oxyfuels the fuel,
Exhaust gas recirculation means for guiding a part of the combustion exhaust gas from the exhaust gas line on the discharge side of the induction fan to the combustion gas supply line;
The exhaust gas recirculation means includes
An exhaust gas recirculation line branched from the exhaust gas line on the discharge side of the induction fan and joined to the combustion gas supply line on the discharge side of the forced air fan;
Provided in the combustion gas supply line upstream from the confluence connection point of the exhaust gas recirculation line and on the discharge side of the forced air blower, the opening degree is controlled from fully open to fully closed at the time of transition from air combustion to oxyfuel combustion. A first switching damper
A first flow rate adjustment damper that is provided in a combustion gas supply line on the suction side of the forced air blower, and that is controlled to be fully closed from a set opening degree at the time of transition from air combustion to oxyfuel combustion;
An exhaust gas recirculation fan provided in the exhaust gas recirculation line and driven and controlled from a stopped state to a set flow rate discharge state at the time of transition from air combustion to oxyfuel combustion;
A second switching damper which is provided in the exhaust gas recirculation line on the discharge side of the exhaust gas recirculation fan and whose opening degree is controlled from a fully closed state to a set opening degree at the time of transition from air combustion to oxyfuel combustion;
A second flow rate adjustment damper that is provided in the exhaust gas recirculation line on the suction side of the exhaust gas recirculation fan and is controlled to open from a fully closed position to a set opening degree when shifting from air combustion to oxyfuel combustion. Branch of the exhaust gas recirculation line A third switching damper that is provided in the exhaust gas line downstream from the point and that is controlled to open from a fully open position to a set opening degree when shifting from air combustion to oxyfuel combustion,
The first flow rate control damper after opening control completed fully closed from set opening when moving to oxyfuel combustion from the air combustion, by being configured to opening control to fully closed the first switching damper from the fully opened A featured oxyfuel boiler system.

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