A flue gas denitration system includes a catalytic reactor accommodating a plurality of catalytic modules, into which a flue gas flows, and a flue gas heater provided on an upstream side of the catalytic reactor in a flow direction of the flue gas. In the flue gas denitration system, switched are a first denitration state in which the flue gas is denitrated by using the plurality of catalytic modules in the catalytic reactor and a second denitration state in which the flue gas is denitrated by using a catalytic module(s) less than those used in the first denitration state while a temperature of the flue gas flowing into the catalytic reactor is made higher than that in the first denitration state by using the flue gas heater. Thus, by making the temperature of the flue gas flowing into the catalytic reactor higher, it is possible to suppress deterioration in denitration performance in the case of using part of the plurality of catalytic modules for denitration.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Stage of PCT/JP2017/004421, filed Feb. 7, 2017, which in turn claims priority to Japanese Patent Application No. 2016-108480, filed May 31, 2016. The contents of each of these applications are incorporated herein by reference in entirety.

TECHNICAL FIELD

The present invention relates to a flue gas denitration system, an incinerator, and a flue gas denitration method.

BACKGROUND ART

It is well known that in a flue gas denitration system using catalysts, ammonium sulfate and acidic ammonium sulfate are deposited as reaction products on catalyst surfaces, with an operating temperature of a catalytic reactor and concentrations of moisture, sulfur trioxide, and ammonia in a flue gas as factors. With the deposition of the reaction products, the catalytic activity is deteriorated and required denitration performance cannot be achieved. Then, by regularly carrying the catalysts outside and performing a water washing treatment or a heating treatment on the catalysts, the catalysts are recovered. In the case of performing the above operation, however, it is necessary to stop the operations of the flue gas denitration system and a facility including the system. Then, Japanese Patent Application Laid-Open No. 10-192657 (Document 1) discloses a method of recovering catalysts without stopping a facility. In this method, the inside of a catalyst tower (catalytic reactor) is divided into two or more chambers, and recovery of the catalysts is performed in each chamber while a flue gas is caused to pass through the other chambers, to be thereby denitrated.

Further, in a combustion flue gas cleaning method disclosed in Japanese Patent Application Laid-Open No. 10-15345, a combustion flue gas is introduced to a moving layer type desulfurization layer, to be thereby desulfurized, and then the desulfurized combustion flue gas is divided into two, temperature rise adjustment is performed in accordance with a desulfurization state of each divided flue gas, and ammonia catalytic reduction denitration is performed thereon in a denitration layer.

In the method of Document 1, when it is understood that a plurality of catalytic modules are provided in the catalyst tower (catalytic reactor), the number of catalytic modules to be used for denitration decreases during the recovery of the catalysts in each chamber and therefore the denitration performance is deteriorated.

SUMMARY OF INVENTION

The present invention is intended for a flue gas denitration system, and it is an object of the present invention to suppress deterioration in denitration performance in the case of using part of a plurality of catalytic modules for denitration.

The flue gas denitration system according to the present invention includes a catalytic reactor accommodating a plurality of catalytic modules, into which a flue gas flows, a flue gas heater provided on an upstream side of the catalytic reactor in a flow direction of the flue gas, and a control unit, and in the flue gas denitration system, the control unit switches between a first denitration state in which the flue gas is denitrated by using the plurality of catalytic modules in the catalytic reactor and a second denitration state in which the flue gas is denitrated by using a catalytic module(s) less than those used in the first denitration state while a temperature of the flue gas flowing into the catalytic reactor is made higher than that in the first denitration state by using the flue gas heater.

By the present invention, it is possible to suppress deterioration in denitration performance in the case of using part of the plurality of catalytic modules for denitration.

In a preferred embodiment of the present invention, the catalytic reactor has a plurality of catalytic chambers arranged in parallel with the flow of the flue gas, the plurality of catalytic modules are accommodated in the plurality of catalytic chambers, and a plurality of flow paths of the flue gas leading from the flue gas heater to the plurality of catalytic chambers are individually openable and closable.

In this case, preferably, the flue gas denitration system further includes a catalyst recovery part capable of selectively supplying the plurality of catalytic chambers with a catalyst recovery gas.

More preferably, the catalyst recovery part includes a circulation flow path for circulating a circulating gas and a circulating gas heater provided in the circulation flow path, for heating the circulating gas, the control unit includes a catalytic chamber selected out of the plurality of catalytic chambers in part of the circulation flow path, and the catalyst recovery gas is the circulating gas which has been heated to a predetermined temperature or higher by circulation.

For example, a desulfurization apparatus is provided in an exhaust path for discharging the flue gas from a generation source of the flue gas, and the catalyst recovery gas passing through the selected catalytic chamber flows into an upstream side of the desulfurization apparatus in the exhaust path.

In another preferred embodiment of the present invention, the catalytic reactor includes a catalytic chamber into which the flue gas flows and a catalyst recovery chamber provided adjoining the catalytic chamber, to which a catalyst recovery gas is supplied, and the control unit selectively arranges each of the plurality of catalytic modules into the catalytic chamber or the catalyst recovery chamber.

The present invention is also intended for an incinerator. The incinerator according to the present invention includes a combustion chamber in which waste is burned, an exhaust path for discharging a flue gas generated in the combustion chamber, from the combustion chamber, and a flue gas denitration system defined as above which is provided in the exhaust path.

The present invention is still also intended for a flue gas denitration method in the flue gas denitration system.

DESCRIPTION OF EMBODIMENTS

FIG. 1is a view showing a configuration of an incinerator1in accordance with a preferred embodiment of the present invention. The incinerator1is, for example, a stoker-type furnace which burns garbage that is waste while conveying the same by using a plurality of grates. The incinerator1may be a furnace (e.g., a fluidized bed furnace, a kiln furnace, or the like) other than the stoker-type furnace.

The incinerator1includes a combustion chamber2and an exhaust path3. The combustion chamber2burns garbage and burns a combustible gas generated from the garbage. The exhaust path3discharges a flue gas (combustion gas) generated in the combustion chamber2, from the combustion chamber2, and guides the gas to a stack35. Specifically, the flue gas generated from the combustion chamber2as a generation source flows inside the exhaust path3from the combustion chamber2to the stack35. The stack35discharges the flue gas to the atmosphere. InFIG. 1, the exhaust path3is indicated by a heavy solid line.

In the exhaust path3, from the combustion chamber2toward the stack35, i.e., from an upstream side toward a downstream side in a flow direction of the flue gas, provided are a gas cooler31, a chemical agent supply part32, a bag filter33, a flue gas denitration system4, and an induced draft fan34in this order. The gas cooler31reduces a temperature of the flue gas by supplying the flue gas with water. The chemical agent supply part32causes dechlorination and desulfurization reactions on the flue gas flowing in the exhaust path3inside the exhaust path3and the bag filter33by blowing chemical agents for dechlorination and desulfurization (for example, hydrated lime powder) into the exhaust path3on an inlet side of the bag filter33, to thereby remove the reaction products and dust contained in the flue gas. In other words, the chemical agent supply part32and the bag filter33are both a dechlorination apparatus and a desulfurization apparatus. The bag filter33also removes dust contained in the flue gas. The flue gas denitration system4injects ammonia on an inlet side thereof, to decompose a nitrogen oxide (NOx) by catalytic reaction and decompose dioxin generated by combustion of waste, depending on the catalysts to be used. The induced draft fan34guides the flue gas in the exhaust path3to the stack35.

The flue gas denitration system4includes a flue gas heater41, an ammonia supply part42, a catalytic reactor43, a catalyst recovery part44, and a control unit400ofFIG. 2. The control unit400performs general control of the flue gas denitration system4. The control unit400includes a flue gas temperature control part410, a denitration control part420, a switching control part470, and a circulating gas temperature control part460.

The flue gas heater41ofFIG. 1is provided in the exhaust path3. To the flue gas heater41, a heat source411is connected through a valve412. Further, in the vicinity of a downstream side of the flue gas heater41in the exhaust path3, provided is a temperature detection part413which detects a temperature of the flue gas discharged from the flue gas heater41. A detection value of the temperature detection part413is inputted to the flue gas temperature control part410, and by the control over the degree of opening of the valve412on the basis of the detection value, a flow rate of a heating medium to be supplied from the heat source411to the flue gas heater41is changed. The heat source411is, for example, a boiler21provided on an upper portion of the combustion chamber2, and steam from the boiler21is supplied as the heating medium to the flue gas heater41. The flue gas discharged from the bag filter33is heated to a predetermined temperature by the flue gas heater41.

The ammonia supply part42is connected to the exhaust path3through a valve421, and supplies ammonia as a reducing agent to the flue gas discharged from the flue gas heater41on an upstream side of inflow paths381to383leading to the catalytic reactor43which branches into a plurality of chambers. The ammonia supply part42may be provided on an upstream side of the flue gas heater41, and is preferably provided on a downstream side of the bag filter33. A denitration control part420is connected to the ammonia supply part42in order to control the supply amount by the control over the degree of opening of the valve421or the control over the stroke, the number of rotation, and the like of an aqueous ammonia supply pump. The denitration control part420has the function of controlling the ammonia supply amount on the basis of an input value from a NOx concentration detection part37which detects a NOx concentration in the flue gas discharged from the stack35. Sometimes a NOx concentration detection part is also provided at an outlet of the bag filter33in order to improve the controllability. The catalytic reactor43which is a catalytic reactor has a plurality of catalytic chambers431,432, and433. The plurality of catalytic chambers431to433accommodate a plurality of catalytic modules439, respectively. In the exemplary case shown inFIG. 1, one catalytic module439is accommodated in each of the catalytic chambers431to433. In the present preferred embodiment, the same volume of catalysts is held in each of the plurality of catalytic chambers431to433.

In the vicinity of an upstream side of the catalytic reactor43, the exhaust path3branches into a plurality of inflow paths381to383, and the plurality of inflow paths381to383are connected to respective inflow ports of the plurality of catalytic chambers431to433. The inflow paths381to383are provided with dampers4011to4013, respectively. A plurality of outflow paths391to393in the exhaust path3are connected to respective outflow ports of the plurality of catalytic chambers431to433and are joined and connected to the induced draft fan34. The outflow paths391to393are provided with dampers4021to4023, respectively. In the flue gas denitration system4, provided are the flue gas heater41, the ammonia supply part42, and the catalytic reactor43in this order from the upstream side toward the downstream side of the exhaust path3. In the exemplary case shown inFIG. 1, three catalytic chambers431to433are provided, and in the following description, are referred to as a “first catalytic chamber431”, a “second catalytic chamber432”, and a “third catalytic chamber433”, respectively.

The catalyst recovery part44has a circulation flow path45, a circulating gas heater46, and a circulating gas fan450. The circulating gas heater46and the circulating gas fan450are provided in the circulation flow path45. The circulation flow path45has a plurality of first auxiliary flow paths4511to4513and a plurality of second auxiliary flow paths4521to4523. The plurality of first auxiliary flow paths4511to4513are connected to the plurality of inflow paths381to383, respectively. The first auxiliary flow paths4511to4513are provided with dampers4711to4713, respectively. The plurality of first auxiliary flow paths4511to4513are joined to one another into one flow path on an opposite side of the inflow paths381to383and connected to the circulating gas fan450. The plurality of second auxiliary flow paths4521to4523are connected to the plurality of outflow paths391to393, respectively. The second auxiliary flow paths4521to4523are provided with dampers4721to4723, respectively. The plurality of second auxiliary flow paths4521to4523are joined to one another into one flow path on an opposite side of the outflow paths391to393and connected to the circulating gas heater46.

In the catalyst recovery part44, one of the first to third catalytic chambers431to433is selectively included in the circulation flow path45. In a case, for example, where the circulation flow path45including the first catalytic chamber431is formed, the damper4711of the first auxiliary flow path4511connected to the inflow path381of the first catalytic chamber431and the damper4721of the second auxiliary flow path4521connected to the outflow path391of the first catalytic chamber431are opened and the remaining dampers4712,4713,4722, and4723are closed. Further, the damper4011of the inflow path381of the first catalytic chamber431and the damper4021of the outflow path391thereof are also closed. The circulation flow path45leading from the first catalytic chamber431through (part of) the inflow path381, the first auxiliary flow path4511, the circulating gas fan450, the circulating gas heater46, the second auxiliary flow path4521, and (part of) the outflow path391back to the first catalytic chamber431is thereby formed. The circulation flow path45including the second catalytic chamber432and the circulation flow path45including the third catalytic chamber433are also formed in the same manner as described above. In the flue gas denitration system4, a switching part which includes the selected one of the plurality of catalytic chambers431to433in part of the circulation flow path45is implemented by the dampers4711to4713(generally referred to as a “damper471” inFIG. 2) of the plurality of first auxiliary flow paths4511to4513and the dampers4721to4723(generally referred to as a “damper472” inFIG. 2) of the plurality of second auxiliary flow paths4521to4523, and the switching part is controlled by the switching control part470. The switching control part470also performs control over the dampers4011to4013(generally referred to as a “damper401” inFIG. 2) of the plurality of inflow paths381to383and the dampers4021to4023(generally referred to as a “damper402” inFIG. 2) of the plurality of outflow paths391to393.

In the exemplary case shown inFIG. 1, the gas (hereinafter, referred to as a “circulating gas”) inside the circulation flow path45is circulated by driving of the circulating gas fan450through the circulating gas heater46, one of the second auxiliary flow paths4521to4523, the catalytic chamber, and one of the first auxiliary flow paths4511to4513in this order (counterclockwise inFIG. 1). The circulating gas may be circulated clockwise in the circulation flow path45ofFIG. 1. The circulating gas heater46heats the circulating gas flowing inside the circulation flow path45by the heating medium from the heat source461, and the like. In the vicinity of a downstream side of the circulating gas heater46(between the circulating gas heater46and the second auxiliary flow paths4521to4523) in the circulation flow path45, provided is a temperature detection part462which detects a temperature of the circulating gas. A detection value of the temperature detection part462is inputted to the circulating gas temperature control part460, and the amount of heat of the circulating gas heater46is thereby controlled.

In the circulation flow path45, to a position453(hereinafter, referred to as an “introduction position453”) between the plurality of first auxiliary flow paths4511to4513and the circulating gas fan450, connected is an air introduction part48. The air introduction part48has a damper481. By opening the damper481, outside air is introduced into the circulation flow path45by the circulating gas fan450. In the circulation flow path45, one end of a connection flow path49is connected between the circulating gas fan450and the circulating gas heater46. The other end of the connection flow path49is connected to a position between the gas cooler31and (a supply position of the chemical agent from) the chemical agent supply part32in the exhaust path3. The connection flow path49is provided with a damper491. By opening the damper491, part of the circulating gas flowing inside the circulation flow path45flows into the exhaust path3through the connection flow path49.

FIG. 3is a flowchart showing an operation flow relating to denitration in the incinerator1, andFIG. 4is a time chart showing an operation relating to denitration. In an upper stage ofFIG. 4, a period while each catalytic chamber is used for denitration is indicated by a heavy solid line and another period while the catalytic chamber is not used is indicated by a blank rectangle. In a lower stage ofFIG. 4, shown is a heating temperature of the flue gas by the flue gas heater41, i.e., an operating temperature of the catalytic reactor43. In the incinerator1ofFIG. 1, while garbage is burned in the combustion chamber2, denitration of the flue gas is performed in succession by the flue gas denitration system4. During a normal operation in the flue gas denitration system4, the flue gas discharged from the bag filter33is heated by the flue gas heater41to a constant preset temperature for normal operation of catalytic reactor (170° C. inFIG. 4). InFIG. 4, a period while the normal operation is performed in the flue gas denitration system4is indicated by an arrow with reference sign P1.

Further, in the normal operation, the dampers4011to4013of all the inflow paths381to383and the dampers4021to4023of all the outflow paths391to393are opened. The flue gas flowing in the exhaust path3thereby flows into the first to third catalytic chambers431to433through the plurality of inflow paths381to383in succession and is denitrated by the plurality of catalytic modules439. In the preferable flue gas denitration system4, a flowmeter and a differential pressure gauge which are not shown are provided, and the respective degrees of opening of the dampers4011to4013of the plurality of inflow paths381to383, and the like, are controlled so that the flow rates of the flue gases flowing into the first to third catalytic chambers431to433may be equal to one another. The denitrated flue gas is guided to the stack35through the plurality of outflow paths391to393and discharged to the atmosphere. Thus, in the normal operation of the flue gas denitration system4, a state (hereinafter, referred to as a “first denitration state”) in which the flue gas is denitrated by using the catalytic modules439in the first to third catalytic chambers431to433while the temperature of the flue gas flowing into the catalytic reactor43is kept at the preset temperature for normal operation of catalytic reactor is maintained (Step S11). Further, in the first denitration state, the dampers4711to4713of all the first auxiliary flow paths4511to4513and the dampers4721to4723of all the second auxiliary flow paths4521to4523are closed.

After the normal operation has continued for a predetermined time, a high-temperature operation for recovering the catalytic module439in one of the catalytic chambers431to433is performed. InFIG. 4, a period while the high-temperature operation is performed in the flue gas denitration system4is indicated by an arrow with reference sign P2. In the high-temperature operation, first, the heating temperature of the flue gas by the flue gas heater41is gradually raised from the preset temperature for normal operation of catalytic reactor by the control of the flue gas temperature control part410(Step S12). When the heating temperature of the flue gas (i.e., the operation temperature of catalytic reactor) reaches a predetermined preset temperature for recovery operation of catalytic reactor (200° C. inFIG. 4), the heating temperature is maintained constant at the preset temperature for recovery operation of catalytic reactor.

Subsequently, among the plurality of catalytic chambers431to433, a catalytic chamber selected as a catalytic chamber in which the catalytic module439thereinside should be recovered (herein, a catalytic chamber in which a continuous gas passing time is longest, and hereinafter, it will be referred to as a “selected catalytic chamber”) is specified, and a damper of an inflow path connected to the selected catalytic chamber (the damper4011,4012, or4013of one of the inflow paths381to383) and a damper of an outflow path connected to the selected catalytic chamber (the damper4021,4022, or4023of one of the outflow paths391to393) are closed. In the flue gas denitration system4, the catalytic module439in the selected catalytic chamber is not thereby used for denitration of the flue gas. On the other hand, the flue gas at the preset temperature for recovery operation of catalytic reactor higher than the preset temperature for normal operation of catalytic reactor flows in succession into the catalytic chambers used for denitration of the flue gas, i.e., all the catalytic chambers other than the selected catalytic chamber. Thus, in the flue gas denitration system4, a state (hereinafter, referred to as a “second denitration state”) in which the flue gas is denitrated by using catalytic modules439less than those in the first denitration state while the temperature of the flue gas flowing into the catalytic reactor43is made higher than that in the first denitration state by using the flue gas heater41is achieved. The second denitration state is maintained for a predetermined time period.

In the catalyst recovery part44, the damper of the first auxiliary flow path connected to the selected catalytic chamber (the damper4711,4712, or4713of one of the first auxiliary flow paths4511to4513) and the damper of the second auxiliary flow path connected to the selected catalytic chamber (the damper4721,4722, or4723of one of the second auxiliary flow paths4521to4523) are opened by the control of the switching control part470, and the circulation flow path45including the selected catalytic chamber is formed. In other words, the switching control part470includes the selected catalytic chamber in part of the circulation flow path45. Subsequently, by starting to drive the circulating gas fan450, circulation of a gas existing in the circulation flow path45, i.e., the circulating gas is started. The circulation of the circulating gas is performed concurrently with the period of the second denitration state. As described later, the circulating gas is mainly air.

The circulating gas flowing inside the circulation flow path45is heated by the circulating gas heater46and the temperature of the circulating gas is gradually raised. At that time, since the temperature of the selected catalytic chamber itself is near the preset temperature for recovery operation of catalytic reactor, the temperature rise of the circulating gas becomes quicker. When the temperature of the circulating gas is raised to a predetermined catalyst recovery temperature (for example, about 300° C.), heat decomposition of unnecessary substances (herein, ammonium sulfate and acidic ammonium sulfate) adhered to the catalytic module439in the selected catalytic chamber is started (Step S13). For example, ammonium sulfate and acidic ammonium sulfate are decomposed into SO3(sulfur trioxide) and NH3(ammonia) and mixed into the circulating gas. In the catalyst recovery part44, it is understood that the circulating gas at a predetermined temperature or higher is a gas for catalyst recovery.

When it is confirmed, by the temperature detection part462, that the temperature of the circulating gas rises to a first preset temperature (for example, 300° C.), the outside air is introduced from the introduction position453into the circulation flow path45by the air introduction part48. The introduction flow rate of air by the air introduction part48depends on the rate of temperature rise of the circulating gas, which is set in advance. Further, by opening the damper491of the connection flow path49, part of the circulating gas flows into the vicinity of an upstream side of the chemical agent supply part32in the exhaust path3through the connection flow path49. Together with sulfur oxide (SOx) in the flue gas, SO3contained in the circulating gas is removed in the exhaust path3and the bag filter33. Further, NH3contained in the circulating gas is used for denitration reaction in the catalytic reactor43provided on a downstream side of the chemical agent supply part32(denitration reaction in the catalytic modules439of the catalytic chambers other than the selected catalytic chamber). Furthermore, in the circulation flow path45, it is preferable that the degrees of opening of the dampers481and491, and the like, should be adjusted so that the flow rate of the circulating gas flowing out from the connection flow path49may be equal to the flow rate of air flowing into the circulation flow path45by the air introduction part48. Since the flow rate of the circulating gas flowing out from the connection flow path49into the exhaust path3is sufficiently lower than that of the flue gas flowing in the exhaust path3, the temperature of the flue gas is not changed excessively by the mixture of the circulating gas.

In the circulating gas heater46, when it is confirmed that the temperature of the circulating gas rises to a second preset temperature (for example, 370° C.) higher than the first preset temperature, the temperature of the circulating gas is maintained constant at the second preset temperature for a predetermined time. Thus, while maintaining the second denitration state, the removal of the unnecessary substances adhered to the catalytic module439in the selected catalytic chamber, i.e., thermal recovery of the catalytic module439is performed for a certain time (Step S14). In the exemplary case shown inFIG. 4, it is confirmed that the activity of the catalytic module439is recovered to 95% or more.

After that, driving of the circulating gas fan450is stopped and the circulation of the circulating gas in the circulation flow path45is thereby stopped. Further, it is desirable that an SO3concentration meter and an NH3concentration meter are provided in the connection flow path49and after it is confirmed that an SO3concentration and an NH3concentration of the circulating gas flowing from the circulation flow path45toward the exhaust path3are lowered to predetermined values or lower, the circulation of the circulating gas is stopped. When the temperature of the circulating gas is 370° C. or higher, since the unnecessary substances adhered to the catalytic module439are sublimated in a short time, there arises no problem if the above concentration meters are omitted. As a matter of course, in accordance with the type of the catalysts to be used and the like, the temperature of the circulating gas and the required time for recovery may be determined.

When the circulation of the circulating gas in the circulation flow path45is stopped, the damper4711,4712, or4713of the one of the first auxiliary flow paths4511to4513connected to the selected catalytic chamber and the damper4721,4722, or4723of the one of the second auxiliary flow paths4521to4523connected to the selected catalytic chamber are closed and the circulation flow path45including the selected catalytic chamber is cut off (the catalyst recovery part44is stopped). Then, the damper4011,4012, or4013of the one of the inflow paths381to383connected to the selected catalytic chamber and the damper4021,4022, or4023of the one of the outflow paths391to393connected to the selected catalytic chamber are opened and the flue gas flowing in the exhaust path3flows into all the catalytic chambers431to433(Step S15). In other words, all the catalytic chambers431to433are switched into a flue gas passing state. In the flue gas heater41, the heating temperature of the flue gas is gradually lowered from the preset temperature for recovery operation of catalytic reactor (Step S16). When the temperature of the flue gas discharged from the flue gas heater41reaches the preset temperature for normal operation of catalytic reactor, the temperature is maintained constant at the preset temperature for normal operation of catalytic reactor. The catalytic reactor43is thereby returned to the first denitration state (Step S11).

Actually, by selecting each of the catalytic chambers431to433as the selected catalytic chamber in turn at regular time intervals and performing the process steps S12to S16, the respective catalytic modules439in the catalytic chambers431to433are recovered. In the exemplary case shown inFIG. 4, respective timings when the first to third catalytic chambers431to433are selected as the selected catalytic chamber are shifted so that the period P2in which the high-temperature operation is performed may occur at regular intervals (equal intervals), in other words, the recovery interval may be constant. Specifically, in each of the catalytic chambers431to433, the recovery of the catalytic module439is performed once per 1500 hours, and in the whole catalytic reactor43, the recovery of the catalytic module439is performed once per 500 hours. 1500 hours as the recovery interval is only one example, and an actual recovery interval is determined for each plant depending on design conditions, checks in a trial operation, and the like.

Herein, a relation between the temperature of the flue gas flowing into the catalytic reactor43(which is equal to the heating temperature of the flue gas by the flue gas heater41and hereinafter, referred to simply as an “flue gas temperature during denitration”) and the volume of catalysts required in the catalytic reactor43(hereinafter, referred to simply as the “required volume of catalysts”) will be described.FIG. 5is a table showing a relation between the flue gas temperature during denitration and the required volume of catalysts. In the calculation of the required volume of catalysts at each flue gas temperature during denitration, the type of catalysts, the flow rate of the flue gas flowing into the catalytic reactor43, the concentration of nitrogen oxide (or the concentration of dioxin) in the flue gas, the removal rate of nitrogen oxide (or the removal rate of dioxin), the leak amount of ammonia, and the like are set as predetermined conditions.

In the exemplary case shown inFIG. 5, when the flue gas temperature during denitration is always 170° C., the required volume of catalysts is 26.8 m3. In a case where three catalytic chambers are provided in the catalytic reactor43, in consideration of the period in which one catalytic chamber is not used due to recovery of the catalysts (hereinafter, referred to as a “partial use period”), the volume of catalysts required to fill the two catalytic chambers is 26.8 m3. Actually, since the catalytic activity is gradually deteriorated due to the deposition of the unnecessary substances, there is a need to allow for some margin (the same applies to the following). On the other hand, assuming that the flue gas temperature during denitration in the normal operation is 170° C., by raising the flue gas temperature during denitration to 200° C. immediately before the partial use period, the volume of catalysts required to fill the two catalytic chambers becomes 18.6 m3.

In other words, in the case where the flue gas temperature during denitration is always constant (the flue gas temperature during denitration is not raised in the partial use period), in the catalytic reactor43provided with two catalytic chambers and the catalytic reactor43provided with three catalytic chambers, the total volume of catalysts required to fill all the catalytic chambers (hereinafter, referred to as the “volume of catalysts for filling”) becomes twice and 1.5 times the required volume of catalysts, respectively. In contrast to this, in a case where the flue gas temperature during denitration is raised in the partial use period from that in the normal operation, it is possible to reduce the volume of catalysts for filling. Specifically, in the case where the flue gas temperature during denitration is always constant at 170° C., in the catalytic reactor43provided with three catalytic chambers, the volume of catalysts for filling becomes 40.2 m3at the minimum. On the other hand, in the case where the flue gas temperature during denitration is raised to 200° C. in the partial use period, the volume of catalysts for filling becomes 27.9 m3, and it is possible to make the volume of catalysts for filling almost equal to that in the case where the catalytic reactor43is provided with only one catalytic chamber while the flue gas temperature during denitration is always constant at 170° C. In the flue gas denitration system4, assuming that the number of catalytic chambers is n (n is an integer not less than 2), in (n−1) catalytic chambers, the volume of catalysts for filling is determined so that the required denitration performance can be continuously achieved under the preset temperature for recovery operation of catalytic reactor. Actually, the volume of catalysts for filling is determined also in consideration of the deterioration in the catalytic activity in the recovery interval.

As described above, in the flue gas denitration system4ofFIG. 1, provided are the catalytic reactor43accommodating the plurality of catalytic modules439, into which the flue gas flows, and the flue gas heater41provided on the upstream side of the catalytic reactor43in the flow direction of the flue gas. Then, the control unit400switches between the first denitration state in which the flue gas is denitrated by using the plurality of catalytic modules439in the catalytic reactor43and the second denitration state in which the flue gas is denitrated by using a catalytic module(s)439less than those used in the first denitration state while the temperature of the flue gas flowing into the catalytic reactor43is made higher than that in the first denitration state by using the flue gas heater41. Thus, by raising the temperature of the flue gas flowing into the catalytic reactor43, it becomes possible to suppress deterioration in denitration performance in the case of using part of the plurality of catalytic modules439for denitration.

In the denitration with the catalysts, in a case where the flue gas from the bag filter and the like is reheated to 200 to 230° C. by the flue gas heater and caused to flow into the catalytic reactor, it is possible to reduce a rate of catalyst deterioration due to the deposition of ammonium sulfate and acidic ammonium sulfate and thereby possible to suppress deterioration in denitration performance. On the other hand, generally, steam generated in the boiler of the incinerator is often used for power generation, and reduction in the consumption of the steam in the incinerator itself increases power generation efficiency. Therefore, it is preferable that the heating temperature of the flue gas by the flue gas heater using the steam from the boiler should be lower. In a case, for example, where hydrated lime is used as a chemical agent for dechlorination and desulfurization, since the temperature of the flue gas in the bag filter is set at about 150° C., as the heating temperature is made higher in order to reduce the rate of catalyst deterioration due to the deposition of ammonium sulfate and acidic ammonium sulfate, the consumption of steam disadvantageously becomes higher.

In contrast to this, in the flue gas denitration system4, since it is possible to make the flue gas temperature during denitration in the normal operation relatively low (170° C. in the exemplary case shown inFIG. 4), it is possible to make the heating temperature in the flue gas heater41low and reduce the consumption of steam. As a result, it is possible to increase the power generation efficiency in the incinerator1. In a case, for example, where the flue gas at 150° C. in the normal operation is heated to 170° C. by the flue gas heater41, it is possible to increase the power generation efficiency by about 1.5% as compared with another case where the flue gas is heated to a certain temperature (200° C.) in order to suppress the deposition of unnecessary substances. In the exemplary case shown inFIG. 4, though the consumption of steam in the incinerator1temporarily increases with the flue gas temperature during denitration at 200° C. at intervals of 500 hours, even if the incinerator1is operated for 8000 hours per year, the temporary increase in the consumption of steam occurs only 16 times. Since the thermal recovery of the catalytic module439is completed, for example, in about 12 hours, this does not cause a great loss.

In the flue gas denitration system4ofFIG. 1, the catalytic reactor43has the plurality of catalytic chambers431to433arranged in parallel with the flow of the flue gas, and the plurality of flow paths (i.e., the inflow paths381to383) of the flue gas leading from the flue gas heater41to the plurality of catalytic chambers431to433are individually openable and closable. In the flue gas denitration system4, it is thereby possible to continuously perform denitration while the catalytic module439in part of the catalytic chambers is not used. It is thereby possible to ensure an operating time (the amount of incineration) required in the incinerator1.

The catalyst recovery part44is capable of selectively supplying the plurality of catalytic chambers431to433with a catalyst recovery gas (the heated circulating gas in the above description). It is thereby possible to easily recover the catalytic modules439in the catalytic chambers431to433(i.e., on-line). Further, the switching control part470includes the selected catalytic chamber in part of the circulation flow path45, and the circulating gas heater46heats the circulating gas circulated in the circulation flow path45. It is thereby possible to easily prepare (generate) the catalyst recovery gas which is the circulating gas at a predetermined temperature or higher.

Further, in the exemplary case shown inFIG. 4, since the selected catalytic chamber itself accumulates heat by raising the flue gas temperature during denitration to 200° C. immediately before the thermal recovery, the heating temperature by the circulating gas heater46during the thermal recovery becomes, for example, about 120 to 170° C. As an example of thermal recovery, in the catalytic module439in which the preset temperature for normal operation of catalytic reactor is 180° C. and the activity is lowered to 80% immediately before the thermal recovery, by circulating the circulating gas at 320° C. for about two hours, the activity can be recovered to almost 100%.

As already described, the gas used for the thermal recovery of the catalytic module contains noxious SO3and NH3. Herein, a flue gas denitration system of the comparative example is assumed in which a small amount of SO3and NH3are mixed into the flue gas to be discharged and the flue gas is discharged to the atmosphere. In the flue gas denitration system of the comparative example, the thermal recovery of the catalysts is performed while the temperature of the gas to be used for the thermal recovery is lower than respective sublimation temperatures of ammonium sulfate and acidic ammonium sulfate and decomposition rates of ammonium sulfate and acidic ammonium sulfate are made lower. In this case, however, it is necessary to control the decomposition rates of ammonium sulfate and acidic ammonium sulfate while checking the SO3concentration and the NH3concentration, and therefore the processing becomes complicated. Further, though there is a possible case where SO3and NH3contained in the gas used for the thermal recovery should be removed by using a dedicated removal apparatus, the manufacturing cost of the flue gas denitration system disadvantageously increases by additionally providing the removal apparatus in this case.

In contrast to this, in the flue gas denitration system4ofFIG. 1, the desulfurization apparatus is provided in the exhaust path3leading from the combustion chamber2to the flue gas heater41, and the circulating gas passing through the selected catalytic chamber flows into an upstream side of the desulfurization apparatus in the exhaust path3. It is thereby possible to remove SO3and the like contained in the circulating gas passing through the selected catalytic chamber and appropriately discharge the flue gas to the atmosphere without performing a complicate processing such as the control over the decomposition rates of ammonium sulfate and acidic ammonium sulfate. Further, since the desulfurization apparatus is usually provided in the incinerator1, it is possible to suppress an increase in manufacturing cost of the incinerator1and the flue gas denitration system4. As already described, NH3contained in the circulating gas is used for the denitration reaction in the catalytic chambers during denitration (other than the selected catalytic chamber) in the catalytic reactor43.

Though the chemical agent supply part32supplies chemical agents for dechlorination and desulfurization into the exhaust path3in the flue gas denitration system4ofFIG. 1, in a case, for example, where the chemical agent supply part32is omitted and the gas cooler31is a semi-dry scrubber or the like which sprays a hydrated lime slurry by using an atomizer or in a spray, it is understood that the gas cooler31is a desulfurization apparatus. In this case, as indicated by the broken line with reference sign49ainFIG. 1, an end portion of the connection flow path is connected in the vicinity of an upstream side of the gas cooler31and SO3and the like contained in the circulating gas are removed by the gas cooler31.

In the incinerator1, since properties of the flue gas are not stable due to variation in garbage components, the rate of catalyst deterioration is not always constant. Therefore, there may be a case where catalytic performance at each time is calculated from the nitrogen oxide concentration detected by the NOx concentration detection part37provided on an upstream side of the stack35and a timing for the thermal recovery of the catalytic module439is determined. In the flue gas denitration system4ofFIG. 1, since it is possible to perform the thermal recovery of the catalytic module439while operating the incinerator1, the timing for the thermal recovery can be freely determined.

FIG. 6is a view showing another example of a flue gas denitration system4. In the flue gas denitration system4ofFIG. 6, a flue gas introduction part48ais additionally provided in the flue gas denitration system4ofFIG. 1and the flue gas can be introduced into the circulation flow path45of the catalyst recovery part44. Other constituent elements are the same as those shown inFIG. 1and the identical constituent elements are represented by the same reference signs.

The flue gas introduction part48aincludes a flue gas introduction flow path482and a damper483. An end of the flue gas introduction flow path482is connected to a position between the flue gas heater41and the ammonia supply part42in the exhaust path3. The other end of the flue gas introduction flow path482is connected to a position between the plurality of first auxiliary flow paths4511to4513and the circulating gas fan450in the circulation flow path45. The damper483is provided in the flue gas introduction flow path482.

When the thermal recovery of the catalytic module439in the selected catalytic chamber is performed, the circulation flow path45including the selected catalytic chamber is formed. Subsequently, by opening the damper483of the flue gas introduction flow path482, the flue gas passing through the bag filter33and heated by the flue gas heater41is introduced into the circulation flow path45. As already described, in the thermal recovery of the catalytic module439, the temperature of the flue gas discharged from the flue gas heater41is raised to the preset temperature for recovery operation of catalytic reactor (for example, 200° C.) higher than that in the normal operation. Thus, the gas which has been at high temperature in advance is introduced into the circulation flow path45. The flue gas is heated by the circulating gas heater46while being circulated in the circulation flow path45as the circulating gas by driving of the circulating gas fan450. After the flue gas in the required amount is introduced into the circulation flow path45by opening the damper483of the flue gas introduction flow path482for a certain time, the damper483is closed.

When it is confirmed by the temperature detection part462that the temperature of the circulating gas is raised to the first preset temperature (for example, 300° C.), the dampers483and491are opened. Introduction of the flue gas by the flue gas introduction part48ais thereby restarted and part of the circulating gas containing products (SO3and the like) generated by the thermal recovery flows in the vicinity of the upstream side of the chemical agent supply part32in the exhaust path3through the connection flow path49. As already described, SO3and the like in the circulating gas flowing into the exhaust path3are removed in the exhaust path3and the bag filter33. After the thermal recovery of the catalytic module439is completed, the damper483is closed and the damper481of the air introduction part48is opened. The outside air is thereby introduced into the circulation flow path45and the gas in the circulation flow path45is replaced by the air. After that, the dampers481and491are closed and the driving of the circulating gas fan450is stopped. Then, the state is returned to the first denitration state in which the flue gas is denitrated by using the catalytic modules439in all the catalytic chambers431to433.

As described above, in the flue gas denitration system4ofFIG. 6, the flue gas heated by the flue gas heater41is introduced into the circulation flow path45in the catalyst recovery part44, and heated by the circulating gas heater46while being circulated in the circulation flow path45as the circulating gas. As compared with the exemplary case shown inFIG. 1where the outside air is introduced into the circulation flow path45, it is thereby possible to heat the circulating gas to a predetermined catalyst recovery temperature in a shorter time while reducing heat consumption in the circulating gas heater46. Further, in the flue gas denitration system4ofFIG. 6, like in the flue gas denitration system4ofFIG. 1, there may be a case where the outside air is heated and used for the thermal recovery of the catalytic module439.

The method of introducing the flue gas into the circulation flow path45can be performed by another configuration.FIG. 7is a view showing still another example of a flue gas denitration system4. In the flue gas denitration system4ofFIG. 7, the circulating gas fan450is attached in an orientation opposite to that in the case ofFIG. 1so that the circulating gas may be circulated clockwise in the circulation flow path45. Further, in the circulation flow path45, the connection flow path49is connected to a position between the circulating gas fan450and the plurality of first auxiliary flow paths4511to4513and the air introduction part48is connected to a position between the plurality of second auxiliary flow paths4521to4523and the circulating gas heater46. Furthermore, the temperature detection part462is provided between the circulating gas heater46and the circulating gas fan450.

In the first denitration state in the flue gas denitration system4ofFIG. 7, by slightly opening the dampers4721to4723of the plurality of second auxiliary flow paths4521to4523and the dampers4711to4713of the plurality of first auxiliary flow paths4511to4513, the circulation flow path45including all the catalytic chambers431to433is formed. Then, part of the flue gas passing through the catalytic chambers431to433is returned to the catalytic chambers431to433through the second auxiliary flow paths4521to4523, the circulating gas heater46, the circulating gas fan450, and the first auxiliary flow paths4511to4513in this order. The temperature of almost the whole of circulation flow path45thereby becomes near the preset temperature for normal operation of catalytic reactor (for example, 170 to 200° C.) and occurrence of corrosion (low-temperature corrosion) in the circulation flow path45is suppressed. Further, the circulating gas heater46is in an OFF state and heating of the gas is not performed in the circulation flow path45. Most part of the flue gas passing through the catalytic chambers431to433is guided to the stack35through the outflow paths391to393. In the first denitration state, by slightly opening also the damper491of the connection flow path49, part of the flue gas in the circulation flow path45flows in the vicinity of the upstream side of the chemical agent supply part32in the exhaust path3through the connection flow path49. It is thereby possible to also suppress occurrence of corrosion in the connection flow path49.

When the thermal recovery of the catalytic module439in the selected catalytic chamber is performed, the circulation flow path45including the selected catalytic chamber is formed. In a case, for example, where the first catalytic chamber431is the selected catalytic chamber, the circulation flow path45including the first catalytic chamber431is formed. At that time, the flue gas from the flue gas heater41does not flow into the first catalytic chamber431but flows into only the second catalytic chamber432and the third catalytic chamber433. Further, the dampers4722and4723of the second auxiliary flow paths4522and4523connected to the second catalytic chamber432and the third catalyst chamber433, respectively, are also opened. Part of the flue gas passing through the second catalytic chamber432and the third catalytic chamber433is thereby introduced into the circulation flow path45including the first catalytic chamber431. InFIG. 7, the circulation flow path45and the second auxiliary flow paths4522and4523are indicated by heavy solid lines. The flue gas is heated by the circulating gas heater46while being circulated as the circulating gas in the circulation flow path45by driving of the circulating gas fan450. After the flue gas in the required amount is introduced into the circulation flow path45, the dampers4722and4723are closed. Further, in the introduction of the flue gas into the circulation flow path45, the damper4722or4723of only one of the two second auxiliary flow paths4522and4523may be opened.

Similar to the exemplary case shown inFIG. 6, when it is confirmed by the temperature detection part462that the temperature of the circulating gas is raised to the first preset temperature (for example, 300° C.), the dampers491,4722, and4723are opened. The introduction of the flue gas from the second auxiliary flow paths4522and4523is thereby restarted and part of the circulating gas containing SO3and the like flows in the vicinity of the upstream side of the chemical agent supply part32in the exhaust path3through the connection flow path49. After the thermal recovery of the catalytic module439is completed, the circulating gas heater46is turned off. Then, after a certain time has elapsed, the damper491is closed and the state of the catalytic reactor43is returned to the first denitration state in which the flue gas is denitrated by using the catalytic modules439in all the catalytic chambers431to433. Further, in the state, the dampers4721to4723of the plurality of second auxiliary flow paths4521to4523and the dampers4711to4713of the plurality of first auxiliary flow paths4511to4513are slightly opened, and the circulation flow path45including all the catalytic chambers431to433is formed.

Herein, in the flue gas denitration system4ofFIG. 6in which the circulation flow path45is cold in the first denitration state, it is necessary to slowly warm the pipe when the thermal recovery of the catalytic module439is performed. In contrast to this, in the flue gas denitration system4ofFIG. 7, in the first denitration state, the circulation flow path45is always warmed (warmed up) since the flue gas passing through the catalytic chambers431to433flows in the circulation flow path45. It is thereby possible to increase the rate of temperature rise of the circulating gas and reduce the time required for the thermal recovery of the catalytic module439.

FIG. 8is a view showing yet another example of a flue gas denitration system4. The flue gas denitration system4ofFIG. 8is different from that ofFIG. 6in that two additional flow paths455and456are additionally provided in the flue gas denitration system4ofFIG. 6. In more detail, in the circulation flow path45, a damper457is provided between the introduction position453of the air introduction part48and the circulating gas fan450, and a damper458is provided between the circulating gas fan450and the circulating gas heater46. An end of the first additional flow path455is connected between the introduction position453of the air introduction part48and the damper457and the other end of the first additional flow path455is connected between the circulating gas fan450and the damper458. The first additional flow path455is provided with two dampers4551and4552. An end of the second additional flow path456is connected between the damper457and the circulating gas fan450and the other end of the second additional flow path456is connected between the damper458and the circulating gas heater46. The second additional flow path456is provided with one damper4561.

When the thermal recovery of the catalytic module439in the selected catalytic chamber is performed, the dampers457and458provided on both sides of the circulating gas fan450in the circulation flow path45are opened and the dampers4551,4552, and4561of the first additional flow path455and the second additional flow path456are closed. Like in the flue gas denitration system4ofFIG. 6, the circulation flow path45including the selected catalytic chamber is thereby formed. Further, the flue gas heated by the flue gas heater41is introduced into the circulation flow path45through the flue gas introduction flow path482. InFIG. 8, the circulation flow path45including the first catalytic chamber431and the flue gas introduction flow path482are indicated by heavy solid lines. The operation relating to the thermal recovery of the catalytic module439is the same as that in the case ofFIG. 6.

On the other hand, in the first denitration state in the flue gas denitration system4, the circulation flow path45including the catalytic chamber in which the thermal recovery should be performed next is warmed up. In a case, for example, where the catalytic chamber in which the thermal recovery should be performed next is the second catalytic chamber432, the damper4722of the second auxiliary flow path4522and the damper4712of the first auxiliary flow path4512shown inFIG. 9are slightly opened. Further, the dampers457and458provided on both sides of the circulating gas fan450in the circulation flow path45are closed and the dampers4551,4552, and4561of the first additional flow path455and the second additional flow path456are opened. Part of the flue gas passing through the second catalytic chamber432is returned to the second catalytic chamber432through the second auxiliary flow path4522, the circulating gas heater46, the second additional flow path456, the circulating gas fan450, the first additional flow path455, and the first auxiliary flow path4512in this order (see the heavy solid line inFIG. 9). Further, the circulating gas heater46is in an OFF state and heating of the gas is not performed in the circulation flow path45.

Thus, in the flue gas denitration system4, the circulation flow path45including the second catalytic chamber432is warmed in the first denitration state. As a result, when the thermal recovery of the catalytic module439in the second catalytic chamber432is performed, it is possible to increase the rate of temperature rise of the circulating gas and reduce the time required for the thermal recovery. The same applies to cases where the catalytic chamber in which the thermal recovery should be performed next is the first catalytic chamber431and where the catalytic chamber in which the thermal recovery should be performed next is the third catalytic chamber433.

Next, a flue gas denitration system having only one catalytic chamber will be described.FIG. 10is a view showing a still further example of a flue gas denitration system and shows part of the flue gas denitration system4a.FIG. 11is a cross section showing a catalytic reactor43in the flue gas denitration system4aand shows a cross section perpendicular to the flow direction of the gas in the catalytic reactor43.

In the flue gas denitration system4a, the catalytic reactor43has a catalytic chamber434and a catalyst recovery chamber435. In more detail, the catalytic reactor43has a substantially cylindrical shape with a predetermined central axis J1as its center, and in an internal space of the catalytic reactor43, provided is a plate-like partition wall436in parallel with the central axis J1. In the internal space, one of spaces partitioned by the partition wall436is the catalytic chamber434and the other space is the catalyst recovery chamber435. In other words, the catalytic chamber434and the catalyst recovery chamber435are provided adjacently to each other. The partition wall436has a plurality of rotation parts437aligned along the central axis J1, and to each rotation part437, the semicircular and plate-like catalytic module439is attached. The rotation part437rotates the catalytic module439around the central axis J1and selectively arrange the catalytic module439into the catalytic chamber434or the catalyst recovery chamber435. The catalyst recovery chamber435is included in part of the circulation flow path45. The circulation flow path45has the circulating gas fan450and the circulating gas heater46.

In the normal operation in the flue gas denitration system4a, the plurality of (all the) catalytic modules439are arranged in the catalytic chamber434. The flue gas flows into the catalytic chamber434and denitrated by using the plurality of catalytic modules439. Further, when the thermal recovery is performed on one of the plurality of catalytic modules439, this catalytic module439is arranged in the catalyst recovery chamber435by the rotation part437. The circulating gas (catalyst recovery gas) heated by the circulating gas heater46is supplied to the catalyst recovery chamber435and the recovery of the catalytic module439is performed. The circulating gas used for the recovery of the catalytic module439flows into the exhaust path3through the connection flow path (not shown), like in the flue gas denitration system4ofFIG. 1. On the other hand, in the catalytic chamber434, the flue gas is denitrated by using the remaining catalytic modules439other than the above catalytic module439. At that time, the heating temperature of the flue gas by the flue gas heater41(seeFIG. 1) is made higher than that in the case where all the catalytic modules439are used.

As described above, also in the flue gas denitration system4aofFIG. 10, the first denitration state in which the flue gas is denitrated by using the plurality of catalytic modules439in the catalytic reactor43and the second denitration state in which the flue gas is denitrated by using the catalytic modules439less than those in the first denitration state while the temperature of the flue gas flowing into the catalytic reactor43is made higher than that in the first denitration state by using the flue gas heater41are switched to each other. Thus, in the case where part of the plurality of catalytic modules439is used for denitration, by making the temperature of the flue gas flowing into the catalytic reactor43higher, it is possible to suppress deterioration in denitration performance.

Further, in the catalytic reactor43, the plurality of rotation parts437operate as a position switching part, which selectively (and individually) arrange the plurality of catalytic modules439into the catalytic chamber434or the catalyst recovery chamber435. The position switching part is controlled by a position switching control part (not shown) of the control unit400. When one catalytic module439is recovered, it is thereby possible to arrange only this catalytic module439into the catalyst recovery chamber435and perform recovery of this catalytic module439concurrently with the second denitration state.

In the incinerator1and the flue gas denitration systems4and4adescribed above, various modifications can be made.

Though the plurality of catalytic modules439are arranged in one catalytic chamber434in the flue gas denitration system4aofFIG. 10, even when the plurality of catalytic chambers431and432are provided as shown inFIG. 12, the plurality of catalytic modules439may be provided in each of the catalytic chambers431and432. The catalytic module439is a group of almost continuous catalysts, and assuming that a smallest handleable lump of catalysts is a catalyst cell (or a catalyst element), for example, each catalytic module439is formed of a plurality of catalyst cells which are adjacent to one another.

In the flue gas denitration system4aofFIG. 10, there may be a case where the catalyst recovery chamber435is omitted and the catalytic module439arranged outside the catalytic chamber434by the rotation part437is detached and recovered by an external catalyst recovery apparatus. Further, in the flue gas denitration system4ofFIG. 1, there may be a case where each of the catalytic chambers431to433is openable and closable and the catalytic module439in the selected one of the catalytic chambers431to433is detached and recovered by the external catalyst recovery apparatus. Furthermore, the detached catalytic module439may be replaced by a new catalytic module439. In the flue gas denitration systems4and4a, during recovery or replacement of part of the catalytic modules439, it is possible to suppress deterioration in denitration performance by raising the temperature of the flue gas flowing into the catalytic reactor43.

InFIGS. 10, 12, and 1, though the number of catalytic chambers is one to three, the number of catalytic chambers may be four or more. Further, in a case where the number of catalytic chambers is three or more, depending on the design of the system, a plurality of catalytic chambers less than the total number of catalytic chambers may be selected as the selected catalytic chambers simultaneously. In order to reduce the volume of catalysts for filling in the catalytic reactor43, however, it is preferable that the number of selected catalytic chambers should be one.

The flue gas heater41may heat the flue gas by using a heating medium other than the steam of the boiler21. Further, the circulating gas heater46may also heat the circulating gas by using other energy such as a gas or the like.

Depending on the temperature of the flue gas flowing into the flue gas denitration system4or4a, there may be a case where only when part of the plurality of catalytic modules439is used for denitration, the flue gas is heated by the flue gas heater41.

In the above-described preferred embodiment, though high-temperature air heated by the circulating gas heater46is used as the catalyst recovery gas, the catalyst recovery gas has only to remove deposits which deteriorate the denitration performance in the catalytic module439, and may be, for example, a specific type of gas.

In the circulation flow path45, a removal apparatus for removing SO3and NH3in the circulating gas may be provided. Further, in the exhaust path3, in a case where a desulfurization apparatus is provided on a downstream side of the catalytic reactor43, and the like case, the whole or part of the catalyst recovery gas discharged from the selected catalytic chamber in the catalyst recovery part44may flow directly into the exhaust path3. In the exemplary case shown inFIG. 13showing part of the incinerator1, in the exhaust path3, a gas-gas heater361and a wet scrubber362are provided on the downstream side of the catalytic reactor43. The wet scrubber362is provided with a chemical agent supply part363. The flue gas discharged from the catalytic reactor43passes through the gas-gas heater361and flows into the wet scrubber362. Inside the wet scrubber362, a chemical agent (sodium hydroxide or the like) is injected by the chemical agent supply part363, and dechlorination and desulfurization are thereby performed. In other words, a desulfurization apparatus is implemented by the wet scrubber362. The temperature of the flue gas passing through the wet scrubber362is raised by the gas-gas heater361and the flue gas is discharged to the atmosphere through the stack35. In the chemical agent supply part32provided on an upstream side of the bag filter33, a chemical agent such as hydrated lime or the like is injected.

In the catalytic reactor43ofFIG. 13, when the thermal recovery of the catalytic module439in one catalytic chamber, e.g., the first catalytic chamber431inFIG. 1is performed, by slightly opening the damper4021, the gas used for the thermal recovery of the catalytic module439is guided to the wet scrubber362inFIG. 13. It thereby becomes possible to remove SO3and the like contained in the gas passing through the selected catalytic chamber (herein, the first catalytic chamber431) in the wet scrubber362. In the flue gas denitration system4ofFIG. 13, the connection flow path49ofFIG. 1may be omitted.

The flue gas denitration systems4and4amay be used in a facility other than the incinerator1and an apparatus such as a diesel engine or the like.

The configurations in the above-discussed preferred embodiments and variations may be combined as appropriate only if those do not conflict with one another.

REFERENCE SIGNS LIST