JP2010172855A - Apparatus for purifying exhaust gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for purifying exhaust gas rendering ammonia hard to leak, and capable of reducing efficiently nitrogen oxides in the exhaust gas. <P>SOLUTION: The apparatus for purifying exhaust gas which reduces nitrogen oxides contained in the exhaust gas exhausted from combustion appliances includes an exhaust pipe, a reducing agent ejecting means ejecting a reducing agent in the exhaust pipe, an ammonia SCR catalyst means disposed farther downstream than a position where the reducing agent is ejected, an ammonia concentration measuring means disposed farther downstream than the catalyst means with respect to an exhaust gas flowing direction and measuring an ammonia concentration in the exhaust gas passing the ammonia SCR catalyst means, and a control means controlling the ejection of urea water based on an ammonia concentration measured by the ammonia concentration measuring means. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus that reduces nitrogen oxides discharged from combustion equipment.

  Nitrogen oxides (NOx) are contained in gas discharged from combustion equipment such as a garbage incinerator and gas turbine, that is, exhaust gas. Therefore, a device for reducing nitrogen oxides is provided in the exhaust pipe of the combustion equipment. As an apparatus for reducing nitrogen oxide, urea water is injected into an exhaust pipe that guides exhaust gas, ammonia is generated from urea water in the exhaust pipe, and the generated ammonia and nitrogen oxide in the exhaust gas There is an apparatus for reducing nitrogen oxide from exhaust gas by reacting and removing oxygen from nitrogen oxide and returning it to nitrogen. Further, instead of injecting urea water, there is also a device that directly injects ammonia water or ammonia gas as a reducing agent, and reacts ammonia generated from the injected ammonia water or ammonia gas with nitrogen oxides.

  For example, Patent Document 1 measures the NOx concentration of the pretreatment gas, the ammonia concentration in the exhaust gas after treatment, the NOx concentration of the exhaust gas, and the flow rate of the exhaust gas, and the NOx flow rate before treatment from the measurement results, Calculate the NOx concentration after treatment, the actual NOx removal rate in the denitration facility, and the ammonia concentration in the exhaust gas after treatment, calculate the deviation between each calculated value and the target value, and calculate the correction amount from the deviation. A denitration control method is described in which a corrected NOx flow rate is calculated based on at least one of the calculated correction amounts, and the ammonia flow rate injected into the pre-treatment exhaust gas is controlled based on the calculated corrected NOx flow rate.

  Further, Patent Document 2 describes an exhaust gas purification system for an internal combustion engine. However, an exhaust gas purification system in which a DPF device and a selective catalytic reduction catalyst device are arranged in this order from the upstream in the exhaust passage of the internal combustion engine is described. . Further, in Patent Document 2, the NOx emission amount is calculated from the NOx emission map for normal operation during normal operation, and the NOx emission amount is calculated from the NOx emission map for forced regeneration during forced regeneration of the DPF device. And calculating the supply amount of the ammonia-based aqueous solution corresponding to the calculated NOx emission amount, and the aqueous ammonia solution is added to the exhaust gas upstream of the selective catalytic reduction catalyst device so as to be the calculated supply amount. An apparatus for feeding is described.

JP 2005-169331 A JP 2007-154849 A

  As described in Patent Document 1, it is also possible to correct nitrogen oxide flow rate deviation by correcting at least one of nitrogen oxide concentration, denitration rate, and ammonia concentration of exhaust gas after treatment. The amount of ammonia can be reduced, and the amount of ammonia can be adjusted. Moreover, as described in Patent Document 2, nitrogen oxides can be reduced and the amount of ammonia can be adjusted by controlling the injection amount of urea based on a map created in advance.

  However, as in Patent Document 2, even when the injection amount of urea is adjusted using a map created in advance, there is a problem that nitrogen oxide may leak or ammonia may leak depending on the operation state. is there. Further, as in Patent Document 1, in order to calculate the NOx flow rate, it is necessary to detect and calculate the flow rate of exhaust gas and the concentration of NOx (nitrogen oxide), which is problematic. Further, there is a problem that even if the injection amount of ammonia is controlled based on the NOx flow rate, the amount of nitrogen oxide and leaking ammonia cannot be reduced sufficiently.

  The present invention has been made in view of the above, and calculates an appropriate amount of urea to be injected into the exhaust pipe, makes it difficult for ammonia to leak downstream, and efficiently reduces nitrogen oxides in the exhaust gas. It is an object of the present invention to provide an exhaust gas purifying apparatus that can perform the above-described process.

  In order to solve the above-described problems and achieve the object, the present invention provides an exhaust gas purifying apparatus that reduces nitrogen oxides contained in exhaust gas discharged from a combustion device, wherein the exhaust gas discharged from the combustion device is reduced. Exhaust piping to be guided, reducing agent injection means for injecting at least one of urea water, ammonia water and ammonia gas into the exhaust piping as a reducing agent, ammonia generated from the injected reducing agent and the nitrogen oxidation An ammonia SCR catalyst that promotes a reaction with an object, and a support mechanism that is disposed inside the exhaust pipe and supports the ammonia SCR catalyst inside the exhaust pipe, and the reducing agent is injected in the flow direction of the exhaust gas. Catalyst means disposed downstream of the catalyst position, and disposed downstream of the catalyst means in the flow direction of the exhaust gas, Ammonia concentration measuring means for measuring the ammonia concentration of the exhaust gas that has passed through the ammonia SCR catalyst, and control for controlling injection of the reducing agent by the reducing agent injection means based on the ammonia concentration measured by the ammonia concentration measuring means And means.

  Thus, based on the ammonia concentration contained in the exhaust gas that has passed through the ammonia SCR catalyst detected by the ammonia concentration measuring means, the control means controls the injection of the reducing agent by the previous urea water injection means, thereby purifying the exhaust gas. While further reducing the ammonia in the exhaust gas discharged from the apparatus, the nitrogen oxides in the exhaust gas can also be reduced. Further, by controlling the injection amount of the reducing agent based only on the detected value of ammonia, the amount of calculation can be reduced and the apparatus configuration can be simplified.

  Here, the exhaust gas purification device is further disposed downstream of the catalyst means in the flow direction of the exhaust gas, and measures the nitrogen oxide concentration after treatment for measuring the nitrogen oxide concentration of the exhaust gas that has passed through the ammonia SCR catalyst. It is preferable that the control unit controls injection of the reducing agent by the reducing agent injection unit based on the nitrogen oxide concentration measured by the post-treatment nitrogen oxide concentration measuring unit.

  In this way, by controlling the injection of the reducing agent using the nitrogen oxide concentration of the exhaust gas that has passed through the ammonia SCR catalyst measured by the nitrogen oxide concentration measuring means after treatment, the nitrogen oxide contained in the exhaust gas can be further reduced. Can be reduced.

  Further, when both of the ammonia concentration detected by the ammonia concentration measuring means and the nitrogen oxide concentration measured by the post-treatment nitrogen oxide concentration measuring means exceed a reference concentration, the ammonia SCR catalyst It is preferable to have a recovery means for performing recovery. The recovery means preferably heats the ammonia SCR catalyst at a predetermined temperature.

  Thus, by recovering the ammonia SCR catalyst by the recovery means, it is possible to further suppress leakage of ammonia and nitrogen oxides. Further, by determining the capability of the ammonia SCR catalyst based on both the ammonia concentration and the nitrogen oxide concentration, the state of the urea SCR catalyst can be grasped more accurately, and unnecessary recovery processing is suppressed. be able to. Further, as the recovery process, the ammonia SCR catalyst can be easily recovered by heating the ammonia SCR catalyst.

  Further, when both of the ammonia concentration detected by the ammonia concentration measuring means and the nitrogen oxide concentration measured by the post-treatment nitrogen oxide concentration measuring means exceed a reference concentration, the ammonia SCR catalyst It is also preferable to have a notification means for notifying that it is necessary to replace the battery.

  In this way, the notification means notifies the operator that the capacity of the ammonia SCR catalyst has been reduced, and requests the operator to replace the ammonia SCR catalyst, thereby suppressing the continued use of the ammonia SCR catalyst having the reduced ability. It is possible to suppress the leakage of ammonia and nitrogen oxide. Moreover, by judging the ability of the urea SCR catalyst based on both the ammonia concentration and the nitrogen oxide concentration, it is possible to grasp the state of the ammonia SCR catalyst more accurately and to suppress unnecessary replacement. Can do.

  Furthermore, it is arranged between the reducing agent injection means and the catalyst means in the flow direction of the exhaust gas, and has a pre-treatment nitrogen oxide concentration measuring means for measuring the nitrogen oxide concentration of the exhaust gas, the control means, It is preferable to control the injection of the reducing agent by the reducing agent injection means based also on the nitrogen oxide concentration measured by the pretreatment nitrogen oxide concentration measuring means.

  In this way, the amount of ammonia necessary for the reduction of nitrogen oxides is controlled by controlling the injection of the reducing agent by the reducing agent injection means based on the nitrogen oxide concentration measured by the nitrogen oxide concentration measuring means before treatment. In addition, the injection of the reducing agent can be controlled, and the nitrogen oxides in the exhaust gas can be further reduced while the ammonia in the exhaust gas discharged from the exhaust gas purification device is further reduced.

  Further, an isocyanic acid concentration measuring unit that is disposed between the reducing agent injection unit and the catalyst unit in the flow direction of the exhaust gas, and that measures the isocyanate concentration of the exhaust gas, and the reducing agent injection unit in the flow direction of the exhaust gas. And a temperature adjusting means for adjusting the temperature of the exhaust gas flow path between the catalyst means and the temperature adjusting means based on the isocyanate concentration measured by the isocyanate concentration measuring means. It is preferable to adjust the temperature.

  In this way, by adjusting the temperature of the exhaust gas flow path based on the isocyanic acid concentration in the exhaust gas, the injected reducing agent can be made more reliably ammonia, and the ammonia concentration in the exhaust gas can be more easily Can be controlled.

  Furthermore, the pretreatment ammonia concentration measuring means is disposed between the reducing agent injection means and the catalyst means in the exhaust gas flow direction, and measures the ammonia concentration of the exhaust gas, and the reducing agent injection means in the exhaust gas flow direction. And a temperature adjusting means for adjusting the temperature of the exhaust gas flow path between the catalyst means and the temperature adjusting means to adjust the temperature of the exhaust gas flow path based on the ammonia concentration measured by the pre-treatment ammonia concentration measuring means. It is also preferable to adjust the temperature.

  In this way, by adjusting the temperature of the exhaust gas flow path based on the ammonia concentration in the exhaust gas before treatment, the injected urea water can be more reliably converted to ammonia, and the ammonia concentration in the exhaust gas can be further increased. It can be controlled easily.

  In order to solve the above-described problems and achieve the object, the present invention provides an exhaust gas purifying apparatus that reduces nitrogen oxides contained in exhaust gas discharged from a combustion device, wherein the exhaust gas discharged from the combustion device is reduced. Exhaust piping to be guided, reducing agent injection means for injecting at least one of urea water, ammonia water and ammonia gas into the exhaust piping as a reducing agent, ammonia generated from the injected reducing agent, and the nitrogen oxides An ammonia SCR catalyst that promotes the reaction with the exhaust gas, and a support mechanism that is disposed inside the exhaust pipe and supports the ammonia SCR catalyst inside the exhaust pipe, and the reducing agent is injected in the flow direction of the exhaust gas. A catalyst means disposed downstream of the position, and disposed between the reducing agent injection means and the catalyst means in the flow direction of the exhaust gas. A pre-treatment nitrogen oxide concentration measuring means for measuring the nitrogen oxide concentration of the exhaust gas, and a nitrogen oxidation of the exhaust gas that is disposed downstream of the catalyst means in the flow direction of the exhaust gas and that has passed through the ammonia SCR catalyst. A post-treatment nitrogen oxide concentration measuring means for measuring an object concentration; a nitrogen oxide concentration measured by the pre-treatment nitrogen oxide concentration measuring means; and a nitrogen oxide concentration measured by the post-treatment nitrogen oxide concentration measuring means; Control means for calculating the ammonia concentration in the exhaust gas that has passed through the catalyst means based on the difference between the control means and controlling the injection of the reducing agent by the reducing agent injection means based on the calculated ammonia concentration. And

  As described above, the ammonia concentration in the exhaust gas is calculated using the pre-treatment nitrogen oxide concentration and the post-treatment nitrogen oxide concentration, and the injection amount of the reducing agent is controlled based on the calculated ammonia concentration. While further reducing the ammonia in the exhaust gas discharged from the purification device, the nitrogen oxides in the exhaust gas can also be reduced. In addition, the apparatus configuration can be simplified by controlling the injection amount of the reducing agent based only on the calculated value of ammonia.

  The exhaust gas purifying apparatus according to the present invention further reduces the ammonia in the exhaust gas discharged from the exhaust gas purifying apparatus by controlling the injection of the reducing agent based on the ammonia concentration contained in the exhaust gas that has passed through the ammonia SCR catalyst. In addition, nitrogen oxides in the exhaust gas can be reduced. Further, by controlling the injection amount of the reducing agent based only on the detected value of ammonia, the amount of calculation can be reduced and the apparatus configuration can be simplified.

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of a waste incineration system having an exhaust gas purification apparatus of the present invention. FIG. 2 is a block diagram showing a schematic configuration of the exhaust gas purification apparatus of the refuse incineration system shown in FIG. FIG. 3 is a block diagram showing a schematic configuration of the concentration measuring means shown in FIG. FIG. 4 is a flowchart showing an example of a method for controlling the urea water injection amount by the control means. FIG. 5-1 is a graph showing the relationship between nitrogen oxide (NOx) concentration and time. FIG. 5-2 is a graph showing the relationship between the measured ammonia concentration and time. FIG. 5-3 is a graph showing the relationship between the temperature of the urea SCR catalyst and time. FIG. 5-4 is a graph showing the relationship between the flow rate of ammonia injected into the urea SCR catalyst and time. FIG. 6 is a block diagram showing a schematic configuration of another embodiment of the exhaust gas purifying apparatus. FIG. 7 is a flowchart showing an example of a method for controlling the urea water injection amount by the control means. FIG. 8 is a block diagram showing a schematic configuration of another embodiment of the exhaust gas purifying apparatus.

  Hereinafter, an embodiment of an exhaust gas purifying apparatus according to the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited by this embodiment. In the following embodiment, the exhaust gas purification device will be described as being attached to a waste incineration system that incinerates garbage in an incinerator, but the combustion equipment to which the exhaust gas purification device is attached is not limited to this, but a pyrolysis furnace, melting It can be used for various combustion equipment such as furnaces, boilers, and external combustion engines. Note that the combustion equipment of the present invention does not include an internal combustion engine. In addition, various types of waste can be targeted as garbage. It can also be used in an incineration system that incinerates things other than garbage in an incinerator.

  FIG. 1 is a block diagram showing a schematic configuration of an embodiment of a waste incineration system having an exhaust gas purification apparatus of the present invention. As shown in FIG. 1, the waste incineration system (waste combustion system) 1 basically includes a charging hopper 2, an incinerator 3, an ash treatment unit 4, a boiler 5, an incineration temperature reducing tower 6, It has a duster 7, an exhaust gas purification device 9, a fan 10, and a chimney 12.

  The input hopper 2 is a dust input unit, and the dust conveyed from the dust accumulation unit by a conveying means such as a crane is input. The input hopper 2 is connected to the incinerator 3.

  The incinerator 3 is a combustion device that burns garbage, and burns the garbage input from the input hopper. As the incinerator 3, various incinerators such as a stoker type incinerator, a fluidized bed type incinerator, and a burner type incinerator can be used. For example, when a stoker type incinerator is used as the incinerator, the primary air is introduced from the primary air inlet located below the grate while transferring the waste (garbage) received from the input hopper 2 on the grate. Exhaust gas generated in the primary combustion chamber in the secondary combustion chamber formed by the introduction of secondary air above the incinerator main body and burned in the primary combustion chamber formed above the grate Reburn unburned gas inside. Combustion ash generated by burning garbage in the incinerator 3 is sent to the ash treatment unit 4, and exhaust gas is sent to the boiler 5 through piping.

  The ash treatment unit 4 collects combustion ash that is generated when garbage is burned in the incinerator 3. Here, the ash treatment unit 4 may discard the recovered combustion ash as it is. For example, the recovered ash is melted in an ash melting furnace to generate molten slag obtained by melting. Is preferred. Thus, the created molten slag can be recycled for various uses such as roadbed materials, concrete aggregates, asphalt mixing aggregates, and the like.

  The boiler 5 recovers heat from the high-temperature exhaust gas discharged from the incinerator 3. The exhaust gas whose heat has been recovered by the boiler 5 is sent to the incineration temperature reducing tower 6.

  The incineration temperature reduction tower 6 is connected to a temperature reduction water tank 13 in which the temperature reduction water is stored, sprays the temperature reduction water from the temperature reduction water tank 13 on the exhaust gas sent from the boiler 5, and cools the exhaust gas. The exhaust gas cooled by the incineration temperature reducing tower 6 is sent to the dust collector 7.

  Here, the slaked lime storage tank 14, the activated carbon storage tank 15, the special reaction agent storage tank 16, and the pushing fan 17 are connected to the piping connecting the incineration temperature reducing tower 6 and the dust collector 7. The slaked lime stored in the slaked lime storage tank 14, the activated carbon stored in the activated carbon storage tank 15, and the special reaction agent stored in the special reaction agent storage tank 16 are incinerated by the incineration temperature reducing tower 6 by the pushing fan 17. And sent to a pipe connecting the dust collector 7. By supplying slaked lime and activated carbon to the exhaust gas flowing from the incineration temperature reducing tower 6 toward the dust collector 7, harmful substances contained in the exhaust gas are neutralized. Specifically, acidic gas such as HCl and SOx in the exhaust gas can be neutralized with slaked lime, and dioxins in the exhaust gas can be removed with activated carbon. Moreover, the clogging of the filter cloth can be suppressed by introducing a special agent (diatomaceous earth).

  The dust collector 7 is connected to the incineration temperature reducing tower 6 via a pipe, and the exhaust gas that has passed through the pipe is supplied from the incineration temperature reducing tower 6. The dust collector 7 removes salts, fly ash (dust), and acid gas obtained by the neutralization reaction between the exhaust gas and slaked lime or the neutralization reaction between the exhaust gas and activated carbon, contained in the exhaust gas. The exhaust gas from which salts, fly ash (dust), and acid gas have been removed by the dust collector 7 is sent to the exhaust gas purification device 9.

  The exhaust gas purification device 9 is connected to the dust collector 7 via a pipe, and the exhaust gas that has passed through the pipe is supplied from the dust collector 7. The exhaust gas purification device 9 removes nitrogen oxides contained in the exhaust gas. The exhaust gas purification device 9 will be described in detail later. The exhaust gas from which nitrogen oxides have been removed by the exhaust gas purification device 9 is discharged from the chimney 12 to the outside by the fan 10. The garbage incineration system 1 burns garbage as described above. Moreover, the waste incineration system 1 discharges the exhaust gas generated by the combustion of waste from the chimney 12 after removing and reducing harmful substances in the exhaust gas.

Next, the exhaust gas purification device 9 will be described. Here, FIG. 2 is a block diagram showing a schematic configuration of the exhaust gas purification device of the refuse incineration system shown in FIG. 1, and FIG. 3 is a block diagram showing a schematic configuration of the concentration measuring means of the exhaust gas purification device shown in FIG. It is. Hereinafter, the pipe through which the exhaust gas flows is referred to as an exhaust pipe 21. The exhaust gas purification device 9 includes urea water injection means 22, urea water tank 24, ammonia water supply means 25, urea SCR catalyst means 26, concentration measurement means 28, and control means 30. The exhaust gas purification device 9 is a urea SCR (Selective Catalytic Reduction) system that reduces nitrogen oxides (NO, NO ₂ ) contained in the exhaust gas. Here, the urea SCR system includes a urea water injection unit 22, a urea water tank 24, and a urea SCR catalyst unit 26.

  The urea water injection means 22 is an injection device that injects urea water into the exhaust pipe 21, and an injection port is provided in a portion of the exhaust pipe 21 on the downstream side of the dust collector 7. The urea water injection means 22 injects urea water into the exhaust pipe 21 from the injection port. The urea water tank 24 is a tank that stores urea water, and supplies urea to the urea water injection means 22. The urea water tank 24 is provided with a replenishing port for replenishing urea water from a device for supplying external urea water, and urea water is replenished from the replenishing port as needed.

  The ammonia water supply means 25 is a supply means for supplying ammonia water into the exhaust pipe 21, and an injection port is provided in a portion of the exhaust pipe 21 downstream of the urea water injection means 22. Note that the ammonia water supply means 25 is not necessarily provided.

  The urea SCR catalyst means 26 is more than a plurality of urea SCR catalysts 26a, which are urea selective reduction catalysts that promote the reaction between ammonia generated from urea and nitrogen oxides, and the urea water injection means 22 of the exhaust pipe 21. A support mechanism 26b provided inside the downstream portion and supporting the urea SCR catalyst. Here, a vanadia / titania catalyst or a zeolite catalyst can be used for the urea SCR catalyst 26a. Further, the support mechanism 26b is formed with a hole for allowing exhaust gas to pass therethrough, and supports the urea SCR catalyst 26a on the surface thereof. The support mechanism 26b may be a frame as long as it can support the urea SCR catalyst 26a on the exhaust pipe 21. Further, the urea SCR catalyst means 26 can replace the plurality of urea SCR catalysts 26a and the support mechanism 26b one by one.

  Here, in this embodiment, the part where the urea SCR catalyst means 26 of the exhaust pipe 21 is disposed is a denitration tower 21a having a larger opening area than other parts. In the denitration tower 21a, a plurality of urea SCR catalysts 26a and a support mechanism 26b for holding them are stacked. Therefore, the exhaust gas passing through the urea SCR catalyst means 26 passes through the plurality of urea SCR catalysts 26a.

The urea SCR system is configured as described above, and urea water is injected into the exhaust pipe 21 by the urea water injection means 22. The injected urea water becomes ammonia (NH ₃ ) due to the heat in the exhaust pipe 21. Specifically, ammonia is produced from urea water by the following chemical reaction.
(NH ₂ ) 2 CO + H ₂ O → 2NH ₃ + CO ₂
Thereafter, the generated ammonia and the ammonia water supplied from the ammonia water supply means 25 flow in the denitration tower 21 a of the exhaust pipe 21 together with the exhaust gas, and reach the urea SCR catalyst means 26. A part of the urea water does not become ammonia but reaches the urea SCR catalyst means 26 as the urea water. Therefore, ammonia is also produced from the urea water by the above reaction in the urea SCR catalyst means 26. The ammonia that has reached the urea SCR catalyst means 26 reacts with nitrogen oxides contained in the exhaust gas, removes oxygen from the nitrogen oxides, and is reduced to nitrogen. Specifically, nitrogen oxides are reduced by the following chemical reaction.
4NH ₃ + 4NO + O ₂ → 4N ₂ + 6H ₂ O
4NH ₃ + 2NO ₂ + O ₂ → 3N ₂ + 6H ₂ O

  The concentration measuring means 28 is arranged in the exhaust pipe 21 downstream of the urea SCR catalyst means 26 in the exhaust gas exhaust pipe 21, and measures the concentration of ammonia in the exhaust gas that has passed through the urea SCR catalyst means 26. As shown in FIG. 3, the concentration measurement unit 28 includes a measurement unit main body 40, an optical fiber 42, a measurement cell 44, and a light receiving unit 46.

  The measuring means main body 40 has a light emitting means for emitting laser light in a wavelength region absorbed by ammonia, and a calculating means for calculating the concentration of ammonia from the signal, outputs the laser light to the optical fiber 42, and receives the light receiving unit 46. Receives the received signal.

  The optical fiber 42 guides the laser beam output from the measuring means main body 40 and makes it incident on the measuring cell 44.

  The measurement cell 44 is disposed in a part of the exhaust pipe 21, and an incident part that makes the light emitted from the optical fiber 42 enter the inside of the measurement cell 44 and laser light that has passed through a predetermined path of the measurement cell 44. And an output unit for outputting.

  The light receiving unit 46 receives the laser light that passes through the measurement cell 44 and is output from the output unit, and outputs the intensity of the received laser light to the measuring means body 40 as a light reception signal.

  The concentration measuring unit 28 is configured as described above, and the laser light output from the measuring unit main body 40 is output from the output unit after passing through a predetermined path in the measuring cell 44 from the optical fiber 42. At this time, if the exhaust gas in the measurement cell 44 contains ammonia, the laser light passing through the measurement cell 44 is absorbed. For this reason, the output of the laser beam reaching the output unit varies depending on the ammonia concentration in the exhaust gas. The light receiving unit 46 converts the laser light output from the output unit into a light reception signal and outputs the light reception signal to the measuring means main body 40. The measuring means main body 40 compares the intensity of the output laser light with the intensity calculated from the received light signal, and calculates the ammonia concentration of the exhaust gas flowing in the measuring cell 44 from the decrease rate. As described above, the concentration measuring unit 28 uses the TDLAS method (Tunable Diode Laser Absorption Spectroscopy) and measures based on the intensity of the output laser light and the received light signal detected by the light receiving unit 46. The ammonia concentration in the exhaust gas passing through a predetermined position in the cell 44, that is, the measurement position is calculated and / or measured. Further, the concentration measuring means 28 of the present embodiment can continuously calculate and / or measure the ammonia concentration.

  In the measurement cell 44, only the incident part and the output part may be formed of a material that transmits light, or the entire measurement cell 44 may be formed of a material that transmits light. Alternatively, at least two optical mirrors may be provided in the measurement cell 44, and the laser light incident from the incident part may be reflected by the optical mirror and then output from the output part. As described above, the multiple reflection of the laser light allows a larger area in the measurement cell 44 to pass. As a result, the influence of the concentration distribution on the exhaust gas flowing in the measurement cell 44 can be reduced, and the concentration can be accurately detected.

  The control means 30 controls the amount of urea water injected from the urea water injection means 22 and the injection timing based on the detection result of the concentration measurement means 28 by PID control. Specifically, when the ammonia concentration is lower than a predetermined value, the amount of urea water injected at a time is increased, or the interval at which urea water is injected is shortened. Further, when the ammonia concentration is higher than a predetermined value, the amount of urea water to be injected at a time is decreased, or the interval for injecting urea water is increased.

  FIG. 4 is a flowchart showing an example of a method for controlling the urea water injection amount by the control means 30. Note that the flowchart shown in FIG. 4 is a case where the ammonia concentration is adjusted by the amount of urea water injected from the urea water injection means 22. First, when the ammonia concentration measured by the concentration measuring means 28 is input to the control means 30, the control means 30 determines whether the measured ammonia concentration is larger than the target value as step S12. If the control means 30 determines that the ammonia concentration measured in step S12 is larger than the target value (YES), the control means 30 proceeds to step S14 and reduces the urea water injection amount that is currently set by a certain amount. That is, the amount of urea water injected from the urea water injection means 22 is reduced by a certain amount. Thereafter, the control means 30 proceeds to step S20.

  In step S12, if the control means 30 determines that the measured ammonia concentration is equal to or lower than the target value (NO), the process proceeds to step S16 to determine whether the measured ammonia concentration is smaller than the target value. If it is determined in step S16 that the measured ammonia concentration is smaller than the target value (YES), the control means 30 proceeds to step S18 and increases the currently set urea water injection amount by a certain amount. That is, the amount of urea water injected from the urea water injection means 22 is increased by a certain amount. Thereafter, the control means 30 proceeds to step S20. If the control means 30 determines in step S16 that the measured ammonia concentration is equal to or higher than the target value (NO), the control means 30 proceeds to step S20.

  In step S20, the control means 30 determines whether exhaust gas emission has stopped (that is, whether the refuse incineration system 1 has stopped). If it is determined in step S20 that exhaust gas emission has not stopped (NO), the control means 30 proceeds to step S12 and repeats the above-described processing. On the other hand, the control means 30 will complete | finish a process, if it determines with discharge | emission of waste gas having stopped in step S20 (YES). As described above, the control unit 30 controls the urea water injection amount of the urea water injection unit 22. In the above control, the urea water injection amount is increased or decreased by a certain amount, but the present invention is not limited to this. For example, when the ammonia concentration is equal to or lower than the target value, the urea water injection amount may be set as a reference value set in advance, and when the ammonia concentration is equal to or higher than the target value, the urea water injection amount may be set to zero. The urea water injection amount may be adjusted by the number of injections or may be adjusted by one injection amount. Also, the upper limit target value and the lower limit target value of the ammonia concentration may be different values. That is, the target value used in step S12 and the target value used in step S16 may be different target values. By setting the upper limit target value and the lower limit target value of the ammonia concentration to different values, the ammonia concentration range in which the urea water injection amount is not changed can be made a constant concentration range.

  The exhaust gas purification device 9 of the garbage incineration system 1 is basically configured as described above. The exhaust gas generated in the incinerator 3 is supplied to the exhaust gas purification device 9 after impurities are removed at each part. The exhaust gas supplied to the exhaust gas purification device 9 flows through the exhaust pipe 21, and after urea water is injected from the urea water injection means 22, it passes through the urea SCR catalyst means 26 together with urea water and ammonia generated from the urea water. . Exhaust gas passes through the urea SCR catalyst means 26 together with ammonia, so that nitrogen oxides contained in the exhaust gas are reduced by the urea SCR system. Thereafter, the exhaust gas is discharged from the chimney into the atmosphere. Here, as described above, the exhaust gas purifying device 9 measures the ammonia concentration of the exhaust gas that has passed through the urea SCR catalyst means 26 by the concentration measuring means 28, and the urea water injection means 22 injects based on the measurement result. The amount of urea water and injection timing are controlled.

  The exhaust gas purifying device 9 measures the ammonia concentration that has passed through the urea SCR catalyst means 26, and controls the injection amount of urea water according to the result. Thus, by controlling the injection amount of urea water based on the ammonia concentration that has passed through the urea SCR catalyst means 26, the injection amount of urea water is controlled in accordance with the reaction state of ammonia and nitrogen oxides. Can do.

  Hereafter, it demonstrates in detail using a measurement example concretely. In this measurement example, the temperature of the urea SCR catalyst was changed to change the treatment capacity of the exhaust gas. In this case, the ammonia injection amount is controlled based on the ammonia concentration, and the ammonia concentration change, the nitrogen oxide concentration change, the ammonia until the measured value of the ammonia concentration reaches the target value, that is, the steady state is reached. Changes in injection volume were measured. The ammonia injection amount corresponds to the injection amount of urea water. For comparison, changes in ammonia concentration, changes in nitrogen oxide concentration, and changes in ammonia injection amount were also measured when the ammonia injection amount was fixed without performing control according to the ammonia concentration. The measurement results are shown in FIGS. Here, FIG. 5-1 is a graph showing the relationship between nitrogen oxide (NOx) concentration and time, and FIG. 5-2 is a graph showing the relationship between measured ammonia concentration and time. 5-3 is a graph showing the relationship between the temperature of the urea SCR catalyst and time, and FIG. 5-4 is a graph showing the relationship between the amount of ammonia injected into the urea SCR catalyst and time. Here, the time axes of the graphs of FIGS. 5-1 to 5-4 are the same time axis. The target value of ammonia concentration is set to 125 ppm.

  As shown in FIGS. 5-1 to 5-4, when the ammonia concentration becomes higher than the target value, the ammonia injection amount is decreased, and when the ammonia concentration is lower than the target value, the ammonia injection amount is increased. You can see that By controlling the ammonia injection amount according to the ammonia concentration, it is possible to prevent the amount of ammonia contained in the exhaust gas from changing abruptly and to reduce the amount of ammonia leakage compared to when the ammonia injection amount is constant. I understand. Specifically, it can be seen that the ammonia slip integrated value can be reduced by 50% to 67% as compared with the case where the ammonia injection amount is constant. From the above, the effects of the present invention are clear.

  Further, the urea SCR catalyst means 26 changes the reaction amount between nitrogen oxides and ammonia and the adsorption rate of ammonia due to a plurality of factors such as temperature and concentration. Even if the injection amount is controlled, there is a possibility that ammonia will increase and ammonia will leak, or there will be less ammonia and nitrogen oxides cannot be reduced and nitrogen oxides will leak, but the ammonia concentration in the exhaust gas that has passed through the urea SCR catalyst By measuring this, it is possible to more appropriately control the injection amount of urea water. Further, since only one sensor that can control the urea water injection amount from only the ammonia concentration needs to be provided, the apparatus configuration can be simplified.

  In addition, by performing control based on the ammonia concentration on the outlet side of the urea SCR catalyst means 26, when a part of the urea SCR catalyst 26a of the urea SCR catalyst means 26 is replaced, the processing capacity of the urea SCR catalyst means 26 is increased. Even if it is not possible to calculate, it is possible to calculate the appropriate urea water injection amount and ammonia water supply amount.

  Here, the exhaust gas purification device 9 can suppress the leakage of ammonia as described above, but oxidizes the ammonia downstream of the urea SCR catalyst means 26 in order to further reduce the ammonia leaking into the atmosphere. It is preferable to provide an oxidation catalyst. Even if an oxidation catalyst is provided, the exhaust gas purifying device 9 can reduce the amount of ammonia leaking out as described above, so that the oxidation catalyst can be made smaller than before. Thereby, the apparatus configuration of the exhaust gas purification apparatus can be further simplified, and the weight can be reduced. Furthermore, nitrogen oxides generated by oxidizing ammonia can be reduced.

  Further, the control means 30 may change the target value of the ammonia concentration at the measurement position depending on the operating condition of the incinerator, or may be constant regardless of the operating condition. When the target value is changed depending on the operating conditions, the injection amount of urea water can be controlled in accordance with the increase or decrease of the amount of nitrogen oxides contained in the exhaust gas, and the nitrogen oxides are more appropriately reduced. The ammonia concentration at the measurement position can be maintained at a value close to the target value. The same applies to the case where the target value is kept constant and the injection amount and the injection timing of the urea water are controlled from the relationship between the target value and the operating conditions. Further, when the target value of the ammonia concentration is constant regardless of the operating conditions, it is not necessary to detect the operating conditions, the number of measuring means can be reduced, and the apparatus configuration of the exhaust gas purifying apparatus can be simplified. . Further, since it is not necessary to calculate the target value according to the conditions, the control is simplified.

  Further, by using a zeolite-based catalyst as the urea SCR catalyst, even if the exhaust gas is at a high temperature, it can function properly as a catalyst. In addition, the zeolite system has a large amount of ammonia adsorbed, and its performance changes due to temperature and catalyst deterioration, so that it is difficult to control by a map or the like. By measuring the ammonia concentration and controlling the urea water injection amount based on the measurement result, it is possible to suppress leakage of ammonia even when a zeolite-based catalyst is used as the urea SCR catalyst.

  In the exhaust gas purifying apparatus 9, ammonia can be measured continuously as the concentration measuring means 28 without detecting nitrogen oxides. Therefore, laser light in a wavelength region that is absorbed by ammonia is output, and the absorption ratio of the laser light. Although the ammonia concentration was measured by the TDLAS method for detecting γ, it is not limited to this. Various measuring means capable of measuring the ammonia concentration in the exhaust gas can be used in the present invention. For example, a branch pipe is provided at the measurement position so that a part of the exhaust gas also flows through the branch pipe. The ammonia concentration of the flowing exhaust gas may be measured.

  Moreover, in the said embodiment, although the quantity of urea water injected from the urea water injection means 22 was controlled, this invention is not limited to this, In addition to or instead of the injection quantity of urea water, the ammonia water supply means 25 The supply amount of ammonia water supplied from may be changed. In addition to or instead of the urea water injection means and the ammonia water supply means, ammonia gas injection means for supplying ammonia gas may be provided to adjust the amount of ammonia gas supplied. As described above, the present invention provides a reducing agent injection means (supply means) for supplying a reducing agent capable of generating ammonia, urea water, ammonia water, ammonia gas, etc., and the reducing agent supplied from the reducing agent injection means. Adjust the amount. When ammonia water or ammonia gas is used, the urea SCR catalyst can be said to be an ammonia SCR catalyst. Note that the urea SCR catalyst and the ammonia SCR catalyst are the same catalyst only with different names.

  Moreover, when using for a garbage incineration system and a boiler like this embodiment, since a lot of exhaust gas is discharged | emitted and the opening area of exhaust piping becomes large, it is preferable to measure the ammonia concentration of several points. Here, it is preferable that the measurement points are the same in the flow direction of the exhaust gas but different in the position of the exhaust pipe, that is, the ammonia concentration at different points on the same cross section of the exhaust pipe. By measuring the ammonia concentration at a plurality of points in this way, the ammonia concentration in the exhaust gas can be measured more accurately even when the ammonia concentration is uneven in the exhaust pipe. The method for calculating the ammonia concentration from a plurality of measurement results is not particularly limited, and an average value may be obtained, or a concentration distribution may be calculated from the measurement results to obtain an overall ammonia concentration. Good.

  Further, in the exhaust gas purification device 9, only the concentration measuring means 28 is provided and the urea water injection amount is controlled only from the ammonia concentration of the exhaust gas that has passed through the urea SCR catalyst means 26, but the present invention is not limited to this. Hereinafter, another embodiment of the exhaust gas purification apparatus of the present invention will be described with reference to FIG.

  FIG. 6 is a block diagram showing a schematic configuration of another embodiment of the exhaust gas purifying apparatus. The exhaust gas purifying device 50 shown in FIG. 6 is the same as the exhaust gas purifying device 9 shown in FIG. 2 except for a part of the configuration, so the description of the same components is omitted. A point peculiar to the exhaust gas purification apparatus 50 will be described mainly. The exhaust gas purifying device 50 shown in FIG. 6 includes a urea water injection means 22, a urea water tank 24, an ammonia water supply means 25, a urea SCR catalyst means 26, a concentration measuring means 28, and a pretreatment ammonia concentration measuring means 54. A non-treatment nitrogen oxide concentration measurement means 58, a post-treatment nitrogen oxide concentration measurement means 60, a temperature adjustment means 62, and a control means 64. Since the urea water injection means 22, the urea water tank 24, the ammonia water supply means 25, the urea SCR catalyst means 26, and the concentration measurement means 28 have the same configuration as each part of the exhaust gas purification device 9 described above, Detailed description is omitted. For the sake of explanation, FIG. 6 also shows a dust collector 7.

  The pretreatment ammonia concentration measuring means 54 is upstream of the urea SCR catalyst means 26 in the exhaust gas exhaust path, specifically, downstream of the dust collector 7 and urea water injection means 22 and from the urea SCR catalyst means 26. Is also arranged in the upstream exhaust pipe 21 and measures the concentration of ammonia in the exhaust gas supplied to the urea SCR catalyst means 26. The pre-treatment ammonia concentration measuring means 54 has a measuring means main body, an optical fiber, a measuring cell, and a light receiving section, like the concentration measuring means 28. Since the ammonia concentration measuring method by the pretreatment ammonia concentration measuring means 54 is the same as that of the concentration measuring means 28, the description thereof is omitted. The pretreatment ammonia concentration measuring means 54 continuously measures the ammonia concentration contained in the exhaust gas before passing through the urea SCR catalyst means 26, and sends the measurement result to the control means 64.

  The isocyanate concentration measuring means 56 is arranged upstream of the urea SCR catalyst means 26 in the exhaust gas exhaust path, and measures the concentration of isocyanate in the exhaust gas supplied to the urea SCR catalyst means 26. As the isocyanic acid concentration measuring unit 56, a sensor having the same configuration as the concentration measuring unit 28 can be used. Specifically, laser light in a wavelength region that is absorbed by isocyanic acid is emitted from the light emitting unit, light that is emitted from the light emitting unit and passed through the exhaust gas is received by the light receiving unit, and from the intensity of the received light, Isocyanic acid concentration can be detected. The isocyanate concentration measuring means 56 continuously measures the isocyanate concentration contained in the exhaust gas before passing through the urea SCR catalyst means 26, and sends the measurement result to the control means 64. As the isocyanic acid concentration measuring means, various sensors can be used as long as they detect and measure only isocyanic acid without detecting nitrogen oxides and ammonia in the exhaust gas.

  The pretreatment nitrogen oxide concentration measuring means 58 is disposed upstream of the urea SCR catalyst means 26 in the exhaust gas exhaust path, and the concentration of nitrogen oxides in the exhaust gas supplied to the urea SCR catalyst means 26 is determined. measure. As the pre-treatment nitrogen oxide concentration measuring means 58, a sensor having the same configuration as the concentration measuring means 28 can be used in the same manner as the isocyanate oxide concentration measuring means 56. Specifically, laser light in a wavelength region absorbed by nitrogen oxides is emitted from the light emitting unit, light emitted from the light emitting unit and received through the exhaust gas is received by the light receiving unit, and the exhaust gas is determined from the intensity of the received light. The concentration of nitrogen oxide in it can be detected. The pretreatment nitrogen oxide concentration measuring means 58 continuously measures the nitrogen oxide concentration contained in the exhaust gas before passing through the urea SCR catalyst means 26 and sends the measurement result to the control means 64. As the nitrogen oxide concentration measuring means, various sensors can be used as long as they detect and measure only nitrogen oxide without detecting isocyanic acid and ammonia in the exhaust gas.

  The post-treatment nitrogen oxide concentration measuring means 60 is disposed in the exhaust pipe 21 downstream of the urea SCR catalyst means 26 in the exhaust gas exhaust path, and the concentration of nitrogen oxides in the exhaust gas that has passed through the urea SCR catalyst means 26. Measure. As the post-treatment nitrogen oxide concentration measuring means 60, a sensor having the same configuration as the pre-treatment nitrogen oxide concentration measuring means 58 can be used. The post-treatment nitrogen oxide concentration measuring means 60 continuously measures the nitrogen oxide concentration contained in the exhaust gas that has passed through the urea SCR catalyst means 26, and sends the measurement result to the control means 64.

  The temperature adjusting means 62 is provided in the exhaust pipe 21 upstream of the urea SCR catalyst means 26 in the exhaust gas exhaust path, specifically, in the exhaust pipe 21 between the urea water injection means 22 and the urea SCR catalyst means 26. The temperature of the exhaust gas flowing through the exhaust pipe 21 is adjusted. As the temperature adjusting means 62, the exhaust pipe 21 is heated and cooled to warm or cool the exhaust gas flowing through the exhaust pipe 21, thereby adjusting the temperature of the exhaust gas. As the temperature adjusting means 62, various heating mechanisms and cooling mechanisms such as a heater, a Peltier element, and an air cooling device can be used.

  The control means 64 adjusts the urea water injection amount by the urea water injection means 22 based on the measurement results sent from the concentration measurement means 28, the pre-treatment nitrogen oxide concentration measurement means 58 and the post-treatment nitrogen oxide concentration measurement means 60. Then, based on the measurement results sent from the pretreatment ammonia concentration measuring means 54 and the isocyanate concentration measuring means 56, the exhaust gas temperature is adjusted by the temperature adjusting means 62.

  First, adjustment of the urea water injection amount by the control means 64 will be described. The control means 64 has passed through the urea SCR catalyst means 26 sent from the nitrogen oxide concentration measuring means 60 after the treatment, because the ammonia concentration of the exhaust gas that passed through the urea SCR catalyst means 26 sent from the concentration measuring means 28 becomes below the target value. The urea water injection amount is set so that the nitrogen oxide concentration of the exhaust gas is equal to or less than the target value. The control means 64 purifies the nitrogen oxides contained in the exhaust gas based on the nitrogen oxide concentration of the exhaust gas before passing through the urea SCR catalyst means 26 sent from the pretreatment nitrogen oxide concentration measuring means 58. The amount of ammonia required for this is calculated. Hereinafter, an example of the control method will be described in detail with reference to FIG. FIG. 7 is a flowchart showing an example of a method for controlling the urea water injection amount by the control means 64. 7 is a control method for controlling the urea injection amount so that the ammonia concentration and the nitrogen oxide concentration in the exhaust gas that has passed through the urea SCR catalyst means 26 are optimal, and the urea SCR catalyst means 26. This is a control method that does not consider controlling the urea water injection amount based on the nitrogen oxide concentration of the exhaust gas before passing through the exhaust gas.

  First, when the ammonia concentration measured by the concentration measuring unit 28 and the nitrogen oxide (NOx) concentration measured by the post-treatment nitrogen oxide concentration measuring unit 60 are input to the control unit 64, the control unit 64 performs step S30. Then, it is determined whether the measured ammonia concentration is larger than the target value. If the control means 64 determines that the ammonia concentration measured in step S30 is larger than the target value (YES), the control means 64 proceeds to step S32 and determines whether the measured nitrogen oxide (NOx) concentration is smaller than the target value. judge.

  If it is determined in step S32 that the measured nitrogen oxide (NOx) concentration is smaller than the target value (YES), the control means 64 reduces the currently set urea water injection amount by a certain amount in step S38. To do. That is, the amount of urea water injected from the urea water injection means 22 is reduced by a certain amount. Thereafter, the control means 64 proceeds to step S44. On the other hand, if it is determined in step S32 that the measured nitrogen oxide (NOx) concentration is equal to or higher than the target value (NO), the control means 64 performs a recovery process in step S36. Here, the recovery process is a process for recovering the catalytic ability of the urea SCR catalyst means 26, for example, a process for heating the urea SCR catalyst of the urea SCR catalyst means 26. As a means for heating the urea SCR catalyst, for example, a heater can be used. Further, a heating means may be provided in the exhaust pipe 21 to increase the temperature of the exhaust gas. As described above, when both the ammonia concentration and the nitrogen oxide concentration are equal to or higher than the target values, the ability of the urea SCR catalyst means 26 as a catalyst is reduced, and the reaction between ammonia and nitrogen oxide does not occur appropriately. By performing the recovery process, the urea SCR catalyst means 26 can suitably cause the reaction between ammonia and nitrogen oxides.

  Next, when it is determined that the ammonia concentration measured in step S30 is equal to or lower than the target value (NO), the control unit 64 determines whether the nitrogen oxide (NOx) concentration is larger than the target value in step S34. . If it is determined in step S34 that the nitrogen oxide concentration is higher than the target value (YES), the control means 64 proceeds to step S40 and determines whether the ammonia concentration is lower than the target value. On the other hand, if it is determined in step S34 that the nitrogen oxide concentration is equal to or lower than the target value (NO), the control means 64 adjusts the urea water injection amount because both the nitrogen oxide concentration and the ammonia concentration are equal to or lower than the target value. Without proceeding to step S44. Next, if the control means 64 determines in step S40 that the ammonia concentration is smaller than the target value (YES), the control means 64 proceeds to step S42, and increases the currently set urea water injection amount by a certain amount. That is, the amount of urea water injected from the urea water injection means 22 is increased by a certain amount. Thereafter, the control means 64 proceeds to step S44. On the other hand, if the control means 64 determines in step S40 that the ammonia concentration is equal to or higher than the target value (NO), the control means 64 proceeds to step S44. As described above, when ammonia is equal to or higher than the target value in step S40, ammonia in the exhaust gas discharged from the exhaust pipe 21 is not increased by increasing the amount of ammonia even when the nitrogen oxide concentration is higher than the target value. Can be reduced.

  In step S44, the control means 64 determines whether the exhaust gas emission has stopped (that is, whether the refuse incineration system 1 has stopped). If it is determined in step S44 that the exhaust gas emission has not stopped (NO), the control means 64 proceeds to step S30 and repeats the above-described processing. On the other hand, the control means 64 will complete | finish a process, if it determines with discharge | emission of exhaust gas having stopped in step S44 (YES). As described above, the control means 64 controls the urea water injection amount of the urea water injection means 22. In the above control, the urea water injection amount is increased or decreased by a certain amount. However, the control is not limited to this as in the above control. The upper limit target value and the lower limit target value of the ammonia concentration may be different values. In the above control, the recovery process is performed in step S36, but the notification unit may notify the user that the urea SCR catalyst of the urea SCR catalyst unit 26 needs to be replaced. Here, as the notification means, a display for displaying a message or a voice output device for giving a voice notification can be used.

  Moreover, in the said embodiment, although the nitrogen oxide density | concentration measured by the nitrogen oxide density | concentration measurement means 58 before a treatment is not used, it is in the waste gas from the nitrogen oxide density | concentration of the waste gas before passing the urea SCR catalyst means 26. The amount of ammonia required for the purification (neutralization) of nitrogen oxides is calculated, and the urea water injection amount calculated from the ammonia concentration and the nitrogen oxide concentration in the exhaust gas after passing through the urea SCR catalyst means 26 is corrected by the control means. You may make it do. Further, the urea water injection amount is calculated from the ammonia concentration in the exhaust gas after passing through the urea SCR catalyst means 26 without using the nitrogen oxide concentration in the exhaust gas after passing through the urea SCR catalyst means 26, and the calculated urea water injection amount. May be corrected based on the amount of ammonia required for purification (neutralization) of nitrogen oxides in the exhaust gas calculated from the nitrogen oxide concentration of the exhaust gas before passing through the urea SCR catalyst means 26.

  Next, a method in which the control unit 64 adjusts the exhaust gas temperature by the temperature adjusting unit 62 based on the measurement results sent from the pretreatment ammonia concentration measuring unit 54 and the isocyanate concentration measuring unit 56 will be described. The urea water injected from the urea water injection means 22 generates isocyanic acid from urea and ammonia from isocyanic acid by the heat of the exhaust pipe 21 and the heat of the exhaust gas. However, when the reaction is insufficient, a part of the urea water remains as urea or is in the state of isocyanic acid and may not become ammonia. In order to solve this problem, the control means 64 determines the ammonia concentration and / or the isocyanate concentration of the exhaust gas before passing through the urea SCR catalyst means 26 sent from the pretreatment ammonia concentration measurement means 54 and the isocyanate concentration measurement means 56. Then, it is determined whether the injected urea water is appropriately ammonia. Specifically, when the isocyanic acid concentration is above a certain level, it is determined that the reaction has not occurred appropriately. Further, when the theoretical ammonia concentration is calculated from the urea water injection amount and the measured value measured by the pretreatment ammonia concentration measuring means 54 is lower than the calculated value by a certain concentration or more, the reaction does not occur properly. judge. When the control means 64 determines that the reaction has not occurred properly and urea water and isocyanic acid remain, the temperature adjusting means 62 raises the exhaust gas temperature to ammonia the urea water and isocyanic acid. Promote to be ammonia upon arrival at the urea SCR catalyst means 26.

  The exhaust gas purifying device 50 is configured as described above, and the exhaust gas generated in the incinerator 3 and passing through each part is injected with urea water by the urea water injection means 22 and then the temperature adjusting means 62 of the exhaust pipe 21. Flows through the area where Thereafter, the exhaust gas flows through an area of the exhaust pipe 21 where the pretreatment ammonia concentration measurement means 54, the isocyanate concentration measurement means 56, and the pretreatment nitrogen oxide concentration measurement means 58 are disposed. At that time, each concentration measuring means measures the concentration of the substance to be measured for exhaust gas. Thereafter, the exhaust gas passes through the urea SCR catalyst 26a, flows through a region where the concentration measuring means 28 and the treated nitrogen oxide concentration measuring means 60 of the exhaust pipe 21 are disposed, and is discharged to the outside. Here, when the exhaust gas passes through the urea SCR catalyst, nitrogen oxides contained in the exhaust gas react with ammonia generated from the urea water, and the nitrogen oxides are reduced. Each concentration measuring means measures the concentration of the substance to be measured for exhaust gas.

  The exhaust gas purifying device 50 uses the urea water injection means 22 based on the measurement results of the pre-treatment nitrogen oxide concentration measurement means 58 and the post-treatment nitrogen oxide concentration measurement means 60 in addition to the measurement results of the concentration measurement means 28. By adjusting the urea water injection amount according to, it is possible to further reduce nitrogen oxides in the exhaust gas while suppressing ammonia from leaking out. Further, by adjusting the exhaust gas temperature by the temperature adjusting means 62 based on the measurement results of the pretreatment ammonia concentration measuring means 54 and the isocyanate concentration measuring means 56, the urea water can be more appropriately converted to ammonia, Ammonia and nitrogen oxide can be reacted appropriately.

  In the above embodiment, the concentration measuring means 28, the pre-treatment nitrogen oxide concentration measuring means 58, the post-treatment nitrogen oxide concentration measuring means 60, the pre-treatment ammonia concentration measuring means 54, and the isocyanate concentration measuring means 56 are used. At least the concentration measuring means 28 may be used, and other sensors may be used in appropriate combination. The above effect can be obtained by adjusting the urea water injection amount or the urea water injection amount and the exhaust gas temperature based on the measurement results measured from the concentration measuring means 28 and each sensor.

  The exhaust gas purification device further has a temperature detecting means for detecting the temperature of the urea SCR catalyst, stores the history of the temperature of the urea SCR catalyst and the measurement result measured by each measuring means, and stores the history in the urea SCR catalyst. Calculate the amount of adsorbed ammonia, calculate the amount of ammonia necessary for purifying nitrogen oxides in the exhaust gas based on the calculated amount of ammonia, and inject urea water based on the calculated amount of ammonia Is preferred. In this way, by controlling the urea water injection amount in consideration of the ammonia amount adsorbed on the urea SCR catalyst, the ammonia amount adsorbed on the urea SCR catalyst is converted into ammonia and nitrogen oxide by the urea SCR catalyst. Can be made into the quantity which can be made to react with high efficiency. Thereby, the amount of ammonia leaking from the exhaust pipe can be further reduced. Also, ammonia and nitrogen oxide can be efficiently reacted with the urea SCR catalyst, so that the urea SCR catalyst can be made smaller and smaller.

  The nitrogen oxides detected by the pre-treatment nitrogen oxide concentration measuring means 58 and the post-treatment nitrogen oxide concentration measuring means 60 may detect only nitrogen monoxide or only nitrogen dioxide. Both nitric oxide and nitrogen dioxide may be detected. Even if only nitrogen monoxide, nitrogen dioxide only, or both nitrogen monoxide and nitrogen dioxide are detected, the concentration of nitrogen oxide concentration in the exhaust gas can be measured suitably, and the measured value is the injection amount of urea water It can be used for calculation. It is preferable that the pre-treatment nitrogen oxide concentration measuring means 58 and the post-treatment nitrogen oxide concentration measuring means 60 detect only nitrogen monoxide.

  In the exhaust gas purifying apparatus described above, the ammonia concentration of the exhaust gas that has passed through the urea SCR catalyst means is detected by the concentration measuring means 28. However, the present invention is not limited to this, and the pre-treatment nitrogen oxide concentration measuring means and the post-treatment The ammonia concentration may be calculated from the nitrogen oxide concentration measured by the nitrogen oxide concentration measuring means. Hereinafter, this will be described in detail with reference to FIG. FIG. 8 is a block diagram showing a schematic configuration of another embodiment of the exhaust gas purifying apparatus. Since the exhaust gas purifying device 72 shown in FIG. 8 is the same as the exhaust gas purifying device 9 shown in FIG. 2 except for a part of the configuration, the description of the same components will be omitted. A point peculiar to the exhaust gas purification device 72 will be described mainly.

  The exhaust gas purification device 72 shown in FIG. 8 includes urea water injection means 22, urea water tank 24, ammonia water supply means 25, urea SCR catalyst means 26, pre-treatment nitrogen oxide concentration measurement means 76, and post-treatment. Nitrogen oxide concentration measuring means 78 and control means 80 are provided. Since the urea water injection means 22, the urea water tank 24, the ammonia water supply means 25, and the urea SCR catalyst means 26 have the same configuration as each part of the exhaust gas purification device 9 described above, detailed description is omitted. .

  The pretreatment nitrogen oxide concentration measuring means 76 is disposed upstream of the urea SCR catalyst means 26 in the exhaust gas exhaust path, and measures the concentration of nitrogen oxide in the exhaust gas supplied to the urea SCR catalyst means 26. To do. The pretreatment nitrogen oxide concentration measurement means 76 is a measurement means similar to the pretreatment nitrogen oxide concentration measurement means 58 shown in FIG.

  The post-treatment nitrogen oxide concentration measuring means 78 is disposed in the exhaust pipe 21 downstream of the urea SCR catalyst means 26 in the exhaust gas exhaust path, and the concentration of nitrogen oxides in the exhaust gas that has passed through the urea SCR catalyst means 26. Measure. The post-treatment nitrogen oxide concentration measurement unit 78 is a measurement unit similar to the post-treatment nitrogen oxide concentration measurement unit 60.

  The control means 80 includes the nitrogen oxide concentration in the exhaust gas before passing through the urea SCR catalyst means 26 detected by the pretreatment nitrogen oxide concentration measurement means 76 and the urea SCR catalyst means detected by the posttreatment nitrogen oxide concentration measurement means 78. The amount of reacted ammonia is calculated based on the nitrogen oxide concentration in the exhaust gas after passing through 26, and the ammonia concentration contained in the exhaust gas that has passed through the urea SCR catalyst means 26 is calculated. The control means 80 controls the urea water injection amount by the same method as the control means 30 of the exhaust gas purification device 9 based on the calculated ammonia concentration. Thus, as in the exhaust gas purification device 72, the urea concentration in the exhaust gas that has passed through the urea SCR catalyst means 26 is calculated from the nitrogen oxide concentration in the exhaust gas, so that the urea concentration does not have to be directly measured. The amount of water injection can be controlled. Note that, as described above, the urea SCR catalyst has a lower measurement accuracy than the direct measurement of the ammonia concentration because the amount of ammonia to be adsorbed varies depending on the temperature or the like. Therefore, the effect of suppressing ammonia leaking from the exhaust pipe is lower than that of each of the exhaust gas purification apparatuses described above.

  As described above, the exhaust gas purifying apparatus according to the present invention is useful for purifying exhaust gas discharged from combustion equipment, and is particularly suitable for purifying exhaust gas discharged from incinerators and boilers.

DESCRIPTION OF SYMBOLS 1 Garbage incineration system 2 Input hopper 3 Incinerator 4 Ash processing part 5 Boiler 6 Incineration temperature reduction tower 7 Dust collector 9, 50, 72 Exhaust gas purification apparatus 10 Fan 12 Chimney 13 Temperature reduction water tank 14 Slaked lime storage tank 15 Activated carbon storage tank 16 Special agent storage tank 17 Push fan 22 Urea water injection means 24 Urea water tank 25 Ammonia water supply means 26 Urea SCR catalyst means 28 Concentration measuring means 30, 64, 80 Control means 40 Measuring means body 42 Optical fiber 44 Measuring cell 46 Light receiving Unit 54 Pre-treatment ammonia concentration measurement means 56 Isocyanic acid concentration measurement means 58, 76 Pre-treatment nitrogen oxide concentration measurement means 60, 78 Post-treatment nitrogen oxide concentration measurement means 62 Temperature adjustment means

Claims (9)

An exhaust gas purification device that reduces nitrogen oxides contained in exhaust gas discharged from combustion equipment,
An exhaust pipe for guiding exhaust gas discharged from the combustion device;
Reducing agent injection means for injecting at least one of urea water, ammonia water and ammonia gas as a reducing agent into the exhaust pipe;
An ammonia SCR catalyst that promotes a reaction between ammonia generated from the injected reducing agent and the nitrogen oxide; and a support mechanism that is disposed inside the exhaust pipe and supports the ammonia SCR catalyst inside the exhaust pipe. Catalyst means disposed downstream of the position where the reducing agent is injected in the flow direction of the exhaust gas,
An ammonia concentration measuring means that is disposed downstream of the catalyst means in the flow direction of the exhaust gas and measures the ammonia concentration of the exhaust gas that has passed through the ammonia SCR catalyst;
An exhaust gas purifying apparatus comprising: a control unit that controls injection of the reducing agent by the reducing agent injection unit based on the ammonia concentration measured by the ammonia concentration measuring unit. Furthermore, it has a post-treatment nitrogen oxide concentration measuring means that is disposed downstream of the catalyst means in the flow direction of the exhaust gas and measures the nitrogen oxide concentration of the exhaust gas that has passed through the ammonia SCR catalyst,
2. The exhaust gas according to claim 1, wherein the control unit controls injection of the reducing agent by the reducing agent injection unit based on the nitrogen oxide concentration measured by the post-treatment nitrogen oxide concentration measuring unit. Purification equipment.   When both the ammonia concentration detected by the ammonia concentration measuring means and the nitrogen oxide concentration measured by the post-treatment nitrogen oxide concentration measuring means exceed a reference concentration, the ammonia SCR catalyst is recovered. The exhaust gas purifying apparatus according to claim 2, further comprising a recovery unit that performs the operation.   The exhaust gas purifying apparatus according to claim 3, wherein the recovery means heats the ammonia SCR catalyst at a predetermined temperature.   If both the ammonia concentration detected by the ammonia concentration measuring means and the nitrogen oxide concentration measured by the post-treatment nitrogen oxide concentration measuring means exceed the reference concentration, the ammonia SCR catalyst is replaced. The exhaust gas purifying apparatus according to claim 2, further comprising notification means for notifying that it is necessary to perform the operation. Furthermore, it is disposed between the reducing agent injection means and the catalyst means in the flow direction of the exhaust gas, and has a pre-treatment nitrogen oxide concentration measuring means for measuring the nitrogen oxide concentration of the exhaust gas,
The said control means controls injection of the reducing agent by the reducing agent injection means based on the nitrogen oxide concentration measured by the pre-treatment nitrogen oxide concentration measuring means. The exhaust gas purifying apparatus according to claim 1. Furthermore, an isocyanate concentration measuring means that is disposed between the reducing agent injection means and the catalyst means in the flow direction of the exhaust gas and measures the isocyanate concentration of the exhaust gas,
Temperature adjusting means for adjusting the temperature of the exhaust gas flow path between the reducing agent injection means and the catalyst means in the flow direction of the exhaust gas,
The exhaust gas purification according to any one of claims 1 to 6, wherein the temperature adjusting means adjusts the temperature of the exhaust gas flow path based on the isocyanate concentration measured by the isocyanate concentration measuring means. apparatus. Further, the pretreatment ammonia concentration measuring means is disposed between the reducing agent injection means and the catalyst means in the flow direction of the exhaust gas, and measures the ammonia concentration of the exhaust gas,
Temperature adjusting means for adjusting the temperature of the exhaust gas flow path between the reducing agent injection means and the catalyst means in the flow direction of the exhaust gas,
The exhaust gas purification according to any one of claims 1 to 7, wherein the temperature of the exhaust gas passage is adjusted by the temperature adjusting means based on the ammonia concentration measured by the pretreatment ammonia concentration measuring means. apparatus. An exhaust gas purification device that reduces nitrogen oxides contained in exhaust gas discharged from combustion equipment,
An exhaust pipe for guiding exhaust gas discharged from the combustion device;
Reducing agent injection means for injecting at least one of urea water, ammonia water and ammonia gas as a reducing agent into the exhaust pipe;
An ammonia SCR catalyst that promotes a reaction between ammonia generated from the injected reducing agent and the nitrogen oxide, and a support mechanism that is disposed inside the exhaust pipe and supports the ammonia SCR catalyst inside the exhaust pipe. Provided with catalyst means disposed downstream of the position where the reducing agent is injected in the flow direction of the exhaust gas;
A pre-treatment nitrogen oxide concentration measuring means that is disposed between the reducing agent injection means and the catalyst means in the flow direction of the exhaust gas, and measures the nitrogen oxide concentration of the exhaust gas;
A post-treatment nitrogen oxide concentration measuring means that is disposed downstream of the catalyst means in the flow direction of the exhaust gas and measures the nitrogen oxide concentration of the exhaust gas that has passed through the ammonia SCR catalyst;
Based on the difference between the nitrogen oxide concentration measured by the pre-treatment nitrogen oxide concentration measuring means and the nitrogen oxide concentration measured by the post-treatment nitrogen oxide concentration measuring means, in the exhaust gas that has passed through the catalyst means An exhaust gas purification apparatus comprising: a control unit that calculates an ammonia concentration and controls injection of the reducing agent by the reducing agent injection unit based on the calculated ammonia concentration.

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