JP2017006813A - Denitration apparatus and treatment method of nitrogen oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a treatment technology of nitrogen oxides capable of efficiently performing the denitration treatment of the nitrogen oxides in a combustion exhaust gas over a wide temperature range by using a plurality of kinds of denitration catalysts having high denitration activity at different operation temperatures using ammonia as a reducer.SOLUTION: A denitration apparatus 10 for a thermal power station using ammonia as a reducer, disposes: a high temperature denitration catalyst A for accelerating a rection between ammonia and nitrogen oxides at a high temperature of 250°C or higher in the upstream side to the inlet of a combustion exhaust gas in the denitration apparatus 10 and having a decomposing function to nitrogen and water; and a low temperature denitration catalyst B for accelerating a rection between ammonia and nitrogen oxides at a low temperature of less than 250°C in the downstream side of the high temperature denitration catalyst A and having a decomposing function to nitrogen and water.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to a method for treating nitrogen oxide (NOx) discharged from a thermal power plant or the like and a denitration apparatus.

Thermal power plants include a denitration technology for decomposing nitrogen oxides into nitrogen and water as a processing technology for nitrogen oxides (NOx) generated with fuel combustion. Common denitration technologies include ammonia and urea as reducing agents, ammonia catalytic reduction method (NH ₃ -SCR) that decomposes nitrogen oxides into nitrogen and water, and hydrocarbon catalytic reduction using hydrocarbons as reducing agents. Method (HC-SCR), a discharge method for supplying energy necessary for decomposition of nitrogen oxides by corona discharge or the like, and an adsorption method using an adsorbent for nitrogen oxides. Of these, the ammonia reduction method is often used for denitration technology for thermal power plants.

  With the spread of renewable energy, there is a concern about the instability of the electric power system, and the operation method of the thermal power plant is expected to be diversified to adjust the load of the electric power system. When the operation method of a thermal power plant is diversified, it is expected that the composition change of nitrogen oxides (NOx) and the exhaust gas temperature of the combustion exhaust gas discharged from the combustor will change. When the exhaust gas temperature changes, there is a concern that the reactivity of nitrogen oxides changes greatly.

  By the way, in the ammonia catalytic reduction method, it is known that the reaction temperature and the composition of nitrogen oxides greatly affect the reactivity. Nitrogen oxides generally have low reactivity at low temperatures, exhibiting the highest reactivity at a certain optimum temperature range, and the behavior that the reactivity decreases again at higher temperatures. .

Further, when the ratio of nitrogen monoxide (NO) and nitrogen dioxide (NO ₂ ) in nitrogen oxide (NOx) changes, the reactivity of the catalytic reduction method using ammonia also changes greatly. When nitric oxide and nitrogen dioxide are in a ratio of 1: 1, the reduction efficiency is high, and nitrogen oxides exhibit the best processing performance.

  At present, in order to cope with load fluctuation operation of thermal power plants, a denitration device equipped with a denitration catalyst that combines a low-temperature operation catalyst and a high-temperature use catalyst so that it can be operated at an optimum catalyst temperature, or a catalyst layer There has been proposed a denitration device that switches an exhaust gas flow path in response to a change in temperature.

  In addition, by arranging an oxidation catalyst or the like in front of the denitration catalyst, it varies depending on the denitration device that oxidizes nitrogen monoxide, ammonia, nitric acid and adjusts the composition of nitrogen oxide, and the composition of nitrogen oxide (NOx) A denitration apparatus that supplies a reducing agent and a denitration apparatus that combines an ammonia SCR catalyst with a layer that adsorbs nitrogen oxide (NOx) at a low temperature have been proposed.

Special table 2009-538735 gazette Japanese Patent Laid-Open No. 10-15355 JP 2013-221466 A JP-A-6-319951 JP-A-8-103636 JP-A-8-266868 JP-A-9-94437 JP-A-5-245338 JP-T-2006-519332

In a thermal power plant, the combustion exhaust gas temperature and the nitrogen oxide (NOx) composition in the exhaust gas change with load fluctuation operation. In particular, when the exhaust gas temperature and the nitrogen oxide composition in the exhaust gas change so that nitrogen dioxide (NO ₂ ) increases compared to nitrogen monoxide (NO), the reduction efficiency of NO and NO ₂ in the denitration catalyst in the denitration device Therefore, it is difficult to sufficiently effectively remove nitrogen oxides in the combustion exhaust gas.

  In addition, among the conventional denitration techniques described in patent documents, there is one in which catalyst layers of two types of denitration catalysts having different activation temperature ranges in the denitration apparatus are provided. However, this denitration equipment uses hydrocarbons, alcohol, etc. as a reducing agent, arranges a low-temperature denitration catalyst upstream of the flow of combustion exhaust gas, and arranges a high-temperature denitration catalyst downstream of the downstream Denitration technology.

  The denitration technology described in the patent literature is effective when the concentration of nitrogen oxides and reducing agent in the combustion exhaust gas is high. However, as with a denitration system for thermal power plants, a gas turbine is used with combustion gas from a combustor. In exhaust gas systems where the temperature of combustion exhaust gas decreases due to driving, working in a boiler, or active heat exchange, it is difficult to efficiently perform denitration treatment of nitrogen oxides in combustion exhaust gas, and sufficient denitration function Cannot be obtained.

  Embodiments of the present invention have been made in consideration of the above-described circumstances. Ammonia is used as a reducing agent, and a plurality of types of denitration catalysts having high denitration activity at different operating temperatures can be used to reduce nitrogen oxides in combustion exhaust gas. An object of the present invention is to provide a denitration apparatus and a nitrogen oxide treatment method that can efficiently perform a denitration treatment in a wide temperature range.

  Another object of the embodiment of the present invention is that there is little loss of ammonia used as the reducing agent, nitrogen oxide denitration treatment can be carried out efficiently over a wide temperature range, and nitrogen oxidation is performed regardless of the composition of the nitrogen oxide. The present invention provides a denitration apparatus and a nitrogen oxide treatment method for a thermal power plant that can efficiently perform denitration treatment of an object.

  In order to solve the above-described problems, an embodiment of the present invention is a denitration apparatus using ammonia as a reducing agent. In the denitration apparatus, ammonia and nitrogen are heated at a high temperature of 250 ° C. or more upstream of the combustion exhaust gas inlet of the denitration apparatus. A high-temperature denitration catalyst having a function of accelerating the reaction with oxides and decomposing into nitrogen and water is disposed, and the reaction between ammonia and nitrogen oxides is promoted from a low temperature of less than 250 ° C. downstream of the high-temperature denitration catalyst, The denitration apparatus is characterized in that a low temperature denitration catalyst having a function of decomposing into nitrogen and water is arranged.

  In order to solve the above-described problem, an embodiment of the present invention is a denitration apparatus using ammonia as a reducing agent. In the denitration apparatus, a reaction between ammonia and nitrogen oxides is performed at a high temperature of 250 ° C. or higher. High-temperature denitration catalyst that has the function of promoting nitrogen and decomposing into nitrogen and water, and the partial reduction of nitrogen dioxide that promotes the reaction between ammonia and nitrogen dioxide from less than 250 ° C. and that partially reduces nitrogen dioxide to nitrogen monoxide A denitration apparatus comprising: a catalyst; and a low-temperature denitration catalyst having a function of accelerating a reaction between ammonia and nitrogen oxide from below 250 ° C. and decomposing into nitrogen and water.

  Furthermore, in order to solve the above-described problem, an embodiment of the present invention provides a denitration apparatus using ammonia as a reducing agent, and oxidizes ammonia and nitrogen at 250 ° C. or higher upstream of the combustion exhaust gas inlet of the denitration apparatus. A high-temperature denitration catalyst having a function of promoting the reaction with the product and decomposing into nitrogen and water is installed, and the reaction between ammonia and nitrogen dioxide is promoted at a temperature lower than 250 ° C. downstream of the high-temperature denitration catalyst. Catalyst mixing layer of a nitrogen dioxide partial reduction catalyst having a function of partially reducing nitrogen monoxide to nitrogen monoxide, and a low-temperature denitration catalyst having a function of promoting the reaction of ammonia and nitrogen oxide at a temperature lower than 250 ° C. This is a denitration device characterized in that it is installed.

  Furthermore, in order to solve the above-described problems, an embodiment of the present invention is a denitration apparatus using ammonia as a reducing agent, and a catalyst disposed in the most downstream with respect to the combustion exhaust gas inlet inside the denitration apparatus. The layer is a denitration catalyst layer that is a denitration catalyst layer that promotes an unreacted ammonia decomposition reaction in the upstream catalyst layer.

  On the other hand, in order to solve the above-described problem, an embodiment of the present invention is a method of selectively reducing nitrogen oxides in combustion exhaust gas using ammonia as a reducing agent in a denitration apparatus, and a high temperature of 250 ° C. or higher. The high temperature denitration catalyst having high denitration activity promotes the reaction between ammonia and nitrogen oxides and decomposes into nitrogen and water, and low temperature denitration with high denitration activity at less than 250 ° C. downstream of the high temperature denitration catalyst layer. It is a nitrogen oxide treatment method characterized in that the reaction between ammonia and nitrogen oxide is promoted using a catalyst to decompose into nitrogen and water.

  Furthermore, in order to solve the above-described problem, an embodiment of the present invention is a method of selectively reducing nitrogen oxides in combustion exhaust gas using ammonia as a reducing agent in a denitration apparatus, and a high temperature of 250 ° C. or higher. The high temperature denitration catalyst having high denitration activity promotes the reaction between ammonia and nitrogen oxides and decomposes into nitrogen and water. At the downstream side of the high temperature denitration catalyst, the activity is high at less than 250 ° C. Nitrogen monoxide generated by the nitrogen dioxide partial reduction catalyst can be quickly produced by the low temperature denitration catalyst by the catalyst mixed layer of the nitrogen dioxide partial reduction catalyst to be partially reduced to nitrogen oxide and the low temperature denitration catalyst having high denitration activity at less than 250 ° C. A nitrogen oxide treatment method characterized in that it is denitrified and decomposed into nitrogen and water.

  The denitration apparatus according to the embodiment of the present invention uses ammonia as a reducing agent and burns by a plurality of types of denitration catalysts (at least upstream high temperature denitration catalyst and downstream low temperature denitration catalyst) having high denitration activity at different operating temperatures. Nitrogen oxides in exhaust gas can be efficiently denitrated over a wide temperature range and decomposed into nitrogen and water.

  In addition, by installing a high-temperature denitration catalyst, a nitrogen dioxide partial reduction catalyst, and a low-temperature denitration catalyst inside the denitration device, there is little loss of ammonia used as a reducing agent, and regardless of the composition of nitrogen oxides, Denitration treatment can be performed efficiently.

The block diagram of the denitration apparatus which shows 1st Embodiment which concerns on this invention. The block diagram of the denitration apparatus which shows 2nd Embodiment concerning this invention. The block diagram of the denitration apparatus which shows 3rd Embodiment which concerns on this invention.

  Hereinafter, embodiments according to the present invention will be described with reference to the accompanying drawings.

In a thermal power plant, the flue gas discharged from a gas turbine combustor that uses liquefied natural gas, shale gas, coal gas, etc. as fuel is guided to the gas turbine, and the flue gas that has worked is the flue gas. It is led to the denitration device through the system flue. In a denitration apparatus for a thermal power plant, an ammonia catalytic reduction method using ammonia (NH ₃ ) as a reducing agent is often used.

As a denitration catalyst, one or more supports selected from the group consisting of Al ₂ O ₃ , SiO ₂ , ZrO ₂ , TiO ₂ and zeolite, for example, a honeycomb support, Pt, Cu, Fe, Ag, Mn, Ni, Ti, One containing at least one metal selected from the group consisting of Ni, Zi and In is known.

The denitration catalyst accelerates a reaction with nitrogen oxide (NOx) in combustion exhaust gas and ammonia (NH ₃ ) as a reducing agent, promotes a denitration reaction represented by the following, and nitrogen (N ₂ ) and water ( To H ₂ O).
[Chemical 1]
4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O ... Reaction formula (1)
NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O... (2)
6NO ₂ + 8NH ₃ → 7N ₂ + 12H ₂ O (reaction formula (3))

Further, the denitration reaction is accompanied by a slight increase in temperature and may promote the ammonia decomposition reaction as a side reaction. The ammonia decomposition reaction generally proceeds at a temperature higher than the temperature range suitable for the denitration reaction.
[Chemical formula 2]
4NH ₃ + 3O ₂ → 2N ₂ + 6H ₂ O ... Reaction formula (4)
4NH ₃ + 5O ₂ → 4NO + 6H ₂ O (5)
2NH ₃ + 2O ₂ → N ₂ O + 3H ₂ O ... Reaction formula (6)

  In a thermal power plant, a denitration technique for decomposing nitrogen oxides (NOx) into nitrogen and water is performed by a denitration apparatus as a technique for treating NOx generated by the combustion of fuel.

[First Embodiment]
FIG. 1 is a configuration diagram showing a first embodiment of a denitration apparatus. This denitration device for a thermal power plant shows a configuration example in which a high-temperature denitration catalyst A and a low-temperature denitration catalyst B are combined in the denitration device 10. In a thermal power plant, combustion exhaust gas from a combustor 11 such as a gas turbine combustor is guided to a denitration device 10 through a flue 12 after working with a gas turbine (not shown). On the flue 12 leading to the denitration device 10 or the denitration device 10, that is, on the combustion exhaust gas inlet side of the denitration device 10, a reducing agent supply means 13 for supplying a NOx reducing agent is provided. The reducing agent supply means 13 supplies, for example, ammonia (NH ₃ ) as a NOx reducing agent. The reducing agent supply means 13 can use urea, ammonium hydroxide, ammonium formate and other nitrogen-containing substances as a generation source of ammonia as a reducing agent.

The exhaust gas obtained by removing NOx in the combustion exhaust gas by the denitration device 10 passes through the flue 15 and is guided to the exhaust gas facility or chimney 16. The exhaust gas equipment performs exhaust gas treatment such as desulfurization and dust collection, and it is released from the chimney into the atmosphere. In a 200,000 kW class thermal power plant, the amount of flue gas discharged from the combustor 11 is a large amount of about 26,000 m ³ / min, for example.

By the way, the denitration apparatus 10 is provided with at least two types of denitration catalyst layers, for example, a high temperature denitration catalyst layer 17 and a low temperature denitration catalyst layer 18, which are different in the activation temperature range of the denitration reaction with NOx. The high temperature denitration catalyst layer 17 is disposed upstream of the combustion exhaust gas flow, and the low temperature denitration catalyst layer 18 is disposed downstream thereof. The high-temperature denitration catalyst A has a function of promoting the reaction of nitrogen oxide (NOx) in the combustion exhaust gas and NH _{3 as} the reducing agent to decompose into nitrogen and water at a high temperature of 250 ° C. or higher. The low-temperature denitration catalyst B has a function of promoting the reaction between nitrogen oxides and ammonia at a low temperature of less than 250 ° C. and decomposing into nitrogen and water.

  The high temperature denitration catalyst layer 17 is a high temperature denitration catalyst A which is an ammonia catalytic reduction catalyst having a high denitration activity at a high temperature of 250 ° C. or higher, and the low temperature denitration catalyst layer 18 is an ammonia catalytic reduction having a high denitration activity at a low temperature of less than 250 ° C. A low-temperature denitration catalyst B of the catalyst is used.

The high temperature denitration catalyst A used for the high temperature denitration catalyst layer 17 and having high denitration activity in a high temperature range of 250 ° C. or higher includes, for example, a group consisting of Al ₂ O ₃ , SiO ₂ , V ₂ O ₅ , ZrO ₂ , TiO ₂ and zeolite. A plurality of types of carriers selected, for example, a honeycomb carrier containing a metal selected from the group consisting of Cu, Mo, Mn, Fe, Ti, and V is used.

In addition, the low temperature denitration catalyst B having high denitration activity in a low temperature region of less than 250 ° C. includes, for example, a plurality of types selected from the group consisting of Al ₂ O ₃ , SiO ₂ , V ₂ O ₅ , ZrO ₂ , TiO ₂ and zeolite. A support (for example, a honeycomb support) containing one or more metals selected from Ag, Ti, and V is used. For example, Ag-supported zeolite, V ₂ O ₅ is used.

On the other hand, with the load fluctuation operation of the thermal power plant, the flue gas temperature at the flue 12 outlet side or the flue gas inlet side of the denitration apparatus 10 fluctuates in a temperature range of 130 ° C. to 400 ° C., and during normal operation, the exhaust gas temperature Is, for example, about 400 ° C., and is sent to the denitration apparatus 10, where NOx in the exhaust gas is denitrated. In the denitration apparatus 10, the NOx in the exhaust gas undergoes selective catalytic reduction (SCR) with the reducing agent NH ₃ while passing through the high temperature denitration catalyst layer 17 and the low temperature denitration catalyst layer 18, and the reaction formula (1) , (2) and (3), the denitration reaction is promoted. As the high temperature denitration catalyst layer 17 and the low temperature denitration catalyst layer 18 in the denitration apparatus 10, catalyst layers of high temperature and low temperature denitration catalysts A and B that remove NO and NO ₂ from nitrogen oxide (NOx) in combustion exhaust gas are used. It is done.

  Of these, NOx in the combustion exhaust gas at 250 ° C. or higher passes through the high temperature denitration catalyst layer 17, and 90% or more of NOx is expressed by the reaction formula (1) by the high temperature denitration catalyst A having high denitration activity in a high temperature range of 250 ° C. or higher. ) To (3) are performed, and the reaction between ammonia and nitrogen oxides is promoted and decomposed into nitrogen and water. In addition, an ammonia decomposition reaction represented by the reaction formula (4) as a side reaction occurs and is decomposed into nitrogen and water. The NOx in the remaining exhaust gas that has passed through the high-temperature denitration catalyst layer 17 is guided to the low-temperature denitration catalyst layer 18, where the denitration reaction is again performed by the low-temperature denitration catalyst B having high denitration activity in a low-temperature region of less than 250 ° C. The reaction between ammonia and nitrogen oxides is accelerated and decomposed into nitrogen and water.

  The exhaust gas that has been treated with NOx in the denitration apparatus 10 reaches a temperature of about 100 ° C., is led to the flue 15, passes through the flue 15, and is discharged to the exhaust gas facility or chimney 16. In the exhaust gas facility, exhaust gas treatment such as desulfurization, dust collection, and white smoke prevention is performed, and the exhaust gas is discharged into the atmosphere from the chimney.

  Inside the denitration apparatus 10, a high-temperature denitration catalyst layer 17 and a low-temperature denitration catalyst layer 18 are disposed upstream and downstream of the combustion exhaust gas flow, respectively. By disposing the high-temperature denitration catalyst layer 17 and the low-temperature denitration catalyst layer 18 in this order, when the combustion exhaust gas temperature and the catalyst layer temperature are lower than 250 ° C., for example, 200 ° C., nitrogen oxide (NOx) in the combustion exhaust gas. ) And ammonia mostly pass through the high-temperature denitration catalyst layer 17 unreacted and are sent to the low-temperature denitration catalyst layer 18 on the downstream side, where the denitration reaction proceeds. In a high temperature state where the combustion exhaust gas temperature and the catalyst layer temperature are, for example, 250 ° C. or higher, NOx and ammonia in the combustion exhaust gas react with each other in the high temperature denitration catalyst layer 17 and a denitration reaction that decomposes into nitrogen and water proceeds. Decomposition reaction has occurred.

The denitration apparatus 10 has a high temperature denitration catalyst layer 17 on the upstream side and a low temperature denitration catalyst layer 18 on the downstream side, thereby promoting the denitration reaction of nitrogen oxides in the combustion exhaust gas and decomposing it into nitrogen and water. can do. For this reason, the increase in nitrogen oxides (NO, N ₂ O) due to the progress of the reactions in the reaction formulas (5) and (6) can be suppressed.

When the inside of the denitration device 10 is used with a high temperature denitration catalyst layer alone, when the combustion exhaust gas or the like is in a non-reacted state where the denitration reaction does not occur at a low temperature of 200 ° C. or less, or when the low temperature denitration catalyst layer is used alone. In addition to the fact that the ammonia decomposition reaction accelerates at a high temperature of 300 ° C. or higher and the supplied reducing agent, ammonia, cannot sufficiently contribute to the denitration reaction, the reaction of the reaction formulas (5) and (6) advances the nitrogen oxides. There is a risk of an increase in (nitrogen monoxide (NO) or nitrous oxide (N ₂ O)).

  By the way, the denitration reaction hardly occurs in the high temperature denitration catalyst layer 17 at a low temperature of the combustion exhaust gas temperature of 200 ° C. or less, and the NOx denitration reaction occurs only about less than 10% at the exhaust gas temperature of 200 ° C. to less than 250 ° C. In this case, the denitration treatment of nitrogen oxide is performed in the low temperature denitration catalyst layer 18 on the downstream side.

  Further, when the arrangement order of the high-temperature denitration catalyst layer 17 and the low-temperature denitration catalyst layer 18 is reversed in the denitration apparatus 10, it is almost the same as the case where the low-temperature denitration catalyst B layer is used alone, and is arranged on the downstream side. In order for the high-temperature denitration catalyst A to function in the denitration reaction, a process such as adding an ammonia supply mechanism immediately before the high-temperature denitration catalyst A is required.

  Further, when the thermal power plant uses LNG as the fuel, the combustion exhaust gas from the combustor 11 is a relatively clean exhaust gas, and therefore, an electrostatic precipitator is installed in the exhaust gas facility provided on the downstream side of the denitration apparatus 10. It is not always necessary to provide a desulfurization device, and the temperature of the flue gas discharged from the denitration device 10 drops to 100 ° C. or less while passing through the flue 15, and the water (steam) generated by condensation turns into white smoke. Therefore, a heating device for heating the exhaust gas temperature to about 120 ° C. is provided. This heating device can prevent the combustion exhaust gas from becoming white smoke.

  When coal gas, coal, or shale gas is used as fuel, the exhaust gas equipment contains sulfur (S), soot, etc., so the exhaust gas equipment must be equipped with a dust collector such as an electric dust collector or sulfur. A desulfurization device for removal and a white smoke prevention device by a heating device are provided.

Further, for example, in the denitration apparatus 10 for a thermal power plant of 200,000 kW class, a high temperature denitration catalyst layer 17 or a low temperature denitration catalyst of the denitration apparatus 10 is processed in order to process a combustion exhaust gas amount of about 26,000 m ³ / min during operation. As the layer 18, denitration catalyst layers 17 and 18 having a flat honeycomb structure that allows a large amount of exhaust gas flow to pass therethrough are used. The denitration catalyst layers 17 and 18 are configured in a flat three-dimensional structure having a thickness of, for example, 1 m or less in the exhaust gas flow direction, for example, several tens of centimeters, and a surface area (length in the vertical and horizontal directions) of about several m × 10 several m. Is done.

[Effect of the first embodiment]
In the first embodiment, the upstream side in the denitration apparatus 10 promotes the reaction between nitrogen oxides and ammonia in the combustion exhaust gas at a high temperature of 250 ° C. or higher, and has a function of decomposing into harmless nitrogen and water. A denitration catalyst A and a low-temperature denitration catalyst B having a function of promoting the reaction between nitrogen oxides in exhaust gas and ammonia as a reducing agent at a low temperature of less than 250 ° C. and decomposing into harmless nitrogen and water on the downstream side Since it is installed, it is possible to effectively perform a denitration reaction of nitrogen oxides in exhaust gas over a wide temperature range in the denitration apparatus 10 and to perform an environment purification function of decomposing harmless nitrogen and water.

  In addition, since the high temperature denitration catalyst A having a high denitration activity of 250 ° C. or higher and the low temperature denitration catalyst B having a high denitration activity of less than 250 ° C. are arranged on the downstream side in the denitration apparatus 10, the temperature ranges from low to high. In a wide temperature range of combustion exhaust gas, it promotes the reaction of nitrogen oxide (NOx) in the exhaust gas with ammonia as the reducing agent, decomposes it into harmless nitrogen and water and purifies the environment, while the exhaust gas temperature is 200 ° C The ammonia decomposition reaction can be accelerated at the above temperature and decomposed into harmless nitrogen and water.

  Furthermore, the exhaust gas equipment connected to the flue downstream of the denitration device 10 is provided with a dust collector and a heating device that heats the combustion exhaust gas temperature to 100 ° C. or higher, for example, about 120 ° C. It is possible to prevent water from condensing and generating white smoke.

[Second Embodiment]
FIG. 2 shows a second embodiment of the denitration apparatus.
The denitration device for a thermal power plant according to the second embodiment is different from the first embodiment in the configuration in which the number of catalyst layers disposed inside the denitration device 10A is increased, and other configurations are the same as those in the first embodiment. Therefore, the same components are denoted by the same reference numerals and redundant description is omitted or simplified.

  The denitration apparatus for a thermal power plant of the second embodiment is a configuration example in which three catalyst layers of a high-temperature denitration catalyst layer 17, a nitrogen dioxide partial reduction catalyst layer 20, and a low-temperature denitration catalyst layer 18 are combined inside the denitration apparatus 10A. It is what. Inside the denitration apparatus 10A, a high temperature denitration catalyst layer 17, a nitrogen dioxide partial reduction catalyst layer 20, and a low temperature denitration catalyst layer 18 are sequentially arranged from the upstream side. Each of the catalyst layers 17, 20, and 18 has a flat three-dimensional structure.

  The high-temperature denitration catalyst layer 17 and the low-temperature denitration catalyst layer 18 use the same high-temperature and low-temperature denitration catalysts A and B as the high-temperature and low-temperature denitration catalyst layers 17 and 18 of the denitration apparatus 10 shown in the first embodiment. . For the nitrogen dioxide partial reduction catalyst layer 20, for example, a nitrogen dioxide partial reduction catalyst C made of zeolite carrying a metal selected from Cu, Mn, and Fe is used.

The denitration apparatus 10A shown in FIG. 2 reacts NOx and ammonia (NH ₃ ) in the flue gas at a high temperature of 250 ° C. or higher in the first layer upstream of the flue gas inlet to the denitration apparatus 10A. A high-temperature denitration catalyst A having a function of promoting and decomposing into nitrogen and water, a nitrogen dioxide partial reduction catalyst C arranged in the second layer, and a NOx in the exhaust gas at a low temperature of less than 250 ° C. It has a low-temperature denitration catalyst B that promotes the denitration reaction of ammonia and decomposes into nitrogen and water.

The nitrogen dioxide partial reduction catalyst layer 22 disposed in the second layer promotes the partial reduction reaction of ammonia and nitrogen hydroxide at a temperature of less than 250 ° C., and converts nitrogen dioxide (NO ₂ ) into nitrogen monoxide (NO). Has the function of partial reduction.

The nitrogen dioxide partial reduction catalyst C accelerates the reaction between nitrogen dioxide in the combustion exhaust gas and ammonia supplied as a reducing agent, and generates nitrogen monoxide by promoting the partial reduction reaction represented by the reaction formula (7).
[Chemical formula 3]
3NO ₂ + 2NH ₃ → 3NO + N ₂ + 3H ₂ O (7)

As shown in the second embodiment, by arranging the catalyst layers 17, 20, and 18 in this order in the denitration apparatus 10A, in addition to the denitration effect described in the first embodiment, nitric oxide ( In a state in which the ratio of nitrogen dioxide (NO ₂ ) to NO) is high, the ratio of NO and NO ₂ , which is a nitrogen oxide (NOx) composition, can be adjusted to an environment close to 1: 1. By matching the ratio of NO and NO ₂ to 1: 1, the reduction efficiency of NO and NO ₂ can be improved and the denitration reaction can be performed efficiently.

By the way, the nitrogen dioxide partial reduction catalyst C has a possibility of accelerating the decomposition reaction of NH ₃ when the temperature becomes higher than 200 ° C. For this reason, when the nitrogen dioxide partial reduction catalyst C is installed in the front stage of the high-temperature denitration catalyst A, NO and NO ₂ that are nitrogen oxides are reduced due to a decrease in the amount of ammonia that contributes to the denitration reaction and reaction progress of the reaction equations (5) and (6) And increase. However, by installing the nitrogen dioxide partial reduction catalyst C on the downstream (downstream) side of the high-temperature denitration catalyst layer 17, the denitration reaction is promoted, so that the ammonia decomposition reaction according to the reaction formulas (5) and (6) can be performed. In addition, an increase in nitrogen oxides (NO, NO ₂ ) can be suppressed.

Further, when the nitrogen dioxide partial reduction catalyst C is arranged downstream from the low-temperature denitration catalyst B, the nitrogen dioxide partial reduction catalyst C adjusts the ratio of nitrogen dioxide oxide NO and NO ₂ and then promotes the denitration reaction. There is a possibility that the catalyst layer (low-temperature denitration catalyst layer) does not exist and the denitration reaction does not proceed sufficiently.

Therefore, by arranging the nitrogen dioxide partial reduction catalyst layer 20 as an intermediate layer between the upstream high-temperature denitration catalyst layer 17 and the downstream low-temperature denitration catalyst layer 18 inside the denitration apparatus 10A, NO is disposed. Even in a state where the ratio of NO ₂ is high, the ratio of NO and NO ₂ can be adjusted to a 1: 1 environment. By matching the proportions of NO and NO ₂ , the denitration reaction in the low-temperature denitration catalyst layer 18 can proceed sufficiently efficiently, and the denitration reaction can be improved.

[Effects of Second Embodiment]
In addition to the effects of the denitration apparatus 10 shown in the first embodiment, the denitration apparatus 10A of the second embodiment has the nitrogen dioxide partial reduction catalyst layer 20 disposed as an intermediate layer inside the denitration apparatus 10A. even when the proportion of nitrogen dioxide is often compared to nitric oxide, the ratio of NO and NO ₂ by NO ₂ partial reduction 1: in alignment into one environment, improving the reduction efficiency of NO and NO ₂ Therefore, the denitration reaction at the low-temperature denitration catalyst layer 18 on the downstream side becomes good.

  Further, a high temperature denitration catalyst layer 17, a nitrogen dioxide partial reduction catalyst layer 20, and a low temperature denitration catalyst layer 18 are sequentially disposed in the denitration apparatus 10A from the upstream side to the downstream side of the combustion exhaust gas, and three catalyst layers 17, 20, 18 are arranged. Since the catalyst layers 17, 20, and 18 are installed independently, maintenance of the individual catalyst layers 17, 20, and 18 is facilitated.

[Third Embodiment]
A third embodiment of the denitration apparatus will be described with reference to FIG.
The denitration apparatus for a thermal power plant shown in the third embodiment includes a mixed catalyst D in which a high temperature denitration catalyst A, a nitrogen dioxide partial reduction catalyst C, and a low temperature denitration catalyst B are combined inside a denitration apparatus 10B. Compared to the denitration apparatus 10 shown in the first embodiment, the catalyst layer disposed inside the denitration apparatus 10B is changed. The same components as those of the denitration apparatus 10 for a thermal power plant according to the first embodiment are denoted by the same reference numerals, and redundant description is omitted or simplified.

The denitration device for a thermal power plant shown in the third embodiment is a combination of a high temperature denitration catalyst A, a nitrogen dioxide partial reduction catalyst, and a low temperature denitration catalyst from the upstream side with respect to the combustion exhaust gas flow inside the denitration device 10B. The mixed denitration catalyst D is arranged in this order. The catalyst mixing layer 21 of the nitrogen dioxide partial reduction catalyst of the mixed catalyst D and the low-temperature denitration catalyst may be arranged alternately with the nitrogen dioxide partial reduction catalyst and the low-temperature denitration catalyst, or may be mixed and arranged. Combination is free. The nitrogen dioxide partial reduction catalyst is the same as the N ₂ O partial reduction catalyst provided in the nitrogen dioxide partial reduction catalyst layer 20 arranged in the second embodiment, and the low-temperature denitration catalyst B is arranged in the second embodiment. It is not different from the denitration catalyst of the low temperature denitration catalyst layer 18.

  The denitration apparatus 10B for a thermal power plant shown in the third embodiment can obtain substantially the same denitration effect as the denitration action obtained by the denitration apparatuses 10 and 10A shown in the first and second embodiments. Nitrogen monoxide (of the reaction formula (7)) generated on the nitrogen dioxide partial reduction catalyst of the mixed catalyst D is quickly consumed by the adjacent low-temperature denitration catalyst and subjected to denitration reaction treatment.

Further, the reaction with the nitrogen species adsorbed on the nitrogen monoxide and the denitration catalyst (nitrogen adsorbing species N-ab) when nitrogen monoxide increases in the combustion exhaust gas on the nitrogen dioxide partial reduction catalyst C of the mixed catalyst D As it proceeds, the partial reduction reaction represented by the reaction formula (8) is promoted, and there is a possibility that dinitrogen monoxide (nitrous oxide) N ₂ O is generated.
[Chemical formula 4]
NO + (N−ab) → N ₂ O... Reaction formula (8)

However, in the third embodiment, in the catalyst mixed layer 23 of the nitrogen dioxide partial reduction catalyst and the low-temperature denitration catalyst, the mixed catalyst D in which the low-temperature denitration catalyst is mixed or mixed is arranged in the immediate vicinity of the nitrogen dioxide partial reduction catalyst. Therefore, the nitric oxide produced in the reaction formula (7) by the promotion of the partial reduction reaction is quickly consumed by the latest low-temperature denitration catalyst, and the denitration reaction is promoted, so that the monoxide is oxidized on the nitrogen dioxide partial reduction catalyst. Generation of dinitrogen monoxide (nitrous oxide) N ₂ O which may occur when nitrogen is increased can be suppressed.

By suppressing dinitrogen monoxide, it is possible to suppress the generation of a gas having a greenhouse effect that is about 300 times that of CO ₂ . Suppression of N ₂ O, which is a water-insoluble and chemically stable substance, is an excellent technology for environmental measures to prevent global warming.

[Effect of the third embodiment]
In the third embodiment, a denitration effect equivalent to that of the denitration apparatuses 10 and 10A shown in the first and second embodiments is obtained, and nitrogen monoxide and nitrogen dioxide, which are harmful to nitrogen oxides in combustion exhaust gas, are obtained. The removing denitration process can be performed effectively.

In addition, a nitrogen-dioxide partial reduction catalyst C and a low-temperature denitration catalyst are combined or mixed in the denitration apparatus 10B on the downstream side of the high-temperature denitration catalyst layer 17, and a mixed catalyst mixed layer 23 is disposed. It is possible to suppress the generation of dinitrogen monoxide (N ₂ O) that can occur when nitrogen monoxide increases on the partial nitrogen reduction catalyst, and to suppress the generation of greenhouse gases. Become.

[Fourth Embodiment]
A fourth embodiment of the denitration apparatus will be described.
The denitration apparatus for a thermal power plant shown in the fourth embodiment includes an arrangement configuration example of the denitration apparatus 10C shown in FIGS. The denitration device 10C has a low temperature denitration catalyst layer 18 (see FIGS. 1 and 2) or a catalyst mixed layer 21 of a nitrogen dioxide partial reduction catalyst and a low temperature denitration catalyst (see FIG. Reference) is arranged. Inside the denitration apparatus 10C, a low temperature denitration catalyst B or a mixed catalyst D of a low temperature denitration catalyst and a nitrogen dioxide partial reduction catalyst is disposed on the most downstream side with respect to the combustion exhaust gas flow. Since the structure of the denitration apparatus for other thermal power plants is the same as that of the first to third embodiments, the same reference numerals are given to the same structures, and the duplicate description is omitted.

In the fourth embodiment, the thermal power plant is started and the operating state is stabilized, the denitration device 10 (10A, 10B) is sufficiently warmed, and the high temperature denitration catalyst layer 17 exhibits a denitration function at a temperature range of 250 ° C. or higher. Then, most of the nitrogen oxides in the combustion exhaust gas and ammonia supplied as a reducing agent, for example, about 90% or more of the nitrogen oxides (reaction formulas (1) to (3) in the high temperature denitration catalyst layer 17). The nitrogen oxide (NOx) is decomposed into harmless nitrogen (N ₂ ) and water (H ₂ O).

  At that time, the low-temperature denitration catalyst layer 18 or the catalyst mixed layer 21 of the nitrogen dioxide partial reduction catalyst and the low-temperature denitration catalyst has catalytic activity for ammonia decomposition of the reducing agent, and has not reacted in the high-temperature denitration catalyst layer 17. Is decomposed by ammonia decomposition reaction.

It is known that combustion exhaust gas has a higher NOx removal rate when the ratio of nitrogen monoxide (NO) and nitrogen dioxide (NO ₂ ) is 1: 1 in the nitrogen oxide composition. In an actual thermal power plant, when flue gas having a low temperature is generated, the concentration of nitrogen dioxide (NO ₂ ) increases. However, it has not been confirmed that there is a significant difference in the proportion of the combustion exhaust gas composition, such as NO and NO ₂ between 130 ° C. to 140 ° C.. However, compared with the normal operation (when the outlet of the combustor 11 is about 1000 ° C. and the catalyst layer temperature is about 300 ° C.), the temperature of exhaust gas is low, the nitrogen dioxide (NO ₂ ) becomes high.

  In general, in order to sufficiently treat nitrogen oxide (NOx) in combustion exhaust gas, ammonia is often supplied in a larger amount than the minimum amount necessary for NOx treatment. Therefore, unreacted ammonia may remain. Since ammonia is subject to regulation, it is desirable to avoid losing ammonia while NOx remains, but it is desirable to treat ammonia when NOx is exhausted. The denitration apparatus of the fourth embodiment is configured to realize treatment of unreacted ammonia by an ammonia decomposition reaction in the high temperature denitration catalyst layer 17.

[Effect of the fourth embodiment]
In the fourth embodiment, in the denitration apparatus 10C, the low temperature denitration catalyst B or the mixed catalyst D of the nitrogen dioxide partial reduction catalyst and the low temperature denitration catalyst is disposed on the most downstream side with respect to the combustion exhaust gas flow. In the temperature range in which the NOx removal activity is present, most of the nitrogen oxides and supplied ammonia in the combustion exhaust gas are denitrated by the high temperature denitration catalyst layer 17. At that time, the low-temperature denitration catalyst B or the mixed catalyst D of the nitrogen dioxide partial reduction catalyst and the low-temperature denitration catalyst has catalytic activity for ammonia decomposition, and actively decomposes ammonia that has not reacted in the high-temperature denitration catalyst layer 17. Then, nitrogen (N ₂ ) and water (H ₂ O) can be generated by an ammonia decomposition reaction.

  As mentioned above, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 10,10A, 10B, 10C ... Denitration device, 11 ... Combustor, 12, 15 ... Flue, 13 ... Reducing agent supply means, 16 ... Exhaust gas facility or chimney, 17 ... High temperature denitration catalyst layer, 18 ... Low temperature denitration catalyst layer 20 ... Nitrogen dioxide partial reduction catalyst layer, 21 ... Nitrogen dioxide partial reduction catalyst and low temperature denitration catalyst mixed layer, A ... High temperature denitration catalyst, B ... Low temperature denitration catalyst, C ... Nitrogen dioxide partial reduction catalyst, D ... Nitrogen dioxide Mixed catalyst of partial reduction catalyst and low-temperature denitration catalyst.

Claims (8)

In denitration equipment using ammonia as the reducing agent,
A high temperature denitration catalyst having a function of accelerating the reaction between ammonia and nitrogen oxide at a high temperature of 250 ° C. or higher and decomposing into nitrogen and water is disposed upstream of the combustion exhaust gas inlet of the denitration device,
A denitration apparatus comprising a low-temperature denitration catalyst having a function of accelerating a reaction between ammonia and nitrogen oxides from a low temperature of less than 250 ° C and decomposing into nitrogen and water downstream of the high-temperature denitration catalyst. In denitration equipment using ammonia as the reducing agent,
A high-temperature denitration catalyst having a function of accelerating the reaction between ammonia and nitrogen oxides at a high temperature of 250 ° C. or higher and decomposing it into nitrogen and water;
A nitrogen dioxide partial reduction catalyst having a function of promoting the reaction between ammonia and nitrogen dioxide from below 250 ° C. and partially reducing nitrogen dioxide to nitrogen monoxide,
A denitration apparatus comprising: a low-temperature denitration catalyst having a function of accelerating a reaction between ammonia and nitrogen oxide from less than 250 ° C. and decomposing into nitrogen and water. The high-temperature denitration catalyst is disposed in the first layer upstream of the combustion exhaust gas inlet of the denitration device,
The nitrogen dioxide partial reduction catalyst is disposed in the second layer downstream of the high temperature denitration catalyst,
The denitration apparatus according to claim 2, wherein the low-temperature denitration catalyst is arranged in a final layer downstream of the nitrogen dioxide partial reduction catalyst. In denitration equipment using ammonia as the reducing agent,
A high-temperature denitration catalyst having a function of promoting the reaction between ammonia and nitrogen oxide at 250 ° C. or higher and decomposing into nitrogen and water is installed upstream of the combustion exhaust gas inlet of the denitration device,
A nitrogen dioxide partial reduction catalyst having a function of promoting the reaction between ammonia and nitrogen dioxide at a temperature lower than 250 ° C. and partially reducing nitrogen dioxide to nitrogen monoxide, and ammonia at a temperature lower than 250 ° C. A denitration apparatus comprising a catalyst mixed layer of a low temperature denitration catalyst having a function of accelerating a reaction of nitrogen oxides and decomposing into nitrogen and water. In denitration equipment using ammonia as the reducing agent,
The denitration apparatus, wherein the catalyst layer disposed in the most downstream with respect to the combustion exhaust gas inlet in the denitration apparatus is a denitration catalyst layer that promotes an unreacted ammonia decomposition reaction in the upstream catalyst layer. . In a method of selectively reducing nitrogen oxides in combustion exhaust gas using ammonia as a reducing agent in a denitration apparatus,
Using a high-temperature denitration catalyst with high denitration activity at a high temperature of 250 ° C. or higher, the reaction between ammonia and nitrogen oxide is promoted to decompose into nitrogen and water,
Downstream of the high-temperature denitration catalyst layer, using a low-temperature denitration catalyst having a high denitration activity at less than 250 ° C., the reaction between ammonia and nitrogen oxide is promoted and decomposed into nitrogen and water. Processing method. A nitrogen dioxide partial reduction catalyst installed on the downstream side of the high-temperature denitration catalyst, the reaction between ammonia and nitrogen dioxide is promoted from less than 250 ° C. to partially reduce nitrogen dioxide to nitrogen monoxide, and then the nitrogen dioxide partial reduction The method for treating nitrogen oxide according to claim 6, wherein the nitrogen oxide is denitrated by the low-temperature denitration catalyst installed downstream of the catalyst and decomposed into nitrogen and water. In a method of selectively reducing nitrogen oxides in combustion exhaust gas using ammonia as a reducing agent in a denitration apparatus,
Using a high-temperature denitration catalyst with high denitration activity at a high temperature of 250 ° C. or higher, the reaction between ammonia and nitrogen oxide is promoted and decomposed into nitrogen and water.
On the downstream side of the high-temperature denitration catalyst, a catalyst mixing layer of a nitrogen dioxide partial reduction catalyst that is highly active at less than 250 ° C. and that partially reduces nitrogen dioxide to nitrogen monoxide and a low-temperature denitration catalyst that has a high denitration activity at less than 250 ° C. A method for treating nitrogen oxides, characterized in that nitric oxide produced by the nitrogen dioxide partial reduction catalyst is rapidly denitrated by the low-temperature denitration catalyst and decomposed into nitrogen and water.

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