JP2013017934A - Denitration device and denitration method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a denitration device and a denitration method capable of efficiently making nitrogen oxide harmless even when the proportion of nitrogen dioxide in nitrogen oxide contained in exhaust gas is high.SOLUTION: The denitration device includes: a denitration catalyst 11 disposed in a flue 1 in which exhaust gas containing nitrogen dioxide flows; an ammonia injection nozzle 12 positioned at the upstream side of the denitration catalyst 11 and injecting ammonia into exhaust gas; and a control part 14 for controlling the ammonia injection amount according to the outlet NOx concentration of the denitration catalyst 11. A nitrogen monoxide injection system 15 is provided for injecting NO into an ammonia supply passage 12a, and a nitrogen oxide measuring means 18 and a nitrogen monoxide measuring means 19 are provided on an inlet side of the denitration catalyst 11. The control part 14 calculates the NOconcentration in exhaust gas from the actual measured values of NOx and NO obtained by each of the measuring means 18, 19, and controls the injection amount of NO from the nitrogen monoxide injection system 15 so that the proportion of NOin NOx in exhaust gas is constantly 0.25 or more and 0.75 or less.

Description

The present invention relates to a denitration apparatus and a denitration method that are used for detoxifying nitrogen oxides (NO _x ) in exhaust gas containing nitrogen dioxide (NO ₂ ) flowing from various combustion facilities.

An example of the above-described denitration apparatus is described in Patent Document 1.
The denitration apparatus includes a denitration catalyst disposed in a flue following the boiler, and an ammonia injection portion located on the upstream side of the denitration catalyst.

  The ammonia injection part injects ammonia into the exhaust gas containing nitrogen dioxide flowing toward the denitration catalyst in the flue, and the denitration catalyst reacts with the exhaust gas into which ammonia has been injected, thereby oxidizing nitrogen. Decomposes things into nitrogen and water to make them harmless.

  In this denitration device, the ratio of nitrogen dioxide in the nitrogen oxides contained in the exhaust gas is obtained, the exhaust gas temperature at which the theoretical denitration rate calculated from this ratio is obtained from the temperature characteristic curve of the denitration catalyst, and based on this temperature Thus, the exhaust gas temperatures for starting and stopping ammonia injection are set.

Japanese Unexamined Patent Publication No. 07-136465

  Although the above-described denitration apparatus can reduce the amount of nitrogen oxides discharged from the flue even when the exhaust gas temperature is low, the ratio of nitrogen dioxide with a very high rate of nitrogen dioxide with a slow reaction rate to the exhaust gas. In this case, for example, in the case of exhaust gas containing nitrogen dioxide at a high ratio (a ratio of 80% or more) as occurs in a gas turbine or nitric acid production plant, the reaction is influenced by the catalytic denitration reaction related to nitrogen dioxide. There is a problem that an efficient denitration reaction system cannot be constructed because the speed and responsiveness are lowered, and it has been a conventional problem to solve this problem.

  The present invention has been made paying attention to the above-described conventional problems, and even if the ratio of nitrogen dioxide in the nitrogen oxide contained in the exhaust gas is high, the nitrogen oxide is efficiently rendered harmless. An object of the present invention is to provide a denitration apparatus and a denitration method that are possible.

In order to achieve the above object, the inventors of the present invention are nitrogen monoxide (hereinafter referred to as NO) and nitrogen dioxide (hereinafter referred to as NO) which are components of nitrogen oxides (hereinafter referred to as NO _X ) contained in the exhaust gas. ₂ ), the difference in each reaction rate was noted.

here,
The NO-based reaction formula is 4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O... Reaction 1
The reaction formula of the NO-NO ₂ system is NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O ... Reaction 2
The reaction formula of the NO ₂ system is 6NO ₂ + 8NH ₃ → 7N ₂ + 12H ₂ O ... Reaction 3
The order of reaction rate is reaction 2, reaction 1, and reaction 3 in order from the fastest.

The denitration reaction of exhaust gas containing NO _X containing both NO and NO ₂ as a component proceeds according to the order of the reaction rate described above. First, the same amount of NO and NO ₂ react rapidly according to reaction 2, then the remaining NO reacts rapidly according to reaction 1, and finally the remaining NO ₂ reacts slowly according to reaction 3.

After grasping this reaction structure, the present inventors proceed according to the reaction 2 in order to efficiently perform the denitration reaction of the exhaust gas containing NO _X containing both NO and NO ₂ as components. to produce the reaction conditions, i.e., the ratio of NO and NO ₂ is 1: 1 ratio of clogging NO _X occupied in NO ₂ (NO ₂ / NO _X) is effective to produce a condition of about 0.5 As a result, the present invention has been completed.

  That is, the invention according to claim 1 of the present invention is a denitration catalyst disposed in a flue through which exhaust gas containing nitrogen dioxide flows, and is located upstream of the denitration catalyst in the flue, and In a denitration apparatus comprising an ammonia injection nozzle for injecting ammonia and a control unit for controlling the ammonia injection amount from the ammonia injection nozzle according to the outlet nitrogen oxide concentration of the denitration catalyst, the exhaust gas flow upstream of the ammonia injection nozzle A nitrogen monoxide injection system for injecting nitric oxide into the ammonia supply path following the side or the ammonia injection nozzle, and a nitrogen oxide measuring means and a nitric oxide measuring means on the inlet side of the denitration catalyst, The control unit measures each of nitrogen oxides and nitric oxide obtained by the nitrogen oxide measuring unit and the nitric oxide measuring unit. From the nitrogen monoxide injection system, the concentration of nitrogen dioxide in the exhaust gas is calculated from the above and the ratio of nitrogen dioxide in the nitrogen oxides in the exhaust gas is always 0.25 or more and 0.75 or less. The present invention is characterized in that the injection amount of nitrogen oxide is controlled, and the configuration of the denitration apparatus is used as a means for solving the above-described conventional problems.

  On the other hand, the invention according to claim 2 of the present invention is a denitration method in which ammonia is injected into an exhaust gas containing nitrogen dioxide flowing through a flue and the nitrogen oxide is catalytically reduced by a denitration catalyst disposed in the flue. The ammonia injection amount is controlled according to the outlet nitrogen oxide concentration of the denitration catalyst, and the nitrogen dioxide concentration in the exhaust gas is calculated from the measured values of nitrogen oxide and nitrogen monoxide on the inlet side of the denitration catalyst. The denitration method is characterized in that nitrogen monoxide is injected so that the ratio of nitrogen dioxide in the nitrogen oxide in the exhaust gas is always 0.25 or more and 0.75 or less. Is a means for solving the above-described conventional problems.

In the denitrification device and a denitration method according to the present invention, when injecting the NO on the upstream side or the ammonia supply path of the ammonia injection nozzle, preferably in the graph representing the relationship between the NO ₂ / NO _X ratio and the denitration rate of 2 As shown in the range, the injection amount of NO may be determined so that the ratio of NO _{2 in} NO _X in the exhaust gas is always 0.25 or more and 0.75 or less, but in order to increase the denitration rate more efficiently. In addition, it is desirable to inject NO so that the ratio of NO ₂ in the NO _X is always 0.4 or more and 0.6 or less, and NO should be adjusted so that the ratio of NO ₂ is as close to 0.5 as possible. It is more desirable to inject.

In the denitrification device and a denitration method according to the present invention, the upstream side of the denitration catalyst of the flue through which exhaust gas containing NO _2, injecting a quantity of ammonia which is calculated in accordance with the outlet concentration of NO _X the denitration catalyst .

At the same time, the concentrations of NO _X and NO on the inlet side of the denitration catalyst are measured, and the NO ₂ concentration in the exhaust gas is calculated by subtracting the measured NO value from the measured NO _X value.

And based on the NO ₂ concentration by this calculation result, the proportion of NO ₂ in the NO _X in the exhaust gas is always 0.25 or more and 0.75 or less, preferably 0.4 or more and 0.6 or less, more preferably When NO is injected into the exhaust gas so as to be about 0.5, the ratio of NO and NO ₂ approaches 1: 1, and the reaction proceeds promptly according to the above-described reaction 2, resulting in efficiency. so that the detoxified well NO _X is made.

Since the denitration apparatus according to the present invention has the above-described configuration, even if the ratio of NO _{2 in} the NO _X contained in the exhaust gas is high, it is possible to detoxify NO _X with high efficiency. This is a very good effect.

1 is a configuration explanatory view showing a denitration apparatus according to an embodiment of the present invention. Is a graph representing the relationship between the NO ₂ / NO _X ratio and the denitration rate. It is a graph which shows together the denitration rate by the denitration apparatus of FIG. 1, and the denitration rate by a comparative example.

Hereinafter, the present invention will be described with reference to the drawings.
FIG. 1 shows a denitration apparatus according to an embodiment of the present invention. In this embodiment, the denitration apparatus of the present invention is applied to detoxify NO _X contained in exhaust gas generated in a boiler. .

As shown in FIG. 1, the denitration apparatus 10 includes a denitration catalyst 11 disposed in a flue 1 through which exhaust gas containing NO ₂ generated in a boiler (not shown) flows, and an upstream side of the denitration catalyst 11 in the flue 1. located in ammonia from the ammonia and the injection nozzle 12, the ammonia injection nozzle 12 according to the NO _X concentration measured in NO _X concentration meter 13 arranged on the exit side of the denitration catalyst 11 to inject ammonia relative to the exhaust gas A control unit 14 for controlling the injection amount is provided, and injection of ammonia from the ammonia injection nozzle 12 is performed by an injection command from the control unit 14 to the ammonia supply source 16.

  Further, the denitration apparatus 10 includes a nitric oxide injection system 15 connected to an ammonia supply path 12 a that connects the ammonia injection nozzle 12 and the ammonia supply source 16, and the nitrogen monoxide injection system 15 includes an NO supply source 17. However, when a NO injection command is received from the control unit 14, NO is injected into the flue 1 through the ammonia injection nozzle 12.

In this case, the nitrogen oxide measuring means 18 and the nitrogen monoxide measuring means 19 are arranged on the inlet side of the denitration catalyst 11, and the control unit 14 includes the nitrogen oxide measuring means 18 and the nitrogen monoxide measuring means 19. from each measured value of the resulting NO _X and NO to calculate the concentration of NO ₂ in the exhaust gas, based on the relationship between the NO ₂ / NO _X ratio and the denitration rate shown in the graph of FIG. 2, NO _X in the flue gas In order to keep the ratio of NO ₂ occupying at all times from 0.25 to 0.75, preferably from 0.4 to 0.6, more preferably about 0.5, the amount of NO from the nitric oxide injection system 15 The injection amount is controlled.
In addition, the code | symbol A in FIG. 1 is the air supply source for dilution connected to the ammonia supply path 12a.

The denitration apparatus 10 according to the present embodiment described above, when detoxifies NO _X contained in the exhaust gas, first, the upstream side of the denitration catalyst 11 of the flue 1 flows exhaust gas containing NO _2, ammonia injection Ammonia is injected from the nozzle 12.

At this time, the injection amount of ammonia is controlled by the control unit 14 to an appropriate amount according to the NO _X concentration measured by the NO _X concentration meter 13 located on the outlet side of the denitration catalyst 11.

In conjunction with injection of ammonia, each concentration of the NO _X and NO at the inlet side of the denitration catalyst 11 is measured respectively by nitrogen oxide measuring unit 18 and nitric oxide measuring unit 19, the control unit 14, the actual measurement of the NO _X The NO ₂ concentration in the exhaust gas is calculated by subtracting the actual measured value of NO from the value.

Then, on the basis of the NO ₂ concentration based on this calculation result, similarly, in the control unit 14, the ratio of NO ₂ in the NO _X in the exhaust gas falls within the preferable range of the NO ₂ / NO _X ratio shown in the graph of FIG. That is, that is, the ratio of NO ₂ in NO _X in the exhaust gas is always 0.25 or more and 0.75 or less, preferably 0.4 or more and 0.6 or less, and more preferably about 0.5. In addition, a NO injection command is output to the NO supply source 17 of the nitric oxide injection system 15.

Thus, when a NO injection command is issued from the control unit 14 to the NO supply source 17 of the nitric oxide injection system 15, a required amount of NO is injected into the flue gas of the flue 1 through the ammonia injection nozzle 12. When the ratio of NO to NO ₂ approaches 1: 1 due to the injection of NO, it reacts quickly according to the above-described reaction 2, and as a result, NO _X is made harmless efficiently.

Therefore, in the denitration apparatus 10 according to this embodiment described above, even if the ratio of NO _{2 in} the NO _X contained in the exhaust gas is high, NO _X can be made harmless with high efficiency. .

Therefore, when NO _X contained in the exhaust gas is rendered harmless by the denitration apparatus 10 according to the present embodiment, the ratio of NO _{2 in} the NO _X contained in the exhaust gas (NO ₂ / NO _X ) is 0.5 (50%). ) When NO was injected into the exhaust gas from the nitric oxide injection system 15 so as to be approximately, the static denitration rate after stabilization was 97.1% as shown in FIG.

In contrast, the ratio of NO _{2 in} NO _X contained in the exhaust gas (NO ₂ / NO _X ) is 0%, and the ratio of NO _{2 in} NO _X contained in the exhaust gas in Comparative Example 1 In the exhaust gas in Comparative Example 2 where (NO ₂ / NO _X ) was 80%, the static denitration rates after stabilization were 92.2% and 80.5%, respectively.

Thus, in the denitration apparatus 10 according to the present embodiment, by making the ratio of NO ₂ occupying the NO _X in the exhaust gas and about 50% is a preferable range of NO ₂ / NO _X ratio, Comparative Example 1, Compared with 2, it was demonstrated that NO _X can be rendered harmless with high efficiency.

  The configurations of the denitration apparatus and the denitration method according to the present invention are not limited to the above-described embodiments. As another configuration, for example, a nitrogen monoxide injection system 15 for injecting NO is used as an exhaust gas flow of the ammonia injection nozzle 12. You may make it connect with the flue 1 in an upstream.

  The denitration apparatus and the denitration method according to the present invention can be used for denitration of exhaust gas generated by combustion by a boiler burner, and can be used for denitration of exhaust gas generated by a gas turbine.

DESCRIPTION OF SYMBOLS 1 Flue 10 Denitration apparatus 11 Denitration catalyst 12 Ammonia injection nozzle 12a Ammonia supply path 14 Control part 15 Nitric oxide injection system 18 Nitrogen oxide measuring means 19 Nitric oxide measuring means

Claims (2)

A denitration catalyst disposed in a flue through which exhaust gas containing nitrogen dioxide flows,
An ammonia injection nozzle for injecting ammonia into the exhaust gas, located upstream of the denitration catalyst in the flue;
In a denitration apparatus comprising a control unit for controlling the ammonia injection amount from the ammonia injection nozzle according to the outlet nitrogen oxide concentration of the denitration catalyst,
A nitrogen monoxide injection system for injecting nitrogen monoxide into an upstream side of the exhaust gas flow of the ammonia injection nozzle or an ammonia supply path following the ammonia injection nozzle, and a nitrogen oxide measuring means on the inlet side of the denitration catalyst; Nitric oxide measuring means is provided,
The control unit calculates a nitrogen dioxide concentration in the exhaust gas from each measured value of nitrogen oxide and nitrogen monoxide obtained by the nitrogen oxide measuring unit and the nitric oxide measuring unit, and oxidizes nitrogen in the exhaust gas. A denitration apparatus, wherein the amount of nitrogen monoxide injected from the nitrogen monoxide injection system is controlled so that the ratio of nitrogen dioxide occupying in the object is always 0.25 or more and 0.75 or less. In a denitration method in which ammonia is injected into exhaust gas containing nitrogen dioxide flowing through a flue and nitrogen oxides are catalytically reduced by a denitration catalyst disposed in the flue,
The ammonia injection amount is controlled in accordance with the outlet nitrogen oxide concentration of the denitration catalyst, and the nitrogen dioxide concentration in the exhaust gas is calculated from the measured values of nitrogen oxide and nitrogen monoxide on the inlet side of the denitration catalyst. Then, nitrogen monoxide is injected so that the ratio of nitrogen dioxide in the nitrogen oxide in the exhaust gas is always 0.25 or more and 0.75 or less.

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