JPH09870A - Device and process for denitrating exhaust gas - Google Patents

Abstract

PURPOSE: To provide the high denitration performance by injecting ammonia of required amount based on the constitution of NO2 and NO and exhaust gas amount after feeding NO2 of required amount into an exhaust pipe in a process for reduction removing a nitrogen oxide in exhaust gas by injecting ammonia into the exhaust gas pipe. CONSTITUTION: When exhaust gas exhausted from a combustion furnace 1 through an exhaust pipe 2 is fed into a denitration device 3, ammonia 9 is injected into the exhaust pipe 2 to reduction remove a nitrogen oxide in the exhaust gas. At that time, the NO and NO2 concentration in the exhaust gas is sensed by a concentration measuring meter 8 and the exhaust gas amount is sensed by a flowmeter 7 and based on the sensed values fuel an NO2 generation accelerating material and combustion air of the amounts computed by a control device 20 are fed to an NO2 generation combustion burner 6 to generate the NO2 gas of required amount. The NO/NO2 ratio in the exhaust gas is almost close to 1 (one) in the exhaust pipe 2, and ammonia 9 of required amount based on the NO2 and NO concentration in the exhaust gas and the exhaust gas amount is injected into the exhaust pipe 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas denitration device and a denitration method, and in particular, nitrogen oxides (NOx) in exhaust gas discharged from various combustion furnaces such as boilers for power plants, gas turbines, and refuse incinerators. The present invention relates to an exhaust gas denitration device and a denitration method capable of efficiently catalytically reducing with ammonia (NH ₃ ) from a low temperature.

[0002]

2. Description of the Related Art In a catalytic ammonia reduction denitration method in which ammonia (NH ₃ ) is injected into exhaust gas, and then nitrogen oxides are reduced to nitrogen by contacting with a catalyst, an oxidizer is pre-injected into the exhaust gas and contained. There are many known attempts to improve the reactivity with NH ₃ and to make it possible to denitrify from a lower temperature by converting a part of nitric oxide (NO) to be used into nitrogen dioxide (NO ₂ ) (for example, JP-A-52-94863, JP-B-56-50613
JP-A-54-23068, etc.).

The above method uses the NO expressed by the following equation (1).
Since the reaction between 1 mol and 1 mol of NO ₂ and ₂ mol of NH ₃ is much faster than the normal denitration reaction represented by the formula (2), a NO ₂ source may be injected in advance or ozone (O 2
₃ ), hydrogen peroxide (H ₂ O ₂ ), nitric acid (HNO ₃ ), etc. are injected to oxidize part of NO into NO ₂ ((3)-
(5)) to reduce the operating temperature of the denitration device.

Denitration reaction NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O (1) Formula NO + NH ₃ +1/402 → N ₂ + 3 / 2H ₂ O (2) Formula NO oxidation reaction NO + O ₃ → NO ₂ + O ₂ (3) Formula NO + H ₂ O ₂ → NO ₂ + H ₂ O (4) Formula NO + 2HNO ₃ → 3NO ₂ + H ₂ O (5) Formula The above effect of coexisting NO and NO ₂ is 100 to 300.
Since the effect is remarkable at ℃, it has been tried for a long time to be applied to low temperature denitration such as exhaust gas from various incinerators, exhaust heat recovery boilers, combustors such as gas turbines, etc. I haven't arrived.

[0005]

One of the causes of hindering the practical use of the above-mentioned prior art is that it is difficult to control the denitration rate. That is, FIG. 6 shows NO alone, N
The graph shows the temperature characteristics in the case of denitration of exhaust gas containing O ₂ alone and equimolar amounts of NO and NO ₂ using a Ti—WV type catalyst, but NO and NO ₂ are equimolar. In this case, NOx is efficiently removed, but NO or NO ₂
When used alone, the removal performance is significantly reduced. Therefore, NOx
In the conventional technique in which the oxidant injection amount and the NH ₃ injection amount are individually controlled with respect to the fluctuation of, there are many problems as follows. (A) When the oxidizing agent is insufficient and the NO ₂ content in the exhaust gas is small, the denitration reaction rate decreases, and a large amount of unreacted ammonia flows out. (B) When the NO ₂ concentration in the exhaust gas exceeds the NO concentration, NO ₂ and NH ₃ will react as shown in the following formula (6), making it difficult to control the injection amount of NH ₃ .

3NO ₂ + 4NH ₃ → 7 / 2N ₂ + 6H ₂ O Equation (6) Furthermore, when NO ₂ becomes excessive beyond the NO concentration, NO
Ammonium nitrate is produced from ₂ and NH ₃ to gradually deteriorate the catalyst and also to produce N ₂ O as a by-product. (C) If NH ₃ does not match the NO ₂ content ratio, NO _{2 which} is more likely to cause pollution than NO is discharged from the chimney, and the smoke color turns yellow. (D) Chemicals such as HNO ₃ and H ₂ O ₂ are used, and strict treatment and management are required for their storage and handling.

In view of the above problems of the prior art, the present invention has the same device structure as the NOx denitrification device for ammonia catalytic reduction of exhaust gas, which is widely used nowadays.
Provided are a denitration device capable of handling high denitration performance and an operating method thereof.

[0008]

The invention claimed in this application to achieve the above object is as follows. (1) In an exhaust gas denitration method in which exhaust gas is sent to a denitration device through an exhaust pipe and ammonia is injected into the exhaust pipe in the upstream region of the denitration device to reduce and remove nitrogen oxides in the exhaust gas, the exhaust gas in the upstream region of the denitration device NO and NO _{2 in}
The process of detecting the concentration and the exhaust gas flow rate, and the required amount of fuel, NO ₂ generation promoting material, combustion air and flame cooling material, which are calculated based on these detected values, are supplied to the NO ₂ generation combustion burner. The step of generating the NO ₂ gas, the step of supplying the generated NO ₂ gas into the exhaust pipe in the upstream region of the denitrification device to make the NO / NO ₂ ratio in the exhaust gas close to 1, and after supplying the NO ₂ gas And a step of injecting a necessary amount of ammonia into the exhaust gas in the upstream region of the denitration device based on the concentrations of NO ₂ and NO in the exhaust gas and the amount of the exhaust gas. (2) In Claim 1, the ratio of the amount of air supplied to the NO ₂ generating combustion burner and the amount of fuel (air burning ratio) is adjusted to be smaller than 0.8 and larger than 1.2. Exhaust gas denitration method (3) In an exhaust gas denitration device for injecting ammonia into the exhaust gas and then contacting it with a catalyst of the denitration device to reduce and remove nitrogen oxides in the exhaust gas, a means for supplying fuel, NO ₂ generation promoting material, combustion air, and flame NO ₂ with quenching means
An exhaust gas denitration apparatus comprising: a combustion burner for generation; and means for supplying a NO ₂ -containing gas generated by the burner into the exhaust gas in the upstream region of the denitration apparatus. (4) The exhaust gas denitration device according to claim 3, wherein the exhaust gas is a combustion exhaust gas from a combustion device, and the NO ₂ generating combustion burner is arranged in a downstream region of the combustion chamber of the combustion device.

[0009]

[Operation] NO due to combustion of combustion burner, etc.₂Can be generated
And will be described in more detail. Under normal combustion conditions
The ratio of fuel to air is close to 1, but occurs during combustion
To reduce NOx emission
Is usually done. Combustion strip adopted in the present invention
The problem is that, unlike these combustion conditions, NO₂To generate
As the combustion condition, the combustion gas is rapidly cooled, more preferably
Lean burn strip with fuel to air ratio other than 0.8 to 1.2
Conditions or rich fuel combustion conditions. These
Depending on the combustion conditions, the reaction mechanism shown in equation (7) below
More NO₂Have been estimated to be generated. hydrocarbon
NO due to₂HO promotes production ₂Considered to increase
available.

NO + HO₂ → NO₂+ OH (7) Formula In this case, N is added by adding hydrocarbon such as propane.
O₂It is also clear that the generation of
Radicals associated with the decomposition and oxidation of hydrogen halide are HO ₂Generate
Promote and as a result NO₂Is promoting the generation of
Have been. In addition, NO of NO generated by combustion₂Change to
It also shows that the cooling rate of the gas contributes significantly.
HO, which is secondarily generated in the combustion cooling process.₂Is above
Reacts with NO according to the equation (7) and NO₂Produces
It is said that. Figure 2 is a conceptual diagram of a typical combustion burner.
So, for example, propane that becomes air and fuel in the center of the burner
The ratio is outside the range of 0.8 to 1.2
So as to put cooling air or cold combustion on the outer periphery
It has a structure that allows gas to flow. With such a combustion burner structure
By doing, NO₂Easy to generate and control concentration
be able to. Note that the generated NO₂Concentration control
Burn and NO or NO₂If the substance becomes
But usually an organic nitrogen compound such as
Jin (C_FiveH₆N) etc. are often used.

FIG. 7 shows data in which the amount of NO ₂ produced is large when the ratio of air to fuel is outside the range of 0.8 to 1.2. As described above, addition of a hydrocarbon such as propane is also effective for the generation of NO ₂ , and therefore the organic nitrogen compound and the hydrocarbon may be added. As in the present invention, when NO ₂ is directly generated by combustion in the exhaust gas containing NO and is injected, when either NO or NO ₂ in the exhaust gas, which is a problem in the prior art, becomes excessive. There is no decrease in the denitrification rate, NO ₂ leak, N ₂ O by-product, or ammonium nitrate production that causes catalyst deterioration.

In actual operation, the exhaust gas is present from the beginning.
Existing NO concentration and injected NO ₂Measure the concentration,
Perform denitration by adding ammonia corresponding to the sum.
In the present invention, it is generally performed now.
There is no particular difference from the driving method, and it is as easy as the conventional method
You can operate the device at. NO by hydrocarbon species₂Promotion
The mechanism of is considered as follows. Charcoal
The basic NO oxidation reaction in the presence of hydrogen fluoride is
Referring to the reaction of smog formation in the air,
Conceivable.

RH + OH → R + H ₂ O (8) Formula R + O ₂ → RO ₂ (9) Formula RO ₂ + NO → NO ₂ + RO (10) Formula RO + O ₂ → R′O + H ₂ O (11) Formula Here, RH is carbonized. It is hydrogen. The radicals mentioned above include RO, R'O, and RO ₂ . That is, NO ₂ is generated by the HO ₂ mechanism of the direct generation of the formula (10), the reaction of the formula (11), and the reaction of the formula (7), and its generation rate depends on the decomposition of hydrocarbons and the concentration of hydrocarbon radicals. It is considered.

The means adopted in the present invention uses a combustion burner for rapidly cooling high-temperature combustion gas, and the ratio of air to fuel is preferably other than 1/1, particularly preferably smaller than 0.8,
It is characterized in that a combustion burner which burns in excess of fuel or lean burns larger than 1.2 is installed upstream of the denitration catalyst device to generate NO ₂ by the combustion method.

[0015]

FIG. 1 shows a basic system diagram according to the present invention. The combustion burner according to the present invention is arranged on the downstream side of the combustion furnace, the NO concentration in the exhaust gas is monitored, and the NO concentration is equimolar to the NO concentration.
₂ is injected into the exhaust gas by the combustion burner. At this time, in order to make the NO ₂ concentration equimolar to the NO concentration in the exhaust gas,
The method of controlling the amount of O ₂ generated is NO when burning.
It includes any control means such as adding a substance that becomes (NO ₂ ), for example, an organic compound containing N, or a hydrocarbon that has been clarified by conventional knowledge. As a result, since NO and NO ₂ are present in the exhaust gas in equimolar amounts, the denitration reaction on the catalyst proceeds at a remarkably fast reaction rate as shown in the above equation (1), and denitration can be performed from a lower temperature. Become.

The basic construction of the apparatus of the most preferred embodiment of the present invention is as shown in FIG. The combustion burner 6 according to the present invention is installed on the downstream side of the exhaust gas source (combustion furnace) 1 (upper part in the figure).
It is installed in. The structure of the combustion burner 6 is as shown in FIG. 2, in which fuel such as propane, light oil, etc., fuel for controlling NO ₂ concentration (for example, pyridine), and air are supplied.
The structure is such that the cooling air or the exhaust gas 18 is flown from the outer periphery thereof in the central part of. Exhaust gas flow rate and NO concentration and NO emitted from the combustion furnace 1 which is a combustion source of fuel
_{The two} concentrations are measured by the flow meter 7 and the NOx concentration measuring device 8, respectively. Based on both signals, the NO ₂ generating combustion burner 6 injects a NO ₂ generating substance into the combustion burner portion so that the NO ₂ concentration becomes a predetermined value, and NO ₂ is generated by combustion.
As a result, NO and NO ₂ become equimolar, and the ammonia injecting device 9 injects a predetermined amount of ammonia on the upstream side of the denitration device in response to the signal.

Here, the NOx measuring device 8 may be a normal NOx concentration measuring device such as an infrared type or a chemiluminescent type, and generates a signal corresponding to the NOx concentration in the exhaust gas. Further, the exhaust gas flow rate may be a flow meter or may be independently measured such as a Pitot tube or an orifice, and is not particularly limited as long as it can be taken out as a flow rate signal. In FIG. 1, reference numeral 20 denotes a control device, which is an exhaust gas flow rate signal 10 flowing through the exhaust pipe 2 and NOx in the exhaust gas.
(NO and NO ₂ ) concentration signals 11 are input to supply to the burner 6 diesel fuel, NO such as pyridine
₂ Controls the amount of generation accelerator, air, and combustion exhaust gas for cooling so that a predetermined amount of NO ₂ is generated by the burner 6, and the detected NO and NO ₂ concentrations and the NOx amount by the exhaust gas amount are set. The corresponding NH ₃ injection amount signal 12 is transmitted to the NH ₃ injection device 9. NO on the downstream side of the combustion furnace 1
By providing the combustion burner 6 for ₂ generation, NO and NO ₂ are present in equimolar amount in the exhaust gas, and ammonia is added to the NOx removal device 3 to be introduced into the denitration device 3. Therefore, in the denitration unit, only the very fast reaction is a condition that selectively progresses, so that the operating temperature in the denitration unit can be remarkably lowered and 100 to 300 ° C., particularly 150 to 250 ° C.
The amount of catalyst at ℃ can be reduced significantly.

The number of combustion burners 6 for NO ₂ generation,
The arrangement is not particularly limited, and N generated in the combustion furnace
O concentration, and may be determined from the feeding NO ₂ generation amount of substance of NO ₂ generation combustion burner 6 per one. Also,
The combustion burner 6 for NO ₂ generation has a conventional low NO
An after-air burner that is often used as the x combustion method may be used. In this case, it is more convenient to operate the fuel-air ratio under lean fuel conditions.

The present invention is particularly effective when the denitration apparatus is operated at a low temperature, but it may be used by raising the temperature of the denitration apparatus inlet for reasons such as corrosion of the constituent materials of the apparatus. Also,
Even for exhaust gas purification at low temperatures when the gas turbine is started, by operating this combustion burner irregularly, low-temperature denitration, which was not applicable in the past, will be possible. Another embodiment of the present invention is shown in FIG. The NO ₂ generation combustion burner 6 NO ₂
Is generated and the NO ₂ containing gas is injected into the upstream side of the denitration device 3. In this case, the cooling unit 17 is provided so as to cool the combustion burner outlet pipe in order to promote the generation of NO ₂ and to make the temperature at the inlet of the denitration device equal. Exhaust gas flow rate and NOx at combustion furnace outlet
The concentrations of (NO and NO ₂ ) are measured, and the amount of fuel, the amount of air, and the amount of NO ₂ production substance input in the combustion burner are determined from the signals.

FIG. 4 shows another embodiment according to the present invention, in which the dust collecting device 1 is provided between the combustion furnace 1 and the denitration device 3.
4 is provided, and is suitable for exhaust gas with a large amount of dust such as exhaust gas from a refuse incinerator. Further, FIG. 5 is an example in which a heat exchanger or a heat recovery device is installed in the exhaust gas system. In each case, the NO ₂ generation combustion burner 6 is shown as an example installed on the downstream side of the combustion furnace, but when the NO ₂ generation combustion burner 6 is installed on the upstream side of the denitration device 3 as shown in FIG. But it is effective.

According to the controller 20 in the embodiment of FIG.
NO₂NO generated by the burner 6 ₂For controlling the concentration
This will be described more specifically. Generated in the combustion furnace 1
The NOx that comes in is usually NO, and its concentration is 100 to 2
It is about 00 ppm. In this example, the density equal to this
NO₂NO₂It is generated by the combustion burner 6 for generation. Burning
NO with a burner₂Quenching and
When the ratio of fuel to air is outside the range of 0.8 to 1.2, N
O₂Promote the production of.

The method of controlling the NO ₂ concentration and the like will be described below with specific numerical values. As the combustion furnace 1, a relatively small waste incinerator is taken as an example. The combustion exhaust gas amount is 10,000 m ³ N
/ h; NO = 200 ppm. Considering the ratio of fuel to air in combustion furnace 1 is 1, and the ratio of total air to fuel including main combustion burner 6 is 1.2 (combining main combustion burner 6 with normal two-stage combustion burner) However, the amount of gas in each of the combustion furnace 1 and the main combustion burner 6 is approximately 8,000 m ³ N / h and 2,000 m ³ N / h.

NO is generated by combustion with an air amount of 2,000 m ³ N / h for the combustion burner 6. That is, thermal NOx
However, since the gas amount of the main combustion burner 6 is 1/4 of that of the combustion furnace, it is necessary to mainly generate a high concentration of NO ₂ in the combustion burner 6 as shown below. In order to simplify the calculation of
Ignore the generation of NOx for the time being. When NO ₂ is generated by adding pyridine, the combustion burner 6 of this embodiment is used.
Therefore, it is necessary to generate NO ₂ = 200 ppm, and the maximum addition amount of pyridine will be calculated. Since 200 ppm of NO is present in the combustion furnace gas of 8,000 m ³ N / h, the amount of NO produced by the combustion burner is

[0024]

[Equation 1]

Here, assuming that the generated NO can be changed to 100% NO ₂ by the rapid cooling method according to the present invention, it is 2 m ³ N / h.
The amount of pyridine required to become NO ₂ is PV = nRT
Therefore, n≈82 mol / h, which is about 6.5 kg / h. The gas volume of fuel propane in the combustion burner, 80 m ³
N / h. Therefore, NO and NO ₂ are measured by the NOx concentration measuring instrument 8 at the inlet of the denitration device 3, and the addition amount of the NO ₂ -producing substance such as pyridine is calculated by the above calculation method.

In the NOx concentration measuring instrument 8 of FIG. 1, NO and N
Both O ₂ are measured. Normally, a NOx meter measures NO, but NO ₂ can also be measured by converting NO ₂ to NO by the reaction of NO ₂ → NO + 1 / 2O ₂ by installing a high-temperature NOx converter.

[0027]

As described above, when the present invention is applied to a denitration device, it can be carried out with the same simplicity as the conventional denitration control method, and denitration with high efficiency and low temperature becomes possible.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a denitration device showing an embodiment according to the present invention.

FIG. 2 is a structural diagram of a combustion burner for NO ₂ generation in an example.

[Fig. 3]

[Fig. 4]

FIG. 5 is a structural diagram of a denitration device showing another embodiment according to the present invention.

FIG. 6 is a diagram for explaining a problem of the conventional technique.

FIG. 7 is a diagram showing the relationship between NO ₂ generation, fuel and air in the combustion burner used in the present invention.

FIG. 8 is an explanatory view of a specific example of control of the combustion burner in FIG.

[Explanation of symbols]

 1 ... Exhaust gas source (combustion furnace) 2, 5 ... Exhaust pipe, 3 ... Denitration equipment
Placement, 4 ... Catalyst, 6 ... NO₂Combustion burner for generation, 7 ... Flow rate
Total, 8 ... NOx (NO, NO₂) Densitometer, 9 ... Ammo
Near injection device, 10 ... (exhaust gas) flow rate signal, 11 ... NO
x (NO, NO ₂) Concentration signal, 12 ... Ammonia injection amount finger
Command signal, 13 ... predetermined NO₂Finger to burner for volume generation
Command signal, 14 ... Dust collector, 15 ... Heat recovery device (heat exchange
Container), 17 ... Cooling unit, 18 ... Fuel + air + NO₂Generation
Quality, 19 ... Cooling air or exhaust gas, 20 ... Control device.

Claims (4)

[Claims] 1. An exhaust gas denitration method in which exhaust gas is sent to a denitration device through an exhaust pipe, and ammonia is injected into the exhaust pipe in an upstream region of the denitration device to reduce and remove nitrogen oxides in the exhaust gas. Of detecting NO and NO ₂ concentrations in exhaust gas and exhaust gas flow rate, and using a predetermined amount of fuel calculated based on the detected values, NO ₂ generation promoting material, combustion air and flame cooling material for NO ₂ generation combustion A step of supplying the burner with a required amount of NO ₂ gas, and a step of supplying the generated NO ₂ gas into the exhaust pipe in the upstream region of the denitration device to make the NO / NO ₂ ratio in the exhaust gas close to 1 And NO ₂ and NO in the exhaust gas after the above NO ₂ gas supply
And a step of injecting a required amount of ammonia into the exhaust gas in the upstream region of the denitration apparatus based on the concentration of the exhaust gas and the amount of the exhaust gas. 2. The ratio of the amount of air supplied to the NO ₂ generating combustion burner to the amount of fuel (air-burning ratio) is 0.8.
A method for denitration of exhaust gas, which comprises adjusting the particle size to be smaller than 1.2 and larger than 1.2. 3. Denitration after injecting ammonia into the exhaust gas
Contact with the catalyst of the equipment to reduce and remove nitrogen oxides in the exhaust gas.
Fuel and NO in the exhaust gas denitration device to leave ₂Acceleration
Equipped with wood and combustion air supply means and flame quenching means
NO₂Combustion burner for generation and NO generated in the burner
₂Supply the contained gas into the exhaust gas in the upstream area of the denitration equipment
And an exhaust gas denitration device. 4. The exhaust gas denitration device according to claim 3, wherein the exhaust gas is a combustion exhaust gas from a combustion device, and the NO ₂ generating combustion burner is arranged in a downstream region of a combustion chamber of the combustion device.