JPS5995922A - Denitration method of gas containing nox - Google Patents

Abstract

PURPOSE:To denitrate efficiently NO2 in NOx-contg. gas without by-producing N2O by reducing at least a part of NO2 in said gas to NO then subjecting the same to a denitration treatment by an ammonia catalytic reduction method. CONSTITUTION:The NOx-contg. gas which contains the NO2 introduced through a line 1 is heated to a prescribed temp. with a heater 5 and is then introduced into an NO2-NO converter 6. The above-mentioned gas is brought into contact with a catalyst 9 contg. the oxide of metal such as Co as an active component in said converter, so that at least a part of NO2 is reduced by a reducing agent such as H2 and is converted to NO, thereby decreasing the ratio of NO2 in the NOx to more preferably <=50%. NH3 is added to said gas through a line 7 and the gas is introduced into a denitration reactor 8. The gas is brought into contact with a catalyst 10 combined with the oxides of Ti, V, Mo and W in said reactor and NO2 is denitrated with high efficiency by reduction reaction.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for denitrifying gas containing nitrogen oxides, and in particular to a $11 original denitrification method using ammonia contact for highly efficient denitrification of gas containing high concentration nitrogen dioxide (NO2). It is.

Conventionally, cleaning methods such as water, acid, or alkaline chloride have been used to treat waste gas containing high concentration No. 2 from nitric acid plants, metal pickling factories, etc. ,: Dissolution rate of No. 2 into the absorption liquid 75-membered order: 1. There are problems such as when l'l increases in size and when nitric acid and nitrous acid combine to produce a large amount of effluent containing nitrous acid. However, in recent years, in the exhaust gas treatment of nuclear fuel +iT processing plants, NO2 in the exhaust gas has been removed with high efficiency to prevent explosions in the 1T cold molecule '+ (I process) that recovers radioactive krypton and xenon. I am confused about how to do this.] In this case,
According to the wet method, wastewater containing radioactive substances is treated during a large amount of time.

As mentioned above, alkaline cleaning - No. 1000 (by wind method)
Removal of JO2 fish has been unsuccessful for various reasons, and a simpler and more effective alternative to this method, the dry method, JO2 fish removal process, has been established.

As a process of adding such a request to i'+M, using ammonia (NI(a) as reduction j11) @1
'The so-called ammonia catalytic reduction denitrification process, which uniquely reduces No 2 to nitrogen and water, has been considered, and many proposals have already been made.

However, according to the studies of the present inventors, when the above-mentioned NO2-containing gas is treated with ammonia contact and a one-component method, NO2 is not converted to nitrogen (N2) by +41,
It has been found that nitrous oxide (N20) is generated in large amounts as a by-product during the reduction process, which is a major hindrance to practical application. From this, Fukagawa cannot use the ammonia contact 1π element method for denitrification of high, l,', 1 degree No2-containing gas.
It is essential to develop strategies to suppress N20 byproducts.

An object of the present invention is to solve the drawbacks of the conventional technique 0tff described above.
1. The present invention aims to provide a method that can efficiently denitrify No2 by an ammonia catalytic reduction method without producing N20 as a by-product.

As a result of studying the N20 by-product +f9 when NO2 is fused with NH3, the inventors discovered that the generation of N2° occurs in the following manner, and were able to complete the present invention. It was. That is, No. 2 is first prevented by the activation of 3, which is expressed by equation (1), and N.

is generated. The number generated in this way is further calculated as (2
) is reduced to produce N2 and I20.

On the other hand, for the activation of N1-13, No 2 which was not cooled
generates N2o and I20 by the reaction of formula (3). This N20 is a stable gas with very little reactivity, and unless it is reduced to a certain extent, a small amount of N2o will remain.

2NH3+ NO2→2NI(2+ No + lI2
0...-(1)NH20NO-+N2+
I20 --(2)Nl(2+ NO2→N20
+f(20·old=(3) where NH2 represents the active intermediate on the catalyst.

As shown in above + je, activation of NH3 by NO2 generates twice as many moles of NH3 (Equation (1)), and only one mole of NH2 is the same as the NO generated in Equation (1). It reacts to become N2 and I20 (formula (2)), but the remaining 1 mole of *NHz has no choice but to react with Not in the exhaust gas to generate NzO, and the N20 generation during NO2 denitrification is Therefore, in order to suppress the No 2 by-product, it is necessary to react the generated 2 moles of N1-I2 with NO as much as possible in the reaction of equation (2). It is.

Therefore, the gas that should be reduced should first be converted to NOK, and most of the NO gas should be converted to NOK.

0 degree to No 2 concentration or higher (hereinafter referred to as T NO/No 2
(denoted as 41), the denitrification reaction using NH3 is carried out by -B
If this is allowed to occur, all of the contained No 2 will be quenched by the reaction of equation (1), and the generated No and remaining NO will be (
2) It is all reduced to N2 by the reaction of formula.

The present invention converts part or all of the NO2 in the gas to be treated into NO in advance, and converts the NO2 in the NOx to be treated.
After reducing the o v ratio to 50 or less, the ammonia contact method is carried out, thereby suppressing the by-product of N20 and improving the denitrification performance.

According to the present invention, methods for converting NO into NQ in the gas include pyrolysis, fusion pyrolysis, and reduction using a reducing agent, but cobalt, manganese, The catalytic/self-thermal separation method, which uses a medium containing oxides of metals such as chromium and carbon dioxide as active ingredients, is the most sluggish because it has a high rate of conversion to NO. As the reducing agent used in the above reduction method, for example, hydrogen, hydrocarbon, -carbon oxide, solid carbon such as graphite, etc. are used. Still, No. 2 in the gas to be treated is transferred to N0vc. -'1 is N(L
7::I degree is NO2? Condition equal to or greater than Q degree (N.

/NO, ≧0.5). However, considering the above 1''-■, it is best to set NO/NO to 0.5.Furthermore, set NO2 to No;
As a tactile agent to be used in the denitrification process of boiler exhaust gas, any material that is suitable for denitrification of No-containing gases such as boiler exhaust gas can be used.
The combination of titanium, vanadium, molybdenum, and tungsten gives good results.

Hereinafter, the present invention will be roughly explained in detail with reference to the drawings.

FIG. 1 is a typical system diagram showing one practical implementation of the present invention. Here, a gas containing NO2 (NO/
NO2<1) is led to the NOJD heater 5 via the pipe α1, brought to a predetermined temperature at a ratio of n1:1, and then led to the NO2NO converter 6. The converter 6 is filled with a catalyst 9 that promotes the reaction of the following formula (4), and NO2 in the p1 processing gas is converted into heat iQ.

NOz 4 No 10], / 202 (4) The gas to be treated whose No/No2 value has become 1 or more is subjected to a denitrification reaction after N1 (3ci) is added from the human line 7. The denitrified gas is brought into contact with the catalyst 10 filled in the vessel 8 to perform a denitrification reaction.The clean gas after denitrification is discharged from the system through the pipe 4.

Note that the first system of the above equipment includes a converter 6 and a denitrification reaction 218.
It may be operated at different temperatures, or a heater or heat exchanger may be installed as appropriate for purposes such as waste heat recovery.

Next, FIG. 2 shows another embodiment 1 of the present invention,
The difference from the PJ1 diagram is the NO2 No. 1, 1 use method foundation 9.
The denitrification catalyst 10 was made of two 46f structures, of which 111
A N1(s) injection pipe 7 was installed in the reactor to form a 2) 13 type reactor 11. According to this embodiment, since the f'J02NO converter and the denitrification reactor are integrated, it is possible to downsize the device and reduce heat loss.

Next, the present invention will be specifically explained using Experiment 1.

Embodiment: The equipment system shown in FIG.
Under the conditions shown in Table 1, the denitrification rate and N20 by-product rate during No.21:Q were set to 1.゛Kobe/ko. Here, the deionization rate and N20 by-product rate are determined as follows.

Figure 7 shows the denitrification rate and N20 by-product rate of the denitrification reactor when the N O/NOz ratio at the inlet of the denitrification reactor is changed by changing the temperature of the heater 5.

When the NO/NO2 ratio increases from 1 to 1, the N20 by-product liquid becomes less than a few I--, which is within the measurement limit, indicating that the method of the present invention is an excellent method for suppressing N20 by-products. There is one thing. Furthermore, by converting NO2 into NO, the denitrification performance was greatly improved, and it can be concluded that this method is excellent in terms of denitrification performance as well.

Next, Table 2 shows the N20 by-product suppression effect (N
This figure shows the effect of increasing the O/N02 conversion ratio from 0.08 to 1 to 1,06.

From the results shown in Table 2, even when the present invention is applied to monopolized yarns with non-V group denitrification, the N20 and 71j production rates are significantly reduced, indicating that the present invention is effective. It's obviously a sword.

As described above, according to the present invention, the NO2 gas contained in the NO2 gas is With the original method, it is possible to perform denitrification with high efficiency while suppressing the by-product of N20.
For example, in the conventional method, it is possible to reduce the by-product N20, which corresponds to 20 to 3 degrees of NO2 in the gas to be treated, to almost 0 degrees, and moreover, the denitrification performance has been increased by more than 1.5 times. can be improved.

[Brief explanation of the drawing]

FIGS. 1 and 2 are system diagrams showing an embodiment of the present invention, and FIG. 3 is a graph showing the effects of the January embodiment. 1... Processing gas distribution 'U15... Heater, 6...
No2-NO converter, 7...N1 (s injection product 71,8
...Denitrification reactor, 9...NoP thermal decomposition catalyst, 1o.
...Irjl independent media.

Claims (1)

[Claims] (1) Before the process of denitrifying nitrogen dioxide (NO2)-containing gas by the ammonia catalytic reduction method,
o At least a portion of the
o) The process of converting to gold film! Timely denitrification method for nitrogen oxide-containing gas. (2. In claim 1, i?a refers to the fact that the conversion reaction is carried out so that the ratio of No2 in the nitrogen oxides in the gas becomes 50 parts or less. Method of denitration of contained gas.