JPH0727755A - Method and apparatus for checking efficiency of converter for nitrogen oxides - Google Patents

Abstract

PURPOSE:To provide a simple checking method which can check the efficiency of a converter with good reliability and to provide its apparatus. CONSTITUTION:NO gas or a sample gas which contains NO is reduced via an NOx converter 5, and the concentration of NO is measured. On the other hand, NO gas or the sample gas which contains NO is made to flow through a heated SUS (stainless-steel) pipe 2, it is heated and reduced via NOx converter 5, and the concentration of NO is measured. The efficiency of the converter is found on the basis of the ratio of the concentration of NO after reduction to the concentration of NO after heating and reduction.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a method and apparatus for checking the efficiency of nitrogen oxides for converter (hereinafter referred to as NO _X Converter) for reducing NO _X to NO.

[0002]

2. Description of the Related Art A NO _x converter is filled with a reducing agent mainly composed of carbon, for example, and its reducing ability is reduced by its use. Therefore, it is necessary to properly check the converter efficiency (reduction efficiency). is there.

For example, by adding O ₃ gas to NO gas, N
Without O + NO _{2, while} obtaining the NO concentration with the NO analyzer, after passing the NO _X gas through the converter,
The NO concentration after reduction was determined with an NO analyzer, and the converter efficiency was determined from the ratio of both concentrations.

[0004] Alternatively, the after the NO ₂ gas was discharged from the NO ₂ gas cylinder is via a converter to measure the NO concentration NO analyzer compares its NO concentration, the concentration of NO ₂ NO ₂ gas cylinder I was looking for converter efficiency.

[0005]

However, the former of the above conventional methods requires dry air for generating O ₃ , and it is not easy to control the concentration of O ₃ to be added.

Further, in the latter case, since the concentration of the NO ₂ gas cylinder changes with time, it is difficult to always obtain the converter efficiency with high reliability.

The present invention has been made in view of such circumstances.
It is an object of the present invention to provide a simple check method and a device for checking the converter efficiency with high reliability.

[0008]

The present invention comprises means for solving the above-mentioned problems as follows. That is, in the first aspect of the present invention, the NO gas or the sample gas containing NO is passed through the NO _X converter to reduce the N
While measuring the O concentration, the NO gas or the sample gas containing NO was heated to stainless steel (hereinafter referred to as SUS
After passing through the pipe, the NO concentration after heating / reducing is measured via the NO _X converter, and the converter efficiency is calculated from the ratio of the NO concentration after heating / reducing to the NO concentration after reducing. It is characterized by that.

In the second aspect of the invention, the SUS pipe with heating means provided in the gas flow path for passing the NO gas or the sample gas containing NO, the switching valve provided downstream of the SUS pipe, and the switching thereof A NO _x converter connected to the valve, an NO analyzer connected to the downstream side of the NO _x converter, and a bypass flow passage connected between the NO analyzer and the switching valve. It is characterized by that.

[0010]

Operation: First, by operating the switching valve, the SUS pipe is connected to the NO analyzer via the NO _X converter, and N
NO gas or sample gas containing NO is passed from a non-heated SUS tube through a NO _X converter to NO
It is introduced into an analyzer and the NO concentration (a) after reduction is measured.

Next, the heating means is operated to heat the SUS pipe, and the NO gas or the sample gas containing NO is
It is heated and oxidized by passing it through a heated SUS tube,
After changing from 2NO + 1 / 2O ₂ → NO + NO ₂ , NO
Measure NO concentration (b) after heating and reduction with NO analyzer via _X converter.

Then, by operating the switching valve, the heated SU
If the S pipe is connected to a NO analyzer through a bypass flow passage and the NO concentration (c) after heating and oxidation is measured, the converter efficiency C _E is C _E = {(b) − (c)} ÷ { (A)-
It can be calculated from (c)}.

Further, for example, if the heating temperature of the SUS pipe is determined, the oxidation rate of NO + 1 / 2O ₂ → NO ₂ under the measurement gas condition, that is, NO: NO _{2 at the} SUS pipe outlet is substantially determined. If NO: NO ₂ = 1: 1, the NO concentration at the converter inlet is about 1/2 (a), N after heating.
The O ₂ concentration is about 1/2 (a). Therefore, converter efficiency C _X = from NO concentration (b) at the converter outlet
It can also be roughly estimated from {(b) -1/2 (a)} / {(a) -1/2 (a)}.

[0014]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram of an efficiency check device for a NO _x converter, where reference numeral 1 is a gas flow path through which a NO gas or a sample gas containing NO is passed, and 2 is a SUS30.
It is a reaction tube composed of 4 and is equipped with a heater (heating means) 3 capable of variably adjusting the heating temperature in the range of 300 ° C to 500 ° C. 4 is a switching valve consisting of a normally closed electromagnetic three-way valve, and 5 is a NO _X converter that is the target of efficiency check. It is removably attached to the gas flow passage 1 because the inside is filled with a reducing agent mainly composed of carbon. Has been. 6 is an NO analyzer for measuring the NO concentration, 7 is a NO _x converter 5 for the NO gas or the sample gas containing NO.
It is a bypass flow path for introducing the bypass into the NO analyzer 6 without passing through.

With the NO _x converter efficiency check device having such a configuration, the efficiency of the NO _x converter 5 can be checked very simply and reliably as follows (see FIGS. 2A and 2B). ].

First, the switching valve 4 is normally closed as shown in the drawing, the reaction tube 2 is connected to the NO analyzer 6 via the NO _X converter 5, and the NO gas or the sample gas containing NO is not heated. It is introduced into the NO analyzer 6 from the reaction tube 2 via the NO _X converter 5, and the NO concentration (a) after reduction is measured.

Next, the heater 3 is operated to set the reaction tube 2 to 3
The sample is heated to 50 ° C. to 450 ° C., NO gas or a sample gas containing NO is passed through the reaction tube 2 to be heated and oxidized, and the reaction formula: 2NO + 1 / 2O ₂ → NO + NO
After being heated and oxidized as shown in ₂ , the NO concentration (b) after heating / reduction is measured by the NO analyzer 6 via the NO _X converter 5.

Then, the switching valve 4 is turned on to connect the heated reaction tube 2 to the NO analyzer 6 via the bypass flow path 7, without passing through the NO _X converter 5, the NO after the thermal oxidation. If the concentration (c) is measured, the converter efficiency C
_E is C _E = {(b)-(c)} ÷ {(a)-(c)}
It can be more roughly calculated. For the sake of simplicity, C
It can also be obtained as _E = (b) / (a).

Incidentally, FIG. 2 (A) shows the concentration changes of NO (solid line) and NO ₂ (broken line) at the heater (reaction tube) outlet, and FIG. 2 (B) shows the NO _x converter outlet (NO analyzer 6). Immediately before), (a): when the NO _x converter 5 is passed without heating, (b): when the heated reaction tube 2 and the NO _x converter 5 are passed, (c) : Shows the case where the heated reaction tube 2 and the bypass passage 7 are passed.

In the heating oxidation in the above concentration range (350 ° C. to 450 ° C.), as shown in FIG. 3, the NO oxidation keeps the equilibrium state at about 50%. Such SUS3
Regarding the NO _X thermal oxidation reaction using the 04 tube, for example, experimental data as shown in Tables 1, 2, and 3 below are obtained.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

[Table 3]

Table 1 shows that, in the presence of dry O ₂ , 21%,
With respect to 17 ppm NO, the concentration% of NO and NO ₂ when the heating temperature is changed in the range of 300 ° C. to 500 ° C. is shown (shown as a graph in FIG. 3).

Table 2 shows the concentration% of NO and NO ₂ when the heating temperature of NO of 4.85 ppm is constant (500 ° C.) and the coexisting O ₂ amount (dry / wet) is changed.

Table 3 shows that 5.05 ppm of NO ₂ was added to O ₂ (dry
), NO when heated to 500 ° C. in the presence of 21%
And the concentration% of NO ₂ are shown respectively.

By clearly grasping the characteristics of the SUS 304 in advance, when the NO _X converter 5 is deteriorated, the indicated value of the NO analyzer 6 becomes a value lower than the above value. This makes it possible to easily detect the deterioration state.

A Pt-based catalyst can be used to oxidize NO, but NO _X is adsorbed even when it is not heated, and therefore it cannot be directly provided in the gas flow path 1 and the above-mentioned catalyst is used. Like SUS3, which does not adsorb NO _x at low temperature and oxidizes NO when heated
No. 04 is arranged in the gas flow path 1, and the heater 3 can heat the same in a variable temperature, thereby realizing the device.

By changing the temperature of the heater 3, it is possible to easily change the conversion rate from NO to NO ₂ and thereby to change the NO ₂ concentration in a wide range, and to check the converter efficiency in various ways. It is possible to perform a highly reliable check by using the above NO ₂ concentration.

Since the flue gas which is the object of NO measurement contains O ₂ , only by connecting the gas passage 1 of the converter efficiency check device as described above to the sampling line of the flue, It is not necessary to use a separate NO ₂ cylinder, and the converter efficiency can be calculated very simply and reliably. By the way, when arranging such a converter efficiency check device on site, a normally closed electromagnetic three-way valve is adopted as the switching valve 4, and the NO _X converter 5 is detachably mounted, and the reaction tube is always installed. 2 through the bypass flow path 7
The NO concentration may be measured by connecting to the analyzer 6, and the switching valve 4 may be turned on and off at the time of checking.

[0031]

As described above, according to the method of the present invention, NO gas or NO-containing sample gas is NO.
After measuring the NO concentration after reduction via the _X converter, after passing the NO gas or sample gas containing NO through the heated SUS pipe, after heating / reducing via the NO _X converter NO concentration after heating / reduction with respect to the NO concentration after reduction
Since the converter efficiency is calculated from the concentration ratio, NO ₂
Converter efficiency can be checked easily and reliably without the need for a cylinder or O ₃ generator.

Further, a SUS pipe with heating means is provided in the gas flow passage, a switching valve is provided between the SUS pipe and the NO _X converter, and a bypass flow passage is provided between the switching valve and the NO analyzer. It is possible to easily check the converter efficiency from the exhaust gas of the flue without bringing in a NO ₂ cylinder, an O ₃ generator, etc. from the connected device with a simple structure.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an efficiency check device for a NO _x converter according to the present invention.

FIG. 2A is a graph showing NO and NO ₂ concentration changes at the heater (reaction tube) outlet, and FIG. 2B is a graph showing NO concentration changes at the NO _x converter outlet (immediately before the NO analyzer).

FIG. 3 NO and NO during thermal oxidation by SUS304 tube
₆ is a graph showing the change in concentration of ₂ .

[Explanation of symbols]

1 ... Gas flow path, 2 ... SUS pipe, 3 ... Heating means, 4 ... Switching valve, 5 ... NO _X converter, 6 ... NO analyzer, 7 ... Bypass flow path.

Claims (2)

[Claims] 1. N after reducing by passing a NO gas or a sample gas containing NO through a nitrogen oxide converter.
While measuring the O concentration, the NO gas or the sample gas containing NO was passed through the heated stainless steel pipe, and then the NO concentration after heating / reduction was measured via the nitrogen oxide converter. A method for checking the efficiency of a nitrogen oxide converter, characterized in that the converter efficiency is obtained from the ratio of the NO concentration after heating / reducing to the NO concentration after reducing. 2. A stainless steel pipe with heating means provided in a gas flow path through which a NO gas or a sample gas containing NO flows, a switching valve provided downstream of the stainless steel pipe, and a switching valve connected to the switching valve. A nitrogen oxide converter, a NO analyzer connected downstream of the nitrogen oxide converter, and a bypass flow passage connected between the NO analyzer and the switching valve. A device for checking the efficiency of nitrogen oxide converters.