JPS59209630A - Desulfurization and denitration of exhaust gas - Google Patents

Abstract

PURPOSE:To solve an NH3-leak problem, in a method for treating exhaust gas containing NOx and SOx in a first and a second direct and counter stream type moving bed reactors while mixing NH3 in said gas, by dividing gas in the latter reactor while mixing NH3 into both gas streams. CONSTITUTION:Exhaust gas conditioned in a temp. is introduced in a first direct and counter stream type moving bed reactor through a line 1 while adding NH3 into said gas from a line 2 and contacted with the carbonaceous catalyst bed 4 falling in the reactor 3 to be subjected to desulfurization and denitration treatment prior to exhausion. This exhaust gas is introduced into a second orthogonal stream type moving bed reactor 7 through a line 5. In this case, the exhaust gas introducing parts of the reactor 7 are provided in two upper and lowr directions and the exhaust gas is divided into two parts while NH3 is respectively injected into gases introduced to the upper and the lower parts of the reactor high and low in a NH3 leak amount in a slightly small amount or a slightly large amount. The exhaust gas treated in the reactor 7 similarily as mentioned above is discharged into the air through a dust collector 10.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for desulfurizing and denitrating exhaust gas containing sulfur oxides and nitrogen oxides, and more particularly to a method for solving the problem of leakage of ammonia mixed in during exhaust gas treatment.

Sulfur oxides (SOx) and nitrogen oxides (NO
As a method for treating exhaust gas containing a high concentration of x), a method is known in which ammonia is mixed into the exhaust gas and then the exhaust gas is passed through a packed bed of carbonaceous catalyst. In this method, SOx and NOx'! It has the advantage that it can be removed at the same time and that the catalyst can be easily regenerated.

However, with this method, K
is at least 200°C or higher, preferably 220-25
A reaction temperature of about 0° C. is required, and NOx cannot be removed sufficiently at temperatures lower than this. However,
At a reaction temperature of 200° C., there is a problem that a part of the carbonaceous catalyst is consumed by oxygen in the exhaust gas as C+O, →CO1. Further, since the exhaust gas from Zein etc. is approximately 15'O<0>C at the outlet of the air heater, etc., it is disadvantageous in that the exhaust gas must be preheated to a temperature of 200[deg.]C or higher.

In contrast, a method has been proposed that can remove not only SOx but also NOx at a high removal rate even at a temperature of about 150°C. In this method, ammonia is mixed into the exhaust gas, this mixed gas is introduced into the first cross-flow moving bed reactor to remove most of the SOx, and then ammonia is mixed into the treated gas again, and this mixed gas is introduced into the flue gas. The gas is guided to a second cross-flow moving bed reactor for reprocessing.

However, in this method, although a high denitrification rate can be obtained in the second reactor, a large amount of ammonia leaks into the treated gas, resulting in the risk of secondary pollution. If the amount of ammonia mixed into the outlet gas of the first reactor is reduced, NH, I
Although the amount of J-reduction is reduced, this results in a decrease in the denitrification rate.

The reason why this problem of NH,+1- was unresolved was because
This is thought to be because the reaction characteristics of the contact between the carbonaceous catalyst and the exhaust gas containing ammonia in the cross-flow reactor have not been fully elucidated.

The inventors of the present invention, NHs! As a result of studies to solve the problem of J-reduction, it was found that the amount of N15 leaked was significantly different between the upper and lower parts of the reactor. Figure 1 shows So
! 50 ppm, NOx 170 ppm, I(
,07,8ch, 150p for exhaust gas containing 0,3.8%
pm of ammonia was injected, and the mixed gas was heated to 15 pm.
NOx, SOx removal rate and N at each part of the reactor outlet when passing through a second cross-flow type moving bed reactor packed with a carbonaceous catalyst at a space velocity of 800 hr at 0 ° C.
It is a graph showing the amount of H and IJ. Note that the residence time of the catalyst in the reactor in this case is 25 hours. As shown in FIG. 1, it is understood that ammonia leaks significantly in the upper part of the reactor.

(This phenomenon will be explained in detail later.) The present invention was completed by paying attention to this phenomenon. That is, the above 2
In the method of desulfurizing and denitrating exhaust gas using a cross-flow moving bed reactor, the outlet gas of the first cross-flow reactor is divided into two or more parts above and below the reactor, and the gas is then added to the second cross-flow reactor. The system is characterized by introducing ammonia into each divided introduced gas.

The present invention will be explained with reference to FIG. The exhaust gas whose temperature is controlled to about 100 to 170°C is introduced into the first cross-flow type moving bed reactor 3 via line 1. In this case, ammonia is added to the exhaust gas via line 2. The exhaust gas is discharged from the reactor 3 after being desulfurized and denitrated by contacting the carbonaceous catalyst bed 4 descending within the reactor 3 . This discharged exhaust gas is introduced into the second cross-flow moving bed reactor 7 via line 5. At this time, at least two or more exhaust gas introduction parts of the reactor 7 are provided in the vertical direction, and after the exhaust gas is divided,
An appropriate amount of ammonia is injected from each line 6. The amount of ammonia to be injected is determined in consideration of the phenomenon shown in FIG. That is, a small amount of ammonia is injected into the gas introduced into the upper part of the reactor where the amount of NH, IJ- is large, and a larger amount of ammonia is injected into the gas introduced into the bottom part of the reactor where the amount of NH, IJ- is small.

Denitrification and
The desulfurized exhaust gas is passed through line 9 to dust collector 1.
After being introduced into the air tank 0 and subjected to dust collection processing, it is discharged to the atmosphere through a line 11.

On the other hand, the catalyst discharged from the reactors 3 and 7 is transferred to the regenerator 12.
300-600 m under an inert gas atmosphere.
After being heated and ladled to 0° C., it is returned to the top of each of reactors 3 and 7 to be reused. Alternatively, the catalyst discharged from the second reactor 7 is transferred to the first reactor 3 as a catalyst stream.
The catalyst discharged there may be supplied to the regenerator 12 for regeneration, and then supplied to the second reactor 7 for circulation.

In the first and second reactors of the present invention, a carbonaceous catalyst such as activated carbon or activated coke grains obtained by heat treating coal or activating it with steam is generally used. It is also possible to support metal oxides such as copper.

The phenomenon of NH, IJ-reduction was explained with reference to FIG.

Although this phenomenon is very complex and is not clear at present, it can be inferred as follows.

Some of the injected NH8 becomes H! on the catalyst. SO reacts with O4 and is captured as sulfate on the carbonaceous catalyst, and the remaining NH
, reacts with No present in the exhaust gas to form No + NH
s 10”/40! →Nl +3/2 Hto (2
) is consumed more and contributes to denitrification. On the other hand, there is a reducing substance on the carbonaceous catalyst circulating from the regenerator, and this substance also becomes Ar ・”N + No →1% + Ac ”・0
(3) (Here, Ae...N means a reducing substance on the catalyst, and formula (3) shows a tentative reaction formula.) It contributes to denitrification.

The main reactions in the reactor are as described above, and these and NH
, and the relationship with leakage is shown in Figure 3 in the vertical direction of the reactor. The processing conditions are the same as in FIG.

As is clear from Figure 3, there is a large amount of reducing substances in the upper part of the reactor, and this reducing substance reacts with NO, so equation (3) takes precedence over equation (2), resulting in NH5 consumption is low. Therefore, the amount of NH and IJ is large in the upper part of the reactor. On the other hand, since NH3 is slightly adsorbed by the carbonaceous catalyst as shown in the curve in FIG. 3, almost no leakage occurs at the beginning of gas flow (corresponding to the vicinity of the top of the reactor).

After that, as the carbonaceous catalyst descends and reducing substances are consumed and reduced, the formula (2) takes precedence over the formula (3) and the NH
, consumption increases. Therefore, at the bottom of the reactor, NH, U-
The amount is small.

That is, I'tlH, leakage is NH3 breakthrough curve (A)
and the increase in consumption of injected NH3 due to the reduction of reducing properties and substances (
This can be explained by the difference between B). In addition, as the residence time of the catalyst in the reactor increases, the degree of consumption of reducing substances increases.
s The difference in leakage amount becomes significant. On the other hand, as the I-spooling time of the catalyst is decreased, the degree of consumption of the reducing substance is decreased, and therefore the difference in the amount of NH31J between the upper and lower portions of the reactor is decreased.

However, the residence time of the catalyst is usually set to about 15 to 50 hours, and at least within this range, the same tendency as in FIG. 1 or FIG. 3 is shown.

The present invention can solve the problem of NH leakage because it is possible to inject an appropriate amount of ammonia into each of the divided second reactor introduced gases in consideration of the above-mentioned NH3 leak phenomenon. .

Furthermore, since ammonia can be made to sufficiently contribute to denitrification, a high denitrification rate can be maintained.

Hereinafter, the effects of the present invention will be clarified through Examples.

Example 1050 ppm SOx and 200 ppm NOx
After mixing 500 ppm of ammonia gas with the exhaust gas containing Space velocity 6 in cross-flow moving bed reactor
It passed at a speed of 00 hr"". In this case, the residence time of the catalyst in the reactor was set to 33 hours. The desulfurization rate in this reactor was 95%, and the denitrification rate was 15%.

In addition, the amount of Nl leaked was 2 ppm.

The first reactor outlet gas is divided into the upper 1/3 of the reactor.
For the gas introduced into the section, 70 ppm of NH8 is added.
, for the gas introduced at the bottom, 160 ppp of NH.
m injected into the second cross-flow moving bed reactor at a space velocity of 80 m.
It passed at a speed of 0 hr-. The residence time of the catalyst in the reactor in this case is set to 25 hours.

The desulfurization rate and the denitrification rate in the second reactor were 100% and 85%, respectively, relative to the gas introduced into the second reactor. That is,
The overall desulfurization rate and denitrification rate were 100% and 87%, respectively. Further, the amount of NH4 leakage was 6 pPm.

As a comparative example, when 150 ppm of Nu was injected into the second reactor without dividing the gas at the outlet of the first reactor, the desulfurization rate and the denitration rate in the second reactor were each 1.
00chi, 83%.

Further, the amount of NH and IJ was 15 ppm.

[Brief explanation of the drawing]

Figure 1 shows the NOX, SOX removal rate and NH,! at each part of the reactor outlet. FIG. 2, which is a graph showing an example of the J-reduction amount, is an explanatory diagram of the present invention. Figure 3 shows NH. FIG. 3 is an explanatory diagram of a leak phenomenon. 3...First cross-flow moving bed reactor 7...Second cross-flow moving bed reactor 12...Regenerator patent applicant Sumitomo Heavy Industries, Ltd.

Claims (1)

[Claims] 1. Ammonia is mixed into exhaust gas containing nitrogen oxides and sulfur oxides, and this mixed gas is introduced into a first cross-flow moving bed reactor filled with a carbonaceous catalyst to perform desulfurization and denitrification treatment, In a method for denitrification and desulfurization treatment by mixing ammonia into this treated gas again and introducing this mixed gas into a second cross-flow type moving bed reactor filled with a carbonaceous catalyst,
The first cross-flow moving bed reactor outlet gas is sent to the top and bottom of the reactor.
A method for desulfurization and denitration of exhaust gas, characterized in that the gas is divided into two or more parts and introduced into a second cross-flow moving bed reactor, and ammonia is injected into each divided part of the introduced gas.