JPH0366006B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an ammonia injection method in a dry desulfurization and denitrification method.

The dry simultaneous desulfurization and denitrification method, in which waste gas is passed through a moving bed formed by a carbonaceous adsorbent to remove sulfur oxides from the waste gas and also remove nitrogen oxides by adding ammonia, is well known. It is being In this case, the conventional method is to inject ammonia alone or after dilution with other suitable gas into the waste gas duct before entering the moving bed (FIG. 1). That is,
In the figure, waste gas 1 contacts a moving bed 4 made of carbonaceous adsorbent 2 in cross flow with ammonia gas or ammonia-containing gas injected from an ammonia mixing device 6. In this method, ammonium sulfate or acidic ammonium sulfate is generated and adhered to the flue and the exhaust gas inlet part of the moving layer held by a louver or perforated plate, and grows, reducing the flow path area of the exhaust gas. This had the disadvantage of increasing the pressure loss of the gas, causing the waste gas to flow unevenly, and reducing the desulfurization and denitrification performance.

In addition, the temperature of the waste gas handled by the dry simultaneous desulfurization and denitrification equipment is usually between room temperature and 180°C, and in this temperature range, the reaction between ammonia and sulfur oxides precedes the reaction between ammonia and nitrogen oxides, so the The conventional method of using a moving bed and injecting ammonia into the waste gas before it flows into the moving bed has the disadvantage that a large denitrification rate cannot be obtained and the amount of ammonia consumed is significantly increased. Therefore, as shown in FIG. 2, two moving beds made of carbonaceous adsorbent 2 are installed, and the waste gas 1 passes through the first moving bed 4, then the second moving bed 5, and then the first moving bed. Before the moving bed, no ammonia is added, or a small amount of ammonia 3' is added, and after desulfurization is mainly performed by the adsorption action of the carbonaceous adsorbent, ammonia is added to the waste gas that has passed through the first moving bed. A method has also been proposed in which denitrification is mainly carried out in the second moving bed by injecting NOx, but this method requires the installation of two moving beds and has the disadvantage of increasing the equipment cost. However, ammonia injection is still performed in the waste gas duct before entering each moving bed.
Although the occurrence of blockages caused by the formation, adhesion, and growth of ammonium sulfate and acidic ammonium sulfate on the perforated plates or louvers in the flue and at the entrance of the moving bed has been reduced, it has not yet been completely resolved.

The present inventors conducted extensive research in order to eliminate the drawbacks of the conventional methods described above, and as a result, they discovered that this objective could be achieved by directly adding ammonia to the moving bed made of carbonaceous adsorbent, and arrived at the present invention. did.

That is, in the present invention, waste gas containing sulfur oxides and nitrogen oxides is passed through a moving bed formed by a carbonaceous adsorbent, and nitrogen oxides are simultaneously removed from sulfur oxides by the reducing action of ammonia added separately. A dry desulfurization and denitrification method for removing ammonia, characterized in that ammonia is directly injected into the moving bed through an ammonia dispersion device installed inside the moving bed, and at the same time, waste gas is passed through in cross-flow contact with the moving bed. This is the method to do so.

The carbonaceous adsorbent used here includes commonly used activated carbon, semi-formed coke, etc., and ammonia is used as ammonia gas or diluted with a suitable gas. Further, the temperature of the moving layer is usually maintained at room temperature to 180°C.

FIG. 3 shows one embodiment of the present invention, in which ammonia or ammonia diluent gas 3
is directly injected into the moving bed through an ammonia dispersion device 7 installed inside the moving bed 4 formed of the carbonaceous adsorbent 2, and at the same time, the waste gas 1 is passed through so as to be in cross-flow contact with the moving bed.

According to the method of the present invention, ammonia is directly injected into the moving carbonaceous adsorbent layer, so ammonium sulfate and acidic ammonium sulfate are generated only on the moving carbonaceous adsorbent and flow out of the moving bed. Continuously discharged. Therefore, unlike conventional methods, there is no clogging due to the formation or growth of ammonium sulfate or acidic ammonium sulfate on the perforated plate or louver in the flue or at the inlet of the moving bed, and as a result, there is no significant pressure loss in the waste gas. This makes it possible to prevent waste gas from flowing unevenly, and to ensure a uniform flow over a long period of time.

FIG. 4 shows another embodiment, in which a plurality of ammonia gas dispersion devices 7, 7' are installed in a single moving bed to inject ammonia in portions.
In this case, the effect similar to that obtained by installing a plurality of moving beds is exhibited, so that the amount of ammonia consumed can be reduced and the denitrification rate can be improved with a simple device. That is, the effect of reducing the equipment cost and operating cost of the dry simultaneous desulfurization and denitration equipment is significant.

It goes without saying that the direct ammonia injection method according to the present invention is not limited to a single moving layer.

The present invention will be explained in more detail below using Examples and Comparative Examples.

Example 1 Heavy oil combustion waste gas having an SO ₂ concentration of 860 ppm and a NO _x concentration of 170 ppm was passed through a moving bed of granular activated carbon with a displacement of 40/H at a temperature of 155° C. and a flow rate of 1000 Nm ³ /H. Ammonia was diluted with the waste gas that had passed through the moving bed and was directly injected into the moving bed through a gas dispersion device installed immediately after the louver on the exhaust gas inlet side of the moving bed. The amount of ammonia injected was 0.43Nm ³ /H. As shown in FIG. 6, there is almost no change in the pressure loss of the waste gas in the moving bed over time. Furthermore, after 100 hours, the SO ₂ concentration in the waste gas at the exit of the moving bed was 80 ppm, and the NO _x concentration was 90 ppm.

Comparative Example 1 The same equipment, waste gas conditions, movement amount of granular activated carbon, and ammonia injection amount as in Example 1 were used, and the same dilution method and dilution ratio were used, but ammonia was injected into the waste gas duct before flowing into the moving bed. The change in pressure loss of waste gas in the moving bed over time is shown in Figure 5. The pressure drop gradually increased and reached 235 mmAq after 168 hours.

Furthermore, after 100 hours, the SO ₂ concentration in the waste gas at the exit of the moving bed was 91 ppm, and the NO _x concentration was 100 ppm.

Example 2 Heavy oil combustion waste gas with an SO ₂ concentration of 900 ppm and a NO _x concentration of 300 ppm was passed through a moving bed of granular activated carbon with a displacement of 80/H at a temperature of 155° C. and a flow rate of 1000 Nm ³ /H. Ammonia is diluted with waste gas after passing through the moving bed, and the amount is 0.18Nm ³ /H to the inlet of the moving bed and 0.27Nm ³ /H to the middle part.
Injected in divided doses. _SO2 in the waste gas after passing through the moving bed
The concentration was 0-2 ppm, and NO _x was 63 ppm.

Comparative Example 2 Using the same equipment, exhaust gas conditions, and movement amount of granular activated carbon as in Example 2, ammonia was diluted in the same manner and injected only into the inlet portion of the moving bed. The SO ₂ concentration in the waste gas after passing through the moving bed is 0 to 2 ppm, and the NO _x concentration is
It became 156ppm.

[Brief explanation of drawings]

1 and 2 are schematic diagrams showing the ammonia injection method according to the conventional method, FIG. 3 and FIG. 4 are schematic diagrams showing the ammonia injection method according to the present invention, and FIG. 5 and FIG. 3 is a graph showing the change in pressure drop of waste gas passing through the moving bed over time in the case according to the present invention and the case according to the present invention.

Claims (1)

[Claims] 1 Waste gas containing sulfur oxides and nitrogen oxides is passed through a moving bed formed by a carbonaceous adsorbent, and sulfur oxides and nitrogen oxides are simultaneously oxidized by the reducing action of ammonia added separately. In a dry desulfurization and denitrification method for removing substances, ammonia is directly injected into the moving bed through an ammonia dispersion device installed inside the moving bed, and at the same time, waste gas is passed through in cross-flow contact with the moving bed. A dry desulfurization and denitrification method characterized by: 2. The method according to claim 1, wherein ammonia gas or ammonia-containing gas is injected in portions from a plurality of dispersion devices provided inside a single moving bed made of carbonaceous adsorbent.