JPH0249122B2 - HAIGASUDATSURYUHOHO - Google Patents

Description

[Detailed description of the invention]

The present invention is desired to remove sulfur oxides (hereinafter referred to as _SOx ) released into the atmosphere along with various exhaust gases because they are harmful substances that cause air pollution and other pollution. As this dry method, a method is known in which exhaust gas is brought into contact with the amount of movement of a carbonaceous adsorbent such as activated carbon. In addition, in this method, for the purpose of improving the desulfurization performance of the carbonaceous adsorbent or for the purpose of simultaneously denitrating, there is a method in which NH ₃ is injected into the exhaust gas in advance and then passed through the carbonaceous adsorbent layer. However, this method has a problem in that the removal rate of _SOx is limited and the desulfurization performance is insufficient. Therefore, in order to maintain the desired desulfurization performance, a method is adopted in which the amount of adsorbent transferred is increased during operation, but there is a problem in that the amount of adsorbent is increased. The limestone-gypsum method, which is a wet method, is the mainstream method for removing _SOx contained in exhaust gas. However, the wet method has problems such as securing water, processing waste liquid, processing by-product gypsum, and raising the temperature of the process gas, so the dry method has recently been reconsidered. The present invention improves the method of removing _SOx by introducing the exhaust gas containing _SOx as it is or by injecting ammonia gas (hereinafter referred to as _NH3 ) into a carbonaceous adsorption layer such as activated carbon. This is an attempt to improve removal performance. Particularly in the adsorption and removal of _SO
Although the coexistence of oxygen is necessary, the present invention aims to improve the performance of a direct/alternating current moving bed desulfurization apparatus by adjusting the horizontal oxygen concentration in the exhaust gas. The performance deterioration of the carbon-based adsorbent in the cross-flow moving bed varies depending on the residence time of the adsorbent in the reactor and the properties and amount of exhaust gas introduced, but in general, it is as shown in Figure 2. It shows a certain tendency. That is, when the residence time in the reactor (contact time with exhaust gas) is set to 50 hours, there is almost no performance deterioration for the initial 20 hours, and it is from 30 to 50 hours that the performance decreases significantly. In other words,
There was no performance deterioration in the initial 2/5 (upper 2/5 in the reactor), but there was a significant performance deterioration in the latter 2/5 (lower 2/5 in the reactor). The present invention aims to improve the adsorption performance by increasing the moisture and/or oxygen concentration in the exhaust gas only in areas where the performance is significantly degraded. Examples will be described below with reference to the drawings. The exhaust gas is introduced into a cross-flow type moving bed reactor 1 containing a carbonaceous adsorbent such as activated carbon, either directly or by injecting NH ₃ in the middle as shown in the figure, and dividing it into two parts by a flow rate distributor or damper 4. Ru. In this case, water and/or air are injected into the exhaust gas introduced from the lower inlet of the reactor 1, and the exhaust gas is introduced into the reactor 1. The treated gas passes through the dust collector 2 and is released into the atmosphere. Further, the adsorbent that has been inactivated after leaving the reactor 1 is regenerated by heating in the regenerator 3 and reused. The highly concentrated SO ₂ gas generated in the regenerator 3 is sent to the sulfuric acid/ammonium sulfate or sulfur recovery system. Now, the amount of exhaust gas introduced from the lower inlet of the reactor 1 is at most 4/5 of the total amount, preferably 2/5 or less, and especially about 1/3 as shown in the embodiments. The water to be injected may be steam, industrial water, waste water, plant cooling water, etc.
Exhaust gas with a high oxygen concentration may be added. Furthermore, the carbonaceous adsorbent used is not limited to the conventionally used carbonaceous adsorbents obtained by heat treatment or steam activation of activated carbon and coal, etc. Of course, adsorbents can also be used. Further, if necessary, a carbonaceous adsorbent containing a metal oxide such as vanadium may be used. Now, conventionally, there has been known a method of desulfurizing exhaust gas by directly or injecting NH ₃ in advance and then passing it through a moving amount of carbonaceous adsorbent. However, since _SOx in the exhaust gas is adsorbed as sulfuric acid and ammonium salt, the performance of the carbonaceous adsorbent gradually decreases as shown by curve a in FIG. 2 due to contact with the exhaust gas. Furthermore, in desulfurization using a carbonaceous adsorbent, it has been known that the higher the moisture and oxygen concentrations in the exhaust gas, the better the adsorption effect of _SOx on the adsorbent, that is, the desulfurization effect can be improved. However, adding water and air to a large amount of exhaust gas to increase their concentration requires a large amount of water and/or air, which is undesirable as it leads to an increase in the amount of exhaust gas. The present invention aims to improve this problem, and is characterized by increasing the moisture and/or oxygen concentration in the exhaust gas at the portion where the performance of the adsorbent is significantly degraded, as shown by curve b in Figure 2. ing. That is, in the present invention, the exhaust gas is divided into two parts, and water and/or air are added only to the exhaust gas introduced from below. This makes it possible to increase the concentration of moisture and/or oxygen only in areas where the performance of the adsorbent in a cross-flow moving bed containing a carbonaceous adsorbent is significantly reduced, so that the desulfurization effect is achieved without the need for large amounts of water or air. can be raised. Three experimental examples of the present invention will be shown below, and the superiority of the efficiency improvement will be clarified. - Experimental Example 1 - After adding pitch and water to pulverized coal and kneading it, it was press-molded into a columnar body with a diameter of about 4 mm and a length of about 5 mm, and this was carbonized at a temperature of 850°C using combustion exhaust gas. A cross-flow moving bed reactor filled with 16.7 m ³ of adsorbent had a gas flow rate of 10,000 Nm ³ /h, a gas temperature of 145°C,
SO ₂ 1050ppmdry NO _X 300ppmdry, H ₂ O7.0%,
After injecting NH ₃ to the coal-fired boiler exhaust gas containing 4.0% O ₂ and 12.0% CO ₂ to a concentration of 525 ppmdry, the gas is divided into 1/3 from the bottom of the reactor, and water vapor is added to this portion of the exhaust gas. The solution was heated to 12% H ₂ O and passed through. In this case, the residence time of the adsorbent in the reactor is
It is set to 48h. Further, the adsorbent discharged from the reactor is regenerated by heating and reused. Under these conditions, the results shown in the table below were obtained for desulfurization performance and denitrification performance.

[Table] - Experimental Example 2 - Under the same boiler gas conditions and operating conditions as Experimental Example 1, the gas was divided into 1/3 from the bottom of the reactor,
Add air to the exhaust gas in this part to increase O ₂ to 7%
It was tempered and passed. Under these conditions, the results shown in the table below were obtained for desulfurization performance and denitrification performance.

[Table] - Experimental Example 3 - Under the same boiler gas conditions and operating conditions as in Experimental Example 1, the gas was passed through without being split and H ₂ O and O ₂ were tempered. Under these conditions, the results shown in the table below were obtained for desulfurization performance and denitrification performance.

[Table] As is clear from the above three experimental examples, the desulfurization performance is further improved by dividing the exhaust gas into two and conditioning the gas introduced from the bottom with water and/or air as in the present invention. I understand that.

[Brief explanation of drawings]

FIG. 1 shows an example of an apparatus for carrying out the desulfurization method according to the present invention. Figure 2 is a graph of the relationship between contact time with exhaust gas and desulfurization performance. In the figure: 1... moving bed reactor, 2... dust collector, 3... regenerator, 4... flow rate distributor (or damper).

Claims (1)

[Claims] 1. In the method of removing sulfur oxides by introducing the exhaust gas containing sulfur oxides directly or by injecting ammonia gas into a cross-flow type moving bed reactor filled with a carbonaceous adsorbent such as activated carbon, two or more exhaust gases are removed. An exhaust gas desulfurization method characterized in that water and/or air is injected into the exhaust gas flowing into the lower part of the exhaust gas to increase the water and/or oxygen concentration.