JPS6111650B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for reducing SO ₂ in exhaust gas to sulfur, and more specifically, before introducing SO ₂ -containing exhaust gas into a reduction reactor in which carbonaceous particles are present, The present invention relates to a pretreatment method for SO ₂ -containing exhaust gas, which includes washing with water and then dehumidifying it.

SO ₂ using carbonaceous particles such as coal and coke
The method of reducing SO ₂ to sulfur has been used for a long time as a dry desulfurization method for exhaust gas containing SO 2 .
A relatively high concentration of SO ₂ in the exhaust gas is generally preferred in this method. Therefore, when treating exhaust gas with a relatively low SO ₂ concentration, such as exhaust gas from a coal boiler, using the above reduction method, the exhaust gas is removed using a flue gas desulfurization device containing an adsorbent such as activated carbon.
A method has been adopted in which SO ₂ is concentrated in advance and then supplied to the reduction reactor.

By the way, as methods for reducing SO ₂ using carbonaceous particles as a reducing agent, there are two methods: the classical method, which is carried out at a temperature of about 900 to 1300 °C without almost any water vapor in the reaction system, and the classical method, which is carried out at a temperature of about 1150 to 1550 °C in the presence of water vapor. 〓(approximately 621~
A method is known in which the reduction reaction is carried out at a temperature of about 843° C., but the latter method is currently mainly used because the reduction reaction can be carried out at a relatively low temperature. In this method, it is customary to additionally mix water vapor with the _SO2- containing gas supplied to the reduction reactor, so approximately 15 to 40% of the gas sent from the flue gas desulfurization equipment to the reduction reactor is Conventionally, the presence of water has not been a problem at all.

However, when the present inventors tried the above-mentioned reduction method, which can reduce SO ₂ to sulfur at a relatively low temperature, it was found that this reduction method, like the classical method that is carried out at a relatively high temperature, caused a loss in the reaction system. It was found that the absence of water vapor in the SO ₂ reduction can suppress the by-product of hydrogen sulfide, and therefore improve the sulfur production rate. In addition, SO ₂ -containing exhaust gas that is conventionally treated in a reduction reactor, including SO ₂ -containing gas discharged from flue gas desulfurization equipment, generally contains halides, ammonium salts, and sulfates. It is preferable to remove the above-mentioned impurities from the SO ₂ -containing exhaust gas in advance before introducing it into the reduction reactor, since it has an adverse effect not only on the reduction reactor but also on the sulfur condenser and the like following the reactor.

The present invention embodies these findings, and is characterized by introducing SO ₂ -containing exhaust gas into a reactor in which a moving bed of carbonaceous particles exists,
In the method of reducing SO ₂ in exhaust gas to vaporized sulfur in the temperature range of 700 to 900°C, the exhaust gas containing SO ₂ is washed with water and then dehumidified before being introduced into the reactor. There is a particular thing.

Hereinafter, the present invention will be explained in more detail with reference to Examples. Fig. 1 is a flow sheet in which SO ₂ in coal boiler exhaust gas is concentrated in a flue gas desulfurization equipment and then reduced to sulfur according to the method of the present invention. shows. 1st
In the figure, the exhaust gas from the coal boiler is in line 1.
The gas is supplied to a flue gas desulfurization device 2 containing an adsorbent such as activated carbon. In the desulfurization equipment 2, the SO _{2 in the exhaust gas is concentrated by adsorbing the SO 2 in} the exhaust gas onto an adsorbent and then desorbing it.
Gas containing SO ₂ at a higher concentration than the gas flowing through line 1 is discharged from flue gas desulfurization device 2 to line 3 . Line 3 flue gas desulfurization equipment exhaust gas is normal
At temperatures of 200 to 400°C, impurities such as halides, ammonium salts, and sulfates are usually entrained.

According to the method of the present invention, the SO ₂ -containing gas discharged from the flue gas desulfurization device into the line 3 is first introduced into the water washing tower 4 . In the water washing tower 4, the washing water supplied into the tower from the line 5 is brought into contact with the SO ₂ -containing gas, and through this contact, the water-soluble impurities in the SO ₂ -containing gas are transferred to the washing water, and the SO ₂ -containing gas is transferred to the washing water. The gas itself is slowly cooled. Washing water containing dissolved water-soluble impurities is sent to the washing tower 4.
from the bottom via line 6 to storage tank 7.
The cleaning liquid in the storage tank is sprayed into the washing tower together with make-up water from line 9 via pump 8 and line 5. The cleaning waste liquid whose cleaning ability has decreased is taken out from the storage tank 7 to the line 10 and used as makeup water after water treatment.

The SO ₂ -containing gas washed and cooled in the water washing tower 4 is taken out from the top of the tower into a line 11 and supplied to a dehumidifier 12 . Dehumidifier 12 used in this example
is a type of shell-and-tube heat exchanger, in which _SO2- containing gas passes through many vertically arranged pipes.
The coolant supplied from line 13 and discharged from line 14 passes through the outside of the pipe. The SO2 _- containing gas passing through the inside of the tube is cooled by indirect heat exchange with the coolant, so moisture (water vapor) in the gas is condensed and separated from the gas, and this condensed water is sent to the dehumidification tower 12. Storage tank 7 via line 15 from the bottom
sent to. SO ₂ thus sent to the dehumidifier 12
The contained gas is dehumidified to less than a few percent moisture, and the temperature is 0℃~
It is taken out from the dehumidifier 12 into the line 16 at a temperature of several degrees Celsius.

The cooled and dehumidified SO ₂ -containing gas in the line 16 is then heated to 200° C. to 400° C. in an indirect heater 17 and then introduced into the reduction reactor 18 . The reduction reactor 18 has a moving bed of anthracite and is heated to approximately 800°C.
It is maintained at a temperature of ~840℃. Contact with this moving bed reduces the SO ₂ in the gas to vaporous sulfur, and the reactor effluent containing vaporous sulfur is taken off to line 19 and then sent to a sulfur condenser (not shown) in the conventional manner. Processed with a sulfur recovery system equipped with

Figure 2 shows the relationship between reduction reaction temperature and sulfur yield in the example shown in Figure 1 (see curve A),
This is a graph showing the relationship between the reduction reaction temperature and the sulfur yield (see curve B) when the SO ₂ -containing gas flowing through the line 3 is directly supplied to the reduction reactor 18 without passing through the water washing tower 4 and the dehumidifier 12. be. As shown in the figure, by dehumidifying the SO ₂ -containing gas introduced into the reduction reactor in advance, the sulfur yield can be improved by about 10% compared to the case without dehumidification.

In addition, since the present invention includes a dehumidification process for SO ₂ -containing gas, the gas can be washed with water before the dehumidification process, and impurities in the gas are removed by this water washing, which is different from the conventional method. Thus, the reduction reactor, sulfur condenser, etc. are not adversely affected by impurities in the gas.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing an example of the present invention, and FIG. 2 is a graph showing the relationship between reduction reaction temperature and sulfur yield. 2; flue gas desulfurization device, 4; water washing tower, 7; washing water storage tank, 8; pump, 12; dehumidifier, 17; indirect heater, 18; reduction reactor.

Claims (1)

[Claims] 1 In a method for reducing SO ₂ in the exhaust gas to vaporized sulfur in a temperature range of 700 to 900°C by introducing the SO ₂ -containing exhaust gas into a reactor in which a moving bed of carbonaceous particles exists, the SO ₂ -containing exhaust gas A method for reducing SO ₂ in exhaust gas to sulfur, which comprises washing with water and dehumidifying SO 2 before introducing it into a reactor.