Exhaust-gas treatment apparatus and exhaust-gas treatment method

Abstract

An object is to provide an exhaust-gas treatment apparatus capable of realizing a dissolved-salt spray method easily and at low cost. An exhaust-gas treatment apparatus that removes SO2 and SO3 contained in combustion exhaust gas includes a desulfurization apparatus based on the lime-gypsum method. Desulfurizing effluent, containing dissolved salt, from the desulfurization apparatus is sprayed to an upstream side of the desulfurization apparatus to remove SO3. A wet electrical dust precipitator may be provided downstream of the desulfurization apparatus. Furthermore, effluent from the wet electrical dust precipitator may be made to merge with the desulfurizing effluent from the desulfurization apparatus.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application is a divisional application of U.S. Ser. No. 12 / 593,300, filed Sep. 28, 2009, which is a National Phase filing of PCT / JP2008 / 056300, filed Mar. 31, 2008, which is based on and claims the benefit of priority in Japanese Patent Application No. 2007-092512, filed Mar. 20, 2007, the entire contents of all which are incorporated herein by reference.TECHNICAL FIELD[0002]The present invention relates to an exhaust-gas treatment apparatus and an exhaust-gas treatment method for removing SO3 from combustion exhaust gas.BACKGROUND ART[0003]Combustion exhaust gas including sulfur oxides, such as SO2 and SO3, is emitted from a combustion furnace in which fuels containing at least 0.5 wt % sulfur content, such as heavy fuels or coal fuels, are combusted.[0004]SO3 is produced as a result of partial oxidation of SO2 at high temperatures. Therefore, the presence of SO3 is about a few percent relative to SO2. Nevertheless, the concentrati...

AI Technical Summary

Benefits of technology

"The present invention provides an exhaust-gas treatment apparatus and method that includes a desulfurization apparatus based on the lime-gypsum method and a spray section that sprays desulfurizing effluent from the desulfurization apparatus to an upstream side of the desulfurization apparatus. The apparatus can easily and at low cost realize the dissolved-salt spray method, which is a process for removing sulfur dioxides and sulfur trioxides from combustion exhaust gas. The desulfurization apparatus uses a dissolved salt that is easily obtained and can be recovered and reused without the need for a new chemical. The spray section sprays the desulfurizing effluent to the upstream side of the desulfurization apparatus, where the moisture content evaporates and the particles of dissolved salt adsorb and fix contaminants in the gas. The recovered dissolved salt is then sprayed again, resulting in a higher concentration of dissolved salt in the effluent and reduced operating costs. The spray section should have an exit temperature equal to or higher than the water evaporation temperature and the reaction with the dissolved salt should occur at the dew point temperature or higher to ensure optimal performance."

Problems solved by technology

Desulfurization apparatuses based on the caustic soda method or the water magnesite method can process only about 200,000 to 300,000 Nm3 of combustion exhaust gas, considering that the chemical solution to be used is expensive and that the effluent flow rate is high.

However, it is believed that a dissolved salt in desulfurizing effluent is difficult to use with the lime-gypsum method because this method involves poorly soluble gypsum (CaSO4) in the desulfurizing effluent, and hence, a dissolved salt has been obtained from a separately provided small-scale desulfurization apparatus based on the caustic soda method (refer to FIG. 2 in Patent Document 1).

Because such an approach is disadvantageous in that additional cost is entailed in the new facility, there has been a growing need for an exhaust-gas treatment apparatus that includes a desulfurization apparatus based on the lime-gypsum method yet is still capable of realizing the dissolved-salt spray method more easily at lower cost.

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