Patent ID: 8302388

Claim:
An exhaust gas treating method comprising: preheating a combustion air of a combustion apparatus by an exhaust gas discharged from the combustion apparatus; recovering heat from the exhaust gas by a heat recovery unit after the air preheating; and recovering soot/dust in the exhaust gas at an exit of the heat recovery unit by a dry precipitator; wherein a nitrogen oxide in the exhaust gas is denitrated by a denitration catalyst before the air preheating; and a sulfur oxide in the exhaust gas is desulfurized at the exit of the dry precipitator, and wherein, after adjusting an exhaust gas temperature at the exit of the heat recovery unit to not more than a dew point temperature of sulfur trioxide, a heavy metal adsorbent is supplied into the exhaust gas at an entrance of the dry precipitator or into an intermediate position within the dry precipitator, and wherein the heat of the exhaust gas is recovered in a heating medium in the heat recovery unit, the heating medium is circulatingly supplied to a reheater, disposed for heating the desulfurized exhaust gas by the heating medium supplied from the heat recovery unit, or to a cooler, disposed for cooling the heating medium supplied from the heat recovery unit, and after adjusting the exhaust gas temperature at the exit of the heat recovery unit to not more than the dew point temperature of sulfur trioxide by at least one among a circulation amount of the circulating heating medium between the heat recovery unit and the reheater, a heating amount of the heating medium, and a cooling amount of the heating medium, the heavy metal adsorbent is supplied into the exhaust gas at the entrance of the dry precipitator or into the intermediate position within the dry precipitator.