Exhaust gas treatment device for an oxygen combustion system

Abstract

In an exhaust gas treatment device provided with: an exhaust gas treatment unit in which an oxygen combustion boilerusing coal as fuel, a denitration device, an air preheater, a dust-collection device, a desulfurization device, and a carbon dioxide recovery deviceare sequentially arranged from the upstream side to the downstream side of an exhaust gas duct; and an exhaust gas circulation unit which branches off from the exhaust gas duct at an outlet of the dust-collection deviceor an outlet of the desulfurization deviceand through which the exhaust gas is preheated by the air preheaterand returned to the oxygen combustion boiler, a heat-recovery heat exchangerthat adjusts a gas temperature at an inlet of the dust-collection deviceto be not greater than an acid dew point of SOand not lower than a water dew point is provided between the air preheaterand the dust-collection device, a reheating heat exchangerthat adjusts a gas temperature to be not lower than the acid dew point of SOis provided in the vicinity of a branch of the exhaust gas circulation unit, adjusting the gas temperature at the inlet of the dust-collection deviceto be not greater than the acid dew point of SOmakes it possible to prevent corrosion of pipes in the exhaust gas circulation unit and to avoid a decrease in fluidity or combustibility of the pulverized coal in the pipes in the mill.