Patent ID: 8778041

Claim:
An exhaust gas treatment device for an oxygen combustion system, the exhaust gas treatment device comprising: an exhaust gas treatment unit in which a denitration device that denitrates a nitrogen oxide in an exhaust gas generated from an oxygen combustion boiler using coal as fuel, an air preheater that preheats combustion air of the oxygen combustion boiler with the exhaust gas at an outlet of the denitration device; a dust-collection device that collects smoke dust in the exhaust gas at an outlet of the air preheater, a desulfurization device that desulfurs a sulfur oxide in the exhaust gas at an outlet of the dust-collection device, and a carbon dioxide recovery device that recovers a carbon dioxide in the exhaust gas at an outlet of the desulfurization device are sequentially arranged from the upstream side to the downstream side of an exhaust gas duct; and an exhaust gas circulation unit comprising an exhaust-gas circulation line which branches off from the exhaust gas duct at the outlet of the dust-collection device or the outlet of the desulfurization device and through which the exhaust gas is preheated by the air preheater and returned to the oxygen combustion boiler as the combustion air, wherein a heat-recovery heat exchanger that recovers heat from the exhaust gas at the outlet of the air preheater and comprises a first heat transfer pipe that recovers the heat of the exhaust gas into a heat medium is provided to the exhaust gas duct between the air preheater and the dust-collection device, and a reheating heat exchanger, comprising a second heat transfer pipe that heats the exhaust gas in the exhaust-gas circulation line by the heat medium supplied from the heat-recovery exchanger is provided to the exhaust-gas circulation line in the vicinity of a branch of the exhaust gas circulation unit, and an exhaust gas circulation fan provided to the exhaust-gas circulation line, wherein the reheating heat exchanger is provided between the branch of the exhaust gas circulation unit and the exhaust gas circulation fan, the exhaust gas treatment device further comprises: a heat medium circulation line communicatively connecting the first heat transfer pipe and the second heat transfer pipe such that the heat medium circulate in interiors of the first and second heat transfer pipes; a controller that controls an exhaust gas temperature at an inlet of the dust-collection device to be not greater than an acid dew point of SO3 and not lower than a water dew point, the controller controlling an exhaust gas temperature in the exhaust-gas circulation line, at an outlet of the reheating heat exchanger, to be not lower than the acid dew temperature of SO3; and an adjusting unit that is controlled by the controller to adjust at least one among a circulation amount of the heat medium flowing through the heat medium circulation line, a heat medium heating amount, and a heat medium cooling amount.