Air pollution control system and air pollution control method

An air pollution control system, comprising:

• a flue gas duct through which flue gas flows;
• a heat exchanger disposed in part of the flue gas duct;
• a limestone supply device for reducing SO3 in the flue gas provided to an upstream of the heat exchanger which supplies CaCO3to the flue gas;
• an upstream SO3 measurement device provided to a stream upper than a position where the limestone supply device for reducing the SO3 in the flue gas supplies the CaCO3, the upstream SO3 measurement device measures the SO3 in the flue gas,
• a downstream SO3 measurement device provided to a stream downer than the heat exchanger, the downstream SO3 measurement device measures the SO3 in the flue gas;
• and
• a control device which determines a quantity supplied of the CaCO3 based on a relationship between a quantity of the SO3 measured by the upstream SO3 measurement device and a molar ratio of SO3 to CaCO3, which corrects the determined quantity supplied of the CaCO3 based on a quantity of the SO3 measured by the downstream SO3 measurement device and which supplies to the flue gas duct the corrected quantity supplied of the CaCO3 from the limestone supply device for reducing the SO3 in the flue gas,
• wherein, among the upstream SO3 measurement device and the downstream SO3 measurement device, at least the downstream SO3 measurement device is configured to measure the gaseous SO3 and the mist-like SO3 in the flue gas independently each other.