JPH05306813

PURPOSE:To avoid combustion in an excess air ratio and perform combustion in a proper air ratio by recovering a large amount of water having an intermediate temperature, which is obtained by cooling and washing a heated exhaust gas generated by combustion, utilizing water thus obtained as heat source water for operating a heat pump, and also humidifying the exhaust gas after it is cooled and washed. CONSTITUTION:An exhaust gas generated after combustion of fuel in a combustion device 1 is washed by pouring water in a washing column 11. Heat is recovered from the wash liquid, whose temperature is elevated by pouring water, by a heat exchanger 14. After the exhaust gas is washed, it exchanges heat with combustion air in a humidifying column 13 to elevate a temperature of the combustion air and to humidify said air. The air thus treated is used as combustion air for combustion.