To inhibit the soot blower from rising in temperature by forming the blower along a water-wall tube, bonding the blower to the water-wall tube with a metallic plate and cooling the blower by means of the water-wall tube.

A crude gas cooler 3 which cools a synthesis gas produced from a coal gasifier and based on CO, CO2 and H2 into a vapor is provided with many vertical water-all tubes 11. The soot adhering to the surfaces of the water-wall tubes are removed by means of one, per seven water-wall tubes, soot blower having many openings and a nitrogen gas feed pipe 13. The temperature of each water-wall tube is kept lower than that of the synthesis gas owing to the latent heat of vaporization of water. Since a nitrogen gas is fed into the soot blower and blows soot, it is cooled during that time; it is however exposed to the high-temperature synthesis gas except that time. However, because the stainless water-wall tube 11 is bonded to the blower 12 with a metallic plate 15, heat is transferred to the water-wall tubes 11c and 11e through the plate 15 to inhibit the blower 12 from rising in temperature.