readily separable powder form it is advantageous that the temperature is higher than room temperature preferably higher than 40 u00b0 c a mixture of water and removed scale collected in the upper compartment of the prenum chamber 80 is sent to a water scale separator 41 where the scale is collected in a cyclon collector 42 while the water separated is returned to the fuel pool not shown through a back filter 44 by a pump 43 energized by a switch 45 a gas water separator 57 is supplied with water in the fuel pool by a water pump 52 via pipes 51 and 56 a valve 53 and an ejector 55 when water passes through the ejector 55 a negative pressure is created to draw the gas in the tank 31 via pipe 50 and valve 54 the drawn out gas is discharged into the gas water separator 57 through pipe 56 together with the water passing through the ejector 55 the gas in the gas water separator 57 is discharged to the outside in a harmless state by a pump 62 via a pipe 58 a valve 59 a water remover 60 and a dust filter 61 which removes harmful dust which may remain in the gas the water.