Dust-removing method

A method of removing dust collected from a gas passing through a filter group installed in a vessel body, the dust being removed from filter surfaces by backwashing in which an ejecting operation and a non-ejecting operation of a backwash high-pressure medium from a backwash nozzle toward the filter group are repeated, the method comprising:

• providing a dust-removing apparatus comprising:
• a high-pressure-medium source;
• a high-pressure-medium passage;
• a high-pressure-medium pressure accumulator tank disposed in the high-pressure-medium passage, the high-pressure-medium passage configured to enable the backwash high-pressure medium to be guided from the high-pressure-medium source to the backwash nozzle;
• an upstream open-close valve disposed in the high-pressure-medium passage between the high-pressure-medium pressure accumulator tank and the high-pressure-medium source;
• a downstream open-close valve disposed in the high-pressure-medium passage between the high-pressure-medium pressure accumulator tank and the backwash nozzle;
• an accumulator tank pressure gauge for detecting an accumulated pressure Pt in the high-pressure-medium pressure accumulator tank;
• and
• a filter inlet pressure gauge for detecting a filter inlet gas pressure Pf of the gas at the inlet of the filters,
• the method further comprising:
• opening the downstream open-close valve to perform the ejecting operation based on a control instruction signal in order to eject the high-pressure-medium stored in the high-pressure-medium pressure accumulator tank;
• and
• closing the downstream open-close valve to perform the non-ejecting operation based on a control instruction signal,
• wherein the downstream open-close valve is closed to perform the non-ejecting operation based on said control instruction signal generated before the accumulated pressure Pt becomes equal to or less than nine tenths of “1/critical pressure ratio” times the filter inlet gas pressure Pf.