Patent ID: 8202370

Claim:
A method for removing an acidic deposit containing a sulfur compound, which comprises: preparing an aqueous cleaning fluid comprising a prescribed molar amount of an alkali metal carbonate or alkali metal hydrogen carbonate; contacting the acidic deposit with a prepared aqueous cleaning fluid by spraying; collecting the contacted cleaning fluid; and recycling the collected cleaning fluid; measuring a rate of concentration increase of sulfate ion (SO 4 −2 ) in the aqueous cleaning fluid by repeated measuring at time intervals ranging from 20 to 60 minutes; determining a percent increase of the sulfate ion concentration per hour; and terminating the contact with the aqueous cleaning fluid after the increase per hour of the measured per cent increase becomes not more than 10%, wherein the prescribed molar amount of alkali mental carbonate is in the range of 1 to 2 moles per mole of the sulfur component and the prescribed molar amount of the alkali metal hydrogen carbonate is 2 to 4 moles per mole of the sulfur component.