PURPOSE: To obtain high-purity gypsum by efficiently desulfurizing exhaust gases contg. Al-contg. dust at a high ratio and having a high HP concn.
CONSTITUTION: The charging of an alkaline metal compd. is started when the actually measured value of the pH of the circulating liquid in an absorption column falls to the value smaller than the predicted value of the pH of the circulating liquid in the absorption column based on the operating conditions of the above-mentioned desulfurization method and the device conditions of the absorption column. The charging of the above-mentioned alkaline metal compd. is continued until the actually measured value of the pH mentioned above attains the same value as the predicted value of the pH mentioned above or the value higher than this value or the alkaline metal compd. of the amt. to maintain the preset concn. of the alkaline metal ions in the circulating liquid in the absorption column is charged, by which the formation of hardly-soluble apatite (contg. F and Al) on the surface of a calcium absorbent is prevented.
UCHIYAMA MASAO
HIRUTA RYUICHIRO
NISHIMURA MASAKATSU
NOZAWA SHIGERU
MASUTOMI HIROSHI
BABCOCK HITACHI KK