| 摘要 |
The subject of the invention is a new method to be used in connection with the recovery of pulping chemicals from the spent pulping liquor produced by kraft- type pulping at very high sulphidity. The sulphidity is most preferably in the range 70–100 %. In the new method, spent pulping liquor (5) is acidified to a relatively low pH, preferably below 7, most preferably below 6, in order to convert a large part, or all, of the sulphide and hydrosulphide in the liquor into H2S. Sulphur containing gases (19), mainly H2S, released from the spent pulping liquor, together with other sulphur gases collected at the pulp mill, are converted into an acid compound, preferably H2SO4 (9), which is then employed as an acidification agent in the previously mentioned acidification step. The amount of acid thus generated is sufficient to provide most, if not all, of that required for the acidification step. The acidification of the spent pulping liquor may be further exploited as a means to increase recovery of by-products and/or to purge non-process elements from the chemical-recovery cycle. |
