Abstract: A method of utilizing lignin-containing material separated from spent kraft pulping liquor including: acidifying the liquor to a pH not less than seven thereby precipitating solid particles, separating precipitated solid particles from the accompanying liquid, and subjecting the separated precipitated solid particles to a washing process in which: the separated precipitated solid particles are washed with an aqueous medium or aqueous media in one or more washing steps, in each one of the washing steps, the aqueous washing medium contains, in a dissolved form, significant amounts of one or more added sodium salts, and a combined concentration of the added sodium salts in the washing medium in each of the washing step exceeds three percent by weight; and utilizing as fuel in a lime kiln at least part of the washed lignin-containing material is utilized as fuel in a lime kiln of a pulp mill.

Abstract: A method used in connection with the recovery of pulping chemicals from spent pulping liquor produced by kraft-type pulping at very high sulphidity. In the method, spent pulping liquor is acidified to a relatively low pH which converts a most or all of the sulphide and hydrosulphide in the liquor to hydrogen sulfide. Sulphur containing gases released from the acidification of the spent pulping liquor, together with other sulphur gases collected at the pulp mill, are converted into an acid compound. This acid compound is employed as an acidification agent in the acidification of the spent pulping liquor. The amount of acid compound generated by the conversion of sulphur containing gases may be sufficient to provide most, if not all, of the acid needed for the acidification of the spent pulping liquor.

Abstract: A method to be used in conjunction with a single-stage or multi-stage process for leaching ash originating from the recovery boiler of a pulp mill, particularly when the ash contains a significant amount of carbonate, wherein calcium compounds, such as calcium oxide (CaO) or calcium hydroxide (Ca(OH)2), are employed as additives in one or more leaching stages, a liquid fraction formed in the leaching process is utilized outside the main chemical recovery cycle, such as a substitute for purchased sodium hydroxide in the bleaching line of the pulp mill, and a solids fraction may be mixed with a black-liquor stream of the mill or subjected to further processing to separate calcium compounds for recycle.

Abstract: A method for handling spent wash solution produced in the washing of lignin that has been precipitated and then separated from spent alkaline pulping liquor. At least part of the spent wash solution is introduced into the chemical recovery cycle at a location in that part of the cycle which starts at, and includes, the smelt dissolving stage and ends at, and includes, the pulping stage. In preferred embodiments, input of other water and/or aqueous solution into the chemical recovery cycle after the recovery boiler is adjusted so that, as a consequence of the introduction of the spent wash solution, the amount of water in the white liquor going to the pulping line is not significantly increased. Among others, two preferred locations for the introduction of the spent wash solution are (1) the smelt dissolver and (2) the location where unwashed lime mud is diluted.

Abstract: A method of utilizing lignin-containing material separated from spent kraft pulping liquor including: acidifying the liquor to a pH not less than seven thereby precipitating solid particles, separating precipitated solid particles from the accompanying liquid, and subjecting the separated precipitated solid particles to a washing process in which: the separated precipitated solid particles are washed with an aqueous medium or aqueous media in one or more washing steps, in each one of the washing steps, the aqueous washing medium contains, in a dissolved form, significant amounts of one or more added sodium salts, and a combined concentration of the added sodium salts in the washing medium in each of the washing step exceeds three percent by weight; and utilizing as fuel in a lime kiln at least part of the washed lignin-containing material is utilized as fuel in a lime kiln of a pulp mill.

Abstract: A method to be used in conjunction with a single-stage or multi-stage process for leaching ash originating from the recovery boiler of a pulp mill, particularly when the ash contains a significant amount of carbonate, wherein calcium compounds, such as calcium oxide (CaO) or calcium hydroxide (Ca(OH)2), are employed as additives in one or more leaching stages, a liquid fraction formed in the leaching process is utilized outside the main chemical recovery cycle, such as a substitute for purchased sodium hydroxide in the bleaching line of the pulp mill, and a solids fraction may be mixed with a black-liquor stream of the mill or subjected to further processing to separate calcium compounds for recycle.

Abstract: A method used in connection with the recovery of pulping chemicals from spent pulping liquor produced by kraft-type pulping at very high sulphidity. In the method, spent pulping liquor is acidified to a relatively low pH which converts a most or all of the sulphide and hydrosulphide in the liquor to hydrogen sulfide. Sulphur containing gases released from the acidification of the spent pulping liquor, together with other sulphur gases collected at the pulp mill, are converted into an acid compound. This acid compound is employed as an acidification agent in the acidification of the spent pulping liquor. The amount of acid compound generated by the conversion of sulphur containing gases may be sufficient to provide most, if not all, of the acid needed for the acidification of the spent pulping liquor.