초록 ▼

Acid and alkaline filtrates are separated from the bleach plant of a bleached pulp mill for use in washing unbleached pulp free from entrained pulping liquor. Acid effluent is neutralized with sodium hydroxide solution prior to use in the washing as the last washing step while alkaline filtrate is u

Acid and alkaline filtrates are separated from the bleach plant of a bleached pulp mill for use in washing unbleached pulp free from entrained pulping liquor. Acid effluent is neutralized with sodium hydroxide solution prior to use in the washing as the last washing step while alkaline filtrate is used in the remainder of the washing. Part of both the acid and alkaline filtrates are not used in the washing to allow bleed of calcium value and caustic extraction stage solids which otherwise would build up on the washed pulp mat passing to the bleach plant.

대표청구항 ▼

In a pulp mill system having a pulping and recovery and regeneration cycle and a bleaching and purification operation including the steps of digesting new raw cellulosic fibrous material in a pulping liquor, washing the digested cellulosic fibrous material substantially free from spent pulping liquo

In a pulp mill system having a pulping and recovery and regeneration cycle and a bleaching and purification operation including the steps of digesting new raw cellulosic fibrous material in a pulping liquor, washing the digested cellulosic fibrous material substantially free from spent pulping liquor, forming an aqueous spent liquor containing spent pulping liquor and spent wash water from said washing step, subjecting said aqueous spent liquor to furnacing to form a smelt, subjecting said washed digested cellulosic fibrous material to said bleaching and purification operation using bleaching chemicals including chlorine atoms and sodium hydroxide extraction solutions, washing said bleach and purified pulp substantially free from residual bleaching and purification chemicals, recovering a washed, bleached and purified pulp from said bleaching and purification operation, separating from said bleaching and purification operation an acid aqueous filtrate and an alkaline aqueous filtrate, said latter filtrates in combination including all the aqueous material introduced to said bleaching and purification operation less any water present in said washed, bleached and purified pulp, introducing said latter filtrates to said pulping and recovery and regeneration cycle, whereby said smelt contains sodium chloride, regenerating pulping liquor from the components of said smelt, recycling said regenerated pulping liquor as at least part of said pulping liquor in said digestion step, and separating solid sodium chloride from said pulping and recovery and regeneration cycle subsequent to said furnacing step and prior to said recycling step, the improvement wherein said introduction of said filtrates to said pulping and recovery and regeneration cycle is carried out by: neutralizing part only of said acid filtrate with fresh aqueous sodium hydroxide solution for use as wash water, using said neutralized filtrate as wash water for washing said digested cellulosic fibrous material in the portion of said washing step immediately prior to passage of washed pulp to said bleaching and purification operation, and using part only of said alkaline filtrate as wash water for washing said digested cellulosic fibrous material prior to said washing with said neutralized filtrate in the remainder of said washing step, whereby said washing step is carried out wholly by said neutralized filtrate and said part of said alkaline filtrate.