Abstract Method for reducing the amount of waste products discharged from cellulose pulp mills to limit the pollution of recipient water into which the wastes are finally discharged. The amounts of coarse pulp waste products as well as fines which pass the dewatering wire cloths are reduced in a single treatment stage, while sulphides and resin acids with black liquor residues left in the pulp are chlorinated and/or oxidized before they are discharged into the recipient water. The volume of waste water is kept small. The process is characterized by the omission of the conventional washed unbleached pulp screening operation and passage of the unbleached pulp and wash medium directly to the bleaching operation. The unbleached pulp washing step is performed with aqueous supplanter, e.g., white water or vapor condensate, and is to be distinguished from fresh water washing.
A method according to claim 1 wherein a fraction of incompletely converted material passing from the oxidation step (b) is separated by immediate screening of pulp in suspension with the aqueous solubilized chemicals-pregnant discharge and then added to the brown stock and returned therewith to the oxidation step with an additional amount of the oxidizing chemical for repeated fibre liberating delignification, thereby reducing the discharge of oxidized waste materials and further increasing the yield of finally bleached cellulose fibre.
Claim 2
Dependent Claim
44 words
A method according to claim 1 wherein sodium compounds are used with oxygen in step (b), producing an aqueous extraction discharge from step (d), said chemicals-pregnant discharge containing alkaline solubilized oxidation products, and including passing said sodium compounds to a digestion liQuor regeneration process.
Claim 3
Dependent Claim
50 words
A method according to claim 1 in which the pulp manufacturing process is the sulphate process and pulp-entrained black liquor containing toxic and malodorous sulphide compounds from the brown stock washing step (a) is recovered to a digestion liquor regeneration process as a component of the discharge of step (d).
Claim 4
Dependent Claim
128 words
A method according to claim 1 when chlorinating chemicals are selected for oxidation in step (b) wherein an amount of the chlorinating oxidizer is consumed in addition to the demand of the actual pulp bleaching and wherein chlorine dioxide replaces chlorine to achieve high efficiency oxidation of black liquor and vapor condensate residues which are extractable by water, while the transport of aqueous solubilized chemicals-pregnant and incompletely digested material to the subsequent alkaline extraction washing stage is adjusted by recovery of solubilized products containing alkaline filtrate with only small amounts of chlorine compounds to a digestion chemicals regeneration process by supplanting residual black liquor from the brown stock in step (a) with said alkaline filtrate from step (d) and then with vapor condensate and a chlorinating stage effluent.