Chemical Recovery
The spent cooking liquor from sulfite pulping is usually called brown liquor, but the terms red liquor, thick liquor and sulfite liquor are also used (compared to black liquor in the kraft process). Pulp washers, using countercurrent flow, remove the spent cooking chemicals and degraded lignin and hemicellulose. The extracted brown liquor is concentrated, in multiple effect evaporators. The concentrated brown liquor can be burned in the recovery boiler to generate steam and recover the inorganic chemicals for reuse in the pulping process or it can be neutralized to recover the useful byproducts of pulping. Recent developments in Chemrec's black liquor gasification process, adapting the technology to use in the sulfite pulping process, could make second generation biofuels production an alternative to the conventional recovery boiler technology.
The sulfite process can use calcium, ammonium, magnesium or sodium as a base.
Read more about this topic: Sulfite Process, Processes Involved in Sulfite Pulping
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