sulfatkraftprocess

The sulfatkraftprocess, commonly known as the Kraft process or sulfate process, is the dominant pulping process used worldwide for producing wood pulp. It is a chemical recovery process that converts wood into wood pulp by separating lignin from cellulose fibers. The process uses a mixture of sodium hydroxide and sodium sulfide, known as white liquor, to chemically break down the wood chips. This breaks the lignin bonds and allows the cellulose fibers to be liberated.

The wood chips are cooked under high pressure and temperature in a digester with the white liquor. This cooking process results in a mixture of pulp fibers and spent cooking liquor, called black liquor. The black liquor contains dissolved lignin, residual pulping chemicals, and other organic matter. The pulp is then washed and screened to remove impurities.

A crucial aspect of the Kraft process is its efficient chemical recovery system. The black liquor is concentrated and then burned in a recovery boiler. This combustion process generates heat, which is used to produce steam for power generation and also recovers inorganic chemicals. The inorganic chemicals are then reconstituted into white liquor, ready for reuse in the digester. This closed-loop system significantly reduces chemical consumption and waste.

The Kraft process is favored for its ability to pulp a wide range of wood species and produce strong fibers suitable for paper and paperboard products. However, it also produces a distinctive odor due to sulfur compounds, hence its historical name "sulfate process" and the term "sulfatkraftprocess" in some languages.