Pulping

It is obtained by removing lignin and other impurities from the wood & other raw materials used by a cooking process (Lignin is the glue that holds the fibers of the wood in three form). The cooking process requires wheat straw, wood bamboo or other raw materials. The wheat straw are loaded into a digester and a cooking liquor is added. Then by pressure and steam cooking, the wheat straw or other fibers are separated from other unwanted ingredients. Either batch digester or continuous digesters are used in cooking.

The chips and liquor are mixed as the chips are pumped to the top of the digester. The top section of the digester is pressurized. to 160 psi and more. As the chip mass passes downward the cooking liquor penetrates the chip. After about 45 minutes or more as per raw material the chips have to be passed through the impregnation zone where hot liquor (340 degree F) is circulated through the chips for heating. The actual pulping occurs at 355 degree F in about 90 minutes, a period known as the cooking period. After passing through the cooking zone, the chips (which have not become pulp) are washed with weak liquor from washing stages that follow.

Within the chemical process there are two types -

Sulphate Process "(Alkaline process)"

Sulphite Process "(Acid process)"

Some hard woods may be dissolved with difficulty by the sulphite process. On the other hand, the sulphate process most of the chemicals are recovered and reused. Used Paper is another important source of paper fiber. The paper is shredded and mixed with water..