PULP MILL
Trees provide the primary raw material for the paper and board industry. Wood is made from cellulose fibres that are bound together by a material called lignin. In a pulp mill, the fibres are separated from one another into a mass of individual fibres and after separation, the fibres are washed and screened to remove any remaining fibre bundles. The pulp may then be used directly to make unbleached paper, or be bleached for white paper. Pulp may be fed directly to a paper machine in an ‘integrated paper mill’ or dried and pressed into bales to be used as a raw material by paper mills worldwide. Chipping is not necessary when mechanical pulp is produced as it can be made of round wood.
The pulp-making process
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Timber and de-barking  |
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Chipping machine and pulping process |
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4. Washing and drying  |
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Chemical pulp is stronger, but more expensive than mechanical pulp
Using chemical pulp to produce paper is more expensive than using mechanical pulp or recovered paper, but it has better strength and brightness properties. Softwood kraft pulp, one of the main chemical pulp grades, is used to provide the required strength when producing lightweight publication papers. Fine papers (for example copy papers, writing papers etc.) are an example of the type of paper produced mainly from hardwood pulp, which is reinforced by a small amount of stronger and more expensive softwood kraft pulp. Pine and spruce provide the strongest pulp (for example softwood kraft), while hardwood kraft is produced from birch, eucalyptus, aspen, acacia and many other mixed tropical species.
Today, the fast growing species of tree (such as planted eucalyptus and acacia) are the most rapidly growing pulp raw material.
| . | Mechanical Pulp | Chemical Pulp |
| Energy consumption | 1000 KW/tonne of pulp | Self-sufficient |
| Yield (from wood material) | 95% | 45% |
| Fibre length | Fibres broken | Mainly longer fibres |
| Paper strength | Lower | High |
| Production costs | Lower | Higher than in case of mechanical pulp |
