The paper industry is one of the five industries with the largest energy consumption in the world - ranked 5th and accounts for 4% of global energy each year. According to a survey and assessment of Vietnam Paper Corporation, energy costs in pulp and paper production account for 20 - 30% of production costs. The main energy sources used are electricity, coal, DO oil and FO oil.
This energy is mainly used to run engines, burn boilers, dry and heat. In particular, boilers now play an important role for the paper industry to meet the growing demands and environmental standards of the global market.
The production of paper from pulp involves several steps that require heat and energy from steam boilers.
Flowchart of paper production from wood and recycled paper. Source: Internet
Pulping is the first step, which separates and cleans the fibers from wood, pulp, or recycled paper. In this step, steam boilers supply heat and steam for cooking the wood chips or pulp in chemical or mechanical pulping methods. The steam also helps to remove impurities and lignin from the fibers.
Refining, which beats and fibrillates the fibers to improve their bonding and strength. In this step, heat and steam from steam boilers are used for refining the pulp in disc refiners or conical refiners .
Dilution is the third step, which forms a thin fiber mixture with water and chemicals. In this step, the temperature and consistency of the stock are adjusted by heat and steam from steam boilers .
Formation is the fourth step, which lays out the fibers on a wire or forming fabric to form a wet paper web. In this step, water is drained from the web by gravity and vacuum suction boxes, which are heated by steam boilers .
Pressurization is the fifth step, which squeezes out more water from the web by passing it through nip rollers. In this step, steam boilers heat the press felts and rolls.
Drying is the sixth step, which evaporates the remaining water from the web by passing it over steam-heated cylinders. In this step, steam boilers provide heat and steam for drying the paper web to the desired moisture content
The final step is finishing, which smooths, sizes, coats, and calenders the paper web to improve its surface quality and properties. In this step, starch, coating materials, and gloss agents are applied to the paper web by heat and steam from steam boilers.
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