There are quite a few steps to the process of turning trees into premium office paper. We take pride in doing it with great devotion and attention to details – two out of many ways in which the Multicopy staff ensure that the raw material turn into premium-quality paper, every time. Once the wood is harvested and transported to Nymölla Mill (most of it from less than 100km radius) it’s time to turn the raw material into pulp.
Pulp is the foundation of paper. The mission with the pulp mill is to separate the cellulose fiber from the lignin and other wood substances, which is done in large pressure vessels called digesters. Lignin is a complicated chemical compound which connects wood fibers to each other.
There are two types of processes that can be used to remove the lignin from the wood chips; sulphite or sulphate. At Nymölla mill where Multicopy is produced we are using the magnesium based sulphite process. A great benefit of the sulphite process is easier bleaching methods. Both the sulphite and the sulphate processes are chemical pulping, combination of wood chips and chemicals.
The wood raw material consists of roundwood (mostly spruce, pine, beech and aspen) and sawmill chips. In the woodroom, the wood is debarked in 25 metre-long barking drums and chipped. The bark is collected, dewatered and burned in the boilerhouse to produce energy. It is essential that each chip is the right size and is cut at the correct angle. Everything is carefully calculated so that the lignin that holds the wood fibers together is dissolved to just the right extent during cooking.
Soft wood chips must be stored in chip piles for about 6 weeks to break down resin and other extractive substances. The huge pile of chips is used up section by section, to ensure that we are using chips that have been stored for the requisite length of time. After storage, the chips are transported to the digester.
During the cooking of the chips, the cellulose fibers are separated from the lignin and other wood substances, which are dissolved in the digester liquor. This consists of magnesium bisulfite, which is why the pulp is called magnefite pulp. Cooking is done in batches, each of which cooks for approximately eight hours.
After the chips have cooked to paper pulp, the pulp is screened and washed. The digester liquid, with its content of dissolved wood substances and digester chemicals, is separated from the pulp in a form known as weak liquor.
The recovery process for digester chemicals includes the evaporation of the weak liquor to thick liquor, combustion of the thick liquor in two recovery boilers and the preparation of new cooking liquor from the recovered chemicals. The recovery rate for digester chemicals is at least 95%. In addition to the recovery boilers, there is a solid fuel boiler. In this, bark, twigs, screening rejects, fuel chips, ultrafiltration concentrate and sludge from the wastewater treatment plant, as well as oil and LPG, are burned. The steam from the boilers is transported to two back-pressure turbines that produce approximately 30 MW of electrical power.
After screening and washing, the pulp is bleached. Oxygen, sodium hydroxide and hydrogen peroxide are used as bleaching chemicals. All the pulp produced at Nymölla is thus totally chlorine-free (TCF) pulp, since no chlorine-based chemicals are used for bleaching. The bleaching process takes from 8-12 hours. After bleaching, the pulp is screened one last time.
Keep an eye out for ”From wood to fine paper, part 2: Paper making”, it will be presented shortly/later this season.
Humans’ urge to communicate has always been strong – and with the evolution of paper, the written form of communicating opened a whole new world of efficiency, suddenly dismantling geographical boundaries. Naturally, the history of papermaking is closely connected to societal, industrial, and cultural events.
Eco-awareness and higher demands on sustainability features among customers tend to lead to good things. One current example is the initiated project at Stora Enso to certify all paper pulp grades as compostable, to helps consumers make more eco-friendly choices.
In 2021, the Multicopy production base in Nymölla mill took a step further in the fossil free journey, with Stora Enso entering a partnership with energy company Gasum. We had a talk with Erik Woode, Director, Project Development & Execution, at Gasum, to get a status update after one year of turning residue water from production into fossil free fuel.