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1. Wood
Celbi produces a high quality short fibre pulp from Eucalyptus globulus.
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2. Debarking and Chipping
The wood is debarked and converted into chips that are gathered in an open silo.
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3. Wood Cooking
After a screening process, the chips are fed into a continuous digester together with white liquor (cooking chemicals) and steam. These chemicals dissolve the lignin, which is the substance responsible for binding the cellulose fibres together, freeing these fibres. The result is the so called unbleached pulp.
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4. Pulp Washing
The unbleached pulp is then washed to remove residual products, organic and inorganic, which result from the cooking process and it is next submitted to screening operations that will remove uncooked particles and other impurities. After these operations, the unbleached pulp is pre-bleached with oxygen, thus becoming semi-bleached pulp – a yellowish pulp that is sent to the bleaching plant.
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5. Pulp Bleaching
When entering the bleaching plant, the pulp still contains residual compounds resulting from the degradation of lignin. These are gradually removed through chemical reactions with bleaching agents such as oxygen, hydrogen peroxide and chlorine dioxide. By the end of this phase, the pulp looks like a white bulky suspension.
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6. Pulp Drying
The bleached pulp suspension is subject to a final screening and depuration before entering a running wire where most of the water is taken away by vacuum. A subsequent set of roll presses and steam heated cylinders do the drying. When dried, the wide pulp sheet is cut into smaller sheets that are wrapped in bales of 250 kg each and then carried to the pulp warehouse.
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7. Pulp Bales
In the pulp warehouse, the bales are grouped and wired into units of 8 bales each that are neatly piled up until they are transported by truck either to the commercial seaport or directly to the client.
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8. Chemicals Recovery
The diluted black liquor resulting from the cooking of the wood chips is concentrated by evaporation after leaving the digester, until a thick bio-fuel is achieved. This concentrated black liquor is then burnt in the recovery boiler. The inorganic chemicals of the black liquor form a substance that after dilution in water turns into green liquor, mainly consisting of sodium carbonate and sodium sulphide. In the so called causticizing process, lime is added to the green liquor, thus producing white liquor (sodium hydroxide and sodium sulphide) and calcium carbonate. The latter, in suspension, is then removed and dried, to be transformed back into lime in the lime kiln. Closing this cycle, the white liquor regenerated at the causticizing plant is re- used in the cooking process.