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Industrial Process
Bleaching
Pulp’s natural color is white, but during removal of lignin in the early stages of production it is changed to light brown by the oxidation of organic matter in the wood. To remove this coloration and return it to white, the pulp is submitted to chemical treatment with oxidizing agents in reactors with controlled temperature, pH and retention time. This process is carried out in 3 stages (Ado/EP/D), and at the end of each stage the pulp is washed in DDW rotational filters in order to remove colored oxidized compounds.
Acid Stage (ADo – A) - The objective is to remove the hexenuronic acids by acid hydrolysis. This stage uses retention times of approximately 3 hours, with controlled pH and temperature. Lwarcel’s acid stage is unique in relation to other pulp plants because it uses residual acid from the chlorine dioxide generating plant rather than sulfuric acid. Zero Dioxidizing Stage (ADo – Do) - This is the first dioxidizing stage in bleaching. Its objective is to oxidize the compounds which color the pulp, using chlorine dioxide. This stage uses retention times of 15 minutes, with controlled pH and temperature. Oxidative Extraction Stage with Hydorgen Peroxide (EP) – The objective of this stage is to make soluble in an alkaline medium the chromophoric (color-giving) compounds oxidated in the previous stages and to increase whiteness, utilizing hydrogen peroxide. This stage uses retention times of 90 minutes, with controlled pH and temperature. Dioxidation Stage (D) - This is the second dioxidation stage. Its objective is to oxidize the compounds which color the pulp, utilizing chlorine dioxide. This stage uses retention times of 3 hours, with controlled pH and temperature. All bleached pulp is stored in a storage tower before being sent for the final stage in the process.
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