In addition to liquor recovery, pulp mills recover a significant portion of energy from burning waste materials and by-products of the process in power boilers. Materials such as bark, wood waste and dried sludge collected from effluent treatment systems may be burned to provide steam to power electrical generators.
Pulp and paper mills consume vast amounts of fresh water. A 1,000 tonne per day bleached kraft pulp mill may use more than 150 million litres of water a day; a paper mill even more. In order to prevent adverse effects on mill equipment and to maintain product quality, the incoming water must be treated to remove contaminants, bacteria and minerals. Several treatments are applied depending on the quality of the incoming water. Sedimentation beds, filters, flocculants, chlorine and ion exchange resins are all used to treat water before it is used in the process. Water that is used in the power and recovery boilers is further treated with oxygen scavengers and corrosion inhibitors such as hydrazine and morpholine to avoid deposits forming in the boiler tubes, to reduce metal corrosion, and to prevent carry-over of water to the steam turbine.