A pulp mill is a facility where wood chips or other plant materials get converted into a thick board of fibre after this it can be shipped to a paper mill to be further processed. Wood chips and the other plant materials used to produce pulp are made up of three main components: cellulose, lignin and hemicellulose. The main aim of pulping is to break down the plant material or wood into their constituent fibres. 1 This process occurs in many steps.
The first is to shred the wood or plant material to increase the surface area. Now that the material has been shredded they are cooked under high pressure with chemicals to separate the lignin. The added chemical is white liquor. The lignin will dissolve into the white liquor and get pumped out of the digester, you know that the lignin has dissolved into the white liquor as it is a dark colour and will turn the liquor a black colour. After the dark liquor has been pumped out it can be recycled and used again. Not all the lignin will be removed this gives the pulp a brown colour.
So, the brown pulp is washed to remove any remaining lignin and chemicals present. This is achieved by using chemicals such as chlorine or hydrogen peroxide. At this point the pulp will have a very high-water content and will behave more like a liquid than a solid. The pulp is laid out in a larger sheet, suction and gravity are used to reduce the water content from about 99% to around 70%. Then a hot press roller will squeeze more water out it will then be passed through an industrial drier, these to processes will reduce the water content to about 10%. After this process the pulp is cut, pressed the packaged. 2 The pulp will then be used to produce cardboard, paper or other materials.
The pulp mill industry produces large amounts of water pollution. As the mills use chlorine in the ‘Kraft’ bleaching process to turn the brown stock into white stock, paper, the average mill will discharge around 40 million gallons of untreated water into the near shore areas. The discharged water will contain chlorinated organic compounds due to chlorine and chlorine dioxide being used in the pulping and bleaching process. These chlorinated organic compounds, they include chlorinated phenols and dioxins, may be toxic. The chlorine can change the pH of the water and harm animals, as suffers I areas where there are mills have complained of nausea and rashes when surfing in areas where the waste and be put into seas and oceans. The pulp mills also produce air emissions, which can be hazardous and irritating. 3A pulp mill produces not only pulp, it will also produce electricity and heat.
The gases produced contain large quantities of carbon dioxide. This carbon dioxide can be used in the production of vegetable and fish, as these processes require heat, electricity and small amounts of carbon dioxide. This carbon dioxide helps a great deal because the demand for fish is only increasing and 80% of the fish stocks of the ocean are fully exploited, so the only solution is to increase the fish production, and this is a good use for the carbon dioxide produced. 4 Deinking Mill OperationDeinking is the process of removing ink from paper fibres to produce deink pulp. The deinking process occurs in 5 steps which are as follows: 1) pulping 2) Ultrasonic treatment 3) Floatation Deinking 4) Wash deinking 5) Sludge Treatment. The purpose of pulping in a deinking process is to defibre paper and to detach the ink particles from the paper fibres.
The chemicals used in this process include hydrogen peroxide, chelating agents, sodium hydroxide and other chemicals. The use of ultrasound is to increase the efficiency of the deinking process. The ultrasound loosens large particle and helps to turn them into smaller particles. This benefits the process at a later stage in the floatation and washing deinking stages. The floatation deinking stage involves the use of a floatation cell to help remove ink that’s been released during the two previous steps. A fatty acid soap can be added at this process to collect the freed ink particles, so they can be removed by air bubbles.
The fatty acid soap added is a sodium soap, which needs to be converted to a calcium soap for it to be effective. The source of calcium is usually calcium carbonate used as coatings and fillers. The wash dinking stage is the last stage in which the fibres are deinked.
Chemicals such as fatty alcohol ethoxylates and other chemicals are used in this stage. The purpose of these chemicals is to take in ink and dirt particles that have been freed in the previous stages and ensure that they remain suspended, so they can be removed during the thickening and washing stages. The goal of this stage is to keep the particles small enough, so they can move through the screens while remaining hydrophilic enough, so they can be drained easily. The final stage is the sludge treatment, this stage involves a process like the floatation stage that has a quiescent stage by screening fibres that have been collected in order to reduce the ash content. 5