Production of paper and liquid filtration, what exactly is the correlation?

It’s universally accepted that in order to produce a batch of paper, a paper mill will require at least two key ingredients – trees and water. You may be surprised to learn, however, that water, is by far the most important process material. About 100 litres of fresh water is needed to produce 1kg of paper. Despite sophisticated waste water treatment plants and closed loop systems, which allow for over 90% of water to be recycled, if not utilised properly, it can cause several problems to papermills including loss of production time, damage to the equipment components and inconsistent product finish, not to mention increased wastewater production and wider environmental issues. Liquid filtration utilised in the correct way at relevant stages of the papermaking process can help the paper mills to prevent such problems and ensure smooth paper production.

 

What is the paper making process and where is filtration needed?

In brief, logs are initially fed into a rotating drum to produce wood chips, these are transferred to a pulp mill and fed into the digester where they are cooked with an acid solution. To ensure a consistent finish and to prepare the solution for the actual papermaking stage, the soft and fibrous mixture is washed out of the acid solution and bleached. Liquid filtration plays an important role here as this process is extremely prone to chemical contamination. Filtration is used at this stage to filter out any contaminants such as tank rust, dirt and scale which occur during transportation and storage, just before components are mixed together in the reactor.  Wound polypropylene filters are often used in this process, however, a better solution would be the use of a TruDepth polypropylene depth filter, delivering up to 97% efficiency of particle reduction and the melt-bonded exterior minimises the risk of any fibre migration.

Once the mixture has been transformed into paper, the product is ready for the finishing stage. At this point, the paper is vulnerable and in order to avoid breakage, it is important to ensure it remains consistently wet whilst moving down the production line. To do so, spray nozzles are used which, if not fed with water free from contaminates, can get plugged, damaged and essentially delay production. The set-up, recommended by Fileder, for the treatment of incoming water includes combination of the EBEP bags, SSP depth filters, SCB carbon and SRO membrane technologies, to remove particulate and other contaminants to prevent premature blocking. This is a common practice among paper mills as it helps to set consistent water quality ready for not only the nozzle spraying stage but also as an ingredient used in actual paper production.