Pulp & Paper
The production of paper is one of the oldest cultural technologies that has been based on the same principle since its discovery more than 2,000 years ago: When dehydrated, water-soluble plant fibres combine on a sieve to form a coherent mat – the paper.
Modern paper machines shorten the time from the first impact of the fibre-water suspension on the screen to the finished paper to a few seconds. They differ mainly by the type of paper or cardboard produced and by the type of raw materials used.
The procedure can be divided into four main areas:
- the stock preparation,
- the paper machine,
- the finishing, and
- the equipment.
Since a lot of water is used in the process, paper mills often have their own wastewater treatment plants.
Various pump types are used in all process steps and wastewater treatment.
Successful application examples
Waste paper, chemically produced pulp and mechanically shredded pulp are dissolved with the addition of water; non-paper substances are sorted out. Depending on the desired type of paper, various fillers and auxiliary substances are added to the mixture to improve the paper quality and increase the productivity of the system.
Large centrifugal pumps are usually used to convey the fibre-water suspension.
The stock ramp serves to apply the fibre-water suspension to the screens so that the fibres distribute and orient themselves as best as possible. Excess water runs off or is sucked off at the same time. In the subsequent drying, the paper webs first pass through a complex press system, which extracts water from the paper structure, increases its strength and influences the surface quality, before the remaining water is evaporated by steam-heated drying cylinders. The raw paper is wound up in long webs on the so-called tambour.
Pumps are needed in this manufacturing process, especially for the discharge of water.
Depending on the further use of the base paper, it is coated in the coating kitchen with pigments and binders of the existing colour coating to achieve a smooth printable surface.
Typical media in this area are starch, kaolin, calcium carbonate, caustic soda, synthetic latex, wet strength agent, etc.
Further smoothing can be carried out subsequently by supercalendering in a calender in which the paper runs under pressure over heatable rollers.
This term refers to the further processing of the paper webs into smaller rolls, sheets or other precursors, which are needed, for example, for the production of corrugated board and cardboard. Pumpes are not involved in this process step.
In paper production, wastewater is produced when manufacturing the pulp, which dissolves resins and lignins from the wood fibres. Bleaching agents like hydrogen peroxide and chlorine compounds are also used.
But even when processing the waste paper, the fibres must be freed from foreign bodies such as adhesives, plastics or paper clips. In so-called deinking, printing inks are dissolved with water, caustic soda and soap from the waste paper fibres.
In the paper machine, it is all about the removal of the water, which is withdrawn from the fibre-water mixture in the various drying steps on the way to finished paper.
Various pump technologies are used depending on the type of pollution and amount of wastewater.