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Stock preparation:

The stock preparation of the paper machine covers a wide range, starting with the fibre dispersion and auxiliary materials preparation and ending at the machine chest of the paper machine. A paper machine can only produce a product in a cost-effective manner and in the best quality if the pulp is optimally prepared. Swiss Paper Consulting GmbH strives for the following requirements in stock preparation:

  • Adequate output
  • Consistent stock quality
  • High screening efficiency
  • Lowest possible fibre loss
  • Low specific energy demand
  • High degree of automation
  • Low noise emission
  • Optimised grade change

Pulper

Pulper

Stock chest

Stock chest

Deflaker

Deflaker

Refiner

Refiner

Stock chest

Stock chest

Cleaner

Cleaner

Screening

Screening

Paper machine

All paper machines have three basic sections: wire or forming section, press section and dryer section. In the area around the dryer section, there may be process steps that improve the surface finish of the product, such as coating and calendering equipment. The latter finish stage can be found on older machine offline.
Whether publication, packaging, hygiene or speciality papers, Swiss Paper Consulting GmbH offers solutions for all paper machines.

Forming
section

Forming section

Press
section

Press<br/>section

Drying section

Drying section

Film
press

Film<br/>press

Drying section

Drying section

Finishing

Finishing

Finishing

In the finishing department, the paper reel is prepared for the customer who expect following reel characteristics:

 

  • Even winding hardness profile
  • Even reel outer diameter profile
  • Dust-free and non-bonded roll end faces
  • Moisture wrinkle-free reel

Drying section

The focus of the dryer section is the thermal drying of the paper web, in which the water, which cannot be removed mechanically, is expelled by heat. The dry content increases up to 95 %. Depending on the paper machine, the drying of the paper can be designed for contact drying, convection drying or radiation drying. Thermal dewatering is more expensive than mechanical dewatering. It is therefore inevitable to adjust the input dry content into the dryer section as optimally as possible.

Film press

In modern paper machines, the coating of paper is done online. They are used for surface treatment and property improvement. The objectives of coating systems can be, among other things, to improve printability, haptics or gloss. If the coating process is not performed in the right way, this can lead to an uneven surface and surface defects.

Drying section

The focus of the dryer section lies in the thermal drying of the paper web, in which the water, which can no longer be removed mechanically, is driven out by heat. The dry content increases to up to 95%. Depending on the paper machine, the drying of the papers can be designed for contact drying, convection drying or radiation drying. Thermal drainage is more expensive than mechanical drainage. It is therefore inevitable that the dry content entering the dryer section should be set as optimally as possible.

Press section

Sheet formation and drainage in the wire section are followed by further mechanical drainage in the press section. Here, the dry content of the paper or board web is increased from about 20 % to about 50 %, depending on the product and the dewatering capacity of the wire section. The following advantages result from the pressing process:

  • Better and more stable web behaviour when passing through the dryer section
  • Strength increase of the wet paper web
  • Reduction of energy consumption in the dryer section
  • Higher production speed
  • Shortened drying times

The energy consumption of the press section in relation to the dryer section is about 5%. Mechanical pressing therefore requires significantly less energy than drying.

Forming section

The headbox is the first unit of a paper machine. Its main function is to distribute the mix evenly across the width of the wire section. During the forming process, the basic structure of the final paper produced is created. The driving forces for optimum sheet formation, cross and machine direction profiles are fibre orientation are:

 

  • Feeding of the suspension into the headbox (flow and pulsation)
  • Fibre and filler distribution in the cross machine direction
  • Wet sheet formation

Screening

In nearly all papermaking operations, at least one pressure screen is mandatory right before the head box. The inlet stock flow enters the upper part of the screen housing tangentially. Inside a fixed screen basket, the rotor rotates and its pressure pulsations ensure that the screen is kept free. At the same time the stock suspension is forced to flow downwards along the screen. The accepted stock passes the holes or slots of the screen basket. The rejects are sorted out by means of an overflow. By improving the screen baskets, introducing new rotors and housing corrections, the screening effect can be improved with lower specific energy consumption.

Cleaner

The main purpose of cleaning and screening is to ensure clean stock by removing bundles, flakes, foreign material from the stock suspension. The qualitative and economic optimum of the cleaning and screening depends on the design of the cleaner systems and on the selected screens procedure. Screens are often not discharging reject continuously in an effort to reduce the loss of fibres.

Stock chest

As the paper mill process involves treatment of stock in different consistencies, stock chests are an essential part of the process. Their main tasks are:

 

  • Storage of stock
  • Blending and mixing of various stock components, fillers and additives
  • Equalising variations in quality
  • Smoothening the flow variations in batch processes

Refiner

Refining of pulp is one of the most important unit operations of the stock preparation system. In refining, the properties of pulp fibres are modified so that the strength of the fibre network improves, the paper surface can be made smoother or the paper formation improves. Achieving specific paper properties by means of refining process control requires a comprehensive know-how and know-why of the development of the paper properties as a function of refining energy while keeping an eye on energy consumption. We perform refiner diagnosis to review the current refiner performance and determine energy saving potentials and paper properties optimisations.

Deflaker

For adequate disintegration of fibres a deflaker will treat a pumpable fibre slurry further so that fibre flakes, fibre bundles or separated but still dry and stiff fibres are disintegrated into individual, wetted and flexible fibres. A deflaker diagnosis can lead to cost and quality optimisation.

Stock chest

As the paper mill process involves treatment of stock in different consistencies, stock chests are an essential part of the process. Their main tasks are:

  • Storage of stock
  • Blending and mixing of various stock components, fillers and additives
  • Equalising variations in quality
  • Smoothening the flow variations in batch processes

Pulper

The first stage in the stock preparation after bale handling is slushing of the baled pulps in the pulper. Energy consumption for slushing has to be considered. The aim should be to achieve adequate disintegration of fibres. In the case of virgin pulp, the residual flake content should be as low as possible, whereas in the case of waste paper it is often not desirable to achieve a high degree of deflaking, since undesirable components such as plastic adhesives are easier to remove from the process in a subsequent process unit if there are not shredded.