DWR Application note: Paper & Packaging

Optimizing starch penetration in test liner – Less energy for after size press drying

Problem
More than 65% of the total energy required for the whole paper making process is used in drying section. Optimization of the drying can decrease the energy usage significantly since the drying section is the largest energy user. The surface sizing of liner/fluting requires a relatively big wet amount that there could be applied a high starch amount for strength improvement and penetration. The solids content of starch is low. This means there is a lot water transferred to the base sheet in the size press. This water must be evaporated in the drying section after size press. It requires a lot energy and is costly.

Solution
ACA DWR penetration tester is a lab analyser that evaluates the liquid flow in dynamic conditions. Its main benefit is the fact that you can measure the liquid penetration using your own base paper or board and adjust the time and pressure to reflect real process conditions. The analyser has shown for example the influence of starch solids content (Figure 2) on penetration rate. This information helps to optimize solids content level as high as possible and reduce the energy needed for after size press drying (Figure 1).

Learning
There is needed 1 kg of steam to evaporate 0.8 kg water. By one percentage point increase in starch solid content there can be saved about 2000 kg steam per hour*. This means about 400 000 EUR savings per year in drying energy costs**. Also quality can be optimized. High speed size press application is very dynamic process and the penetration degree is depending on porosity of the substrate as well as the flow properties of the starch solution and machine conditions such as nip pressure. With ACA DWR penetration tester all these parameters can be simulated in lab conditions with very easy and fast procedure.
*= production 1000 tons/day
**= cost of steam, 40 eur/ton

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