Hallsta Paper Mill, which is a part of Holmen Paper, uses the Thermo Mechanical Pulping process to produce paper pulp. One of their process steps is a plug screw feeder that transport and compresses chips. Jams often occur in the plug screw and there is currently a lack of knowledge of how it should be operated for the highest possible production quantity. The purpose of the thesis is to identify the causes that lead to failures of the plug screw and to find an optimal way of operating it.  In order to gain a deeper understanding of the different areas covered by the study, the theory of the Thermo Mechanical Pulping process used at Holmen for production of paper pulp has been presented. Also, theory about how the chips is being processed, the plug screw and its dimensions, the improvement strategy used in the study and about maintenance.  Collecting documents was done using business systems such as IFS and WinMops and interviews were conducted. The data analysis method used were a regression analysis and a fishbone diagram. From this, optimal parameters for operating the plug screw have been developed.  From the results, an improvement proposal has been designed to create clear guidelines for operating and maintaining the screw as well as other production steps that have an impact on the screw, in order to avoid unnecessary wear and failures of the plug screw.

Thermomechanical pulping (TMP) is a highly energy intensive process where most of the energy is used in therefining of chips to fibres. Various ways of reducing the energy consumption have earlier been studied, for examplechange of refiner pattern, addition of various chemicals, and also some biochemical implementation in the form of fungus and enzymes. This study includes pre-trials with the enzymes pectin lyase and pectin esterase,multipectinase, xylanase, and mannanase. The results are studied via a reducing sugar assay, an enzymatic assayusing spectrophotometry, and capillary zone electrophoresis. The study also includes results from a pilot scalerefining with multipectinase, xylanase, and mannanase, performed with a wing refiner at Helsinki University.Reductions of energy consumption in TMP by pre-treatment of Norwegian spruce chips are investigated and apotential reduction of energy consumption of 6 % is indicated.