Current issue: 55(5)
Under compilation: 56(1)
A mathematical model was developed for determining the value of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) H. Karst.) stems on the basis of sawing and pulping. The model was based on selling prices of sawn goods, pulp and other products as well as processing costs. Sawing was applied to large-dimension parts of stems and pulping to other parts and small stems. Bark and other residues were burned. The quality of pine stems was described by the distance of the lowest dead branch. In spruce only stem size affected the quality-
According to the results, the size of stem affects considerably the value of pine stems and clearly that of spruce stems. The main reason is an increase in the productivity of frame sawing as the stem size increases. In pine another factor is the higher price of sawn goods. The effect of pulp price increases as the stem size decreases. Even in large sized stems the effect of pulp was notable as the value of chips and saw dust was determined on the basis of product values in export. The competition ability of mechanical pulp was greatly affected by the price of electricity.
The PDF includes an abstract in English.
In the first part of the study, the selected wood and fiber properties were investigated in terms of their occurrence and variation in wood, as well as their relevance for thermomechanical pulping process and related end-products. It was concluded that the most important factors were the fiber dimensions, juvenile wood content, and in some cases, the content of heartwood being associated with extremely dry wood with low permeability in spruce. The following pulpwood assortments of which pulping potential was assumed to vary were formed: wood from regeneration cuttings, first-thinnings wood, and sawmill chips.
In the experimental part of the study, the average wood and fibre characteristics and their variation were determined for the raw material groups. Subsequently, each assortment – equalling about 1,500 m3 roundwood – was pulped separately for 24 h period. The properties of obtained newsgrade thermomechanical pulps were then determined.
Thermomechanical pulping (TMP) from sawmill chips had the highest proportion of long fibres, smallest proportion of fines, and had generally the coarsest and longest fibers. TMP from first-thinned wood was the opposite, whereas that from regeneration cuttings fell in between these two. High proportion of dry heartwood in wood originating from regeneration cuttings produced a slightly elevated shives content. However, no differences were found in pulp specific energy consumption. The obtained pulp tear index was clearly the best in TMP made from sawmill chips and poorest in pulp from first-thinned wood, which had generally inferior strength properties. No big differences in any of the strength properties were found between pulp from sawmill residual wood and regeneration cuttings. Pulp optical properties were superior in TMP from first-thinnings. No noticeable differences were found in sheet density, bulk, air permeance or roughness between the three pulps.
The most important wood quality factors were the fibre length, fibre cross-sectional dimensions and percentage juvenile wood. Differences found in the quality of TMP assortments suggest that they could be segregated and pulped separately to obtain specific product characteristics and to minimize unnecessary variation in the raw material and pulp quality.