Optimisation of wheat straw Triticum drum kraft pulping

Abstract

This paper explains the problems brought about by the raw material and pulping method used in the Afyon-SEKA Pulp Mill producing bleached pulp from mixed wheat straw ( Triticum drum L.) (65%) and reed ( Phragmites communis) (35%). The use of mixed raw material causes such problems, as heterogeneous pulping, low freeness level, drainage difficulties and wet sheet breaks during the papermaking operations. In addition, silica in raw material results in rather serious difficulties during recovery process. To overcome these problems, first of all, pulping of wheat straw and reed had to be carried out separately. In this case, sulphate pulping characteristics of wheat straw were investigated and optimum parameters were found to be: active alkali charge 14%, sulphidity 20%, maximum temperature 160 °C, time to maximum temperature 55 min, time at maximum temperature 40 min and liquor to straw ratio 4:1. Some properties of wheat straw sulphate pulp produced at optimum cooking conditions were determined to be: screened yield 42%, kappa number 31, SCAN viscosity 1114 ml/g, breaking length 9.8 km, burst index 4.6 kPa m 2/g, tear index 5.1 mN m 2/g and brightness 29 ISO%. Consequently, it was possible to produce bleachable grade pulp from pure wheat straw in a shorter pulping time and lower active alkali than that of Afyon-SEKA Pulp Mill. Thus, this study showed that production capacity of the mill could be increased and freeness level of pulp improved.