A pilot-scale three tube continuous pulping digester was designed and fabricated to convert wheat straw into pulp for papermaking using the soda pulping delignification process. The physical and chemical properties of wheat straw were investigated to characterize wheat straw. The bulk density, porosity, moisture content, and fiber diameter were observed as 0.18 g/cm3, 65.30%, 2.01% (w/w), 15–20 m, respectively. Chemically, the wheat straw is contained 40% cellulose, 68.1% holo-cellulose, 18.30% lignin and 8.85% ash (w/w). The influence of various process variables on delignification process was studied at 117–159ºC and 0.5–5.88 kgf/cm2. The white liquor concentration, white liquor flow rate, and screw feeder speed (RPM) were considered as process variables. The obtained pulp was analyzed in terms of kappa number and residual alkali as a measure of pulp quality and extent of delignification. The minimum value of kappa number and residual alkali were obtained as 19.58 and 54 g/L. It was observed that the high concentration and high white liquor flow rate results in a high value of residual alkali. The higher pressure and temperature inside the digester tubes were found suitable for better delignification operation.
Wheat straw, white liquor, soda pulping, delignification, continuous pulp digester