Water disposal minimization of a screw press in the tissue manufacturing process

Abstract

Dewatering is a major process in a wide range of manufacturing industries. One of the most commonly used technologies for dewatering is the screw press. The optimized setting of the screw press increases the amount of recycled water for further production. Additionally, it reduces waste disposal costs by lowering the weight of discharged sludge. In this paper, we used the design of experiments to determine the parameters that affect the dryness of the final waste. Our study showed the significant parameters were the pump speed, the screw rotation speed, and the properties of inflowing sludge. Using the significant factors, a regression model was developed to predict the dryness of the final waste. Then, the regression model was used as the objective function of an optimization model to find the optimal settings of the screw press that maximizes the dryness of sludge. The optimum setting of the screw press increased the dryness of sludge by 2.3%, saving 387 metric tons of water annually. The financial effects of improving the dryness of the sludge leaving the screw press were calculated showing a reduction in disposal costs and reduction in water usage costs because the water extracted from the sludge is recycled. Further investigations showed that the amounts and types of chemicals used to pretreatment the inflowing sludge to the head box can affect the dryness of the sludge leaving the screw press.