Simultaneous Water and Energy Minimization for Brown Stock Washing System

Pulp and paper mills are huge consumers of water and energy. Hence, much research works have been dedicated to simultaneous reduction of water and energy in the past decades. However, none of those works are addressing the brown stock washing system (BSWS), which is the core processing section that determines the amount of energy required in black liquor (BL) concentration. The latter is the largest energy consumption in a typical pulp and paper mill. Therefore, minimizing water consumption in the BSWS will lead to energy saving too. In this work, mass balances of the BSWS is first analyzed in a process simulation software (Cadsim), and adopted as the base case model for the study. Next, a mixed integer non-linear programming (MINLP) optimization model is developed to minimize the total annualized cost incurred in the project. The synthesized water network features significant reduction in both energy and water consumption in the BSWS.