Design and Optimisation of Water Recovery System for a Polylactide Production Process

Abstract

Development of water recovery system improves sustainability of industrial water supplies and minimises water cost. This paper proposes an integrated simulation-optimisation approach for the design and optimisation of a water recovery system for a polylactide (PLA) production process. The latter is among the industrial processes that are known for consuming a high amount of water during its operation. In this work, an integrated simulation-optimisation approach is adopted to address water minimisation problem in a PLA production process. A steady-state process simulation software is first used to model the PLA production process, in order to obtain its mass and energy balances, as well as to identify the important process parameters that affect water recovery. The model simplifies the non-linearity of the reactor model, and also determines the relationship between reactor operating conditions with the water source flowrates. Mathematic programming technique is next used to synthesise its water recovery network which involves multiple impurities. Several water recovery scenarios with different optimisation objectives were used for the evaluation, i.e. minimising flowrate (scenario 1), minimising cost (scenario 2) and maximising profit (scenario 3). Both scenarios 2 and 3 that involve process optimisation at the reactor achieve the minimum freshwater and wastewater flowrates, with maximum profitability for the process. As compared with the base case process, the water reuse/recycle scheme for these scenarios leads to extra 34.3% and 17.5% reduction in freshwater demand and wastewater flowrates respectively.