Synthesis of an optimal schedule and water network for a multipurpose multiproduct textile industry through a sequential MILP-NLP technique

Abstract

Textile factories are usually batch plants. Their high freshwater consumption and large emissions of toxic wastewater present a threat to water availability and public health. Wastewater minimization can be used to reduce this impact. This paper presents a framework for combining the unit-specific continuous-time approach and the global continuous-time approach in batch water minimization. The unit-specific approach is used to obtain an optimal schedule, which is mapped onto a global time grid using a bridging algorithm before performing water minimization. The objectives are to minimize the process makespan and freshwater consumption, respectively. This research is applicable to large batch problems which are intractable using conventional techniques. An industrial case study from a textile factory in India is used to demonstrate the applicability of the formulation, followed by a sensitivity analysis to determine the number of storage tanks required to facilitate wastewater reuse. Results indicate freshwater savings of up to 94%.