Integration of Energy and Wastewater Treatment Alternatives with Process Facilities to Manage Industrial Flares during Normal and Abnormal Operations: Multiobjective Extendible Optimization Framework

Abstract

This work reports an extendible multiobjective optimization framework to find the optimal configuration of energy utilization and wastewater treatment facility of the process. It incorporates two sustainable energy integration alternative tools, i.e., a cogeneration (COGEN) unit and thermal membrane distillation (TMD), as available add-ons to the process during normal operation and for abnormal situation management. The objective of the framework is to reduce the environmental footprint of abnormal flares by enumerating and assessing possible process configurations in order to manage flares from uncertain sources and to utilize unused energy resources for wastewater treatment. The core of this optimization framework is developed using a genetic algorithm and its objective function is aimed at minimizing the total annualized cost which accounts for the fixed and operating costs of the system, the value of produced coproducts (i.e., power, wastewater treatment savings, income from permeate), and taxes/credits associated with greenhouse gases. An ethylene process plant is used to demonstrate the applicability of the developed framework. The results of different alternative configurations demonstrate the economic, energetic, and/or environmental trade-offs of integrating TMD and the COGEN unit with the process plant both for flare mitigation and during normal operation. It was seen that the total annualized cost (TAC) dropped around 35% and the payback period reduced from 7.01 to 4.61 years when an integrated process plant (ethylene plant), utility unit (COGEN), and wastewater treatment facility (TMD) was considered instead of separate divisions. Moreover, utility savings were achieved up to 8% and annual incomes from coproducts were increased around 20% for the integrated ethylene plant, COGEN, and TMD unit. Besides, prolific recycling opportunities of unused flare streams and treated wastewater were identified to make some valuable products from waste streams.