(165f) Environmental Impact Reduction through Simultaneous Design and Scheduling

Processing facilities are normally designed with sufficient flexibility to handle nominal variations. When the process features planned changes in feedstocks and products, scheduling is often used to optimize process operation. Proper scheduling may be limited to existing design or may entail retrofitting. Traditionally, economic objectives have served as the primary drivers for the design, retrofitting, and scheduling of industrial processes. Once a base design and scheduling plan have been established, environmental issues are addressed in many cases as an afterthought. As a result of this sequential approach, valuable synergisms and tradeoffs of economic and environmental objectives are often missed. The objective of this work is to develop a systematic framework and the associated mathematical formulation for process design and scheduling while simultaneously addressing economic and environmental objectives. First, a procedure is developed to enable the development of a process retrofitting scheme while incorporating scheduling issues for typical process and market variations. This step parametrically maximizes the use of existing process infrastructure and introduces process modifications as needed towards the optimization of process scheduling and operation. Next, the environmental issues pertaining to the parametrized process retrofitting, scheduling, and operation strategies are integrated with the environmental impact of these changes. The resulting framework identifies opportunities for synergism between the economic and environmental objectives. It also determines points of diminishing return beyond which tradeoffs between economic and environmental objectives are established. The devised procedure is illustrated with a case study on an oil refinery. The scheduling activities of oil refineries are becoming difficult due to newly introduced environmental regulations (e.g., SOx, NOx, wastewater discharge, etc.). For a variable feedstock and/or market demand of product quantities and qualities, a retrofitting and scheduling approach is established. Several units are considered including the crude distillation units (CDU), fluid catalytic cracking (FCC), hydrocracker (HYC), hydrtreater (HYT), hydrodeslfurizer (HDS), catalytic reformer (CatRef) and delayed coker (COK) units. The design and operational performance, supply, demand, technical constraints, environmental impact are all included an optimization formulation. The solution established insightful synergisms and tradeoffs. Various results will be discussed for the case study and for the broader aspects of a typical processing facility.