Modelling and Optimization of Sequencing of Processes for Ethylene Production

The separation process for distillation column involves handling a various multi-component mixtures. Particularly for ethylene production, we deal with a number of hydrocarbon components. The objective of this project is to separate each of these components at minimum cost without compromising the feasibility. We develop a superstructure model to determine the optimal design of distillation sequencing for ethylene production. The optimization model is formulated based on a process flowsheet superstructure representation that embeds many possible and feasible structural alternatives for the sequences of processing a multicomponent hydrocarbon mixture constituting liquid naphtha or gaseous ethane. The compositions of the feed will determine the split fractions of the components. We adopt linear mass balance reactor models for conversion of materials into desirable products and simple sharp and non-sharp separation for distillation column. Then, we will formulate a mixed-integer linear program (MILP) that involves two types of variables: (1) discrete 0–1 binary variables for selecting the tasks for an economically-optimal configuration, and (2) continuous variables for determining the optimal operating levels of flowrates into each selected tasks. Using a mathematical modelling, we compare two different feedstocks; liquid naphtha and gaseous ethane. The goal is to select a configuration of separation tasks and their corresponding units. The simulation of our model suggests a different optimal separation sequence from the typical industrial configuration due to the reconditioning of the logical and switching constraints. A more rigorous constraints that consider cost raw material cost, capital investment, production cost and profitability for the olefin production process in order to justify the feasibility of the olefin production is recommended to produce a more reliable output.