A novel modelling and decomposition strategy for overall refinery optimisation

Abstract

In this paper, a novel decomposition strategy is presented to tackle large-scale overall refinery optimisation problems. This decomposition approach is derived from analysis of the mathematical structure of a general overall plant model, which contains common elements and independent elements. This understanding forms the basis for decomposing the overall plant model into two levels, namely a site level (master model), and a process level (submodels). The master model determines common issues among processes, such as allocation of raw materials and utilities, etc. With these common issues determined, submodels then optimise individual processes. The results from submodel optimisation are fed back to the master model for further optimisation. This procedure terminates when convergence criteria are met. In this way, individual process optimisations are effectively controlled and co-ordinated by the centre master model. This decomposition provides the flexibility of replacing existing process models by using better models supplied by vendors without affecting the optimisation infrastructure.