11/10/2022 0 Comments Casrto logic world widde![]() (11) proposed a novel MINLP unit-specific model for marine-access refineries that contrary to inland refineries have just charging tanks to crude distillation units rather than a sequence of storage and charging tanks. An important aspect is that the considered single grid continuous-time model features a set of big-M sequence constraints that are known to decrease the performance of mixed-integer models. Using a single time grid to keep track of events taking place was found to be a better approach, with the continuous-time representation scaling better with problem size, and hence outperforming its discrete-time counterpart. Later, (10) the MILP part of the model (without the blending constraints) was compared to models relying on different time representation concepts. The nonlinearities involved by composition constraints were handled by a two stage MILP-NLP procedure identical to Jia et al., (5) which, however, led to small optimality gaps due to the objective function that was selected namely maximizing gross margins. ![]() The advantage is that generic constraints can be used to break symmetries and reduce the size of the search space. (9) considered yet another type of continuous-time formulation, called single operation sequencing model, which represents a schedule as a sequence of priority slots. We also show that adopting a two-step MILP-NLP algorithm where the mixed-integer linear relaxation is derived from multiparametric disaggregation can reduce the optimality gap by orders of magnitude. Through the solution of a set of test problems from the literature, we show that the resulting mixed-integer nonlinear programs can be solved close to global optimality by the commercial solver GloMIQO for the objective of gross margin maximization but not for operating cost minimization. The new single time grid formulation has the advantage of avoiding computationally inefficient big-M constraints, unlike previously proposed unit-specific and priority-slot based models. Casrto logic world widde how to#Guidelines are given on how to generate a Resource-Task Network superstructure that implicitly handles the complex logistics, while extending the scope of a well-known continuous-time formulation to variable recipe tasks with multiple input materials. ![]() This paper addresses the modeling of crude oil operations in refineries assuming that all properties blend linearly. ![]()
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