Improved continuous-time model for gasoline blend scheduling

• New version of continuous-time gasoline blend scheduling model.
• Reduction of binary variables by using demand data and additional equations.
• Inclusion of nonlinear constraints for octane blending based on ethyl RT-70 models.
• New version of the model solves faster than previous models.

This work introduces a reduced-size continuous-time model for scheduling of gasoline blends. Previously published model has been modified by (i) introducing new model features (penalty for deliveries in order to reduce sending material from different product tanks to the same order, product and blender-dependent minimum setup times, maximum delivery rate from component tanks, threshold volume for each blend), (ii) by reducing the number of integer variables, and (iii) by adding lower bounds on the blend and switching costs, which significantly improve convergence. Nonlinearities are introduced by ethyl RT-70 equations for octane blending. Medium-size linear problems (two blenders, more than 20 orders, 5 products) are solved to optimality within one or two minutes. Previously unsolved large scale blending problems (more than 35 orders, 5 product, 2 or 3 blenders) have also been solved to less than 0.5% optimality gap.