Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.
Heat integration to minimise energy usage in multipurpose
batch plants has been in published literature for more than two
decades. In most present methods, time is fixed a priori
through a known schedule, which leads to suboptimal results.
The method presented in this paper treats time as a variable,
thereby leading to improved results. Both direct and indirect
heat integration are considered together with optimisation of
heat storage size and initial temperature of heat storage
medium. The resulting model exhibits MINLP structure, which
implies that global optimality cannot generally be guaranteed.
However, a procedure is presented that seeks to find a globally
optimal solution, even for nonlinear problems. Heatlosses from
the heat storage vessel due to idling are also considered. This
work is an extension of MILP model of Majozi , which was
more suited to multiproduct rather than multipurpose batch
facilities. Optimising the size of the heat storage vessel as well
as the initial temperature of the heat storage fluid decreased the
requirement for external hot utility for an industrial case study
by 33% compared to using known parameters.