A MILP Model for Energy Optimization in Multipurpose Batch Plants Using Heat Storage

The concept of heat integration in batch chemical plants has been in literature for more than a decade. Heat integration in batch plants can be effceted in 2 ways, i.e. direct and indirect heat integration. Direct heat integration is encountered when both the source and the sink processes have to be active over a common time interval, assuming that the thermal driving forces allow. On the other hand, indirect heat integration allows heat integration of processes regardless of the time interval, as long as the source process takes place before the sink process so as to store energy or heat for later use. The thermal driving forces, nonetheless, must still be obeyed even in this type of heat integration. It is, therefore, evident from the foregoing statements that direct heat integration is more constrained than indirect heat integration. Presented in this paper is a mathematically rigorous technique for optimization of energy use through the exploitation of heat storage in heat integrated multipurpose batch plants. Storage of heat is effected through the use of a heat transfer fluid. The resultant mathematical formulation exhibits a mixed integer linear programming (MILP) stucture, which yields a globally optimal solution for a predefined storage size.