Economic optimization of a combined heat and power plant: solution strategy
This contribution presents the optimization strategy of the parallel repartition between electric and heat production for a geothermal plant. The geothermal fluid, assimilated to liquid water at 185 °C, has a flow of 350 m3/h, which is separated in two streams. Its reinjection temperature is an optimization variable, submitted to a minimum value constraint. The superstructure includes the ORC components among which an optional internal heat exchanger which allows exchange between the outlet streams of the turbine and the pump. Each component characteristic dimension (used in the installation cost) is an optimization variable. The operating cost of the ORC is proportional to the installation cost. The superstructure also includes the heat network constituted by a definite consumer and optional consumers. In this contribution, since we do not consider the detailed structural optimization of the DHN, its investment cost is proportional to the supplied heat and its length. The selling price of the electrical net power is a function of the heat recovered by the network. A Mixed Integer Non-Linear Programming (MINLP) optimization problem is solved using the GAMS software. The strategy used to overcome the critical point of the initialization of the MINLP problem is presented. It consists in splitting the general problem in sub-problems which are solved successively.