Exergy analysis for maximizing power of organic Rankine cycle power plant driven by open type energy source

An attempt is made in the present work to classify the energy sources that can drive the ORC (organic Rankine cycle) power plants. Concepts of the open and sealed type of the energy sources are introduced as well as the difference between the energy source capacity and the energy supplied to the power plant cycle is presented. By application of the exergy analysis it has been proved via examples of calculations that, for the open type energy sources, an external loss of exergy occurs due to the lacking utilization of a still usable output product. The term product refers here to the power plant exit flow of the source heat carrier. It is shown that, for each cycle working fluid, there is a specific evaporation temperature at which the cumulative cycle energy losses drop to minimum and the power plant output reaches its maximum value. It is also proved that, in case of the ORC power plants driven by the open energy sources, there is no justification to apply the internal heat regeneration in the power plant cycle. The internal heat regeneration is, in fact, lowering the exergy loss in the condenser, but is also increasing losses due to unused waste product. Neither the power plant output nor the power plant efficiency is improved.