Efficiency enhancement in existing biomass organic Rankine cycle plants by means of thermoelectric systems integration

This work investigates, from a thermodynamic point of view, the possibility of integrating thermoelectric systems (TES) in existing solid biomass-fuelled ORC CHP plants in a cost-effective way. Thus, a simple plant layout was proposed. The benefits achieved in the overall plant performance, constrained by several technical parameters of the subsystems involved, are assessed in terms of the Second Law efficiency and other characteristic parameters such as the First Law efficiency and the Primary Energy Savings Ratio. The main conclusion obtained is anticipating the fact that exists a certain optimal TES driving temperature value leading to the maximisation of the plant's performance. According to the specific results extracted from the examples evaluated (TES integrated in Toluene and MDM ORC CHP plants), this temperature is about 245°C and 210°C, respectively, which leads to an increase in the overall Second Law efficiency of the plant up to 7-8%. Hence, it is clear that thermoelectric systems can contribute to the enhancement of the performance and to do so, there are guidelines to be considered prior to the detailed design of such systems to be integrated in existing ORC CHP plants.