ORC Cycles Research Articles

HD Diesel engine equipped with a bottoming Rankine cycle as a waste heat recovery system. Part 1: Study and analysis of the waste heat energy

Abstract This paper describes the study of different bottoming Rankine cycles with water-steam and/or ORC configurations in classical and innovative setups such as a waste heat recovery system in a Heavy Duty Diesel (HDD) Engine. This work has been divided in two parts. This first part describes the model of the studied HDD engine and the available waste energy sources in this HDD Engine. The waste energy sources are studied from the standpoint of energy analysis to determine which are the most appropriate for their application in bottoming cycles attending to minimizing external irreversibilities. Finally, two configurations are chosen as the most appropriate, in a balance between external irreversibilities and technological complexity, and they have been analyzed to determine global efficiencies, power increments and necessary modifications to implement these cycles in the HDD engine. The second part of this article will analyze additional innovative setups in the HDD engine to fit this engine with ORC cycles.

Bottoming micro-Rankine cycles for micro-gas turbines

This paper investigates the possibility of enhancing the performances of micro-gas turbines through the addition of a bottoming organic Rankine cycle which recovers the thermal power of the exhaust gases typically available in the range of 250–300 °C. The ORC cycles are particularly suitable for the recovery of heat from sources at variable temperatures, and for the generation of medium to small electric power. With reference to a micro-gas turbine with a size of about 100 kWe, a combined configuration could increase the net electric power by about 1/3, yielding an increase of the electrical efficiency of up to 40%. A specific analysis of the characteristics of different classes of working fluids is carried out in order to define a procedure to select the most appropriate fluid, capable of satisfying both environmental (ozone depletion potential, global warming potential) and technical (flammability, toxicity, fluid critical temperature and molecular complexity) concerns. Afterwards, a thermodynamic analysis is performed to ascertain the most favourable cycle thermodynamic conditions, from the point of view of heat recovery. Furthermore, a preliminary design of the ORC turbine (number of stages, outer diameter and rotational speed) is carried out.