Wet to dry cycles for high temperature waste heat valorisation using a diphenylbiphenyl oxide mixture

International audience ; Waste heat recovery at temperatures ranging from 300°C to 400°C suffers from a lack of working fluids supporting well such high temperatures. Biphenyl-diphenyl oxide mixtures could be used as high temperature working fluids thanks to their good thermal stability up to 400°C. The paper explores the possibility of using a eutectic mixture known as Dowtherm A in a ''wet to dry'' cycle for high temperature heat-to-power conversion. The paper presents first a Dowtherm A cycle alone for mechanical work and heat generation; the sensitivity of the cycle to the turbine inlet quality and to the hot source inlet temperature is analyzed. Then an ORC cascade is presented where the Dowtherm A is used in the topping cycle and toluene in the bottom cycle. The sensitivity to the hot source temperature and top cycle boiling temperature are presented. The simulations show that the mechanical power output can be increased compared to a standard cycle thanks to a better matching between the hot source and working fluid temperatures. Besides, the analysis shows that the value of the expansion inlet vapor quality leading to the maximal power output depends on the hot source temperature.