Diphenyl-diphenyl oxide eutectic mixture for high temperature waste-heat valorization by a partially evaporated cycle cascade

International audienceOrganic Rankine Cycle power production plants are very promising heat-to-power systems. High-temperature waste-heat valorization presents a great potential for the development of this technology. However, the operating limit of usual organic working fluids is close to 300 • C. To increase this limit, Diphenyl-Diphenyl Oxide mixtures could be used as high-temperature working fluids thanks to their thermal stability limit of 400 • C. This work presents an original cascade of a Diphenyl-Diphenyl Oxide Partially Evaporated Cycle and an Organic Rankine Cycle. This solution can help in increasing the power output of an ORC system used for high temperature sensible waste-heat valorization. The paper presents first an original state of the art of Diphenyl Oxide used in Rankin Cycles. Then, a single stage Diphenyl-Diphenyl Oxide Partially Evaporated Cycle is explored to analyze its thermodynamic particularities before the presentation of the cascade system optimization. Besides, a comparison to a simple Organic Rankine Cycle system is done to assess the performance improvement achieved by the proposed cascade. This is done for various bottom cycle fluids and hot source temperatures. The power production can be increased by 4%-17% for source temperatures ranging between 400 • C and 500 • C. The proposed Diphenyl-Diphenyl Oxide cycle could be used as a plug-in system in heat recovery and transport oil loops

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

International audienceWaste 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