IMPROVING TRAIN ENERGY EFFICIENCY BY ORGANIC RANKINE CYCLE (ORC) FOR RECOVERING WASTE HEAT FROM EXHAUST GAS

asme-orc2015 Tracking Number 193

In a context of energy cost increase, reducing engine fuel consumption has become a key issue for transportation industry. Many paths exist to achieve substantial fuel savings: downsizing, hybridization, energy recovery… IFPEN has carried out an analysis of heat losses showing that recovering exhaust heat energy is a promising solution for improving fuel economy. Thus, IFPEN and ENOGIA have co-developed an Organic Rankine Cycle (ORC) system for direct recovering energy from exhaust heat. This system has been designed in order to be implemented on a Diesel-electric regional train manufactured by ALSTOM TRANSPORT. The train has several Diesel engines that produce mechanical torque needed for generators used for train electric propulsion. The ORC recovers energy from the exhaust heat of the different Diesel engines. The project funded by the French national agency for research (ANR) started with 0D simulations in order to identify the optimal ORC architecture as well as some promising working fluids. More than 100 fluids were evaluated and finally two fluids were retained for this application thanks to their safety features, eco-friendliness and thermodynamic potential. A pre-design study defined the main components (boiler, condenser, pump…) that answer to the major constraints: cost, compactness, efficiency. ENOGIA developed the “heart” of the ORC, a dedicated turbine coupled with a high-speed generator on the same axle. The objective is that the electricity produced by the turbo-generator is re-injected for the train electrical propulsion. An ORC prototype has been assembled with a special care for avoiding any organic fluid leaks. The prototype has then been tested in an engine bench with the same Diesel engine as in the regional train. At the engine bench, the electricity produced by the ORC is re-injected in the French grid by means of inverters and transformers. Based on previous experiences, IFPEN has developed an advanced control system for this application, which allows transient control of ORC operation by regulating vapor superheating at evaporator outlet. The machine has been largely instrumented for monitoring Rankine cycle operation. At the time of paper writing, around 10kW of ORC electricity output power has been reached in stable conditions.