To cite this version:Paola Bombarda, Costante Invernizzi, Claudio Pietra. Heat recovery from Diesel engines: a thermodynamic comparison between Kalina and ORC cycles. Applied Thermal Engineering, Elsevier, 2009, 30 (2-3) This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Although the obtained useful powers are actually equal in value, the Kalina cycle requires a very high maximum pressure in order to obtain high thermodynamic performances (in our case, 100 bar against about 10 bar for the ORC cycle). So, the adoption of Kalina cycle, at least for low power level and medium-high temperature thermal 2 ACCEPTED MANUSCRIPT sources, seems not to be justified because the gain in performance with respect to a properly optimized ORC is very small and must be obtained with a complicated plant scheme, large surface heat exchangers and particular high pressure resistant and no-corrosion materials. ACCEPTED MANUSCRIPT

Among the various fuel cell (FC) systems, molten carbonate fuel cells (MCFC) are nowadays one ofthe most promising technologies, thanks to the lower specißc costs and a very high electrical efficiency (net low heating value (LHV) electric efficiency in the range 45%-50% at MWei scale using natural gas as fuel). Despite this high performance, MCFC rejects to the ambient almost half of the fuel energy at about 350^00° C. Waste heat can be exploited in a recovery Rankine cycle unit, thereby enhancing the electric efflciency ofthe overall system. Due to the temperature ofthe heat source and the relatively small power capacity of MCFC plants (from few hundred kW^i to ¡OMW^i), steam Rankine cycle technology is uneconomical and less efficient compared to that of the organic Rankine cycle (ORC). The objective of this work is to verify the practical feasibility ofthe integration betn'een a MCFC system (topping unit) and an ORC turbogenerator (bottoming unit). The potential beneflts ofthe combined plant are assessed in relation to a commercial MCFC stack. In order to identify the most suitable working fluids for the ORC system, organic substances are considered and compared. The figure of merit is the maximum net power ofthe overall system. Finally, the economical beneflts of the integration are determined by evaluating the levelized cost of electricity (LCOE) of the combined plant, with respect to the standalone MCFC system. In order to assess the economic viability of the bottoming power unit, two cases are considered. In the flrst one, the ORC power output is approximately 500 kW^¡; in the latter, about I h/TW^i. Results show that the proposed solution can increase the electrical power output and efficiency of the plant by more than 10%, well exceeding 50% overall electrical efficiency. In addition, the LCOE of the combined power plant is 8% lower than the standalone MCFC system.