Optimization of the performance of an Organic Rankine Cycle used as waste heat recovery system in a bio-liquid diesel engine power plant

Verkefnið er unnið í tengslum við Háskóla Íslands og Háskólann á AkureyriEnergy savings and efficiency improvements of energy systems are an important task on the path towards a more sustainable future. This thesis describes an optimization of a heat recovery system for an electric power plant running on bioliquid. This system is a part of an electric power plant being designed by Utras Engineering in Great Britain. Plant oils are chosen in this investment to be used as fuel, and therefore the availability of plant oils and their properties as a fuel for diesel engines is examined in the thesis. The heat recovery system uses heat contained in the cooling water from the engine block as well as heat in exhaust gases, and converts it into electric energy. It is also a part of a larger more intricate system where a part of the heat is used for heating buildings, preheating fuel, running an absorption cooling unit. The recovered heat is converted to electricity using Rankine Cycle, different working fluids are addressed. The Steam and Organic cycles are examined. The system is optimized using three different objective functions: power output, exergetic efficiency and net present value. The optimization process is solved in the mathematical model implemented into Engineering Equation Solver. The model is able to perform a complex simulation of the waste heat recovery system. The model simulates the energy and exergy balance of the system and is also equipped with economical instrument: net present value. The results show that according to all of the objective functions Organic Rankine Cycle with isopentane as working fluid used as a recovery system is the most optimal solution. Its electrical output is 1741 kW, exergetic efficiency 27,6% and the system pays back in 6 years. Also further heat recovery is examined. And it is found that there are possibilities for recovering more heat out of the Organic Rankine Cycles. It was found that the superheated steam leaving the turbine is at insufficient temperature and does not contain enough enthalpy for it to be a feasible source for the heating applications though it could be used for regeneration improving cycle efficiency. But this issue is not studied in this work. After the optimization process the case study is performed to examine if such a power plant with waste heat recovery system could be implemented at different conditions. Poland is examined as a location for the power plant. It is concluded that Poland is not a feasible place for this type of power plant. That is because undeveloped plant oil industry and not sufficient political incentives for biofuels