Thermal and economic assessment of organic Rankine cycles for waste heat recovery in cement plants

Abstract

This work aimed to investigate the thermodynamic and economic performance of simple and regenerative organic Rankine cycles (ORCs) working under subcritical and subcritical conditions, with superheating operating conditions. These were used in waste heat recovery (WHR) in Brazilian cement factories with clinker productive capacities from (3000 to 6300) ton/d. After selecting the most appropriate organic fluids, the cycles were modelled in terms of their thermodynamic and economic properties using Engineering Equation Solver (EES) software. The key operating parameters of the cycles were optimized using the same software via the genetic algorithm method. The results show that the organic fluids with highest performance from the point of view of their net power output, thermal and exergy efficiencies were R141b, R11, and R123. For all the cycles analysed, the payback period was less than two years, the net present value varied from 130 to 170 million reais, and the internal rate of return exceeded 80%/year. In addition, the proposed ORCs were able to produce around (4000–9000) kW (or ~80 MW for the cement sector of the Minas Gerais state in Brazil, thus eliminating the production of 221,069 kgCO2/year), and had to reach specific costs of investment and specific electricity generation costs ranging from (2250 to 4300) R$/kW and (0.09–0.11) R$/kWh, respectively. Based on the obtained results, we can conclude that the proposed ORCs for WHR in the Brazilian cement industry are environmentally interesting and extremely competitive in terms of their financial and technical properties.