Abstract
The organic Rankine cycle (ORC) has recently emerged as a practical approach for generating electricity from low-to-high-temperature waste industrial streams. Several ORC-based waste heat utilization plants are already operational; however, improving plant cost-effectiveness and competitiveness is challenging. The use of thermally efficient and cost-competitive working fluids (WFs) improves the overall efficiency and economics of ORC systems. This study evaluates ORC systems, facilitated by biogas combustion flue gases, using n-butanol, i-butanol, and methylcyclohexane, as WFs technically and economically, from a process system engineering perspective. Furthermore, the performance of the aforementioned WFs is compared with that of toluene, a well-known WF, and it is concluded that i-butanol and n-butanol are the most competitive alternatives in terms of work output, exergy efficiency, thermal efficiency, total annual cost, and annual profit. Moreover, the i-butanol and n-butanol-based ORC systems yielded 24.4 and 23.4% more power, respectively, than the toluene-based ORC system; in addition, they exhibited competitive thermal (18.4 and 18.3%, respectively) and exergy efficiencies (38 and 37.7%, respectively). Moreover, economically, i-butanol and n-butanol showed the potential of generating 48.7 and 46% more profit than that of toluene. Therefore, this study concludes that i-butanol and n-butanol are promising WFs for high-temperature ORC systems, and their technical and economic performance compares with that of toluene. The findings of this study will lead to energy efficient ORC systems for generating power.
Highlights
The global energy demand has been increasing because of economic and population growth and lifestyle improvements in the developing world
The results show that the thermal efficiency of toluene based organic Rankine cycle (ORC) systems ranges from 5.2 to 21% (Maraver et al, 2014)
The optimum working fluid (WF) is selected based on thermo-physical parameters, such as critical temperature and pressure, latent heat of vaporization (LHv), fluid density, degree of superheating, heat capacity, and viscosity
Summary
The global energy demand has been increasing because of economic and population growth and lifestyle improvements in the developing world. Bruno et al (2008) have simulated an ORC system using the Aspen Plus software and have calculated its thermal efficiency for different WFs; they have not performed a detailed thermodynamic evaluation based on parametric and composite curve analyses. (Lee et al, 2017) have studied an ORC system using liquefied natural gas cold energy utilizing the Aspen Plus software and have optimized the proposed process using a genetic algorithm Their optimized results revealed that the thermal efficiency of the analyzed ORC system was 26%. They have analyzed the proposed process using composite curve analysis but have not evaluated the WFs using a parametric study. The economic benefits of selected unconventional WFs are determined in comparison with toluene
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