• Energy Research

Abstract The aim of this study is to obtain more realistic estimations of the achievable capacity factor and availability of waste-to-energy power plants to better understand their economics, and hence facilitate appropriate deployment. Towards this aim, we introduce Markov analysis and off-design considerations into the calculation of plant performance. Parameters such as increasing failure rates as a result of aging, infant mortality failures, and overhauls are all taken into account with our approach. Meanwhile, the effect of failures on such plant’s operating mode is evaluated, and Stodola’s cone law is applied to calculate the actual power generation in off-design mode. A system divided into three main sub-components, two steam generation blocks and a power generation block, each of which has its own failure and repair rates, is proposed for this study. The state-space diagram of the proposed system is constructed and simplified, and the transient differential equations governing the state-space diagram are solved numerically. Having obtained the availability of the system and off-design performance, the capacity factor is calculated and compared with actual field data. Also, a new availability-based formulation is presented to obtain the net present value of the cash flow. Results show that by using a time-varying failure rate, the availability of the power plant declines about 23% over 20 years, a significant difference to estimated availability if a constant failure rate was assumed. Our findings highlight that the present price of electricity, $0.057 per kWh, for generation from the plant is insufficient to encourage investment in this technology in Iran at present, and greater deployment will require some form of policy intervention.

Abstract The aim of this study is to obtain more realistic estimations of the achievable capacity factor and availability of waste-to-energy power plants to better understand their economics, and hence facilitate appropriate deployment. Towards this aim, we introduce Markov analysis and off-design considerations into the calculation of plant performance. Parameters such as increasing failure rates as a result of aging, infant mortality failures, and overhauls are all taken into account with our approach. Meanwhile, the effect of failures on such plant’s operating mode is evaluated, and Stodola’s cone law is applied to calculate the actual power generation in off-design mode. A system divided into three main sub-components, two steam generation blocks and a power generation block, each of which has its own failure and repair rates, is proposed for this study. The state-space diagram of the proposed system is constructed and simplified, and the transient differential equations governing the state-space diagram are solved numerically. Having obtained the availability of the system and off-design performance, the capacity factor is calculated and compared with actual field data. Also, a new availability-based formulation is presented to obtain the net present value of the cash flow. Results show that by using a time-varying failure rate, the availability of the power plant declines about 23% over 20 years, a significant difference to estimated availability if a constant failure rate was assumed. Our findings highlight that the present price of electricity, $0.057 per kWh, for generation from the plant is insufficient to encourage investment in this technology in Iran at present, and greater deployment will require some form of policy intervention.

Abstract The current paper aims to compare the four fundamental Organic Rankine Cycle (ORC) structures with a zeotropic mixture of Pentane and Hexane, utilized as the working fluid. The studied variants of ORCS include simple single and dual-pressure ORCs alongside their recuperative configurations. Each configuration is optimized in different mole fractions to obtain the parameters that generate the highest power. The energy and exergy efficiencies are then calculated and compared besides a detailed view of the exergy destructions of each component. Next, the Levelized Cost of electricity is calculated for each mole fraction to carry out the thermoeconomic analysis. The optimum mole fractions of each structure are then obtained to conduct a techno-economic analysis to elaborate more on the superiority of cycles than each other, considering both economic and thermodynamic results. According to the results, the recuperative dual-pressure ORC is the most efficient and has the most generated power (2038 kW), while the other’s performances decline regarding their complexity level. Its performance is found to be more than 16% better than the simple ORC structure which proves a significant improvement. In addition, using a zeotropic mixture can boost the cycle performance and reduce the exergy destructions. Moreover, it is revealed that the dual-pressure ORC is not an economically acceptable option due to its relatively lower net present value, 4.29 M$, while the recuperative structures result in a NPV of 4.53 M$ after the 20-year lifetime. Finally, by conducting a sensitivity analysis, it is concluded that either of the recuperative configurations can be of more desire depending on the power demand and electricity price.

Abstract The current paper aims to compare the four fundamental Organic Rankine Cycle (ORC) structures with a zeotropic mixture of Pentane and Hexane, utilized as the working fluid. The studied variants of ORCS include simple single and dual-pressure ORCs alongside their recuperative configurations. Each configuration is optimized in different mole fractions to obtain the parameters that generate the highest power. The energy and exergy efficiencies are then calculated and compared besides a detailed view of the exergy destructions of each component. Next, the Levelized Cost of electricity is calculated for each mole fraction to carry out the thermoeconomic analysis. The optimum mole fractions of each structure are then obtained to conduct a techno-economic analysis to elaborate more on the superiority of cycles than each other, considering both economic and thermodynamic results. According to the results, the recuperative dual-pressure ORC is the most efficient and has the most generated power (2038 kW), while the other’s performances decline regarding their complexity level. Its performance is found to be more than 16% better than the simple ORC structure which proves a significant improvement. In addition, using a zeotropic mixture can boost the cycle performance and reduce the exergy destructions. Moreover, it is revealed that the dual-pressure ORC is not an economically acceptable option due to its relatively lower net present value, 4.29 M$, while the recuperative structures result in a NPV of 4.53 M$ after the 20-year lifetime. Finally, by conducting a sensitivity analysis, it is concluded that either of the recuperative configurations can be of more desire depending on the power demand and electricity price.

Abstract Similar to other energy systems, economic analysis of cogeneration systems is one of the most important steps in their design procedure. In this paper, a novel method is suggested for economic optimization of cogeneration systems. This method provides an opportunity to consider uncertainties in various economic parameters. Accordingly, by providing the probability distribution function of the net present value or payback time, this method offers further insights in economic evaluations of cogeneration systems. As a common practice for demonstrating novel methodologies in design and optimization of cogeneration systems, the proposed method of this study is applied to a well-known cogeneration case in the literature. In a coupled scheme, Monte Carlo approach is applied with net present value method to optimize the system. Accordingly, the obtained result is the probability distribution function of the net present value of the maximum profit. The results verify that compared to previously used methods which did not consider uncertainties in economic parameters, this probability distribution function provides a more general point of view on the profitability of the system. Therefore, by showing economic risks, these considerations make investments in this cogeneration system far more interesting.

Abstract Similar to other energy systems, economic analysis of cogeneration systems is one of the most important steps in their design procedure. In this paper, a novel method is suggested for economic optimization of cogeneration systems. This method provides an opportunity to consider uncertainties in various economic parameters. Accordingly, by providing the probability distribution function of the net present value or payback time, this method offers further insights in economic evaluations of cogeneration systems. As a common practice for demonstrating novel methodologies in design and optimization of cogeneration systems, the proposed method of this study is applied to a well-known cogeneration case in the literature. In a coupled scheme, Monte Carlo approach is applied with net present value method to optimize the system. Accordingly, the obtained result is the probability distribution function of the net present value of the maximum profit. The results verify that compared to previously used methods which did not consider uncertainties in economic parameters, this probability distribution function provides a more general point of view on the profitability of the system. Therefore, by showing economic risks, these considerations make investments in this cogeneration system far more interesting.