Design and optimization of staged ORC power plant by waste heat

Reducing CO2 emissions to zero is the biggest challenge facing humanity (Nelson & Allwood, 2021). Therefore, technologies for the production of low-grade thermal energy are very important to achieve the goal (Hafner, Jones, & Anger-Kraavi, 2012), which can recycle waste industrial heat and improve the efficiency of fossil fuel use, they can be applied to some low temperature renewable energy sources (Loni, ve diğerleri, 2020). The Organic Rankine cycle (ORC) may have the greatest potential among all low order heat generation technologies (Anastasovski, Raskovski, & Guzovic, 2020). As a result, many researchers have focused on improving the thermodynamic and economic performance of ORC over the past decade. One of the most effective ways to improve ORC's performance is to increase the ORC's cycle count. Double-loop ORC (DLORC) has shown great potential in thermodynamic and economic performance. In addition, DLORC has a low carbon footprint and high CO2 emission reduction. Ouyang et al. (Ouyang, et al., 2019). Boyaghchi and Chavoshi studied the environmental impact rates of DLORC driven by solar energy. The analysis results revealed that DLORC's lowest environmental impact rates occurred in April. A thermodynamic analysis was performed on DLORC (Sciubba, Tocci, & Toro, 2016). Analysis results showed that using two base ORCs for a single source can significantly improve thermal efficiency and heat source utilization rate. Sciubba et al. also performed the fluid selection for DLORC. The results showed that R245fa has a better thermodynamic performance compared to R600. Xia et al. performed the working fluid selection for series-parallel DLORC using multi-objective optimization. The targets for optimization are the payback period, annual emission reduction, exergy efficiency. Study selection results showed that cyclohexane/butane was the most suitable working fluid among the 18 candidate working fluid pairs for the series-parallel configuration. The concept of a triple loop was proposed to achieve better performance. In the article, two types of triple loops are reported, one in series and the other in parallel. The results obtained in the referenced studies showed that both types can improve the performance of the system. Dwinanto analyzed the thermodynamic performance of the triple cycle. Research showed that triple loops have a higher energy use. Zhang et al. proposed an innovative multi-loop ORC. Parametric analysis showed that Multi-Loop ORC (MLORC) can significantly improve system performance. In a study, thermal economic optimization and analysis of the ORC-ORC combined power system were also studied. (Braimakis & Karellas, 2018) optimized the use of ORC-ORC for waste heat recovery. Select the upper and lower circulation evaporator pressure, the minimum temperature difference of the upper circulation evaporator, the condenser temperature as optimized variables. The researchers aim to explore the potential to increase the exergy efficiency of the ORC-ORC combined power system compared to a single-stage ORC and maximize the net power output at a heat source temperature of 100 to 300 °C. Comparing the results obtained with ORC-ORC with single-stage cycles, they concluded that the power output and exergy efficiency of ORC-ORC can be increased with different heat source temperatures, compared with single-stage cycles for these operating temperatures. Literature reviews have shown that double-cycle, triple-cycle and multi-cycle ORC outperform a single ORC for recovery of a single waste heat source. Moreover, according to the literature review, three different types of double-stage cycles are compared to a single cycle. It can significantly improve the performance of ORC. However, as far as we know, although the ORC-ORC combined power system has been studied in the literature, very few studies have been done with three stages. Therefore, comparative thermodynamic energy and exergy analysis results using the combined power cycle of 3-stage ORC will make a significant contribution to the literature. The aim of this study is to select the appropriate configuration, working fluid combinations and number of cycles for multistage ORC. The method used is energy and exergy analysis of the thermodynamic performance of Multi-Loop ORC (MLORC) in various configurations. Configurations are single, double and triple cascade configurations. In addition, multi-objective optimization and multi-attribute decision making methods are performed to search for the best working fluid combination, the number of cycles, and configuration for Multi-Loop ORC.