Abstract
Low-grade heat sources such as solar thermal, geothermal, exhaust gases and industrial waste heat are suitable alternatives for power generation which can be exploited by means of small-scale Organic Rankine Cycle (ORC). This paper combines thermodynamic optimization and economic analysis to assess the performance of single and dual pressure ORC operating with different organic fluids and targeting small-scale applications. Maximum power output is lower than 45 KW while the temperature of the heat source varies in the range 100–200 °C. The studied working fluids, namely R1234yf, R1234ze(E) and R1234ze(Z), are selected based on environmental, safety and thermal performance criteria. Levelized Cost of Electricity (LCOE) and Specific Investment Cost (SIC) for two operation conditions are presented: maximum power output and maximum thermal efficiency. Results showed that R1234ze(Z) achieves the highest net power output (up to 44 kW) when net power output is optimized. Regenerative ORC achieves the highest performance when thermal efficiency is optimized (up to 18%). Simple ORC is the most cost-effective among the studied cycle configurations, requiring a selling price of energy of 0.3 USD/kWh to obtain a payback period of 8 years. According to SIC results, the working fluid R1234ze(Z) exhibits great potential for simple ORC when compared to conventional R245fa.
Highlights
In the last decades, the interest in improving energy efficiency of industrial processes has increased and new technologies have been proposed to reduce the consumption of fossil fuels [1,2]
This paper proposes a comprehensive thermodynamic and economic study of a small scale dual pressure Organic Rankine Cycle (ORC) configuration operating with low temperature waste heat recovery and generating a net power of less than 45 kW
In the case of simple ORC (Figure 5a), fluids develop almost the same net power output and thermal efficiency when heat source temperature is below 130 °C and net power is optimized
Summary
The interest in improving energy efficiency of industrial processes has increased and new technologies have been proposed to reduce the consumption of fossil fuels [1,2] To achieve this goal, new thermodynamic cycles have been proposed and some of them have been introduced in the market as competitive commercial alternatives to conventional heat-to-power cycles such as gas turbines and internal combustion engines. New thermodynamic cycles have been proposed and some of them have been introduced in the market as competitive commercial alternatives to conventional heat-to-power cycles such as gas turbines and internal combustion engines Some of these new thermodynamic cycles employ pure and zeotropic mixtures of organic fluids due to their low boiling temperatures, which results in an efficient utilization of the heat source [3,4,5]. On the other hand an ORC system of 6–18 kW power output for heat recovery in the ceramic industry showed a payback period of 5 years [13,14]
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