Abstract
Power conversion systems based on the Organic Rankine Cycle (ORC) have been identified as a potential technology especially in converting low-grade renewable sources or waste heat. However, it is necessary to improve efficiency of ORC systems. This paper focuses on use of low geothermal resources (for temperature range of 80–128 °C and mass flow 100 kg/s) by using modified ORC. A modification of conventional binary power plant is conducted by combining gas turbines to increase quality of steam from a geothermal well. An analysis has been conducted for three different working fluids: R245fa, R1233zd(E) and R600. The paper discusses the impact of parameter changes not only on system efficiency but on other performance indicators. The results were compared with a conventional geothermal Organic Rankine Cycle (ORC). Increasing of geothermal steam quality by supplying exhaust gas from a gas turbine to the installation has a positive effect on the system efficiency and power. The highest efficiency of the modified ORC system has been obtained for R1233zd(E) as a working fluid and it reaches values from 12.21% to 19.20% (depending on the temperature of the geothermal brine). In comparison, an ORC system without gas turbine support reaches values from 9.43% to 17.54%.
Highlights
In recent years, energy is considered to be one of the basic factors conditioning the growth of individual countries, as well as one of the basic goods, without which economic development is inhibited
The simplicity, reliability, and flexibility of Organic Rankine Cycle (ORC) is due to the fact that it can be successfully applied to used heat from renewable sources and waste heat processes [23]
The thermal input provided by the gas turbine for ORC system is constant because of the assumptions made at the beginning of this analysis
Summary
Energy is considered to be one of the basic factors conditioning the growth of individual countries, as well as one of the basic goods, without which economic development is inhibited. The work investigated their potential as a replacement of traditional refrigerants in ORC installations due to their good impact on environment zero ODP (Ozone Depletion Potential) and a very low GWP (Global Warming Potential) They found that some of the investigated HFOs obtained promising system efficiency especially for low and medium temperature geothermal ORC power generation. The superheat degree of vapor from geothermal brine is low, it would be much better to heated it before expanding it in a steam turbine Such an action could improve a thermal efficiency of the geothermal power plant. The novelty 3ofof this paper is in analyzing and modeling such modified ORC cycle, where gas turbine has been used as support subsystem to increase the enthalpy of geothermal brine.
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