11:10
Session 7B: System Design - Operating Parameters
Chair: Stratis Varvagiannis
11:10
20 mins
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Uncertainty Quantification of Performance Parameters in a Small Scale ORC Test Rig
Michele Bianchi, Lisa Branchini, Andrea de Pascale, Francesco Melino, Saverio Ottaviano, Antonio Peretto, Nicola Casari, Ettore Fadiga, Michele Pinelli, Pier Ruggero Spina, Alessio Suman
Abstract: Thermodynamic measurements are affected by a certain level of uncertainty due to the sensor/probe characteristics, installation, calibration procedure, and references. In power cycle for energy production, such as standard Rankine cycles and Organic Rankine Cycles (ORC), pressure, temperature, and mass flow rate are used as the basis for estimating the cycle performance, as well as, they are used for monitoring the entire cycle and its operating conditions. In the present work, a small-scale ORC system is taken as reference for performing the assessment of the uncertainty sources and their propagation in the estimation of the cycle performance. The analysis is referred to an ORC system that operates with a temperature of the hot source lower than 100 °C, a net electric power at the generator lower than 1 kW and the R134a as the working fluid. Since the accuracy of the performance estimation is related to the performance of measurement system and to its calibration, three different scenarios have been analyzed in relation to the sensor/probe performance, calibration process, and acquisition devices’ operating conditions. For the performance uncertainty estimation, temperature, pressure, and mass flow rate measurement uncertainties are taken into consideration, as well as the effect of the thermodynamic library used for calculating enthalpy values. The uncertainty values of performance parameters that characterize an ORC system such as expander work, expander power, and overall system efficiency have been assessed showing how the calibration process represents the mandatory step in the way of reducing the uncertainty band. Acquisition module and calibrator performance have to be assessed in comparison with the performance of the sensors and probes installed in the ORC system.
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11:30
20 mins
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Operating Characteristics of Working Fluid Pump in a 315 kW Organic Rankine Cycle System
Zhe Wu, Zhiwei Yuan, Long Chen, Jianzhao Li
Abstract: In the organic Rankine cycle (ORC) power generation system, the working fluid pump, as a boosting component, determines the stability, efficiency and safety of the system. This paper is based on ORC power generation test of 315kW, which uses R134a as the working fluid and variable frequency multistage centrifugal pump as the working fluid pump. In order to explore the effect of the cold source on the operating characteristics of the working fluid pump, the system load and the pump speed (960~2960rpm) are all increased at different cooling water temperatures (279K、283K、287K、291K) while maintaining the evaporator outlet superheat degree at 20±1K. The parameters such as the temperature, pressure and flow rate were measured, and the performance curve, output power , the Net Positive Suction Head available (NPSHa) and efficiency of the pump under off-design conditions were studied. The experimental results show that the rotational speed of the working fluid pump has a significant effect on the NPSHa. As the pump speed increasing, the temperature and pressure of the working fluid at the pump inlet are affected, leading to NPSH rising first and then decreasing.. When the cooling water temperature is 291K and the pump speed is 2250 rpm the NPSHa reaches the maximum value of 10.8m water head. In addition, at the same speed, the increase of the temperature of the cooling water increases the flow rate and the pump outlet pressure, at the same time, the NPSHa of the pump increasing. The research results could provide guidance and reference for the efficient operation and cavitation protection of the working fluid pump in the ORC system.
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11:50
20 mins
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Experimental Investigation on the Effect of a Separator on Operating Parameters of an ORC
Tomasz Z. Kaczmarczyk, Grzegorz Żywica, Eugeniusz Ihnatowicz
Abstract: The article presents the results of the experimental investigation on the effect of a vapour-liquid separator used for a low-boiling medium on operating parameters of an organic Rankine cycle (ORC). A biomass boiler with a thermal power of 25 kWt was used as a heat source. Pellets were used as its fuel. In the ORC system, the working medium (HFE7100) was heated with thermal oil. Expansion of the low-boiling medium took place in a four-stage radial-flow microturbine whose rated electric power and rotational speed are respectively 2.5 kWe and 24 krpm. It is important that the operation of this microturbine is both stable and failure-free. For this, an appropriate vapour overheating degree is needed at the microturbine’s supply side. Therefore, a prototypical inert vapour-liquid separator for the working medium was designed and built. This device allows for two modes of operation for the system; bypass mode and turbine mode. The effect the vapour-liquid separator has on the operating parameters was described and shown using heat and flow characteristics. Those characteristics were prepared on the basis of measurements conducted with thermodynamic flow meters. Observing the process was made possible by using a specifically designed sight vane. It was observed that the tested separator worked as heat storage in the ORC installation. Both during transition states of the microturbine and instantaneous fluctuations in the thermal power of the boiler (stemming from its thermal inertia and the cyclical feeding of fuel), the separator provided stable operating conditions at the proper overheating degree of the working medium’s vapour. It was found that in vapour-fed systems such a separator can also work as a clarifier or a filter for solid particles.
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