The effect of the relative hot-to-cold side volume-ratios on dynamic characteristics of a closed Brayton cycle (CBC) with supercritical carbon-dioxide (sCO 2) as the working-fluid is investigated in this study. The analysis of the CBC is conducted in the context of power generation in a direct-heated (no thermal-oil loop) and dry-cooled parabolic-trough solar thermal power plant, using a control-oriented model. Dynamic performance of the sCO 2 CBC with different relative volume-ratios between the hot and cold sides of the sCO 2 CBC is compared using simulations for conditions on a representative summer day. The CBC hot-to-cold side volume-ratio influences CO 2 mass movement and hence power output. Increasing the hot-to-cold side volume-ratio in the CBC results in slower, more gradual dynamic response when there are fluctuations in solar heat input and ambient air temperatures. The dynamic response characteristics of a CBC with a hot-to-cold side volume-ratio lower than one is shown to differ significantly from one with a volume-ratio greater than or equal to one.
The use of organic refrigerants or supercritical CO2 (sCO2) as a working fluid in closed loop power cycles has the potential to revolutionise power generation. Thermodynamic cycle efficiency can be improved by selecting bespoke working fluids that best suit a given combination of heat source and heat sink temperatures, but thermal efficiency can be maximised by pairing this with a custom made turbine. This work describes the development and design of a new 100kW thermal laboratory-scale test loop at the University of Queensland. The loop has capabilities for characterising both simple and recuperated refrigerant and sCO2 organic Rankine cycles in relation to overall cycle performance and for the experimental characterisation of radial inflow turbines. The aim of this facility is to generate high quality validation data and to gain new insight into overall loop performance, control operation, and loss mechanisms that prevail in all loop components, including radial turbines when operating with supercritical fluids. The paper describes the current test loop and provides details on the available test modes: an organic Rankine cycle mode, a closed loop Brayton cycle mode, and heat exchanger test mode and their respective operating ranges. The bespoke control and data acquisition system has been designed to ensure safe loop operation and shut down and to provide high quality measurement of signals from more than 60 sensors within the loop and test turbine. For each measurement, details of the uncertainty quantification in accordance with ASME standards are provided, ensuring data quality. Data from the commissioning of the facility is provided in this paper. This data confirms controlled operation of the loop and the ability to conduct both cycle characterisation tests and turbomachinery tests.
Small-bore piping and instrument tubing vibration failures are not just a hidden risk to production, reliability, and safety, but also a frequent source of emissions through leaks and plant flaring when issues arise. Vibration-induced failure risks are often overlooked and detected too late, despite making up a significant portion of leaks and lost production incidents. Conventional approaches to managing these hidden risks have resulted in recurring failures and unplanned downtime at process plants. Large inventories of Small-Bore Fittings (SBFs) and tubing generally require management as most are integral parts of the plant and can be classed as safety and/or production critical. Small-bore tubing assemblies are at risk of fatigue failure due to a general lack of awareness of the best-practice design for reducing vibration response and how to manage this risk. A holistic approach to manage and pro-actively reduce small-bore piping and tubing vibration anomalies in the field is presented in this paper. This involves a risk-based assessment approach combined with the use of digital tools to register, manage, and visualise the status of the risk to the plant and the improvement in risk with the implementation of remedial actions. Best-practice and a short case study is discussed to demonstrate how the approach can be implemented to effectively reduce and manage vibration-induced small-bore piping and tubing failure incidents.
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