•Methodology presented to assess the potential of thermal storage optimal operation.•Average gain in yearly revenue around 5% obtained with respect to usually adopted short-sighted strategies.•Above ...figure amplified to more than 10% in terms of net present value of the investment.•Unveiled also potential of optimal control in terms of investment cost reduction.•Operation strategy constitutes a new important design variable for CSP systems with storage.
Concentrated solar power plants are increasingly considered worldwide, in order to meet the demand for renewable power generation. A distinctive feature of these plants is the possibility of integrating thermal energy storage such that full-load operation can be sustained for several hours in the absence of solar radiation. A number of design software tools are available for sizing the plant and evaluating the return on investment. These usually assume a short-sighted strategy for storage management. This work presents a new methodology aimed at assessing the potential of optimal control techniques when applied to the operation of energy storage systems in general. The design method is applied to a test case, a state-of-the-art central receiver plant with direct storage, using molten salts as working fluid, and operating in a context of variable electricity prices. The system modeling and optimization problems are formulated and implemented using modern high-level modeling languages, demonstrating the potential of the approach. The different operating strategies are compared based on a detailed financial analysis. A wide system design space is explored, and the results presented for all the foreseeable combinations of solar field size and storage system capacity, considering two plant locations, i.e., Daggett (US-CA) and Almeria (ES). Potential gains up to 10% in terms of yearly revenue are estimated, in case improved control strategies are adopted. These figures translate into increases of more than 30% of the investment profitability by considering over-life financial figures. It is further shown how, in case of state-of-the-art systems, it is always profitable to adopt optimal control to the end of increasing electricity production. However, the potential of these techniques is discussed also under the point of view of investment cost reduction, since the same yearly revenue can be harvested with smaller energy storage, if optimally operated. This aspect, unveiled here for the first time, might become significant if technologies with different cost structure are of interest, i.e., in case the storage cost constitutes a comparatively large part of the total investment. The novel method is thus an additional decision tool allowing to treat the storage operation strategy as a new relevant variable for the design of next generation energy systems.
Integrated Gasification Combined Cycle (IGCC) power plants are an effective option to reduce emissions and implement carbon-dioxide sequestration. The combination of a very complex fuel-processing ...plant and a combined cycle power station leads to challenging problems as far as dynamic operation is concerned. Dynamic performance is extremely relevant because recent developments in the electricity market push toward an ever more flexible and varying operation of power plants. A dynamic model of the entire system and models of its sub-systems are indispensable tools in order to perform computer simulations aimed at process and control design. This paper presents the development of the lumped-parameters dynamic model of an entrained-flow gasifier, with special emphasis on the modeling approach. The model is implemented into software by means of the Modelica language and validated by comparison with one set of data related to the steady operation of the gasifier of the Buggenum power station in the Netherlands. Furthermore, in order to demonstrate the potential of the proposed modeling approach and the use of simulation for control design purposes, a complete model of an exemplary IGCC power plant, including its control system, has been developed, by re-using existing models of combined cycle plant components; the results of a load dispatch ramp simulation are presented and shortly discussed.
▸ The acausal dynamic model of an entrained gasifier has been developed. ▸ The model can be used to perform system optimization and control studies. ▸ The model has been validated using field data. ▸ Model use is illustrated with an example showing the transient of an IGCC plant.
Shape optimization in unsteady flow problems enables the consideration of dynamic effects on design. The ability to treat unsteady effects is attractive, as it can provide performance gains when ...compared to steady-state design methods for a variety of applications in which time-varying flows are of paramount importance. This is the case, for example, in turbomachinery or rotorcraft design. Given the high computational cost involved in time-accurate design problems, adjoint-based shape optimization is a promising option. However, efficient sensitivity analysis should also be accompanied by a significant decrease in computational cost for the primal flow solution, as well. Reduced-order models, like those based on the harmonic balance concept, in combination with the calculation of gradients via adjoint methods, are proposed for the efficient solution of a certain class of aerodynamics optimization problems. The harmonic balance method is applicable if the flow is characterized by discrete finite dominant flow frequencies that do not need to be integer multiples of a fundamental harmonic. A fully-turbulent harmonic balance discrete adjoint formulation based on a duality-preserving approach is proposed. The method is implemented by leveraging algorithmic differentiation and is applied to two test cases: the constrained shape optimization of both a pitching airfoil and a turbine cascade. A key advantage of the current approach is the accurate computation of gradients as compared to second order finite differences without any approximation in the linearization of the turbulent viscosity. The shape optimization results show significant improvements for the selected time-dependent objective functions, demonstrating that design problems involving almost-periodic unsteady flows can be tackled with manageable computational effort.
•Fully-turbulent discrete adjoint method based on harmonic-balance.•Shape optimization for quasi-periodic unsteady problems.•Application to the constrained shape optimization of problems characterized by a set of discrete frequencies.•Increased significantly the performance of a pitching airfoil and a turbine cascade subject to unsteady inflow conditions.
•New thermal storage concepts specific to solar ORC power plants.•Contains a review of thermal storage concepts for Rankine cycle power systems.•New thermodynamic cycle configuration for ...high-temperature ORC systems.•Simulation of test case: 100kW modular system.
The feasibility of energy storage is of paramount importance for solar power systems, to the point that it can be the technology enabler. Regarding concentrated solar power (CSP) systems, the implementation of thermal energy storage (TES) is arguably a key advantage over systems based on photovoltaic (PV) technologies. The interest for highly efficient and modular CSP plants of small to medium capacity (5kWE–5MWE) is growing: organic Rankine cycle (ORC) power systems stand out in terms of efficiency, reliability and cost-effectiveness in such power-range. In this paper a thorough investigation on thermal storage systems tailored to high-temperature (≈300°C) ORC power plants is addressed first, stemming from the observation that the direct storage of the ORC working fluid is effective thanks to its favourable thermodynamic properties. The concept of complete flashing cycle (CFC) is then introduced as a mean of achieving an unmatched system layout simplification, while preserving conversion efficiency. This is a new variant of the Rankine cycle, whereby the vapour is produced by throttling the organic working fluid from liquid to saturated vapour conditions. The presentation and discussion of a case study follows: a 100kWE CFC system with direct thermal energy storage, coupled with state-of-the-art parabolic trough collectors. The proposed turbogenerator achieves an estimated 25% efficiency, which corresponds to a value of 18% in design conditions for the complete system. Considering siloxanes as working fluids, the estimated values of storage density are around 10kWeh/mstorage3.
Compressible flows of fluids whose thermophysical properties are related by complex equations are quantitatively and can be qualitatively different from high-speed flows of ideal gases. Nonideal ...compressible fluid dynamics (NICFD) is concerned with these fluid flows, which are relevant in many processes and power and propulsion systems. Typically, NICFD effects occur if the fluid is an organic compound and its vapor state is close to the vapor–liquid critical point, at high-reduced temperature and pressure (even supercritical). Current design and analysis of devices operating in the nonideal compressible regime demand for validated simulation software, characterized in terms of uncertainty. Moreover, experiments are needed to further validate related theory. Experimental data are limited as generating and measuring these flows is challenging given their high pressure or temperature or both. In addition, flows of organic compounds can be flammable, can thermally decompose, and sealing may demand for special materials. Recently, more research has been devoted to the measurement of these flows using both intrusive and less intrusive techniques relying on optical access and lasers. The transparency and refractive properties of these dense vapors pose additional problems. The ORCHID (organic Rankine cycle hybrid integrated device) at the Aerospace Propulsion and Power Laboratory of Delft University of Technology is a closed-loop facility, used to generate a continuous nonideal supersonic flow of siloxane MM with the vapor at 4
bar
and 220 °C at the inlet of the test section. Within this work, we have employed particle image velocimetry for the first time to obtain the velocity field in a de Laval nozzle in such flows. Measured velocity fields (expanded uncertainty within 1.1% of the maximum velocity) have been compared with those resulting from a CFD simulation. The comparison between experimental and simulated data is satisfactory, with deviation ranging from 0.1 to 10 % from the throat to the outlet, respectively. This discrepancy is attributed to hardware limitations, which will be overcome in the future experiments. The feasibility of PIV with uncontrolled but fixed seeding density to measure high-speed vapors of organic vapors has been demonstrated, and future experimental campaigns will target flows for which nonideal effects are more pronounced, other paradigmatic configurations, and improvements to the measurement techniques.
Catastrophic cervical spine injuries are rare in rugby union but require close monitoring. The aim of this study was to analyse the incidence of severe cervical spine injuries and determine the ...impact of a national prevention programme and new scrum rules implemented by the French Rugby Union.
A prospective study was performed between 2006 and 2013 including all players affiliated to the French Rugby Union. All cervical spine injuries resulting in death, tetraplegia or a permanent neurological deficit were included. Prevention programmes were implemented from 2007 to 2013 and a change in scrum rules in 2010. To measure the impact of rule changes, results between 2006-2010 and 2010-2013 were compared using a Poisson regression.
Altogether, 31 injuries were observed and the mean annual incidence was 1.6 per 100 000 players. There were significantly more injuries in senior players compared to junior players (3.5 vs 0.6 per 100 000 players; CI 95% (2.1 to 4.9) vs (0.1 to 1.0)). Incidence decreased from 1.8 in 2006 to 1.0 per 100 000 players in 2013 (p<0.0001). After 2010, there were significantly fewer injuries during scrums (p=0.02). In contrast, there were significantly more injuries in backs during 2010-2013 compared to 2006-2010 (p=0.003).
The incidence of catastrophic cervical spine injuries has declined in French Rugby Union. The implementation of specific prevention programmes and scrum law changes has notably resulted in a decrease in scrum injuries in forwards. This prospective study should be continued to monitor the future progression of injuries and adapt prevention programmes accordingly.
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