Perfomance analysis of hybrid systems based on externally heayed closed-cycle engines

This work presents a comparative analysis of hybrid systems that make use of closed-cycle externally heated bottoming systems. Two options are considered: reciprocating (Stirling) engines and supercritical carbon dioxide turbines. These engines share the common feature of working on closed cycles with optimised fluids (H2 and CO2 respectively). However, they differ in their internal structure: Stirling engines make use of volumetric machinery whereas the SCO2 system is composed by turbomachinery. In both cases, the working fluid is subjected to very high pressure and temperature in the range of 50-200 bar and 40-650 ºC. A brief description of both bottoming systems is provided in the article along with the expected performance of each case in on-design and off-design (part load) conditions. The analysis is therefore split into two stages. First, a comparison is shown for on-design operation aiming to evaluate the maximum efficiency attainable by the proposed systems. Second, a preliminary analysis of off-design operation is presented. The paper concludes that hybrid systems based on atmospheric fuel cells and externally heated closed-cycle bottoming engines have the potential to outperform conventional pressurised fuel cells and gas turbines hybrids while preserving the topping system from the demanding operating conditions of the latter configuratio

Preliminary investigation on the adoption of CO2-SO2 working mixtures in a transcritical Recompression cycle

This paper investigates the interest and potential of using working fluids based on Carbon and Sulphur Dioxide mixtures (CO2-SO2) in a transcritical Recompression cycle. In order to assess the actual thermodynamic potential of the concept proposed, the influence of dopant (SO2) content is assessed for two different turbine inlet temperatures (550 °C and 700 °C). The results obtained are compared with other CO2 mixtures already proposed in literature (CO2-C6F6 and CO2--TiCl4) and for two alternative cycle layouts (Recuperated Rankine and Precompression). The results pf the analysis reveal that, at high ambient temperature, the Recompression cycle operating on CO2-SO2, with Sulphur Dioxide content between 20% and 30%(v), is a very interesting option for Concentrated Solar Power plants, able to achieve thermal efficiencies of approx. 45% and 51% at 550 °C and 700 °C respectively. At a minimum cycle temperature of 50 °C, the proposed configuration leads to thermal efficiency gains of 6% and 2% with respect to the Brayton and Recompression cycles working on pure CO2. This performance enhancement of the Recompression cycle with CO2-SO2 is comparable to or higher than that enabled by other CO2 mixtures proposed in literature, but with significantly higher specific work (smaller footprint) and temperature rise across the solar receiver (lower installation costs).Unión Europea H2020-814985University of Seville - Internal Research Programme (Plan Propio de Investigación) contract No 2019/00000359Junta de Andalucía - Programme for Youth Employment 2014–202

Potential of Supercritical Carbon Dioxide Power Cycles to Reduce the Levelised Cost of Electricity of Contemporary Concentrated Solar Power Plants

This paper provides an assessment of the expected Levelised Cost of Electricity enabled by Concentrated Solar Power plants based on Supercritical Carbon Dioxide (sCO2) technology. A global approach is presented, relying on previous results by the authors in order to ascertain whether these innovative power cycles have the potential to achieve the very low costs of electricity reported in the literature. From a previous thermodynamic analysis of sCO2 cycles, three layouts are shortlisted and their installation costs are compared prior to assessing the corresponding cost of electricity. Amongst them, the Transcritical layout is then discarded due to the virtually impossible implementation in locations with high ambient temperature. The remaining layouts, Allam and Partial Cooling are then modelled and their Levelised Cost of Electricity is calculated for a number of cases and two different locations in North America. Each case is characterised by a different dispatch control scheme and set of financial assumptions. A Concentrated Solar Power plant based on steam turbine technology is also added to the assessment for the sake of comparison. The analysis yields electricity costs varying in the range from 8 to over 11 g/kWh, which is near but definitely not below the 6 g/kWh target set forth by different administrations. Nevertheless, in spite of the results, a review of the conservative assumptions adopted in the analysis suggests that attaining costs substantially lower than this is very likely. In other words, the results presented in this paper can be taken as an upper limit of the economic performance attainable by Supercritical Carbon Dioxide in Concentrated Solar Power applications.Unión Europea (Programa Horizonte 2020) 81498

Innovative Desalination System Driven by a Solar Micro Gas Turbine for Off-Grid Applications

Past work by the authors has suggested that Solar micro Gas Turbines (SmGTs) can be used cost-effectively to produce electric power and heat for freshwater production through desalination, mainly in off-grid locations. This is further studied in this work, presenting a detailed description of system performance at design and part-load conditions, as well as the characteristics of the components of the SmGT and the desalination unit. To this end, the SmGT is assessed first, considering techniques that achieve a greater off-design performance such as incorporating Variable Inlet Guide Vanes (VIGVs) at the compressor inlet, and including the sensitivity to control strategies and ambient conditions, exploring their expectedly very negative impact on the SmGT performance. Water treatment system is comprised of two elements. A Reverse Osmosis desalination unit is driven by the electric power produced by the SmGT. This produces brine with high salt concentration to be partially treated further in a Zero Liquid Discharge (ZLD) unit driven by the exhaust gases of the microturbine (at about 250-300ºC), where the sensible heat of this stream is harvested by the ZLD unit to “dry” and concentrate the effluent. Finally, the potential and the operational limitations of the ZLD system are discussed, supplemented by an experimental proof of concept where its feasibility was verified

Optimum design and performance of a solar dish microturbine using tailored component characteristics

Versión revisada. Embargo 24 mesesThe aim of the paper is to find the optimum design and performance of solar microturbines powered by parabolic dish collectors using an innovative methodology which integrates the design and off-design models of the total system. In contrast to the common practice of assigning an estimated efficiency to the engine turbomachinery (generalized performance maps), the procedure hereinafter produces the specific geometry and the characteristic maps of compressor and turbine, according to their inlet/outlet thermodynamic states and working cycle boundary conditions. With this global approach, a sensitivity analysis is performed to search for the pressure ratio that maximizes the solar-to-electric efficiency at design point for a constant air mass flow rate and turbine inlet temperature. Maximum values in the range 18.0–21.7% are obtained for a pressure ratio of 3.2 when the turbine inlet temperature changes between 800 °C (base-case system) and 900 °C. The methodology allows also to simulate the performance of the system when different design DNIs are considered with the aim to maximize the annual yield of the system. Simulations performed for Beijing, Seville and San Diego showed that quite different DNIs (610–815 W/m2) are to be chosen to get the maximum annual (average) efficiency: 11–16% for the base-case system and 14–19% for a more advanced design.Comisión Europea Grant Agreement No. 30895

Estudio del flujo meridional en turbomáquinas axiales

En este trabajo se presenta un estudio numérico del flujo meridional en turbomáquinas axiales. Para ello se ha implementado un código numérico que resuelve el flujo meridional tanto a partir de las ecuaciones de equilibrio radial simplificado, como mediante las ecuaciones completas que modelan el flujo meridional, usando la función de corriente, mediante la teoría clásica del disco actuador. El trabajo ha partido del estudio para flujo incompresible, siendo validado para las configuraciones encontradas en bibliografía y se ha implementado una aplicación informática genérica para la resolución del problema de análisis directo así como para el problema inverso (en el caso de imponer una ley torsional genérica). Asimismo se ha extendido el análisis de cascadas aisladas de estator y rotor a escalonamientos y turbomáquinas con múltiples escalonamientos. Finalmente tras el proceso de análisis y validación de los métodos implementados se ha pasado a la extensión del análisis a escalonamientos de cascadas en turbomáquinas térmicas. Para ello se ha complementado el método del disco actuador, mediante la inclusión de los términos asociados a densidad variable, tratándolos como términos fuente correctores.In this work a numerical analysis of meridional flow in axial turbomachinery has been performed applying the actuator disk theory. A numerical tool for non compressible flows was implemented based on the actuator disk theory, improving the results from the simple radial equilibrium analysis. Later on the model was also extended to the analysis for compressible flows under the actuator disk theory

Adoption of CO2 blended with C6F6 as working fluid in CSP plants

The adoption of CO2-based mixtures as power block working fluid for CSP plant can turn supercritical CO2 cycles into efficient transcritical cycles even at high ambient temperature, with significant performance improvement and potential power block cost reduction. In this work, the use of CO2+C6F6 mixture as working fluid for a power cycle coupled with a solar tower is analyzed. Two different cycle maximum temperatures (550°C and 650°C) are considered and for both configurations the overall plant design is performed. The yearly energy yield is computed with hourly data and the LCOE is minimized varying storage and cycle recuperator sizes. Results show comparable results for the innovative working fluid and for the sCO2 cyclesEuropean Union’s Horizon 2020 No 81498

Market Opportunities of Water Treatments Powered by Solar Micro Gas Turbines: Chile and Ecuador Case Studies

Throughout the last decades the developments on desalination field have been focused on energy consumption and costs reduction. However, water recovery and brine disposal are becoming a matter of concern to desalination industry. In this work, a Zero Liquid Discharge (ZLD) unit coupled with a Solar Micro Gas Turbine (SMGT) system is presented to address, among others, the challenges of mining industry in remote areas, in particular, fossil fuel dependence, water availability and pollution derived from effluents disposal. As a way to assess the feasibility of the proposal, a techno-economic analysis of the application in two Southern American regions (Chile and Ecuador) of photovoltaic modules, wind turbines and Solar Micro Gas Turbines is performed. Afterwards, the main novel feature of the new system—i.e., the ZLD unit—is described and a sensitivity analysis on its functioning whilst coupled with the SMGT is carried out. The aim is to propose a preliminary design of the ZLD process. The selection of the optimal ratio between exhaust gases and brine mass flow rates is analyzed, as well as variation in inlet salinity and temperatures. Furthermore, the water which could be recovered from effluents, at the same time that the heat of exhaust gases from SMGT is harvested, is quantified. Lastly, according to the results obtained, a preliminary design of a 10 kWe rated power SMGT system, coupled to Reverse Osmosis (RO) and ZLD units, is proposed.Ministerio de Ciencia, Innovación y Universidades - Agencia Estatal de Investigación (AEI) - Fondo Europeo de Desarrollo Regional (FEDER) RTI2018-102196-B-100FEDER - Interreg Atlantic Area (EERES4WATER project) EAPA 1058/2018Universidad de Sevilla 2019/0000035

Mechanical analysis of Genoa 03 stirling engine

Due to the new technologies development based on renewable sources of energy, in recent years Stirling engines have become very important in the energetic sector. Many of them do not allow the use of fluid lubricants and, thus, the effect of friction losses is important. For this purpose, a mathematical model has been developed based on the force balance in the crankshaft using the pressure distribution in the cylinders. The aim of this work is to characterize the mechanical losses in a Genoa 03 Stirling engine using a numerical model and experimentally via the drag method. The results of this model have been compared with those obtained experimentally on Genoa 03 Stirling engine. In the experimental results, a proportional increase in friction torque due to the average pressure and the speed of the crankshaft is observed. The first of these is caused by an increase of dry friction forces and the second, by the viscous friction between the working fluid and the inner walls of the engine. Also in this paper, irreversible processes in a beta type Stirling engine have been investigated in order to highlight the impact of losses on mechanical power and its performance. This article develops the first study of the mechanical losses of Genoa 03 experimental Stirling engine, which has an output power of 3 kW. Although the model response follows the same trends as the experiments, those simplifications provide errors which become more significant as the engine speed increases.Ministerio de Economía y Competitividad ENE2013-43465-

Modelo cinético para la simulación de la autoignición en un proceso de combustión homogénea de encendido por compresión (HCCI)

El conocimiento del punto de autoignición de los motores bajo combustión HCCI es un apartado fundamental en el futuro desarrollo de estos motores. En este trabajo tratamos de proporcionar una herramienta computacional, con un detallado estudio de la cinética química, la cual resulta imprescindible para la compresión del fenómeno HCCIThis paper reviews some of the engine research results and available data from HCCI combustion kinetics studies. Homogeneous Charge Compression Ignition (HCCI) combustion has recently emerged as a viable alternative combustion process to the conventional spark ignition or compression ignition process for internal combustion engines, owing too its potential for high efficiency and extremely low NOx and particulate emissions. Methods for automatic quasi-steady-state reduction of reaction mechanisms a life time measure to detect equilibrated species has been developed and applied to homogeneous model of HCCI engine fuelled with its two fuels