109 research outputs found
Modeling, Simulation and Optimal Operation of Multi-Extraction Packed-Bed Thermal Storage Systems
Solar thermal power technologies require storage systems to mitigate the natural variability
of solar irradiation. Packed bed thermal storage systems (PBTES) offer a cost-effective solution using
air as heat transfer fluid and rocks as a storage medium. Compared to its alternatives, however,
PBTES presents a limited flexibility of operation due to the conventional unidirectional flow, which
involves the progressive reduction of the outlet temperature during discharge and thus lowers the
thermodynamic efficiency of the power cycle. The present study summarizes the progress on the
design and optimal operation of a novel multi-extraction PBTES, a project that aims at mitigating its
typically poor operational flexibility for solar power applications. To this end, a one-dimensional
model with a high spatial resolution of a PBTES was developed, which includes four intermediate
outlet points along the axial direction to investigate the benefits of optimal extraction operation.
In order to reduce the computational burden, a coarser model of the storage system is used in
combination with non-linear model predictive control (NLMPC). Through the optimal manipulation
of the extraction valves, the output temperature is maintained close to a prescribed temperature
throughout the discharge. The control admits not only constant temperature targets, but also
time-varying scheduled profiles. This work describes the limitation of such a design and control
approach and sets the direction for the future, more detailed analyses needed to demonstrate its
applicability.Fondo Nacional de Investigación Científica F.4526.1
Techno-Economic Analysis of Rural 4th Generation Biomass District Heating
Biomass heating networks provide renewable heat using low carbon energy sources.
They can be powerful tools for economy decarbonization. Heating networks can increase heating
efficiency in districts and small size municipalities, using more efficient thermal generation
technologies, with higher efficiencies and with more efficient emissions abatement technologies.
This paper analyzes the application of a biomass fourth generation district heating, 4GDH
(4th Generation Biomass District Heating), in a rural municipality. The heating network is designed
to supply 77 residential buildings and eight public buildings, to replace the current individual diesel
boilers and electrical heating systems. The development of the new fourth district heating generation
implies the challenge of combining using low or very low temperatures in the distribution network
pipes and delivery temperatures in existing facilities buildings. In this work biomass district heating
designs based on third and fourth generation district heating network criteria are evaluated in terms
of design conditions, operating ranges, effect of variable temperature operation, energy efficiency
and investment and operating costs. The Internal Rate of Return of the different options ranges
from 6.55% for a design based on the third generation network to 7.46% for a design based on the
fourth generation network, with a 25 years investment horizon. The results and analyses of this
work show the interest and challenges for the next low temperature DH generation for the rural area
under analysis
Transcritical Carbon Dioxide Charge-Discharge Energy Storage with Integration of Solar Energy
New and improved energy storage technologies are required to overcome
non-dispatchability, which is the main challenge for the successful integration of large
shares of renewable energy within energy supply systems. Energy storage is proposed to
tackle daily variations on the demand side, i.e., storing low-price energy during off-peak
or valley periods for utilization during peak periods. Regarding electrical energy storage,
several technologies are available with different potentials for scalability, density, and
cost. A recent approach for grid-scale applications is based on transcritical carbon
dioxide charge and discharge cycles in combination with thermal energy storage systems.
This alternative to pumped-hydro and compressed air energy storage has been discussed
in scientific literature, where different configurations have been proposed and their
efficiency and costs calculated. The potential of the concept has been demonstrated to be
an economical alternative, including hybrid concepts with solar thermal storage. Even at
low temperatures, the addition of solar energy has proved to be cost effective. This paper
explores the effect of introducing solar-based high temperature heat on the performance
of different configurations of “Transcritical carbon dioxide ‒ thermal energy storage
system” cycles. A base-cycle with 8-hour discharge time is compared with different
layouts. Discussions include details on the models, parametric analyses -including solar
technology alternatives-, and simulation results. Round trip efficiency of the base case,
without solar support and at pressure ratio of 9.4, is 52%. When solar input is considered,
the efficiency is above 60%, increasing the turbine inlet temperature to 950 K. Estimated
levelized cost of electricity values are in the range of pumped hydro and compressed air
energy storage, 90-140 USD/MWh in agreement with other works on this thermal storage
technology. The global analysis shows clear advantages for advancing in the study and
definition of this technology for exploitation of synergies at different power ranges,
integrated with mid/high temperature solar power plants and with smaller-scale
renewable installations.Unión Europea. Fondo Europeo de Desarrollo Regional SOE1 / P3 / P0429E
The Ammonia Looping System for Mid-Temperature Thermochemical Energy Storage
Thermochemical reactions have a great potential for energy storage and transport. Their application to solar
energy is of utmost interest because the possibility of reaching high energy densities and seasonal storage
capacity. In this work, thermochemical energy storage of Concentrated Solar Power (CSP) based on an
ammonia looping (AL) system is analysed. The AL process for energy storage is based on the reversible reaction
of ammonia to produce hydrogen and nitrogen. Concentrating solar energy is used to carry out the
decomposition endothermic reaction at temperatures around 650 ºC, which fits in the range of currently
commercial CSP plants with tower technology. The stored energy is released through the reverse exothermic
reaction. Our work is focused on energy integration in the system modelled by pinch analysis to optimize the
process performance and competitiveness. As result a novel configuration is derived which is able to recover
high-temperature heat for electricity production with a thermal-to-electric efficiency up to 27 %. The current study
shows a clear interest of the system from an energy integration perspective. Further research should be
conducted to access the potential for commercial applications
Sodium carbonate-based post combustion carbon capture utilising trona as main sorbent feed stock
Peer reviewedPostprin
The Calcium-Looping (CaCO3/CaO) Process for Thermochemical Energy Storage in Concentrating Solar Power Plants
Articulo aceptado por la revista. * No publicado aún [28-06-2019]Energy storage based on thermochemical systems is gaining momentum as potential alternative to molten salts in Concentrating Solar Power (CSP) plants. This work is a detailed review about the promising integration of a CaCO3/CaO based system, the so-called Calcium-Looping (CaL) process, in CSP plants with tower technology. The CaL process relies on low cost, widely available and non-toxic natural materials (such as limestone or dolomite), which are necessary conditions for the commercial expansion of any energy storage technology at large scale. A comprehensive analysis of the advantages and challenges to be faced for the process to reach a commercial scale is carried out. The review includes a deep overview of reaction mechanisms and process integration schemes proposed in the recent literature. Enhancing the multicycle CaO conversion is a major challenge of the CaL process. Many lab-scale analyses carried out show that residual effective CaO conversion is highly dependent on the process conditions and CaO precursors used, reaching values as different as 0.07-0.82. The selection of the optimal operating conditions must be based on materials, process integration, technology and economics aspects. Global plant efficiencies over 45% (without considering solar-side losses) show the interest of the technology. Furthermore, the technological maturity and potential of the process is assessed. The direction towards which future works should be headed is discussed.Ministerio de Economia y Competitividad CTQ2014-52763-C2, CTQ2017- 83602-C2 (-1-R and -2-R)Unión Europea Horizon 2020 Grant agreement No 727348, project SOCRATCES
Hybrid solar power plant with thermochemical energy storage: a multi-objective operational optimisation
Energy storage is key to decarbonising the energy sector by reducing intermittency and increasing the integration of renewable energy. Thermochemical energy storage (TCES) integrated with concentrated solar and photovoltaic power plants, has the potential to provide dispatchable and competitive energy. Here we develop a multi-objective optimisation framework to find the best operational strategy of a hybrid solar power plant with a TCES system. The model uses a typical meteorological year to optimise one-year hourly operation. The results demonstrate that the integration of a calcium-looping process as TCES in a concentrated solar power plant provides dispatchability and, when hybridised with photovoltaic, enhances its competitiveness with current electricity prices. The low mismatch between supply and demand, even when a fixed commitment is required throughout the year, together with a high overall efficiency, indicates that the integration of calcium-looping in hybrid solar power plants is an opportunity to increase the penetration of solar energy in the power sector. Through the optimisation framework presented, a seasonal energy storage analysis can be developed, although a second optimisation stage is required to improve the sizing of the main components of the system in order to further reduce the energy costs.Comisión Europea. Horizon 2020. Project Socratces, 727348.Ministerio de Economia y Competitividad (MINECO- Fondos FEDER) CTQ2017- 83602-C2 (-1-R and −2-R
Modelo integral de motores alternativos con aplicaciones docentes: motores diesel de inyección directa
Con fines docentes se ha desarrollado un programa en MATLAB que simula el comportamiento de un
MDID utilizando un modelo de combustión de una zona incluyendo renovación de la carga, de fugas y
perdidas mecánicas. Para la validación del modelo se han comparado los resultados con los reales de
varios motores a pesar de la falta de información detallada del motor. Las mayores diferencias aparecen
para régimen de giro alto donde los efectos dinámicos, que este modelo no considera, son importantesWith educational aims a program in MATLAB has been developed that simulates a zone combustion
model of compression ignition engine and submodels for the inlet and exhaust processes, for the blow by,
the exhaust emissions and the mechanical losses. For the validation of the model the results with the real
ones of several engines have been observed. The greater differences appear for high rpm where the
dynamics effects, not considered by this model, are more importan
The mOxy-CaL Process: Integration of Membrane Separation, Partial Oxy-combustion and Calcium Looping for CO2 Capture
CO2 capture and storage (CCS) is considered as a key strategy in the short to medium term to mitigate global
warming. The Calcium-Looping process, based on the reversible carbonation/calcination of CaO particles, is a
promising technology for post-combustion CO2 capture because of the low cost and non-toxicity of natural CaO
precursors and the minor energy penalty on the power plant in comparison with amines capture based
technologies (4-9 % compared to 8-12 %). Another interesting process to reduce CO2 emissions in power plants
is oxy-combustion, which is based on replacing the air used for combustion by a highly concentrated (~95 %
v/v) O2 stream. This work proposes a novel process (mOxy-CaL) for post-combustion CO2 capture based on
the integration of membrane separation, partial oxy-combustion and the Calcium-Looping process. An oxygenenriched
air stream, which is obtained from air separation by using highly permeable polymeric membranes, is
used to carry out partial oxy-combustion. The flue gas exiting partial oxy-combustion shows a CO2 concentration
of ~30 % v/v (higher than 15 % v/v typical in coal power plants). After that, the flue gas is passed to the CaL
process where the CO2 reacts with CaO solids according to the carbonation reaction. Thermogravimetric
analysis show that the multicycle CaO conversion is enhanced as the CO2 concentration in the flue gas stream
is increased. Process simulations show that the mOxy-CaL process has a high CO2 capture efficiency (~95%)
with lower energy consumption per kg of CO2 avoided than previously proposed post-combustion CO2 capture
technologies. Moreover, the overall system size is significantly lower that state-of-the-art CaL systems, which
allows for an important reduction in the capital cost of the technology
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