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Maraver D.,Research Center for Energy Resources and Consumption | Quoilin S.,University of Liege | Royo J.,University of Zaragoza
Entropy | Year: 2014

This work is focused on the thermodynamic optimization of Organic Rankine Cycles (ORCs), coupled with absorption or adsorption cooling units, for combined cooling heating and power (CCHP) generation from biomass combustion. Results were obtained by modelling with the main aim of providing optimization guidelines for the operating conditions of these types of systems, specifically the subcritical or transcritical ORC, when integrated in a CCHP system to supply typical heating and cooling demands in the tertiary sector. The thermodynamic approach was complemented, to avoid its possible limitations, by the technological constraints of the expander, the heat exchangers and the pump of the ORC. The working fluids considered are: n-pentane, n-heptane, octamethyltrisiloxane, toluene and dodecamethylcyclohexasiloxane. In addition, the energy and environmental performance of the different optimal CCHP plants was investigated. The optimal plant from the energy and environmental point of view is the one integrated by a toluene recuperative ORC, although it is limited to a development with a turbine type expander. Also, the trigeneration plant could be developed in an energy and environmental efficient way with an n-pentane recuperative ORC and a volumetric type expander. © 2014 by the authors; licensee MDPI, Basel, Switzerland. Source


Maraver D.,Research Center for Energy Resources and Consumption | Royo J.,University of Zaragoza | Lemort V.,University of Liege | Quoilin S.,University of Liege
Applied Energy | Year: 2014

The present work is focused on the thermodynamic optimization of organic Rankine cycles (ORCs) for power generation and CHP from different average heat source profiles (waste heat recovery, thermal oil for cogeneration and geothermal). The general goal is to provide optimization guidelines for a wide range of operating conditions, for subcritical and transcritical, regenerative and non-regenerative cycles. A parameter assessment of the main equipment in the cycle (expander, heat exchangers and feed pump) was also carried out. An optimization model of the ORC (available as an electronic annex) is proposed to predict the best cycle performance (subcritical or transcritical), in terms of its exergy efficiency, with different working fluids. The working fluids considered are those most commonly used in commercial ORC units (R134a, R245fa, Solkatherm, n-Pentane, Octamethyltrisiloxane and Toluene). The optimal working fluid and operating conditions from a purely thermodynamic approach are limited by the technological constraints of the expander, the heat exchangers and the feed pump. Hence, a complementary assessment of both approaches is more adequate to obtain some preliminary design guidelines for ORC units. © 2013 Elsevier Ltd. Source


Vicente S.,Lao Institute for Renewable Energy | Bludszuweit H.,Research Center for Energy Resources and Consumption
Renewable Energy | Year: 2012

Lao People's Democratic Republic (Laos) possesses large hydrologic resources, converting hydropower into the most important renewable energy resource in the country. Recently the Lao government, multilateral organizations and NGOs have developed large hydropower projects in tributaries of the Mekong River. These projects usually do not benefit poor people in remote areas where the prevailing source of electricity consists of private pico-hydropower units (<5 kW). These systems face several challenges such as coping with low quality hardware, risk of electrocution and damage to electronic devices and light bulbs. Non-governmental institutions like Lao Institute of Renewable Energy (LIRE) in collaboration with donor funding organizations are seeking to alleviate this situation. These institutions pursue the upscaling and improvement of quality, safety, efficiency and reliability of pico-hydro technology through projects based on the design and implementation of demonstration sites and training programs in rural areas. During the project presented in this work, a feasibility study is carried out to identify a suitable village for the implementation of a demonstration site. Possible locations are analyzed according to social, environmental and technical aspects. For each option, an electric system is designed. For the final selection of the best option, the following design constraints were considered: flexibility, cost effectiveness (to be affordable to poor communities) and easiness of reproduction by people without deep technical knowledge. © 2012 Elsevier Ltd. Source


Khodr H.M.,Qassim University | Khodr H.M.,Polytechnic Institute of Porto | El Halabi N.,Centro Universitario Of La Defensa | El Halabi N.,Research Center for Energy Resources and Consumption | Garcia-Gracia M.,Research Center for Energy Resources and Consumption
Renewable Energy | Year: 2012

In this paper the optimal operation scheduling of a microgrid laboratory system consisting of a wind turbine, a solar unit, a fuel cell and two storage battery banks is formulated as an optimization problem. The proposed optimization algorithm considers the minimization of active power losses. Due to this type of variable, the problem is formulated as a Mixed-Integer Quadratic Programming model (MIQP) and solved by a deterministic optimization technique implemented in General Algebraic Modeling System (GAMS). This algorithm has been used as Virtual Power Producer (VPP) software to operate the generation units and storage system, assuring a global functioning of all equipment efficiently, taking into account the maintenance, operation and the generation measurement and control considering all involved costs. The VPP software has been implemented in a mini Supervisory Control and Data Acquisition (SCADA) system and controls the microgrid laboratory via Programmable Logic Controllers (PLC) devices. The application of this methodology to a real case study of the laboratory equipment demonstrates the effectiveness of this method for solving the optimal dispatch and online control of a microgrid, encouraging the application of this methodology for larger power systems. © 2012 Elsevier Ltd. Source


Ferreira V.J.,Research Center for Energy Resources and Consumption | Lopez-Sabiron A.M.,Research Center for Energy Resources and Consumption | Royo P.,Research Center for Energy Resources and Consumption | Aranda-Uson A.,University of Zaragoza | Ferreira G.,Research Center for Energy Resources and Consumption
Energy Conversion and Management | Year: 2015

This work addresses the potential environmental effects of thermal energy storage using the life cycle assessment to perform an optimal system framework. The study assesses the recovery of waste thermal energy at medium temperatures through the application of phase change materials and the recovered heat use in other industrial processes avoiding the heat production from fossil fuel. To this end, twenty different situations were analysed in terms of energy and environmentally combining four thermal energy storage systems varying the type of phase change material incorporated (potassium nitrate, potassium hydroxide, potassium carbonate/sodium carbonate/lithium carbonate and lithium hydroxide/potassium hydroxide) which were defined as cases and five scenarios were the heat can be released based on the type of fossil fuel consumed (coal, heavy fuel, light fuel, lignite and natural gas). Moreover, a net zero environmental metric time parameter was calculated to assess the time period in which the environmental impacts associated to the thermal energy system were equal to the avoided impacts by the use of the heat recovered. Values that were lower than the thermal energy system lifetime were obtained in more than 40% of the total study situations. Finally, an additional analysis was performed to identify the most significant parameters for the further development of a mathematical model to predict the net zero environmental metric time. © 2015. Source

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