Driss Stitou

Development and comparison of advanced cascading cycles coupling a solid/gas thermochemical process and a liquid/gas absorption process

Currently marketed double-effect absorption machines attain coefficients of performance (COP) of the order of 1.2 and, therefore, do not enable standard vapour compression air-conditioning systems to compete. The improvement of the COP requires increasing the high driving temperature level of the system in order to make possible additional stages and further refrigeration effects. But at high temperatures, working couples currently used in absorption systems (H2O/LiBr, NH3/H2O) pose corrosion problems for exchangers or decomposition of the working fluid. The implementation at these high temperatures of a solid/gas thermochemical reaction system enables bypassing these restrictions. The coupling of a chemical reaction process thermally cascaded with a liquid/gas absorption process enables leading to triple-effect machines, indeed quadruple effect, the COP of which are from 30% to 60% higher than commercialised double-effect absorption chillers. Numerous coupling configurations are presented in this paper. A method of evaluation of the COP of the global machine is also developed. A comparison of these different configurations is carried out through value criteria characterising the quality of the obtained coupling. In this way, a first selection of combinations of interest can be performed. As part of a Franco–German cooperation, a triple-effect machine based on this approach is currently being realised. This new concept of coupling must lead to a new generation of thermal machines which will be capable in the near future of competing with vapor compression machines by the complementary use of the potentialities appropriate to each of the sorption processes.

Thermodynamic techniques for the conceptual design of thermochemical refrigerators using two salt materials

Abstract A special multi-step thermodynamic technique for the systematic synthesis of energy-efficient configurations of sorption processes acting between four temperatures for cold production has been proposed. In the first step, a special superstructure which embeds all the energy flows going through an ideal sorption system is postulated. The superstructure is represented on a dimensionless Carnot factor vs. heat diagram. In the second step, the minimization of special areas on the diagram, corresponding to the so called “unused” and “excess” exergies, combined with the maximization of desorption temperature to its upper level makes it possible to target the maximum energy performance and COP of the future ideal process ahead of design. In the third step, the process is systematically synthesized on the Clausius–Clapeyron diagram by using the thermodynamic correspondence with the Carnot factor vs. heat diagram. The final step is to conduct a traditional assessment of the thermodynamic performance of real sorption systems that have the same structures as the ideal systems defined in the previous step. A new energy-efficient configuration of a triple-effect thermochemical refrigerator using two salt materials has been designed as an example.

New Sorption Cycles for Heat and/or Cold Production Adapted for Long Distance Heat Transmission

The analysis of the combinations of dipoles, linked by a gas transfer between an endothermic element and an exothermal element, through an exothermal physical-chemical process in thermal contact with an other endothermic process, is the basis of a new process for the transmission at long distance of heat/cold production. The yield of such cycles is identified through the values of the unused exergy, the untapped exergy and the exergy which is produced in excess by the process.Copyright

Internal energy flow analysis within a single effect sorption heat pump

Abstract The knowledge of the characteristics of unused, excess and untapped exergy allows a thorough analysis of internal energy flows distribution within a sorption heat pump. It can be applied to any system based on gas–liquid absorption, adsorption or solid–gas reaction as well as to any process based on the internal recycling of the energy flux. It can also be applied for the case of a simple effect ideal machine, in particular in the definition of processes where the COP is larger than 2: the levels at which the initial exergy is downgraded on the one hand, as well as, the upgraded excess exergy produced on the other allows the designer to make a judicious choice of a system.

Technical data for concentrated solar power plants in operation, under construction and in project

This article presents technical data for concentrated solar power (CSP) plants in operation, under construction and in project all over the world in the form of tables. These tables provide information about plants (e.g., name of the CSP plant, country of construction, owner of the plant, aim of the plant) and their technical characteristics (e.g., CSP technology, solar power, area of the plant, presence and type of hybridization system, electricity cost, presence and type of TES, power cycle fluid, heat transfer fluid, operating temperature, operating pressure, type of turbine, type and duration of storage, etc.). Further interpretation of the data and discussions on the current state-of-the-art and future trends of CSP can be found in the associated research article (Pelay et al., 2017) [1].

Synthesis of Single Effect Solid-Gas Thermochemical Refrigerators

A systematic approach to the energy efficient design of single effect solid-gas Thermochemical Refrigerators (TR) using the appropriate choice of salt materials is proposed. The approach includes three major steps. The first one, the targeting step, is applied to the ideal thermochemical process. It allows identification of the energy performance targets (the ideal Coefficient of Performance, COP i ) as a function of external temperature conditions and the internal distribution of energy flows within a thermochemical system. Targets can be set without actually having to carry out the design of the system. This step characterizes only the thermodynamic feasibility of an ideal thermochemical process. A new graphical technique, a modified Carnot factor vs. heat diagram, is applied to determine the targets. In the second step, in order to achieve the targeted COP i value, the design options of ideal thermochemical systems using different salt materials are generated. The physicochemical feasibility of the options is ensured in this step on the Clausius–Clapeyron diagram. Finally, in the third step, the assessment of the thermodynamic irreversibilities produced within real thermochemical processes using the same materials as the ideal ones allows evaluation of the real COP values. This step is the traditional energy and exergy analysis that ensures the thermodynamic feasibility of the real thermochemical systems.

A New Realistic Characteristics of Real Energy Conversion Process: A Contribution of Finite Size Thermodynamics

The perfection of the energy conversion process is currently gauged through a kind of quality indicator that compares the real performance of the process to that of the ideal reversible Carnot process. The criteria resulting from this commonly used approach give a false idea as to the real quality of the energy conversion process. Indeed, the real energy conversion process that generates true energetic power levels is compared to the ideal associated Carnot process, which generates a zero-output power level. The real conversion process implementing finite heat exchanger areas is then compared to the ideal process that needs an infinite heat exchanger area to fulfill the same power requirements. This paper presents a new thermo-economic approach, based on Finite Size Thermodynamics, that is more suitable for qualifying real energy conversion processes. This approach takes into account the external thermodynamic irreversibilities relative to the heat transfer rate through a finite size heat exchanger surface between the external heat sources or sinks and an ideal process without internal thermodynamic irreversibilities. This new approach enables a more realistical evaluation of ideal performances of real energy conversion processes. It makes possible the definition of new criteria that characterize more reasonably the quality of a real thermal process compared with the corresponding endoreversible process the same power duty (performance criterion) or the same involved total heat exchanger surface (technical criterion).