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A review of the state of the art of adsorption heat powered heat pumps is presented. Interesting results on solar cooling, advanced cycles and consolidated materials were obtained in early developments until 1995 but, at that time, commercialization was not successful. Recently, breakthroughs were achieved on materials (including composite ones) and on coated surfaces but no obvious progresses have been obtained on advanced cycles and this is a gap to be completed. In parallel, commercialization has improved with the perspectives of the boiler new market. A promising future for those components exists if the recent and ongoing innovation yields more efficient commercialized products.

Experimental results of CO2 post-combustion capture for a TSA process including an internal heat-exchanger (indirect heating/cooling) are presented. The comparative experimental study is carried out on 13X and 5A zeolites, with a mixture 90% N2−10% CO2 modeling the flue gas. With 5A zeolite having given the best performances, we tested it with various operating conditions including one with nitrogen purge during desorption. This one showed a good compromise between CO2 capture rate, purity of the desorbate, volumetric productivity, and specific-heat consumption. We obtained a volumetric productivity of 37 kgCO2/m3ads·h and a specific-heat consumption of 6 MJ/kgCO2 at our laboratory scale and 4.5 MJ/kgCO2 for the adiabatic estimate (in the same order of magnitude as those obtained industrially with the reference MEA amine process). These results are promising because our process is not optimized yet and the scale-up on an industrial version involves a reduction in specific-heat consumption.

Climate change induced by global warming is a result of an excess of energy at the earth’s surface due to the greenhouse effect. But a new energy management can reverse the situation taking advantage of the greenhouse effect to produce renewable energy. In fact, both the renewable energy and the energy consumed which are not dissipated into heat are subtracted from the excess of energy produced by the greenhouse effect and contribute to mitigate climate change. This opens perspectives to harness the greenhouse effect [F. Meunier, Domestiquer l’effet de serre, Dunod, 2005]. Should all the primary energy be renewable energy and should part of the energy production not dissipated into heat, the present earth’s energy imbalance should be beneficial and should serve to produce renewable energy.

A life cycle analysis performed on biogas co- or tri-generation units shows that the environmental impact depends on the fraction of heat (or cold) used, the distance for crops collection, the efficiencies of the unit and on the NO x emissions. A high efficiency unit ( η el = 0.4 and η g = 0.8) and low NO x content (80 mg/N m 3 ) based on 20 km crops collection will save CO 2 emissions and act in a CO 2 sink resulting in one of the very few technologies capable of reducing atmospheric CO 2 concentration.

The performances of a recently developed TSA process for gaseous pollutant treatment, based on indirect heating and cooling by means of an internal heat-exchanger, have been investigated both numerically and experimentally. Heating is carried out by condensing steam, and cooling by water circulation. The cycle performances are usually better than those of competing processes, but with increased heat consumption. The sensitivity of the performances to the regeneration temperature and purge flow rates is discussed. Lastly, it is shown that in the conditions of an adsorber scaled-up to a typical practical size including a mass of adsorbent 1000 times higher than in the laboratory column, the specific heat consumption is in the same range as conventional TSA processes.

The aim of this article is to highlight the behavior differences between an indirectly cooled temperature swing adsorption (TSA) adsorber and other adsorbers classically studied in TSA systems (adiabatic, near-adiabatic and isothermal) during adsorption of a mixture of gases. For this purpose, a numerical model is presented and validated from experimental results. By means of this model, the temperature, gas molar fractions and adsorbed concentration profiles are drawn at different times. The various zones of the adsorption patterns are identified and compared. The influence of the feed and initial bed temperatures is discussed too. From these results, the advantages of indirectly cooled adsorbers are pointed out. A new criterion for the possibility of omitting the cooling step in TSA cycles, based on the bed cooling efficiency, is then proposed for the indirectly cooled adsorbers.

The conditions for co- and tri-generation to reduce CO2 emissions are discussed as well as the global impact of these techniques if they were extensively used. CO2 emissions saving will depend on several factors. First, on the efficiency of the co- and tri-generation unit, second on the CO2 emissions of the electric network. CO2 emissions savings will range from 10% to 50% or even more depending on the conditions. The best solutions correspond to the use of non-fossil fuel and total energy systems.

An adsorption air conditioning unit has been built operating with a heat nd mass recovery cycle and a zeolite-water pair. A new consolidated adsorbent composite with good heat transfer properties has been developed and implemented in the adsorber. At an evaporating temperature of 4 C, the experimental specific cooling power (SCP) of 97 W/kg achieved represents a real improvement in comparison with those measured with a packed bed technology. At this evaporating pressure, the mass transfer resistance controls the process. Therefore, at higher evaporating temperature a COP of 0.68 and a SCP of 135 W/kg were experimentally achieved. A new model has been developed to take into account the mass transfer limitations. The model has been validated and can predict the average pressure inside the adsorber and the components temperature of the unit. A new high conductive material with enhanced mass transfer properties has been developed. The predictive model shows that a SCP of 600 W/kg and a COP of 0.74 could be achieved with this new material.

Heat powered solid sorption is a feasible alternative to electrical vapour compression. However, the emergence of that technology takes time. In this review, the possibilities and limits of this technology are analysed. The performances are shown to be very interesting and in progress, and right now applications are foreseen. The use of waste heat for solid sorption air-conditioning may be an attractive application, but, for a large dissemination, higher efficiencies as well as cost reduction are required. With respect to primary energy and global warming, sorption cooling and heat pumping is coherent, except for waste heat or solar applications, only if the cooling COP is larger than about 1 or 1.2 depending on operating conditions. Technical results are close to that point which provide a wider perspective.

The reason why the performance of adsorptive refrigeration cycles is always less than that of the Carnot cycle corresponding to the same heat reservoir temperatures is analysed. This analysis is performed using the entropy production concept and introducing numbers of entropy production which are a direct measure for the efficiency degradation. The thermal entropy production due to the external thermal coupling of the isothermal heat reservoirs to the temperature varying adsorbers is important in all cases considered. It prevails for the basic uniform temperature cycle (about 95% of the total entropy production). For n-adsorber uniform temperature cycles, internal thermal entropy production (due to heat recovery between adsorbers) may reach 50% of the external thermal entropy production. The entropy production due to the refrigerant flow inside the unit does not depend on the process and is small (less than about 10%) in all cases. For thermal wave cycles, the origin of the entropy production depends highly on the cycle time. For very short cycle times, the external thermal entropy production is very small but an important internal thermal entropy production is observed in the adsorbers. For long cycle times, it is the opposite, the external thermal entropy production becomes very large while the internal thermal entropy production in the adsorbers does not increase.

An adsorptive heat pump system with the temperature wave heat generation is numerically analysed, using a two-dimensional model which takes into account both heat and mass transfer processes inside the adsorber. In the model, the gaseous phase flow is described by Darcy's law. The adsorber is heated or cooled by an external thermal fluid which is considered as one-dimensional. The mathematical model is numerically solved using the ADI finite difference method. Numerical simulations are performed on two adsorption systems: zeolite NaX-water and activated carbon AX21-ammonia. The effects of the operating parameters, such as cycle time, permeability and heating temperature, on the cooling coefficient of performance and the power of cold production are discussed. Finally, the temperature wave regenerative heat pump system is compared to the basic adsorptive heat pump process.

Adsorptive heat pumps are promising for providing a safe alternative to CFC-based refrigeration devices. The temperature fronts process (also called thermal regeneration) has been claimed by several authors in recent years as a way for improving performance of adsorptive refrigerating devices. Cooling COPs of at least one are possible. However, up to now, almost no experimental results have been published. Efficient heat transfer is a key point for efficient thermal regeneration. Consolidated composite adsorbents (expanded natural graphite + zeolite) have much better heat transfer characteristics than granular packed beds: from 50 to 100 times larger, according to Guilleminot et al. [Proc. Int. Absorption Heat Pump Conf., ASME, AES 31, 401–406 (1993)]. Therefore, temperature fronts have been studied in an adsorber containing such composite adsorbents. The adsorber is 1 m long, 10 cm in diameter and it is built on the principle of a double pipe (adsorbent inside, heat transfer fluid outside). The heat transfer fluid flows in one direction during the hot front (heating period), and in the other direction during the cold front (cooling period). This experimental set-up permits simulating real refrigeration cycles. Performance analysis deduced from the experimental data (axial and radial temperature gradients in the adsorber, inlet and outlet temperatures and flow-rate of the heat transfer fluid) demonstrates the respective influences of heat transfer fluid mass flow-rate and cycle time. Experimental COPs of 0.9 were obtained.

International audience; Post-combustion CO2 capture remains one of the most-challenging issue to lower CO2 emissions of existing power plants or heavy industry installations because of strong economy and energy efficiency aspects. The major issue comes from CO2 dilution (4% for NGCC and 14% for PC) and the high flow rates to be treated. Furthermore, CO2 purity has to be higher than 95% with recovery at 90%, to match the transportation/injection requirements. The MEA absorption process remains the reference today but its energy consumption (about 3 MJ/kgCO2) and the amine consumption are still challenging drawbacks. The interest of CO2 capture by indirect TSA (Temperature Swing Adsorption) was demonstrated experimentally in a previous work. The aim of this paper is to present the results of a numerical parametric study. Two main parameters are explored: the desorption temperature (100 to 200 °C) and the purge flow rate (0.1 to 0.5 Ndm 3 .min-1). Four performance indicators are evaluated: CO2 purity, recovery, productivity and specific energy consumption. Results show that purity above 95% can be achieved. Keeping the 95% target, it is possible to achieve recovery at 81% with productivity at 57.7 gCO2/kgads.h and a specific 2 energy consumption of 3.23 MJ/kgCO2, which is about the same level than for up to date MEA processes. Comparison with other adsorption processes exhibits that this process has good potential especially since some improvements are still expected from further research.

The effect of heat transfer on the frequency response of sorption kinetics is theoretically investigated using a detailed model incorporating a single diffusion resistance, a surface barrier and heat transfer resistance at the adsorbent surface and at the chamber wall. The steady-state periodic solutions of this model are obtained analytically. Furthermore, a moment analysis is undertaken to establish the time constants of the different transfer mechanisms, which can be quantitatively compared so as to identify the dominant mechanism(s). It is shown that frequency response data can be considerably altered by the heat effect and in certain situations the response assumes a bimodal form. Under the isothermal assumption, this second peak can be erroneously attributed to an additional mass transfer process. Moreover, it is demonstrated that the frequency response of pressure and temperature are independent of variation in the applied volume amplitude. It is also confirmed by the present work that the frequency response is very sensitive to the nature of the transfer mechanisms, making it theoretically feasible to discriminate between surface barrier control and intraparticle diffusion.

L'etude experimentale est realisee avec le systeme eau-zeolite NaX. On obtient un bon accord entre les resultats experimentaux et le modele mathematique. On etudie trois cas de couplage entre la pompe a chaleur et les sources de chaleur exterieures: couplage indirect avec contrainte d'energie (chauffage de l'adsorbeur et refroidissement du condenseur) couplage direct avec contrainte de temperature (evaporateur); et couplage indirect avec contrainte de temperature (refroidissement des adsorbeurs)

A lot of speculation exists on the possibilities of cascading cycles while very few experimental data are available. Herein, experiments on a cascading adsorptive heat pump are reported. The cascading cycle consits of a two adsorber zeolite—water high temperature stage and an intermittent active carbon—methanol low temperature stage. Driving heat is supplied by a boiler to zeolite adsorbers while active carbon adsorber is heated by heat recovered from zeolite adsorber under adsorption. Evaporators from both basic cycles operate at the same temperature and contibute to the evaporating load. Experimental cooling COP is found to be 1.06, much more than the COP of an intermittent cycle (≈0.5) and more than the COP of a two adsorber zeolite water cycle (≈0.75). Despite of the discontinuous operation of the cycle, evaporating rate is nearly constant (≈2.35 kW or 37W per kg of adsorbent). An analysis of the results shows that the components which limit the power of the unit are the evaporators and basically water evaporator. The COP of this cascading cycle is very sensitive to the evaporating temperature lift. If the temperature lift is higher than 45°C, a two adsorber zeolite water cycle has to be preffered. This cycle seems to be well adapted to air conditioning as long as the evaporation temperature lift is less than 45°C.

Experimental results for a new TSA process including a rapid heat exchanger for indirect cooling and heating are presented. Experiments were performed for the removal and recovery of ethane from a nitrogen stream (simulating a VOC in air). In addition, a simplified one-dimensional nonisothermal nonequilibrium model of the process was developed. As temperature swing is the driving force in the process, specific efforts were made to evaluate the heat-transfer coefficient between the heating or cooling medium and the gas stream. From the combination of the experimental and numerical results, the influence of some parameters (e.g., regeneration temperature, initial feed composition) on the process efficiency, analyzed in terms of both recovered mass and energy consumption, was determined.