Xavier Py

Paraffin/porous-graphite-matrix composite as a high and constant power thermal storage material

Abstract A new supported phase change material (PCM) made of paraffin impregnated by capillary forces in a compressed expansed natural graphite (CENG) matrix is presented. High loads of paraffin were obtained: from 65% to 95% weight depending upon the bulk graphite matrix density. Composite PCM/CENG thermal conductivities were found to be equivalent to those of the sole graphite matrix: from 4 to 70 W m −1 K −1 instead of the 0.24 W m −1 K −1 of the pure paraffin. Thermal power and capacity of the composite are theoretically compared to those of conventional systems in the case of two usual external geometries: tubes and spherical hollow nodules. The CENG induced a decrease in overall solidification time and a stabilization of the thermal storage power. An optimization procedure of the composite composition was proposed according to the antagonistic behaviours of the thermal power and the thermal capacity with respect to the CENG content. Within the usual external heat transfer coefficient range, the estimated CENG matrix optimized densities fell within the practicable range.

Contributions of hemicellulose, cellulose and lignin to the mass and the porous properties of chars and steam activated carbons from various lignocellulosic precursors.

In this study, contributions of hemicellulose, cellulose and lignin to the mass and the porous properties of chars and activated carbons from various lignocellulosic materials were studied. A predictive calculation was established using the experimental results obtained for the three components separately to evaluate the carbonization and activation yields and their respective contributions to the chars and to the subsequent activated carbons of various precursors in term of weight fraction. These equations were validated. The results showed that lignin can be considering as being the major contributor of all chars and activated carbons. Besides, the evolution of the mean pore size versus the specific porous volume showed that each component contributes to the porosity of chars and activated carbons whatever is its weight contribution.

Recycled Material for Sensible Heat Based Thermal Energy Storage to be Used in Concentrated Solar Thermal Power Plants

Current technologies of concentrated solar power plants (CSP) are under extensive industrial development but still suffer from lack of adapted thermal energy storage (TES) materials and systems. In the case of extended storage (some hours), thousands of tonnes of materials are concerned leading to high investment cost, high energy and GHG contents and major conflicts of use. In this paper, recycled industrial ceramics made by vitrification of asbestos containing wastes (ACW) are studied as candidates to be used as sensible TES material. The material presents no hazard, no environmental impact, good thermophysical properties (λ= 1.4 W m -1 K -1 ; Cp = 1025 J kg -1 K -1 ; p= 3100 kg m -3 ) and at very low investment cost. Thanks to the vitrification process of the wastes, the obtained ceramics is very stable up to 1200 °C and can be directly manufactured with the desired shape. The vitrified ACW can be used as TES material for all kinds of the CSP processes (from medium up to high concentration levels) with properties in the same range than other available materials but with lower cost and without conflict of use. The proposed approach leads also to sustainable TES allowing a pay back of the energy needed for the initial waste treatment. Furthermore, this new use of the matter can enhance the waste treatment industry instead of land fill disposal.

The effect of the carbonization/activation procedure on the microporous texture of the subsequent chars and active carbons

Abstract Chars obtained by carbonizing coconut shells at different intermediate heat treatment temperatures (IHTT) between 400 and 800 °C were activated at 800 °C in a stream of N2+H2O, following two distinct procedures. In the first procedure, activation follows directly the carbonization, whereas in the second procedure, the sample was first brought back to 25 °C and subsequently heated again to the activation temperature of 800 °C. The data for CO2 adsorption at 25 °C and N2 at −196 °C with immersion calorimetry confirms that the activated carbons derived from chars obtained at low IHTT and in two steps, present a “gate effect” for burn-offs

Elaboration of Conductive Thermal Storage Composites Made of Phase Change Materials and Graphite for Solar Plant

New thermal storage composites made of graphite and PCM (NaNO 3 /KNO 3 eutectic) have been developed for solar thermal power plants using direct solar steam generation. Those materials, obtained using different elaboration routes (compounding, infiltration, cold compression) and graphite types, are presented with their respective properties (enhanced thermal conductivities, thermal storage capacities, stability) and compared together. Both the laboratory and industrial scales and grades are considered and compared. The infiltration route has been found to be inefficient before the two other ones. Compound composites present isotropic properties and thermal conductivity intensification in the medium range (a factor of 10 for 7 wt % in graphite). Cold compressed composites present highly anisotropic properties and strong intensification in thermal conductivity (a factor of 31 at 200°C for 20 wt % in graphite). Their melting and solidification temperatures as well as their intrinsic storage capacity are close to the pure salt ones.

Activated carbon porosity tailoring by cyclic sorption/decomposition of molecular oxygen

Activated-carbon pore size tailoring is usually achieved by pore size reduction, pore size widening or more rarely by direct activation. Successive widening cycles composed of an initial molecular oxygen sorption step, followed by a carbonization step under nitrogen, have been applied to three different materials in order to study their gradual pore size modifications. For years, the whole microporosity obtained after several cycles is known to present better pore size distribution than those inherited from conventional activations. Moreover, as shown in the present paper, the gradual obtained microporosities cover a wide and valuable range of porous textures highly dependent on the initial material origin and initial activation. Gradual mean pore size evolutions of 1 or 2 A per cycle were observed linked to a simultaneous increase in microporous specific volume in the case of pitch-based and coconut activated carbons, respectively. Comparatively, the microporous specific volume of a commercial coconut carbon molecular sieve was increased by 26% without modification of its mean pore size and therefore of its sieving effect. Those results have been used to test a simple textural model of activated carbon porosity proposed in the recent literature.

Microporosity of activated carbons produced from heat-treated and fractionated pitches

Activated carbons with degrees of burn-off ranging from 12 wt.% to 60 wt.% have been prepared from toluene-insoluble (T.I.) fractions of a heat-treated A240 petroleum pitch. After toluene fractionation, the resulting pitches have been stabilized, carbonized and then activated using carbon dioxide at 1173 K. Characterization by high pressure carbon dioxide adsorption has been performed in order to determine the properties of activated carbons and to evaluate their performances for adsorption refrigerating machines. Microporous properties are influenced by pitch composition resulting from toluene fractionation and residual γ-resins inhibit the microporosity development. Due to their high microporous volume, activated carbons prepared from extensively γ-resins extracted pitches appear appropriate for cooling applications.

Waste From Metallurgic Industry: A Sustainable High-Temperature Thermal Energy Storage Material for Concentrated Solar Power

The ambitious DOE SunShot cost target (

Alpha-relaxation of an isotropic petroleum pitch: A controlled stress and strain oscillatory rheometry study

0.06/kWh) for concentrated solar power (CSP) requires innovative concepts in the collector, receiver, and power cycle subsystems, as well as in thermal energy storage (TES).For the TES, one innovative approach is to recycle waste from metallurgic industry, called slags, as low-cost high-temperature thermal energy storage material. The slags are all the non-metallic parts of cast iron which naturally rises up by lower density at the surface of the fusion in the furnace. Once cooled down some ceramic can be obtained mainly composed of oxides of calcium, silicon, iron, and aluminum. These ceramics are widely available in USA, about 120 sites in 32 States and are sold at a very low average price of

DESIGN AND INDUSTRIAL ELABORATION OF THERMAL ENERGY STORAGE UNITS MADE OF RECYCLED VITRIFIED INDUSTRIAL WASTES

5.37/ton. The US production of iron and steel slag was estimated at 19.7 million tons in 2003 which guarantees a huge availability of material.In this paper, electric arc furnace (EAF) slags from steelmaking industry, also called “black slags”, were characterized in the range of temperatures of concentrated solar power. The raw material is thermo-chemically stable up to 1100 °C and presents a low cost per unit thermal energy stored (