Rachamim Rubin

Dry Methane Reforming Without a Metal Catalyst in a Directly Irradiated Solar Particle Reactor

Dry methane reforming with carbon dioxide in a directly irradiated particle receiver seeded with carbon black is presented in this study. Carbon particles were entrained in the reacting gases and acted as heat transfer and reaction surface. The reactions were not catalyzed by a metal catalyst. The molar ratio between the entrained carbon particles and the working gases (Ar, CO 2 , and CH 4 ) was 4-7 mmol carbon/mol gas. The temperature of the reforming experiments varied from 750°C to 1450°C with CO 2 /CH 4 ratios varying from 1:1 to 1:6. Experimental results show that methane reacts at lower temperatures than expected for its thermal decomposition; this indicates that the decomposing reaction is enhanced by the presence of the carbon black particles. At 1170°C 90% of the methane reacted in the receiver during a residence time of 0.3 s. The reaction between carbon dioxide and carbon black is faster than is documented in the literature, but the reaction rate does not seem to change if only carbon dioxide and carbon black are present in the receiver, compared with experiments where methane is also part of the gas mixture. The experimental results indicate that a high solar flux, i.e., about 2500 kW/m 2 or higher, significantly accelerates the reaction rate of methane decomposition. Total or partial blockage of the solar radiation reduced the yield by about 50%, compared with tests when the receiver was exposed to the full solar radiation flux, at the same operating temperature.

Carbon Dioxide Reforming of Methane in Directly Irradiated Solar Reactor With Porcupine Absorber

A new solar volumetric reactor for CO 2 reforming of CH 4 was tested at the Solar Tower of the Weizmann Institute of Science. The reactor design was based on extensive previous experimental work with a volumetric receiver for heating air and simulation of volumetric reformer. The main parts of the reactor were a conical quartz window and a Porcupine absorber as the surface where chemical and thermal energy conversion took place. A specially developed ruthenium catalyst was used. The CO 2 to CH 4 ratio was about 1:1.2, and the total inlet flow rate was between 100 slpm and 235 slpm (slpm denotes standard liter per minute). The maximum absorber temperature was kept below 1450 K. The conversion of CH 4 reached 85%. The total power absorbed was between 10.3 kW and 18.2 kW; of which the thermal power part was 2.3-4.5 kW and the stored chemical enrichment was 7.5-13.7 kW. The results indicate that this type of volumetric reactor can be used effectively for CO 2 reforming of CH 4 , and further work aimed at improving the total efficiency of the system is in progress.

Closed-loop operation of a solar chemical heat pipe at the Weizmann Institute solar furnace

Abstract The performance of a solar chemical heat pipe was studied using CO2 reforming of methane as the vehicle for storage and transport of solar energy. The endothermic reforming reaction was carried out in an Inconel reactor, packed with a rhodium catalyst. The reactor was suspended in an insulated ☐ receiver which was placed in the focal plane of the Schaeffer Solar Furnace of the Weizmann Institute of Science. The exothermic methanation reaction was run in a tubular reactor filled with the same Rh catalyst and fed with the products from the reformer. Conversions of over 80% were achieved for both reactions. In the closed-loop mode the products from the reformer and from the methanator were compressed into separate storage tanks. The two reactions were run consecutively and the whole process was repeated for nine cycles. The overall performance of the closed loop was according to expectations.

Chemical Kinetics Simulation of High Temperature Hydrocarbons Reforming in a Solar Reactor

This study is aimed at developing a simulation model of a solar volumetric reactor for hydrocarbon reforming, operating at high temperature and pressure. It will then be used to optimize the reactor design and analyze its performance. The model development utilizes previous and on-going experimental work on volumetric receiver and catalyst development. The reactions kinetics are computed, using the CHEMKIN II simulation package. The chemical kinetic modeling of the relevant C-H-O system is based on: (i) Definition of the relevant computation domain and parameters: temperature, pressure, reactant compositions, residence time, and catalyst load, (ii) Utilizing laboratory measurements at 700-1400 K and 1-4 bar to quantify the kinetic parameters for both, H 2 O, and CO 2 reforming of CH 4 and for the Reverse Water Shift reaction. Calculated and measured data are compared for three representative cases, showing a good agreement. The results indicate that the Arrhenius method can be a viable and practical way to predict the behavior of steam and CO 2 reforming over a range of temperatures and pressures. Furthermore, it is shown that the present approach can provide a method for estimating the desirable dimensions of the reactor for reforming of CH 4 . Additional, on-going computational and experimental work, which would provide a more accurate simulation, can easily be implemented using the present numerical model.

Generation of a radiation absorbing medium for a solar receiver by elutriation of fine particles from a spouted bed

In high-temperature solar-thermal systems the conversion of solar to thermal energy requires a radiation absorbing surface to transfer the radiative solar energy to the working fluid. The present study focuses on the generation of a moving radiation absorber using particles suspended in the working fluid. Three methods of particle entrainment in a gas were investigated. Elutriating fine particles from a spouted bed was found to be the preferred method. The diameter range of the entrained carbon black particles was 0.030-25 μm, with 99.7% of the particles having an equivalent diameter less than 1 μm, and 48% of the projected surface area was due to agglomerated particles with average equivalent diameter >5 μm. The moving radiation absorber was tested in a solar receiver using nitrogen as a working fluid. The inner wall temperatures in the receiver cavity were below the gas exit temperature, which shows that the bulk heat transfer from the incoming solar radiation to the gas takes place via the moving radiation absorbing particles.

Methanation of synthesis gas in a solar chemical heat pipe

The reversible reaction CH4 + CO2 = 2H2 + 2CO is under investigation as a chemical heat pipe for storage and transport of solar energy. In this paper, the study of the back exothermic reaction, the methanation of CO-rich synthesis gas, is reported. Three different methanators were constructed and operated in a closed-loop, with the reforming products from the reaction carried out in the solar furnace. The best performance was obtained with a six-stage adiabatic methanator. The experimental results are compared with computer calculations, assuming equilibrium at each stage. The agreement between experimental and calculated results is satisfactory. Scale-up work on a 400 kW unit is in progress.

The study of the photovoltaic cells parameters in concentrated sunlight

The photovoltaic cell parameters are very important for researchers and manufacturers to improve the efficiency of these devices. There are many studies for these parameters in sunlight at one sun or at some suns, but few studies at hundreds or thousands suns. In this paper is presented the study of all important parameters of three types of photovoltaic cells under concentrated sunlight.

Remote controlled robot for automatic measurements in concentrated sun

The concentrated sunlight is very important because the amount of energy is very high and concentrated in a very small area. In this situation, the heating is a big issue and in order to make safe measurements a remote controlled robot is needed. This robot will assume the duty of protect the measured sample and to expose for a precise time to the concentrated sun. Also for easy operating, all the duties including the initial conditions, triggering the measurements, and conditioning the signals must be assured by the robot.

Dry Methane Reforming in a Directly Irradiated Solar Particle Reactor Without a Metal Catalyst

Methane reforming with carbon dioxide in a directly irradiated particle receiver seeded with carbon black is presented in this study. Carbon particles were entrained in the reacting gases and acted as heat transfer and reaction surface. The reactions were not catalyzed by a metal catalyst. The molar ratio between the entrained carbon particles and the working gases (Ar, CO2 and CH4 ) was 4–7 mmol carbon/mol gas. The temperature of the reforming experiments varied from 900°C to 1450°C with CO2 /CH4 ratios of 2–6. Experimental results show that methane reacts at lower temperatures than expected for its thermal decomposition; this indicates that the decomposing reaction is enhanced by the presence of the carbon black particles. At 1170°C 90% of the methane reacted in the receiver during a residence time of 0.3 s. The reaction between carbon dioxide and carbon black is faster than is documented in the literature, but the reaction rate does not seem to change if only carbon dioxide and carbon black are present in the receiver, compared to experiments where methane is also part of the gas mixture. The experimental results indicate that a high solar flux, i.e., about 2500 kW/m2 or higher, significantly accelerates the reaction rate of methane decomposition. Total or partial blockage of the solar radiation reduced the yield by about 50%, compared to tests when the receiver was exposed to the full solar radiation flux, at the same operating temperature.Copyright