Natural gas pyrolysis in double-walled reactor tubes using thermal plasma or concentrated solar radiation as external heating source

The thermal pyrolysis of natural gas as a clean hydrogen production route is examined. The concept of a double-walled reactor tube is proposed and implemented. Preliminary experiments using an external plasma heating source are carried out to validate this concept. The results point out the efficient CH4 dissociation above 1850 K （CH4 conversion over 90%） and the key influence of the gas residence time. Simulations are performed to predict the conversion rate of CH4 at the reactor outlet, and are consistent with experimental tendencies. A solar reactor prototype featuring four independent double-walled tubes is then developed. The heat in high temperature process required for the endothermic reaction of natural gas pyrolysis is supplied by concentrated solar energy. The tubes are heated uniformly by radiation using the blackbody effect of a cavity-receiver absorbing the concentrated solar irradiation through a quartz window. The gas composition at the reactor outlet, the chemical conversion of CH4, and the yield to H2 are determined with respect to reaction temperature, inlet gas flow-rates, and feed gas composition. The longer the gas residence time, the higher the CH4 conversion and H2 yield, whereas the lower the amount of acetylene. A CH4 conversion of 99% and H2 yield of about 85% are measured at 1880 K with 30% CH4 in the feed gas （6 L/min injected and residence time of 18 ms）, A temperature increase from 1870 K to 1970 K does not improve the H2 yield.

Production of metallic nanopowders(Mg,Al)by solar carbothermal reduction of their oxides at low pressure

The carbothermal reduction of MgO and Al_(2)O_(3) in argon flow at low pressure allows to lower the onset temperature of metal vapor formation.Thermodynamic calculations indicate that metal formation begins at 1400 and 1700 K for a primary vacuum(1000 Pa),respectively,for Mg and Al.In the experimental section,concentrated solar energy was used for the process heating in order to favor energy savings.The products of the reaction between MgO or Al_(2)O_(3) and 2 varieties of carbon(graphite,carbon black)in flowing argon atmosphere at a total pressure of around 1000 to 1600 Pa were studied using X-ray diffraction,and microstructure observations revealed the formation of metallic nanopowders with some by-products.Metallic conversions close to 45 wt%and 52 wt%,respectively,for Mg and Al,were obtained.The low conversion yield of the carbothermal reduction of MgO can be attributed to a backward reaction reforming MgO powder and to a sintering process between oxide particles at high temperature.Aluminum production challenge is to avoid formation of undesired by-products:Al_(2)O,Al_(4)C_(3) and Al-oxycarbides.Advantages and weaknesses of the used process are described and some improvements are proposed to increase metallic yields.

Study of the wind-pressure distribution of flat-roof parabolic condensers based on wind-tunnel tests

The structure of parabolic condensers makes them susceptible to wind load because of their thin and large windward mirrors.In this paper,the wind pressure on a model of a condenser mirror(1:35)on multistorey flat roofs is analysed via pressure measurement in a wind tunnel.The mean wind-pressure distribution law of flat-roof condenser mirrors(including the change law with working conditions and the maximum distribution characteristics)and the distribution law of fluctuating and extreme wind pressure are obtained.Furthermore,by comparison with the ground-based condenser distribution law,similarities and differences between the two are obtained.Research results show that the wind-pressure distribution law of flat-roof parabolic condenser mirrors is the same as those on the ground,but the mean wind-pressure coefficient(absolute value)is generally~30%smaller.Furthermore,the maximum effect is generally located at the windward mirror edge and the mirror is more susceptible to wind pressure in wind directions of 30°and 135°-150°.The results of this study can provide a theoretical reference for wind-resistant structure design and multistorey flat-roof condenser-related research.