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Vodík - produkt tepelné konverze uhlí
Kříž, Vlastimil ; Brožová, Zuzana
Hydrogen fixed in the coal structure was converted to gaseous form using two-stage pyrolysis. The hydrogen volume in the pyrolytical gas strong increased along with the temperature in the cracking module. There was verified the possibility to obtain hydrogen by thermal decomposition of coal pyrolysis volatile products.
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Termodynamické možnosti a omezení pro výrobu čistého vodíku pomocí chromu, manganu a niklu s využitím cyklického chemického procesu za nižších teplot
Siewiorek, A. ; Svoboda, Karel ; Rogut, J.
Thermodynamics and chemical equilibrium for reduction of Cr2O3 , Mn3O4 and NiO by hydrogen, carbon monoxide, model syngas and methane and for oxidation of the relevant Cr, MnO and Ni by steam has been studied in a temperature range 400 – 1000 K. Attention was concentrated also on possible formation of undesired soot, carbides and carbonates during reduction step leading to CO and CO2 formation in the steam oxidation step. Reduction of Cr2O3 and MnO to metallic Cr and Mn by hydrogen, CO or CH4 at temperatures 400 – 1000 K is thermodynamically excluded. Reduction of Mn3O4 and NiO by hydrogen, CO and CH4 at such lower temperatures is thermodynamically favourable.
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Termodynamické možnosti a omezení pro výrobu čistého vodíku pomocí železa s využitím cyklického chemického procesu za nižších teplot
Svoboda, Karel ; Slowinski, G. ; Rogut, J. ; Siewiorek, A.
Iron offers possibility of transformation of a reducing gas ( CO, syngas, methane etc.) into hydrogen by a cyclic process based on iron oxide reduction and release of hydrogen in the next step by steam oxidation. Thermodynamics and chemical equilibrium for reduction of magnetite by hydrogen, carbon monoxide, model syngas and methane and for oxidation of iron by steam has been studied in a temperature range 400 – 850 K. Attention was concentrated also on possible formation of undesired soot, iron carbide and iron carbonate as precursors for CO and CO2 formation in the steam oxidation step. Oxidation of iron by steam is thermodynamically favoured at temperatures 400 – 800 K enabling high hydrogen yields. Iron oxide (magnetite) reduction is the more difficult step, requiring rather higher temperature and higher CO, H2 or methane concentrations in gaseous mixtures.
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Degradation of protective effect of surface layer on Ni3Al-Cr in hydrogen environment
Čermák, Jiří ; Rothová, Věra
Protective effect of surface layer on Cr-doped (4 and 8 at. % Cr) Ni3Al intermetallic was studied by high-temperature hydrogen permeation tests that were carried out at temperatures in the interval 775-1223 K. Hydrogen with about 1 vol. ppm O2 and 2 vol. ppm of H2O was used for the gas-permeation tests. It was observed that the addition of Cr degrades the - otherwise very good - high-temperature protective ability of oxide-containing surface layer of Ni3Al-Cr at strongly reducing hydrogen environment.
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Modification of transmissivity of hydrogen through the surface of Ni3Al by alloying
Čermák, Jiří ; Rothová, Věra
Hydrogen invasion into Ni3Al-M was studied by gas-permeation method in temperature range 573 - 1 223 K. The dependence of hydrogen permeation flux J(d) through the membrane-like samples on the samples thickness d enabled us to assess the influence of the surface upon the rate of permeation. The surface transmissivity was introduced as a quantitative characteristic describing the rate of the process. Influence of three modifying elements M = Fe, Cr and Zr was studied. It was found that Zr supports and, on the contrary, Cr eliminates the inhibiting effect of the surface. The iron did not alter significantly the hydrogen transmissivity, and it causes enhanced grain boundary brittleness in hydrogen environment.
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