Browsing by Author "Svoboda, K."

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    CO2 as moderator for biomass gasification
    (Elsevier, 2013-10-03) Pohorely, M.; Jeremias, M.; Svoboda, K.; Kamenikova, P.; Skoblia, S.; Beno, Z.
    Biomass can be converted into gaseous fuel by high-temperature reactions with a gasifying agent. The gasifying agent consists, in most cases, of oxygen and of a moderator, which is usually water vapour. Here we show that waste CO2 can be used instead of, or together with, water vapour to moderate the process of biomass gasification in a catalytic fluidized bed of dolomitic limestone. Such use of CO2 increased substantially the carbon and energy conversion efficiency and decreased the amount of tars in the produced gas.
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    Gasification of biomass with CO2 and H2O mixtures in a catalytic fluidised bed
    (Elsevier, 2017-09-23) Jeremiáš, M.; Pohořelý, M.; Svoboda, K.; Manovic, Vasilije; Anthony, Edward J.; Skoblia, S.; Beňo, Z.; Šyc, M.
    Steam can be fully or partially substituted by CO2 as a gasification agent. This substitution affects producer gas composition, char conversion and in-situ tar reforming. Here, wood chips were gasified in a spouting fluidised bed using silica sand and catalytic dolomitic lime as the bed material at 850 °C. The use of a gasifying agent composed of CO2 and H2O was compared to the use of CO2 or H2O alone. It was found that mixtures of CO2 and H2O as the gasifying agent improve char conversion, and that the combined gasification agents are very effective in ensuring the decomposition/destruction of tars when lime based materials are used in the fluidised bed.
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    Transient catalytic activity of calcined dolomitic limestone in a fluidized bed during gasification of woody biomass
    (American Chemical Society, 2016-04-14) Pohorely, M.; Jeremias, M.; Skoblia, S.; Beno, Z.; Syc, M.; Svoboda, K.
    Calcined dolomitic limestone mixed with silica sand in a fluidized bed can catalytically enhance the gasification of woody biomass. The lime is prone to attrition and carry over from the reactor and to deactivation caused by pore sintering; therefore, it has to be replenished continuously or periodically to maintain catalytic activity of the fluidized bed. The main aim of this paper was to explore the level of the decrease of the catalytic activity of the fluidized bed if the limestone is not replenished and to estimate a critical period for its top-up. Wood chips were gasified first in a silica sand fluidized bed (1080 g), to obtain background data without the catalytic effect of limestone. After 5 h of operation, dolomitic limestone (1050 g) was added to the fluidized bed and left to calcine. Its catalytic activity was monitored during the following 6 h. During the second part of the experiment, the yield of the main gases (H2, CO, CH4, CO2, and H2O) remained almost unchanged. The yield of minor organic gases and tars rose slightly but still remained far below the value attained with only silica sand. The heavy polyaromatic tar compounds were effectively decomposed during the first 3 h after the addition of dolomitic limestone. It was concluded that the catalytic activity of dolomitic lime remains in an acceptable level during the first 3 h after its addition into the fluidized bed, suggesting that periodic rather than continuous replenishment of limestone should be sufficient.