Browsing by Author "Kasembe, Ethel D."

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    Exergy Analysis of High Temperature Biomass Gasification
    (2012) Kasembe, Ethel D.; John, Geoffrey R.; Mhilu, Cuthbert F.
    Biomass gasification is considered as one of the most promising thermo-chemical technologies but the gasifier unit renders itself to internal inefficiencies. This paper addresses the gasifier performance analysis using the exergy analysis modeling which utilizes both the first and second laws of thermodynamics. An exergy model incorporating a chemical equilibrium model is developed. Gasification is envisaged to be carried out at atmospheric pressure of 1 bar with the typical biomass feed, sugarcane bagasse, represented by the formula CH1.42 O0.65 N0.0026 at the temperature range of 800-1400K. In the model, the exergy contained in the biomass was converted into chemical exergy of the product gas, physical exergy, the rest was the unavailable energy due to process of irreversibilities (losses). The model evaluated the product gas molar concentrations and efficiency. The results from the model showed that the mole concentration of H2 increased from 9.8% to 23.7% and the formation of CO2 ranges from 5.6% to 12.1%. While this is the case for H2 and CO2, CO mole concentration is reduced from 26.9% to 17.4%. The maximum efficiencies value obtained based on chemical energy and physical exergy was lower than the efficiency value based on chemical exergy (84.64% vs. 76.94%). This is because the sensible or physical heat (used for drying biomass) is less beneficial for the efficiency based on total exergy. Hence, the gasification efficiency can be improved by increasing the temperature with the change of equivalence ratio (ER) and with the addition of heat in the process.
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    Syngas Production and Losses Encountered in Gasification of Rice Husks
    (Scientific Research, 2015-01) Kasembe, Ethel D.; Mganilwa, Zacharia M.; John, Geoffrey R.; Mhilu, Cuthbert F.
    This paper addresses the syngas production and evaluation losses in high temperature gasification process using coffee husks. A fast and inexpensive way to evaluate the losses in gasification processes is by the application mathematical models which allow to predict the values needed in full scale. Hence, the quantification of gasifier’s losses at temperatures ranges of 800 K - 1400 K at an equivalence ratios of 0.3, 0.35 and 0.4 at 1 bar are revealed by using exergy model incorporating a chemical equilibrium model. The model evaluated the product syngas compositions, syngas heating values and degree of irreversibility values (losses). The results from the model showed that the production of H2 increased from 9.9% to 18.9% and the formation of CO2 ranges from 7.2% to 12.3%. CO production is from 21.8% to 17.2%. The irreversibility values obtained were less than 27%. Hence, reduction of losses protracts biomass resources to be used in energy generation.