Exergy Analysis of High Temperature Biomass Gasification

8 Pages Posted: 30 Apr 2012

See all articles by Ethel Kasembe

Ethel Kasembe

University of Dar es Salaam - College of Engineering and Technology

Geoffrey John

University of Dar es Salaam - College of Engineering and Technology

Cuthbert Mhilu

University of Dar es Salaam - College of Engineering and Technology

Date Written: April 30, 2012

Abstract

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.

Keywords: Biomass, Efficiency, Equilibrium Model, Exergy Analysis, High Temperature Gasification

Suggested Citation

Kasembe, Ethel and John, Geoffrey and Mhilu, Cuthbert, Exergy Analysis of High Temperature Biomass Gasification (April 30, 2012). OIDA International Journal of Sustainable Development, Vol. 4, No. 1, pp. 53-60, 2012. Available at SSRN: https://ssrn.com/abstract=2048635

Ethel Kasembe (Contact Author)

University of Dar es Salaam - College of Engineering and Technology ( email )

P.O. Box 35046
Dar es Salaam
Tanzania

Geoffrey John

University of Dar es Salaam - College of Engineering and Technology ( email )

P.O. Box 35046
Dar es Salaam
Tanzania

Cuthbert Mhilu

University of Dar es Salaam - College of Engineering and Technology ( email )

P.O. Box 35046
Dar es Salaam
Tanzania

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