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8. Exergy analysis of biomass-to-synthetic natural gas (SNG) process via indirect gasification

Author

Vitasari, C.R., Jurascik, M., Ptasinski, K.J., Nebra, S.A., Oliveira Jr., de, S., Bazzo, E., and Chemical Reactor Engineering

Subjects
SDG 7 - Affordable and Clean Energy
Abstract

Biomass is considered as an important future renewable energy source in order to solve the problems of depletion of fossil fuels and their destructive influence on the environment. From among various biofuels which can be produced from biomass Synthetic Natural Gas (SNG) is expected to play an important role in fulfilling future world energy demand. This paper presents an exergy analysis of SNG production from a woody biomass feedstock based on indirect biomass gasification. In indirect gasification heat needed for endothermic gasification reactions is produced by burning char in a separate combustion section of the gasifier and subsequently the heat is transferred through a dividing wall to the gasification section. Steam is used as a gasifying medium. The advantages of indirect gasification are no syngas dilution with nitrogen and no external heat source required. The production process involves several process units, including biomass gasification, syngas cooler, cleaning and compression, methanation reactors and SNG conditioning. The process is simulated with a computer model using the flow-sheeting program Aspen Plus. The exergy analysis is performed for various operating conditions such as gasifier pressure, methanation pressure, and methanation temperature. The irreversibilities (internal exergy losses) of all process units are evaluated. The largest internal exergy losses occur in the gasifier followed by methanation and SNG conditioning. It is shown that exergetic efficiency of biomass-to-SNG process increases with increasing gasification pressure, methanation pressure, and decreasing temperature in the 1st methanation reactor.

Published
2009

15. THEORETICAL STUDY OF INTERMITTENT DRYING (TEMPERING) IN PROLATE SPHEROIDAL BODIES.

Author

de Lima, A.G. B. and Nebra, S.A.

Subjects
*DRYING, *SPHEROIDAL state, *DIFFUSION
Abstract

The process of intermittent drying in prolate spheroidal bodies was simulated assuming liquid diffusion to be the sole mass transport process, a constant diffusion coefficient and equilibrium conditions at the surface. The mass diffusion equation in a prolate spheroidal coordinate system was used for a two-dimensional case. Due to the use of a dimensionless coordinate system, a Fourier number for tempering is defined, in order to determine the dimensionless time required to achieve a flat moisture content profile. Assuming that the drying process is stopped only once at a fixed point, the tempering Fourier number was determined for aspect ratios of 1.1, 2.0 and 5.0. Many cases were studied, changing the tempering Fourier and aspect ratio of the body. Focusing on the drying rate, the effect of one, two and four drying passes was studied for different interruption points in the process and aspect ratios of 1.1, 2.0 and 5.0, in all cases using the continuous process as a comparison. From the numerical results it was found that during the tempering process, the drying rate and the final mean moisture content are affected by the tempering Fourier number, multipass drying and geometrical dimensions of the body. [ABSTRACT FROM AUTHOR]

Published
2001
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