The technical pre-feasibility to use briquettes made from wood and agricultural waste for gasification in a downdraft gasifier for electricity generation

 

 

Pholoso Malatji^I; Ntshengedzeni Sampson Mamphweli^II; Martina Meincken^I

^IDepartment of Forest and Wood Science, Stellenbosch University
^IIInstitute of Technology, University of Fort Hare,

 

 

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ABSTRACT

Biomass can be converted to energy through various thermochemical and biological processes. Gasification is one of the thermochemical processes that has recently gained popularity, because it achieves higher conversion efficiencies than, for example, incinerators, boilers or furnaces. Fixed-bed downdraft gasifiers are preferred for electricity generation, because they produce very little tar, but on the other hand, they are limited with regard to biomass properties, such as particle size, bulk density and moisture content. Biomass material with a heterogeneous size is usually processed into pellets or briquettes, which have to be mechanically strong enough to be handled. Cohesive strength is provided by residual moisture and lignin present in most biomass. However, the briquetting process becomes more complicated if one wants to add agricultural waste products that do not necessarily contain lignin as binders. The aim of this work was to process wood chips, grape skins and chicken litter into briquettes that are mechanically stable and have a sufficiently high energy content, as well as adequate bulk density for gasification. The performance of these briquettes in a downdraft gasifier was simulated with a program developed for wood, which was modified to optimise the briquette yield. The results showed a gasification performance comparable to solid pine wood, implying that the blended briquettes could be used as fuel for a downdraft biomass gasifier. Unfortunately, the briquettes proved too instable to experimentally verify the performance in a gasifier. This paper describes the properties of the briquettes as well as the gasification simulation results.

Keywords: gasification performance, simulation, various biomass, briquettes

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Full text available only in pdf format.

 

Acknowledgements

The authors wish to acknowledge T. H. Jayah, Lu Aye, R. J Fuller and D. F Stewart for provision of the downdraft gasifier simulation program.

 

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Received 28 October 2010
Revised 2 June 2011