Fluidized Bed Combustion of Cow Dung

H. Tarus, O. Siagi, M. Talai, D. Menzwa


The combustion of cow dung in  a hot, bubbling bed of quartz sand fluidized by  air has been studied for the first time, by feeding the cow dung into the sand bed just above the distributor, via an electric screw feeder. A stable combustion process  using FBC occurred at 30% excess air/fuel ratio.  It  was characterized  by  uniform temperature  distribution  and  minimal  pressure drops  of  less  than  0.1m bars.  It follows therefore that combustion process takes place between points  T5  and  T7  of  the  combustor  i.e.  near  the  freeboard  region.  In  stable  combustion conditions, the amount of CO 2  in flue gas attained a maximum value of 3.5%, while that of CO ranged between 0.000004% and 0.000001%. A close examination of drained bed materials after combustion process revealed few small molten particles. This was considered as agglomeration tendency  which  begins  when  part  of  fuel  ash  melts  and  causes  adhesion  of  the  bed  material. Further experiments carried out using an oven showed that devolatization and char combustion of  cow  dung  starts  at  150°C  and  approximately  350°C  respectively.  The  low  devolatization temperature and the high rate of temperature build up shows that cow dung devolatizes rapidly, ignite easily and burn out within a short duration. Sintering of cow dung ash begins at 800°C. When silica sand is used as bed material, sintering temperature reduces to 750°C while addition of lime has the effect of increasing it to 850°C.


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The African Journal of Technology
ISSN 1998 – 9350 (Print); ISSN 23135549 (Online)

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