Fig. 4C shows the effect of the secondary gas flow rate on the elutriated fly ash and combustion efficiency. In this test, the fly ash was collected at the baghouse, quench tower, and heat exchanger. The elutriated fly ash decreases significantly with secondary gas flow rate. The carbon content in the fly ash was analyzed by a TGA, and the results show that the carbon content of fly ash also decreases significantly with the secondary gas flow rate. This is in
agreement with the results obtained by Okasha (2007). It can be attributed to the intensified combustion caused by the vortexing effect which increased with the secondary gas flow rate. In this figure, the maximum combustion efficiency for peanut shell appears at a secondary gas flow rate of 2.56 Nm3/h.