Bench-scale 유동층 연소로에서 국내무연탄에 대한 freeboard 연소특성을 고찰하였다. 시료로는 회분 함량 60% 발열량 2,500㎉/㎏ 정도의 저열량 무연탄이 사용되었다. Freeboard내 축방향의 온도분포, O₂ 및 CO농도분포, freeboard 탄소연소율 등을 측정하였으며, freeboard에서의 탄소연소반응이 주로 석탄시료의 입자크기, fly ash recycle ratio, bed temperature 등에 좌우됨을 알 수 있었다. Freeboard 탄소연소율은 fly ash 재순환이 없는 상태에서 2-10%이나 재순환이 있는 경우 20% 정도까지 증가하였으며 관련된 조업변수를 토대로 다음과 같은 상관관계식을 얻을 수 있었다. Y_(fc)= -22.50+0.04(T_b)-3.25(U_(gb)) -6.67(d￣_p)+11.57(R/F)

Characteristics of the freeboard combustion were experimentally investigated with the low-grade Korean anthracite in a bench-scale fluidized bed combustor. Korean anthracite used in this study had a heating value of about 2500 ㎉/㎏ and contained about 60% ash. The axial distribution of temperature, O₂ and CO concentration distribution with respect to freeboard were measured. The fraction of carbon combustion in the freeboard were also estimated. The experimental results showed that carbon combustion reaction in the freeboard mainly depended on coal particle size, bed temperature, and fly ash recycle ratio. The fraction of carbon combustion in the freeboard was found to be in the range of 2-10% without fly ash recycle, however it increased up to 20% with recycling of fly ash. The following correlation was obtained for the fraction of carbon combustion in the freeboard: Y_(fc)= -22.50+0.04(T_b)-3.25(U_(gb)) -6.67(d￣_p)+11.57(R/F).