The　solids　circulation　behaviour　in　a　circulating　fluidized　bed　with　a　concentric　annular　feeder　(a-CFB)　was　investigated,　with　a　focus　on　the　effect　of　the　entrance　structure　design　and　gas　flow　rates　in　the　riser　and　the　annular　region　on　the　solids　circulation　rate.　The　pressure　drop　in　the　annular　region　was　found　to　be　strongly　correlated　to　the　entrance　region　configuration　and　solids　circulation　rate　for　a　given　type　of　particles.　Based　on　a　systematic　experimental　study　of　the　riser　bottom　configuration　and　operating　parameters　on　solids　circulation　rate　of　the　a-CFB,　a　new　method　was　proposed　for　in-situ　monitoring　solids　circulation　rate　based　on　the　measurement　of　pressure　drop　in　the　annular　region　of　the　a-CFB.