Experiments were carried out in a circulating fluidized bed (CFB) system. The riser has a cross sectional area of 100 x 100mm(2), while the supply and recycle chambers of the loop-seal have the same cross-sectional areas. Sand having a Sauter mean diameter of 310 mu m was used as bed material. Throughout the experiment, the superficial air velocity of the riser and the height of the solid particles in the storage column were kept constant. Four types of loop-seal categorized by their aeration scheme were investigated: aeration at the bottoms of supply and recycle chambers with side aeration at the supply chamber wall (U(SR)Q(S)), aeration at the recycle chamber bottom with side aeration at the supply chamber wall (U(R)Q(S)), aeration at the supply chamber bottom with side aeration at the recycle chamber wall (U(S)Q(R)), and aeration at the bottoms of supply and recycle chambers with side aeration at the recycle chamber wall (U(SR)Q(R)). The relation between the solid circulating rate and the side aeration flow rate was modeled as a saturated function. The results show that the U(R)Q(S) and the U(S)Q(R) types provide the same initial solid circulation rate, which is higher than for the conventional U type loop-seal. For a certain fluidization number, the loop-seals with side aeration provide higher solid circulation rate and require lower total aeration flow rate. The loop-seal with side aeration at the supply chamber wall tends to provide higher solid circulation rate and sensitivity of the circulation rate. For a certain solid particles height in the storage column, the maximum solid circulation rate was restricted by the flow through the horizontal passage. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.