Various external heat exchangers (EHE) are widely used in large-scale circulating fluidized bed (CFB) boilers. A new type of pneumatically controlled EHE was developed in this paper. The major feature of this EHE system was that the flow of solids to two heat transfer chambers could be controlled. Thereby the quantity of heat transfer of different and multilevel heat transfer surfaces in the EHE could be easily adjusted. Also the EH E and recycle device were connected in order to recycle the solids back to the furnace steadily. Experiments completed in the visible EHE test rig show that the solid mass flow rates to the EHE or the loop seal, to two heat transfer chambers and to two exports of solids can be controlled by the aeration airflow into each chamber and geometrical dimensions like the height of partitions. That is because the change to fluidizing velocity of each chamber leads to the changes in particle entrainment rate and pressure distribution in the EHE. In addition, an empirical correlation between the solid mass flow rate and pressure drop across an orifice has been proposed and a new orifice discharging coefficient has been defined according to the experimental data and theoretical analysis. (C) 2010 Elsevier B.V. All rights reserved.