This paper deals with the development of basic parameters required to operate a multi-stage countercurrent fluidized bed reactor with downcomer illustrating the mechanism of gas-solid contacting in the system. In addition, the reactor was operated in continuous regime for two phase system over a wide range of operating conditions including height of the downcomer to determine the pressure drop due to the solids in the reactor. The data was generated under steady and stable operation of the column without flooding. Based on the data an empirical correlation have been developed for predicting the pressure drop in the system. The result Of this Study has great industrial importance for scale-up, design and steady operation of a multi-stage fluidized bed reactor for control of gaseous pollutants. The fluidizing gas was air and the solid phase was lime. (C) 2008 Elsevier B.V. All rights reserved.