This paper presents a numerical study of gas and solid flow in an internally circulating fluidized bed (ICFB). The gas and solid dynamics has been calculated using the commercial computational fluid dynamics (CFD) software package ANSYS/Fluent and an Eulerian-Eulerian model (EEM) with kinetic theory of granular flow used to calculate solid stresses. A two dimensional geometry was used to represent key parts of a laboratory ICFB. Simulations were conducted to assess the effect of changes to four designs or operating parameters: gas distributor plate angles, presence of a heat exchange tube bundle, superficial fluidizing velocities and initial solid packing heights. The mechanism governing the solid recirculation in an ICFB has been explained based on gas and solid dynamics obtained from the simulations and the effect of the four designs or operating parameters is quantified in terms of solid recirculation rate (SRR). Both of the investigated operating parameters, superficial fluidizing velocities and initial solid packing height, strongly affect solid circulation rate. For the two investigated design parameters, the presence of a tube bundle reduced the solid recirculation rate by 20%, while an inclination angle of 1.5 degrees does not affect the solid recirculation rate significantly. (C) 2011 Elsevier B.V. All rights reserved.