Experiments in a cold model have been conducted to determine lateral solid diffusion coefficients in a narrow fluidised bed. The experimental data have been obtained using an image analysis technique that traces the dispersion of phosphor coated particles in the bed. A diffusion model has been used to describe lateral solids mixing in the configuration proposed for the narrow fluidised bed. The equation proposed by Shi and Fan [1984. Lateral mixing of solids in batch gas-solids fluidized beds. Industrial and Engineering Chemistry, Process Design and Development 23, 337-341] to calculate the diffusion coefficient in the radial direction fits well the available experimental data. The solid diffusion coefficients obtained have been used to solve a heat transfer problem and discuss the feasibility of a fluidised bed system that makes use of narrow fluidised beds arranged to transfer heat from bed to bed through a separating wall between them. This novel configuration of fluidised bed reactors could find application in some emerging systems that make use of solid regenerable sorbents to capture CO2. (c) 2006 Elsevier Ltd. All rights reserved.