A circulating fluidized bed boiler is designed and built to conduct visualization study by combining the circulating fluidized bed heat transfer technology and boiler. Water and polyformaldehyde particles are selected as the working media. The effect of the operating parameters such as the amount of added particles and feedwater flow rate on the fluidization and distribution of particles are investigated by using a charge coupling device. Results show that the particles can be normally fluidized and circulated at proper feedwater flow rate and amount of added particles. The solid holdup in the riser bundle increases with increased feedwater flow rate and amount of added particles. With increased feedwater flow rate, the nonuniform degree of particle distribution decreases. The amount of added particles has less influence on particle distribution than feedwater flow rate. The average solid holdup in the water wall tubes is close to that in the splayed flue tubes. (C) 2020 Elsevier B.V. All rights reserved.