Application of imaging techniques for the characterization of lumps behaviour in gas–solid fluidized-bed reactors

•X-ray imaging and thermal imaging data were obtained and combined.•Lump segregation and dispersion coefficients in a fluidized bed are investigated.•Heat transfer coefficient between a lump and a fluidized bed is determined.•Effects of lump density, gas velocity and bed material particle size are evaluated.•A correlation for Nu as a function of Re and particle size ratio is proposed.