The liquid backmixing characteristics were investigated experimentally using pulse tracing technique in an ebullated bed reactor of 7.2 m in height and 0.3 m in diameter. Air and water were used as the gas and liquid phases

respectively. The superficial gas velocity ranged from 0.26 to 12.97 cm·s-1

while the liquid velocity was fixed at 0.86 cm·s-1. The particles of aluminum oxide with an average diameter of 0.4 mm were used as the solid phase. All experiments were carried out under the solids holdup from 0 to 42.9%(vol). The results showed that each response curve demonstrated obvious long tail phenomenon

which implied that there existed evident liquid backmixing in the ebullated bed reactor at different operating conditions. A tanks-in-series with backflow model was adopted to interpret the response data

which showed an excellent agreement between the prediction and experimental data. It also indicated that the number of stages N was 8

while the backmixing coefficient k varied between 1.320 and 4.218. Most of the variances of the predicted model were within +18% of their corresponding experimental values.