A trickle bed reactor model and calculation method are presented that allow simulating partial external and internal wetting. Additional mass transfer terms are to be included in the gas, liquid and solid phase species continuity equations. Furthermore, the presence of both gas and liquid in the catalyst has to be accounted for. The calculation of the external partial wetting requires the definition of a critical film thickness.
Gas volume fraction inside the catalyst particles can be calculated without additional model equations provided that the total pressure inside the catalyst is equal to the bulk total pressure. The approach is illustrated with a case study.