An industrial process for the direct chlorination of ethylene at low temperatures to yield 1,2-dichloroethane has been considered. The reactor, whose configuration corresponds to a bubble column with external recirculation loop, has a working capacity of 19 m(3) and a production capacity of 54 000 ton of 1,2-dichloroethane per year. In order to describe its operation, both a model and a numerical simulation program were developed. In the model, the distinctive features of the different zones that constitute the reactor were considered in detail. The predictions obtained with the simulation program were compared with experimental measurements taken at the real plant for a wide range of operating conditions. Predicted values for different variables that characterise the reactor's operation proved to be very good approximations.