- Abstract This paper compares the use of one-dimensional (1-D) and a three-dimensional (3- D) models to simulate the flow of a gas–solids mixture through a pipeline. Both models solve steady flow conservation equations for mass, momentum and energy. The implementation of each model is presented in terms of the changes made to the generic model in order to describe this type of flow. Performance data was obtained for a pneumatic conveying system used to convey pulverised fuel ash (PFA) in a power station. Each model was used to simulate the behaviour of this ash transfer line.