Some Aspects of the Performance of Rotating Fluidized Beds

Abstract

A Survey of the literature showed that little has been published on how to design a rotating fluidized bed combustor and that most work had concentrated on fluidization conditions. This thesis describes investigations into the design, construction and operation of rotating fluidized bed combustors. Experiments to determine the fluidization and combustion characteristics were performed in which many parameters were identified. These included minimum fluidizing velocity, fully fluidized bed pressure drop, effect of particle size and limits for fluidized bed combustion. The fluidization results were compared with modified stationary fluidized bed theories and empirical correlations developed for minimum fluidizing velocity and fully fluidized bed pressure drop. Design criteria were developed for the distributor plate, plenum chamber and air distribution systems. Three rotating bed devices were designed and built, namely a perspex model purely to investigate fluidization properties at ambient temperature and two combustors. The combustors were used to extend the range of ambient temperature fluidization studies and to investigate the combustion of pre-mixed air and propane. The combustion experiments demonstrated that satisfactory start-up and steady state operation was practicable and that stable complete high intensity combustion of propane could be achieved. It was further shown that the rotational speed could be used as an additional variable to extend the range of operation. The combustion of solid fuel was found to be more difficult both with regards to start-up and steady state operation. The experiments identified a number of problems such as an accurate method of predicting the coal feed rates for start-up and continuous operation, particle mixing, segregation and localised particle fusion. The work shows the areas where advances have been made which allows the design of a rotating fluidized bed combustor to be decided on with greater assurance.