Particle Injection and Mixing Experiments in a One Quarter Scale Model Bubbling Fluidized Bed

One significant factor in the operation of a fluidized bed combustor is the manner in which coal particles disperse and mix with the bed material upon entering the bed. A thermal tracing technique was used to study the mixing characteristics in a 1/4 scale model of a pressurized bubbling fluidized bed combustor. Particles cooled by liquid nitrogen are injected into the bed in the same way that pulverized coal will be injected. An array of thermistors is mounted inside the bed. They are used to trace the path of the cooled particles as they enter the bed and mix with the other bed material. The approximate concentrations can also be determined since heat transfer from the cooled particles to the fluidizing gas is negligible during the course of the experiment. Time resolve images of the particle concentration show that the lateral motion of the injected particles is much greater than the lateral motion of an injected gas jet. The extended lateral motion is due to the substantial momentum of the injected particles. Introduction Bubbling fluidized bed combustors offer an alternative power generation technique that has several advantages over traditional pulverized coal combustors, including smaller boiler size and fewer harmful effects on the environment, such as a near complete elimination of sulfur dioxide emissions and a sizable reduction in nitrogen oxide emissions. One significant factor in the operation of a fluidized bed combustor is the manner in which coal particles mix with the bed particles upon entering the bed. This is a particular concern as the size of the units increase. Bubbling beds have a high particle concentration, making lateral mixing of coal feed particularly difficult. Although there have been considerable study of gas and liquid jet penetration and mixing in a fluidized there are very few studies of particle laden jets. In this paper, a thermal tracer technique was used to study the mixing characteristics in a one-quarter scale model of a pressurized bubbling fluidized bed combustor, the Tidd 70MWE plant in Brilliant, Ohio, that was operated by American Electric Power, Inc. Apparatus The mixing experiments carried out in this study made use of the one-quarter-scale, room-temperature, and oneatmosphere model of the Tidd plant. The constructed model matches to one-quarter scale all the linear dimensions of the actual bed (Figure 1). For scaling of a bubbling bed, Glicksman, et al. (1) showed that the following simplified set of dimensionless scaling parameters must be matched between the model and the actual plant: