CFD-based modeling of kraft char beds - part 2: a study on the effects of droplet size and bed shape on bed processes

This is the second of two papers. The first paper presented the char bed burning model used in this work. In this paper, the effects of liquor droplet size and bed shape on kraft char bed processes and lower furnace combustion are studied using a computational fluid dynamics (CFD)-based furnace model. The simulations show that droplet size affects not only the amount of in-flight conversion and the amount of combustible material reaching the bed, but also to what degree char carbon conversion in the char bed is due to direct oxidation or gasification. Droplet size also affects char bed burning indirectly through bed shape. Char bed shape affects the degree to which combustion air jets impinge on the bed surface, increasing carbon conversion by direct oxidation. In addition, changes in bed shape over time affect char bed processes. The results suggest that when a char bed starts to grow, the local carbon input to the bed could increase with bed height. In addition, carbon conversion decreases in locations of air jet impingement if the bed shape is not maintained.