1. Field of the Invention
This invention relates to fluid bed dryers and more particularly concerns a process and apparatus for injecting particles of material into a fluid bed dryer.
2. Description of the Prior Art
Fluid bed dryers are used for drying particulate material by passing streams of fluidizing gases through a bed of material in a so-called fluidizing chamber. These chambers are usually separate removable units, frequently cylindrical in form and have perforate or screen-like bottom portions which have holes sufficiently small to retain the particulate material while permitting air or other fluid to flow therethrough. Fluid bed dryer operation involves passing sufficient air or other fluid through the chamber to suspend solid particles in a stream of air. If each particle is bathed with a stream of fluid such as air to produce the so-called "fluid bed", uniform drying throughout the entire mass is achieved and critical product qualities can be preserved.
Product loading operations of prior art fluid bed dryers are typically batch operations which involve the removal of the fluidizing chamber from the dryer, filling the chamber with particulate material, and replacing the chamber into the dryer. For some types of product, e.g., cheese and yeast, the individual particles readily adhere to one another and tend to agglomerate in the fluidizing chamber before the chamber can be returned to the dryer and the dryer activated. Problems of localized heavy air streams being channelled through the fluid bed chamber, product matting and non-uniform drying are increased by product agglomeration.
Of particular interest to agglomeration problems is an improved fluid bed dryer as disclosed in U.S. Pat. No. 3,849,900. The improved fluid bed dryer of this patent is characterized by the use of a rotating apertured disc positioned below and out of contact with the product to be dried. The disc delivers streams of air moving in rotary fashion throughout the fluidizing chamber. This improved drying apparatus provides a mixing or agitation action in a fluidized bed of particulate material contained within the fluidizing chamber to free or break up particles which have agglomerated. The apparatus of the above-identified patent also eliminates localized heavy streams of air which tend to develop in the fluidizing chambers of prior art dryers and avoids mechanical agitation and contact with the particles which is undesirable for products that tend to crush, smear or agglomerate.
Although the rotating disc dryer is a notable improvement over prior art fluid bed dryers, it only partially overcomes the problem of initial agglomeration which occurs when certain products are loaded into the product containing chamber of the fluid bed dryer in the conventional batch loading step. The initial agglomeration which occurs due to the batch loading of cheese, yeast or other soft particles frequently is not entirely broken up by the agitation in the ordinary operation of the rotating disc dryer. Thus, initial agglomeration results in nonuniformly dried products and a lack of uniformity in the particle size of the product due to the presence of agglomerates even in this improved prior art dryer.