Mechanism of fluid bed dryer

Mechanism of fluid bed dryer

Mechanism of fluid bed dryer

A fluid bed dryer for processing a particulate material includes a housing providing a series of chambers with adjacent chambers separated by a longitudinally extending common wall and connected by a turn-around section to provide a serpentine path leading from an entrance end of a first chamber to an exit end of a last chamber. Each turn-around section is open at one end of one of the common walls to the adjacent chambers separated by the common wall and serves to receive and turn particulate material distributed across the width of one of the chambers through an arcuate path of 180 and deliver the material to the other chamber. Each of the chambers and turn-around sections have a base including at least one bottom plate with a number of gas introduction openings distributed across each plate and oriented to introduce gas into said chamber in a specific direction to fluidize and move a particulate material in that direction. The gas introduction openings in each of the chambers are oriented to uniformly fluidize and move the particulate material in a direction parallel to the common wall and the gas introduction openings in each turn-around section are oriented to successively receive and turn incremental vertical columns of the particulate material with each incremental vertical column of the particulate material received and turned successively in accordance with the distance each incremental vertical column is spaced from the common wall. A plenum chamber provides pressurized gas beneath each bottom plate and a source of pressurized gas is connected to each plenum chamber.

In a still further preferred embodiment, the base of each of the chambers extends into a connecting turn-around section and terminates in an edge that extends from the one end of the common wall at an oblique angle relative to the common wall, and a bottom plate having a pair of edges that intersect at an angle and a plurality of gas introduction openings oriented to fluidize and move the particulate material in a direction substantially perpendicular to the direction of movement of the particulate material in said chambers, is inset with the pair of intersecting edges abutting the edges of the base of each chamber in the connecting turn-around section. In this embodiment vertical columns of the particulate material delivered from one of the chambers to the turn-around section are successively and incrementally turned after each vertical column transverses each of the intersecting edges of the bottom plate.

In a still further preferred embodiment, in a non-plug flow pre-drying chamber adjacent a plug flow fluid bed dryer and having a common wall one end of which is open to the entrance end of the first chamber of the fluid bed dryer, the base of the pre-drying chamber extends into a connecting turn around section without termination comprising a bottom plate having a pair of edges one of which intersects the bottom plate of the non-plug flow dryer at the common wall and the other of which intersects the bottom plate of the plug flow dryer at the common wall.

Fluid bed dryer used for drying thermally sensitive materials are generally of the plug flow type operated at relatively low temperatures and requiring relatively long material residence times in the equipment to satisfactorily dry the material. Such dryers are usually provided in a folded design providing a serpentine flow path for the material whereby economies of space, gas ducting and thermal energy can be obtained. In a folded or serpentine flow path dryer design the material being processed loops back and forth as it passes through the equipment. Although this design minimizes the space and distances required in operating the equipment, in folded fluid bed dryers using a conventional bottom plate design as shown in FIG. 6, there is a tendency for some materials being processed to stop fluidizing and pile up at the turn around sections between the adjacent chambers thereby requiring the process to be shut down due to malfunction of the equipment. That is, conventional plug flow fluid beds are fitted with bottom plates rectilinear in form and are placed with no particular consideration as to the energy required to maintain the desired fluidization and directional transport of the material being processed in the turn around sections of a folded, plug flow fluid bed.

This invention teaches an improved fluid bed dryer design and more specifically, an improved fluid bed base or bottom plate design wherein each incremental volume of the material being processed adjacent an incremental area of the gas distribution bottom plate is provided with that energy required to maintain the bed in a fluid condition and to transport the material adjacent the plate in a specific desired direction away from that incremental area of the plate and to an area from which additional material is being removed in a specific direction with a minimum loss of fines.

The object of the present invention is to provide an improved fluid bed dryer particularly suited for drying a readily decrepitateable, feed material of broad particle size distribution which is capable of sustained operation without process interruption because of fluidization or material transport failure while continuously producing a product having a minimum of fines.

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