Revolving drum drying apparatus and method

#This invention relates to a method of drying and to drying apparatus, in particular for drying wet materials in suspension, slurry or sludge form, for example sewage, industrial effluent and the like and also certain granular materials. The invention may also be applied to the cooling of materials.

#According to the invention, apparatus for drying wet materials comprises a drum mounted for revolution about a substantially horizontal axis, the drum having inlet means for material to be dried and outlet means for dried material, characterised in that the drum includes inner deflecting wall means defining a spiral pathway having a plurality of coils between the said inlet and outlet means with concentric inner and outer oppositely-handed spirals interconnected at their ends, the drum in use containing a charge of a solid heat exchange and pulverising medium in particulate form, the drum also including means to heat the said medium and means to vent vapours from within.

#The invention also includes a method for drying a wet material, the method comprising introducing the material into a revolvable drum having a substantially horizontal axis of revolution and containing a heated solid heat exchange and pulverising medium in particulate form and revolving the drum to mix the material and the heat exchange medium, the drum having inner deflecting wall means defining a spiral pathway having a plurality of coils with concentric inner and outer oppositely-handed spirals interconnected at their ends between the said inlet and outlet means, whereby the material and heat exchange medium are contained within the pathway and propelled axially of the drum while drying takes place, vapours being vented from within the drum, separating the dried and pulverised material from the heat exchange and pulverising medium and removing the said dried and pulverised material from the drum and recirculating the pulverising medium.

#Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, of which

#FIG. 1 shows a cross-sectional side view of drying apparatus FIG. 1A is an enlarged fragmentary view inset taken at location "1A" of FIG. 1;

#FIG. 2 is a cross section along the line II--II of FIG. 1,

#Referring to FIGS. 1 and 1A, the apparatus as shown consists of a drum 11 mounted horizontally on a base 12 via rollers 13 and 14. Rollers 13 are connected to a drive motor 15. A charge hopper (not shown) for material to be dried is connected to a pipe 16 which is in axial communication with the end wall 17 of the drum, for example via a gland; the pipe 16 contains a screw conveyor which, depending on the pitch, may act as a macerator.

#At the other end of the drum, the outer circular wall is constituted by a series of grid elements 18 which communicate with the interior of a receiving hopper 19 which sealingly surrounds the screen material by means of a cover 20.

#The interior of the drum has deflecting walls which define a pathway constituted by an outer spiral 21 and an inner spiral 22 which are oppositely-handed. Each loop of the spirals contains a charge of steel balls, typically of 25 mm diameter. For clarity, these are shown only in one loop of each respective spiral, at 23 in the outer spiral and at 24 in the inner spiral.