Drying of suspension and pastes in fluidized bed of inert particles

Abstract

A fluid bed dryer with inert particles was used for the drying of suspensions and pastes. The effects of the operating conditions on the dryer throughput and on the product quality were investigated. Experiments were performed in a cylindrical column 215 mm in diameter and 1200 mm in height with 0.925 mm diameter glass spheres as the fluidizing media. Cineb fungicide, copper hydroxide and pure water were used as the feed material. With respect to the main efficiency criteria, i.e., specific water evaporation rate, specific heat consumption and specific air consumption, a fluid bed dryer with inert particles represents a very attractive alternative to other drying technologies. A high drying efficiency results from the large contact area and from the large temperature difference between the inlet and outlet air. A rapid mixing of the particles, due to aggregative fluidization and mechanical agitation, leads to nearly isothermal conditions throughout the bed. In our experiments, suspensions and very dense pastes were successfully treated. Suspension and product hold-up in the bed varies between 6 and 8 % by mass and a product with the same particle size as the raw material is obtained. .

Izvršeni su ogledi sušenja suspenzija i pasta u fluidizovanom sloju inertnog materijala. Ispitivan je uticaj operativnih uslova na kapacitet sušionika i kvalitet produkta. Eksperimenti su izvršeni u cilindričnoj koloni prečnika 215 mm i visine 1200 mm. Kao inertne fluidizovane čestice korišćene su staklene sfere prečnika 0.925 mm. Tretirane su suspenzije cineb fungicida, bakar hidroksida kao i čista voda. U odnosu na osnovne kriterijume efikasnosti, tj. u pogledu specifične isparljivosti, specifične potrošnje toplote i specifične potrošnje vazduha sistem sušenja u fluidizovanom sloju inertnog materijala predstavlja vrlo atraktivnu alternativu ostalim tehnikama sušenja. Visoka efikasnost sušenja posledica je velike kontaktne površine i velike razlike temperatura između ulaznog i izlaznog vazduha. Intenzivno mešanje inertnih čestica usled agregativne fluidizacije i mehaničkog mešanja ima za posledicu približno ravnomernu temperaturu po celom volumenu sloja. U našim ogledima uspešno su tretirane retke suspenzije i vrlo guste paste. Hold-up materijala koji se suši u sloju kreće se od 6 do 8 mas. %, a u svim ogledima granulometrijski sastav produkta je praktično isti sa granulometrijskim sastavom polazne suspenzije odnosno paste.