Performances of continuous dryer with inert medium fluidized bed

Abstract

A fluid bed dryer with inert particles represents a very attractive alternative to other drying technologies according to the main efficiency criteria, i.e. specific water evaporation rate, specific heat consumption and speci­fic air consumption. 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 leads to nearly isothermal conditions throughout the bed. A fluid bed dryer with inert particles was used for drying of slurries. Experiments were performed in a cylindrical column 215 mm in diameter with glass spheres as inert particles. In this paper, results of drying experi­ments with slurries of Zineb fungicide, copper hydroxide, calcium carbo­nate and pure water used as the feed material are presented. In our fluidized bed we successfully dried a number of other materials such as: fungicides and pesticides (Ziram, Propineb, Mangozeb, copper oxy-chloride, copper oxy-sulphate, Bordeaux mixture), other inorganic compounds (calcium sulphate, cobalt carbonate, electrolytic copper, sodium chloride), and a complex compound (organo-bentonite). The effects of operating conditions on dryer throughput and product quality were investigated. Main performance criteria, i.e. specific water evaporation rate, specific heat consumption and specific air consumption, were quantified. Temperature profile along the bed was mapped, and nearly isothermal conditions were found due to thorough mixing of the particles. Analysis of drying and energy efficiencies as a function of inlet and outlet air temperature difference was performed for deeper insight in dryer behavior and for optimizing dryer design and operation from an energy point of view. A simple mathematical model based on an overall heat balance predicts the dryer performance quite well. The industrial prototype with fluid bed of 0.8 m in diameter and capacity 650 kg of evaporated moisture per hour was realized on the basis of presented investigations on pilot unit. The most important results are 50% decrease in energy consumption and no-additional grinding of dried product in comparison with old tunnel drying technology.

U radu su prikazani rezultati istraživanja na pilot postrojenju za sušenje suspenzija i pasta nominalnog kapaciteta isparavanja 20 kgH2O/h čiji je centralni deo cilindrična kolona prečnika 215 mm sa fluidizovanim slojem staklenih sfera. U radu su prikazani rezultati dobijeni pri tretmanu suspenzija cineb fungicida, bakar hidroksida, kalcijum karbonata, i čiste vode. Ispitivan je uticaj operativnih uslova na performanse sistema za sušenje i na kvalitet praškastog produkta. Izvršena je analiza efikasnosti sušenja i energetske efikasnosti u funkciji razlike temperatura između ulaznog i izlaznog vazduha u cilju boljeg sagledavanja performansi sistema za sušenje sa energetskog aspekta. Jednostavni bilansi prenosa mase i toplote adekvatno predviđaju radni rezim sistema za sušenje u fluidizovanom sloju inertnog materijala.