Spray drying has long been used in generating powdered products from fluid feed streams, primarily with rotary, motor-driven machines or static spray nozzles used to generate the fine mists necessary for efficient liquid evaporation. High maintenance costs have long plagued dryer systems employing the rotary atomizer, due mainly to the high speed, limited life of conventional anti-friction bearings. The energy efficiency of these machines has also improved little over decades in service.
An advanced rotary atomizer has been developed for spray dryers to combat these issues. It features the use of modern motor and bearing technology, thereby improving service life and reducing maintenance costs, while achieving extreme operating motor efficiencies. The introduction of an adjustable hot air distributor, along with a family of resealable, flat and curved explosion venting doors rounds out the line of spray drying equipment now being offered.
Magnetic Spray Machine
A direct-drive, magnetic spray machine (MSM) is in production. It consists of an atomizer disc, mounted to a custom 250 kW (330 hp) permanent magnet motor, and is fitted with a set of non-contact magnetic bearings. This combination results in a spray machine extremely compact in size, capable of high disc peripheral speeds, no bearing lubrication required and low maintenance costs. Compared with high-pressure spray nozzles, rotary atomizers offer flexibility in controlling final product particle size with a simple change in disc speed, accomplished using the dedicated high-frequency VFD provided with each MSM atomizer. These units can also accommodate higher feed solids along with variable feed rates, using the same mechanical setup. Atomizer equipped systems include a mobile 360° rotatable atomizer maintenance stand for ease of cleaning and servicing.
An atomizer control panel houses the Magnetic Bearing Controller (MBC), as well as the PLC that monitors and controls the atomizer system, while a subsequent utility panel provides air and water to the atomizer for cooling. Remote atomizer system monitoring and technical support is accomplished via an interactive panel PC with built-in camera.
Proper design of the air distributor, located in the top of the spray chamber, is crucial to optimum flow conditioning where feed fluids are introduced and atomized. The new device features externally adjustable air chamber controls to vary air velocity into the drying chamber, which can range from 4000 to 10,000 fpm, as well as externally adjustable swirl vanes, providing a +/-30° range of vane positioning. Control actuators have manual handwheels as standard, while electric actuators are optionally available for remote actuation. These tuning features allow for optimization of chamber air and particle flow characteristics, thereby insuring chamber roof and walls remain free of product build-up. Additionally they allow variability in the air flow pattern when the dryer system must operate with both rotary and nozzle type atomizers.
Based on industry regulations for personnel and equipment protection in the event of a dust explosion, termed a deflagration, NFPA-68 compliant sanitary explosion doors have been developed that feature insulated and hinged doors, in either curved or flat versions, with the curved version designed to be flush with the interior skin of the vessel. These doors feature aluminum construction with stainless steel interior skin, spring release latches, and dual seals that are air and water tight. The contoured doors may be mounted on a cyclone body, which reduces the pressure Pred value during a deflagration, and can function as an access port for cleaning and/or inspection.
Guy Lonergan is president, Dedert Corp. (Homewood, IL), which specialists in integrating drying and evaporating technologies within the process industries. Dedert is the driving force behind the recent innovation in spray dryers and recently launched its patent-pending advanced rotary atomizer, an adjustable air distributor, and a range of re-sealable flat and curved explosion venting doors. For more information, visit www.dedert.com.
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