Batch Agitated Pan Dryers. Pan dryers consists of a circular, pressure-rated vessel with a flat or conical-shaped bottom. An agitator, often heated, can be bottom mounted or top mounted. Top mounting is preferred for most pharmaceutical applications because it eliminates dead spots where product can accumulate. The vessel top head, sidewall, and base are provided with a heated jacket to reducing the likelihood of solvent condensing on these surfaces during the drying operation. The top-mounted agitator is provided with both rotational and up and down movement. The agitator for a pan dryer provides good mixing and efficient contact between the product and the heated vessel surfaces, including the agitator itself. The agitator also helps discharge dried solids. A large nozzle, mounted on the sidewall, is opened, and the agitator arms push product through the opening whenever they pass by it.
Things to Consider: Internal diameter, Cylindrical part length, Geometric volume, Useful volume, Minimum useful volume, Heater surface, Pan axial stroke, Solids discharge valve diameter, Agitator rotation speed, Agitator motor power, Dust filter surface area, Number of filtering elements, Nitrogen tank capacity, Product contact parts, Materials of construction, Heel removal part, Clean-in-place system, Dimensions, Weight, Warranty.
Conical Screw Dryers. Also called conical mixer dryers, gets their name from their conical shape. The drying chamber is mounted vertically, with the narrow end down. The dryer’s agitator is a long screw conveyor, pivoted at the bottom of the chamber, that rotates, as well as orbits in the vacuum, around the dryer housing, continuously cycling the material to be dried. Some dryers, directed at the pharmaceutical, chemical, and food industries, are provided with a heated screw conveyor to provide more heat exchange area. These dryers are used to process high value, high quality products, and are capable of performing several unit operations such as mixing, drying under vacuum, granulation, heating, cooling, crystallization, reaction, and deodorizing.
Things to Consider: Heat source/transfer, Secondary process capabilities, Applications/media, Applications/materials processed, Dimensions, Weight, Warranty.
Double-Cone Conical Blender Dryer. This is a batch dryer. It is mounted horizontally for the drying operation. Like other batch dryers, it has a heated wall, and a vacuum is applied to remove vapor. When drying is complete, the machine is moved to a vertical position to discharge the dried solids from a nozzle at the bottom of the cone. Its tumbling action provides good mixing and regular contact between the solids and the heated wall. These dryers are manufactured in a number of materials, including glass-lined steel, which provides some nonstick property and corrosion resistance.
Things to Consider: Gross capacity, Working capacity, Discharge height, Discharge valve, Overall dimensions, Motor HP, Sturdy stand, Control panel, Welded joints, Mirror finish inside, Warranty.
Fluid Bed Dryers: In fluid bed drying, heat is supplied by a fluidization gas, but gas flow need not be the only source. Heat may be introduced by heating surfaces immersed in the fluidized layer. In fluid bed cooling, cold gas is used. Heat may also be removed by cooling surfaces immersed in the fluidized layer. In fluid bed drying, particle fluidization gives easy material transport, high rates of heat exchange at high thermal efficiency while preventing overheating of individual particles. It is suited for powders, granules, agglomerates, and pellets with an average particle size normally between 50 and 5,000 microns.
Things to Consider: Type of fluid bed dryer: Open cycle plant, Close cycle plant, Static, Continuous, Vibrating, Turbo Fluid, Moisture evaporation rate, Inlet & Outlet temperatures, Materials of construction in contact with feed or dry powder, Dry powder properties, Feed properties, Electrical requirements, Fuel or steam requirements, Compressed air requirements, Installation location (indoor or outdoor), Hot air generator type, Continuous production capability, Suitability for crystalline material, Degree of automation, On-line particle size reduction capability, Processing volume capability, Flexible residence time, Air exhaust configuration, Balanced draft capability with fans provided, Adequate cleaning access and viewing windows, Capability of maintaining initial particle size if desired, Dimensions, Weight, Warranty.
Ribbon Blender Dryers. These dryers consist of a U-shaped horizontal trough and a specially fabricated ribbon agitator, which is a set of inner and outer helical agitators. The outer ribbon moves materials in one direction and the inner ribbon moves the materials in the opposite direction. The ribbons rotate at approximately 300 feet per minute and moves materials both radially and laterally to ensure thorough drying in short cycle times.
Things to Consider: Working volume, Holding volume, Stainless steel contact parts, Safety switch for cover, Ribbon design details, Heavy duty anti-friction bearing on non-drive end, 2-piece stainless steel stuffing boxes with adjustable and replaceable Teflon packing, Motor HP, Motor electrical requirements, Agitator speed, Clearance under discharge valve, Dimensions, Weight, Warranty.
Rotary Drum Dryers. These are industrial dryers that remove or minimize moisture from a product by putting it in direct or indirect contact with hot air. This type of dryer has a rotating cylinder through which hot air passes. The dryer is classified as an indirect heated type when it uses gas preheated by other means. This type has low risk of product contamination. A direct heated dryer uses an air steam composed of furnace fumes and air. Two types of commonly used rotary dryers are counter-current rotary dryers and co-current rotary dryers. In the first type, heated air flows in a similar path as the material. In the other type, air flow against the direction of the material. Both models expose the material to hot air heated by a source. While the drum rotates, fins that line the inner wall of the drum lift the product into the stream of air.
Things to Consider: Drum diameter, Drum length, Dryer area, Heat source, Pressure for heating media, Drive source and power requirements, Overall dimensions and weight, Warranty.
Spray Dryers. These dryers atomize the product into a spray of droplets, which are put in contact with hot air in a drying chamber. Evaporation of moisture from the droplets and formation of dry particles proceeds under controlled temperature and airflow. Powder is continuously discharged from the drying chamber to be recovered from the exhaust gases using a cyclone or a bag filter. Spray drying is well suited to the continuous production of dry solids in powder, granulate, or agglomerate particle form from liquid feedstocks, which can include solutions, emulsions, and pumpable suspensions.
Things to Consider: Type of spray drying plant, Type of atomization, Drying chamber inlet/outlet temperature to suit specific product, General material of construction of parts in contact with feed/dry powder, Moisture evaporation rate, Product output, Dry powder properties, Moisture content in dry powder, Powder granulometry (coarse to fine), Type of feed input, Electrical requirements, Fuel required, Compressed air requirments, Installation (indoor/outdoor), Hot air generator type, Dimensions, Weight, Warranty.
Thin-Film Evaporators. Film Type Evaporation involves generation of a thin product film over the heat transfer surface to promote minimal resistance to heat transfer. The material is heated until the lower boiling component starts to evaporate. These vapors are then liquefied on the cold tubes of a condenser. The device usually consists of a jacketed cylindrical heating section, a top vapor section with an entrainment separator, a top cover with mechanical seal housing and roller bearings, and a bottom conical section housing the lower bearing. An internally revolving rotor equipped with either wipers or blades provides internal distribution and rapid transport of the product film over the heated area. Evaporation often takes place under vacuum. The disengaged vapors are either condensed externally in a tubular/spiral condenser, or led to a column, or to another downstream process.
Things to Consider: Area, Materials of construction, Pressure/vacuum rating, Drive power, rpm, Vertical vapor column height, Tapered section dimensions, Shell & tube heat transfer method, Dimensions, Weight, Warranty.
Tray Dryers. These are well insulated, temperature controlled dryers used for drying small and medium material quantities. The materials are held in trays with a screen or perforated sheet bottom. Hot air is blown through the material in up and down directions alternately. Drying is fast and uniform. The heat source can be electric, steam or gas.
Things to Consider: Control panel with process timer, Digital temperature controller/indicator, Tray capacity, Tray size, Stainless steel construction, Heating method, Caster wheels, Air filter with HEPA option, Easy accessibility of impellers for cleaning, Motor power input, Heating load (kW), Steam consumption if applicable, Dimensions, Weight, Warranty.
V-Cone Blender Dryers: Also called V Blenders, are used for mixing of solid-solid or solid with liquid in powder or granulated form. It has a V-shaped body held by two horizontal shafts mounted on a sturdy structure. The vessel has openings at two ends with covers and outlet butterfly valve for discharge. All parts that are in contact with the process media are usually made of stainless steel. These machines provide smooth mixing without deforming the particles.
Things to Consider: Ease of cleaning and maintenance, Ease of loading, Ease of unloading, Contact parts stainless steel, Gross capacity, Working capacity, Overall dimensions, Motor HP, Warranty.
