Often times a process requires material to be dried/heated/cooled/reacted to meet proper production and quality requirements for a given process. This can be accomplished with a wide array of apparatuses such as direct or indirect drying equipment. The equipment is usually a heated or cooled, mechanically agitated, highly efficient device for adding or removing energy from a process mass. The process involved can be drying, heating, sterilizing, cooling, reacting, torrefying, melting, pasteurizing, stripping solvents, calcining, roasting, cooking, or crystallizing a wide variety of materials such as chemicals, pharmaceuticals, biosolids, food, waste, minerals, polymers, and metals, among others. In many cases the equipment is used for drying, which can be defined as a process whereby liquid is transferred from a solid state into a vapor phase. In most cases, the drying process is accompanied by the application of “heat” which facilitates the phase change and expedites the drying operation.
Direct and Indirect Drying/Cooling
Direct drying or cooling are mechanisms that add or remove energy from a material by intimately mixing treated gas with the material. This treated gas will transfer energy and liquid to and from the material. The process mass will come in direct contact with the heated or cooled gas facilitating the drying process which is a viable alternative to indirect drying/cooling.
Indirect drying or cooling is a process of energy transfer where the process mass is heated indirectly, typically via saturated steam or thermal fluid or cooled via water/glycol mixture. The process mass and heating/cooling mediums are kept separated by a barrier. In most cases a stainless steel wall is used for the isolation between the mass and heating medium due to its durability and resistance to corrosion. The heating medium’s energy is conducted through the metal wall of the equipment to the material on the process side of the thermal processor during a drying process, and vice versa in a cooling process. In the case of drying, the solvent in the process mass is brought to its boiling point and as the material dries, the liquid changes phases and enters the vapor space above the process mass. The vapor then leaves the indirect dryer through the off-gas outlet. One example of this equipment is a paddle dryer/cooler.
The paddle dryer/cooler has dual counter-rotating agitators with intermeshing hollow wedge shape paddles resulting in uniform heating (or cooling) and optimized heat transfer. The use of hollow heated (or cooled) paddles and a jacketed trough provides for a large amount of heat transfer area in a compact machine. Localized mixing around each self-cleaning paddle creates a homogeneous mixture.
In certain applications there are restrictions that limit indirect drying capabilities such as thermal decomposition at the solvents boiling temperature, residence time, temperature restricted materials with low residual moisture requirements, feed material size, etcetera. These types of applications may be better suited for direct drying/cooling equipment such as a vibrating fluid bed dryer (VFBD).
Vibrating Fluid Bed Dryer
The VFBD is a direct drying system that is used for a wide variety of materials. It provides a cost-effective way to process many different pastes, cakes, powders, and granules using direct heat transfer in a highly controllable manner. In addition, the VFBD “fluidizes” the material by a combination of vibration and air that passes upward through it, allowing for uniform heat and mass transfer.
The VFBD can be used in a variety of heating, drying, and cooling applications such as pharmaceutical, food, nutraceuticals, chemicals, pesticide, plastics, fibrous material, biomass, and many other applications. The VFBD can handle material with a minimum particle size of 1 mm being fed and processed in the VFBD.
The VFBD is a fully enclosed design that prevents outside contamination from entering the process material. Material enters the dryer via the feed inlet and is conveyed along the vibrating drying zone in a continuous movement. Treated gas is passed through the perforated plate for direct heat transfer and removes moisture from the material. The VFBD achieves uniform product moisture content. The treated gas is discharged from the top off-gas outlet of the VFBD, while the dry material is discharged at the product outlet of the unit. The off-gas and ultra-fines entrained in the off-gas are then sent through the off-gas outlet to a cyclone and baghouse. The cyclone allows the course particles to drop out while off-gas is sent down stream to a baghouse for final separation before ejecting into the atmosphere. Overall, the VFBD is simple to operate, easy to clean, and requires little maintenance.
The VFBD provides the following advanced features:
• Negligible particle entrainment
• Uniform air flow and gradual removal of moisture
• Ease of maintenance
• Long equipment life
• Compact design across a wide range of sizes
• Ability to handle temperature sensitive material
• Residence time control
• Batchwise or continuous operation
• Easy to clean
• Energy efficient
• Cost effective
A good way to determine if the VFBD is a good fit for your applications is to perform a pilot test at a facility such as Komline-Sanderson’s technical center, located in Peapack, NJ. This facility is equipped to run both bench and pilot scale tests for liquid/solids separation and thermal processing applications. The technical facility also offers rental equipment for field testing or small production runs. Testing is used to obtain process design information for scale up to commercial size machines and develop optimized processes.
For more information, contact Komline-Sanderson Corp. at 908-234-1000 or visit www.komline.com.