What is Flash Drying within Custom Toll Processing?

Charles Casale, Jan 31, 2020 4:59:23 PM

Flash dried white powder

Toll processors have numerous options for drying a material.

During flash drying, a powder, granular material or slurry is briefly exposed to a high-temperature gas jet stream within a duct, causing rapid evaporation. This allows for heat-sensitive materials to be dried without degradation; plus it reduces agglomerating, or clumping.

The process of flash drying, especially when it comes to toll processing, provides numerous efficiency advantages over other drying methods.

Flash drying is fast, as you’d expect by its name, as truckloads of material can be processed rather quickly. Additional advantages of flash drying compared to other drying options include its precision and its many applications

How Does Flash Drying Work?

  1. Within the flash dryer, a gas-fired burner heats air
  2. A blower moves the air rapidly into a large, circular duct loop
  3. A feeder drops material into the air stream where it is conveyed and dried
  4. The material leaves the dryer through a product collector, where sleeves let air through but collect the dried material in a cyclone or bag house.
  5. The dried material is then packaged according to the customer’s specifications. 

What Materials Can Be Flash Dried?

In order to be flash dried properly, material needs to be a size that can be pneumatically conveyed and carried in the moving air stream. Heavy material will simply drop out of the air stream. The best materials are powders and granules (2 microns up to 2mm or larger), pastes, gels, and slurries.

Although the temperature of a flash dryer can be adjusted, the material needs to be able to withstand higher temperatures to be dried quickly. 

Highly combustible or flammable materials are not a good fit due to the risk of fire or explosion.

Products in many industries typically contain material that has been flash dried:

  • Chemicals
  • Agricultural products
  • Paints and resins
  • Minerals and mining materials
  • Ceramics
  • Wood
  • Plastics and polymers

What Are The Critical Elements To Flash Drying Success?

As previously stated, pneumatically conveying the material is critical. A flash dryer is good at drying sludges and cakes as long as they’re not too heavy — otherwise the moving airstream can’t suspend the material.

Because flash dryers use direct fire to heat the air, temperature-sensitive material may not hold up well in a flash dryer. A heat exchanger’s indirect heat may be better, for instance. One possible way to get around that is to reduce the temperature and conduct multiple passes through the flash dryer to achieve the desired moisture level. This doesn’t maximize a flash dryer’s efficiencies, but it may be possible to achieve moisture level goals this way.

How Do You Test A Material?

Speaking of moisture level goals, the only sure way to know if a material is right for a flash dryer is to test a sample.

An operator examines the physical properties of the material: a cake/sludge/mud needs to be small enough to disperse and convey throughout the dryer. Now, with a desired moisture percentage as the goal, an operator calculates the flash dryer’s ability to handle and heat the material during a given time.

After the material runs through the flash dryer, a Moisture Balance accurately measures the material’s moisture using the loss-on-drying method. Simply put, a table-top device calculates a sample’s moisture content.

How Do You Determine A Flash Dryer’s Performance?

The two most obvious measures of a flash dryer’s performance are its ability to meet moisture specifications and that the material arrives contamination-free.

Toll processors, by their nature, are obsessed with cleanliness. Being ISO 9001-compliant brings with it the capability to properly dismantle equipment and clean it to ensure no cross-contamination of materials. 

Other performance indicators are the material’s delivery (is it timely and consistent?), the quality of the final packaging (does it pass the eye test?), and final cost (is the quoted price met?). If a flash dryer isn’t performing in a certain area, another drying method may be required.

The most important thing is choosing a micronization service provider that understands the nuances of flash drying as well as other drying techniques. In other words, a well-rounded toll processor that has mastered many drying methods.

It’s easy to get confused about all of the drying options available from toll processors, or toll manufacturers … or is it contract manufacturers? Some people get slowed down by terminology, so we’ve created a quick comparison of “toll manufacturing” and “contract manufacturing.” Just click the button below.

Toll Manufacturing vs Contract Manufacturing

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