Loop Mill Case Studies

Fluid Energy Mill Overview

The original invention of loop or donut mill is credited to Cleo Harold Kidwell and Nicholas NK Stephanoff (founder of Fluid Energy Processing and Equipment).1

An early application of the Fluid Energy Jet-O-Mizer was for pulverizing solid, heating fuels.2

Since that time, pulverization applications have expanded to other granular solids.

Here we share a few examples of material comminution with this type of jet mill.


Propellant Grinding

A Fluid Energy Model 0304 Jet-O-Mizer was designed to grind solid rocket propellant to a 2 m average particle size at a rate of 500 lbs/hr.

When designing systems for propellants/explosives, special construction features are utilized.

In these cases, Fluid Energy Processing applies procedures that are found in US government specifications relating to the fabrication of milling systems for propellant/explosives use.

Due to its grinding characteristics, the Jet-O-Mizer is most frequently used in the milling of RDX, HMX and black powder. Our Micro-Jet is typically used to grind oxidizers, such as Ammonium Perchlorate.

Mineral and Pigment Grinding

A Fluid Energy Model 0808 Jet-O-Mizer utilizes 1,200-2,200 SCFM of air compressed to 100 psig for mineral and pigment grinding.

It is equipped with replaceable cast Ni Hard liners for superior abrasion resistance. The outlet is equipped with adjustable vanes for fine-tuning the particle size distribution.

The Model 0808 is routinely used to grind carbon black, talc, calcium carbonate and kaolin.

When grinding carbon black or minerals used in the filler industry, super-heated steam is typically used as the grinding fluid. Typical steam rates range from 2,000-7,000 lbs/hr. Steam pressure and temperature requirements can range up to 200 psig and 750ºF (400ºC).

Sanitary Drug Grinding System

A sanitary Model 0101 Tabletop Jet-O-Mizer System was designed for the continuous production of a topical anesthetic. The Model 0101 produces 5 lbs/hr of product at a less than 5 m average particle size.

The system includes all integral piping and instruments, a screw feeder, filter silencer, cyclone collector and laboratory baghouse. Product collection cans were provided for cyclone and baghouse collection.

All components are constructed in type 316 stainless steel with a pharmaceutical polish and are completely assembled on a 4-foot square, portable table. The system utilizes 15-30 scfm of air or nitrogen compressed to 100 psig.

These case studies are just a few examples of granular solids that can be jet-milled in a loop mill. A table of additional applications can be found here on the Jet-O-Mizer equipment web page.

The Jet-O-Mizer has been developed with many distinct design features to consume less power, provide a greater range of throughput (50 gram/hr to 20,000 lb/hr) and ensure exceptional finished product quality. Thorough application engineering allows the determination of the ideal operating conditions for specific raw materials. Production requirements are integrated into a complete Jet-O-Mizer system.

1. R.H. Perry and D.W. Green, Chemical Engineering Handbook, 8th Ed., 2007, p. 21-62.
2. Stephanoff, Nicholas NK, 1951, Method for Treating Fuel, US2550390.

Pneumatic Ring Dryer Case Studies

The Fluid Energy Thermajet Flash Dryer

Pneumatic conveyor dryers often referred to as flash dryers, consist of a duct carrying gas at high velocity.

The solids can be fed by various methods:  screw feeders, venturi sections, high-speed grinders, and dispersion mills.

Selecting the correct feeder to properly disperse the solids in the gas is critical for efficient drying.1

A Fluid Energy ThermaJet style ring dryer is a variant of the flash or pneumatic dryer.  An advantage of our ring style pneumatic dryer is a short retention time.

In a conventional, straight tube flash dryer, the residence time is basically fixed for all particle sizes of material, even though larger particles may take longer to dry.

This limits the application to materials in which the drying mechanism is not diffusion-controlled (i.e. constant rate drying, not “falling rate” drying) and where a range of moisture within the final product is acceptable.

Advantages of the Flash Dryer

A ring configuration offers two advantages over the straight tube. First, residence time varies with the particle size of the material.

Finer particles, which dry quickly, will be carried out with the airflow sooner, while larger particles, which dry more slowly, will make multiple cycles in the outer part of the dryer loop due to their heavier weight and the centrifugal forces created by the airflow within the ring.

The larger particles will now have a longer residence time for drying.

Second, although the dryer typically operates at lower pressures than a loop or torus jet mill, cycling through the ring can grind the material while drying. Even if grinding doesn’t occur, the internal forces are strong enough to break apart (de-agglomerate) wet cakes and clumps. This unit operation can control product particle size and moisture in the same process step.

Alumina Slurry Drying

A Fluid Energy Model 4 ThermaJet was built to dry alumina slurry from an initial moisture content of 80% to a final level of 0.2%.

The dryer includes a rotary valve feed inlet, replaceable abrasion-resistant liners, and a high-temperature manifold with inlet expansion joints.

Additional system components include a process blower, direct-fired natural gas heater, cyclone, baghouse and exhaust fan.

A slurry pump, screw conveyor, and continuous mixer were added to handle slurry feed. It recycles a percentage of dry product through a paddle mixer, increasing the solid content of the slurry to form a filter cake-like consistency for feeding through the inlet rotary valve.

Agricultural Chemical Drying

A Fluid Energy Model 14 ThermaJet, shown in the drawing at the left, was designed in a horizontal configuration in order to meet a customer’s space requirements.

The unit dries a heat-sensitive agricultural product from an initial moisture content of 10% to a final level of 0.2%.

Since some solvent is driven off in the drying process, the ThermaJet system operates with a closed-loop, nitrogen recycling package using a steam coil heat exchanger.

A condenser has been included in the system to remove solvent and water vapor from the process stream prior to recycling.

Drying & Calcining of Iron Oxide

The Model 10 ThermaJet, shown in the picture to the right, dries yellow oxide from an initial moisture content of 40% to 10% bound moisture.

The Model 10 was combined with a Model 12 to provide calcination of the dried oxide. The system begins with a yellow iron oxide wet cake and produces a dry, fine red iron oxide pigment.

Drying temperatures run from an inlet of 800ºF (430ºC) to an outlet of 210ºF (99ºC). Calcining temperatures include an inlet of 900ºF (480ºC) and an outlet of 650ºF (340ºC)

The calcining portion of the system includes an evaporative cooler located after a cyclone to cool down the process stream before entering the baghouse.


Silicate Drying

The Model 26 ThermaJet was designed to process a silicate filter cake from an initial moisture content of 40% down to 10% bound moisture. The Model 26 includes a separate hot air manifold to operate at 1200ºF (650ºC) with inlet nozzle expansion joints.

This unit also accepts direct feed from a volumetric screw feeder. Additional system components include a process blower, a direct-fired natural gas heater, and a reverse pulse collector & exhaust fan with actuated damper. Process controls were integrated into an existing PC-based control system.

These case studies summarize a few applications of the ThermaJet dryer. Additional applications can be found here on the ThermaJet webpage. The case studies demonstrate the versatility and capability of flash drying systems:

Capable of processing heat-sensitive and volatile materials. Able to process materials including wet powders, slurries, sludges, and filter cakes.
• Flexible feed capacities for laboratory, pilot, and full-scale production with feed rates ranging from 10 to 100,000 pounds per hour.
• Produces dry, discrete, deagglomerated products from raw feeds containing up to 95% moisture, often eliminating the need for additional grinding.
• Incorporate a broad range of operating temperatures and pressures for specific drying applications.
• Allows for calcining operations with immediate response time and instantaneous changes in product characteristics.
• Capable of integration with virtually any air heating system and offered with a variety of control options for customized drying applications.
• Able to operate continuously with superior reliability and minimal maintenance.

1. Czeslaw Strumillo and Tadeusz Kudra, Drying: Principles, Applications, and Design, Gordon and Breach Science Publishers, 1986.
2. Irene Borde and Avi Levy, 16-Pneumatic and Flash Drying, Handbook of Industrial Drying, Editor Arun S. Mujumdar.