BACKGROUND

Depending on the flow properties of material to be handled and operating conditions, gravity discharge is not always the most practical solution when designing bins, silos, and hoppers for handling bulk solids. One alternative to consider for fine powders is fluidized handling.

Handling a bulk solid in a fluidized condition can be beneficial for several reasons, including the ability to obtain higher discharge rates with smaller outlets and to maximize the use of available space.

By keeping a material fluidized, much higher discharge rates can be achieved and arching conditions can be overcome, while using a reasonably sized outlet.

FINE LIMESTONE EXAMPLE

Manufacturers of asphalt roofing shingles often use fine, hot limestone as filler with liquid asphalt. In order to maintain uniform mix viscosity and temperature, flow of limestone into the batch mixer must be controlled and reliable.

One manufacturer tried various surge bin designs for fine limestone which were unacceptable. Vibrating bin dischargers were most unsatisfactory since the discharge rate varied from no flow to uncontrolled flow, or flooding.

After considering the material flow properties and handling conditions, Jenike & Johanson corrected these problems by designing mass flow bins with mass flow screw feeders. This approach resulted in reliable flow at the required range of discharge rates.

At another facility, space constraints limited the size of the surge bin. The combination of a small bin and high required flow rates resulted in a low residence time for the material in the bin. Depending on the operating conditions, the material density could vary significantly, creating discharge rate control problems.

Jenike & Johanson designed, fabricated, and supplied a fluidized bin. Fluidization is accomplished through a 3 ft. diameter twin permeable membrane, the top portion of which is made from KEVLAR® because of high operating temperatures. Discharge is controlled by an existing rotary valve and weigh belt.

Since the bin was installed, several years ago, it has worked extremely well, providing reliable, controlled discharge at rates in excess of 20 tons/hr.

DETERGENT INGREDIENT EXAMPLE

Jenike & Johanson was asked to design a surge bin for a laundry detergent manufacturer to handle material that would be ground prior to processing. The tests confirmed and defined the poor handling characteristics of the material.

The company also had several design requirements for the bin which conflicted with the ultimate goal of reliably handling the material. We offered a unique design to satisfy the manufacturer’s needs, while also ensuring that the material would still be reliably handled.

The solution was to use two smaller bins instead of one large bin. This dramatically improved the design by eliminating the need for a "pant-leg" arrangement to divide the discharge to two pneumatic transporters.

A fluidized discharger and a lower cone, lined with air pads maintain a fluidized volume of material at the outlet of the bin. The capacity of the lower cone is equivalent to the capacity of the pneumatic transporter, which is filled on a batch basis. The bin also contains an insert, designed to ensure that mass flow is obtained when material is discharged from the bin.

Jenike & Johanson engineers performed a structural analysis and provided detailed fabrication drawings of the bins, as well as assisting during startup. The fluidizing surge bin worked as intended, reliably discharging the material to the pneumatic transporters

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