Equipping bulk handling systems

High-volume bakeries place a high value on bulk ingredient handling systems. For major ingredients, these systems must provide proper storage and sanitation, and be able to transport ingredients quickly and efficiently to the mixer. A baker's formulation begins with the bulk ingredient handling system.

Bulk ingredient handling systems typically are composed of silos, sifters and conveyors. From storage tanks and silos, liquid and dry ingredients must be transported to the mixer at the right temperature, without extraneous and hazardous material, and with little downtime for changeover or equipment malfunctions.

Before bakers make such a large investment, whether purchasing an entire bulk ingredient handling system or individual pieces, they should analyze their ingredient handling needs. For each piece of equipment in the system, many options are available.

The first priority for bakers before purchasing an ingredient handling system is to identify their major ingredients. Bakers use a sufficient quantity of these ingredients on an annual basis to warrant buying them in bulk quantities. These ingredients are transported to bakeries in trucks, which hold about 50,000 lbs. of material, or by railcars, which hold as much as 200,000 lbs. of materials.

Silos
Bulk ingredients convey from trucks or railcars to silos. Silos can be inside or outside of a plant and hold liquid and dry ingredients. Many manufacturers will construct silos to a certain storage capacity based on the baker's usage.

"For example, if you were purchasing and receiving your flour in 50,000 lb. quantities from trucks and you used two truckloads a day," one manufacturer of ingredient handling systems says, "then you would want to size your silo to hold two-and-a-half to three truckloads, or 125,000 lbs. to 150,000 lbs."

The most widely used silos are constructed from stainless steel or aluminum. Another type of silo is constructed from fiberglass. The insulation value is 2,000 times higher in fiberglass silos than steel silos, one silo manufacturer says. This eliminates condensation, requires less cleaning and protects the ingredients from heating, the manufacturer says.

Condensation, cleaning and ingredient temperature are important factors that bakers must consider before purchasing silos. Condensation collects when new material is loaded into silos. The material sitting in silos is surroundedby ambient air, and when that mixes with warm air and material, condensation occurs. Condensation also occurs when silos are in a humid location. One way to combat this is to purchase a silo that is equipped with a dehumidification process that blankets silos with dry air.

Bakers also should consider how a silo accepts and discharges ingredients before purchasing an ingredient handling system. When an ingredient is conveyed out of a silo, the ingredient creates a funnel as it discharges. Some of the material at the top of the silo folds down as it discharges, which causes the ingredient at the bottom of the silo, close to the cone, to become trapped to the cone's sides. This creates problems because the ingredient is not consistently aged, one ingredient handling manufacturer says.

To combat funnel effect, this manufacturer offers a silo with a live bottom discharge. The lower cone has a vibrating bottom, which promotes a massflow effect, or, first in, first out.

Bakers also should track how much material remains in a silo at any given point. One manufacturer offers level measurement devices that incorporate load cells on the silo. This provides the baker with a continuous readout on the amount of flour remaining in the silo.

Sifters
Similar to silos, bakers also must consider how their formulations and plant setups affect the type of sifters they purchase. Sifters are necessary for scalping (to remove oversize materials), removing lines (to eliminate undersize materials and dust), and grading (to control oversize and undersize materials), one sifter manufacturer says.

There are two main types of sifters available: gravity and inline. In a gravity flow sifter, ingredients are conveyed through the sifter from above it to below it.

Inline sifters are more popular, one sifter supplier says, because they can be directly inserted in a pressure or vacuum conveying line. Bakers can place the sifters anywhere along the ingredient handling system, but the sifter manufacturer recommends that they be placed just prior to the mixer. Wherever the sifter is located, it must allow for easy access for cleaning and inspecting.

Because sifters must be cleaned and inspected on a daily basis, it is best for them to be located indoors. "It's kind of like out of sight, out of mind," one ingredient handling manufacturer says. "But if [the sifter is] inside, you walk by it on a regular basis and it gets attention."

Purchasing a sifter relies on many variables: What ingredients will flow through the sifter; moisture content and temperature; what shifting motion the sifter will have, which includes centrifugal, vibratory, gyratory and gyratoryreciprocal; and the screen type and mesh size.

One sifter manufacturer recommends a horizontal gyratory sifter. Material is sifted on a horizontal plane while a screen moves in a circle. "It presents more openings to the material and it is more gentle in its handling, compared to centrifugal type sifters," he says.

Conveyors
Conveyors are the beginning, middle and end of ingredient handling systems. Bulk material is conveyed from trucks or railcars to silos, then conveyed out of silos to any drop-off points, ending at the mixer.

Generally bakers use two types of ingredient handling conveyors: screw and pneumatic. Screw conveyors are typically the simplest and lowest cost conveyor. "If you are going from point A to point B, this is the easiest way to do it," one conveyor manufacturer says. Its disadvantage is that it does not convey all of the material. This is a problem if one conveyor is handling more than one ingredient at a time, the manufacturer says, because incorrect amounts of the ingredients are being conveyed to the mixer.

Pneumatic conveyors are available in a pressure system or vacuum. Pressure conveyors are less expensive than vacuum conveyors, and they are ideal to move bulk amounts of ingredients in a hurry, one conveyor manufacturer says. However, pressure conveyors can break and spill ingredients. To prevent line breaks, it is important to purchase pressure conveyors with at least four-bolt couplings, the manufacturer says. His company manufactures pressure conveyors with this feature. The system also has two side bands that are bolted tightly to the pipe, with clamps and bands holding everything together.

With a vacuum system, the ingredient is sucked to its next point. Vacuum conveyors transport material with ambient air, eliminating the heat compression that is used with pressure conveyors, one ingredient handling manufacturer says.

This manufacturer suggests that bakers use pressure conveyors to fill silos and vacuum conveyors to take the ingredients into the plant and to the mixer. "Vacuum conveyors are a much more effective and accurate way of conveying to a scale," he says. "But when you're just filling the silo, you're not concerned about hitting a set point, you're just unloading."

As long as bakers are aware of their processing and ingredient specifications and requirements, they will find a bulk ingredient handling system to suit their needs. These systems offer many options for customized silos, sifters and conveyors. •