Sodium Bicarbonate

Bulk Handling and Storage

Bulk Handling of Sodium Bicarbonate

In designing a system for the unloading of bulk sodium bicarbonate from hopper cars or trucks of the bottom dump variety, the selection of methods of conveying the material should be based on:

(1) distance to be conveyed; (2) required rate; (3) tolerance for particle breakage; and (4) cost factors.

Pneumatic, screw, drag chain, belt conveyers, and bucket elevators have been used for sodium bicarbonate. Although carbon steel is an acceptable material of construction, nonrusting materials such as line steel, stainless steel or aluminum may be preferred for USP/FCC Grade applications. Also, sodium bicarbonate tends to be dusty, and dust collection provisions should be considered.

Screw Conveyors

Screw conveyors offer a satisfactory means of conveying sodium bicarbonate. They should only be used in horizontal runs in conjunction with bucket elevators. They are generally more economical than pneumatic conveyors for hori- zontal runs of less than 200 feet. They tend to do a minor amount of grinding of the conveyed material and may be unsuitable on coarse granular product, if no particle breakage can be tolerated. Special attention must be given to design of bearings in order to avoid contamination of the lubricant with sodium bicarbonate, which will destroy the lubricating properties of grease very quickly. Utilizing a 30% design loading to prevent direct contact of sodium bicarbonate with the bearings, and providing non-lubricated (white nylon) bearings minimizes this problem. Each flight of a screw conveyor should, of course, be arranged so that it can be lifted vertically for maintenance without disturbing adjoining flights.

The internal ribbon type conveyor has no particular advantage over the screw conveyor and has the disadvantage of being rather difficult to free of product if it becomes plugged.

Screw type conveyors are available in a wide range of sizes and capacities.

Additional information can be obtained from manufacturer catalogs.

Elevators

These are the simplest and most dependable units for making vertical lifts. Spaced-bucket centrifugal discharge units are most economical and are suitable for sodium bicarbonate. The buckets may be chain or belt mounted. Careful attention to the design of the elevator is necessary in order to avoid overloading which may cause a plugged chute or may burn the belt. A fairly deep elevator boot should be provided, so the buckets can be loaded on the vertical leg and are not forced to dig out of the boot. In addition, a curved plate should be installed at the head end on the ascending leg in order to prevent product from being discharged before it has passed the head pulley.

Pneumatic Conveyors

Conveyors of this type fluidize sodium bicarbonate with air and either suck or blow the material through a pipeline to a separator which recovers the material from the air stream and discharges the cleaned air. Pneumatic conveyors of either type have high horsepower requirements and may be unsuitable on coarse granular product if some breakage of the particles cannot be tolerated. Also, filtering or other precleaning of the transport air may be required for food-grade material.

Depending on the length of the conveyor line, the constancy of feed and the capacity of the blowers, this type of system is usually considered to be capable of handling five to fifteen tons per hour through a four-inch line. Five hundred feet is generally considered the maximum distance over which this system can be used economically. The pneumatic system has the advantage of being totally enclosed and may be less expensive than screws and elevators for long hours with complex layouts.

Drag Chain Conveyors

This type of conveyor, which consists of one or more chains with moving attachments or flights running through a trough or set of guides, may be used in handling sodium bicarbonate. Some versions of this type of conveyor may be more satisfactory than pneumatic or screw-type systems when minimization of particle breakage is critical. Drag conveyors can be used to move product horizontally or up inclines. They have the disadvantage of being noisy and requiring more

maintenance than screw conveyors.

Belt Conveyors

Belt conveyors are not recommended for grades finer than Coarse Granular because of the probability of excessive dusting, due to the fineness of the crystals. They may be considered for Coarse Granular product, especially where no breakage can be tolerated. They offer low installation and maintenance costs. For FCC/USP Grade sodium bicarbonate, these conveyors should be totally enclosed. Some types f belt conveyors can be designed for use on an incline. o