Handling of Borates in Bulk
Neobor® Borax Pentahydrate: This product is the most stable of the three sodium borates and is ideally suited to bulk transfer. It shows little tendency to cake, except after prolonged storage, or if it becomes severely wetted by rain or other substantial water ingress.
Optibor® Boric Acids: Optibor Boric Acids are ideally suited to bulk transfer. They show little tendency to cake, except after prolonged storage, or if they become severely wetted by rain or other substantial water ingress.
Borax Decahydrate: Of the sodium borates, Borax Decahydrate is the material that shows the greatest tendency to cake. However, if proper precautions are taken, Borax Decahydrate can be shipped and handled in bulk.
Dehybor® Anhydrous Borax: Dehybor generally handles well in terms of its flow characteristics, but attention must be given to the abrasive nature of the particles. Where large quantities and long-term continuous operation of the unloading plant are involved, preference should be given to mechanical transfer equipment rather than pneumatic systems.
Bulk Delivery Systems – Railcars, Trucks, and Containers
Railcars generally have a bottom gate for discharge between the tracks. However, some cars are available equipped for pneumatic discharge either with their own pneumatic systems or utilizing customer’s own equipment. The average hopper car is approximately 4,450 ft3 (126 m3 ) and will hold 100 tons (90,700 kg). Cars are available upon request, with dual systems such that unloading can be accomplished using either gravity or pneumatic methods. All cars are equipped with center dump gates.
Trucks are generally equipped with their own pneumatic discharge systems operating at pressures of about 29.4 psi (2 atmospheres) and are capable of delivering into silos up to a height of 100 ft (30 m). Long horizontal runs of piping should be avoided.
Containers (either with or without liners) are emptied by gravity or by suction using customer’s own equipment.
Generally, gravity unloading is more commonly used, especially with those products, such as borax decahydrate, that tend to cake and form lumps under certain conditions of humidity and temperature.
Gravity unloading is accomplished by discharging product directly from a rail hopper car to a pit located between the rail tracks. It is recommended that an air-operated impact wrench be used for opening and closing the slide gate which can bind with the build-up of product in the slide tracks. Product can then be discharged from the track hopper, at a controlled rate, through an adjustable slide gate to a mechanical conveying system to a storage silo.
Pneumatic unloading is done by vacuum, or combination vacuum-pressure techniques. Neobor and Optibor are non-abrasive and can be easily conveyed by this procedure directly from the car to the silo. A flexible hose with quick coupler is usually attached to a side port on the car with the other end attached to the permanent piping which runs parallel to the silo. This method of unloading has the advantage that the product is not exposed to the elements. Since it is a closed system, contamination from outside sources is eliminated.
Borax Decahydrate contains a higher percentage of water than either Neobor or Optibor and is more prone to caking. While mechanical unloading for Borax Decahydrate is strongly recommended, pneumatic unloading is possible. It is strongly recommended that Borax Decahydrate be gravity discharged through a double-finger crusher and into a holding bin before being pneumatically conveyed to the silo.
Transfer of Borates
Mechanical conveying system can consist of belt conveyors, screw conveyors, and centrifugal bucket elevators. Electric or air vibrators mounted near the discharge opening of the track hopper will facilitate discharge if necessary. It is recommended that mechanical systems incorporate sealed transfer chutes and/or dust extraction.
Pneumatic conveying systems have the advantage of being dust-free. Neobor, Optibor and Borax Decahydrate can be air conveyed by pneumatic pipe systems or air slides. Dehybor, because of its abrasive nature, will require the use of ceramic or hard faced liners at specific points where abrasive wear is expected. These include elbows, transition pieces, and impingement surfaces in cyclones, diverters and receivers. The same precautions noted for the pneumatic unloading of Borax Decahydrate would apply if air slide unloading is to be considered. It is also important that dry, cooled air be used and care be taken to maintain air conveying temperatures below 95°F (35°C). The use of air conveying, for locations that are frequently humid with high ambient air temperatures, is not recommended.