In the past, the large export facilities in New Orleans traditionally used unloading devices known as "marine legs." Quite different in size and capacities from the modern Continuous Barge Unloader, or CBU, these machines are equipped with small buckets that travel at high speed. Their maximum capacity is usually in the range of 20,000 to 25,000 bushels per hour, roughly 600 to 750 tons per hour.
By nature of its design, the marine leg leaves a great amount of material remaining in a barge. The clean-up process is very time consuming. A front-end loader is used to gather the remaining product together, and then a pneumatic-type vacuum is used to thoroughly clean up the product that is left over. Besides relatively low offloading rates and high power consumption, studies showed that this method of unloading was responsible for product degradation at the arte of 0.2 to 1%, generated as foreign material. Product degradation was especially prevalent while unloading corn and soybean.
Unloading methods which used only pneumatic vacuums produced offloading rates of 20,000 bushels per hour, or 600 tons per hour. Once again, generated foreign material could be created, depending on the product being unloaded.
In 1965, one of the large grain export companies became aware of the success the steel and utility industries were experiencing in using the CBU for their barge unloading. They commissioned a study and field tests to determine if the CBU could offer the same benefits to the grain export industry. The tests proved that the entire barge offloading function could be streamlined, that less power was consumed and that less foreign material was generated by using the CBU. It was also determined that materials that were extremely difficult or even impossible to offload, such as soybean meal, screenings and corn gluten feed were easily handled by the CBU. The conclusion was that the value of the entire terminal was enhanced by faster offloading times, better machine availability, and the ability to unload by-products and improve make-up of delays caused by rain. Machines were commissioned with free digging rates ranging from 80,000 to 100,000 bushels per hour.
In order to fully utilize the CBU and offset its higher costs, the traditional barge handling and operational sequence was modified. The operationa sequence of a CBU used of offload grain and related products will differ from installation to installation. Proper cover handling is important to the success of a high capacity operation.
In most circumstances, a structure is built at the approach of the unloader. The covers are removed from the loaded barges and replaced onto the empty barges. The barge haulage cables are connected to the barge at this location and the barge is moved to the digging head of the unloader boom. The boom is slowly lowered with the hoist engines to the center of the barge, and the bucket/chain line is started.
As material is unloaded, the boom continues to be lowered until it reaches the bottom of the barge. At this point, the trolley traversing sequence is started and the boom travels to the barge sides. When a pathway has been cleared, the barge haulage system advances at a proper rate to deliver the loaded material to the CBU boom. This operation continues until the barge is entirely unloaded. It should be noted that this unloading sequence differs from most other industries where a two-pass operation is used.
Due to barge interior configurations, a certain amount of material will be left in a barge. The remaining product is cleaned by utilizing a front-end loader to scrape the product into a pile that is within range on the unloader's reach, or transfers the product directly into the unloader buckets. In many instances, the front-end loader is placed within the barge as the CBU is offloading the opposite end. This can be done safely, and speeds cleanup time to less than 15 minutes. Most operation report conservative unloading times of less than one hour for a 1500-ton barge.
Larger export facilities have employed a double-slip CBU to speed throughput. The double slip machine spans two barge widths, allowing one barge to be unloaded while a second is undergoing the cover handling function.
Most modern machines are equipped with dust collection systems to meet today's environmental regulations. The boom is provided with ducts that have pick-up points at the area of the digging head, as well as the bucket return chute. Additional ducts and pick-up points are provided on both sides of the discharge chute to gathering conveyor meeting point. All ducts interconnect at the trolley, and from there interface with a stationary "zipper duct" mounted on the unloader structure.
Optimal-design installations mount a baghouse over the main yard conveyor, just beyond the CBU gathering conveyor discharge point, and collected dust is deposited on the yard conveyor.
Heyl & Patterson has designed and manufactured grain CBUs for decades, and many can be found near the New Orleans area and along the Mississippi River. We also offer a complete line of replacement parts and upgrades, regardless of the original manufacturer. Mechanical upgrades include buckets, lubrication systems and trolley wheels, while electrical upgrades include control systems, fiber optics and variable frequency drives.
To learn more about Heyl & Patterson's Continuous Barge Unloaders and other types of barge unloading equipment, click here: