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Is bigger always better? Not in the case of grease distribution systems. This article explores some of the more common problems with designing grease distribution systems, highlighting several issues that could lead to improper sizing.
Bulk vs. Individual Containers
Three major factors that must be considered when choosing the method of receipt for grease include operational needs, grease consumption by type and volume, and total cost impact. For instance, the volume may be large, but if several greases are used at various times, a bulk system may not be the best choice. Changeover expense and the risk of adverse affects from contamination between greases may outweigh the cost savings normally achieved with bulk deliveries. Furthermore, if flexibility of the operation requires usage units to access separate greases at different times, a central system and bulk grease would be more of a detriment than a benefit. Elements such as volume, operating time, product(s) used and cost are all major factors to be evaluated when choosing a system.
The most efficient way to store grease is in bulk tanks. However, there are numerous considerations in selecting a storage system. Obviously, bulk versus packaged receipt carries a major cost consideration. Hidden factors should not be overlooked when evaluating the options. The same factors apply when considering bulk versus packaged distribution. Even if packaged distribution is considered the best for the operation, bulk receipt with subsequent on-site packaging could be a possibility if the annual volume of a grease product is sufficient. Intermediate bulk containers (IBC) can be filled on-site, either from a bulk tank within the facility or directly from the tank truck. Storage space, maneuver space and labor are all factors that affect the selection.
Location and Disposal
An important factor often overlooked is the physical location of the bulk grease tank in relation to the unloading spot. Environmental aspects (heat and cold) can impact unloading operations. The lack of heat tracing and/or insulation on the lines can result in high-pressure requirements for the unloading pump, resulting in a ruptured hose. If the hydraulics have not been properly calculated for grease unloading, excessive time and damage could be encountered when unloading a bulk grease truck. Because grease is a non-Newtonian, pseudo-plastic fluid, calculations must be based on the actual shear rate characteristics for the selected grease. Keep in mind that if the grease is changed, the new shear rate data must be used to check the hydraulics.
If direct receipt of packaged grease is considered, factor in the storage space and handling required and the disposal of the empty containers. Empty IBCs may need to be returned to the supplier; this adds the return freight and container repair costs to the ultimate cost of the grease. If drums are used, the user may experience additional costs for empty drum disposal, which in some cases could be high depending on local environmental regulations.
Bulk/Central Systems - The design of a grease central distribution system must consider not only the volume of grease used but the distribution of the grease to the using units by rate, distance from the source, environmental conditions (mainly temperature) and the grease-specific shear rate data. Unfortunately, a typical error in the development of hydraulic calculations is using methods common to Newtonian fluids, which will likely result in oversizing the lines. Oversizing the lines is one case where bigger is seldom better. Oversized lines will cause the grease to channel through the middle of the pipe, cutting a "doughnut hole" and leaving stagnant grease along the walls. The larger the pipe, the larger the stagnant layer. Depending on the grease, the stagnant layer can harden. This creates the potential to break off solid particles that can clog distribution nozzles. Furthermore, if the grease being pumped through the distribution system is changed, it will be difficult to clean the line of the old grease prior to introducing the new grease. If the old grease is not cleared from the line, there is a contamination risk between the new and old grease that may affect the end user.
Another factor when considering a central distribution system is flexibility of the supported system and the potential for expansion. A central system does not lend itself to flexible operations. If flexibility is needed, a parallel system could be installed to provide the using unit flexible access to a second grease product. Economics will usually dictate the value of parallel central systems.
Drum/IBC System - Operational flexibility may dictate if grease is received by drum or IBC, though it may have a higher unit cost and require extra handling. Multiple products and the corresponding lower annual volume for each product tend to shift the decision to local distribution systems. The same considerations outlined above should be included in the decision and design process. However, the use of grease supplied in drums can aggravate the logistics of the supply to the user, as well as result in additional housekeeping problems. On the other hand, grease supplied in IBCs can alleviate some of the logistics of the supply, but may result in partially filled bins when changeovers occur. Partially filled bins often contain wasted grease which impacts the overall cost.
When considering the installation or modification of a grease supply system for multiple users, the factors listed in this article are among many that must be considered when selecting and designing the distribution system. Improperly sized systems can be detrimental to a cost-effective operation, both in the present and the future. Neither large nor small is, by nature, better.