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BULK TRUCK LOADING & UNLOADING
Tank truck loading systems typically include a transfer pump, a pigged piping system, some means of measuring the product being loaded and a loading arm to deliver the product into the tank truck. In addition, a tank truck loading system may also incorporate product filters, vapor recovery, over-flow protection, and grounding systems.
Tank trucks can be top or bottom loaded. Top loading operations require an operator platform, where bottom loading does not. Generally, loading rates can be somewhat higher with bottom-loading systems. The amount of product transferred can be determined volumetrically or by mass. Volumetric measurement can be performed by measuring the level of the material in the tank truck compartment with a tape or a stick, or by using an in-line positive displacement meter. Mass measurement can be achieved using a Coriolis mass flow meter or by loading the truck on a scale.
A pigged piping system can be used to ensure that the transfer pipeline is emptied after each loading operation, or to allow the metering system to be mounted some distance from the tank truck. In the latter case, the metering system discharges into the pigged pipeline and the pig clears the pipeline forward to the tank truck. Pigged piping reduces product losses and cross-contamination, and helps minimize the number of pipelines required for the loading operation.
Loading systems can be fully automated and equipped with a variety of interlocks to improve operator safety, reduce operator error, minimize the chance of over-flow and otherwise enhance the efficiency of the operation. Card readers and operator terminals can be installed to communicate with plant control systems. This type of communication can be used to check inventories prior to loading, ensure that the tank truck receives the correct product or products, print bills of lading or certificates of analysis when the loading is complete, or to perform other administrative tasks.
Tank truck unloading typically involves the connection of a hose between the tank truck manifold valve and the suction line of a transfer pump. However sometimes the tank truck is equipped with an "onboard" pump which is used instead of an installed "unloading pump". Depending on the viscosity of the material being handled, the diameter of the hose may be 2,3, or 4 inches in diameter. The product to be unloaded may require heating prior to unloading, or may arrive at the plant at the required pumping temperature. This is possible when working with tank trucks, because the transit time for the truck is only a few hours instead of a few days, as is common for tankcars. When the transit time is short, the product in the tank truck retains much of the heat it possessed when it was loaded.
After the product has been transferred from the tank truck, the hose must be disconnected to prepare for the next unloading operation. During this activity, the residual material in the hose is often drained to a slop system and some of it may be spilled to the environment. If the hose is not completely drained, any product remaining may create cross-contamination issues the next time it is used. The unloading rate is a function of piping system hydraulics and is affected by the capacity of the pump, the viscosity of the material being handled, the length & diameter of the suction hose, and the piping system through which it must be transferred.
Beamer & Associates, Inc. is sensitive to these issues and employs proven methods to maximize unloading efficiency while minimizing product losses. In certain circumstances a Portable Unloading Pig launcher/receiver (PUP) can be used as part of a system to pig the hose and piping from the tank truck all the way the destination tank.
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