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TANK CAR LOADING & UNLOADING
TANK CAR LOADING
Tank car loading systems typically include a transfer pump, pigged piping system, some means of measuring the product being loaded and a loading arm to deliver the product into the tank car. In addition, a tankcar loading system may also incorporate product filters, vapor recovery, over-flow protection, grounding systems, tankcar indexing equipment, and tank car rinsing systems.
Tankcars can be top or bottom loaded, although top loading is by far the most common. The amount of product transferred can be determined volumetrically, using the ullage gauge in the tankcar or an in-line positive displacement meter, or by mass, using a Coriolis mass flow meter or load cells installed under the tank car. 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 tankcar. In the latter case, the metering system discharges into the pigged pipeline and the pig clears the pipeline forward to the tankcar. Pigged piping reduces 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, to ensure that the tankcar receives the correct product, to print bills of lading or certificates of analysis when the loading is complete, or to perform other administrative tasks.
TANK CAR UNLOADING
Tank car unloading typically involves the connection of a hose between the tankcar bottom valve and the suction line of a transfer pump. Depending on the viscosity of the material being handled, the diameter of the hose may be 2,3, or 4 inches in diameter. If the material being unloaded must be kept hot during transfer, then the hose may also be steam-jacketed and insulated (increasing its diameter even further). Low clearances under the tankcar and the physical weight of the hose can make connecting the hose difficult. Beamer & Associates 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 unloading hose and piping from the tankcar all the way to the destination tank.
After the product has been transferred from the tankcar, 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 effected 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.
If the viscosity of the material being unloaded is too high, then flow (and pressure) at the suction of the pump will fall below minimums and cause the pump to cavitate. Repeated and/or prolonged cavitation will reduce the useful life of the pump. Beamer & Associates can suggest approaches that will eliminate cavitation, while maximizing pumping rates.
Finally, there is always the concern for spills during the unloading process. While concern for the environment is paramount; spills can also be quite costly due to product loss, clean-up and disposal costs, and potential employee exposure. Beamer & Associates can suggest systems and devices to help prevent spills in the first place, and to help contain them should they occur.
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