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A. More and more often, the railroads have been encouraging their customers to receive products in larger lots and unload them quickly. As a result, the railroads have established grain "unit train" rates which typically require the receipt of 65-, 75-, or 90-car trains that must be turned around in 24 hours or less.
Thus the first requirement to be confronted is the ability to receive a total of 65, 75, or 90 cars. Typically the facility must have a series of ladder tracks or a loop track that can accommodate strings of cars totaling 65, 75, or 90 cars, each with a length of 60 feet or more. The delivering railroad should be consulted as to the design car length. While some cars may be shorter, the railroads are replacing older short cars with longer ones. Additional storage track is required for non-unit train cars such as liquid and softstock ingredient cars.
In the design of the track system, the design standards of the delivering railroad must be followed. Typically, industrial tracks require #8 turnouts minimum, 12-degree curves, and a minimum of 110#/yd. rail. Adequate clearance (14 feet) between adjacent rails and turnout clearance points must be provided. Also, the number of ladder tracks must be minimized as unloading time is lost shuttling car cuts into and out of the unloading area.
A typical 62-foot railroad car holds 3,900 bushels of grain. In the unloading analysis, it is common to allow 20-25 minutes to receive each cut of cars into the dump area and return them to the spur track when emptied. Individual car handling should include a minimum of three minutes per car for gate opening, closing, and advancing to the next car.
This rate requires a powered gate opener, adequate moving equipment, and an unloading pit length as long as the out to out of the overall car gates. If origin weights need to be confirmed and a rail scale is utilized, additional time will be required. A bulk weighing garner scale is also an option, which will not require extra time.
If we assume a 90-car unit train with five cuts of cars, 18 cars each, the following times are consumed in car handling:
5 cuts @ 25 minutes per cut = 125 minutes
90 cars @ 3 minutes per car = 270 minutes
Total = 395 minutes
Total time available for unloading (24 hours) = 1440 minutes
Time available for discharging (1440 min. - 395 min.) = 1045 minutes
1045 minutes / 90 cars = 11.61 minutes per car
3,900 bushels / 11.61 min. = 336 BPM (20,155 BPH)
The facility material handling system must be capable of continuously achieving an unloading rate of over 20,000 BPH.
Certainly, many more aspects of the facility, like storage capacity, must be analyzed in preparing to handle unit trains. The above example does, however, provide a basis for understanding the requirements.
Answered by James Schuster, Senior Engineer at WL Port-Land Systems, Inc.