|Fuel Storage- LNG Locomotive Fuel Tender
Necessary vaporization hardware shown on the BNGT 101 tender.
Typically for freight locomotives, the preferred natural gas medium is liquid natural gas (LNG). Due to its density, five times more LNG can be stored in the same size container than compressed natural gas (CNG), saving valuable space and making refueling less frequent.
The tandem of 7890 and 7149, for example, used a single 20,000 gallon LNG fuel tender on its 1600 mile coal route, refueling once each way at a fueling system located at the halfway point. The 800 mile range per locomotive pair far exceeds the 80-100 mile range that the same sized tender filled with CNG would provide.
Despite the energy density advantage of LNG, there are certain applications for which CNG may be preferable. For instance, switch locomotives usually remain close to a station, and can be refilled easily during long idle periods. Commuter rails may also favor CNG due to their frequent and routine stops, and their typically close proximity to available gas supplies.
In order to keep natural gas in a liquid state, It must be refrigerated to -260 degrees Fahrenheit. To maintain such low temperatures the fuel tender is of a double walled stainless steel "thermos bottle" design, capable of keeping the LNG cold for as long as 14 days.
A heat exchanger aboard the fuel tender converts the LNG back to a gaseous state, making use of waste heat from the locomotive cooling system.
Gas then flows to the locomotive through a flexible hose connection between the tender and the locomotive engine. No cryogenic fuel is ever transferred onboard the locomotive. Safety features built in to the coupling inhibit the release of gas in the event of train-tender disconnect.
For a detailed discussion on the economics and safety issues of using natural gas, please see the online version of The ECI Dual Fuel Sourcebook, an informational essay on the use of natural gas as a locomotive fuel.
The LNG tender BNGT101. From the outside it looks like a diesel fuel tender, but it's actually a stainless steel double walled refrigeration storage vessel, which keeps fuel at -260 degrees F for up to 14 days.
Close up of the tender / locomotive connection. Middle hose transfers gaseous natural gas, while the other two hoses contain coolant. Hoses are designed for automatic shutoff in the event of train - tender disconnect.