ESS.WP.924 5 Fueling Challenges for Sub-Base Tanks
Solve the 5 Fueling Challenges for Sub-Base Generator Tanks
General
Sub-Base Tanks are commonly used to provide reliable fuel supply for generators. The sub-base tanks are built into the support frame of the generator and have these important benefits versus free-standing day tanks:
- Save floor space near the generator
- Eliminate fuel piping cost and potential problems
- Allows for pre-packaging with generator enclosure
- May allow for large fuel storage volumes to support generator run time Sub-base tanks are built to UL 142 safety standards as are traditional day tanks and bulk tanks. They are typically double walled for leak containment, and may be built to a UL2085 fire-rated standard if needed. The tanks can vary in depth from 6 inch (150) to 96 inch (2400).
Challenge 1
Overfill Protection in Shallow Tank. Mechanical overfill prevention valves are installed in the fill pipe of standard tanks as a simple and reliable means to prevent overfilling. Most sub-base tanks are too shallow to allow for the effective use of the valves, particularly when designing to fill to 90-95% capacity.
Solution: Earthsafe M40 Tank Filling systems operate actuated valves in the fill pipe outside of the tank itself. The controller accurately monitors the fuel level in the tank to operate the valve and activate alarms at 85-90-95% tank levels.
Challenge 2
Extra Water and Bio Growth Potential. Sub-base tanks have an extraordinary base surface area compared with standard tanks. The tank bottom is the place where water accumulates below the fuel, creating the fuel-water interface that supports biological growth and corrosion potential.
Solution: Earthsafe M30 Fuel Polishing systems circulate the fuel in the sub-base tank to remove particulates and water. The coalescing filter removes water to a 1 micron level assuring the fuel quality required for new generators designed at higher fuel pressures to meet air emissions requirements.
Challenge 3
Accurately Measure Fuel Levels. The shallow tank depth is a challenge for standard analog and point level sensors. Analog sensors typically have a dead band at the top and bottom of the scale, and are usually optimized for 3 – 20 feet (900-6000) fuel tank heights. Point sensors are often grouped on a common stem with minimum distances required between floats, creating a problem between close activations of say 90% and 95% in a shallow tank.
Solution: The new Earthsafe C8 controller and specialized sensors are specifically designed for accurate level sensing in shallow depth sub-base tanks.
The controller has built-in Modbus connectivity to provide fuel level and volume information to generator, switchgear, and other building systems.
Challenge 4
Return Flow Overfill Protection. When refilling sub-base tanks from bulk storage tanks, the safe gravity overflow return mechanism is usually not an option. The sub-base tank construction usually prohibits sidewall connections commonly used for day tank overflows to underground tanks. And aboveground bulk storage tanks are usually at a higher liquid level.
Solution: Earthsafe M55 Gen Tank Refill Kits include a reliable return flow pump and controller. If a high level is detected, the pump is automatically activated to return fuel to the bulk storage tank. Redundant hi-stop valves in the fill pipe may also be activated for redundant protection.
Challenge 5
Fuel Capacity not shared between Generators. Each sub-base tank is a dedicated fuel source for its generator. Unlike a bulk storage system refilling day tanks, the total fuel storage at the site may not be available to support generator operations.
Solution: The Earthsafe C890 controller can manage fuel volumes between multiple sub-base tanks. The controller monitors fuel levels, and allows operator functions to activate return flow pumps in a source tank, and inlet control valves in a receipt tank to put fuel at the generator where it is needed.
Summary
Sub-base tanks are thought to be the easy solution for generator fuel supply, and they do offer important benefits. But it pays to think through the potential problems that can occur, and design for the solutions that maximize these benefits.