Monday, September 3, 2018

Designing Generator Fuel Systems (1)

Backup generator sets (gensets) are critical to business continuity and life safety. To ensure their reliable and efficient operation, the design of the associated fuel system must be approached systematically and thoroughly.


There are 9 Key Considerations when designing fuel oil systems for gensets:-

(1) Runtime Criteria
(2) Fuel Storage
(3) Fuel Pumping
(4) Fuel Cooling
(5) Fuel Piping
(6) Fuel Maintenance
(7) Fuel Filling
(8) System Controls
(9) Applicable Codes and Standards

Understanding the requirements and challenges of each is critical to navigating the design of any fuel system. Note that although there are inherent nuances, some of the same considerations underlying fuel oil design principles can also be applied to systems intended for other applications, such as oil-fired boilers. Design criteria unique to each project will dictate the ultimate application.


Runtime Criteria


Among the first steps of designing a fuel oil system for gensets is to establish runtime criteria in the event of a power outage (see "Runtime requirements"). Often dictated by a combination of applicable codes and owner requirements, the runtime—or how long the genset must operate during an emergency event without refueling-will set the bar for fuel oil design and operations. For example, life safety gensets typically are required to support emergency loads for a period of 2 hours upon loss of power. Critical facilities, such as data centers, typically are expected to support the load for 24 hours or more, depending on site resiliency requirements.

Because runtime criteria have a direct bearing on the fuel storage capacity required onsite, this consideration is critical to explore first. Note that fuel consumption data for gensets at various loads is readily available from the manufacturers.

It is important to note that only 80% to 85% of the tank capacity is typically usable depending on the tank shape and form. The tank cannot be emptied completely during operation nor can it be filled completely because head space is required to accommodate fuel expansion and prevent overflow.


Fuel Oil Storage


Fuel oil can be stored in aboveground storage tanks (ASTs) or underground storage tanks (USTs). Each has advantages and disadvantages, and specifying the appropriate type is critical to ensure the optimum design. Both UST and AST have different internation codes specifies the requirements for protected tanks (fire, impact and and associated corrosion resistant).


ASTs offer ease of maintenance; typically, lower installation costs and the ability to be installed by the project's mechanical contractor; ease of relocation; and the option of custom sizes to suit site conditions. However, employing an AST may not be appropriate for all projects because they require usable real estate, pose a greater fire hazard, allowable storage capacity typically is restricted by applicable codes and insurance carriers, and fuel heaters may be required in cold weather applications where the tank is exposed to subfreezing ambient temperatures.

USTs are available in fiberglass or steel construction. They are almost always cylindrical and require minimal real estate above ground, offer potentially greater fuel storage capacity, pose a lower fire hazard, and can maintain a relatively stable fuel temperature. Conversely, USTs can be difficult to access, maintain, and relocate; they typically have a higher installation cost; require comprehensive leak detection systems; and often require a specialized contractor to install.


Continue Reading: Designing Generator Fuel Systems (2)



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