Monday, September 3, 2018

Designing Generator Fuel Systems (3)

So far we consider (1) Runtime Criteria; (2) Storage; (3) Pumping; (4) Fuel Cooling; (5) Piping; and (6) Fuel Maintenance of the generator fuel system. Let's further look into the

(7) Fuel Filling
(8) System Controls
(9) Applicable Codes and Standards


Filling the Tank


During the design process, it is important to determine what type of delivery truck the fuel-oil vendor will use. Fuel-oil trucks are either a gravity or a pump type (i.e., equipped with an integral fill pump).




Both types of trucks can accommodate USTs and ASTs located at an elevation lower than the truck. Pump trucks are ideal for filling ASTs at higher elevations. Gravity trucks are optimal for filling USTs. However, when the fuel storage tank is at a higher elevation than the truck, a gravity type truck alone won't work. For such applications, an option is a remote fill system with an integral fuel transfer pump that can enable gravity trucks to fill ASTs at a higher elevation. Remote fill systems are equipped with gauges and sensors to aid and alert the operator during the delivery process.

Extreme considerations must be accounted for as well because the need for fuel oil could happen in an emergency state. For example, it is common for a fuel oil vendor to promise one type of truck, but then in the event of a city-wide power outage when everyone needs fuel, the truck isn't available. Extreme situations must be considered during fuel oil system design.


Fuel System Controls


Fuel systems typically use UL 508: Standard for Industrial Control Equipment - listed programmable logic controllers (PLCs) to control and monitor transfer pumps, storage tanks, auxiliary tanks, polishing systems, fill systems, fuel inventory, leak detection, and other related subsystems and equipment. They offer communication capabilities, such as BACnet, Modbus, and local operating networks (LonWorks) for integration with the building management system.




For critical applications, such as data centers, the control system typically uses dual independent PLCs and dual power inputs to ensure there are no single points of failure. The fuel system control architecture and sequence of operations should be reviewed in detail during the design phase. The entire scope of work associated with fuel systems (equipment, controls, startup, and training) preferably should be provided by a single vendor who specializes in that field.


Codes and Standards


Due to its combustible nature and the detrimental impact on the environment upon a leakage, fuel oil storage and system design is regulated by city, state, and federal authorities. Careful consideration to a multitude of factors is essential during design. Meeting the worst-case scenario is vital to compliance.

There also are code-mandated requirements related to maximum allowable fuel storage on the property, tank construction, spill containment, location relative to buildings and property lines, fire suppression, high-rise building limitations, and much more. The requirements are specifically stringent for applications involving indoor storage of fuel due to inherent fire hazards. Frequently, the requirements listed in various codes and standards differ significantly.


To avoid surprises at a later stage, it is beneficial to approach the authority having jurisdiction to review the proposed design early in the project - specifically with representatives from the fire department to ensure that all bases are covered.


Continue Reading: Designing Generator Fuel Systems (4)



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