When Bigger is Not Better
By Jeanne Murphy Murck, VP Operations
About the Author
In our industry, there have been many articles and studies published related to the changes to fuel composition and the resulting fuel maintenance headaches. By making cleaner fuels that are better for the environment, we have removed additives that killed destructive bugs (microbes). These reformulated fuels are more likely to take on water that boosts the growth of these bugs and accelerates corrosion.
In the case of fuel oil used in emergency power, microbe growth is further intensified by the lack of turnover and the EPA limits to burning fuel for the purposes of exercising generators. If we had storms twice a month and the fuel in these tanks was actually needed more regularly, then the fuel would be consumed more rapidly and the bugs wouldn’t have as much time to grow. But, alas (or shall I say thankfully), true weather-related emergency events necessitating the use of back-up generators are not that frequent. Undoubtedly, we could say that these events are on the uptick due to climate change, but the through-put of these systems never approaches the level of that of a gas station, for example.
Here’s what happens when fuel sits:
- it gets stale
- it takes on water from the atmosphere
- it can become contaminated with microbes
- it becomes more susceptible to the formation of asphaltene and wax residues
- its cetane number may decrease
Solutions to fuel quality issues that will arise in this setting typically include the following:
- Periodically replacing fuel that has become stale due to lack of use. Most diesel in this country has some component of biodiesel in it and industry standards and engine manufacturers recommend storing any diesel that has biodiesel in it no more than six months.
- Using a high quality fuel filtration system to remove water and particulate.
- Cleaning the inside of the tank.
- Using Biocide.
However, an important and often overlooked solution is the proper sizing of your fuel storage tanks to begin with! As stated in NFPA 110 (220.127.116.11), tanks should be sized so that the fuel is consumed within its storage life. The NFPA 110 Handbook also recommends several moderately sized tanks over one large tank.
Using several moderately sized tanks that meet the total fuel oil storage requirements of an emergency power fuel oil system can be very helpful on a couple of levels – first, you ensure fuel is consumed and turns over within its recommended storage life and second, you mitigate the risk of having your only fuel tank contaminated.
For example, let’s assume that an engineer has calculated the fuel oil capacity requirements for the back-up power system at a particular site to be 20,000 gallons. He then decides to specify that all the fuel (aside from that in the day or belly tanks) be stored in one 20,000 gallon main fuel oil storage tank. What happens if that one and only tank becomes contaminated by sitting unused and becoming affected as noted above, OR by the delivery of a bad batch of fuel from the terminal? Or, what if the pumping system tied to that one main storage tank fails? During an emergency event, the system would not be able to perform as needed.
A better strategy would be to specify two 10,000 gallon tanks including redundant fuel oil pumping systems for each tank to ensure fuel will be delivered when needed and that your risk of having an entire fuel system of contaminated fuel is greatly mitigated. In conclusion, specifying one large tank puts the entire back-up power system’s proper functioning during an emergency event in peril.
Core Engineered Solutions can help you size the fuel storage tanks with these issues in mind, as well as the redundancy requirements found in NFPA 110, NFPA 99, and NFPA 70.
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