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Technical Paper: Biodiesel
The Uptime Institute Technical Paper series responds to data center owner and operator concerns
regarding future regulations, emerging or established technologies, or other issues specific to facilities
operations. The objective of the Biodiesel Technical paper is to provide context, insight, and industry
experience with biodiesel fuel(s). The use of biodiesel fuels has been mandated in select U.S. states
and is anticipated to be mandated in additional states and countries shortly.
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UPTIME INSTITUTE Technical Paper: Biodiesel
Issue
Select U.S. states mandate that owners of stationary engine generators use a mix of biodiesel fuel and low sulfur diesel (LSD) or
ultra-low sulfur diesel (ULSD) in their engine-generator plants as an additional air quality management measure. Biodiesel is a cleanburning alternative to the traditional petroleum-based diesel fuel. Pure 100% biodiesel fuel is derived from vegetable oils or animal
fats and contains no petroleum. It is also essentially free of sulfur and aromatics, whereas typical petroleum-based diesel (petro
diesel) products such as LSD and ULSD are not.
The addition of the biodiesel component to engine-generator fuels stocks has been reported by some Site Uptime Network®
(Network) members. Namely, the issues include accumulations of water, accelerated growth of biological organisms, and increased
contamination in fuel storage tanks. Any of these issues put at risk a data center’s capability to meet continuous availability
requirements.
Background
As reported by the National Biodiesel Board (NBB) in the spring of 2010, the states that currently have biodiesel mandates for
on-road and stationary diesel engines include Minnesota, Oregon, and Washington. The states that have pending legislation for
biodiesel mandates include Louisiana, Massachusetts, New Mexico, and Pennsylvania.
Some of the above listed states also have pending changes to their existing biodiesel mandates. The Uptime Institute (Institute)
recommends that data center owners and operators regularly check the NBB Web site at www.biodieselboard.org for updates on
existing mandates and planned legislation.
Biodiesel Blends
For ease of reference, biodiesel “blends” are referred to with the letter “B” followed by a number that indicates the percentage of
pure biodiesel in the blend. Examples: B2: 2% of pure biodiesel (B100) and 98% of LSD or ULSD; B20: 20% of pure biodiesel and 80%
of LSD or ULSD.
B20 and higher blends have different properties than B5 and lower blends. In fact, the latest version of American Society for Testing
and Materials (ASTM) Standard D975 states that there is essentially no difference in physical properties and available energy values
among biodiesel blends of B5 and lower and petro diesel. B5 and lower blends must also meet D975 requirements.
Ultra-Low Sulfur Content in Diesel Fuel
Diesel engine emission monitoring in the past three decades has shown that higher sulfur content in petro diesel fuel elevates the
quantity of emissions, which results in degraded air quality. Over the past two decades, the U.S. Environmental Protection Agency
(EPA) and state regulatory agencies have mandated a series of lower sulfur contents in petro diesel fuel:
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LSD, containing less than 500 parts per million (ppm) sulfur, was mandated until 2008.
ULSD, containing less than 15 ppm sulfur, has been mandated as recently as 2008 as the currently required fuel for stationary
and on-road diesel engines.
Diesel engine operators have noted that as the sulfur content of fuel is reduced, the following occur:
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Biological organisms form more easily as the reduction of sulfur content also reduces a natural inhibitor to biological
growth.
The fuel holds more ppm of water.
There is a reduction in the oxidation stability of the fuel.
The fuel does not lubricate engine parts as well as high sulfur content fuels (although the addition of biodiesel in B2 and
higher restores the lost lubricity).
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UPTIME INSTITUTE Technical Paper: Biodiesel
Water Contamination
All fuel accumulates water; biodiesel blends accumulate more water than other fuels, including regular unblended petroleum
diesel. As a fuel holds more water, the environment required for biological growth expands and the formation of biological
organisms accelerates.
Water is introduced to fuel in many ways, including:
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Fuel exposure to humid air and cooler temperatures (e.g., through storage tank pressure equalization vents or residual
water left in delivery trucks).
Condensation from interior storage tank walls due to temperature and humidity differentials.
Open or vented fuel system.
Water in fuel takes three different forms:
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Free water: Nearly all water with almost no fuel in it, which accumulates at the bottom of the fuel tank and is generally
removed by “stripping” it off with a tank bottom suction action.
Suspended water: Water suspended in the fuel, which makes the fuel appear cloudy and dull as opposed to the bright
and shiny appearance of new fuel. This water must be mechanically removed by a fuel coalescer or other water separation
process.
Dissolved water: Water that has become chemically attached to the fuel and cannot be separated with current technology.
Accordingly, effective fuel storage design and fuel management includes protocols for continuous water removal from diesel fuel.
Fuel Storage Temperature Considerations
As fuel changes temperature in the delivery truck, storage tank, or delivery piping, these temperature changes (in conjunction with
any humidity variations that the fuel may encounter) affect the accumulation of water and the growth of biological contamination
in the fuel. Care must be taken to ensure that stored fuel is managed through an acceptable and stable range of temperature and
humidity.
Consult required ASTM documentation (D975, D6751-07b, D2709, D4176, etc.) for specific details.
Shelf Life of Diesel Fuels
The shelf life of all fuels, particularly diesel fuels, is significantly dependent on:
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Environmental conditions (temperature and humidity) that the fuel is exposed to.
Ability to “polish” the fuel: remove water, biological organisms, and other contaminants once the fuel has been placed in
storage tanks.
Use of fuel additives designed to reduce suspended water and inhibit biological growth.
The industry has yet to establish standards regarding shelf-life expectations for petroleum diesel and biodiesel fuels. There is,
however, some general agreement that:
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Biodiesel blends without additives have a short shelf life (6 months or less).
Without additives, petroleum diesel has a longer shelf life than biodiesel blends without additives (12 months or less).
Additives can be used to essentially double the respective useful shelf lives of both biodiesel blends and petro diesel fuels.
An on-site fuel polishing system will increase the shelf life of petroleum diesel fuels and could do the same for biodiesel
fuels—if the polishing system could successfully remove suspended water. However, there is currently no commercially
available coalescing media for a polisher that can accomplish removal of suspended water during polishing.
The shelf life of a biodiesel blend increases as the amount of B100 in it decreases.
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UPTIME INSTITUTE Technical Paper: Biodiesel
Recommended Biodiesel Management Actions
The Institute recommends the following actions when corporations are required by law or voluntarily choose to utilize a biodiesel
blend as a fuel source in engine-generator plants for mission critical data centers.
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Ensure that fuel storage and delivery systems are appropriately designed to accommodate existing and future requirements
for the storage and use of biodiesel. This includes:
‚ Evaluation of the impact of likely site temperature and humidity ranges on the stored fuel when determining whether to
install above ground or underground storage tanks and piping, vaulted or non-vaulted tank configurations, temperature
and humidity controlled storage capabilities.
‚ Inclusion of a fuel polishing system in the fuel system design.
‚ Inclusion of the capability for the fuel system to be able to strip free water from tank bottoms.
‚ Integration and use of desiccant breathers on all tank vents or at a minimum the main storage tanks.
‚ Provision of a delivery storage tank segregation scheme to accommodate new biodiesel delivery. This delivery tank
keeps new fuel separate from existing on-hand stocks until the new fuel can be tested and receive an initial polishing.
‚ Consideration of fuel storage tank size and the number of storage tanks installed in accordance with the planned
expenditure rate for the fuel. It is not prudent to have extremely large storage tanks when biodiesel will be used at a
rate that will exceed expected shelf life as this can lead to a situation where the fuel will go “bad” before it is used. Then,
the tank must be emptied, the unusable fuel disposed of, and the tank must then be mucked and completely cleaned
prior to refilling with usable fuel. All of these tasks have an associated cost in terms of both budget and resources.
A comprehensive fuel management protocol must be developed, implemented and followed, including, but not limited to:
‚ Establish maximum levels of water, biological growth, and other contaminants acceptable on a site-by-site basis.
‚ Conduct frequent monitoring and sampling for the previously listed contaminants as well as fuel stability.
‚ Establish a site-suitable fuel polishing schedule.
‚ Adhere rigorously to the set fuel polishing schedules.
‚ Monitor fuel tank and delivery piping temperatures continuously to ensure that polishing schedules are modified when
environmental conditions exceed expected ranges.
‚ Establish a fuel consumption plan that includes aggressive rotation and use of fuel stocks to ensure that stored fuel is
burned before it becomes unusable.
‚ Stipulate that biodiesel deliveries from suppliers include appropriate additives as required (and as allowed by law) to
control water retention and biological growth in the fuel.
Future Revisions
Future revisions of this Technical Paper will broaden the scope to include biodiesel requirements from a global perspective.
Credits
This Technical Paper is authored by Rick E. Schuknecht, Vice President of Operational Sustainability. The Institute also credits the Site
Uptime Network Biodiesel Task Group members (comprised of representatives from Delta Air Lines, Inc., UnitedHealth Group, U.S. Bancorp,
and three other companies) with investigating this technical issue and with co-authorship of this Technical Paper.
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