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Diesel on Demand

15 February 2007

When the power goes off FMs need to be certain that stand-by generators fire up immediately. However, unless the quality of diesel fuel is carefully managed, you could be let down as Richard Massara explains.

STORAGE OF DIESEL IS OFTEN AN OVERLOOKED AREA – a popular misconception is that diesel fuel is ‘good for life’. Like ripe fruit, diesel fuel goes ‘off’ over time. If you do not look after your stored fuel, it has the real potential to let you down when you need it most. UK diesel fuel ex-refinery is generally of a very high quality, but can be contaminated by mixing or poor storage conditions. Diesel is surprisingly fragile and difficult to keep. If you keep it clean, cool and dry, diesel fuel can be stored six months to 1 year (at 25ºC) without significant quality degradation but if it is held for any longer than six months, the product could be expected to deteriorate in quality.

Diesel can degrade in three different ways:
1. Fuel ageing/oxidisation: From the moment it is produced diesel will degrade and oxidise, and start to break down into composite parts to form sediment and gum. This will block the fuel filtersystem and in turn choke the engine/generator of fuel causing it to stop working. Cleaning the filter will treat the result, not the cause and it will not stop it happening again.
2. Water: Water in fuel is bad news. It typically arrives via condensation formed due totemperature variations outside the tank or on the tank's skin, but it can also enter via pipes or taking on fuel from a poor source can be the cause. Removal of the water at the fuel store is vital using a water separator.
3. Bacteria: 'The fuel bug' often referred to as ‘alga’ is essentially bacterial problem. These bacterial microbes form a slimy colony that lives at the fuel/water interface clinging to the side of the tank. They grow quite rapidly in warmer temperatures but they can also grow in cold weather when fuel tank heaters are installed. Parts of the colony can break off and clog the fuel lines and fuel filters. This growth can be killed with a biocide treatment, but the biocides attack the cell wall of microbes resulting in ‘lysis’ - the death of a cell by bursting. The risk of filter clogging may continue for a short period after biocide treatment until cellular residues break down and are absorbed into the fuel.

If fuel is not correctly managed, not only will it degrade over time naturally, but its storage environment will work against it. Unmaintained fuel will typically contain water from condensation, gum from aging, bacteria, yeastand fungus (which all grow in the water and feed from the fuel’s hydrocarbons). These infections can have the unhappy side effect of creating more water – which in turn means more contaminate can grow. This cycle can reproduce rapidly, and if left unattended can spoil an entire tank.

Additionally dirt, dust, sand and similar contaminants commonly enter through fill pipes, access hatches and breather pipes. Normally it settles on the bottom of the storage tank and does not cause a problem unless stirred up or held in suspension by some other contamination. After filling a storage tank it should be left for a period of time to allow dust and dirt to settle. Metallic contaminants, notably rust, occur mostly as corrosion debris from storage tanks and distribution system parts.These contaminants can plug filters, support fungal growth and encourage fuel degradation. Fungal contamination if left untreated will increase corrosion producing more rust.

For everyday diesel usage such as in cars, vans, trucks and buses, the problem simply will not occur. The fuel is not kept long enough for the growth to occur. However where the diesel is stored for long periods of time in storage tanks for back up generators, bulk fuel storage or reserve storage for vehicle fleets, then the problem will soon become all too apparent.

BP advises that maintaining fuel at a high quality over time includes:
● Ensuring that the fuel is not in contact with any surfaces containing zinc or copper and/or add a metal deactivator additive
● Regularly removing water and dirt from storage tanks
● Draining water from the storage tanks weekly
● Keeping tanks full to reduce the space for water to condense
● Ensuring tanks have a well-defined low point where water will collect and can be drained.
● Filtering the contents of the main storage tank through a re-circulating filter system to remove sediment and gums.
● Emptying and cleaning tanks at least once every 10 years, or more frequently if there is a major contamination.
● Ensuring that the fuel supplied conforms to a recognised specification and always purchase fuel to replenish stocks in the winter season April – August
● Taking samples at regular intervals to monitor the condition of the fuel.
● Regularly turning the fuel over. Plan the fuel usage so that it will all be used within 1-5 years and replaced with fresh fuel.

In Separ’s experience, most companies do not have this kind of fuel maintenance schedule in place. It alternative, is a Fuel Polishing System (FPS) that has proved to be a reliable, electro/mechanical solution to combating the problems related to storing diesel. FPS conditions, cleans and optimises the fuel to ensure the stored diesel is kept ready to be used whenever required. Moreover it is designed as an ‘offline system’ meaning it can process the stored fuel separately to any fuel being used to run a generator etc. The system removes water, bacterial growth and other contaminate from diesel, and being an electro/mechanical process, it can be operated without requirement for specialised hazardous substances training.

The FPS is mounted on or next to the fuel tank as a totally independent solution. It should be plumbed to pull fuel from the bottom of the storage tank, process it and then return it to the top, opposite end of the same tank. It can handle all sizes of storage tank, and independently process diesel as part of a regular maintenance schedule. There is no requirement to regularly check the fuel for water or contaminate as the FPS will achieve just that, and ensuring clean fuel, ready for use.
● Richard Massara is sales manager from Separ Distribution UK.

More info
Specific files for diesel fuel storage and known / acknowledged problems can be found at:

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