Fuel Cleaning

In any large fuel tank, where diesel based fuels are stored for any period of time, contaminants build up both within the fuel, but due to the relative low density of the fuel, at the lower levels of the tank – often the base.

Water build up is normally the cause of the main problem, due to the build up of micro-organisms whenever the fuel is in direct contact with it forming a sludge. The actual bacteria which forms the sludge at the bottom of the tank, exists naturally within all mineral diesel fuels, but has become a greater problem since the introduction of higher levels of bio-diesel since 2011.

The hygroscopic (water soaking) nature of bio-diesel draws much higher levels of moisture out of the surrounding atmosphere and the resulting water is either held in suspension within the fuel or as free water at the bottom of the tank. As soon as this water starts to build, the bacteria react
and the sludge forms very quickly.

54% of Craggs Environmental customers who
had their fuel sampled had fuel which was
outside of specification.

Both the water and the sludge (also known as diesel bug) cause major problems if pulled through the fuel lines into whatever system the fuel is being used for. This tends to happen if the levels of contamination rise above the fuel take off point (usually positioned some distance above the bottom of the tank for this reason). The contamination can also be pulled through if the levels of suspended contaminants are high, or if the fuel is agitated during a delivery.

In general terms, more than 90% of the contamination is to be found at the bottom 10% of the tank, and where the tank has a cleaning valve positioned at the very bottom of the tank, the contaminated fuel can be drained into an appropriate collection vessel and treated as waste. In many industrial environments, no such drain valves are present, to avoid the risk of fuel leakage if the valve fails, and in this case, the contamination can be drawn up from the bottom levels of the tanks using a range of specialist probes, pipes, pumps and tanks – a tank base clean.

Having removed the highest concentration of contamination, if the fuel is being stored for any form of critical application, for example a standby power generation or an emergency sprinkler system, and the fuel tests show higher than desired levels of suspended water or particulate contamination, the remaining fuel can be processed via an onsite fuel cleaning (polishing) system.

This system is designed to take high volumes of fuel and pump it through a selection of filters and water removal vessels. The system is also equipped with various in-line fuel testing probes which can provide a real time measure of the fuel quality and determine when the fuel is back within ISO specification levels and hence suitable for critical applications.
Craggs Energy has a range of fuel cleaning platforms, depending on the size and nature of the fuel to be cleaned. The systems are capable of processing more than 100,000 litres in a single day and at the end of the process, a full report and certification of the fuel is provided to give customers the assurance that the fuel will be fit for purpose when required.
The service is priced on a per litre basis, with a price range depending on the volume to be processed. Historically, it has not been economic to clean fuel on site, but this is a very effective and efficient method to maintain the fuel quality for fuel stores from 5,000 up to more than 100,000 litres. Above this level, customers may wish to consider a permanent fuel filtration system, which can be specified, installed and maintained by Craggs Environmental.

Craggs Environmental is fully licenced to remove and transport any contaminated fuel and has all the required skills, equipment and experience to either drain via a valve or utilising a system of pipes to draw the contamination up through the fill / access point at the of the tank. Both the Tank Base Clean and the Fuel Cleaning service can be delivered on an ad hoc basis, or as part of a regular maintenance service from Craggs Environmental.

Once the contaminated fuel is removed, Craggs Environmental will provide all appropriate waste certification, under the terms of its EA waste permit licence.

Craggs Environmental has designed a methodology to categorise fuels into 5 standard grades, based upon a range of factors which can be tested. This simple, but very effective approach helps customers to make sensible decisions as to what quality of fuel is acceptable for the various applications each site might require.

Craggs Environmental Stored Fuel Categorisation

Quality Characteristics Appearance
Grade 1 Quality: Grade 1
  • Refinery quality fuel
  • Fully specified ISO and British Standard quality
  • Cherry Red in colour
  • Water below 100 ppm
  • No visible particulate
  • Cetane Level 45
  • Starts to degrade almost immediately fuel is stored in tank
  • Maximum shelf life of around 6 months at this grade
  • Can be used for any Gas Oil requirement
Grade 2 Quality: Grade 2
  • Stored fuel (more than 6 months)
  • Slight darkening in colour from particulate contamination
  • Still within ISO and BS quality
  • Water levels below 200ppm
  • Maximum shelf life of 18 months at this grade, assuming additive
  • Can be used for any Gas Oil requirement
Grade 3 Quality: Grade 3
  • Stored Fuel (more than 18 months)
  • May fall outside of Gas Oil standards
  • Water levels may be above 200ppm
  • Fuel darker red from higher particulate content
  • Possible small quantities of visible particle contamination or free water at bottom of sample
  • Not recommended for any use in critical environment or in combustion engine (Generator etc)
  • Flash point levels likely to be reduced, hence higher chance of “dirty burning” carbon build up
  • Still generally usable for boiler / heating applications
  • Fuel polishing can bring the fuel back to Grade 2 and within ISO standards
Grade 4 Quality: Grade 4
  • Long term stored fuel
  • Much darker colouring of fuel from particle contamination
  • Likely to see levels of both fungal contamination and free water at bottom of sample
  • Sample likely to be slightly cloudy, due to water particles suspended in fuel
  • Will cause significant damage and likely failure in critical applications
  • Likely to cause filter clogging issues for heating or boiler applications
  • Fuel polishing may be able to bring fuel to Grade 2 (depending on levels of degradation)
Grade 5 Quality: Grade 5
  • Very long term stored fuel
  • High visible contamination
  • More “grey” than “red” in colour
  • Should be consigned as waste
  • Unlikely suitable for fuel polishing
  • Often found at very bottom of tanks with cleaner fuel above
  • Should never be used as Gas Oil, will damage boiler and cause failure