No. 401-97 |
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MANAGEMENT & STORAGE OF DIESEL FUEL
OVERVIEW Correct fuel storage is an important factor in mine operations and good storage practice can save downtime and cost due to premature wear of engine and fuel system components. Due to changing petroleum product off take patterns, current refining process of distillate fuels includes a proportion of catalytically cracked cycle oil, which is more pro-oxidative than straight run distillates which were the standard in the past.
Field experience has highlighted the fact that current distillate fuels containing cycle oil have a much lower level of storage stability, which is further reduced under Australia’s high summer ambient temperature conditions.
Experience suggests that three months is probably the limit to maintain distillate fuels in good condition, without encountering the problem of degradation resulting from oxidation of the fuel.
The temperature extremes experienced in Australia, result in fuel storage tanks vent systems not only expelling air as the fuel expands during the heat of the day, but also drawing in air as the fuel contracts during the cool of the night. When moist air enters the tank, condensation occurs and water settles on tank bottoms. Any dust present in the air also settles mixing with the condensed water and oxidation by products to form a sludge. The presence of sludge or water in the fuel over long periods of time results in darkening colour and in extreme cases unpleasant odour (fuel decomposing). Water also provides the ideal environment for bacterial growth, eg. Cladisporium resinae. These fungal growths in fuel if permitted to propagate will form acidic deposits and cause filter blockage.
Fuel Degradation Causes
A. Long term storage (oxidised fuel)
B. Water and sludge
C. Bacterial growth
Prevention of Fuel Degradation
A. Oxidised Fuel
Minimising oxidation of fuel in storage requires good tank rotation practices to be implemented ensuring regular turnover by consumption of the fuel. Filling into and drawing from all storage tanks simultaneously should be prevented as fresh fuel mixed with existing oxidised fuel will result in an acceleration of the oxidation problem.
B. Water and Sludge
Water and sludge formation is difficult to prevent but water accumulations in tank bottoms can be overcome by regular drainings, at least monthly. Many tanks in the field are not fitted with drain valves or have inadequate fall to the drain outlet. These problems must be rectified. Where tanks are located in extremely dusty areas, superior filtration should be fitted to breathers and maintained on a regular basis.
C. Bacterial Growth
Bacterial growth will not form unless water is present in the fuel. Commonly found bacteria in fuel storages propagates at the water-fuel interface and feeds off the fuel.
Application of good house-keeping as outlined above will provide a saving in downtime of machinery, cost of filter replacement and engine components.
The table on the following page details common fuel contaminants and is a useful guide to cause, effect and control.
USEFUL GUIDE TO CAUSE, EFFECT AND CONTROL OF COMMON FUEL CONTAMINANTS
Types of Contaminant |
Effect |
Action Recommended |
| Water — introduced directly or as condensation in storage tanks. | Corrosion to fuel injection equipment. | Allow fuel to settle (24 hours), drain off sediments. Install sediment and/or coalescing type filters. |
| Sediment, eg. rust scale, weld slag, dirt, etc. | Deposits, corrosion, wear to fuel injection equipment. | Allow fuel to settle (24 hours). Extra filtration, if sediment greater than 0.05%. |
| Sludge and fibres | Severe filter blockage | Service filters until contaminated fuel used. Clean out tanks. |
| Ashphaltenes — high molecular weight compounds typical of heavy or residual fuels. | Filter blocking; engine deposits. | Settling fuel. Drain off sediments. |
| Microbial growths: algae and bacteria growing at water-fuel interface. | Filter blocking. Fouling and corrosion of fuel injection equipment. | Drain sediments. Reduce fuel storage time. Use of recognized biocide, eg. FTC. |
| Sulphur: occurs naturally in most crude oils; usually higher in heavier fuels. | Corrosion to valves, guides, liners, bearings. Noxious emissions. | For S levels greater than 0.5% reduce engine oil drain cycles and/or use higher TBN lubricating oil. |
| Sodium: occurs naturally in some crudes and is mainly a problem in residual fuels. Can also result from salt water contamination or tanks breathing moist salt air. | Fouling deposit and corrosion. | Minimize exposure to salt water /air. |
| Carbon residue: more critical for modern, high speed diesels. Residue from catalytic cracking. | Formation of soot, carbon deposits and reduced engine efficiency, piston and liner wear, sticky rings. Deposits on engine, injector, valve and turbo deposits. | More regular filter service. Use of recognized combustion catalyst, eg. FTC. More frequent engine oil and filter changes. Settling of fuel. Drain sediments. |
Acknowledgement is given
to:
1. Australian Institute of Petroleum "Automotive diesel fuel storage and
handling".
2. Caterpillar Inc. SEBD 0717 "Diesel fuel and your engine".
Fuel Technology Pty. Ltd.
ACN 100 293 490