Recognition and Prevention of Distillate Fuel Emulsions

This paper describes a case study involving chronic plugging of 5μm particulate filters in a gas turbine diesel fuel system in a Red Sea refinery. Rapid plugging of the filters was caused by water-in-diesel emulsions generated in diesel fuel supply tanks. Sludge with a wax-like appearance recovered from the 5 μm filters was, in fact, found to be composed of up to 50 percent water with no significant wax content. X-ray studies of the filter catch solids revealed a variety of iron oxide phases, sodium chloride, and high concentrations of sodium sulfate. Microbial cultures inoculated from storage tank ‘rag’ layers yielded moderate to high counts of general aerobic bacteria (GAB), moderate fungal cultures (yeast and molds) and low sulfate reducing bacteria (SRB). Elemental analysis of water in supply tanks where microbial activity was highest revealed ion concentrations similar to those found in Red Sea water. Sulfur isotope ratios in sulfate from filter catches suggest that much of the sulfate was derived from microbial metathesis of sulfur-bearing hydrocarbons. Frequent contamination of on-shore liquid hydrocarbon fuel tanks with sea water can cause corrosion and create a favorable environment for bacterial growth. Surfactant byproducts of microbial activity are capable of stabilizing emulsions, suspending water soluble salts such as sodium sulfate, and metals such as lead and copper. Copper is well known to promote gum formation, while all of these contaminants are potentially corrosive to gas turbine hot gas path components.