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Water Removal

Water is always present. Fuel accumulates water during refining, transportation and storage. No matter how carefully it is handled, water will find its way into fuel. The question is, “How much water is too much?” The answer will vary depending on the type of product. Free water is the most damaging. Once saturation is reached – 100% RH – water will begin to drop out of suspension and settle to the bottom of the tank. In reality, conventional fuels should be kept below 200 ppm. Aviation fuels have a more stringent requirement, below 30 ppm. Ethanol enriched gasoline can hold around .398% water to fuel volume before full phase separation occurs. While there are many different specifications limiting water in fuel, the ideal is to reduce water down to the lowest possible amount.

Removing water from fuel depends on the type of water and the type of fuel. Ethanol enriched fuels require a different remediation process than other fuels due to the chemical composition of ethanol. It does not take much water to cause fuel to phase separate. Less than 20 gallons of water in 5,000 gallons of fuel will result in phase separation. Tank monitoring systems may not be able to detect that small amount and water finding paste can be difficult to read if this is the method used for identifying water in fuel. The only sure way of determining water in fuel is to take a sample of the fuel. Bottom sampling is the first line of defense against phase separation. The use of a water detection field test kit can help to quantify the amount of water in suspension. System inspections are important to minimizing water issues and can often catch a problem before it becomes unmanageable.

Can phase separated fuel be remediated? The simple answer is yes. Most phase separation can be corrected, although if there is a catastrophic event that causes large volumes of water to enter the fuel, the alternative may be disposal. There are a few simple steps to correcting phase separation.

  1. Determine the volume of phase at the bottom of the tank. This can be accomplished by using a fuel sampler. First take a sample on the very bottom of the tank, then at 1 inch increments until you determine where the phase ends and the fuel begins. There is a definite difference in the phase layer and the fuel layer on top (see photo). After determining how many inches of phase you have in your tank, you will know how much needs to be pumped out. Once the ethanol drops out of the fuel and forms a layer on the bottom of the tank, it cannot be reintroduced into the fuel. It must be properly disposed of with the water and contaminants.
  2. Pump off the water/ethanol phase and properly dispose of the waste. Take bottom samples from the lowest accessible point in the tank to verify you have removed all of the phase before moving on to the next step. Keep in mind that it may be necessary to remove the STP for proper access to the lowest point in the tank. It is also important to refrain from stirring the fuel too much. Stirring can cause emulsification.
  3. Use a filtration system that has coalescing and water separation capability to remove any remaining dissolved water. It is likely that some water remains and needs to be removed. Remember not to stir the fuel during filtration. The suction hose should be placed on the bottom of the slowest access point in the tank and the return should be above the fuel level in order to minimize any unnecessary agitation. Speed is not your friend when removing water from ethanol enriched fuel. Moving the fuel across the filters at a slower velocity will allow for improved water removal. Once the water has been adequately removed, the fuel octane level will need to be tested.
  4. If phase separated fuel was 87 octane E10, it is possible to blend 93 octane E10 fuel at a ratio of 1:1 to correct the octane level in the fuel. For example, if you have 3,000 gallons of regular remaining in the tank, blending 3,000 gallons of 93 octane premium fuel should correct the octane deficiency. Always verify octane through testing once blending is complete. If the phase separated fuel was 93 octane E10, then the fuel should be usable as 87 octane fuel. Again, octane testing should be completed to verify results.

A second problem attributed to water and ethanol is corrosion – specifically microbial influenced corrosion or MIC. Fuel deterioration has been documented since 1895 and accelerated deterioration since 1994. So what has changed and why is corrosion such an issue today? Since the mandated use of ethanol, MIC has increased and become a serious problem. MIC costs the United States an estimated $50 billion per year in damage. Oil production, transportation and storage are all affected. In the most recent research, accelerated corrosion has been associated with the presence of ethanol in fuel.

Water must be present for there to be microbial growth. Because ethanol is both hydrophilic and hygroscopic, ethanol blended fuels are more water soluble. In other words, water is more easily dispersed in fuel. Condensation is more easily absorbed. It is also thought that ethanol serves as a food source for microbial growth.

The combination of water and ethanol serve as the perfect breeding ground for microbes. These hydrocarbon utilizing microbes produce acids. The most prevalent, Acetobacter, produces acetic acid. Once the colony gains control of a fuel system, corrosive growth accelerates. Unlike typical corrosion that can take years to seriously damage a fuel system, MIC can form overnight and severely damage a system within months. Costly damage has been seen in fuel systems less than six months old.

How does the damage occur? A microbial colony begins to grow when water is present and feeds on the hydrocarbon producing an acidic byproduct. This acid will lay on the bottom of the tank and remain suspended in the fuel with any water that may be present. The combination of water, microbes, acids and deteriorating fuel form a biomass. At the fuel-water-tank interface, all of the necessities of life are present: a carbon source, water, an electron donor (the hydrocarbon/ethanol blend and/or metals in the tank), and an electron acceptor such as O2 or previously oxidized metal (e.g., rusted steel).” Even cathodically protected stainless is susceptible to corrosion. Carbon steel definitely proves no match.

As the biomass grows and accumulates on the tank bottom, an acidic off-gassing is common. The vapor fills the tank and enters the dry spaces within the fuel system. Corrosion in submerged turbine pump (STP) sumps is often a result of MIC.

While ethanol is the catalyst to an abundance of problems, there are some simple answers. No doubt phase separation and corrosion present challenges to the industry but neither are insurmountable. For both of these problems the common denominator is water. Neither phase separation nor MIC are an issue without water. If you can keep your fuel dry, then you can minimize the problems. All it takes is a little management.

Biodiesel presents several maintenance challenges especially as it pertains to water removal. Because biodiesel is more hygroscopic than ULSD, more suspended water is likely. Dissolved water in biodiesel promotes the breakdown of fuel molecules resulting in surfactancy increase and lower IFT. Because most biodiesel already has lower IFT, the problems are exacerbated. The more biodiesel in a fuel, the more water and particulate holding potential. A combination of filtration media may be necessary to remove water from biodiesel. Monitoring the quality of the fuel and the water content while filtering will help determine the need. Using Dixon cleaning and filtration equipment and filters will mean CleanFuel!

Conventional fuels have similar problems with water contamination. While not as challenging to clean, the problems are still present. The most efficient way to remove water from conventional fuels is through coalescing and water separation. Dixon’s two stage filter housings provide the desired results – capable of removing water down to as low as 50 ppm. Absorption filters are another option for removing water, especially when the fuel is highly emulsified. With the right filter element, water content can be brought down below 30 ppm. Knowing the application and the cleanliness requirement helps determine the type of filter and system.