WATER IN FUEL

• Who Said Oil and Water Don't Mix?
• The Source
• The Problems
• The Solutions
• Air Sentry

WE HAVE THE SOLUTIONS
Who Said Oil and Water Don't Mix?

Tank maintenance is an essential part of any successful premium diesel or heating oil program. As little as .01% (100ppm) water in a fuel storage tank can cause operational problems. AFS and its partners have invested countless resources into the design and implementation of our ODT-20 water solution, to provide optimum, trouble-free performance for our heating oil additive and diesel fuel customers. All this work can be ruined, however, by poor tank maintenance.


The Source

Water cannot be completely eliminated from distillate fuels. It can get into the fuel at various stages as it progresses through the distribution network from the refinery to the end-user. Water can get into the fuel during its production, when the hot fuel is in contact with process water. Most of this water is removed in the stripping units at the refinery and more will separate as the fuel cools, but still, some water remains in solution with the diesel. This entrained water may cause a haze in distillate fuel.

Refiners typically make their diesel fuel to some fungible specification to make pipeline shipments. Colonial Pipeline, for instance, mandates that diesel fuel shipped on their lines have a maximum haze rating of 2 as tested in the ASTM D4176 Haze Rating test.

The following picture illustrates fuels with varying amounts of entrained water. Fuels with more water show up as hazy (i.e. opaque) and fuels with less water appear to be "clear and bright".

The fuel on the top-left has a haze rating of one and the fuel on the lower-right has a haze rating of six.

Off-road diesel may contain more water than on-road diesel/heating oil because the hydro treating process used to produce low sulfur, on-road diesel fuel can also reduce the amount of water in the fuel.

Most of the water present in fuels will drop out as it is heavier than the fuel and will sink to the bottom if given time. The temperature of the fuel has an impact on its water-shedding tendencies as well. Warmer fuel can hold more water in suspension than can colder fuel.

There are times, however, when the water can be held in an emulsion, a stable mixture of water and oil. Constant agitation, by mixing or adding fuel to the tank will tend to help hold an emulsion, as the mixture is not allowed sufficient time to settle.

An emulsion can also be held stable by many other forces, including contamination with Hydrocarbon Utilizing Microorganisms (HUM-bugs), additives used in the fuel, acid salts from refinery carryover and the presence of other, high viscosity components in the fuel.

The following picture shows two test tubes that have had 20ml of water added to the fuel. They were shaken vigorously to mix the water and oil together and then allowed to set for a short period of time. The tube on the right shows a clean "break" or interface between the water and oil. The water has all dropped out and the water measures the original 20ml. The tube on the left, however, has formed an emulsion. Note the absence of a clean "break".

Problems caused by this type of emulsion are often puzzling, as the emulsion is difficult to detect with water-finding paste. The paste does a good job of detecting free-standing water, but does not work well in showing an emulsion.

Water can also be introduced during transportation and storage of the fuel as well. Sea-going vessels can sometimes introduce water into distillate fuel, which can then drop out into storage tanks. Tanks themselves have inherent problems at roof seals and vent pipes which can allow rain water to seep into the system. During fuel withdrawals, tanks can breathe in large volumes of humid air. Moisture in the air will condense when the ambient temperature falls, collecting in tank bottoms. This is particularly prevalent in the spring and fall when the day-night temperature fluctuations can be extreme.

As you can see, there are numerous ways in which the water can get into the fuel storage and delivery system, now let's look at the problems it can cause.



The Problems

In cold weather, many water-related problems are incorrectly attributed to the fuel. Water in tanks can freeze 20oF - 30oF above the temperature at which fuel-related problems begin (cloud point). Ice crystals can build up on filters, restricting flow and compromising performance. They can also restrict fuel flow in tank pumping lines.

In warmer weather, the presence of water in tanks may encourage the growth of fungi or bacteria which live in the tank water bottoms and feed on the fuel. Under the power of a microscope, these bugs look like deep-sea creatures.

To the naked eye, these bugs show up as slimy mats of substance that can be any color from green to black .

Under ideal conditions, these bacteria can double in number in as little as four hours. When left unchecked, they can be drawn out through suction lines and plug filters. In addition, the by-products of their fuel consumption are very acidic and can cause pitting and decay in tank bottoms.

Many tanks go unchecked for years, accumulating water from any number of sources. When fuel inventory is low, water bottoms can be stirred up during deliveries, and if not allowed to settle out, can be suctioned out into a transport truck or into a diesel vehicle's tank.

Water also causes corrosion in storage tanks and engine systems. The by-products of this corrosion, including scale and rust, can all lead to filter plugging or injector fouling and can help make a stable emulsion.

Fuel injection pumps are often times lubricated only by the fuel they are pumping and are, therefore, very susceptible to seizing if water gets into them. These high-pressure pumps are not at all tolerant of dirt, debris and organic deposits, all of which can be carried into them with water. The barrel and plunger clearance is often times only 1-2 microns. This tight tolerance is necessary to maintain fuel injection pressures and ensure minimal leakage past the plunger shaft.



The Solutions

Ideally, storage tanks should be checked with a stick treated with water-finding paste prior to every delivery. Many tanks are, however, difficult to gauge for water due to limited access.

Underground tanks can settle to one side and unless you are checking at the low end, you can get a misleading indication of how much water is present. Most tanks have more water than can be easily detected so err on the side of caution.

All water should be drained from storage tanks periodically. The frequency will depend on the ease of removal, volume of fuel throughput and tolerance of water-related problems. It is not always an easy task, but tanks should never go more than 6 months without having bottoms removed.

Be sure to remove water and bottoms until the product being removed is "clear and bright". Remember, emulsions being held stable at the bottom of the tank due to sediment or biological growth can cause problems just as bad as if you were pumping straight water.

If all the water cannot be removed, drain as much as possible and treat the remaining in-tank water with a water-soluble biocide. Fuel which must be stored for long periods of time in tanks containing water can also be treated with a fuel-soluble biocide, to reduce the chance of problems.

Pump suction lines should be far enough off tank bottoms to prevent problems. This will vary by tank and operating conditions. For instance, if a tank is easily accessible and water bottoms are frequently and consistently removed, it may be acceptable to have a draw-off line near the bottom. If, on the other hand, the tank is not serviced routinely and there is a likelihood that water could accumulate at the bottom, then suction lines should be raised an appropriate distance from the bottom.

Once the existing water is removed, steps should be taken to prevent further water from building up in the system. Fuel tanks should be kept at or near capacity to minimize water contamination due to breathing. This is especially true during colder months. Diesel fleets should be refueled in the evening when returning from their routes, not the next morning.

This prevents condensation from accumulating when the temperature drops at night. Even partially filled tanks should be topped off to minimize potential problems.

Additive usage should also be closely monitored. Over treatment with certain types of additives can result in the formation of an emulsion, which can lead to operational problems. Select an additive with good water-shedding tendencies and use it per the manufacturer's recommendations only.

Implementing a tank maintenance program can drastically reduce your chances of having problems with your diesel fuel program. Now AFS can offer a solution to this fuel contamination issue, call and ask us about "Air Sentry" contamination control breathers for enclosed fluid systems. Contact Paul @ 978-664-5923 or write info@fuelsolution.com.



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