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Fuel Dehazer for Gas Turbine Distillate Fuel Oils


Water is commonly found in most hydrocarbon fuels and can occur in various quantities and in several different forms. For example, small amounts of "soluble" water in the order of 50 to 100 ppm may remain in fuels after refinery processing. This type of water is present as a true solution in the hydrocarbon and will not settle or separate due to gravity. Much greater quantities of water (up to 5,000 ppm or higher) are often introduced through contamination during marine transportation, and may exist as "free" water or as "emulsified" water droplets. These forms of insoluble water will attempt to separate over time by gravity settling, but the settling rate is likely to be extremely slow and is influenced by the degree of emulsification and the amount of physical mixing – for example through transfer pumps etc.

Residual-grade oils and crude oils have a greater tendency to form stable water emulsions due to the presence of naturally-occurring emulsion stabilizers (such as asphaltenes and naphthenic acids), and settling rate is further hindered by the relatively high density of these type fuels. Light density distillates will shed free water much faster than heavy fuels, and being almost pure hydrocarbons they are less likely to form stable emulsions. However, some degree of interaction with entrained water usually occurs, and in practical terms the rate of water settling is unacceptably slow.

Distillate fuels containing only "soluble" water will maintain a bright and clear appearance because this water is present as a true solution. However, water solubility is extremely temperature dependent and decreases with decreasing temperature. Thus, a fuel stored at a lower temperature can hold less soluble water than if the same fuel were stored at a higher temperature. This is a major factor in the storage of distillates, and accounts for the appearance of a haze or opacity in the fuel (due to the creation of discrete water droplets) as storage temperature falls or fluctuates according to seasonal changes.

Distillate fuels can normally hold at least 50 ppm water in complete solution (except at extremely low temperatures) and haze formation typically occurs with water content in the range 50 to 100 ppm. If water content is higher than about 100 ppm the cause of the haze can usually be attributed to the presence of free water contamination and some degree of emulsification – usually as a result of agitation through pumps.

Haze and emulsions mean that water will be carried throughout the entire fuel distribution system, and can result in very serious fungal and bacterial contamination problems. Wet fuel is also corrosive to tank internals, and corrosion products can lead to filter plugging and additional fuel contamination. Furthermore, seawater contamination from marine transportation will introduce sodium and other undesirable trace metals, thus presenting a major risk of high temperature sulphidation-type corrosion to gas turbine hot section components.

Allowing hazy fuel to clarify by natural settling is time consuming, and also ties-up a lot of product storage capacity. However, these problems can be efficiently overcome by treating the fuel with a chemical "dehazer". These type products enhance the coalescence of small water droplets suspended within the fuel, and thereby increase water separation rate and reduce settling time. Separated free water can then be removed from the bottom of fuel storage tanks on a regular and routine basis.

TURBOTECT EP-390 fuel dehazer is formulated to aid water separation and removal in distillate storage tanks and speed-up settling time. The product is designed to treat a wide variety of distillate-grade gas turbine fuels.

Note that the coalescence mechanism relates to water droplet size, and a high water-content haze is not necessarily more difficult to treat than a low water-content haze. However, separation rate is influenced by the stability and age of the haze. In this regard Turbotect can provide custom-designed dehazer formulations to address specific fuel and storage problems. In these cases a sample of the hazy fuel is required, and should be taken during the unloading operation at the plant. The sample should then be sent to Turbotect for laboratory testing.

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