Cloud point blended fuel

Different steps are taken to prevent and avoid this situation. Utilization of low-cloud-point diesel fuel and blending with kerosene are two possible solutions. Sometimes these measures are viewed as costly and impractical. 

A secondary problem may occur whenever CPI treated fuels are blended with other fuels in a fungible system. The effect of the cloud point improver may be lost due to dilution or limited performance in other fuels. 

For most distillate fuels, cloud point temperatures can range from 50°F to -10°F (10.0°C to -23.3°C) or lower. However, typical cloud point temperatures fall between 6°F and 16°F (-14.4°C and -8.9°C). Distillate blends having a high paraffin content will often have cloud point and pour point values close together, sometimes within 5°F (2.8°C). Highly aromatic blends will usually have cloud and pour point values further apart in temperature. 

Lowering the cloud point and pour point values of a distillate fuel can be accomplished by blending the fuel with a low-wax-content distillate stream such as a kerosene or jet fuel. Also, additives are frequently used in conjunction with kerosene blending or as a substitute for kerosene blending to reduce the pour point of diesel fuel. Additives are not as frequently used to reduce the cloud point of diesel fuel. 

The cloud point test is one of the most commonly used methods to evaluate the low-temperature characteristics of distillate fuel. The cloud point temperature identifies the point when wax begins to form into crystals large enough to become visible in the fuel. At this temperature, wax can settle from fuel, deposit onto fuel filters, and interfere with the flow of fuel through small tubes and pipes. During cold weather months, distillate fuels with lower cloud point values are refined and blended to minimize the low-temperature problems associated with wax. 

Determine whether a cloud point improver was utilized in the fuel by checking blending records. 

Two processes are commonly used to produce fuels within a given specification. The use of additives, such as cloud point depressants, and, fuel blending where a fuel with an excessively high cloud point is mixed with a low-cloud-point fluid to produce a fuel that meets the specifications. Most often both approaches are used simultaneously, since cloud point depressants have a limited action. 

At the present time the problems associated with cloud points which are too high are addressed in three ways. These are (a) cold filtration, (b) the use of additives, and (c) the blending with conventional diesel fuel. The recent inclusion of B20, a 20% blend of methyl esters with diesel fuel, as an allowable friel under the US FT ACT program, is not arbitrary. At the 20% level, significant reductions in CFPP of the esters can be achieved. This reduction obviously is related to the individual cloud points of the diesel friel and methyl esters separately. As an example, a beef tallow methyl ester (CFPP = +20), when blended at the 20% level with a petrodiesel having a CP of -3, d a resulting CP of 11. The reduction effect is not linear over the whole range and has the maximum benefit below 20%. 

The recommended cloud point of a fuel is 6°C above the pour point, which is the temperature at which the fuel ceases to flow readily. A fuel is normally blended so as to make the pour point at least 6°C below normal driving temperatures. The ASTM (D-975-78) specification of diesel fuel oils is given in Table 4.2. 

Typically, fuels products are blended under computer control. There are constraints against which the blend recipe is constantly checked. The constraints are typically product specifications (cetane, octane, cloud point, distillation points, etc.) and blend stock quality and availability. The quality of the on-going blend is monitored using key quality analyzers that feed back to the blend control computer the current quality status. The blend recipe is then adjusted to optimize the quality (specifications) using the currently available blending components. 

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