Cloud point diesel

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. 

Heraud, A., and Pouligny, B. 1992. How Does a Cloud Point Diesel Fuel Additive Work /. Colloid Interface Sci., 153, 378-391. 

The characteristics of diesel fuel taken into account in this area are the cloud point, the pour point, and the cold filter plugging point (CFPP). 

At lower temperatures, the crystals increase in size, and form networks that trap the liquid and hinder its ability to flow. The pour point is attained which can, depending on the diesel fuel, vary between -15 and -30°C. This characteristic (NF T 60-105) is determined, like the cloud point, with a very rudimentary device (maintaining a test tube in the horizontal position without apparent movement of the diesel fuel inside). 

Figure 5.9 shows an example of the efficiency of these products. The reductions of CFPP and pour point can easily attain 6 to 12°C for concentrations between 200 and 600 ppm by weight. The treatment cost is relatively low, on the order of a few hundredths of a Franc per liter of diesel fuel. In practice, a diesel fuel containing a flow improver is recognized by the large difference (more than 10°C) between the cloud point and the CFPP. 

The properties of straight run diesel fuels depend on both nature of the crude oil and selected distillation range. Thus the paraffinic crudes give cuts of satisfactory cetane number but poorer cold characteristics the opposite will be observed with naphthenic or aromatic crudes. The increasing demand for diesel fuel could lead the refiner to increase the distillation end point, but that will result in a deterioration of the cloud point. It is generally accepted that a weight gain in yield of 0.5% could increase the cloud point by 1°C. The compromise between quantity and quality is particularly difficult to reconcile. 

It is mainly in cold behavior that the specifications differ between bome-heating oil and diesel fuel. In winter diesel fuel must have cloud points of -5 to -8°C, CFPPs from -15 to -18°C and pour points from -18 to 21°C according to whether the type of product is conventional or for severe cold. For home-heating oil the specifications are the same for all seasons. The required values are -l-2°C, -4°C and -9°C, which do not present particular problems in refining. 

The nature of these paraffins and their concentration in diesel fuel affect the three temperatures that characterize the cold behavior. The cloud point is the temperature at which crystals of paraffins appear when the temperature is lowered. The cold filter pluming point is defined as the temperature under which a suspension no ionger flows through a standard filter. Finally, the pour point is the temperature below which the diesel fuel no longer flows by simple gravity in a standard tube. These three temperatures are defined by regulations and the refiner has three types of additives to improve the quality of the diesel fuel of winter. 

Damin, B., A. Faure, J. Denis, B. Sillion, P. Claudy and J.M. Letoffe (1986), New additives for diesel fuels cloud point depressents . SAE paper No. 86-1527, International fuels and lubricants meeting and exposition, Philadelphia, PA. 

This condition is of concern only when equipment operates in subzero ambient temperatures. Since diesel fuel extracted from crude oil contains a quantity of paraffin wax, at some low ambient temperatures this paraffin will precipitate and create wax crystals in the fuel. This can result in plugging of the fuel filters, resulting in a hard or no-start condition. Any moisture in the fuel can also form ice ciystals. Cloud point temperatures for various grades of diesel and other fuels should be at least 12°C (21.6°F) below the ambient temperature. In cases where cloud point becomes a problem, a fuel water separator and a heater are employed. 

Lower cloud point in the diesel fuel. Isoparaffins in the light cycle oil boiling range improve the cloud point. 

Fuels such as diesel fuel and heating oil are sometimes stored in large tanks for extended periods of time. At temperatures below the cloud point of the fuel, wax can form and fall from solution. Accumulated wax within fuel systems can deposit onto component parts and settle into areas of low turbulence. Problems such as filter plugging and flow limitations can be due to accumulated wax. 

At low temperatures, the wax in most distillate fuels can cause severe problems with fuel pumping and filtration. As diesel fuel cools, wax begins to crystallize and become visible. The temperature at which crystallized wax becomes visible is known as the cloud point. 

It is possible to dilute diesel fuel such as 2-D low sulfur with kerosene, 1 fuel oil, or jet fuel to reduce the fuel cloud point. Also, additives are also marketed which have the ability to inhibit nucleation of wax crystals in some fuels, thereby lowering the cloud point of the fuel. These products are called cloud point improvers. 

Since highly aromatic fuels have little wax, they possess better natural low-temperature handling properties than paraffinic fuels. Also, the cloud point, pour point and low-temperature filtration of aromatic diesel fuel will typically be much lower than a paraffinic diesel fuel. 

FIGURE 6-9. Typical Response of an EVA in a +18°F (-7.8°C) Cloud Point Hydrotreated Low-Sulfur Diesel Fuel... 

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. 

Diesel fuel may have been stored for several days below its cloud point temperature wax settling has resulted... 

In recent years, the middle distillates have been in growing demand as fuel oils and Diesel fuel. As mentioned under the discussion on Diesel-fuel additives, it has been possible to meet this demand only by the inclusion of distillates from catalytic cracking operations. These have higher volumetric heat contents and lower pour and cloud points, but their use has caused problems of stability and compatibility in storage, necessitating use of anti-screen-clogging agents (14, 41, 4 )-... 

The products from these hydrotreated syncrudes lack paraffins and have low cloud points. Therefore, they are excellent cold climate No. 2D fuels, as shown in Table VI. For diesel fuel used in typical climates, the 300°F+ products have viscosities and D 86 90% points just below the ASTM minimums. To meet this specification, the initial point could be adjusted upward. 

However, one of the limitations of using biodiesel fuel for diesel engines is higher cold flow properties compared with petroleum diesel fuel (4). Cold properties consist of cloud point, pour point, and cold filter plugging point. The cloud point is a temperature at which the fuel starts to thicken and cloud, the pour point is a temperature at which the fuel thickens and no longer pours, and the cold filter plugging point is the lowest temperature at which fuel still flows through a specific filter. These... 

Damin, B., Faure, A., Denis, J., Sillion, B., Claudy, P., and Letoffe, J. M. 1986. New Additives for Diesel Fuels Cloud-Point Depressants, in Diesel Fuels Performance and Characteristics. In SAE Spec. Publ. SP-675 (Diesel Fuels Performance and Characteristics). Warrendale PA Society of Automotive Engineers (Paper No. 861527). 

Cold flow properties are of major importance in winter diesel. Cold performance limits are set to guarantee lack of crystallization. These are expressed as Cloud Point (CP), Pour Point (PP), or as Cold Filter Plugging Point (CFPP). For B100 biodiesel these have to be fully met with the biodiesel, and, if needed, with extra crystal retardation additives. In B2-B30 blends, though, the tendency is rather towards two types of Biodiesel, one for summertime (for example with CFPP of 0°C), and one for wintertime (for example with CFPP -10 °C). 

Specifications of other oil fractions obtained may involve (diesel oil) a cetane index, measures of unsaturation, or handling or safety data, such as cloud point or flash point. 

Catalytic isomerization dewaxing on the other hand preferentially isomerizes the paraffins, reducing the diesel pour point and cloud point while keeping the high-cetane components in the diesel product. It also favourably decreases the boiling range of the fuel (T95) and produces a higher mid distillate yield. 

The solubility of linear alkanes present in diesel quickly decreases with temperature. The temperature at which the first crystals appear is called the cloud point and is one of the most important specifications for fuels concerning their low temperature behaviour. The utilization of a fuel is restricted to temperatures above their cloud point. Cloud point measures the temperature at which the wax crystals form a haze. Below the cloud point, the presence of crystals in suspension impairs the flow, plugging fuel filters. Immediately below the cloud point the fluid stops flowing, reaching what is known as pom point. The CFPP test measmes the highest temperature at which wax separating out of a sample... 

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