Fuel oils pour point

Pour point ranges from 213 K (—80°F) for some kerosene-type jet fuels to 319 K (115°F) for waxy No. 6 fuel oils. Cloud point (which is not measured on opaque fuels) is typically 3 to 8 K higher than pour point unless the pour has been depressed by additives. Typical petroleum fuels are practically newtonian liqmds between the cloua point and the boiling point and at pressures below 6.9 MPa (1000 psia). 

The pour point of residual fuel is not the best measure of the low-temperature handling properties of the fuel. Viscosity measurements are considered more reliable. Nevertheless, residual fuels are classed as high pour and low pour fuels. Low-pour-point fuels have a maximum pour point of 60°F (15.5°C). There is no maximum pour point specified for high-pour-point residual fuels. A residual oil paraffin carbon number analysis is provided in FIGURE 3-1. 

For diesel fuels, ideal behaviour of the solution of paraffins was found and a linear relationship between enthalpies and temperature was determined [3]. For crude oils, the comparison between the enthalpies of melting and precipitation shows a lowering of 20 J/g of the value of the enthalpy of precipitation. This difference can be attributed to the non-ideal behaviour of the solution of n-paraffin in the crude-oil matrix. Another relation between enthalpy and temperature must thus be chosen. Using the complex mixture of paraffins, it was found that the values of enthalpies of precipitation are close to 200 J/g. This constant value is used in the computer programs for the determination of the amount of precipitated waxes. For non-doped diesel fuels, the pour point is reached when 1 wt% of paraffins contained in the fuel has precipitated. Concerning the crude oils, the knowledge of the enthalpy of precipitation allows the amount of precipitated waxes at different temperatures and the pour point to be calculated. 

Grade of fuel oil Rash point, F(=c) Pour point, °F (°C) Water and sediment, % by vol Carbon residue on 10% bottoms, % Ash, % by wt Distillation temperatures, °F (°C) Saybolt viscosity, s Kinematic viscosity, centistokes Gravity, deg API Copper strip corrosion... 

Tests of the fuel oil fraction normally include determination of density or specific gravity, total sulfur, aniline point, total acid number, naphthalenes content, smoke point, total nitrogen, viscosity, cloud point (ASTM Test Method D2500, Cloud Point of Petroleum Oils), pour point (ASTM Test Method D97, Pour Point of Petroleum Oils), and calculation of cetane index. Corrosiveness, ash (ASTM Test Method D482, Ash from Petroleum Products), and carbon residue might also be determined in more thorough evaluations. 

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. 

Although lubricant base stocks have been subjected to dewaxing processes, they still contain large amounts of paraffins that result in a high pour point for the oil. In the paragraph on the cold behavior of diesel fuels, additives were mentioned that modify the paraffin crystalline system and oppose the precipitation of solids. 

Long-chain esters of pentaerythritol have been used as pour-point depressants for lubricant products, ranging from fuel oils or diesel fuels to the high performance lubricating oils requited for demanding outiets such as aviation, power turbines, and automobiles. These materials requite superior temperature, viscosity, and aging resistance, and must be compatible with the wide variety of metallic surfaces commonly used in the outiets (79—81). 

The pour point is an indication of the lowest temperature at which a fuel oil can be stored and still be capable of flowing under gravitational forces. Fuels with higher pour points are permissible where the piping has been heated. Water and sediment in the fuel lead to fouling of the fuel system and obstruction in fuel filters. 

The pour point represents the lowest temperature at which the liquid fuel will pour. This is a useful consideration in the transport of fuels through pipelines. To determine the pour point, an oil sample contained in a test tube is heated up to 115°F (46°C) until the paraffin waxes have melted. The tube is then cooled in a bath kept at about 20°F (11°C) below the estimated pour point. The temperature at which the oil does not flow when the tube is horizontally positioned is termed the pour point. 

The pour point of a crude oil or product is the lowest temperature at which an oil is observed to flow under the conditions of the test. Pour point data indicates the amount of long-chain paraffins (petroleum wax) found in a crude oil. Paraffinic crudes usually have higher wax content than other crude types. Handling and transporting crude oils and heavy fuels is difficult at temperatures helow their pour points Often, chemical additives known as pour point depressants are used to improve the flow properties of the fuel. Long-chain n-paraffins ranging from 16-60 carhon atoms in particular, are responsible for near-ambient temperature precipitation. In middle distillates, less than 1% wax can be sufficient to cause solidification of the fuel. ... 

Cold flow improvers (pour point depressants) These viscosity improvers are often specified in cold climates for unheated gas oil or where existing residual oil heaters are inadequate. The use of these paraffin crystal modifiers permits fuel to continue to flow at temperatures of 30 to 40 °F lower than the point at which wax crystallization would normally occur. 

The lowest temperature at which fuel oil will flow. Residual oil (No. 6 oil) will not usually flow at ambient temperature and requires heating to reduce the viscosity and raise the pour point. 

Low-pour-point fuel for use in residual fuel oil burners... 

It is recommended that any higher-viscosity product such as residual oil or heavy distillate fuel be evaluated for changes in low-temperature handling properties over time. Testing for reversion in pour point by the Shell Amsterdam Reversion Test or the British Admiralty Pour Point Reversion Test are recommended. Also, viscosity increase versus temperature decrease determinations are recommended for products stored at low temperatures for extended periods of time. 

Testing of the pour point of crude oil and certain residual fuel products requires an understanding of how these oils can behave under certain conditions of heating and shearing. 

When determining the pour point of certain heavy residual products such as 6 fuel oils, bunker fuels, vacuum gas oils, vacuum resids, atmospheric resids, and visbreaker bottoms, it is important to pay close attention to the temperature applied to the oil prior to pour point testing. In some cases, preheating an oil to temperatures greater than 212°F (100°C) prior to pour point testing can result in a pour point value which is lower than the value obtained for the same oil preheated to 110°F (43.3°C). 

In addition to refining techniques, compounds identified as wax crystal modifiers are available for use in contending with the effects of wax in fuels. Wax crystal modifiers, also called pour point depressants or cold flow improvers, are typically polymeric compounds which have the ability to crystallize with fuel wax as it forms. By co-crystallizing with wax, the modifiers typically effect a change in the size, shape, and conformation of wax crystals. Other wax crystal modifiers function by dispersing or inhibiting the nucleation or growth of wax crystals within a fuel or oil. 

The pour point and low-temperature viscosity of a residual fuel or heavy fuel oil can be reduced by using a heavy fuel wax crystal modifier. Often, pour point reversion can be prevented by using the correct wax crystal modifier. 

The pour point test is used to determine the lowest temperature at which a fuel can be effectively pumped. However, the pour point value can be misleading, especially when it is used to determine the low-temperature handling characteristics of residual fuel oil and other heavy fuels. Low-temperature viscosity measurements are considered more reliable than pour point values for determining the flow properties and pumpability of these oils. 

Crude oil and high-boiling-point, high-viscosity petroleum fractions such as 6 fuel oil, atmospheric tower bottoms, and vacuum gas oil can contain wax which crystallizes at temperatures often above room temperature. It is not unusual for these oils to have base pour points of 100°F (37.8°C) or greater. In order to utilize these heavy oils, the pour point and viscosity of these oils must be reduced. One method which is used to accomplish this is to dilute the heavy oil with lower-viscosity components such as diesel fuel or kerosene. The oil then becomes pumpable at lower temperatures. 

Another common method which is used to improve the handling characteristics of heavy oils is to treat the oils with a wax crystal modifier. The process is similar to that used in diesel fuel treatment. Wax crystal modifiers for use in heavy oils are typically higher in molecular weight than those used in diesel fuel applications. The pour point method ASTM D-97 is also used to evaluate crude oil and heavy oils. 

This procedure can be utilized to determine whether heavy fuel wax crystal modifiers will lose their performance properties after long-term storage at fluctuating temperatures. Daily heating and overnight cooling may interfere with the ability of some wax crystal modifiers to maintain their performance properties in some residual oils and crude oils. This loss of performance is frequently termed pour point reversion. The British Admiralty Pour Point Test can be utilized to help predict these reversion tendencies. 

This method describes a procedure for determining the critical pour point of residual fuel oils. 

PROBLEM INCREASE IN POUR POINT OF RESIDUAL FUEL OIL OR CRUDE OIL AFTER HEATING OR SHEARING... 

An unusual behavior can be seen in some crude oils and residual fuel oils after they have been heated or have been sheared through a high-rpm pump. When sampled at the pump outlet, some oils can experience an increase in pour point above that of the same oil prior to heating or shearing by pumping. 

PROBLEM REVERSION AND ACTUAL INCREASE IN THE POUR POINT OF A CRUDE OIL OR RESIDUAL FUEL OIL... 

This problem differs from the problem of pour point increase after shearing and heating. In the case of pour point reversion, an increase in the pour point of a crude oil or heavy fuel oil occurs upon long-term storage. 

Contrary to what is seen with vegetable oils, biodiesel produced from animal fats has component units that are dominated by saturated alkyl species, and the observed biodiesel properties reflect the presence of these species. The fuel is more stable and degrades less in the presence of air. However, cloud-points and pour-points are higher, meaning that it may show poor performance at cold temperatures. 

Fuel Oils, Analytical. The following determinations were made at US War Planes during WWII 1) Specific Gravity 2) Moisture 3) Insolubles 4) Flash Point and 5) Pour Point Tests... 

Because the paraffin and mixed-base crudes yield lubricating oil fractions of high quality, means had to be devised in the early days of the petroleum industry to separate the wax from the oil. The removal of wax from petroleum fractions is one of the most important phases in the production of lubricating oils and fuel oils of low pour point, and has received the attention of many investigators. 

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 )-... 

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