Flash-point

Flash point is considered to be an important specification for all finished fuels and oils. The flammability and combustibility characteristics of a material are directly related to the flash point. Also, fuel transportation codes require flammable compounds to be appropriately labeled for safety reasons. 

According to Occupational Safety and Health Administration (OSHA), compounds with flash point values 100°F (37.8°C) are considered flammable. Department of Transportation (DOT) and United Nations (UN) codes rate compounds flammable when the flash point is 141°F (60.5°C). 

The following performance conditions could be attributed to a low flash point  

The presence of low molecular weight, low flash point compounds in diesel fuel could lead to a shortening of the fuel ignition delay period. In a diesel engine, this could cause rough running due to early combustion of the low flash point compounds. 

Vaporization of low-boiling-point, low-flash-point fuel components can increase the vapor pressure of a fuel. For this reason, fuel vapors are being closely monitored and regulated due to their tendency to escape into the atmosphere from fuel storage and distribution systems. Compounds with low flash points can contribute significantly to increasing fuel vapor pressure. 

The flash point is the lowest temperature at atmospheric pressure (760 mmHg, 101.3 kPa) at which application of a test flame will cause the vapor of a sample to ignite under specified test conditions. The sample is deemed to have reached the flash point when a large flame appears and instantaneously propagates itself over the surface of the sample. Flash point data are used in shipping and safety regulations to define flammable and combustible materials. Flash point data can also indicate the possible presence of highly volatile and flammable constituents in a relatively nonvolatile or nonflammable material. 

Of the available test methods, the most common method of determining the flash point confines the vapor (closed cup method) until the instant the flame is applied (ASTM D-56, ASTM D-93, ASTM D-3828,6450, IP 34, IP 94, IP 303) (Fig. 4.5). An alternate method that does not confine the vapor 

Erroneously high flash points can be obtained when precautions are not taken to avoid the loss of volatile material. Samples should not be stored in plastic bottles, because the volatile material may diffuse through the walls of the container. The containers should not be opened unnecessarily. The samples should not be transferred between containers unless the sample temperature is at least 20°F (11°C) below the expected flash point. 

Another test (ASTM E-659) that can be used as a complement to the flash point test involves determination of the auto-ignition temperature. However, the flash point should not be confused with auto-ignition temperature, which measures spontaneous combustion with no external source of ignition. 

The parameters flash point and fire point are used for characterizing flammable liquids. 

The flash point of a liquid is the lowest temperature in °C corrected to 101.3 kPa of a flammable hquid in an open or closed cup at which vapours develop in such a quantity that under defined measuring conditions in the cup a vapour-air mixture is 

Hazard statement H 224 extremely flammable liquid and vapour H 225 highly flammable liquid and vapour H 226 flammable liquid and vapour 

Flammable liquid Flash point in °C (closed cup) Boiling point in °C Categorization 

The next and probably the most important physical characteristic of a flammable liquid is its flash point. Flash point is the most important information for emergency 

Flash point is a measurement of the temperature of the liquid. Therefore, even if the ambient temperature is not at the flash point temperature, the liquid may have been heated to its flash point by some external heat source. For example, the radiant heat of the sun, heat from a fire, or heat from a chemical process may heat the liquid to its flash point. If an ignition source is present, ignition can and probably will occur. In order for ignition to occur if a flammable liquid is at its flash point temperature, there has to be an ignition source present that has a temperature at or above the ignition temperature of the vapor. 

Underflow dams used to stop the flow of flammable liquids that are lighter than water. 

Flash point should not be confused with fire point. Fire point is the temperature at which the liquid is heated to produce enough vapor for ignition and sustained combustion to occur. Fire point temperature is 1 to 3 degrees above the flashpoint temperature. The fact that the fire point is so close to the flash point really does not give it much significance to emergency responders if a liquid is at its flash point, prepare for a fire. 

There is a direct, parallel relationship between boiling point and flash point temperatures. Generally speaking, a liquid that has a low boiling point temperature will have a low flash point temperature. If a flammable liquid has a high boiling point, it will have a high flash point. 

In addition thermophysical properties required for modeling purposes, a complete model must also make predictions regarding several fuel properties routinely measured at the refinery. Typically these fuel or product properties include measurements such as flash point, freeze point, cloud point and paraffin-naphthene-aromatic (PNA) content. These properties not only serve as indicators of product quality and distribution, but may also be limited by government or internal refinery regulations. We can often justify the use of process modeling in the refinery by making sure that models also include predictions of these useful fuel properties. We will briefly discuss two approaches in this area and give concrete examples with flash point, freeze point and PNA content We choose these particular properties because they display characteristics common to many types of fuel property correlation methods. We refer the reader to API standards [35] and Riazi [4] for more detailed expositions on various types of correlations for fuel properties not discussed in this section. 

The last sets of correlations we will address are composition correlations. These correlations identify chemical composition in terms of total paraffin, naphthene and aromatic (PNA) content of a particular feed based on key bulk measurements. These correlations are useful in two respects. First, we use these correlations to screen feeds to different refinery reaction units. For example, we may wish to send a more paraffinic feed to a reforming process when we want to increase the yield of aromatic components from the refinery. Secondly, these types of correlations form the basis of more detailed lumping for kinetic models that we will discuss at great length in subsequent chapters of this book. We will use these types of correlations to build extensive component lists that we can use to model refinery reaction processes. 

Compositional information is quite useful to the refiner and many correlations are available in the literature that attempt to correlate PNA content to various bulk measurements. In general, these correlations rely on density or specific gravity, molecular weight, distillation curve and one or more viscosity measurements. The n-d-M (refractive index, density, and molecular weight) [4], API/Riazi-Daubert [35,4], and TOTAL [19] correlations are just a few of the correlations available. 

The Riazi-Daubert correlation relies on the most directly observed information and we expect it to show the smallest deviation from measured values. The other correlations require parameters (aniline point, etc.) that may not be routinely measured for all feeds. The Riazi-Daubert correlation takes the form  

We have extended the correlation by Riazi [4] to include the specific gravity, refractive index and the stream viscosity. Our updated correlation is given by  

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The flash point measures the tendency of a petroleum material to form a flammable mixture with air. It is one of the properties to be considered when evaluating the flammability of a petroleum cut. 

The flash point is measured in the laboratory following procedures that depend on the sample being tested. 

Calculating the flash point starting from the mixture s composition is not very accurate however an estimation can be obtained if 7) is determined as-the temperature for which the following relation holds true [ 9 )... 

The flash points obtained experimentally according to the different procedures differ slightly. The present estimation refers to the flash point called the closed cup method. 

Diesel Fuel Safety as Characterized by Its Flash Point... 

The flash point of a petroleum liquid is the temperature to which it must be brought so that the vapor evolved burns spontaneously in the presence of a flame. For diesel fuel, the test is conducted according to a closed cup technique (NF T 60-103). The French specifications stipulate that the flash point should be between 55°C and 120°C. That constitutes a safety criterion during storage and distribution operations. Moreover, from an official viewpoint, petroleum products are classified in several groups according to their flash points which should never be exceeded. 

The flash point depends closely on the distillation initial point. The following empirical relationship is often cited ([, 1 ... 

It should be noted finally that adding gasoline to diesel fuel which was sometimes recommended in the past to improve cold behavior conflicts with the flash point specifications and presents a serious safety problem owing to the presence of a flammable mixture in the fuel tank airspace. Adding a kerosene that begins to boil at 150°C does not have the Scune disadvantage from this point of view. 

Petroleum solvents are very flammable and can cause an explosion in the presence of air. For this reason, their flash points, directiy related to volatility, are always specified. 

Volatility can be characterized either indirectly, by measurement of the flash point (the temperature to which the oil must be heated for inflammation of its vapor to become possible) or by direct measurement, following the Noack method. 

Performance can be illustrated for example by the time necessary for deaeration or de-emulsification of oils, anti-rust properties, copper strip corrosion test, the flash point in closed or open cup, the cloud and pour points, the foaming characteristics, etc. 

Flash point (cutbacks, fluxed bitumen). Standards NF T 66-009 and IP 113... 

White oils can be characterized by their physical properties as base oils density, viscosity, flash point, etc. 

Flash point Luchaire (NF T 60-103) Pensky-Martens (NF EN 22719) > 70°C > 60°C (bunker and fishing boats) ... 

Flash point, Cleveland Neutralization index Saybolt color Aromatics... 

Vapor Pressure and Flash Point of Crude Oils... 

The measurement of the vapor pressure and flash point of crude oils enables the light hydrocarbon content to be estimated. 

Safety standards govern the manipulation and storage of crude oil and petroleum products with regard to their flash points which are directly linked to vapor pressure. 

One generally observes that crude oils having a vapor pressure greater than 0.2 bar at 37.8°C (100°F), have a flash point less than 20°C. 

Table 8.4 gives the vapor pressures and the flash points of some crude... 

Crude oil name Country of origin RVP (bar) Flash point (°Q... 

Reid vapor pressures and flash points of selected crude oils. 

It is possible to calculate the properties of wider cuts given the characteristics of the smaller fractions when these properties are additive in volume, weight or moles. Only the specific gravity, vapor pressure, sulfur content, and aromatics content give this advantage. All others, such as viscosity, flash point, pour point, need to be measured. In this case it is preferable to proceed with a TBP distillation of the wider cuts that correspond with those in an actual refinery whose properties have been measured. 

Flash point - Abel NFM 07-011 Cyclic approaches of a flame over a heated closed cup... 

Flash point (bitumen) NF T 66-009 As above, closed cup (modified Abel)... 

Flash point - Cleveland NF EN 22592 ISO 2592 ASTM D 92 As above, open cup... 

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