S-Value Analyser to Determine Fuel Stability and Fuels Compatibility – ASTM D 7157
Jul 13 2020
Author: ROFA FRANCE on behalf of ROFA France
What is the definition of ‘Fuel Stability’?
Fuels are composed of many constituents such as asphaltenes, maltenes and resins. Asphaltenes are dispersed in a colloidal state into the maltenes phase. In cases of fuel instability a formation of granular deposits will appear, called “flocculation” or “peptization”. These formations can occur due to environmental conditions but it is more frequent when mixing two or more fuels.
When this flocculation or peptization occurs, this means that the limit threshold stability of the fuel or the mixture of fuels has been reached.
When the instability threshold is reached or exceeded, particles in the form of granular deposits, will be generated, how much this occurs, depends on the nature and the mass of asphaltenes present in the fuel. There are many reasons for the transition from liquid to granular state. They are complex and sometimes difficult to identify.
The operational consequences of using unstable or incompatibly mixed fuels, include the formation of an asphaltenic sludge, which can block filters, separators and other components.
Factors influencing stability:
• Fuel formulation, thermal and mechanical stress, storage time and condition.
• Stability is a key factor for the quality of fuels. It is the responsibility of the fuel supplier to provide stable fuels.
• Stability is the first of two applications of the S-Value analyser.
• Stability determination can be done down to 0.05 % of asphaltenes mass. It can be used for any of the below mentioned market applications.
Compatibility is the term used to evaluate if fuels can be mixed without flocculation and detection of asphaltenes. Compatibility is the second application of S-Value analyser. Compatibility can be determined with ROFA’s application “prediction stability calculator”. There are two approaches to calculate compatibility. In cases of good component compatibility the software uses the different stability test results for each individual component. If the compatibility is not good and instability is detected or suspected by the operator, the “prediction stability calculator”, will instruct the operator to perform at least one more S-Value test. This test will be done on a mixture of the components, so the calculator can confirm or adjust the blend stability results.
S-Value technology is in constant development reacting to the permanent changes of the fuels supplied on the market. The analyser is delivered ready for use. Very low maintenance is required to run the unit. Support by local offices, representatives and online support from the manufacturer is available. An example of a result screen with all different important information concerning the test.
The prediction stability calculator is an important tool available with the S-Value analyzer.
For the standard stability test there are 3 different ranges of products: Crude Oils, Marine Fuels, Distillates. Calculator will determine “Stability Prediction”: GOOD, POOR or BAD. “Stability factor” allows user to see where his fuels are located in the range of stability.
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