Filterability limit

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The term filterability limit or cold filter plugging point (CFPP; officially according to DIN: temperature limit value of filterability) describes a cold property of diesel fuels and heating oil EL (extra light). It is the temperature in degrees Celsius at which a test filter becomes clogged under defined conditions by precipitated (n-) paraffins. With this method, the sample is cooled at a constant rate and conveyed through a test filter at defined intervals. Before the filterability limit is reached, crystals form at the so-called cloud point (CP), but they still fit through the filter. The filter clogs only when the crystals become too large. The filterability limit of goods without additives (see below) is generally just below the cloud point. If the spread between the cloud point and the filterability limit is to be increased (for example, with winter diesel roughly 13 K), additives must be used.

Diesel fuel

Example of a measuring device for determining the low-temperature operability according to DIN EN 590 of diesel fuel, biodiesel, diesel mixture and gas oils.

The filterability limit is important for the operational safety of diesel vehicles in winter. At low temperatures (n-) paraffins in the fuel precipitate and form wax crystals that clog the vehicle's fuel filter. The filterability limit can be influenced by four methods: by reducing the cloud point / the filterability limit in the base product (the boiling point of the heaviest component, heavy gas oil , is reduced; the paraffins then remain in the atmospheric residue ), by increasing the addition of kerosene and using additives . Furthermore, the filterability limit can be reduced by removing the n-alkanes from the mixture. This can be achieved using molecular sieves; alternatively, the n-alkanes can be isomerized to iso-alkanes by so-called dewaxing.

Lowering the end of boiling point (SE) reduces the cloud point and the filterability limit in equal measure. The desired filterability limit of around −12 ° C to −20 ° C cannot be achieved by reducing the boiling point alone, as the subsequent high vacuum system, which breaks down the atmospheric residue into its components, cannot maintain the vacuum.

The increased addition of kerosene also reduces the cloud point and the filterability limit equally. Here, too, the desired filterability limit cannot be achieved by simply adding kerosene, since more kerosene would have to be added than was originally diesel, which would violate other specifications. Furthermore, the use of kerosene (as a basic product for the production of aviation fuel) is too expensive under normal price conditions. The use of additives therefore also has an economic aspect.

Additives can modify the crystal growth in such a way (many small crystals instead of a few large ones) that the crystals can continue to pass the fuel filter and the filterability limit shifts to the colder area. Further additives ensure that the crystals do not settle on the ground, but remain evenly in suspension (Wax Antisettling Additive; WASA). A diesel fuel that has a filterability limit below −20 ° C is called winter diesel. However, it can happen that summer diesel or transitional goods also contain additives. The “additives” criterion cannot therefore be used to define winter diesel.

Since the filterability limit can only be reduced to a limited extent by adding additives, the cloud point for winter diesel is lowered to around −7 ° C (lowering the boiling point and / or with kerosene), and the filterability limit is then reduced to −20 ° C by adding additives . Brand manufacturers therefore also specify the cloud point for their fuel.

For diesel fuel , the filterability limit in DIN EN 590 is determined depending on the season (summer, winter and transitional goods).

The reliability of the CFPP is criticized as weak - the ADAC had subjected commercial winter diesel to a cold test. Although all types of diesel further exceeded the laboratory test according to DIN, real diesel engines failed in the cold chamber above the DIN specification. In particular, there was no direct correlation between the CFPP values ​​of the various types of mineral oil and the actually observed cold start capability of the diesel engines - it is therefore proposed that a new test standard be established.

Extra light heating oil

The DIN 51603 Part 1 controls for heating oil extra light, the cold filter plugging point, depending on the cloud point:

  • maximum −12 ° C with a CP of +3 ° C
  • maximum −11 ° C with a CP of +2 ° C
  • maximum −10 ° C with a CP <+1 ° C

For extra-light heating oil, the low-temperature properties play an important role in tank storage in the refinery, in transport by tanker truck and in outdoor storage at the customer's premises. If the filterability limit is not adhered to, the burner system may fail if the burner is stored outside, or paraffins that have already crystallized out and cause malfunctions are delivered by tanker.

Individual evidence

  1. DIN EN 116: 1998-01  ( page no longer available , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.@1@ 2Template: Toter Link / www.beuth.de  
  2. Szynkarczuk, Renata Robinson, Michelle Huve, Laurent G: dewaxing Challenging paraffinic feeds in North America. Retrieved July 27, 2016 .
  3. ↑ You cannot rely on the norm . ADAC blog on all tests from technology and mobility. January 29, 2013. Archived from the original on September 23, 2013. Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved March 11, 2013. @1@ 2Template: Webachiv / IABot / adactestblog.wordpress.com