Conradson

The specifications require a maximum Conradson Carbon of 0.35%. This limit is very easily met in fact the values obtained on commercial products rarely exceed 0.1%. On the other hand, for heavy fuels, the Conradson Carbon can often reach 5 to 10%, as we will show later. 

The Conradson Carbon of a heavy fuel can often reach 5 to 10%, sometimes even 20%. It is responsible for the combustion quality, mainly in rotating tip atomizing burners. 

The asphaltene content is found either directly by precipitation using n-heptane (NF T 60-115 or ASTM D 32), or indirectly by correlation with the Conradson Carbon. It can vary from 4 or 5% to as much as 15 or 20% in extreme cases. 

Residue cuts fmm Arabian Light crude. Pour point and Conradson carbon as a function of residue yield. 

Vacuum distillation of the atmospheric residue complements primary distillation, enabli r.ecoyery of heavy distillate cuts from atmospheric residue that will un r o further conversion or will serve as lube oil bases. The vacuum residue containing most of the crude contaminants (metals, salts, sediments, sulfur, nitrogen, asphaltenes, Conradson carbon, etc.) is used in asphalt manufacture, for heavy fuel-oil, or for feed for others conversion processes. 

Problems sulfur and nitrogen transferred to the products (and coke) Solutions feed hydrotreating, reduction of S, N, Conradson carbon, metals Results higher quality products reduction in pollution better yields of valuable products reduced post-treatment... 

Conradson carbon NFT60-116 ISO 6615 ASTM D 189 ASTM D 4530 ISO 10370 Weighing after combustion then pyrolysis Micro method... 

It has been shown that coke yield as a fraction of feed does give a linear relationship with second-order conversion (13) indicating a positive coke yield at 2ero conversion. This coke yield at 2ero conversion is the additive coke contribution to the total coke yield and is related to feed properties, particularly Conradson carbon content. The amount of this additive coke is significantly less than the Conradson carbon value of the feed (14), probably in the range of 50% of the Conradson carbon. 

When simple Hquids like naphtha are cracked, it may be possible to determine the feed components by gas chromatography combined with mass spectrometry (gc/ms) (30). However, when gas oil is cracked, complete analysis of the feed may not be possible. Therefore, some simple definitions are used to characterize the feed. When available, paraffins, olefins, naphthenes, and aromatics (PONA) content serves as a key property. When PONA is not available, the Bureau of Mines Correlation Index (BMCI) is used. Other properties like specific gravity, ASTM distillation, viscosity, refractive index. Conradson Carbon, and Bromine Number are also used to characterize the feed. In recent years even nuclear magnetic resonance spectroscopy has been... 

The Conradson test (ASTM D-189) measures carbon residue by evaporative and destructive distillation. The sample is placed in a preweighed sample dish. The sample is heated, using a gas burner, until vapor ceases to burn and no blue smoke is observed. After cooling, the sample dish is reweighed to calculate the percent carbon residue. The test, though popular, is not a good measure of the cokeforming tendency of FCC feed because it indicates thermal, rather than catalytic, coke. In addition, the test is labor intensive and is usually not reproducible, and the procedure tends to be subjective. 

The Ramsbottom test (ASTM D-524) is also used to measure carbon residue. The test calls for introducing 4 grams of sample into a preweighed glass bulb, then inserting the bulb in a heated bath for 20 minutes. The bath temperature is maintained at 1,027°F (553°C). Af 20 minutes, the sample bulb is cooled and reweighed. Compared with the Conradson test, Ramsbottom is more precise and reproducible. 

The Micro-method uses an analytical instrument to measure Conradson carbon in a small automated set. The Micro-method (ASTM D4530) gives test results that are equivalent to the Conradson carbon residue test (D189). The purpose of this test is to provide some indication of relative coke forming tendency of such mat al. 

Figure 2-6. Ramsbottom Carbon Residue versus Conradson Carbon Residue. (Copyright ASTM D-524. Reprinted with permission.)...

Hydroprocessing reduces the Conradson carbon residue of heavy oils. Conradson carbon residue becomes coke in the FCC reactor. This excess coke must be burned in the regenerator, increasing regenerator air requirements. 

Feed residue coke is the small portion of the (non-residue) feed that is directly deposited on the catalyst. This coke comes from the very heavy fraction of the feed and its yield is predicted by the Conradson or Ramsbottom carbon tests. 

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