Conradson carbon residue coke

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. 

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. 

The third type is the additional coke related with the feedstock quality. FCC feedstock contains a dissolved carbon, polynuclear aromatic compounds, called Conradson carbon residue (CCR ASTM D-189). It is deposited over the catalyst surface during cracking reactions. In the FCC unit, this material is part of the coke remaining in the catalyst. Some researchers have investigated cracking of heavy feedstock and observed that, in particular cases, the amount of Conradson carbon is linearly related with the carbon-hydrogen ratio of the feedstock [3]. 

Coking processes have the virtue of eliminating the residue fraction of the feed, at the cost of forming a solid carbonaceous product. The yield of coke in a given coking process tends to be proportional to the carbon residue content of the feed (measured as the Conradson carbon residue see Chapter 2). The data (Table 7-11) illustrate how the yield of coke from delayed and fluid coking varies with Conradson carbon residue of the feed. 

Thermal coke the carbonaceous residue formed as a result of a noncatalytic thermal process the Conradson carbon residue the Ramsbottom carbon residue. 

Figure 7 summarizes the main relations, which determine the effect of coke on deactivation. Note that a poor coke selectivity (or low cat-to-oil ratio) will aggravate the poisoning effect of the fraction of the Conradson Carbon Residue which is converted to coke. 

While originally designed for cracking the overhead stream from vacuum distillation units, known as vacuum gas oil (4), most FCC units currently operate with some higher boiling vacuum distillation bottoms (Resid) in the feed. Table 5.1 illustrates the difficult challenges faced by refiners, process licensors and FCC catalysts producers the resid feeds are heavier (lower API gravity), contain many more metals like Ni and V as well as more polyaromatic hydrocarbons prone to form coke on the catalysts (Conradson Carbon Residue, or CCR). 

In resid cracking the high feed metals and Conradson Carbon Residue (CCR) require careful consideration when assessing both catalyst design and performance evaluation. This paper addresses the issues of the latter with respect to coke, delta coke and catalyst deactivation. 

Tests for Conradson carbon residue (ASTM D-189, IP 13), Ramsbottom carbon residue (ASTM D-524, IP 14), the microcarbon carbon residue (ASTM D4530, IP 398), and asphaltene content (ASTM D-893, ASTM D-2006, ASTM D-2007, ASTM D-3279, ASTM D-4124, ASTM D-6560, IP 143) are sometimes included in inspection data on petroleum. The data give an indication of the amount of coke that will be formed during thermal processes as well as an indication of the amount of high-boiling constituents in petroleum. 

The data produced by the nucrocarbon test (ASTM D4530, IP 398) are equivalent to those by the Conradson carbon residue method (ASTM D-189 IP 13). However, this nucrocarbon test method offers better control of test conditions and requires a smaller sample. Up to 12 samples can be run simultaneously. This test method is applicable to petroleum and to petroleum products that partially decompose on distillation at atmospheric pressure and is applicable to a variety of samples that generate a range of yields (0.01% w/w to 30% w/w) of thermal coke. 

Other test methods that are used for determining the coking value of tar and pitch (ASTM D-2416, ASTM D-4715), which indicates the relative coke-forming properties of tars and pitches, might also be applied to asphalt. Both test methods are applicable to tar and pitch with an ash content <0.5% (ASTM D-2415). The former test method (ASTM D-2416) gives results close to those obtained by the Conradson carbon residue test (ASTM D-189, IP 13). However, in the latter test method (ASTM D-4715), a sample is heated for a specified time at 550 10°C (1022 18°F) in an electric furnace. The percentage of residue is reported as the coking value. 

During the refining process, a portion of the asphaltenes is coked to form carbon residue. The actual percentage depends on the refining process. For this reason, the commonly held assumption that asphaltenes in the fuel can be estimated by knowing the Conradson Carbon Residue is erroneous. In actual fact, the asphaltenes vary widely from Conradson Carbon Residue levels and have to be analyzed separately. 

Whitehead et al [1983] point out that the Conradson carbon residue test has a poor correlation with measured particles in the combustion gases. They suggest that the differences are probably due to the very different conditions in the laboratory bench test compared with the practical combustion conditions. In an industrial furnace the oil droplets undergo a high heating rate and under these conditions the level of pyrolysis residue (coke) formed can be considerably reduced. Droplet size (a fonction of atomiser design and performance) is likely to be an important factor that affects the droplet heating rate as described earlier. 

When I had instructed the crude unit operators to reduce vacuum tower wash oil by 50%, the entrainment of resid or tar into the gas-oil FCCU feed had substantially increased. As shown in the above tabulation of laboratory data, the entrainment had caused an increase in conradson carbon residue of the vacuum gas oil. This was of no consequence. The extra coke made due to the higher conradson carbon was compensated for by cutting the FCCU feed preheat temperature to hold the regenerator in heat balance. Of greater importance was the increase in nickel content from 0.5 ppm in vacuum gas oil to 2.0 ppm. This fourfold multiplication in nickel content was reflected by a concurrent increase of nickel accumulation of the circulating catalyst. As the nickel content of the catalyst increased. 

The separate effects of coke formation and metals deposition have been described in a study with two different residual oil feedstocks [18]. Their properties are listed in Table 1. They have a similar tendency to form coke (Conradson Carbon Residue) but much different contents of organometa11ic compounds (nickel and vanadium). 

Carbon Residue—amount left after evaporation and pyrolysis to provide some indication of relative coke-forming propensity (ASTM Test Method D189, Conradson Carbon Residue of Petroleum Products, ASTM Test Method D524, Ramsbottom Carbon Residue of Petroleum Products, or ASTM Test Method D4530, Determination of Carbon Residue (Micro Method)), ASTM Method D4530 having gained wide acceptance. 

The Conradson carbon residue (CCR) results from ASTM test D189. It measures the coke-forming tendencies of oil. It is determined by destructive distillation of a sample to elemental carbon (coke residue), in the absence of air, expressed as the weight percentage of the original sample. A related measure of the carbon residue is called Ramsbottom carbon residue. A crude oil with a high CCR has a low value as a refinery feedstock. 

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. 

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. 

Before TPO analysis it was necessary to Soxhlet extract the FCC samples to remove nonvaporized hydrocarbons and avoid their accumulation in the pores of the catalyst as carbonaceous residue with high hydrogen content. As a result, the interference during TPO analysis caused by the desorption and decomposition of these compounds at high temperatures was eliminated. In this study it was observed that this type of coke is directly related to the Conradson carbon content of the feedstock. 

Conradson Carbon Number ASTM D-189 Determination of the weight of nonvolatile residue formed after evaporation and atmospheric pyrolysis of fuel or oil. This test method provides some information about the relative coke-forming or deposit-forming tendency of a fuel or oil. Products having a high ash value will have an erroneously high carbon residue value. 

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