Sulfur content of coke

Adding residue to the feed increases the sulfur content of coke proportional to the incremental sulfur in the feed (Table 2-6). Thiophenic (ring-type) sulfur compounds crack more slowly, and the uncracked thiophenes end up in gasoline, light cycle oil, and decanted oil. 

Sulfur Content of Coke vs. Quantity of Residue in FCC Feed ... 

Coker feedstocks Reduce sulfur content of coke... 

The four aspects of coke quality that affect price are sulfur, metals, hardness (VCM), and physical structure. The sulfur content of coke will be 40% to 50% higher than that of resid feed. All the metals (mostly vanadium) in resid will concentrate in the coke. The operating engineer has no control over these properties, but he can have a major influence on the hardness of the coke. 

The coking process produces electrode quality coke from vacuum residues of good quality (low metal and sulfur contents) or coke for fuel in the case of heavy crude or vacuum residue conversion having high impurity levels. 

Hydrotreating reduces the sulfur content of all the products. With hydrotreated feeds, more of the feed sulfur goes to coke and heavy liquid products. The same sulfur atoms that were converted to H S in the FCC process are also being removed first in the hydrotreating process. The remaining sulfur compounds are harder to remove. The heavier and more aromatic the feedstock, the greater the level of sulfur in the coke (Table 2-7). 

For nonhydrotreated feed, the gasoline sulfur level is about 10% of the feed sulfur level. For hydrotreated feed, it is about 5%. For example, if the sulfur content of a nonhydrotreated feed is 1.0 r (10,000 ppm), the sulfur in FCC gasoline will be 1,000 ppm. Assuming 80% desulfurization, feed to the FCC unit will contain 0.2% (2000 ppm) sulfur, resulting in FCC gasoline containing 100 ppm sulfur. Sulfur compounds that survive the hydrotreater are in the heav fraction and tend to end up in the LCO, decanted oil, and coke. 

Feed hydrotreating or hydrocracking reduces SOj, emissions and the sulfur content of FCC products. As discussed earlier in this chapter, many benefits are associated with FCC feed hydrotreating. It is important to note that most of the sulfur in a hydrotreated feed is in heavy organic compounds and will be concentrated in the decanted oil and coke. Consequently, for a given sulfur in the feed, more SO, will be produced with hydrotreated feed. 

The amount of SOx produced in the regenerator is determined by the amount of coke produced in the reactor and the sulfur content of that coke (J.). These two factors, in turn, depend on the type of feedstock, the amount of sulfur in the feedstock, the coke-making... 

The specifically formulated CGP-1 catalyst plays a vital role in the MIP-CGP process. Unique catalyst design, such as metal promoted MFl zeolite, phosphorus modified Y zeolite, and a novel matrix with excellent capability to accommodate coke [12] were involved to ensure the primary cracking and secondary reactions to proceed within a defined path. The commercial trial results of the MIP-CGP process in SINOPEC Jiujiang Company showed that, in combination with CGP-1 catalyst, the propylene yield was 8.96 wt%, which increased by more than 2.6% as compared with FCC process. The light ends yield and slurry yield are basically equal. The olefin content of the gasoline produced by MIP-CGP process was 15.0 v%, which was 26.1% lower than that of FCC gasoline. The sulfur content of gasoline was decreased from 400 to 270 pg/g. 

Yields of liquid products from flexicoking are the same as from fluid coking, because the coking reactor is unaltered. As with fluid coking, the extent of desulfurization depends on the sulfur content of the feedstock as well as on the chemical nature of the sulfur in the feed stock. 

Other procedures include high-temperature tube furnace combustion methods for rapid determination of sulfur in coal and coke, using automated equipment. The instrumental analysis provides a reliable and rapid method for determining sulfur contents of coal or coke. By this method, total sulfur as sulfur dioxide is determined on a continuous basis. 

The high sulfur content of fuel grade petroleum coke has also restricted its use as utility power fuel. Additional capital costs would be incurred by a utility choosing to burn petroleum coke to reduce sulfur emissions. 

Desulfurization of coker feedstocks to produce lower sulfur cokes has proven not to be the solution to the problem. Nor is there cause for optimism in this area. Not only is this technology extremely expensive, it doesn t always achieve the expected results. A 50% reduction in feedstock sulfur content usually yields a lesser reduction of the sulfur content of the coke. 

Laboratory tests on two-pound sampl 5 of green petroleum cokes with sulfur contents of 4 wt% to 6 wt% have successfully reduced the sulfur levels to as low as 0.7 wt%. The degree of desulfurization can readily be controlled by adjusting the temperature (nominally between 2500 and 2800°F), the holding time in the reactor (between 5 and 90 minutes), and the reactant concentrations and flow rates. 

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