Case 4 Blended, High Sulfur Feed at 54 Bar

For Case 3, reducing the product sulfur content from 500 wppm to 50 wppm whilst maintaining cycle length requires almost a doubling of reactor volume, and further reduction from 50 wppm to 10 wppm requires the addition of approximately 80% more reactor volume. 

The percentage increase is similar to Case 1, but the absolute reactor volumes are much higher (approximately 3 times) owing to the higher feed sulfur content and a higher proportion of sterically hindered sulfur compounds in the cracked material. The large additional volimie required to meet the low product sulfur levels will result in an increase in pressure drop and may necessitate a revamp of the recycle gas system. 

The low LHSV required at the lowest product sulfur levels may result in significant hydrocracking (to naphtha and gas), thereby reducing diesel yield. The additional cracking will probably also require additional investment in product fractionator overhead equipment. 

The chemical hydrogen consumption is almost 2.5 times that of Case 1 due to the higher feed sulfur content. The hydrogen consumption is similar for all four product sulfur levels. 

There is a deterioration in the other key product properties when the product sulfur level is lowered. Furthermore, the quality of the product with respect to the three properties shown in Table 6.2 deteriorates throughout the run as the temperature is increased to counteract catalyst deactivation. This is illustrated in Table 9 by comparing the PAH content at start-of-run (SOR) and end-of-run (EOR). The PAH content in all cases is very high at EOR, because the equilibrium between mono-ring aromatics and poly-ring aromatics becomes less favorable at the temperatures used at EOR. The PAH concentration affects product density and cetane index (and cetane number), and at EOR, the density will be higher in all three cases and the cetane index (and cetane number) will be lower. 

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