• What is the best way to reduce HCGO end point, apart of increasing the flow on the sprays?



  • Marcio Wagner da Silva, Petrobras, marciows@petrobras.com.br

    Based on your question it seems that your refinery directs the HCGO (Heavy Coker Gas Oil) to a hydrocracking unit once normally these streams are normally only injected under low flow rates to FCC units due to their poor crackability once the stream already suffered thermal cracking. I believe that it's possible to achieve this goal (reduction of the end point of the Heavy Coker Gas Oil) through raising the flow rate of the inferior pumparound of the fractionator, this will lead to a reduction in the bottom temperature of the tower which can limit the feed stream of the delayed coking unit if the fired heaters do not have sufficient thermal charge to compensate this reduction.

    Obviously, if the main fractionator have side stripper column to HCGO stream, it's possible to cut or reduce the flow rate of stripping steam to help to reduce the end point of the stream, but normally these system are not installed or are not operated once the main fractionating tower is able to reach high flash point for this stream being unnecessary to operate the stripper column, furthermore, this will improve the energetic efficiency of the delayed coking unit. Another key parameter to reduce the end point of HCGO is to raise the recycle ratio of the delayed coking unit, but again this can limit the capacity of the delayed coking unit. In summary it's not easy to achieve this goal without improving the internal recycling, an alternative is to blend the HCGO stream with lighter and cleaner streams like straight run gas oil before feeding the consumption unit (hydrocracker or FCC).

    A very good article about this topic was published by Mr. Scott W. Golden in the 2003 issue of the Revamps Magazine (a supplement of PTQ Magazine). You can view the ARTICLE HERE