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(2010) Question 67: Have you experienced coking or other fouling of reboilers in naphtha distillation service (splitter, debutanizer, etc.)? If so, what operational or design changes did you implement to eliminate this problem?

Two types of fouling are common in naphtha reboilers. The first type of fouling is generated as a result of the more reactive cracked stock hydrocarbons and is typically seen only in units like Cokers or FCCUs with a cracking process. The second type of fouling is a more complicated issue related to the presence of sulfides in the naphtha and can be seen in straight run units like the Atmospheric Crude.
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(2010) Question 36: What are the best practices for maximizing catalyst run length in NHT units that are limited by reactor pressure drop?

Marathon’s experience with NHT fouling has been primarily corrosion products from upstream units and oxygen related polymerization of the naphtha. The use of feed filters can help minimize the effects of corrosion products. Oxygen related polymerization has impacted our NHT units from air leakage across intermediate naphtha storage tank seals and in purchased naphtha.
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(2010) Question 37: Silicon poisoning of NHT catalysts has been observed in refineries without coking units. In your experience, what are the potential sources of silicon and what are the best practices to manage risk of such poisoning?

Marathon has had to deal with issues of non-coker silicon in naphtha’s since at least 2001. For background purposes, it is Marathon’s experience that silicon blocks the pores on hydrotreating catalyst and can impact catalyst activity. In severe cases, silicon breaks through to the reforming catalyst can occur where it can form silicon dioxide during the regeneration process which can cover the platinum sites.
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