Q&A

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(2011) Question 7: Are there any standard sampling and analytical methods that can be used in the refinery labs to accurately determine the silicon content in the feed to the coker naphtha hydrotreater?

The issue is how to accurately determine the silicon content. Standard Inductively Coupled Plasma (ICP) techniques will give a result that is equal to or greater than the true amount of silicon present depending on if the silicon is in a volatile form (low molecular weight silicones). So, ICP can be used to screen samples and ensure silicon levels are below a desired limit.

(2011) Question 8: In order to minimize fouling of the hydrotreater reactor feed/effluent exchangers, how important is it to have hydrogen gas in the feed side of the exchanger? Is there a minimum gas flow to see the benefit? Does it matter if it is recycling gas or makeup hydrogen?

Pre-mixing hydrogen with feed ahead of the feed/effluent exchangers improves the velocity and increases the shear stresses. This directionally reduces the fouling tendency; as well as, lowering the film thickness and dependent tube wall temperature in the heat exchanger and the charge heater.

(2011) Question 9: What has been your experience with antimony and phosphorous poisoning on hydrotreating catalyst performance? What is the maximum level?

The effects of antimony in oil on hydrotreating catalyst have not been directly studied, but we can infer the likely impacts of antimony from a variety of information sources and past experiences.

(2011) Question 10: When replacing a noble metal catalyst with a base metal catalyst in a two-stage hydrocracking unit configuration, how can you be certain that under a low sulfur, low hydrogen sulfide environment, the second stage catalyst will remain sulfided?

A base metal sulfide catalyst will always have less, or hydrogenation compared to a noble metal catalyst. However, in certain situations where deep hydrogenation is not needed, the base metal sulfide catalyst can provide adequate hydrogenation activity. Operation with a base metal catalyst will be between 10 to 20o F higher than a noble metal catalyst, and this will shift the yield towards more thermally cracked lighter products.

(2011) Question 11: What is the minimum hydrogen sulfide required in the recycle gas for units with low sulfur feed? Do you inject sulfur compounds to maintain a minimum concentration?

It appears that in these processes the catalyst slowly loses its HDS activity. This is due to the transformation of the Molybdenum present as activator, and Nickel/Cobalt present as promoters, from their active sulfide form to the inactive metal state.

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Q&A

(2011) Question 7: Are there any standard sampling and analytical methods that can be used in the refinery labs to accurately determine the silicon content in the feed to the coker naphtha hydrotreater?

(2011) Question 8: In order to minimize fouling of the hydrotreater reactor feed/effluent exchangers, how important is it to have hydrogen gas in the feed side of the exchanger? Is there a minimum gas flow to see the benefit? Does it matter if it is recycling gas or makeup hydrogen?

(2011) Question 9: What has been your experience with antimony and phosphorous poisoning on hydrotreating catalyst performance? What is the maximum level?

(2011) Question 10: When replacing a noble metal catalyst with a base metal catalyst in a two-stage hydrocracking unit configuration, how can you be certain that under a low sulfur, low hydrogen sulfide environment, the second stage catalyst will remain sulfided?

(2011) Question 11: What is the minimum hydrogen sulfide required in the recycle gas for units with low sulfur feed? Do you inject sulfur compounds to maintain a minimum concentration?