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What are the main impacts, advantages and disadvantages of co-processing coker naphthas in diesel hydrotreating units and VGO hydrotreating units? According to operating conditions, catalyst activity, feed properties, LHSV, residence time, vaporization in the reactors, which the preferred way to co-process coker naphthas - DHT or VGOHT?
 
Answers
13/08/2020 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
It depends on a lot of different factors. Is the naphtha going to be reprocessed in an NHT or does it have to meet catalytic reformer feed specs straight off the DHT or VGOHT? If it has to meet reformer specs, it's possible that meeting the naphtha specs will control the hydrotreater reactor temperature, which will dictate runlength. This is especially a concern if the VGOHT product is not very low in Sulfur content. You also need to consider the Silicon tolerance of your catalyst and how that will impact runlength along with the impact of the increased rate/increased LHSV. Coker naphtha has significant Si, which will reduce catalyst activity and can shorten runlength (depends on whether Temperature or reactor DP sets your R/L). Suggest you get with your licensor/catalyst supplier to get them to do some yield and runlength projections for both options.
11/08/2020 A: keith bowers, B and B Consulting, kebowers47@gmail.com
'Coker Naphtha' is much more difficult to treat to the same quality as straight run naphthas. This is because there are sulfur compounds, nitrogen compounds, and unsaturated compounds that are much more difficult to hydrogenate. Usually a higher hydrogen partial pressure is a key process variable. A 'normal' naphtha hydrotreater is not capable of achieving the necessary conditions.

The best choice for hydrotreating coker naphtha depends on the rest of the refinery capabilities and the refinery operating optimum. This is not a 'stand-alone' answer. The expected catalysts performances and lives must be considered carefully by consultation with their vendors.

A simple generic statement is 'coker naphtha is much more difficult to hydrotreat to quality levels equivalent to those of straight run naphthas. Higher operating and hydroen partial pressures are required and catalysts must be formulated to higher activity and fouling resistance. Hydrogen consumption will be a multiple of that required for straight run naphthas. Run lengths will suffer compared to straight run naphtha operation. Greater fouling of heat transfer surfaces will take place. Corrosion control by use of additives will be necessary

The best processing configuration will be different for an existing refinery than that of a new or major retrofit consideration.