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Hoekstra war stories

In the past two years, there have been many field failures in ultra-low sulfur diesel (ulsd) hydrotreaters. By field failures we mean short cycles of less than half the expected cycle life. The root cause of these failures was overestimating what a catalyst can do in a hydrogen starved unit.

For example, one unit experienced a cycle life of just 1 year versus an estimated 3 year life on a very expensive catalyst. After two more short cycles of less than one year on other expensive catalysts, a new catalyst supplier was brought in with no better results. After recognizing that the unit was actually hydrogen starved, the unit is now being managed against the known hydrogen constraint. Hydrogen supply has been supplemented, more difficult feeds are being processed, cycle life of 18 months has been achieved, and catalyst cost has been reduced by $2 million per year.

The same basic story of overpromising on catalyst performance occurred in five other known cases last year. Three of those were in refineries that have since been shut down for poor economic performance.

These stories, and other war stories of success and failure in the field, have been told first hand by those directly involved during semi-annual gatherings of the clients of Hoekstra Trading’s independent catalyst testing program.

Some expensive catalysts that are very good for ulsd at high pressure are not good at all at low pressure. This sensitivity to pressure is very important when choosing catalysts for low pressure units. It is also important for high pressure units that experience periods of hydrogen starvation due to frequent unit upsets, difficult feeds, or unreliable hydrogen supply. Such units often do not realize the expected benefits of the most expensive high activity catalysts.

It is increasingly common for refiners to push their units to their limits when making ulsd. High end point feeds, syncrudes, visbreaker, and coker distillates are very profitable feeds for ulsd production, but they contain more difficult sulfur, nitrogen, and aromatics. These feeds can usually be handled profitably in controlled concentrations with moderate increases in reactor temperature; but there is a threshold concentration above which no ulsd catalyst will do the job.

When units are pressed to their limits with difficult feeds at low hydrogen partial pressure, desulfurization is constrained by aromatics saturation equilibrium. At this point, increasing reactor temperature actually reverses desulfurization reactions leading to a death cycle.

Today’s high-performance catalysts are excellent investments when your unit has the horsepower to use the kinetic capacity they provide. But when your unit is going to operate near a feed-stressed or hydrogen starved condition, it is better to choose a catalyst that performs well at low pressure and take steps to manage the hydrogen constraint, rather than buy your catalyst supplier’s latest hot product.

Other Literature

Hoekstra war stories

In the past two years, there have been many field failures in ultra-low sulfur diesel (ulsd) hydrotreaters. By field failures we mean short cycles of less than half the expected cycle life. The root cause of these failures was overestimating what a catalyst can do in a hydrogen starved unit.


Cycle life estimates for catalyst reload vary from 7 to 44 months

It is very difficult to accurately predict the cycle life for a hydroprocessing unit. This is especially true with today’s highly variable feed slates. Despite this fact, catalyst suppliers are always asked to estimate cycle life when bidding for a catalyst reload, and they comply with the request ...


High aromatic/nitrogen feeds cause rapid initial deactivation in pilot plants

A feed sent to C Solutions in Thessaloniki, Greece caused catalyst to deactivate very rapidly when introduced on day one of a pilot plant run.  Analysis showed the feed to be full of high boiling aromatics and high in nitrogen. The pilot plant run was restarted with the usual 3-day break-in ...


Hydrogen-starved unit struggles to make ULSD

This is a 36 bar (525 psig) unit that was converted to ulsd service. The first two cycles used Albemarle KF-757 and lasted 6 months compared to one year expected cycle life. They switched to Topsoe catalyst for the next cycle and saw no improvement.

Two suppliers recommended replacing ...


Refinery weighs proposals for 10 ppm diesel

This refinery wanted to make 10 ppm diesel in blocked out commercial trials as preparation for upcoming diesel specifications. Some catalyst vendors said the refinery would need to double the reactor volume to make 10ppm. Other vendors said they had a new drop-in solution, a catalyst that will do the ...


Sulfur speciation analysis helps with feedstock management

Cycle life for successive runs on this diesel hydrotreater has varied from 6 to 18 months.The cycle history was analyzed to assess the difficulty of processing varying feeds. Sulfur speciation analysis enabled measurement of difficult sulfur in the feed components. The unit’s cycle life was found ...