refiners struggle to find the right balance between runlength reliability and unit performance.

On one extreme of the spectrum, refineries can lose a significant amount of profit their catalyst beds deactivate too quickly.  Sometimes unplanned shutdowns are required to dump and re-fill catalyst beds.  Othertimes, unit run-rates need to be reduced to reach a planned maintenance window.  Either way, these mitigating steps cost money, and often scare process engineers into being too conservative with catalyst runlength projections.

There are 3 main components required to develop the right catalyst fill and runlength management strategy for a hydroprocessing reactor. 

• Understand the runlength requirement
• Establish proper deactivation monitoring tools
• Define a prioritized list of catalyst activity management handles

Each of the three components above require in-depth collaboration between multiple groups within the refinery, thus failure to maximize the value of each catalyst load results from a gap in communication.

“failure to maximize the value of each catalyst load

results from a gap in communication”

Let’s start with the first step of understanding a reactor’s runlength requirement.  This will depend on the type of hydrotreating service and the refinery configuration.  Some reasons why hydrotreater catalyst runlengths may require precise management include:

• hydrotreater operations required to operate critical downstream units within the refinery (i.e. Reformer)
• cycle times of upstream unit shutdowns fall within specified periods (i.e. pairing FCC gasoline post-treater with upstream FCC Unit)

In either of the scenarios above, premature catalyst deactivation may result in an unplanned unit shutdown, thus mis-aligning the refinery turnaround strategy.  Therefore, it is absolutely critical that a process engineer procures sufficient catalyst activity to meet the runlength requirement in the scenarios above.  It is often common practice to build 10% contingency in the catalyst fill activity. 

There are some hydrotreater services that are not critically paired with upstream or downstream units, thus sub-optimal runlengths do not have dire consequences.  This may result from a refinery having sufficient intermediate inventory storage capacity, or parallel reactors that can be changed out while the unit is online.  These are the most ideal situations as engineers can truly optimize runlengths with limited downside risk. 

temperatures of reactors beds over time, but should normalize the different factors of feed qualities and unit operating parameters.

Normalization is critical as this ensures that engineers can differentiate routine catalyst deactivation from other drivers of higher reactor severity, such as aromatic saturation or lower unit pressure.  As activity normalization is a detailed topic on its own, I will cover this in a subsequent article.

The most active part of hydroprocessing catalyst activity management is changing operational handles during the runlength.  While the first two steps require collaboration with refinery planning analysts, runlength management requires constant communication with planning analysts as market conditions change frequently.  There are some variables that have high cost during parts of the year, while other parts of the year they do not cost anything to implement. 

To properly manage activity during the run, an engineer must define all of the handles available for use.  Let’s take the example of a diesel hydrotreater in our scenario, and lets imagine a hypothetical where we are 18 months into a 24 month run. 

If we’ve determined from our catalyst activity monitoring tools that we have excess activity beyond our target end of run date, then we can consider the following handles to improve operational efficiency or increase profit capture:

• Increase unit feed rates by increasing diesel endpoint
• Increase processing of challenged feedstocks, such as Coker Light Gas Oil (CLGO) or FCC Light Cycle Oil (LCO).
• Reduce hydrogen partial pressure to save energy or improve hydraulic capacity

 Sure, many of the handles above have risks, but they are not as risky as many believe if the adjustments are made in small incremental steps and monitored appropriately. 

Planning analyst involvement becomes critical when determining which operational handles to optimally adjust.  In the scenario above it may be more economic to trade off diesel endpoint in preference of processing more LCO.  For a FCC feed pre-treater, a planning analyst may be able to advise that selling High Sulfur Gasoil as opposed to reducing hydrotreating severity is the preferred option.  Whatever the situation, an engineer alone should not make the decision on which handles to utilize without getting feedback on all of the refinery implications.  Beyond typical seasonality impacts on the market, there may be unplanned local events that come into play.

At the end of the day, a refinery can increase profitability by properly monitoring hydroprocessing catalyst activity and making operational changes to utilize excess runlength.  We can minimize financial risk by making small changes and actively monitoring these changes. 

In the event that catalyst deactivations takes a turn in the wrong direction, a refiner can just reverse the handles used to consume catalyst activity.  Since catalyst activity is often a zero sum game (unless we are in the regime of accelerated fouling), the economic gains and losses are offset as long as a refinery minimizes catalyst activity giveaway.

In the grand scheme of things, catalyst costs are still relatively cheap compared to the margin capture that they enable.  Even for hydroprocessing reactors that do not have stringent runlength requirements, it often pays off to utilize your catalyst to the maximum capability allowed.