Hydrocracking catalyst needs to be passivated during sulfiding to avoid potential temperature runaway as temperatures are increased to complete the sulfiding process. In our experience, there are four different ways that we attenuate the catalyst activity. The first is to inject ammonia prior to the high temperature sulfiding to passivate the catalyst.

Our experience at Valero has been that turbines are more reliable than electric motors. For electric motors, the failures are not caused by the motor itself, but rather by the availability of electric power. Power failures tend to be the most common concern.

During emergency feed removal or partial feed loss of a hydroprocessing unit, the loss of feed oil as a heat sink through the feed/effluent exchangers can elevate temperatures downstream. Expected temperatures can be estimated through process modelling of normal maximum reactor effluent flow continuing at maximum reactor outlet temperature without feed flow through the reactor effluent cooling train.

As we have all probably experienced, efficient and reliable unit operation can benefit significantly from the application of advanced process control, or APC. For example, most hydrocracking units have implemented some level of advanced control to stabilize fractionation operation or control conversion. Advanced control projects typically pay off very quickly. In the past, the industry has typically focused on implementing advanced process control to optimize one aspect of a processed unit.

The first one is our hydrocracker where we do both straight-run and coker gas oil. What we watch for there are changes in the feed composition due to the cyclical nature of the coker and the affects that we see in the hydrocracker reactor in the fractionation section because of that.

At Flint Hills Resources Pine Bend Refinery, external ultrasonic testing is performed on areas of concern (welds, heat-affected zones, attachments, or identified stress risers) every five years. To date, no areas of concern have been identified in the PSA vessel inventory.

My analysis suggests that this kind of a modification is not economically justified for the small solvent system hydrogen production unit operating at the Flint Hills Resources Pine Bend Refinery. While it is true that a PSA unit is more efficient than a solvent unit, the capital required to convert between the two is too high.

Frequently, market conditions will reward the refineries that have a little flexibility in shifting their product yields among conversion units. We try to do that where that flexibility exists. For a hydrocracker, a primary knob is just overall conversion. Decreasing conversion will enhance distillate yield, increasing conversion, gasoline yield.

It can be a short duration, one to two days, or potentially longer, 21 to 30 days, depending on the response to the events and dependent upon the amount of higher severity feed, higher nitrogen, and higher aromatic content feed. It could be a shorter duration if quickly caught and corrected.

Fundamentally, conversion is probably the most common operating target used for hydrocracking units. Conversion provides us with a measure of the amount of reaction or the amount of work that is accomplished in the unit. The simplest definition for conversion is typically this equation for gross conversion: a hundred times the fresh feed minus the unconverted oil, divided by the fresh feed; unconverted oil being the recovered fractionator bottoms.