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Grading is great - overgrading is not

23.08.2019

Grading layers

Getting the most out of what you’ve got

Grading is all about getting the most out of the all-important bulk catalyst in your reactor setup. The right grading configuration is the most effective “preventive measure” and the ultimate adjustment knob.

It’s a question of balance, of exploiting the full effectiveness of the bulk catalyst you’re using, and using grading to protect it from contamination and blockages that lead to costly pressure drop or premature catalyst deactivation.

Too little grading – not enough protection

If you don’t load in enough grading (with the right specifications and configuration), you won’t be able to filter out all the nasty stuff in the feedstock – and your bulk catalyst will quickly become contaminated.

With insufficient and/or ineffective grading, you’ll probably end up having to carry out an expensive shut-down way too soon.

Too much grading – not enough benefit from your bulk catalyst

Conversely, with the kinds of feedstocks that many refineries now have to deal with, e.g. renewable feedstocks or opportunity crudes, featuring large amounts of contaminants difficult to deal with, we see a growing tendency to use more and more grading as a protective measure.

But if you use too much grading, you’ll end up missing out on the full potential of the unit, as the excess grading material takes up the space from the bulk catalyst.

Your grading load should help you:

  • Provide a stepwise increase in activity to control the hydrogenation of more reactive components present in the feed
  • Make sure all feedstock contaminants are removed
  • Make sure any corrosion products from upstream equipment are removed
  • Control exotherm
  • Prevent catalyst milling
  • Prevent crust formation
  • Prevent pressure drop problems

Finding the right balance for your exact needs

If you are processing an easy straight run and there are no obvious corrosion issues, there is no reason for grading material to take up space that you can put to better use for the workhorse in your reactor – the bulk catalyst.

Optimized grading

In order to get the maximum cycle length out of your catalyst loading, the right balance between bulk catalyst and grading is crucial. If too little grading is loaded, the cycle will be shortened by premature catalyst poisoning or too high pressure drop (top). If too much grading is loaded, the unit will be limited by activity of the bulk catalyst before the grading capacity has been fully utilized (middle). With the right balance, you obtain the optimal (bottom).

It’s all a question of balancing the specifics of your operation’s particular feedstocks, budgets, practical challenges, and operating profiles. Our aim is to enable you to maximize catalyst cycle length and make sure the pressure drop across your reactor doesn’t limit throughput until the activity of the bulk catalysts has reached the scheduled End-Of-Run (EOR).

ARTICLE Avoiding unplanned reactor shutdowns

Full-spectrum expertise

It takes considerable specialist know-how to determine exactly how much and which kind of grading you need for each loading, and how to balance all of the many different requirements and considerations.

We’re probably the only company that can provide you with the full spectrum of expertise, equipment solutions and both grading and bulk catalyst products, and can therefore provide you with unbiased advice. We know from experience that this can – unfortunately – be difficult to get if you source your grading and bulk catalysts from different suppliers.

When grading is not enough

If the quantities of contaminants in the feedstock require a substantial grading load to filter them out, the grading can end up taking up too much of the limited space inside your reactor. But you can easily tackle situations like this by installing Topsoe scale catcher systems above the catalyst itself.

Haldor Topsoe pressure drop control process offering

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