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High-efficiency filtration extends SRU cycle length (ERTC)

At a facility in the heart of Western Europe, engineers had all but resigned to their fate: every 60 days, they would have to 
take down a whole section of their operation just to change out their sulphur recovery unit.

John Burwell
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The de facto standard procedure was to load their Claus reactor with ceramic spheres for filtration. After countless cycles of trial and error, engineers had 
settled on a grading system of 6.4 to 12.7mm spheres. The bed of spheres was already as deep as they could manage; any deeper would cut further into valuable space for catalyst. Besides, it was unclear if a deeper bed would help. Sixty days seemed like the most they could get out of the unit, whatever they tried.

The attitude toward this unit had long been ‘cheap and fast,’ but pressure on the engineers was rising. The SRU was not a profit centre for the company, yet it was absolutely essential to the operation. Other units simply could not run without the SRU. Everything depended on it. Desperate for relief, one engineer set out to find a better way.

Since this company was not strictly in the petroleum or petrochemicals sectors, its engineers were not already familiar 
with the wide reputation of CatTrap technology for controlling pressure drop and extending reactor cycles. But when an SRU case study on seemed far too familiar, the engineer contacted Crystaphase.

At the very next changeout, which wasn’t far off, the company collected samples of the previous loading and sent them to Crystaphase for analysis. In their foulant lab, the company’s technicians found carbon soot deposits in the catalyst bed. It was an answer that raised a question: how was the soot breaking through? Turning to particle size distribution analysis, technicians discovered the culprit: the particles were too small to be captured efficiently by the spheres. The sphere filtration system was, in effect, useless.

The composition and morphology of the foulant, and the apparent depth of the crust layer, indicated a need for a filtration system with a high particle storage capacity. And with the limited space available, high storage efficiency would be the key to unlock longer cycles.

For a high-efficiency filtration system that could hold a high volume of particles, Crystaphase recommended a system based on CatTrap. The company loaded 
it, started up the unit, and began 
gathering data.

After 30 days, historically the first indicator of trouble – pressure drop had yet to climb. Sixty days came and went, and pressure drop remained steady. Another month went by, and then another. Not 
until the fourth month did pressure 
drop begin to rise. The cycle length 
had doubled.

The concept was proven, so the engineers went back to Crystaphase for another round. Further study revealed further optimisations to make. Today, the current cycle is well on its way to six months of uptime, if not more.

Relief once seemed beyond hope, but with the CatTrap system installed, the SRU was going far beyond expectations. Sixty-day cycles turned into six-month cycles. Changeouts fell from five per year to fewer than two. Plant-wide operations improved. The whole facility became 
more profitable, with lower costs and higher uptime.

As for the engineers, they could finally stop dreading their next SRU changeout, and start looking forward to their company’s next big thing. ν

Did you know: Crystaphase can double of triple cycle lengths for more than just Hydroprocessors?

This short article originally appeared in the 2017 ERTC Newspaper, produced by PTQ / DigitalRefining.

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