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Active filtration beats iron fouling problem (TIA)

For hydrocarbon processors, the goal is always to achieve the optimum catalyst reaction and hold it as long as possible.

Chris Alexander
Crystaphase Technologies
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Article Summary
Problematic feedstocks can throw a wrench into the process and profitability of any reactor. Foulants accumulate in the bed, creating pressure drop issues and shorter cycle times. The trick to mitigating the problem is not only identifying the contaminants, but how and where they accumulate. While that sounds logically straightforward, it is not.

Consider the case of a unit on the Gulf Coast. Beleaguered for years by pressure drop issues, engineers had been unable to identify the problem. The filtration system installed above the main catalyst bed had little effect, and the unit was stuck in a 12-month production cycle. After installing specialised reactor internals, catalyst was added atop the distribution tray. Suddenly, the fouling rate doubled, reducing the cycle time to six months.

Late in the skim, the refiner contacted Crystaphase, seeking a solution to the problem. Crystaphase identified the offending foulant as iron sulphide, which is fairly common in reactors but, in this case, had entered the reactor in the form of soluble iron naphthenate, enabling the iron compounds to completely bypass the filtration system. Crystaphase had hypothesised iron was migrating in this soluble form before precipitating in the catalyst bed. To confirm this, the company took samples back to its lab for an overnight analysis.

Scanning electron microscopy (SEM) confirmed the theory that the iron sulphide was a precipitation problem, not a particle problem (see Figure 1). Because the refiner had, at the previous changeover, inadvertently added high activity, main bed catalyst above the distributor tray, Crystaphase was able to identify the problem.

Since the skim was already in process, a partial solution based upon limited space availability was implemented using an active filtration system. It would induce a chemical reaction prior to inert filtration, removing the precipitated iron sulphide before it reached the catalyst. Under this configuration, Crystaphase predicted the unit would run 10 months and 15 days. The actual shutdown date was within three days of that prediction.

At this change-out, Crystaphase was able to completely reconfigure a new solution built around the precipitation issue, comparing comprehensive data from both shutdowns. This optimised configuration would include an active filtration system above the inert filtration system. This solution, ActiPhase, enabled the unit to achieve a 16-month production cycle.

This was the longest cycle the reactor had achieved in 10 years, and the first time in 16 years that the shutdown was for activity, not pressure drop. During the changeover, Crystaphase was able to make additional adjustments for optimisation in dealing with precipitated particles, which then resulted in a 24-month cycle — four times longer than its lowest performance of six months (see Figure 2).

For refiners, active filtration has increasingly proven to be an effective solution, particularly with the prevalence of high TAN VGO feedstocks. Crystaphase has since developed a line of solutions designed to 
filter dissolved iron and other soluble particles that 
can poison catalyst beds and choke reactor performance.

This short case study originally appeared in PTQ's Technology In Action feature - Q4 2015 issue.
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