Emerson Exchange 365

Fluidized bed reactors combine hydrocarbons and air through a powdery solid catalyst to produce useful chemicals, as well as a lot of heat from the resulting chemical reaction.  Water is pumped through coils immersed in the reactor bed, which is hot enough to produce many thousands of pounds of superheated steam per hour for use by the plant and neighboring refinery. 

A water or steam leak from a coil inside a reactor can damage the catalyst and require a lengthy shutdown, costing millions of dollars in lost production in some cases.  These leaks happen rarely, but as John Rezabek of Ashland Chemical Company will explain this week at the 2014 Emerson Global Users Exchange, they can wreak havoc when they do.

After process specialists found a pinhole leak in a coil during a scheduled shutdown at one of Ashland’s plants, they took x-ray images of the piping inside the affected reactor.  The images showed that deposits had built up in some of the coils, but it wasn’t immediately clear how or why.  There were few clues as to how many of the coils were becoming restricted, or how fast.  

“We wondered if another unplanned shutdown was around the corner, or if we could maintain until we were prepared to make some changes,” Rezabek says.  “We had to find a flow measurement solution that could detect any significant variance in flow through the coils once we restarted the reactor, and we had to find it fast. There were no flanges or root valves in the superheated steam headers or passes. In short, we needed a miracle flow measurement.  So we called Emerson.”

The steam lines have no flanges where they enter the reactor vessel—there are no process connections of any kind and no places to easily insert orifice plates.  The extremely high temperature of the superheated steam ruled out ultrasonic meters, and engineers decided that using hot-tap Annubar meters was too risky.

“After considering a range of potential solutions, it was looking like our best bet might be the wireless Rosemount 708 Acoustic Transmitter,” Rezabek continues.  “We weren’t sure whether the 708 would be able to ‘hear’ the flow accurately enough, but time was of the essence so we pressed on.”

The transmitters started arriving a week after Rezabek’s team submitted the purchase order.  They were able to configure the devices before they mounted them, which was very helpful because the mounting locations were hot and difficult for crews to access.   Crews also installed Rosemount 248 Temperature Transmitters on the steam headers using pipe clamps where the temperatures were too high for the 708.

“We installed and commissioned the entire system in two weeks,” Rezabek says. “Once it was up and running we discovered that the acoustic signal levels from some of the steam lines were ‘noisy’ and some weren’t, but changes observed in individual coils revealed where flow was being restricted.  We used the temperature differential to single out problem areas and quantify whether blockages were getting worse over time.”

“Within a matter of days the new instrumentation was fully functional, and in the ensuing weeks and months gave our management the data it needed to make an informed business decision about when to schedule an outage for cleaning, inspection, and repair of the reactor coils, which saved us money and time in the long run.  The flow monitoring ‘miracle’ we hoped for came true.”