Gamma scanning seeks an inside edge

Many companies decide not to build up certain capabilities in-house mainly because they don’t have sufficient regular demand for them. Gamma scanning of distillation columns is a case in point, but on-site scanning specialists may be the wave of the future.

By Mike Spear, editor at large

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Much of the outsourcing now so prevalent in the chemical industry reflects simple economics. Some outsourcing decisions, however, stem more from a lack of internal expertise to tackle the task at hand. Many companies, obviously after considering costs, decide not to build up certain capabilities in-house mainly because they don’t have sufficient regular demand for them.

Gamma scanning of distillation columns is a case in point. A widely accepted process diagnostic tool for a couple of decades now, this technique originated back in the 1960s, when the then Imperial Chemical Industries (now ICI), London, U.K., set up its Physics and Radioisotope Services group at its Billingham, U.K., site.

ICI, which has jettisoned many operations related to commodity chemicals over the past decade or so, doesn’t have anywhere near as many distillation columns as when it was known as the “bellwether of British industry,” and no longer has its own in-house scanning capability. That was transformed long ago first into a group service operation and then in 1986 into the international service division, Tracerco, Billingham, U.K., and Pasadena, Texas, offering commercial gamma scanning and other radioisotope tracing and process diagnostic services. ICI divested itself of Tracerco in 2002 when it sold its catalyst operation Synetix (of which Tracerco was the services arm) to Johnson Matthey, London, U.K.

With the notable exception of Eastman Chemicals, which has a scanning team based at its headquarters in Kingsport, Tenn., chemical companies and refiners today rely primarily on a small number of scanning service companies that can bring their expertise to bear on troubleshooting or monitoring the performance of columns.

Tracerco solidified its position as the major player in the field by last year acquiring Quest TruTec from Koch Industries. Other scanning companies include Quantum Technical Services, Houston, Texas; Nuclear Scanning Services (NSS), Houston; Gamma Surveys, Lafayette, La.; TowerScan, Windsor, Ont.; and Scanning Technologies, Edmonton, Alta.

All of these companies use gamma scanning to perform on-line troubleshooting, optimization and predictive maintenance of trayed or packed distillation columns — without interfering with the process or tower internals in any way. For instance, the density profiles generated in scans can identify damaged trays and packing, liquid maldistribution, rate-related problems such as weeping or entrainment, and process problems such as fouling or foaming.

The basics

In simple terms, scanning involves positioning a sealed source of gamma radiation on the outside of one side of a column and a suitable radiation detector directly opposite on the other side. Radiation from the source, usually Cobalt 60 or Caesium 137, is focused through a collimator in the sealed source holder toward the column wall. The gamma rays penetrate the wall and are absorbed to differing degrees as they pass through column internals and process liquid and vapor, emerging through the opposite wall to be picked up by the detector. Simultaneously moving the source and detector up or down the column produces a scan of transmitted radiation intensity at different levels, which to the expert eye shows what’s actually happening inside the column.

“The technology is quite similar, because you’re not going to alter the laws of physics on which it’s based,” notes Mark Gledhill, president of TowerScan. Having started with ICI in 1989 and run the Tracerco operation in Canada before setting up TowerScan in 2000, Gledhill has had his expert eye fine-tuned on “probably two to three thousand scans over the years.”

Chuck Winfield, another ICI alumnus, founded and ran TruTec before starting up Quantum Technical Services three years ago. “At Quantum,” he says, “I have some of the old hands that started with me at TruTec. They have spent over 20 years scanning towers and looking at the graphs. That’s what we bring to the table — experience. It’s becoming a key for scan companies.”

“There’s something to be said for having someone on-site with 15 years or more experience,” agrees Greg Fox, president of NSS, pointing to the service records of his own staff. “Column scanning is different to other services,” he explains, “because there is an interpretation skill to it. You have to be aware of what affects readings — it may be something internal to the process, flooding or foaming for instance, or it may be something mechanical like tray damage.”

Winfield makes a similar point: “To be an effective scan engineer, you have to combine the scan with your knowledge of distillation and the particular process — put that all together and make your call, particularly in cases where the problem might not be something obvious like tray damage or flooding.”

Educating process engineers

In most cases, the common practice throughout the scanning community is to make that call following discussion of the scan results with the customer’s own process engineers. “We always tell the customer,” says Don Carriere, Scanning Technologies’ president, “we will get the data, but we can only interpret it based on the information you give us. You’re the experts on your process.”

However, those process experts within client companies tend not to be around for very long, lament most of the scanning companies. “The biggest problem with gamma scanning is education,” notes Carriere. “We deal with process engineers coming through [the client company], but in three years they could be gone. And if their replacements coming in haven’t seen a gamma scan, then we have to start all over again.” Over at NSS, Fox relates the same experience: “Sometimes the engineers we deal with on the plant are fresh out of college, and they might never have heard of scanning. We interpret the results and sit there with the customer and try to understand what’s happening. Often it’s a two-way street, but we don’t get people disagreeing with what we say very often.”

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