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MAINTAINING and replacing the tubes, pipes, and brackets used in traditional process analytical sampling systems can take a lot of time. Just saying it can be a mouthful. Technicians have to check drawings, disassemble the system, remove worn or faulty parts, bend new tubes, rethread pipes, check fitting unions, coordinate I/O components, remount brackets, and complete other application-specific tasks. These jobs typically take two to four hours or more, and even then breaking and reinstalling seals can damage their surfaces, and cause chronic leakage problems.
So, it’s no wonder that process analytics users long sought a way to make sampling systems easier to repair and reconfigure. However, even though some found and developed a modular solution that allows them to switch out a regulator in 60-90 seconds and doesn’t leak later, making it a mainstream reality has produced some unforeseen delays and technical snags on the way to the desired happy ending.
Analyzers were first added to industrial process systems in the 1940s, and they’ve progressively evolved from bathtub-sized enclosures into smaller, less intrusive, intrinsically safe packages. However, it wasn’t until the late 1990s that some process analytics users, reportedly from U.S. refineries on the West Coast, observed uniform, surface-mount components being used in semiconductor processes, and reasoned that their sampling systems could use a similarly standardized strategy. These semiconductor components include 1 1/8-in. gas sticks and metal o-rings used that help measure gases used in semiconductor manufacturing.
These users formed the New Sampling/Sensor Initiative (NeSSI) with help from the Center for Process Analytical Chemistry at the University of Washington in Seattle. The group’s initial, surface-mount strategy was adapted for oil, gas, and chemical processing applications by the ISA’s SP76 committee, and became the basis for the international ANSI/ISA-76.00.02 standard for sample flow control, conditioning, and analysis, which was released in 2002.
The modular standard requires compliant sampling systems to be built onto a standard substrate from closely-joined, 1.5-in-square manifolds with 0.110 sample-transfer ports, which are attached with four Allen wrench screws. These “metal Lego blocks” allow users to switch out components from different manufacturers without having to switch out a whole sampling system.
Another of NeSSI’s physical advantages is that it can perform all same functions of a 30x60-in. legacy sampling system in a 16x20-in or 12x16-in space. This can add up to a lot of savings in refinery that may have dozens or hundreds of sampling systems, and where a square foot might be worth $1,000, depending on its location. In addition, a 1-sq-ft legacy valve system can be replaced by a 1.5x3x3-in NeSSI valve.
“I’ve been working with sampling systems since 1969, and NeSSI is the biggest advance in process analytics in the past 50 years,” says Bob Sherman, an ISA fellow and industry specialist for process analytical systems at Circor Tech, which manufactures modular, NeSSI-compliant devices. “Whenever people move from legacy sampling systems to modular substrate systems, they find they can optimize filters much more easily, for example, and achieve many new and far more efficient capabilities.”
|FIGURE 1: STUDENTS’ SAMPLING SYSTEMS|
Student teams had 45 minutes to use a box of substrate components, including Circor Tech’s µMS³ modular substrate sampling system, to assemble this and other functional modular sample conditioning system during ISA Expo 2005’s International Student Games in Chicago.
“NeSSI is cheaper to build and cheaper to own. Its reliability is greater, and it delivers more operating and safety credits than traditional analyzer systems,” says Jeff Gunnell, lead specialist for process analytics at ExxonMobile in the U.K.
The Communications Race
Since it was first conceived and started development, NeSSI has been organized into three successive generations. Generation 1 covers the mechanical components, which were first available in 2001-02. These include flowmeter switches, regulator valves, filters, and other devices. Dave Veltkamp, senior research scientist at CPAC, says NeSSI’s emergence has helped reinvigorate the fittings companies, such as Swagelok, Parker Hannifin and Circor Tech, which modified traditional valve systems to serve in surface-mount settings, and also began making the substrate onto which the surface-mount components fit.
Generation 2 covers and is seeking to define how electrical signals and power are delivered to NeSSI devices. These tasks include how NeSSi should build multidrop networks and how to communicate temperature and pressure signals. However, the biggest stumbling block has been how NeSSI should define its communication network. Several candidates have been evaluated, and each is developing the necessary modifications to be used in NeSSI sampling systems.
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