By Bob Sperber
Process analyzers havent changed much for more than a half century and neither have the pipes and fittings used to transport samples to and from them. Likewise, things didnt change much for Rajko Puzic, instrument engineer at ExxonMobils Imperial Oil Products and Chemicals Div. in Sarnia, Ont., Canada, for more than 27 yearsuntil he discovered a smarter mechanical mousetrap.
That mousetrap is the New Sampling/Sensor Initiative (NeSSI) that seeks to standardize sample transport, digital networking and breakthroughs in analyzer miniaturization. There are three parts, or generations, to NeSSI. Generation 1, defined by ANSI/ISA SP76.00.02-2002, specifies the modular layout of fluid-flow channels and mechanical fixing holes to connect 1.5-sq.in. modular components to a substrate. The ISA SP-76 working group is in the midst of a Gen 2 standard that will provide an intrinsically safe, digital NeSSI bus that will interface with Ethernet and/or existing field and device buses. Finally, a third generation focuses on providing a standard for developers in the emerging lab-on-a-chip and broader microfluidics and microelectro mechanical systems arenas.
Whats available today is a finished Generation 1, with products widely available in the marketplace. Even without the additional layers of standards, users are justifying their NeSSI investment based on sampling benefits such as streamlined design and installation, reduced space requirements and simplified maintenance. Imperial Oils refinery and chemical plant in Sarnia provide a testament to these benefits; of the roughly 500 process analyzers there, Puzic says at least 60% have been connected to NeSSI-based sampling systems in last few years. Other users validate this success.
Speeds Design, Fabrication
In a conventional sampling system project, the typical user might work with a designer to build a bill of materials, lay out the system and generate construction drawings, then send them out for bids. But using NeSSI components to design systems for a plant in Malaysia, Matt MacConnell, analyzer systems technology manager for Air Products and Chemicals Global Engineering outside Allentown, Pa., just worked with the supplier to build what I wanted, and once I got those drawings, I just sent those to the field contractor who interconnected the system.
MacConnell says he didnt have to buy 50 or 100 pieces. With these NeSSI systems, you can cut your bill of materials down to just one or two parts. It pretty much eliminates the designers time, he says.
As with any sampling system, users have to do their up-front engineering. But once they know their system requirements, any up-front price premium paid for NeSSI components is way overcome by cost savings in the fabrication alone, says Steve Jacobs, development associate chemist at Eastman Chemical, Kingsport, Tenn. Research he did some time ago showed NeSSI cuts $5,000 to $25,000 on fabrication alone, depending on the size of the installation.
Three companies currently supply substrates along with other components: Parker Hannifin; Swagelok; and Circor. Companies or end users can assemble the systems using dedicated software configuration tools.
The software is instrumental in reducing up-front design efforts. Circor bases its web-based (and downloadable) configurations on Microsoft Visio. All substrate suppliers offer roughly similar software applications to generate process P&IDs and schematic assembly diagrams automatically from the users bills of material. These software tools generally follow modern expectations by providing a graphical environment with libraries of components from substrate parts to flow indicators and controllers, pressure regulators, valves and pumps from major instrument suppliers.
Saves Precious Space
Users report that NeSSI sampling systems occupy 30% or less space than conventional systems, though there is wide variation because space might not have been a guiding factor in old installations.
Sample heating is more compact and efficient because each supplier provides modular components that directly heat the NeSSI substrate, as opposed to the using radiant heating on larger, conventional systems. Shrinking the footprint of systems also allows cold-climate plants to reduce the size of heated enclosures.
While sample systems dont typically determine the need for constructing analyzer houses, in some cases analyzers and sampling can be co-located with the sample, which is beneficial for space saving, among other things.
And boy, if you have to start dropping analyzer houses in, you start getting into some serious money, says Eastmans Jacobs. With most of these [NeSSI] systems, I can just wrap some environmental control around them or an enclosure if we need it.
In replacing a bunch of systems in one of Eastmans polymer processes, Jacobs replaced two panels measuring roughly 6 x 8 ft with one 3 x 4 ft enclosure that added a lot more functionality than the old system, including automatic sensing of flows, automatic back-flushing and cleaning where none of that existed on those other two boards. He adds that he would have had trouble trying to find a place to put it on the old system.
Tell me: How many refineries have been built in North America in the last 10 years? None, says Puzic, stressing the very precious real estate refineries sit on. He says a four-stream liquid sampling design could be shrunk from a 6 x 6 x 2 ft deep enclosure to something perhaps 10 times smaller, depending upon the space efficiency of an older design.
Lowers Volume for Better Results
Along with its smaller footprint, NeSSI systems greatly reduce piping. Less piping, a shorter flow path, lower dead volume, less liquid circulating in the lines all add up to high reliability and faith in sampling.