Faced with ever increasing competition on price for their products, chemical companies are constantly searching for ways to cut costs across their operations. This, in turn, puts persistent pressure on engineers to reduce both capital and operating expenditures — without compromising their plants’ reliability and performance in any way. Easier said than done, perhaps, but this is precisely what a new approach to the task of delivering process samples to analyzers actually delivers, claim its proponents.
Since coming into being some five years ago, the New Sampling/Sensor Initiative (NeSSI) has become the driving force behind the move to modularize and miniaturize process sampling systems. Now operating under the sponsorship and umbrella of the Center for Process Analytical Chemistry (CPAC) at the University of Washington, Seattle, NeSSI first surfaced as an ad hoc group of people drawn both from equipment manufacturers, keen to adopt the modular approach, and operating companies prepared to put the vendors’ prototype products to the test on their plants.
The initial concept was to build on a standard for modular surface-mounted systems developed for the semiconductor industry. This was modified for use in the oil, chemical and petrochemical industries by the SP76 working group of ISA, Research Triangle Park, N.C., and its resulting design became the basis for the ANSI/ISA-76.00.02 standard in 2002. This international standard lays down the specifications and dimensions for the sampling system substrate and the modular components — for sample flow control, conditioning and analysis — that plug into it. A modular sampling system along these lines consists of a series of close-coupled, 1½-in. square manifolds, each carrying one of the components fastened to the substrate with just four hex (Allen) screws.
Motivation for modular
Compared with traditional sampling systems, this approach seemed to offer significant savings. These were first quantified in 2000 by a team from ExxonMobil that looked at both the “cost of build” and “cost of ownership” of conventional process analyzer systems. Considering project data from around the company’s sites, the team concluded that 38% of the initial outlay was spent on the analyzer, 30% on the sampling system and 27% on providing a controlled environment or enclosure for these. However, if plants switched to the modular approach espoused by NeSSI, the team forecast that 40% savings could be achieved on the overall cost of build by reducing the expenses for the sample transport and conditioning system and eliminating the need for climate-controlled housings. Moreover, it projected a 35% saving in the cost of ownership through a combination of reduced sample volumes — and therefore smaller volumes of carrying and purge fluids — and easier maintenance and support, requiring fewer technicians (or enabling more analyzers to be supported per technician).
Jeff Gunnell, lead specialist for process analytics with ExxonMobil Chemical Company at Mossmorran, Fife, Scotland, was part of that seminal team that helped start spreading the NeSSI message. Asked where the initiative is now, he says: “After the field experiences with ‘Generation I’ NeSSI systems, we now have a solid platform to build on. There has been one round of iteration [in design] since 2001 and I would say the systems have been shown to work fine in the field within a realistic operating window.”
ExxonMobil has a total of 30 modular systems installed across several of its major locations (on two sites at Baytown, Texas, and at Sarnia, Ontario), sampling a variety of hydrocarbon process streams. The systems are currently approaching approval as “Best Practice” within ExxonMobil and that, says Gunnell, “means we are considering them for some major projects — and that could be huge numbers of systems.”
ExxonMobil’s modular sampling systems have come from two of the three main vendors involved in supplying the substrates and other flow components for ANSI/ISA-76.00.02-compliant systems. These are the Instrumentation Division of Parker Hannifin, Jacksonville, Ala., and Swagelok, Solon, Ohio, with Circor Instrumentation Technologies, Spartanburg, S.C. rounding out the trio.
All three companies have been making steady inroads into the process analytical market with their respective systems, reporting a doubling of sales each quarter at a recent CPAC/NeSSI workshop in Seattle. Commenting on the meeting, Swagelok’s manager for marketing resources, Dave Simko, says: “There is a consensus that NeSSI has arrived. Those companies using NeSSI systems have shown that the cost savings are real. Although component cost is higher, savings in design time and manufacture give a net saving — 30% lower in terms of overall cost.”
Swagelok’s MPC (Modular Platform Components) system (Figure 1) consists of a range of fluid-control components — such as shut-off, needle, metering, toggle and check valves, as well as filters — mounted on top of a substrate layer of 1½-in.-square modules containing specialized channel and flow components. Describing one of the first demonstration systems, Simko explains: “One system, which measures ppm H20 and O2 in a high-purity hydrocarbon stream, was built to demonstrate that the modular concept was feasible and practical. The complete system measures 24.6 × 75.2 ×19 cm (approximately 10 × 20 × 7.5 inches), which is considerably smaller than traditional panels and enclosures.”
Not only are the systems smaller but so too is the design effort required. Both Swagelok and Parker now have software packages that enable users to quickly and easily configure complete systems and generate bills of material and final assembly drawings.