Nearer to NeSSI
A large distributed control system (DCS) can use percent analytical process measurements and low-PPM data to influence and improve product quality. Consequently, while we continue to generate analyzer system data to produce correct routine values, APC engineers will use these precise values to make better products!
Likewise, we're beginning to see more sample systems built by SIs that use the New Sampling and Sensor Initiative's (www.cpac.washington.edu/NeSSI) modular substrate platform and components. Some of these components are advertised to perform up to 10 million cycles before needing maintenance. This capability is especially useful in dealing with environmental measurements where we have to measure processes every 15 minutes and do zero and validation procedures every 24 hours. To determine where an analyzer is going to measure, zero is defined as the bottom of the measurement scale, and span is at the top of the measurement scale. Validation is a known measurement value between zero and span. These calibrations are required for every analyzer. Also, when switching from process operation measurements to EPA's CEMS measurements, the NeSSI substrate allows better precision for EPA reporting.
Because users must maintain product quality, avoid plant shutdowns and report accurate data to the EPA, they must require unaligned SI firms to provide better support and build more functional sample probes and sample conditioning systems. They must also demand that analyzer manufacturers cooperate on working with each other's devices when required by a user trying to achieve the absolute best system solution.
To foster better cooperation between unaligned SIs and vendors, users must fill out their process application data sheets and encourage everyone involved to perform the required calculations based on this process data. These ADSs must include the physical parameters that the sample system will be required to control, as well as the upper (MAX) and lower (MIN) characteristics of the overall process in a tabular format. In addition, a sample conditioning system's specifications should describe the specific physical and electrical hazard requirements that it must meet. The data sheets should also provide the system's environmental parameters: temperatures (ambient and process stream) and hazardous atmosphere monitoring (emergency alarm system).
NeSSI is Not a Monster
"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 former industry specialist for process analytical systems at CIRCOR Tech, which manufactures modular, NeSSI-compliant devices. "Whenever manufacturers move from legacy sampling systems to modular substrate systems, they can optimize components such as filters, for example, and achieve many new and more efficient capabilities."
Sherman adds that several hundred NeSSI-compliant components have been installed and tested and are serving in sampling systems in some West Coast refineries for more than five years. The maintenance time they require is 30% to 70% less than the maintenance time required by legacy components in the same services.
One of the first modular systems CIRCOR Tech put in was cleaning up samples for Reid vapor pressure analysis on a gasoline blender. The refiner’s technician said this application was just not going to work with these new modular components. Eight weeks later this same technician was enthusiastically asking, "How many more of these modular systems can we get?" These components became a de facto standard for this refinery.
The question potential users often have is, "Does NeSSI have staying power, or is it just another flash in the pan?" Sherman adds that one major refiner previously required its technicians to go out and read rotameters and pressure gauges each shift, and they couldn’t apply legacy flow controllers and pressure transmitters because these components were too large to fit into the sample conditioning system enclosures. This refiner now uses NeSSI-based mass flow controllers and pressure transmitters that report directly to the process unit’s control room, which means technicians only need to visit the analyzer system in the field if an exception report is generated because the analyzer system isn’t operating within its defined range.
Users, SIs and vendors must draft well-written specification documents that sufficiently describe each party's roles and define all expected results. Users should never say, "Just give me whatever equipment works; we'll fix it later."
In the past couple of years, many users have started requiring better-defined specifications and started filling out process ADSs for every sample conditioning system project. Even though it can be difficult to gather some of this process and ambient information, these users are requiring expected process flow rates, temperatures and pressures at the specific points where samples will be extracted by the in-line sample probe.
Glossary of Process Sampling System Acronyms
ADS Application Data Sheet
Similarly, analyzer technicians and engineers seem to be getting better at arguing that proper design of analyzer sample conditioning systems will reduce overall analyzer system lifecycle costs. Many refining companies encourage their technical personnel to join the American Petroleum Institute (www.API.org), American Society of Testing and Material (www.ASTM.org), get involved and contribute to the International Society of Automation's (www.ISA.org) Analytical Division or one of its other divisions relating to analysis and control aspects of the HPI and CPI, and join supplier user groups and customer advisory boards. The reality is that you can gather significant useful information at these professional forums and bring it back for use within your organization.
Ten or 15 years ago, most analyzer technicians could not get a climate-controlled shelter for their PPM analyzers because finance personnel would argue that if an analyzer in its own enclosed housing was rated to meet field location ambient conditions, then a separate shelter wasn't needed. However, while a manufacturer can say an analyzer in its enclosure is rated to -30 °F, it might also add that, if the internals get below 55 °F, then primary vacuum pump oil will be too viscous for the pump to operate, and it will need to be heated up for several hours.
How would you heat an enclosure filled with electronics and delicate mechanical devices in a northern winter location when this enclosure is located in the middle of an operating process unit? A plastic sheet tent and a steam hose are about all you'd have available, and this combination would be absolutely lethal to the electronics and could possibly also damage delicate mechanical devices. If there is blowing rain or drifting snow where an externally mounted analyzer has been installed, then analyzer and instrument technicians can't open its enclosure because they'll risk getting the internal circuit boards too cold or thoroughly damp. This is why users are currently installing more 8-ft x 8-ft or 10-ft x 10-ft base footprint shelters to protect their process control and environmental analyzers.