chemistry

NeSSI

NeSSI is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand NeSSI rather than just read about it. In short: NeSSI (for New Sampling/Sensor Initiative) is a global and open initiative sponsored by the Center for Process Analysis and Control (CPAC) at the University of Washington, in Seattle. The NeSSI initiative was begun to simplify the tasks and reduce the overall costs associated with engineering, installing, and maintaining chemical process analytical systems.

Key takeaways

NeSSI belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect NeSSI to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NeSSI from memory before moving on to harder problems.

Reference excerpt

NeSSI (for New Sampling/Sensor Initiative) is a global and open initiative sponsored by the Center for Process Analysis and Control (CPAC) at the University of Washington, in Seattle. The NeSSI initiative was begun to simplify the tasks and reduce the overall costs associated with engineering, installing, and maintaining chemical process analytical systems. Process analytical systems are commonly used by the chemical, oil refining and petrochemical industries to measure and control both chemical composition as well as certain intrinsic physical properties (such as viscosity). The specific objectives of NeSSI are:

Increasing the reliability of these systems through the use of increased automation, Shrinking their physical size and energy use by means of miniaturization, Promoting the creation and use of industry standards for process analytical systems, Helping create the infrastructure needed to support the use of the emerging class of robust and selective microAnalytical sensors. To date, NeSSI has served as a forum for the adoption and improvement of an industrial standard which specifies the use of miniature and modular Lego-like flow components. NeSSI has also issued a specification which has been instrumental in spurring the development and commercialization of a plug and play low power communication bus (NeSSI-bus) specifically designed for use with process analytical sample systems in electrically hazardous environments. As part of its development road map, NeSSI has defined the electrical and mechanical interfaces, as well as compiled a list of automated (smart) software features, which are now beginning to be used by microanalytical manufacturers for industrial applications.

Background

Modern chemical and petrochemical processing plants are complex systems containing many steps (often called unit operations) involved in producing one or more products from various raw materials. In order to control the many processes, for both improved product quality and operational safety, many measurements are made at the different stages of processing. These measurements, either from simple sensors (such as temperature, pressure, flow, etc.) or from sophisticated chemical analyzers (providing composition of one or more components in the chemical stream), are typically used as inputs to process control algorithms to give a "snapshot" of the process operation and to control the process to ensure it is operating efficiently and safely. Traditionally, most of the measurements (with the exception of temperature, pressure and flow) were performed "off-line" by taking a sample from the process and analyzing it in the laboratory. Beginning in the latter of part of the 1930s, a trend aimed at moving the analysis from the laboratory to the process plant began. With the advent of more sophisticated analyzers, this concept known as Process Analytics become much more prevalent in the 1980s and a new discipline called Process Analytical Chemistry (PAC) emerged which combined chemical engineering and analytical chemistry. One of the main driving forces for PAC (See also: PAT) is to remove the bottleneck and time lag associated with sending the samples to the lab and waiting for the analysis results. By moving the analysis to the process, results can be obtained closer to real-time which effectively improves the ability for the control action to correct for process changes (i.e., feedback and feed forward control). By far, the most common implementation of PAC (especially for more complex analyzers) utilizes what is known as extractive sampling. This typically involves the continuous (or sometimes periodic) removal of a small portion of sample from a much larger piping system or process vessel. This sample is then conditioned (filtered, pressure regulated, flow controlled, etc.) and introduced to the analyzer where the chemical composition or the intrinsic physical properties of process fluids (vapours and liquids) are measured. In industrial plants, the majority of sample systems and their related analyzers are installed in analyzer houses. The hardware (traditionally metal tubing, compression fittings, valves, regulators, rotameters and filters) associated with extractive sampling is collectively referred to as the sampling system. Sample systems are used to condition or adjust the sample conditions (pressure, amount of particulate allowed, temperature and flow) to a level suitable for use with an analytical device (analyzer) such as a gas chromatograph, an oxygen analyzer or an infra red spectrometer. Despite the simple explanation just given, modern sampling systems can be quite large, complex, and expensive. The design features of analytical sample systems have changed little, when the discipline of Process Analytics began in Germany, right through until the present day. An example of an early analyzer and sample system used at the Buna Chemical Works (Schkopau, Germany), is shown in the following photograph. Process analytics remains exceptional in the fact that it is the last outpost of low level automation (retains manual adjustments and visible checks) within the process industries.

History The rationale for NeSSI originated from focus group meetings held in 1999 at the Center for Process Analytical Chemistry (CPAC) which called out for more reliable sampling and analysis for the manufacturing processes. Early work with NeSSI was started in July, 2000 by Peter van Vuuren (of ExxonMobil Chemical) and Rob Dubois (of Dow Chemical) with the initial aim of adopting new types of modular and miniature hardware which were being addressed in a standard being developed by an ISA (Instrumentation, Systems and Automation Society) technical committee. (Reference 1) The term NeSSI, along with the futuristic concepts of a communication/power bus specifically designed for process analytical (the NeSSI-bus) and fully automated sampling systems were first introduced outside of CPAC at a presentation given in January 2001 at the International Forum of Process Analytical Chemistry (IFPAC) at Amelia Island, Florida, USA. These new concepts were collected in the NeSSI Generation II Specification and released by CPAC in 2003 as an open publication. The specification is located on the CPAC website. (Reference 2)

… excerpt ends here. Continue reading the full article.

Illustrations

NeSSI: An example of a Generation 1.5 system — An example of a Generation 1.5 system

Worked examples

Example 1 — a first encounter with NeSSI

Start with the simplest possible case. Write down what NeSSI claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to NeSSI before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about NeSSI ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of NeSSI

In research: NeSSI appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses NeSSI in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: NeSSI is common in secondary-school and first-year university syllabi. It links to neighbouring topics Chemical engineering, Systems analysis, so understanding it makes those chapters shorter.
In everyday life: Look for NeSSI outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study NeSSI in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NeSSI means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain NeSSI out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NeSSI in simple terms?

Why does NeSSI matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study NeSSI?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on NeSSI.