Continuous process manufacturing cannot exist on pressure, temperature, level, and flow measurements alone. In fact, very few areas of industrial operations exist where chemical composition variables do not need to be measured as part of the control process. In many areas, laboratory measurements still prevail.
Continuous process manufacturing cannot exist on pressure, temperature, level, and flow measurements alone. In fact, very few areas of industrial operations exist where chemical composition variables do not need to be measured as part of the control process. In many areas, laboratory measurements still prevail. The move to measuring these process variables as parts of moving media streams and the control processes are considered state-of-the-art.
Use of this type of instrumentation can begin at the very front of the process. At the feedstock end of the plant, analytical instrumentation is called on to do composition analysis, to check purchase specs, contamination by trace impurities, and exact quantities of materials priced on an active-ingredient (usually the costliest component) basis.
Analysis can take place offline in a lab by taking a sample from the process; online, which automatically draws aside a sample to analyze; or inline, which measures without separating any product from the process.
Analytical instruments can fill many roles in process controls. Online or inline instruments can speed up and improve control by replacing time-consuming laboratory grab samples. They can also be used to improve control by replacing or augmenting inferential measurements (usually pressure and temperature) with more significant composition data. One significant advantage when these instruments function online is the ability to control processes that escaped automatic control previously. Use of these instruments can prove invaluable in studying and overcoming process upsets and improving yields through analysis of materials involved in physical or chemical combination, by-product build up, or product loss.
Invaluable in determining product quality, especially such attributes as color, melting, or boiling points, etc., analytical instrumentation is important in many other areas of process manufacturing: Detection of equipment and piping leaks, occult toxic materials in leaks or spills, and the existence of hazardous gases-especially flammable or explosive-in the plant environment.
One of the most intensive uses of analytical instrumentation is tracking industrial pollution. Prime examples include monitoring waste streams for toxic and other objectionable materials, remediation in water treatment and wastewater plants, and other product recovery applications. Analytical instrumentation also finds application in stack monitoring devices to keep track of excursions and/or accidental discharges of toxic or nuisance gases, vapors, and particulates.
Technologies vary widely
A sampling of technologies, products, and applications follow, to help explain how analyzers are designed and used.
One analyzer approach comes from Ametek Process Instruments (Pittsburgh, PA) in the form of a dry/cold-based analyzer system called Model 921. The online design is engineered to monitor SO 2 and H 2 S unattended, with minimum maintenance. The analyzer measures 0 to 50 ppm SO 2 concentration at the outlet of a tail-gas treater (TGT) reactor and the same H 2 S concentration at the outlet of the TGT contactor. It works together with Ametek Process Instruments Western Research's high-resolution non-dispersive UV photometer. (See Ametek application profile.)
Model 921 uses Ametek Western Research's proprietary high-resolution UV technology in a dual beam, dual wavelength configuration. It has no moving parts, using pulses of ultraviolet light, instead of a filter/chopper wheel to alternate between measure and reference wavelengths. The design increases light throughput, lowers noise, and reduces maintenance.
Gas chromatographs can measure a wide range of different kinds of components in one analysis, compared to other technologies, according to Bob Farmer, product manager, Siemens Applied Automation (Bartlesville, OK). Chromatographs sample and vaporize liquids, move the gas through a column, then measure the absorption rate of mixture components.
Mr. Farmer says the Siemens Maxum edition II gas chromatograph, in use at petrochemical companies, takes online measurements of hydrocarbon and other components in gas and liquid mixtures. ''A high degree of resolving power provides the ability to differentiate and measure components that have very similar chemical characteristics, for example ISO and normal butane, or different alcohol structures, and more.''
Ability to repeat a measurement to better than 0.5% of scale leads to the ability to provide more precise process control, he says. ''Wide dynamic rangeability, ability to measure components concentration ranging from a few parts per billion up to 100% with the same instrument provides process control flexibility,'' Mr. Farmer adds.
Another application is online measurement of total sulfur in fuels, for blending or process-control quality. Bill W. Johnson, product manager-process gas chromatographs, ABB Inc. Analytical and Advanced Solutions (Lewisburg, WV) discusses the capabilities of the 2007 Process Gas Chromatograph with a Flame Photometric Detector (GC-FPD). The ABB analyzer is capable of low-level total sulfur (0-10 ppm) in gasoline or diesel, online, using GC - FPD technology. Results are ''highly repeatable and reliable, allowing online blending of environmentally regulated fuels,'' Mr. Johnson says.
Steps to analysis
The 2007 GC-FPD performs a total sulfur analysis in about five to six minutes, as follows:
The ABB Liquid Injection Valve (LSV) injects a fixed volume of liquid.
Air carrier transports the sample to the furnace, where it oxidizes to carbon dioxide, water, and sulfur dioxide.
Using packed columns, these components are separated before passing to the FPD.
The FPD measures total sulfur in 0-10 ppm concentrations.
Information flows from the analyzer to other process equipment or higher-level systems with ABB VistaNET 2.0 Integrated Process Analyzer Network Architecture, a single-wire connection to existing Ethernet-based systems, Mr. Johnson suggests.
Nuclear magnetic resonance (NMR) technology, used in labs for decades, measures magnetic properties of the nuclei non-intrusively, with no moving parts. It eliminates sample conditioning and concerns about opaque or optically dense samples.
Invensys Process (Foxboro, MA) MRA analyzer is said to be the first NMR spectroscopy technology to offer continuous analysis of process fluids in refineries, chemical plants, and other continuous-process application. The inline analyzer-which measures any chemistry with a hydrogen atom attached to the molecule-integrates into advance process control and optimization schemes.
Marc L. Hunter, MRA consultant for Invensys Process, says these NMR units are well supported, with supplied 'global calibration models and site-specific models... supported at the client's site for 12 months.' In keeping with Class 1, Div. 1 ratings, Mr. Hunter says, NMR units can be remotely calibrated and diagnosed. Mr. Hunter works for Process NMR Associates Ltd. (Danbury, CT), an Invensys Foxboro NMR partner since 1997.
Some technologies suitable for analytical measurements aren't considered ''analyzers'' at all, according to Tom Griffiths, product manager, Honeywell Industrial Measurement and Control Smart Sensors (Fort Washington, PA). DirectLine sensor product line is online technologies for pH, ORP, contacting conductivity, and dissolved oxygen measurements. ''DirectLine combines the sensor and the transmitter into one single device,'' Mr. Griffiths says. ''The transmitter module is small enough to mount directly on the sensor,'' reducing wiring, cable runs, and panel cutouts. A local keypad and display allow easy set-up, calibration, and operation; plug-in replacement sensors reduce maintenance time, Mr. Griffiths adds.
No matter the method, industry, or media, the value of rapid, accurate, measurements remains critical to all stages of the process. Watch for analyzer technologies to be easier to install, maintain, and interconnect to deliver information where needed over their lifecycles.
- Comments? E-mail MHoske@cfemedia.com .
Frank Bartos, Mark Hoske, Dick Johnson, and Jim Montague contributed to this piece.
Technology Sampler: Analyzers
Here's an analyzer technology sampler, helping to illustrate the range of solutions and applications.
FGA 2 , CO 2 , NO, NO 2 , and SO 2 in any combination, using dual sensor analyzer technology, giving high accuracy even at low pollutant levels.
ReactRA 4000 Raman Reaction Analyzer from
Application profile: Analyze savings for crude distillation
Analyzer technology, with faster, more accurate updates of chemistry information for the optimizer and advanced process control systems, results in $0.06 per barrel savings based on magnetic resonance analysis (MRA) for crude distillation. The Refineria Isla, in Curacao, Netherlands Antilles, offers ability to do several measurements with the same equipment, reducing total investment and maintenance costs through the analyzer's lifetime.
Better measurement ability is among benefits, says Marc. L. Hunter, MRA consultant, for Invensys Process. Mr. Hunter works for Process NMR Associates Ltd. (Danbury, CT), an Invensys Foxboro NMR partner.
Other savings are reduced operating costs, since materials that normally would not be used can be used, reducing scrap, rework, variability, and downtime.
Typical savings per barrel produced are:
Crude unit, $0.05-0.15 per barrel;
Fluid catalytic cracking (FCC) unit, $0.12-0.25;
Reformer $0.05 to 0.15;
Gasoline blending, $0.03-0.08; and
Savings for other blends, such as Naphtha feed for ethylene cracking, is being evaluated. In addition, the first gaseous-duty application is under beta testing.
Application profile: Environmental regulations mandate tight SO 2 tracking
A Chevron gas processing facility in Wyoming operates an amine-based tail-gas treatment facility, with a series of Ametek Process Instruments UV analyzers to monitor and control specific stages of the facility.
Modified Claus sulfur recovery units get 98% recovery efficiencies, but environmental regulations often require higher rates. Amine-based tail-gas treaters typically achieve recovery efficiencies of up to 99.9%, limiting SO 2 emission to less than 250 ppm.
In the first step of the application, says Dan Potter, regional manager, Ametek (Pittsburgh, PA), tail-gas treatment reduces sulfur-bearing compounds to H 2 S, typically over a catalyst, in the presence of H 2 . A Model 921 SO 2 analyzer is placed at the outlet of the reduction section to monitor residual SO 2 concentration in the stream. Residual SO 2 present in the stream at that point cannot be further treated, so keeping it as low as possible is necessary.
The second part of the tail-gas treater consists of an amine section to strip H 2 S from the upstream reduction section to levels as low as 50 ppm. An H 2 S analyzer at the outlet of the contactor monitors residual H 2 S concentration, before it's sent to an incinerator, for burning and sending out the stack.
Ametek's UV technologies for these measurements provide immediate measurements, compared to traditional, slower technology. A gas chromatograph, for instance, can take 8-10 minutes to update.
Model 921 UV analyzer can detect a single digit ppm of SO 2 instantaneously. Rising H 2 S levels detect any process upsets, Mr. Potter says.
Sampling systems for analyzers get modular
Design of analyzer sampling systems needs to improve, according to Dave Simko, manager of marketing resources, Swagelok Co. (Solon, OH). As much as 80% of the problems associated with process analyzer systems occur in sampling.
''The incentive for industry is to improve performance of analyzer systems; reduce the cost to design, build, and install the systems; and reduce operating and maintenance costs. One important way to meet these needs is by making sampling systems modular,'' he says.
Modular design is moving to the forefront through an effort at the Center for Process Analytical Chemistry (CPAC), a joint industry-academic research consortium at the University of Washington. The New Sampling/Sensor Initiative (NeSSI) incorporates the efforts of CPAC leadership and industrial affiliates, who are all end-users or suppliers of process analytical chemistry instrumentation.
The initiative is to ''facilitate the state-of-the-art evaluation and ongoing development of the next generation modular sampling system designs,'' explains Mr. Simko.
A key element in the modularization strategy is open architecture. The Instrumentation, Systems, and Automation Society (ISA) SP76 Composition Analyzers Committee added a subcommittee charged to develop interface seal standards to apply to functional fluid control components and the fluid path substrates of a miniature, modular, smart sampling system, he adds.
line extra material to come
Swagelok: Process analyzer sampling systems go modular; components/software package can help;
Related coverage; and