dec05featurestorywireless applications in process plants.pdf

8/10/2019 Dec05FeatureStoryWireless Applications In Process Plants.pdf

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T

he use of wireless equipment isbecoming much more common in

the chemical process industries(CPI). Modern improvementsin error correction, dedicated

wireless-data protocols and securityprotection have greatly increased op-erating reliability standards. In addi-tion to wireless I/O, data modems andEthernet, wireless is now also beingembedded into process transmitters togive wireless sensors.

It is only in the last five years thatengineers have become more accept-ing of wireless technologies to carrysimple on/off control signals and field-bus data in their plants. The technol-ogy, however, has been around for over20 years.1

In the early 1960s, digital processorswere coupled with radio transceiversto modulate simple data messages ontoradio transmissions, giving us radiotelemetry. Early users, such as theU.S. National Aeronautics and Space

Administration, drove this technologyhard as an integral part of the spacemissions. By the 1980s, commercialradio telemetry was being used in util-ity and municipal applications to re-

place unreliable telephone landlines, orin many cases, an operator in a roam-ing truck.

There were also many industrialapplications for radio telemetry inthe early years of this technology, butnone were easy to implement. Radiowas always the last resort the tech-nology used when everything else hadbeen tried and rejected.

Over the years, radio telemetryhas grown and transformed into anever increasing spread of develop-ing technologies, as listed in the firstparagraph of this article. Today, wire-less technology allows easy, flexibleinstallations and enables advancednetworking capabilities that providefast, reliable data transfer. Industrialwireless devices are being found in allindustry sectors and in an increas-ingly wide range of applications.

The driving factors are cost andconvenience. In the wire vs. wirelessdecision making process, wire admit-tedly wins most of the time because ofits superior reliability. In many othersituations, however, the decision is in-

stead between wireless and nothing, ifwire is rejected due to cost or installa-tion difficulty. Wireless becomes muchmore attractive to the plant engineerif it means that a minor project can

proceed.Here are some real-life industrialapplications from the past 20 years.

Going the distanceUp until ten years ago, the only indus-trial wireless applications involvedlong distance, wherever it was justtoo far to run a cable.Underwater pipeline.A large petro-chemical site that made a variety ofplastics took naphtha as feedstock froman oil refinery. The two plants were onopposite sides of a bay and joined by anunderwater pipeline. In the 1960s, anunderwater cable was installed along-side the pipeline to link data from feedtanks at the refinery to an olefins planton the petrochemical site. Age took itstoll on the cable and by the late 1970s,the level-monitoring function providedby the underwater cable had been re-placed by an operator with a two-wayradio. An online radio telemetry sys-tem was proposed, but the engineer-ing manager would not approve it. Astandby system did, however, slip in onthe maintenance budget.

36 CHEMICAL ENGINEERING WWW.CHE.COM DECEMBER 2005

Wireless

Applications InProcess Plants

More engineers are choosing

wireless equipment today than in

the past. In addition to savings in

cost and installation time, wireless

can overcome some obstacles moreeasily than a wired solution can.

Graham Moss

Elpro Technologies

Feature Report

1. For related articles, see Wireless Sensors forEnvironmental Compliance, CE, Aug. 2005,pp.40-43; Industrial wireless: Getting your feetwet, CE July 2004, pp.22-25; and Industrialwireless: Whats beyond the wading pool, CEJuly 2004, pp.26-28.


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In the early 1980s, the old plant wasreplaced with a new olefins plant. Themore-efficient operating regime calledfor much more information than sim-ple tank levels. The engineering alter-natives were either a new cable at a

cost of $150,000 (in 1980 dollars), oran upgrade to the wireless system forless than $5,000.

The wireless option won, but notuntil after a long reliability and haz-ard analysis was conducted. Levelgauges, flowmeters and valve posi-tions at the refinery were connectedby a wireless system to the DCS at thenew olefins plant.

The wireless system worked reli-ably with some occasional failuresfrom power surges. These surges be-came less frequent with the installa-

tion of better grounding equipmentand power protection. Additional sig-nals were later added in the reversedirection, to enable remote control ofemergency isolation valves.

Eventually, the wireless systemoutlasted the life of the petrochemi-cal site, which was decommissionedin the late 1990s. The site is now usedfor port storage, and the underwaterpipeline linking the refinery with thetank farm is still in use. The wirelesssystem is still transferring tank-farmsignals back to the refinery.Custody transfer. A petrochemicalplant supplied solvent feedstock to adyes- and pigments-processing plant. Apipeline, approximately one mile long,carried the solvents from one site to theother. Traditionally, custody transferflowmeters at either end of the pipe-line were read manually. Correlatingthe values between the two separatereadings, however, was troublesome.Each company desired a remote read-ing of the others flowmeter prefer-ably online so that any metering dif-ferences could be easily analyzed. The

cost of the signal cable was more than$50,000, compared to approximately$5,000 for a wireless solution.

In 1997, wireless units were in-stalled at each flowmeter. Every min-ute, the units transmitted and received

the totalized flow count to and fromthe other end. With these automatedreadings, measurement inconsisten-cies were sorted out. Before long, com-munications between the two plantsaccounting groups also improved.

A couple of years later, the wirelesssystem further proved its worth whena significant leak was noticed, beforeit developed into an event report-able to the Environmental Protection

Agency (EPA).Pulp and paper. Another remotesupport service that is a common ap-

plication for wireless systems involvesprocess or cooling-water pumps. Forinstance, a pulp and paper plant takesits process water from a lake that isfive miles from the plant. To monitorthe pump station at the lake, a signalcable was run alongside the pipelineto the plant. When the plant was origi-nally built in the 1970s, the pipelineran through forest and farmland. De-cades of suburban growth, however,forced the pipeline and cable to be putunderground. Gradual deteriorationof the cables multiple joints decreasedits reliability, eventually rendering itunusable.

The option of installing a new cablewas briefly considered, but quickly re-

jected because local residents did notwant digging in their yards and streets.

As an alternative, a landline connec-tion from the telephone company wasleased. It could not, however, providethe 99+% reliability that was needed.In 2001, the plant shut down becausea backhoe cut through the telephonecable to the pump station. This eventprompted the plant engineer to con-

sider his last option, wireless.A programmable logic controller

(PLC) at the pump station was linkedto the PLC system in the plant by awireless data link. Not only did thecontrol system prove to be reliable, but

the new link also provided much moreinformation than the original design-ers had envisaged.

A wireless Ethernet link was lateradded to the lake pump station toprovide security while monitoring theremote site. The plant engineer subse-quently became a champion of indus-trial wireless, and the use of wirelesslinks has been extended to several ad-ditional applications in the plant.

Circumventing obstaclesThe examples given above are applica-

tions where wiring is not a good optionbecause of distance. In other wirelesssolutions, distances are shorter, butobstacles get in the way.Mineral-processing plant. A largemineral-processing complex and its ef-fluent-treatment plant are located onopposite sides of a public-access railline. The effluent plant was designedto be operated manually. As part of anautomation upgrade, however, it wasdesired to connect its controls to theprocessing plants main control cen-ter.

Although the control center is within500 ft of the effluent plant, the onlycabling access was along the existingpiping route, which comprised a totalwiring distance of more than 5,000 ft.The plant applied for another accesscrossing, but the rental charge fromthe railway company was very high.

As an alternative, a wireless I/Olink was installed. The link carries allof the needed level, flow and analysissignals, and the pump and valve sta-tus, and allows remote control of theplant. The wireless system has oper-

CHEMICAL ENGINEERING WWW.CHE.COM DECEMBER 2005 37

IMPORTANT ASPECTS OF WIRELESS-PRODUCTS USAGE

Data rate vs. distance. There is a tradeoff between data rate anddistance when using wireless. High-speed wireless (2.4 GHz, orgreater than 1 Mb/s) has a reliable range of only 100-500 ft inan industrial installation, but a much longer range for line-of-sightapplications. Lower-speed wireless (900MHz, or less than 100 Kb/s) has much better penetration than high speed, with an operatingrange of 1,000-3,000 ft in plants or factories.

Do not be confused between line-of-sight distance specifica-tions and in-plant performance. In obstructed industrial environ-ments, reliable distances are only 1-3% of specified line-of-sightdistances.

Radio Frequency (RF) Power. Check the RF power specifications.The U.S. Federal Communications Commission (FCC) allowsindustrial devices to generate RF power of up to 1 W. Lower-power

units have much shorter operating distances than high-power ones.

Industrial ratings. Check the low-temperature ratings of products this is a fair indication of whether a product has been designed asan industrial unit or has simply migrated from a commercial wirelessrange. Industrial products will generally have ratings down to 40F,

whereas most commercial products are only good down to 0-30F.

Security.Almost all industrial devices use wireless spread-spectrum technology, which gives a good degree of securityprotection but not enough for todays world. Look for products

with security encryption of the wireless data. Modern encryptiontechniques are very secure.

For the IEEE 802.11 family of wireless protocols, commonlycalled "Wifi", look for those products offering military grade (AES)encryption rather than commercial grade (WEP).


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Feature Report

ated reliably without failure since thesystems installation in 2001.Service roads on a chemical site.

A single chemical-processing siteevolved from a large number of small,independent specialty plants. Thesmall plants had been isolated fromeach other by a mesh of service roads,which, over time, became a majormaterials handling network. Truckswere used to transport raw materialsinto each plant, to move intermediateproducts from one plant to another,and to carry the finished product outof the facility. Although the roads weretraversed by overhead piping, safetyconcerns restricted the installation of

additional, new overhead conduits.As the site automated its processes

and moved to a single, centralizedcontrol center, trunk cables crossingthe roads became fully utilized. Aftermuch trepidation, in 1998 the com-pany started using wireless technol-ogy for interplant signals and dataconnection.

Wireless signals were first testedwith trials on low-importance data.

After success with these trials, wire-less became the standard method oflinking signals between the individual

plants. By 2004, the site was usingmore than 20 individual, wireless ap-plications that formed one, integratedwireless network. Although wiringdistances were not long, the difficulty,safety concerns and cost of installingwiring across the roads made wirelessan attractive alternative.

Saving timeIn recent years, the ease of installationof wireless has made it the method ofchoice for many applications that weretraditionally wired.Power station. A power station ex-perienced unusual fouling of cooling-water pipes in 1999. In response, theplant manager asked for continuoustesting of the cooling-water quality.Instrument cables from the controlcenter to the cooling towers had noavailable wires left to use. To savetime, rather than the installing of an-other cable, a wireless link was pur-chased and installed within one day.The plant engineering manager waswary about the reliability of wireless,and he considered the wireless link to

be a temporary solution.With continuous monitor-

ing, the fouling problem was

resolved. To make sure theproblem did not reoccur, thetemporary wireless instal-lation remained in place and eventuallybecame a permanent installation. Thewireless link was expanded to include

vibration monitoring on the tower fans,temperature monitoring of pump bear-ings, and additive dosing monitoring.The operating staff had wanted thesemeasurements for a long time, but dataavailability was restricted because ofthe wiring limitation.

In 2001, these additional monitor-

ing points picked up a gradual per-formance decline in the cooling tower.The availability of these data wascredited with saving an expensiveshutdown. Manual shift-log measure-ments, which had failed to highlightthe performance problem, were even-tually discontinued. The plant decidedto rely completely on the temporarywireless monitoring system, whichcontinues to work reliably.Urea plant.Communication from anonline gas detector in a compressorhouse was cut off when an old cable

joint in a signal cable failed. The loca-tion of the joint made it inaccessiblefor repair unless the compressors and,in turn, the entire plant were shutdown. To avoid a plant shutdown, awireless link was installed to get thegas detector back online quickly. Theelectrical and instrumentation super-

visor had stored a pair of spare wire-less I/O units on the shelf for exactlythis sort of event.

Transmitting data in motionWireless has special advantages for

vehicles and machinery which moveor rotate.Molten casting plant.In a specialtycasting plant, molten alloy is trans-ported short distances by vats on rails.To control movement of the vats, each

vat was fitted with a small PLC, whichwas connected by a trailing cable to acentralized PLC. The original trailingcables were a maintenance nightmare.Cable failure would often leave vats ofmolten metal stranded in the middleof the rail. Operators were then re-quired to manually winch the vats.

In 1999, the trailing cables were re-placed with industrial wireless unitsthat linked the PLCs on the vats tothe factory PLC network. Now, the op-erators cant remember the last timethey have had to winch a vat back intoposition.Batch reactors.A rotating chute dis-tributes ingredients to several batchreactors in a specialty chemical plant.The chute has an integrated weigher

and automatic inlet and outlet flaps.To connect power as well as controlsignals, the chute was built withmulti-segment slip rings.

Continuous maintenance was re-quired to keep the slip rings clean.Intermittent lapses in the slip-ringconnections caused control failure,ultimately leading to batches beingdumped at least once a week.

In 2002, wireless units were in-stalled to link the control signals. Theslip-ring mechanism continues to beused, but only for power connection.

The plant engineers estimate thatthe wireless system paid for itself inless than 2 months.Stockpile transfers. Bulldozers areused at a paper mill to feed stockpilepulp into conveyor feed pits. Flashinglights above the pits were installed toalert someone in case the conveyorsstopped. The lights, however, were oftenmissed and the pits would be buried inpulp. In order to restart the conveyer,the pits would have to be dug out.

To solve this problem, wireless I/Ounits were installed in the bulldozercabins to provide indication of con-

veyor status and alarms. This solutionproved to be very effective. Later, re-mote conveyor trips were also addedin the cabins, to allow operators tostop the conveyors in emergencies.Cement plant.A large cement manu-facturer had difficulty getting reliabletemperature measurements from itsoutside rotating kiln. Thermocouplesin the kiln were connected to indica-tors with slip rings. Performance ofthe rings was poor when they becamedirty and worn. Maintenance costs

38 CHEMICAL ENGINEERING WWW.CHE.COM DECEMBER 2005

FIGURE 1. In this power station, a wireless linkconnects the DCS and a remote PLC, which controlsthe coal conveyer feed system.

Elpro Technologies


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and kiln downtime were high.The cement company solved this

problem by bypassing the slip ringscompletely and using wireless I/Ounits. The thermocouple readingswere connected to the wireless I/Oas analog inputs via a local two-wiretemperature transmitter. The wirelessunit is designed to be run from batter-ies, and shuts down between tempera-ture measurements.

Saving costsThe largest growth in wireless appli-cations in recent years has been insimple wire-replacement applications.In these cases, the only obstacle towiring is cost.Emergency showers. An operator ina fertilizer plant accidentally walkedinto an acid spray from a leakingpump gland. He made it to the nearestemergency shower, but collapsed afterusing it. He was found an hour laterwhen other operators became con-

cerned about his absence. Fortunately,the injured operator survived.After this incident, the operators re-

quested that the emergency showersbe fitted with sensors that would alertanyone in the control center when ashower was used. They also requestedthe installation of strategic, emer-gency call buttons.

A safety committee, consisting ofplant engineering and operating staff,decided to use a wireless system be-cause estimated costs to install wirein the old plant were extremely high.The cost of setting up battery-poweredwireless units was less than 25% of thecost of wiring a system. The wirelessunits were also installed in much lesstime it took less than one month ascompared to the estimated six monthsfor wiring. Now, the wireless systemperforms a self-check every 5 min.Air compressors. At a major chemi-cal site, each of eight large air com-pressors located throughout the sitewere feeding a common distributionsystem. The site-services engineerexpected that a large savings in en-

CHEMICAL ENGINEERING WWW.CHE.COM DECEMBER 2005 39

FIGURE 1. A wireless I/O can connectto level gauges for remote monitoring oftank levels, such as in this tank farm.

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