cs process analytics in vcm plants

8/3/2019 CS Process Analytics in VCM Plants

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Vinyl chloride (VCM) , made fromethylene and chlorine by pyrolysis, isthe feedstock for the production ofthe very common plastic material PVC.Modern VCM plants use integratedprocesses combining endothermicand exothermic reactions in an almostenergy balanced operation. Plants areoperated in view of product quality,plant safety and cost efficiency usingadvanced process control equipmentincluding process analyzers.

Siemens , a leader in processanalytical instrumentation, hasproven over decades its capabilityto plan, engineer, manufacture,implement and service analyzersystems for VCM plants worldwide.This Case Study provides an over-viewof the typical processes and describeshow Siemens with its analyzer and

application know-how meets best theprocess requirements.

Vinyl Chloride (VCM)Vinyl chloride (CH 2=CHCl, M standsfor Monomer, in contrast to Poly-mers, PVC) is a colorless, flammablegas, first obtained in 1912 throughcatalytic hydrochlorination of acety-lene. VCM is heavier than air andmay travel along the ground andcan, under specific circumstances,form peroxides, initiating explosivepolymerization. On burning, VCMdecomposes producing toxic andcorrosive fumes (hydrogen chlorideand phosgene).VCM is used as feedstock in the pro-duction of PVC, polyvinyl chloride)one of the worlds most versatilethermoplastics, which has a widerrange of uses than any other plasticmaterial. As a hard plastic, it is usedas vinyl siding, magnetic stripecards, window profiles, pipe, plumb-

ing and conduit fixtures. It can bemade softer and more flexible bythe addition of plasticizers, the mostwidely used being phthalates. In thisform, it is used in clothing andupholstery, and to make flexiblehoses and tubing, flooring, roofingmembranes, and electrical cableinsulation. The material is oftenused for pipelines in the water andsewer industries because of its inex-pensive nature and flexibility.Beginning in 1940, acetylene asfeedstock was replaced stepwise bythe inexpensive ethylene. Completechangeover to almost exclusive useof ethylene became possible in1955, when the large-scale oxychlo-rination of ethylene to 1,2-dichlore-thane became possible. Today,more than 90% of the world wideVCM production is based on ethy-lene. Modern VCM plants use inte-grated processes combining theboth highly exothermic reactions ofethylene chlorination and oxychlori-nation with the endothermic crack-ing process, which results in analmost energy balanced operation.

Process Analytics inVinyl Chloride (VCM) Plants


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Production of Vinyl Chloride

VCM process in briefA modern VCM production can be con-sidered as balanced process whereethylene, chlorine and oxygen are con-verted into VCM and water. The threeprocess steps direct chlorination, oxy-chlorination and EDC cracking are sum-marized in the VCM synthesis reaction.For details see text box below.Based on the VCM synthesis principledifferent production technologies are inuse. They differ, for instance, in detailsof the reactor design, kind of catalysts,and reaction temperatures applied.Many hundreds of VCM plants are in useworldwide with capacities of 30000 upto 600000 t/year each. All plants areoperated in view of a high and constantproduct quality as well as cost efficiencyand safety (corrosive, poissoneous andexplosive substances are handled).Considerable investments are requiredin instrumentation and control to meetthese requirements.Process analyzer contribute an impor-tant part to that.

Process stepsThe major steps of a VCM productionprocess (Fig. 1) include:Direct chlorinationEthylene and chlorine are fed to a reac-tor where a catalytic reaction ( directchlorination) takes place.1,2-dichlorethan (EDC) is formed, toge-ther with heat, water and HCl-richwaste gas. The EDC is fed to a tank fortemporarily storage. The waste gas isfed to the oxychlorination and re-usedas reacting component.

OxychlorinationEthylene, oxygen and hydrogene chlo-ride are fed into a fluidized-bed reactorfor the oxychlorination process. RawEDC is formed, removed by condensa-tion and fed to the EDC distillation unitfor purification, and heat. Waste gasand effluent are also formed and fed tothe HCl recovery and water treatmentunits.

EDC distillationTo produce pure EDC both the EDC fromthe oxychlorination and the unconver-ted EDC from the cracking process(recycle EDC) are purified in the EDC dis-tillation unit. The purified EDC is thenfed to the EDC tank for temporarily sto-rage.

EDC cracking (pyrolysis process)Cracking of the EDC from the tempora-rily storage tank is performed in a fuelheated cracking furnace at temperatu-res of 500 C and above. Vinyl chlorideMonomer (VCM) and HCl are formedtogether with various by-products.Some EDC remains unconverted and isfed back to the EDC distillation unit.HCl is fed back into the oxychlorinationunit and reused in the process as well.The VCM is either used as feedstock fordirect manufacturing of PVC or stored asproduct for sale.

By-product recoveryThe by-products formed during VCMproduction are further treated and reco-vered in an oxidation process at approx.1250 C and completely converted intoCO2, water and hydrogen chloride. Theprocess heat is used to generate steamand the HCl is recovered as valuablefeed stock and returned into the pro-cess.

Emission monitoringIn most countries VCM plants mustcomply with the statutory regulationsand local specifications regarding thelimit values of polltants that are

released into the atmosphere. With anoptimized operation of the by-productoxidation and recycle process only verylow volume flow rates are emittedthrough the stack. Therefore, very oftenonly discontinuous emisson controlmeasurements of some compounds(see Fig. 1 and Table 1, MP 10) arerequested by the authorities. Samplesare taken at the stack daily or weekly,and measured in the laboratory.

VCM production process

Direct chlorinationC2H4+Cl2 C2H4Cl2EDC (1,2-dichlorethane, DC-EDC) is formed by a highly exothermal directchlorination reaction of ethylene and chlorine

OxychlorinationC 2 H 4 +2HCl+O 2 C 2 H 4 Cl 2 +H 2 O

EDC (1,2-dichlorethane, Oxy-EDC) and water is formed by a highly exo-thermal calytic reaction of ethylene with hydrogen chloride and oxygen.

EDC cracking (pyrolysis)C2H4Cl2 C2H3Cl + HClThe EDC is cracked at high temperatures in a fuel heated furnace in an endo-thermic and incomplete reaction. VCM and HCl are formed together withvarious by-products; some EDC remains unconverted.

VCM synthesis (Balanced Process)2C2H4 + Cl2 + O2 2C2H3Cl + H2OThe three process sections as above can be combined into a one completeVCM synthesis process, in which only VCM and water is formed (balancedon hydrogene chloride).


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Process scheme and analyzer measuring points

Table 1: Sampling points and measuring details of a VCM production plant, according to Fig. 1

* e.g. methyl chloride, ethyl chloride, vinyl acetylene, butadiene, dichloroethanes, dichloroethines

Sampling pointSampling stream

Component MeasuringRange

MeasuringTask

Suitable Analyzer

1 Direct chlorination C2H4O2

0 ... 3%0 ... 10%

Process control,Safety monitoring

ULTRAMATOXYMAT

25

From Direct chlorin.and EDC distillation

HClH2OImpurities

0 ... 10 ppm0 ... 20 ppmppm range

EDC quality LDS 6TPAMAXUM

3 Oxychlorination O2COCO2C2H4pH, Conduct..

0 ... 10%0 ... 10%0 ... 100%0 ... 3%

Process control,Safety monitoring

OXYMATULTRAMATULTRAMATULTRAMATTPA

4 EDC distillation H2O 0 ... 20 ppm Process control TPA

5 See line 2

6 EDC cracking O2 H2O

0 ... 10%0 ... 20 ppm

Process control TPA (ZrO 2 probe)TPA

7 VCM distillation H 2O 0 .. 100 ppm Process control TPA

8 From VCMdistillation

Impurities* ppm range VCM quality MAXUM

9 By-productrecovery

O2pHO2

0 ... 10%

0 ... 10%

Process andemission controlSafety monitoring

OXYMAT (Tantalum)TPALDS 6

10 Plant ambient airand stack

EDC / VCMvarious

ppm rangevarious

Environmentalcompliance

MAXUM IIFIDAMATCEM system(or laboratory devices)

TPA: Third party analyzer

Fig. 1: Generic VCM production process, simplified, with measuring locations

ChlorineDirect

ChlorinationEDCtank

Oxygen

Ethylene

EDCdistillation

Oxy-chlorination

EDCcracking

VCMdistillation

VCM

EDCchlorination

Waste gasand effluent

By-productrecovery

Various by-products

Off gas

Waste gas

EDC

EmissionAir monitoring

1

3

4 5

6 7 82

10

9

HCl

ChlorineDirect

ChlorinationEDCtank

Oxygen

Ethylene

EDCdistillation

Oxy-chlorination

EDCcracking

VCMdistillation

VCM

EDCchlorination

Waste gasand effluent

By-productrecovery

Various by-products

Off gas

Waste gas

EDC

EmissionAir monitoring

11

33

44 55

66 77 8822

10

99

HCl


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Use of process analyzers

Analyzer TasksProcess analytical equipment is an indis-pensable part of any VCM plant becauseit provides the control system and theoperator with key data about the pro-cess and its environment.

Four major applicationsAnalyzer applications can be classifiedin four groups depending on how theanalyzer data are used: Closed-loop control for process

and product optimization

This application helps to increaseyield, reduce energy consumption,achieve smooth operation, and keepproduct quality accoding to the speci-fication

Quality control and documentatione.g. for ISO compliance

Plant monitoring and alarmsThis application protects personneland plant from possible hazard fromtoxic or explosive substances

Emission monitoringThis application helps to keep emis-sion levels in compliance with localenvironmental regulations.

Analyzers and sampling pointsDifferent analyzers are used in VCMplants ranging from simple sensor typemonitors to high technology processgas chromatographs. The list typicallyincludes Process gas chromatographs Continuous gas analyzers

(paramagnetic oxygen analyzers,NDIR analyzers, total hydrocarboncontent analyzers)

Analyzers for moisture and O 2 traces

Low Explosion Level (LEL) analyzers Fig. 1 and Table 1 show typical samplingpoints of a VCM plant along with therespective measuring components andsuitable analyzers.

Analyzer installationAnalyzers are installed partially in thefield close to the sampling locationand/or in analyzer houses (shelter).In modern plants the analyzers are

interfaced to a plant wide data commu-nication system for direct data transferfrom and to the analyzers.The number of analyzers in a VCMplant varies from plant to plant depend-ing on the type of process, specific plantconditions and user requirements.

Special SolutionsOxygen measurementsContinuous monitoring of oxygen in the

process gas in both the direct chlorina-tion and oxychlorination plant units(MP 1 and 3 of Fig. 1 and table 1) is ofexceptional importance. To protectfrom the danger of heavy explosions,the process must be ensured to run out-side the critical ignition levels of theprocess gas at any time. Therefore, theuse of the most reliable and accurateoxygen measuring technology is appro-priate, as provided by the SiemensOXYMAT 6 gas analyzer, see text box.Because of the high importance, thisoxygen measurement is often engi-neered redundantly with two analyzersat the same sampling point and fail-safedata processing.The oxygen measurement at samplingpoint 9 (by-product recovery) has a dif-ferent meaning. Here, the oxygen con-tent reading is used to optimize theincineration conditions in order to mini-mize the remaining emission rate ofpollutants. High measuring accuracy isrequired here as well, but along withcorrosion resistance because of theaggressive gas composition. Again,the OXYMAT 6, in its tantalum version,is most suitable for this task.

Measurement of impuritiesGas chromatographs are standardequipment in VCM plants to measureimpurities in trace concentrations. Theyare used to analyze the product streamat MP 2 and 5 (Fig. 1) and help verymuch to ensure compliance with pro-duct specification and quality.The Siemens Process Gas Chromato-graph MAXUM edition II is very muchsuited for this task, see also pages5 and 6.

Another gas chromatograph applicationin VCM plants is to monitor ambient airfor chemical compounds that mayemerge from certain plant units in caseof sudden leakages (MP 10, combinedwith sample point switching).

Measurement of HCl HCl in the ppm range (MP 2, 5 and 8)

usually is determined by conductivitymeasurements. However, at MP 3with a concentration range of 0 to3%, photomertric measurements arepreferred. With the in-situ Laser Spec-trometer LDS 6, Siemens offers a veryeffective solution for this tasks. LDS 6 (Fig. 7) is a diode laser-based in-situgas analyzer for measuring specificgas components directly in a processgas stream. Measurements are car-ried out free of spectral interferencesand in real-time enabling pro-activcontrol of dynamic processes.

The OXYMAT 6 operates according

to the paramagnetic principle and isdesigned for high-precision measure-ments of oxygen concentrations ingases. The pulsating magnetic fieldcreates minute flow pulses detectedby the Siemens micro-flow sensorand converted into the measuringsignal. Thus, theOXYMAT 6 does not comprise anymoving parts and the sample gasdoes not come into contact with themicroflow sensor, which ensures anextremely long life time and highoperating stability. A good examplefor that is the independence from

humidty which may be present in thesample gas and could cover the sur-face of mirrors (with negative impactto the measuring accuracy) that areused with other oxygen measuringprinciples.


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Siemens Process Analytics at a glanceProducts

Siemens Process AnalyticsSiemens Process Analytics is a leadingprovider of process analyzers and pro-cess analysis systems. We offer our glo-bal customers the best solutions fortheir applications based on innovativeanalysis technologies, customized sys-tem engineering, sound knowledge ofcustomer applications and professionalsupport. And with Totally IntegratedAutomation (TIA). Siemens ProcessAnalytics is your qualified partner forefficient solutions that integrate pro-

cess analysers into automations sys-tems in the process industry.From demanding analysis tasks in thechemical, oil & gas and petrochemicalindustry to combustion control inpower plants to emission monitoring atwaste incineration plants, the highlyaccurate and reliable Siemens gas chro-matographs and continuous analyserswill always do the job.Siemens process Analytics offers a wideand innovative portfolio designed tomeet all user requirements for compre-hensive products and solutions.

Our ProductsThe product line of Siemens ProcessAnalytics comprises extractive and in-situ continuous gas analyzers (fig. 2 to5), process gas chromatographs (fig. 6to 9), sampling systems and auxiliaryequipment. Analyzers and chromato-graphs are available in different ver-sions for rack or field mounting, explo-sion protection, corrosion resistant etc.A flexible networking concept allowsinterfacing to DCS and maintenancestations via 4 to 20 mA, PROFIBUS,

Modbus, OPC or industrial ethernet.

Fig. 2: Series 6 gas analyzer (rack design)

Fig. 3: Product scope Siemens Continuous Gas Analyzers

Extractive Continuous Gas Analyzers (CGA)ULTRAMAT 23 The ULTRAMAT 23 is a cost-effective multicomponent analyser for the

measurement of up to 3 infrared sensitive gases (NDIR principle) plusoxygen (electrochemical cell). The ULTRAMAT 23 is suitable for a widerange of standard applications. Calibration using ambient air eliminatesthe need of expensive calibration gases.

CALOMAT 6/62 The CALOMAT 6 uses the thermal conductivity detection (TCD) methodto measure the concentration of certain process gases, preferably hydro-gen.The CALOMAT 62 applies the TCD method as well and is speciallydesigned for use in application with corrosive gases such as chlorine.

OXYMAT 6/61/64 The OXYMAT 6 uses the paramagnetic measuring method and can beused in applications for process control, emission monitoring and qualityassurance. Due to its ultrafast response, the OXYMAT 6 is perfect formonitoring safety-relevant plants. The corrosion-proof design allowsanalysis in the presence of highly corrosive gases.

The OXYMAT 61 is a low-cost oxygen analyser for standard applications.The OXYMAT 64 is a gas analyzer based on ZrO 2 technology to measuresmallest oxygen concentrations in pure gas applications.

ULTRAMAT 6 The ULTRAMAT 6 uses the NDIR measuring principle and can be used inall applications from emission monitoring to process control even in thepresence of highly corrosive gases.ULTRAMAT 6 is able to measure up to 4 infrared sensitive components ina single unit.

ULTRAMAT 6 /OXYMAT 6

Both analyzer benches can be combined in one housing to form a multi-component device for measuring up to two IR components and oxygen.

FIDAMAT 6 The FIDAMAT 6 measures the total hydrocarbon content in air or even inhigh-boiling gas mixtures. It covers nearly all requirements, from tracehydrocarbon detection in pure gases to measurement of high hydrocar-bon concentrations, even in the presence of corrosive gases.

In-situ Continuous Gas Analyzer (CGA)

LDS 6 LDS 6 is a high-performance in-s itu process gas analyser. The measure-ment (through the sensor) occurs directly in the process stream,no extractive sample line is required. The central unit is separated fromthe sensor by using fiber optics. Measurements are carried out in real-time. This enables a pro-active control of dynamic processes and allowsfast, cost-saving corrections.

Fig. 4: Series 6 gas analyzer (field design) Fig. 5: LDS 6 in-situ laser gas analyzer


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Siemens Process Analytics at a glanceProducts (continued) and Solutions

Fig. 6: MAXUM edition II Process GC

Fig. 7: MicroSAM Process GC

Fig. 8: SITRANS CV Natural Gas Analyzer

Our solutionsAnalytical solutions are always drivenby the customers requirements. Weoffer an integrated design covering allsteps from sampling point and samplepreparation up to complete analysercabinets or for installation in analysershelters (fig. 10). This includes also sig-nal processing and communications tothe control room and process controlsystem.

We rely on many years of world-wideexperience in process automation andengineering and a collection of special-ized knowledge in key industries andindustrial sectors. We provide Siemensquality from a single source with a func-tion warranty for the entire system.Read more in "Our Services.

Fig. 10: Analyzer house (shelter)

Process Gas Chromatographs (Process GC)MAXUM edition II MAXUM edition II is very well suited to be used in rough industrial envi-

ronments and performs a wide range of duties in the chemical and pet-rochemical industries and refineries.MAXUM II features e. g. a flexible, energy saving single or dual oven con-cept, valveless sampling and column switching, and parallel chromatog-raphy using multiple single trains as well as a wide range of detectorssuch as TCD, FID, FPD, PDHID, PDECD and PDPID.

MicroSAM MicroSAM is a very compact explosion-proof micro process chromato-graph. Using silicon-based micromechanical components it combinesminiaturization with increased performance at the same time.MicroSAM is easy to use and its rugged and small design allows mount-ing right at the sampling point. MicroSAM features drastically reducedcycle times, provides valveless sample injection and column switchingand saves installation, maintenance, and service costs.

SITRANS CV SITRANS CV is a micro process gas chromatograph especially designedfor reliable, exact and fast analysis of natural gas. The rugged and com-pact design makes SITRANS CV suitable for extreme areas of use, e.g. off-shore exploration or direct mounting on a pipeline.The special software "CV Control" meets the requirements of the naturalgas market, e.g. custody transfer.

Fig. 9: Product scope Siemens Process Gas Chromatographs


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Siemens Process Analytics at a glanceSolutions (continued) and Services

Our solutions ...Analyzer networking fordata communicationEngineering and manufacturing of pro-cess analytical solutions increasinglycomprises "networking". It is getting astandard requirement in the processindustry to connect analyzers andanalyzer systems to a communicationnetwork to provide for continuous anddirect data transfer from and to theanalysers.The two objectives are (fig. 12): To integrate the analyzer and

analyzer systems seamless into thePCS / DCS system of the plantand

To allow direct access to the analyzersor systems from a maintenancestation to ensure correct and reliableoperation including preventive orpredictive maintenance (fig.11).

Siemens Process Analytics provides net-working solutions to meet the demandsof both objectives.

Our ServicesSiemens Process Analytics is your com-petent and reliable partner world widefor Service, Support and Consulting.Our rescources for that are Expertise

As a manufacturer of a broad varietyof analyzers, we are very much expe-rienced in engineering and manufac-turing of analytical systems andanalyzer houses.We are familiar with communicationnetworks, well trained in service andmaintenance and familiar with manyindustrial pro cesses and industries.Thus, Siemens Process Analytics ownsa unique blend of overall analyticalexpertise and experience.

Global presenceWith our strategically located centersof competence in Germany, USA,Singapore, Dubai and Shanghai, weare globally present and acquaintedwith all respective local and regionalrequirements, codes and standards.All centers are networked together.

Fig. 12: Networking for DCS integration and maintenance support

Fig. 13: Portfolio of services

Fig. 11: Communication technologies


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Siemens Process Analytics at a glanceServices, continued

Our Services ...Service portfolioOur wide portfolio of services is seg-mented into Consulting, Support andService (fig. 13 to 14). It comprisesreally all measures, actions and advisesthat may be required by our clientsthroughout the entire lifecycle of theirplant. It ranges from site survey toinstallation check, from instruction ofplant personnel to spare part stock man-agement and from FEED for ProcessAnalytics (see below) to internet-basedservice Hotline.Our service and support portfolio(including third-party equipment) com-prises for example: Installation check Functionality tests Site acceptance test Instruction of plant personnel on site Preventive maintenance On site repair Remote fault clearance Spare part stock evaluation Spare part management Professional training center Process optimisation Internet-based hotline FEED for Process Analytics Technical consullting

FEED for Process AnalyticsFront End Engineering and Design(FEED) is part of the planning and engi-neering phase of a plant construction ormodification project and is done afterconceptual business planning and prior

to detail design. During the FEED phase,best opportunities exist for costs andtime savings for the project, as duringthis phase most of the entire costs aredefined and changes have least impactto the project. Siemens Process Analyt-ics holds a unique blend of expertise inanalytical technologies, applicationsand in providing complete analyticalsolutions to many industries.

Based on its expertise in analytical tech-nology, application and engineering ,Siemens Process Analytics offer a widescope of FEED services focused on anal-ysing principles, sampling technologies,application solutions as well as commu-nication system and given standards (allrelated to analytics) to support our cli-ents in maximizing performance andefficiency of their projects.Whether you are plant operators orbelong to an EPC Contractor you willbenefit in various ways from FEED forProcess Analytics by Siemens: Analytics and industry know how

available, right from the beginningof the project

Superior analyzer system perfor-mance with high availability

Established studies, that lead to

realistic investment decisions Fast and clear design of the analyzer

system specifications, drawings anddocumentation

Little project management andcoordination effort, due to oneresponsible contact person andless time involvement

Additional expertise on demand,without having the costs, the effortand the risks of building up the capac-ities

Lowest possible Total Costs of Owner-ship (TCO) along the lifecycle regard-

ing investment costs, consumptions,utilities supply and maintenance.

Fig. 14: Portfolio of services provided by Siemens Process Analytics


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www.siemens.com/processanalytics Siemens AG 2007Subject to change

Case Study

Siemens AGAutomation and DrivesSensors and CommunicationProcess Analytics76181 KARLSRUHE

Siemens Process Analytics - Answers for industry

If you have any questions, please contact your local sales representative or any of the contact addresses below:Siemens AGA&D SC PA, Process Analyticsstliche Rheinbrckenstr. 5076187 KarlsruheGermany

Phone:+49 721 595 3829Fax: +49 721 595 6375E-mail:[email protected]/prozessanalytics

Siemens Ltd., ChinaA&D SC, Process Analytics7F, China Marine TowerNo.1 Pu Dong AvenueShanghai, 200120P.R.China

Phone:+86 21 3889 3602Fax: +86 21 3889 3264E-mail: [email protected]

Siemens Energy & Automation Inc.7101 Hollister RoadHouston, TX 77040USA

Phone:+1 713 939 7400Fax: +1 713 939 9050E-mail: [email protected]

www.siemens.com/processanalytics

Siemens LLCA&D 2B.PO Box 2154,Dubai, U.A.E.

Phone:+971 4 366 0159Fax: +971 4 3660019E-mail: [email protected]/processanalytics

Siemens Pte. LimitedA&D SC PS/PA CoC60 MacPherson RoadSingapore 348615

Phone:+65 6490 8728Fax: +65 6490 8729E-mail: [email protected]

www.siemens.com/processanalytics

cs process analytics in vcm plants

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