CS Process Analytics in Methanol Plants

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Methanol production process

Process chainThe methanol processing chain (Fig. 1)consists of a number of fundamentalsteps each of which is important toachieve the final goal of producing highquality methanol.

Step1: Feed purificationNatural gas is compressed and sulphurremoved by hydrodesulphurisation inthe purifier. The desulphurized gas iscooled and flows to the saturator whereit contacts with hot water over a bed of

packing. The saturated gas containsmost of the steam required for laterreforming. Additional steam, generatedin the boiler, is made up to the gasstream to achieve the required steamto carbon ratio for reforming.

Step 2: Feed reforming(Syngas generation)Syngas (from Synthesis Gas) is com-posed of hydrogen (H2), carbon monox-ide (CO) and carbon dioxide (CO2),whereas the ration H2/CO is importantin view of the process efficiency using acertain catalyst material. Syngas is pro-duced mainly from natural gas (NG)through a reforming process. Varioustechnologies are used for that, with orwithout using air or oxygen:Steam Methane Reforming (SMR), Par-tial Oxidation (POX), AutothermalReforming (ATR), e.a.

After cooling, syngas is compressed tosynthesis pressure, which ranges from40 to 110 bar and helps the conversionreaction to occur.

Step 3: Methanol SynthesisThe synthesis gas is fed to the methanolsynthesis converterat about 130 C. Theconverter is of different design (typi-cally in cascades) depending on the par-ticular technology applied. The com-pressed gas is preheated to reactiontemperatures inside the tubes as itflows through the hot catalyst bed. The

hot reacted gas leaves the converterand provides heat to the saturator watercircuit and the loop interchanger beforefinally being cooled. Crude methanol isseparated from the uncondensed gasesand the gases are recirculated back tothe converter via the circulator.

Step 4: Methanol distillationThe crude methanol passes to amethanol distillation section, where itis stabilised and reduced to an eco-nomic water content for transport.Purge gas from the methanol synthesiscascade is treated to recover hydrogen

for recycling with the tail gas passing tothe gas turbine as fuel.

Various technologiesVarious methanol synthesis technolo-gies have been developed and areimplemented worldwide in methanolplants, for example:

Lurgi uses an autothermal reformerfor syngas generation and a two-stage synthesis reactor system con-sisting of a gas-cooled and a watercooled reactor with very favorabletemperature profiles over the catalystbed.

Uhdeuses steam reforming for syn-gas generation and an isothermaltubular reactor with the catalyst con-tained in vertical tubes providing lowby-product formation.

Topsoe uses steam reforming for syn-gas generation and a straight-tubedboiling water reactor for methanolsynthesis. Another technology isbased on autothermal reforming fol-lowed again by a boiling water syn-thesis reactor.

Davy uses a two-stage steam reform-ing followed by a synthesis loop thatcan operate at pressures between 70

to 100 bar.

Wrme

Fig. 1: Generic flowsheet of the methanol process, simplified


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Syngas generation

Feed pretreatmentNG is a mixture consisting primarily ofhydrocarbons, but other gases are alsopresent such as nitrogen, carbon diox-ide and sulfur compounds. In order toavoid poisoning of the catalyst materialin the conversion process, the NG is firstpurified, mainly from sulfur, in a hydro-genation reactor and a washing system.After purification the feed gas is pre-treated (saturated with process conden-sate and process water and preheated)before being fed to the syngas genera-

tion process.

Feed reforming(Syngas generation)Syngas can be made by various technol-ogies which require mostly steam andair or oxygen. During the feed (NG)reforming process, the hydrocarbonmolecules are broken down andstripped of their hydrogen atoms. Thecarbon atoms together with oxygen,introduced as steam, air or as pure gas,form CO molecules. All reactions, inde-pendently of the technology applied,

result in a gas consisting of H2, CO andCO2called Synthesis Gas or Syngas.

Steam-Methane Reforming (SMR)In steam-methane reforming, the mostwidely used technology for syngas pro-duction, natural gas and steam aremixed and passed over a catalystlocated in a firebox. Heat for the reac-tion is supplied by burning some of thefeedstock gas. SMR does not require aseparate air or oxygen supply from aoxygen plant.

Partial Oxidation Reforming (POX)The partial oxidation process is a directnon-catalytic reaction between oxygenand the hydrocarbon gas. It uses nosteam and requires no catalyst. It isoperated at very high temperatures ofabout 1400 C and oxygen is needed.

Autothermal Reforming (ATR)Unlike POX, autothermal reforminguses a catalyst to reform NG to syngas inthe presence of steam and oxygen. Thereaction produces high temperaturesand no additional heat source is needed(autothermal). It produces syngas that

is suitable for most conversion pro-cesses. But an air separation plant isrequired.

Process analysis in NG pretreat-ment and conversionA great number of process analyzersare used in the NG pretreatment and NGconversion sections. Details regarding

analyzers, sampling locations, mea-sured components etc. will differ fromplant to plant depending on the existingprocess technology and plant design.Therefore, Fig. 2 and Table 13 show typ-icalmeasuring point locations and typi-cal measuring tasks. Real plant condi-tions may differ from that.

Table 1: Process analyzer measuring tasks in steam reforming, acc. to Fig. 2

Sampling pointSampling stream

MeasuringComponents

Suitable Analyzer

1.1 SaturatorCondensate stabilizer

Total SH2S

MAXUMMAXUM

1.2 Hydrogenation/Desulphurization

Claus off gas

Total S, H2S, CO2MercaptansO2, SO2

MAXUMMAXUMOXYMAT 6, TPA

1.3 Dehydration/ Mercaptan removal Total S, COS, H2

S,Mercaptans

MAXUM

1.4 LPG Total S, COS, H2S,Mercaptans

MAXUM

1.5 Propane, Butane product C2-C4, C3-C5+ MAXUM/MicroSAM

1.6 Treated NG Sulphur (ppm/ppb) MAXUM

1.7/1.8 Various furnaces flue gases andprocess off gases

O2, SO2, NOx, H2, ... OXYMAT 6,ULTRAMAT 6,CALOMAT 6

1.9 Raw Syngas CH4, CO2 ULTRAMAT 6

1.10 Syngas H2, CO, CO2, N2, CH4,COS, H2S, Total S

MAXUM

TPA: Third party analyzer

Fuel gas

Catalyst

filled tubes

Steam

Raw syngas

Natural Gas

Heat

exchange

Flue gas

1.8

1.2

NG Hydrogenation

NG Desulphurization

NG Saturation

Dehydration

Mercaptane removal

NGL extraction/LPG

NG

pre-treatment

1.3

1.4

Syngasconditioning

Slurry

incineration

Syngas

1.6

NG

reforming

Fired

heater

Flue gas

1.10

1.7

1.1

1.9

Fuel gas

Propane, Butane1.5

1.8

1.6

1.10

1.7

1.9

Fig. 2: Natural Gas conversion to syngas with Steam Reforming Reactor


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Methanol Synthesis and Distillation

Methanol SynthesisIn the Methanol Synthesis section, com-pressed synthesis gas is converted intomethanol in a synthesis reaction, wherecarbon oxides and hydrogen react toform methanol and water according toCO + 2H2CH3OH. This reaction ishighly exothermic and the heat must bepromptly removed in a one or twostages cooler.A methanol synthesis reactor systemtypically comprises main converters,feed/effluent exanger, saturator water-

cooled reactor, and a crude cooler.Different reactor designs are in use,generally based on the concept of syn-thesis gas flowing in the catalyst bedsacross boiler (cooling) tubes to recoverthe reaction heat as qualitative steam.

Methanol DistillationThe crude methanol from the synthesisloop contains both water and low levelsof by-products, which must be removedby distillation to achieve the requiredproduct quality. This is typically per-

formed in a two or three columnsystem. In the topping column, com-pounds with boiling points lower thanmethanol are removed for use as fuels.In the refining column, methanol is sep-arated from water and by-products.Product quality finally ranges from fuelgrade to to highly pure methanol.

Process analysis inMethanol Synthesis

and DestillationProcess analyzers, mainly continuousgas analyzers and process gas chro-matographs, are used in the methanolsynthesis and distillation section tomonitor process function and productquality. Details will differ from plant toplant depending on process technologyand plant design.

Fig. 3: Methanol synthesis (left) and distillation (right) steps


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Steam and oxygen supply

Steam and oxygen supplyUtilities are pieces of equipment orplants to provide services such asheat or electricity necessary to fulfillthe plants main goal. Methanol plantstypically require steam, compressed air,and oxygen.

Steam supplyFor steam generation units (boiler),process analyzers are used to optimizethe combustion process through mea-surement of O2as well as to monitor theflue gas for air polluting componentssuch as SO2, NOx, etc. (according tolocal regulations) using CEM systems.

Oxygen supplyThe production of oxygen is a morecomplex process. Large-scale oxygenproduction units use cryogenic air sepa-ration processes, which are based ondifferences in boiling points to separateand purify products. Cryogenic air sepa-ration plants are referred to as an AirSeparation Unit (ASU) or Oxygen Plant.

Different process configurations are inuse, but all of them include the follow-ing steps (Fig. 4):

Filtering and compressing of air

Removing contaminants, includingwater vapor and carbon dioxide(which would freeze in the process)

Cooling the air to very low tempera-ture through heat exchange andrefrigeration processes

Distilling the partially-condensed airto produce desired products

Warming gaseous products and wastestreams in heat exchangers that alsocool the incoming air

The units of the ASU that operate at verylow temperatures (distillation columns,

heat exchangers and cold interconnect-ing piping sections) must be well insu-lated to minimize energy consumption.Therefore, these components arelocated inside insulated "cold boxes.

Fig. 4 and Table 2 show typical measur-ing point locations and related measur-ing tasks in a ASU plant.

Table 2: Process analyzer measuring tasks in the oxygen production unit

Sampling locationSampling stream

Measuringcomponent

Measuringrange

SuitableSiemens analyzers

1 Feed to high pressure column CO2THCH2O

0 ... 10 ppm0 ... 10 ppm

ULTRAMAT 6FIDAMAT 6TPA

2 Circle gas nitrogen O2 0 ... 21 % OXYMAT 61

3 Low pressure column,liquid phase

O2CO2THC

98 ... 100 %0 ... 10 ppm0 ... 300 ppm

OXYMAT 6ULTRAMAT 6FIDAMAT 6

4 Feed to low pressure column O2 0 ... 50 % OXYMAT 6

5 Liquid nitrogen O2CO2H2O

0 ... 10 ppm0 ... 10 ppm

OXYMAT 64ULTRAMAT 6TPA

6 Liquid oxygen O2CH4, C2H4,C2H6, C3H8

98 ... 100 %low ppmranges

OXYMAT 61

MAXUM

7 Gaseous oxygen O2THCCO2

H2O

98 ... 100 %TracesTraces

OXYMAT 61FIDAMAT 6ULTRAMAT 61

TPA8 Gaseous nitrogen O2

THCH2O

0 ... 10 ppm0 ... 10 ppm0 ... 10 ppm

OXYMAT 64FIDAMAT 6TPA

9 High purity Argon and Krypton H2, O2, N2,CH4, CO

Ultra traces(ppb)

MAXUM with sensitivedetector (PDHID)

10 Process air feed beforemain condenser

CH4, C2H4,C2H6, C3H8

low ppmranges

MAXUM

11 Process air beforemolecular sieve CO2 0 ... 10 ppm FIDAMAT 6

Fig. 4: Oxygen production through air separation (G: gaseous; L, LI: liquid)


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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. 5 to8), process gas chromatographs (fig. 9to 12), 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. 5: Series 6 gas analyzer (rack design)

Fig. 6: Product scope Siemens Continuous Gas Analyzers

Extractive Continuous Gas Analyzers (CGA)

ULTRAMAT 23 The ULTRAMAT 23 is a cost-effective multicomponent analyser for themeasurement 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 ZrO2technology 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-situ 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. 7: Series 6 gas analyzer (field design) Fig. 8: LDS 6 in-situ laser gas analyzer


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Siemens Process Analytics at a glanceProducts (continued) and Solutions

Fig. 9: MAXUM edition II Process GC

Fig. 10: MicroSAM Process GC

Fig. 11: SITRANS CV Natural Gas Analyzer

Our solutionsAnalytical solutions are always drivenby the customers requirements. Weoffer an integrated design covering all

steps from sampling point and samplepreparation up to complete analysercabinets or for installation in analysershelters (fig. 13). 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. 13: 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. 12: 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. 15):

To integrate the analyzer andanalyzer 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.14).

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

ExpertiseAs a manufacturer of a broad variety

of 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. 15: Networking for DCS integration and maintenance support

Fig. 16: Portfolio of services

Fig. 14: 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. 16 to 17). 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 howavailable, 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. 17: Portfolio of services provided by Siemens Process Analytics


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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

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

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CS Process Analytics in Methanol Plants