Alkaline Chloride Electrolysis Plants

Alkaline Chloride electrolysis plantsSuperior membraneprocess

UhdeA companyof ThyssenKrupp

Technologies

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2 Table of contents2

3 Company profile

4 Uhde’s remarkably long experience

6 The Uhde membrane process

8 The only membrane cell of its kind

10 Current through bipolar electrolyser

12 The advantages of a modular concept

14 There is even more in for you

15 Technical data

16 Solutions through innovations

18 Additional Uhde Process Features

19 Services for our customers

The sodium chloride crystal. It consists of tiny cubes tightlybound together. Similar to the Uhde singleelement technology. This modular concept has a significant number of advantages. Find out more about these benefits and oneof the world’s leading suppliersof chlorine plants.

3Company profileUhde and De Nora group to collaborate on electrolysis

Engineering officesand headquarters of Uhde in Dortmund,Germany.

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To date, the Dortmund-basedengineering contractor with itshighly specialised workforce ofaround 3,500 and its interna-tional network of subsidiariesand branch offices, has suc-cessfully completed over 2,000projects throughout the world.

Uhde can offer more than 250different processes coveringmany different sectors of thechemical industry.

In the field of chlorine technologyUhde and De Nora establishedbeginning of 2001 a JointVenture to cooperate in the fieldof electrolysis technology.This cooperation will be basedon the foundation of two jointcompanies domiciled in Milan/Italy and mentioned below:

Uhdenora Technologies S.r.l.

Uhdenora S.p.A.

Uhde was founded in 1921 andis now part of the ThyssenKruppgroup. The company employs3,500 persons around theworld. Its main field of activity,alongside chlorine alkali elec-trolysis, being in the engineering and construction ofplants for fertilisers, organicchemicals, polymers, oil andgas technology and pharma-ceuticals.

Since 1923, De Nora has beenone of the world leaders in the development of new technolo-gies and industrial processes, particularly for the alkalinechlorine industry. The companyemploys a total of 650 staff, with350 in Italy and 300 abroad.

Uhde and De Nora intend tocombine their technologies andexpertise in research and devel-opment, in order to providetheir worldwide alkali chlorineindustry customers with evenbetter performance in the fieldsof planning, design, construc-tion and after-sales service forelectrolysis plants. It is our target to optimise the relevanttechnologies and to reduceeven further the energy con-sumption.Uhde and De Nora have expe-rience stretching back overdecades in this field and haveconstructed over 135 referenceplants around the world. Theynow have subsidiaries on allcontinents.

Our plant construction businessin this technological field will in future be handled by Uhde of Dortmund, Germany and Uhdenora S.p.A. of Milan. The new italian company will bemanaged by Uhde.This cooperation will further improve our service for our cus-tomers in this highly competitivemarket.

Uhde’s remarkablylong experience

The first processes used tomanufacture chlorine and caustic soda involved theelectrolytic splitting of salt(sodium chloride) and wereintroduced to Germany in 1890in the form of the ”Griesheim”diaphragm cell and to the USAin 1897 in the form of the”Castner-Kellner” cell whichworked on a mercury/amalgambasis.

In the 1980s the manufactureof chlorine using these twoprocesses reached maximumcapacity producing approx. 35million tpa. More than 80 of theplants involved were built byUhde.

Today both the diaphragm andthe amalgam processes havebecome obsolete for newinstallations as they have ahigher energy consumption andare less environmentally friendly.They have been replaced by thelatest development in chlorine/caustic soda technology: themembrane process.

In 1973 when the first commer-cial membranes became avail-able, Hoechst AG, Bayer AG andUhde GmbH began researchand development work on themembrane technology.This process is not just energyefficient, it also producesconsistently high-quality causticsoda, is environmentally friendly,and extremely safe.

Until today Uhde’s know-how isbased on the combined effortsof these three companies in theresearch and development ofthis technology.Since 1998 Uhde is the soleowner of this know-how andcontinues to put great effort inthe further development of theUhde membrane cell technology.

In December 2000, Uhde andGruppo de Nora of Milano, Italyagreed on the foundation ofUhdenora Technologies S.r.l. tofurther optimise the technologyand to reduce even further theenergy consumption. Theentrepreneurial management ofthe joint company lays withUhde.

kWh/t NaOH

3 600

3 200

2 800

2 400

2 000

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Mercury process Diaphragm process

DC-power Steam consumption for concentration of the NaOH to 50 %

Membrane process

Comparative energy consumption figures

Conversion factor: 1 t steam ≈ 400 kWh

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Uhde has more than

40 years of experience

in the designing and

construction of chlorine/

caustic soda plants.

Our more than 150

plants throughout the

world have an overall

production capacity in

excess of 9 million tpa

NaOH (100%) and help

make Uhde unique in

its field.

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The SADAF plantin Saudi Arabia,which has a capa-city of 250,000 tpaNaOH (100%). This plant went onstream in 1997and is one of thelargest membraneplants in the world.

6 The Uhde membrane processAll from one hand

NaOCl-

Solution

BrineFiltration

Cl2

The Uhde know-how for themembrane process covers allthe process units as shown in the diagram as well as vari-ous downstream and utilitiessupply units.

A modern chlorine plant isequipped with a brine circulationsystem which is specially desi-gned for the membrane techno-logy. The higher sodium chloridedepletion in the membrane cellsmeans that the recycle rate andthe amount of equipment needed are significantly lowerthan in a mercury plant with thesame capacity. The plant hasan additional brine preparationprocess which uses polishingfilters and ion exchangers toensure that higher quality brineenters the membrane cells.

The chlorine leaves the cells withthe depleted brine. If high-puritychlorine is required (e.g. for adownstream VCM plant), hydro-chloric acid can be added to thefeed brine to reduce the oxygencontent in the chlorine product.

Uhde is the only

contractor able to

supply complete

plant complexes

from one hand.

BrineFiltration

BrinePurification

Brine Clarificationand Precipitation

BrineSaturation

Salt storageand Handling

AnolyteDechlorination

ChlorateDecomposition

ChlorineCompression

ChlorineTreatment

Membrane Electrolysis

Transformer/Rectifier

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Caustic 50 %

NaOH

32 %

Circulation

Caustic

Hydrogen

Chlorine

Bleaching Lye

Hydrogen fromSteam-Reformer

Cl2Tailgas

Cl2 Tailgas Chlorine

Dry

Chlorine

The Uhde membraneprocess providing allunits from one singlesource.

Once the wet chlorine gas iscooled and filtered it can be feddirectly to the consumer plant(e.g. a hydrochloric acid plant).In other cases, it is dried andcompressed before being fed tothe consumer plant (e.g. a VCMplant) or before being liquefiedfor storage in tanks.

The membrane process alsoinvolves a catholyte circulationsystem. A part stream of theproduct NaOH 32% is recycledas catholyte inlet to the mem-brane cells. Before inlet, it isdiluted by demineralised waterto NaOH 30%. The producedcaustic soda can be concentra-ted and fed to a crystallisationunit if necessary.

Hydrogen is a valuable by-pro-duct of the process and can besupplied to hydrogen consum-ers, such as hydrochloric acidplants or hydrogen plants, onceit has been cooled and filtered.

H2

Chlorine Absorption and Safety System

HydrogenTreatment

CausticDilution

ChlorineLiquefaction

ChlorineEvaporation

ChlorineStorage

Catholyteand Cooling

CausticConcentration

8 The only membrane cell of its kind:The single element

The single elementOne of the most significant factors affecting the operatingcosts of a chloralkali plant is its on-stream time which isparticularly dependent upon the reliability of the materialsand the robust construction ofthe cell.

This is especially true in thecase of membrane electrolysisunits in which the relativelysensitive membrane plays thecentral role.

The single cell element, other-wise known as the single ele-ment, is based on an optimalcombination of the ideal mate-rials for the job and simplemaintenance.

The anode half shell is madecompletely from titanium and thecathode half shell from nickel.The seal system comprises aPTFE frame gasket and goretexsealing cords. The externalsteel flanges, which have elec-trically insulated bolting withspring washers, guarantee that the single element has noleakages for the whole servicelife.

Functional descriptionPure brine enters the anodehalf shell via an external tubeand a nozzle and is distributedacross the whole width via aninternal feed pipe.

A downcomer plate uses the

Cathode half shell

Membrane

PTFE frame gasket

Anode half shell

Sealing cord

Discharge pipe

The single element comprisesan anode half shell, a cathode

half shell, a membrane and a sealing system with external

flanges.

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Functional descriptionPure brine enters the anodehalf shell via an external tubeand a nozzle and is distributedacross the whole width via aninternal feed pipe.

A downcomer plate uses thegas lift effect to create a highdegree of internal brine circula-tion ensuring ideal distributionwith uniform density andtemperature.A baffle plate is arranged inthe upper section of the anodehalf shell and has the following 3 basic functions:

● The brine and the chlorineare fed to the upper end ofthe anode half shell ensuringthat this section is completelysupplied with brine for a properfunction of the membrane.

● The chlorine is separatedfrom the brine behind thebaffle plate in a kind of„separation zone“, so thatthe chlorine gas and the brinecan leave the single elementin a homogeneous flowthrough the discharge pipe.

● The gas lift effect also causescirculation around the baffleplate ensuring uniform distri-bution here too.

A similar method involving a feedpipe is used to distribute causticsoda in the cathode half shell.The products, hydrogen andcaustic soda (32%), also leave the single element via adischarge pipe.Due to the fact that there isonly a small difference in thecaustic soda concentration atthe inlet and at the outlet andthat hydrogen and caustic sodaare more easily separated thecathode half shell does nothave a downcomer and a baffleplate.

Foam

Anode half shell

Baffle plate

Contact strip

Discharge

Feed pipe

Feed pipe

Downcomer plate

Cathode half shell

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1.+2.

Principle of the current flowthrough the bipolarstack of single elements.

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The single elements are arranged in series to form anelectrolyser. A parallel connec-tion is used on the electrolyteand product side whilst the serial configuration is used forthe electrical side. The electro-lysis current (direct current) isfed across contact strips fromthe cathode half shells to theanode half shells of the adjacentsingle elements in the electro-lyser. Internal plate conductorsarranged in the half shells ensureuniform current distribution to the anodes and cathodes.

Single elements are assembledand tested in the workshop outside the cell room wherethey can be stored for months.In case of maintenance of asingle element from the cellroom it can be quickly and easily replaced by another onetaken from the stores.

1.

2.

Membrane

Anode

Current through bipolar electrolyser

A direct and short current path ensures low ohmic drop

and ideal current distribution.

Cathode

Plate conductor

Contact strip

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Connection of theinlet and outlet pipes to each individual elementand to the powersupply.

13The advantages of a modular concept

The bipolar membrane electroly-ser is a modular concept, thathas a number of advantagesincluding low investment costs,low energy consumption and along service life.The single elements are sus-pended in a frame and arepressed against each other bya clamping device to form a„bipolar stack“. Slight pressureby spring loaded pressure boltsis exerted on the stack prior to start-up to ensure optimal electrical contact between theelements. In contrast to con-ventional electrolysers with a filter press design, no heavy-duty pressers or track rods areneeded to seal the electrolyser.The elements are all sealed individually beforehand whichleads to increased operationalreliability.

All the elements are connectedto the inlet and outlet headersarranged underneath the elec-trolyser by flexible, transparentPTFE tubes (see picture). Thetubes with smaller cross-sec-tions ensure that a constantstream of electrolyte is suppliedto the half-shells, whilst thetubes with larger cross-sections(corrugated hoses) carry thechlorine gas with anolyte andhydrogen gas with catholyteaway from the cell. This fail-safeconnection system can be usedto check each individual cell forproper functioning by observingthe colour and flow of theproduct streams in these tubes.

Between 20 and 80 elementscan be connected to form astack. Several of these stacksconnected in series create amembrane electrolyser.

Top: Bipolar membrane electrolyser,pictured here in the cell room at BAYERUerdingen: we see 6 bipolar electrolyserswith a total of 158 single elements in eachelectrolyser (79 elements forming a stack).

Contact strip

Single element

Inlet hoses

Outlet hoses

Header

Busbars

Cell rack

External flexiblehose-connectionsfor the inlet andoutlet of fluids, located underneaththe electrolyser.

Below: The singleelement rack: Each element can be exchanged individually

14 There is even more in for you

A number of electrolysers (the number being determinedby the production capacity) are set up side by side andelectrically connected in parallel.A rectifier supplies one or moreof the electrolysers with directcurrent and they can be easilyserviced by disconnecting therectifier or by the individual circuit breakers and isolatingswitches.

The pipelines, which are usedfor supplying the single ele-ments with brine and causticsoda and discharging the chlorine, caustic soda and hydrogen, are arranged under-neath the electrolyser such that the single elements can be easily replaced.

Each electrolyser is equippedwith a control and instrumentunit for adjusting the amount ofelectrolytes and with shut-offvalves.

A header system is attached tothe front side of the electrolysersfor distributing the electrolytes,or for collecting the products.

The Uhde design of the cell room has been

optimised to ensure simple maintenance,

minimal space requirement and low investment

costs. It has been standardised to a large extent

and is shown in detail in a 3D computer model

(PDMS).

Single elements

Product main headers for Cl2+H2

Cell headers for Cl2 + anolyte and H2 + catholyte

Pressure plates

Cell room crane

_ _ _ _ _ _ _ _

15Technical data

Operating data

Current density up to 6 kA/m2

Power consumption see graph

Cell temperature 88 - 90° C

Service life :

anode coating > 8 years

cathode coating > 8 years

membranes > 4 years

gaskets > 4 years

metal elements > 10 years

Active area per element 2.72 m2

Product quality

Caustic soda solution

NaOH 32 % (wt.)

NaCl < 30 ppm

Gaseous chlorine

Cl2 > 98 % (vol.)

O2 0.6-1.5 % (vol.)

H2 < 0.05 % (vol.)

Hydrogen

H2 > 99.9 % (vol.)

U [V]

3,2

3,0

2,8

2,6

2,4

2,2

E[kWh]

2300

2200

2100

2000

1900

1800

Power Consumption per metric ton NaOH

0 1 2 3 4 5 6 7 i [kA/m2]

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16 Solutions through innovations

The single element can be replaced quickly and easily.Elements are assembled in the electrolyser workshop,where leakage tests are carried out.

These features ensure:● highest possible operational

reliability ● easy maintenance● cost-optimised membrane

replacement and electroderecoating according to schedule

● no additional investmentsneeded for back-up electro-lysers

● minimal loss of production

Single element technology

The membranes in the cell elements are fixed betweentwo electrodes using spacers.The electrode spacing can beoptimally adapted to eachmembrane type using spacerswith the appropriate thick-ness.

Each single element is sealedusing a flange, bolting andPTFE gaskets. Each cell element is tested prior to operation to ensure that it is100% leakproof. Costly pressing systems, such asthose used in electrolyserswith a filter press design, arenot necessary.

The anode half shell (Ti), catho-de half shell (Ni), gaskets andtubes (PTFE) are all madefrom corrosion-resistantmaterial and guarantee thecell elements a maximumservice life. The electrolyserheaders are long service lifecomponents and are madefrom PVC/FRP or titanium onthe anode side and fromPP/FRP on the cathode side.

Membrane stability Individual seal systemHigh material quality

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The bipolar arrangementallows the voltage of eachsingle element to be preciselymonitored. Faults can bespotted immediately andconsequent damage avoided.Uhde has been using thebipolar cell arrangement forover 20 years and has muchmore experience in this fieldthan most of its competitors.

The modular construction ofthe single element electroly-sers allows the cell room to be configured in a number of different ways. The electrolysers can have upto 160 elements, whilst thereis no limit to the number ofelectrolysers permitted ineach cell room. Consequently,different cell rooms can be realised for different capacities,areas of application and oper-ations etc. whilst the samecell type is used in all cases.Existing cell rooms can alsobe easily expanded.

Single-element cells can beoperated at a current densityof up to 6 kA/m2. This permitslow investment cost and lowspace requirement for a cellroom.

Stray currents are hardlydetectable, even in the largestelectrolysers which can haveup to 160 cell elements. Thisis attributable to the fact thatthe electrolyte enters andleaves the cells via long tubeswhich are situated outside the cell and which act as insulators.

The single-element techno-logy and the alkali-chloridetechnology are under costantdevelopment and are contin-ually being adapted to meetincreasing demands. Thisensures that our technology is always state-of-the-art andalways at the head of its field.The third cell generation isnow in operation and is compatible with previous generations. Older elementscan be modernised during remembraning and recoatingprocesses.

Bipolar arrangement Modular construction High current densities

No stray currents

State-of-the-art technology

18 Additional Uhde process features

The robust design and excel-lent tightness of the cellsallows that they can be oper-ated at pressures of up to 200 mbar g. Blowers for Cl2and H2 are not necessary as air cannot be sucked into theCl2 or H2 lines.Each electrolyser is equippedwith safety valves for Cl2 andH2 to ensure safe plantoperation. This safety device is exclusive to Uhde.

Pressurised cell operation

Uhde strongly recommendsthat the membrane electrol-ysers are operated with exter-nal circulation loops for thecaustic soda solution and witha heat exchanger. This will al-low plant operators to optimi-se the temperature of the cellsat any load and to cool downelectrolysers in the event of shutdowns thus avoidingthe production of off-spec.caustic soda. Operate with a large volumeof caustic soda solution makesthe plant not sensitive to shortdisturbances e. g. to the demineralised water supply.

Feed brine can be acidified toimprove the Cl2 gas quality.The potential risk of destroy-ing membranes by over-acidi-fication is eliminated in thecell element by the internalcell design (downcomer plate)which provides effective mix-ing within the cells.

The Uhde chlorine dryingtower is part of our range ofproprietary equipment. Oneparticular feature of the toweris the fact that sulphuric acidconsumption is at its lowestwhen the ultimate humidity ofthe chlorine is at its lowest.This is achieved by the two-stage design which is housedin a single tower thus savingspace and investment cost.

External caustic circulation Brine acidification

Any plant using gaseous or liquid chlorine, must complywith stringent environmentalregulations. The waste gasdechlorination unit is an es-sential feature in this respectand the Uhde design ensuresthat chlorine cannot enter theenvironment under any oper-ating conditions.

Waste gas dechlorination

Chlorine drying tower

19Services for our customers

Uhde is dedicated to providingtheir customers with a widerange of services and tosupporting them in their effortsto succeed in their line ofbusiness.With our worldwide network ofsubsidiaries, affiliated companies,experienced local representativesand first-class backing from ourhead office, Uhde has the idealqualifications to achieve thisgoal.We at Uhde place particular im-portance on getting togetherwith the customers at an earlystage to combine their ambitionwith our experience.Whenever necessary we givepotential customers the oppor-tunity to visit operating plantsand to personally evaluate suchmatters as process operability;maintenance and on-streamtime. We aim to build our futurebusiness on the confidence ourcustomers place in us.

Uhde provides more than thespectrum of services associatedwith an EPC contractor from theinitial feasibility study, to financ-ing and project managementright up to the commissioningof units and grass-root plants.

Our large portfolio of services● Feasibility studies/Technology

selection● Project management● Arranging financing schemes● Financial guidance based on

intimate knowledge of locallaws, regulations and taxprocedures

● Environmental studies● Basic/Detail engineering● Utilities/Offsites/Infrastructure● Procurement/Inspection/

Transportation services● Civil works and erection● Commissioning● Training of operating personnel● Plant operation/Plant

maintenance

The policy of our Uhde groupand our subsidiaries is toensure utmost quality in the implementation of our projects.Our head office and subsidiariesworldwide work to the samequality standard, certified DIN /ISO 9001 / EN29001.We remain in contact with ourcustomers even after projectcompletion. Partnering is ourbyword.By organising and supportingtechnical symposia, our ChlorineSymposium for example, wepromote active communication

between customers, partners,operators and our specialists.This enables our customers to benefit fromthe development of new technologies and theexchange of trouble-shooting information.

We like to cultivate our business relationshipsand learn more about the future goals of our customers. Our after-sales service includes regular consultancy visits which keepthe owner informed about latestdevelopments or revampingpossibilities. The direct deliveryof spare parts has always beenpart of the after-sales serviceprovided by Uhde.Uhde stands for tailormadeconcepts and international com-petence. Competence that is based anmore than 79 plants worldwidefeaturing membrane techno-logy.

Process control system configuration.

For more information contactone of the Uhde offices nearyou or see Internet:www.thyssenkrupp.com/uhde

Further information on this subject can be found in the following video:The market is never wrong The success story of ourSingle-Element Technology

The video is available free ofcharge in English, in VHS, PALor NTSC from:Public Relations, Mrs KlimeckTel.: +49 2 31 5 47-20 43Fax: +49 2 31 5 47-26 28