riedhammer/sacmi kilns – latest developments for sanitaryware · riedhammer/sacmi kilns –...

E 128 cfi/Ber. DKG 89 (2012) No. 5

Process Engineering

IntroductionFor new developments of kilns forsanitaryware all plant componentsare to be submitted to thoroughexaminations in view of their designand construction as well as therequired process and materials tech-nology to find possible modificationswhich allow the plant to perfectlyfulfill their function. The focal pointsin this connection are energy saving

and the associated reduction of CO2emissions, including considering theappropriate heating methods andtransport methods, design of heatinsulating and heat absorbing com-ponents. The latest methods fordetermining stationary and transientheat transmission processes and forsimulating flows for the optimisationof heat transmission and tempera-ture uniformity, e.g. via computercalculations, are used for this pur-pose. The respective requirementsare listed in a specification bringingout solutions such as the EnergyManagement System (EMS), Com-bined Heat Supply Network and thecompletely redesigned RiedhammerREKO shuttle kiln. The effectivenessof these newly developed products isdocumented by the respective oper-ational data.

Initial situationThe production of ceramic productsis always closely linked with thermalprocesses. As ceramic sanitaryware isfired at relatively high temperaturesbetween 1180 °C and 1250 °C thetheoretical energy requirement forobtaining such temperatures andwithout consideration of differentheats of transition already amountsto 295–320 kcal/kg. The diverseproducts with their different weightsrequire kiln furniture as refractorysupports during firing which are

used in a weight ratio of ware : kilnfurniture = 1 : 1,1 to 1 : 1,3 [1]. Thisleads to a more than doubled massof ceramic products to be fired andthe theoretical energy requirementincreases accordingly.Whereas only a small quantity ofenergy consuming transport meansare used in roller kilns as no kiln carsare necessary in this kiln type – (taking into account the slightlyincreased radiation losses of thetransport rollers at the outer kilnwall) – the cars with their refractorysuperstructure have to be consid-ered for the energy calculation inshuttle and tunnel kilns with cartransport systems (Fig. 1). In thesekiln types the heating is effectedaccording to the laws of transientheat conduction. With modern com-puter simulation calculation meth-ods [2] the most favourable changein enthalpy can be determined as afunction of the firing cycle and of thetemperature dependent on therefractory car insulation to be select-ed. On average the roller kilns havean approx. 25 % lower energy con-sumption in comparison with tunnelkilns with car conveyance.Riedhammer has always focused onobtaining the lowest possible energyconsumption for its kiln plants.According to Tab. 1 which draws acomparison between standard tun-nel kilns with car transport and standard tunnel kilns available onthe world market, up to 55 % of theenergy costs and, due to the phys-ical connection, also the corres-ponding amount of CO2 emissionscan be saved by using the availabletechnology and experience. For thiscomparison a production capacity of 50 t/d and a natural gas price ofEUR 0,3/m³n were taken as a basis.With up to 103 % the differencesbetween Riedhammer roller kilnsand conventional tunnel kilns areeven more significant which is repre-sented in Tab. 2. The same fuelprices as for Tab.1 were taken as acalculation basis, assuming, howev-er, production capacities of 30 t/d.All kiln types for the sanitary ceram-ic industry are fossil fuel heated. Theenormous capacities – more than50 t/d are no rarity – require largeplant cross sections [3] for which

Riedhammer/Sacmi Kilns – LatestDevelopments for Sanitaryware

Jörg Ridder, David LindlRiedhammer GmbH90411 Nürnberg, GermanyE-mail: [email protected] www.riedhammer.de

Fig. 1 Tunnel kiln with kiln car conveyance for firing sanitaryware

Tab. 1 Comparison of energy and emission data of tunnel kilns

RiedhammerTunnel KilnStandard

Tunnel KilnsAvailable onthe Market

Energy consumption [kcal/kg net]

814 1260

Energy consumption [kcal/kg charge]

387 599

Total fuel costs [EUR/a] 519 767 802 326

Total CO2 emission [kg/a] 3 465 116 5 348 837

Difference +55 %

electrical heating is not suitable forstructural and thermo-technical rea-sons.Due to the inevitable waste gas loss-es the degree of efficiency in fossilfuel heated kiln plant is lower than incase of electrical heating, but thehigh prices for electric energy inmost countries not only neutralisethe efficiency advantage but alsospeak in favour of fossil fuel heatingin view of the operating costs.It does not appear that electric en-ergy generated by renewable en-ergies will be obtainable at lowerprices than fossil-fuel energy in theforeseeable future.In the ceramic sanitaryware industrylight heating oil and fuel gases areused as fossil fuels; the use of heavyoil is very rare. For the transportthrough the pipes to the burner andfor combustion purposes the heavyoil must be brought to a specific andconstant viscosity which can only berealised with considerable effort andcosts by means of piping with con-trolled heating. Components in theheavy oil, such as sulphur, react withthe glaze and lead to higher rejectrates. The use of coal dust as fuel

would contaminate the sanitarywareproducts even more so that this typeof fuel is to be regarded as inappro-priate.In the vast majority of the cases nat-ural gas is used as fuel in the ceram-ic sanitaryware industry.In Central Europe the natural gasprices are mostly bound to the pricedevelopment of light and heavyheating oil due to long-term supplycontracts of the natural gas im-porters with the suppliers of the sup-plying countries. Therefore the priceindex for natural gas follows that forheating oil with a small time delay.However, the upward trend of theimport prices over the last decade(Fig. 2) [4] is to be regarded as anunpleasant common tendency. Dueto the shortage of resources thistrend is most likely to intensify in thefuture. The import prices for naturalgas are indicated on the left coord-inate in EUR t/a, the prices for crudeoil in EUR t/a are shown on the rightcoordinate. The most significantprice increases took place in theyears 2000 to 2001 and 2004 to2008, the prices in the year 2009were only on the decline due to the

worldwide economic crisis. The ten-dencies shown remain unchangedalso in the case of an inflation-adjust-ed consideration. Every combustion process of carbondioxide and hydrocarbons causesthe formation of nitrous oxides andabove all of carbon dioxide gases.The thermal NOx formed duringcombustion mainly consists of NOand 5 % of NO2 These nitrogencompounds act as acid formers inthe presence of water and thereforecause the so-called “acid rain“ in theatmosphere. The reduction of NOxduring combustion is achieved bywell-known primary and secondarymeasures, as described in the rele-vant literature [5].The CO2 gas which is also referred toas ”greenhouse gas“ is a synonymfor harmful impacts on the environ-ment. It heats up the air at groundlevel by absorbing the infrared radi-ation of the earth’s crust and coolsdown the higher spheres by radi-ation.The CO2 emission is directly relatedto the fuel consumption. Low per-cent values in the waste gas are notan indication for a low CO2 emission

Process Engineering

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cation for new development of kilnplants:• Kilns are to be heated with fossil

fuels for reasons of costs and oper-ational safety.

• Despite intensive efforts in view ofthe composition of the materialsthe high firing temperature willnot change considerably in thefuture.

• The mass ratio of the kiln furnitureto product can be improved byusing SiC materials.

• The lowest possible energy con-sumption can be achieved in rollerkilns due to low ballast and/or kilnfurniture quantities.

• Modern computer-assisted calcu-lation methods permit the ener-getic optimisation of the transportcar insulation.

• The CO2 emissions are to bereduced.

• The energy consumption is to beminimised significantly.

The requirements indicated led tothe following new developments byRiedhammer:• Energy Management System

(EMS) for all continuously oper-ated firing kilns

• Combined Heat Supply Networkbetween the firing units and theconsumers in the factory

• REKO shuttle kiln.These new developments are theresult of Riedhammer’s experiencefrom more than 88 years in the con-struction of kilns for the ceramicindustry and the in-house synergyeffects of the new technical kilndevelopments for sanitary and table -ware ceramics, for advanced ceram-ics, refractories and carbon. Itremains the company’s central taskto continue with the design and construction of kilns with the mini-mum possible energy consumption

and CO2 emission, a major concernwhich has been given top priority.

The Energy ManagementSystem (EMS) for all continuously operated kiln plants

In a functioning system – such as kilnplant – many single componentshave to be correctly linked with each other. New components haveto be fitted into an existing and well proven overall concept to beequipped and controlled with state-of-the-art measuring and control technology in the mostadvantageous way according to the latest developments and know-how.As a first basic measure for reducingthe energy consumption of kilnplant, the heat transmission shouldbe optimised according to the fol-lowing points: • Optimal and complete use of the

clear cross section• Installation of performance-adapt-

ed burners• Correct and well-conceived burner

arrangement• Efficient cross circulation of the hot

fluids by means of sufficient injec-tion points

Furthermore the energy manage-ment system EMS comprises of anoptimal combustion adjustment ofthe burners, i.e.:• Combustion air preheating• Measurement of the combustion

air temperature • Measurement of the gas and air

flows• Exact compliance with the preset

gas/air flow ratio and simultaneousconsideration of the current com-bustion air temperature.

E 130 cfi/Ber. DKG 89 (2012) No. 5

but evidence that the waste gas hasbeen diluted with additional air. Fig. 3 illustrates this connection. The alternative to improve the heat transmission coefficient withhigh air excess is not applicable asthe increase in the air quantityinvolves an increase in energy con-sumption which cannot be compen-sated by the improved heat trans-mission.All the facts presented so far under-line the urgent necessity of demand-ing a significant reduction of theenergy consumption in the ceramicindustry in the future.With the European Communitypreparing legislation to require thefurnace industry to reduce fuel con-sumption (the so-called Eco-furnaceStudy Group) as a part of the Eco-design directive Riedhammer is onceagain leading the way.

What are the require-ments on modern kilnplants for firing sanitaryceramics?For the above-mentioned reasonsthe following logical consequencesare to be considered in the specifi-

Process Engineering

Fig. 2 Price development of natural gas and crude oil in Germany

year

natu

ral g

as p

rice

[EU

R/t]

crud

e oi

l pric

e [E

UR/

t]

Fig. 3 Combustion diagram for Russian natural gas

Combustion diagram for Russian natural gas

reduction

was

te g

as a

naly

sis

[mol

-%]

oxidation

air factor

Tab. 2 Comparison of energy and emission data between rollerand tunnel kilns

RiedhammerRoller KilnStandard



620 1260


497 599


Total CO 2 emission [kg/a] 1 581 395 3 209 302

Difference +103 %

natural gas pricecrude oil price

Solely by combustion air preheatingan energy saving potential of morethan 12 % can be achieved.The EMS equipment and processtechnology mainly consists of:• maximum use of kiln waste heat• recuperators installed in the kiln fir-

ing chamber for combustion airpreheating

• regulation and control equipmentfor a fast switchover, for exampleweekend operation

• a large number of burner groups• the supply of sufficient warm air

volumes for up or downstream usein the factory.

The basic function of the EMS con-sists in the transfer of the kiln’s wasteheat produced during the firingprocess to fresh air which can beused as combustion air via a ceram-ic recuperator system installed in thekiln body. This system contributessignificantly to energy savings and toan improved glaze quality.The controlled recuperator systemnot only helps to realise energy sav-ing potentials, but also allows anexact temperature control in thecooling zone, particularly in therange of the quartz inversion point

so that full-scale production can beresumed immediately e.g. after astop during the weekend.Another contribution to energy sav-ing is the well-conceived division ofthe high quantity of burners into alarge number of regulation groups

with the intention to conduct onlythe minimum necessary energy towhere it is required. This procedurealso includes flexible temperaturecontrol of the plant for automaticheating up and cooling down duringnon-production days.

Process Engineering

Fig. 4 EMS injection points in a roller kiln

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corresponding fittings attached toeach burner.The effects of the described meas-ures on the energy consumption andCO2 emission are illustrated in Tab. 3for tunnel kilns with car transport incomparison with tunnel kilns thatare available on the remaining mar-ket. Here the saving of energy costsby using the EMS system as well as the CO2 emission reductionamounts to up to 84 %, withoutconsidering the cost reductionresulting from lower CO2 certifi-cation costs. The calculation is based on a production capacity of 50 t/day and a natural gas price of0,3 EUR/m³n.Tab. 4 shows a similar comparison ofcosts and emissions between rollerkilns with EMS and standard indus-trial tunnel kilns, based on a produc-tion capacity of 30 t/d and the samenatural gas price. As expected, sig-nificant differences in the cost andCO2 savings can be found here, theyamount to up to 125 %.With this saving potential and intimes of constantly rising costs forenergy and CO2 certificates eco-nomically interesting amortisationtimes can be expected.

Combined Heat SupplyNetwork between the firing units and other consumers in the factoryIn general, it is useful to conduct theheat that is produced and releasedfrom the fired product and the trans-port material during the coolingprocess back to the kiln plant, there-by using the shortest possible route.In this process it is not so much theenergy level but rather the tempera-

ture level which is decisive for furtheruse. In the last cooling phase afterthe quartz inversion point the ware iscooled down to temperatures of <80 °C over a relatively short dis-tance. The heat transmission mustbe effected with high convectiveheat transfer coefficients whichrequires considerable cooling airvelocities and thus huge volumeflows with high enthalpy, but lowtemperatures. The cooling air vol-umes are too large to be used com-pletely as combustion air, but in viewof their quantity and temperaturelevel they are suitable for re-usage indriers, spray towers, heaters etc. Asthe respective energy requirementand the CO2 emissions are notinsignificant for the individual units,a Combined Heat Supply Networkbetween these units and the kilnwith the Energy Management Sys-tem (EMS) is ideal. Such a networkreduces the total energy require-ment by the amount of energywhich can be supplied by the kiln viaenergy recovery. The same applies tothe reduced CO2 quantity.There are a large variety of possibil-ities for operating and controllingthe different units in a CombinedHeat Supply Network. It is a matterof course that the respective applica-tion is to be discussed in detailbetween the plant constructor andthe plant operator before being opti-mised.

The Riedhammer REKO shuttle kilnAmong the intermittently operatedkiln plants the shuttle kiln is definite-ly the most frequently used kiln typein the ceramic sanitary ware industry

The precise control and regulationtechnology used for all burnergroups guarantees an optimal com-bustion and consequently a max-imum use of the supplied fuel en-ergy in the entire capacity range ofthe burners. Different adjustmentsfor top and bottom burners ensuringtemperature uniformity over the kilnchannel cross section are possible by

Process Engineering

RiedhammerTunnel Kilnwith EMS


Energy consumption[kcal/kg net]

685 1260

Energy consumption[kcal/kg charge]

325 599



Difference +84 %

Tab. 3 Comparison of energy and emission data of tunnel kilnswith and without EMS

RiedhammerRoller Kilnwith EMS



559 1260


447 599



Difference +125 %

Tab. 4 Comparison of energy and emission data of roller kilns withEMS and tunnel kilns without EMS

4, rue Lavoisier – F 54300 Moncel les LunévilleTél : +33(0) 383 76 39 39; Fax : +33(0) 383 76 39 40www.icar-refractory.com ; [email protected]

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Hall A5 - Stand 104

E 132 cfi/Ber. DKG 89 (2012) No. 5

(Fig. 5). Energy consumption andCO2 emission are somewhat higherthan those of continuous kilns. Thisis on the one hand due to the high-er ballast weight of kiln insulationand kiln car which has to be heatedup again in every cycle from initial tofinal temperature, but on the otherhand also to the waste gas losseswhich naturally reach their highestlevel at the maximum temperature.In modern plants the kiln wall andkiln car insulation is calculated andoptimised with the latest computertechnology according to the prin-ciples of the transient heat transmis-sion. The flow conditions in the kilnfiring chamber are determined byspecial computer programs so thatthe most favourable burner positionsand operating methods can be fixedand the temperature uniformity inthe kiln firing chamber is furtherimproved.

In Tab. 5 the energy-related data of a shuttle kiln designed accordingto the above-mentioned methods is compared with those of a stand-ard industrial shuttle kiln. The meas-ures described are already sufficientto realise energy savings and CO2emission reductions of up to 82 % in comparison with standard indus-trial kiln plants that are available on the market. This calculation isalso based on a fuel gas price of 0,3 EUR/m³n.REKO shuttle kilns use additionally tothe above mentioned calculationmethods innovative patented burn-ers. For each burner the gas and airvolumes are measured on the coldside of the fluid supply which makestemperature correction unnecessary.The electronic components of thegas/air quantity regulation systemguarantee the required optimal

combustion for the entire firingprocess.Instead of a recuperator in a com-mon waste gas pipe, which has beenup until now common practice, aheat exchanger is installed for eachindividual burner in the kiln wall forpreheating the combustion air andgas. As the energy transfer takesplace directly in the kiln body no

Process Engineering

Fig. 5 REKO shuttle kiln for firing sanitaryware

RiedhammerShuttle Kiln

Standard

Shuttle KilnsAvailable onthe Market


1 375 2500


805 1460



Difference +82 %

RiedhammerShuttle Kilnwith REKO

Burners

Shuttle KilnsAvailable onthe Market


1050 2500


614 1460



Difference +138 %

Tab. 5 Comparison of energy and emission data of shuttle kilns

Tab. 6 Comparison of energy and emission data of shuttle kilnswith and without REKO burners

CHARACTERISTICS

Application temperatures

up to 1900 °C

Resistance in highly

reducing atmospheres

Resistance at exceeding

heating and cooling ramps

Supplier of a complete range of products for lining and kiln furniture

QUALITIES

Silica

Cordierite

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Monolithics Resistance against chemical attacks

minimise CO2 emissions. As an opti-mal combustion of fuels accordingto physical laws causes the highestCO2 reaction it is not possible toreduce the concentration of the CO2emissions in the waste gas but onlytheir quantity which can be realisedwith a lower energy input. This hasbeen excellently achieved with thesenew developments as shown by theresults in the tables. Further devel-opment continues.

References[1] Praxishandbuch Thermoprozesstech-

nik, Band II: Anlagen KomponentenSicherheit. 2nd Ed. Essen 2011, 542

[2] Becker, F.: Computersimulation zurLösung wärmetechnischer Aufgabenim keramischen Ofenbau. cfi/Ber.DKG 76 (2001) [5] D9–D13

[3] Becker, F.: Aktueller denn je: Energiesparen, Kosten reduzieren, Qualitäterhöhen durch Innovationen. cfi/Ber.

DKG 85 (2008) [1] D17–D24[4] Bundesministerium für Wirtschaft

und Technologie: Zahlen und Fakten.Energiedaten. Nationale und interna-tionale Entwicklung Stand 07.09.2010, Tab. 26(http://www.bmwi.de/BMWi/Navigation/Energie/Statistik-und Prog-nosen/Energiedaten/gesamtausgabe.html)

[5] Warnatz, J.; Maas, U.; Dibble, R. W.:Verbrennung. 3rd Ed. Berlin 2001

[6] Becker, F.; Lorenz, L.; Walter, G.: Heatexchange in a fast firing kiln for glostfiring of porcelain. cfi/Ber. DKG 83(2006) [9] E1–E5

[7] Schupe, W.: Vereinfachte Berechnungdes Strahlungswärmeübergangs inIndustrieöfen und Vergleich mit Mes-sungen in einer Versuchsbrennkam-mer. Dissertation, Fakultät für Berg-bau, Hüttenwesen und Maschinenwe-sen der TU Clausthal 1974

conduction losses, which are usuallyhigh in conventional processes, areto be expected. This measure per-mits a considerably increased en-ergy efficiency as can be seen fromTab. 6. The comparison is drawnagain between a Riedhammer REKOshuttle kiln and a standard industrialshuttle kiln available on the marketusing the same price for the stand-ard cubic meter of fuel gas of EUR 0,3. A saving of energy costsand CO2 emissions by up to 138 %is achieved with the RiedhammerREKO shuttle kiln. With this enor-mous reduction of the productioncosts the plant operator will surelybenefit from advantages in globalcompetition.

SummaryThe main goal of the developmentspresented is to save energy and to

Process Engineering

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Georg-Steuler-Straße 56203 Höhr-Grenzhausen Germany

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riedhammer/sacmi kilns – latest developments for sanitaryware · riedhammer/sacmi kilns –...

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