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Introduction

Over the last 30 years, the global consump-tion of raw materials for primary energy generation has increased by around 70 %. By the year 2030, an increase in the global primary energy consumption by a further 45 % compared to 2006 is expected (World Energy Outlook 2008). An almost 50-% increase in consumption makes natural gas the fastest growing fossil fuel, and energy effi ciency therefore plays an important role in curbing growth in the global energy demand to a third by 2040, while the global economy is growing by around 150 % (World Energy Outlook 2014). Natural gas is used predominantly as a fuel in the ceramic sanitaryware industry.The combustion of carbon and hydrocar-bons leads to the formation of nitrogen oxides and especially to carbon dioxide gases. CO2 gas is associated with the term greenhouse gas, characterizing the damage effects on the environment. As a result of the absorption of the infra-red radiation of the earth crust, it warms the air near the ground and cools the higher spheres as a result of radiation. At the G8 Summit in 2008 in Japan, “long-term goals” were defi ned, like, for instance, halving emissions by 2050, which is not pos sible without an increase in energy ef-fi ciency (World Energy Outlook 2014).The emission of CO2 is related directly to fuel consumption. Low percentages in the exhaust gas are not an indication of a low CO2 emission, but an indication that the exhaust gas has been thinned down with additional air. The alternative of improving

the heat transfer coeffi cient with high air excess cannot be applied as the increase in the amount of air brings an increase in the energy consumption that cannot be offset with better heat transfer.

Situation in kiln technology with regard to energy and CO2 saving

The above-mentioned requirements are leading to new developments that have been realized by Riedhammer GmbH and can be summarized as follows:• Energy-effi cient engineering (EEE)• Energy Management System (EMS) in the

new generation for all continuously oper-ated kilns

• Reko shuttle kilns• Combined heat utilization of the fi ring

equipment with energy consumers in a plant.

Energy-effi cient engineering (EEE)

Another milestone in the development of thermal process equipment is the introduc-tion of 3D-based design systems. Today, it is possible to represent the plant as an inte-grated model, as a result of which collisions can be reliably avoided at the installation site.The key advantage here is the represen-tation of the design of a plant with every inter esting detail such that all necessary sections can be viewed from every perspec-tive. Such a view, complemented with avail-able calculation and simulation techniques, enables the designer to perfect detail so-lutions. The interconnection of 3D design

programs and the ever-growing capacity of modern computer systems have made the simulation of thermal processes attractive for kiln engineering too. Although a com-plete simulation of the transient heat and fl ow processes in a continuous kiln cannot yet be realized at a reasonable cost, partial simulations of certain special solutions are already performed at Riedhammer within the scope of pre-engineering.

The new generation of the Energy Management System (EMS

Based on the continuous kilns which have been successfully operated in the market for years, Riedhammer has concentrated its amassed experience and integrated this into a new generation of EMS systems as follows (Fig. 1–2).

EMS400-4.0

In this new EMS version, the same results are achieved in respect of energy saving and CO2 reduction, but with half the investment costs for this system compared to the previ-ous EMS400. This new EMS400-4.0 system is based essentially on a combination of the following individual components:• Pulse burners in the preheating zone with

combustion air preheated to 200 °C• Continuously operating burners in the

main fi ring zone with combustion air pre-heated to 400 °C.

• Electronic gas/air ratio control• Combined heat-related operation with

the relief and waste heat systems.

Energy-Effi cient Firing of Ceramic Sanitaryware – Technology Update J. Ridder

In recent years, the issue of energy effi ciency has become fi rmly es-tablished in the production process of ceramic sanitaryware, especial-ly in the fi ring process. The rising price of energy, the efforts to reduce costs accompanied by the necessity for the conservation of resources and environment protection are leading to a rethink and a series of measures in order to improve effi ciency in every respect.

Jörg Ridder

Riedhammer GmbH

90411 Nuremberg, Germany

E-mail: joerg.ridder@riedhammer.de

www.riedhammer.de

Keywords: energy effi ciency, resource con-

servation, emissions reduction, EEE, EMS,

combined heat utilization, cogeneration

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and roller kiln with EMS700-Cyber on the basis of a production capacity of 30 t/day at the same natural gas price compared with standard tunnel kilns.

Riedhammer’s Reko-shuttle kiln 2.0

Among the intermittently operated kiln plants, in the ceramic sanitaryware industry the shuttle kiln has become established as an important element in the production for first firing, refiring and decoration firing. In the past, energy consumption and CO2 emissions were much higher than for con-tinuous kilns. However, this difference has become much smaller in recent years on account of highly efficient combustion systems, like the Reko system described here (Fig. 3). One reason for the still existing difference is the bigger ballast mass of kiln insulation and kiln cars that have to heated up in every cycle from the start to the end temperature, another reason are the exhaust gas losses, which are naturally highest at maximum tempera-ture.Kiln wall and kiln car insulation in modern kilns are designed and optimized according to the principles of transient heat conduc-tion with the latest computer technology. With special computer programs, the flow conditions in the kiln chamber can be de-termined so that optimum burner positions and burner operating modes can be de-fined, while further improving temperature homogeneity in the kiln chamber at the same time.In Tab. 5, the energy data of a shuttle kiln designed according to the above-men-tioned methods are compared with those of a conventional shuttle kiln. Already with the measures described, energy savings and CO

2 emission reductions of around 45 % can be achieved. As a basis for the calcula-tion, here a price of 0,3 EUR/m³n fuel gas was used. This enables the plant operator to achieve an enormous reduction in produc-tion costs and certainly gives him advan-tages over the global competition.In the Reko shuttle kiln, with consideration of the results of the above-mentioned cal-culation methods, novel patented burners have been introduced additionally. For every burner, the volumes of gas and air are measured on the cold side of the fluid feed so that a temperature correction

• Pulse burners in the preheating zone with combustion air preheated to 200 °C

• Continuously operating burners in the main firing zone with combustion air pre-heated to 700 °C

• Controlled recuperator system in the rapid cooling zone

• Electronic gas/air ratio control• Combined heat-related operation with

the relief and waste heat systems.Tabs. 3 and 4 show a consumption/cost and emission breakdown for a tunnel kiln

Tab. 1 and 2 show a consumption/cost and emission breakdown for a tunnel kiln and roller kiln with EMS400-4.0 based on a production capacity of 30 t/day at the same natural gas price compared with standard tunnel kilns.

EMS700-Cyber

This new EMS version EMS700-Cyber built completely on the EMS400-4.0 is based es-sentially on a combination of the following individual components:

Fig. 1 Tunnel kiln with EMS

Fig. 2 Model of a tunnel kiln with EMS

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Tab. 2 Comparison of energy and emission data of roller kilns with EMS400-4.0 and tunnel kilns without EMS

Riedhammer Roller Kiln

with EMS400-4.0

Tunnel Kilns Available on the Market

Energy consumption [kcal/kg net] 543 1260

Energy consumption [kcal/kg charge] 435 599

Total fuel cost [EUR/year] 206 700 481 395

Total CO2-emission [kg/year] 1 378 000 3 209 302

Difference +126 %

Tab. 1 Comparison of energy and emission data of tunnel kilns with EMS400-4.0 and tunnel kilns without EMS

Riedhammer Tunnel Kiln

with EMS400-4.0

Tunnel Kilns Available on the Market

Energy consumption [kcal/kg net] 660 1260

Energy consumption [kcal/kg charge] 315 599

Total fuel cost [EUR/year] 420 132 802 326

Total CO2-emission [kg/year] 2 800 882 5 348 837

Difference +90 %

Tab. 3 Comparison of energy and emission data of tunnel kilns with EMS700-Cyber and tunnel kilns without EMS

Riedhammer Tunnel Kiln with EMS700-Cyber

Tunnel Kilns Available on the Market

Energy consumption [kcal/kg net] 545 1260

Energy consumption [kcal/kg charge] 259 599

Total fuel cost [EUR/year] 346 927 802 326

Total CO2-emission [kg/year] 2 312 850 5 348 837

Difference +131 %

Tab. 4 Comparison of energy and emission data of roller kilns with EMS700-Cyber and tunnel kilns without EMS

Riedhammer Roller Kiln

with EMS700-Cyber

Tunnel Kilns Available on the Market

Energy consumption [kcal/kg net] 462 1260

Energy consumption [kcal/kg charge] 370 599

Total fuel cost [EUR/year] 175 866 481 395

Total CO2-emission [kg/year] 1 172 443 3 209 302

Difference +173 %

Fig. 3 Latest-generation Reko shuttle kiln

is not necessary. The electronic modules for the gas/air volume control guarantee the required optimum combustion for the total firing process.Instead of one recuperator in one com-mon exhaust gas line as often installed as standard, now for every individual burner a heat exchanger is fitted in the kiln wall for the preheating of combustion air and gas. As the energy transfer takes place directly within the kiln structure, the otherwise high line losses are eliminated. With these measures a considerable im-provement in energy efficiency is achieved. The goal of the developments presented is primarily to save energy and minimize CO2 emissions. As an optimum combustion of fuels according to physical laws is associ-ated with a very extreme CO2 reaction, the CO2 emission in the exhaust gas cannot be reduced in terms of concentration, but only in the amount as a result of a lower supply of energy.

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There are very many variations for the oper-ation and control of the various units in a combined heat utilization system. It goes without saying that the plant engineering company discusses the specific require-ments together with the plant operator in detail and then optimizes the system.Attention is currently paid and will continue to be paid in future to the conversion of kiln waste heat into electricity. While waste heat from the kiln is largely utilized in countries with a cold climate, in countries with a warmer climate the waste heat is only sel-dom utilized completely. What, however, is common to all ceramic sanitaryware manufacturers in countries with cold and warm climates is the fact that electric energy is always needed at all times.Riedhammer GmbH has the expertise need-ed to integrate new or alternative possibil-ities for the generation of electricity in the production of sanitaryware. These possibilities are defined under the term cogeneration.The first process describes the utilization of kiln waste heat for the generation of electricity by means of the Organic Rankine Cycle (ORC). The main features of the ORC process are presented in the following. The Organic Rankine Cycle converts heat first into me-chanical and then into electrical energy, ac-cording to the functional scheme shown in Fig. 4.As an efficient ORC concept requires large volume flows and temperatures of 300 °C upwards, the economic feasibility of the installation of such a system must be evalu-ated from case to case. Feasibility will, however, increase in the forthcoming years on account of the im-proved efficiency of ORC machines. More and more firms are switching to series manufacture, which can lead to a cost re-duction for the ORC machines. The second process describes the produc-tion of electricity and more usable waste heat by means of a microgas turbine (Fig. 5). Possible applications are the production of electric current,• to become independent of electricity sup-

pliers• to obtain electricity more economically • to obtain high economic efficiency with

the utilization of exhaust gases• to obtain a decentralized system.

demands considerable cooling air rates and accordingly huge volume flows, which have considerable enthalpy but a low tempera-ture. The volumes of cooling air are too large to be used completely as combustion air, but the volume and temperature level are suit-able for use in dryers, spray towers, heating, etc. As the specific energy demand and the CO

2 emissions for the individual units are not inconsiderable, a combined heat utiliza-tion system between these units and the kiln with the Energy Management System (EMS) presents an expedient option. A combined heat utilization system of this type reduces the total energy demand by the amount of energy supplied from the kiln. This also applies for the lower CO2 amount.

This has been accomplished outstandingly with the new developments presented, as the results in the tables show ... and devel-opment goes on.

Combined heat utilization of the firing equipment with consumers in the plant

It is generally sensible to return the heat given off essentially during cooling of the products and transport equipment to the kiln via the shortest possible route. Here, however, it is less the energy but rather the temperature level that is crucial for further use. In the last stage of cooling, after quartz inversion, the products are cooled to tem-peratures <80 °C in a relatively short zone. The heat must be transferred with high convective heat transfer coefficients, which

Fig. 4 ORC scheme

Tab. 5 Comparison of energy and emission data of shuttle kilns with and without new recuperator burners

Riedhammer Shuttle Kiln with New Recuperator

Burners (Reko 2.0)

Shuttle Kilns Available on the Market

Energy consumption [kcal/kg net] 995 2500

Energy consumption [kcal/kg charge] 582 1460

Total fuel cost [EUR/year] 254 535 638 372

Total CO2-emission [kg/year] 1 696 898 4 244 186

Difference +249 %

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[4] Hajduk, A.: Moderne Trends in der Wärmebehan-

dlung von hochentwickelten Materialien. cfi/Ber.

DKG 92 (2015) [4] D15–D18

[2] Ridder, J.; Lindl, D.: Riedhammer/Sacmi: Kilns –

latest developments for sanitaryware. cfi/Ber.

DKG 89 (2012) [5] E128–E134

[3] Energy reduction for kilns used in the sanitary-

ware production. cfi/Ber. DKG 90 (2013) [5]

E51–E53

Conclusion

The efficient and environmentally compat-ible use of energy has gained significantly in importance in process of ceramic sanitary-ware production. Possibilities for improved energy efficiency result first from the optimization of individ-ual kiln functional groups, e.g. the combus-tion system, and secondly from the no lesser potential of the linked processes, e.g. util-ization of waste heat. Energy efficiency in the process has now a significant influence on the economic effi ciency and competitive-ness of the manufacturers of ceramic sani-taryware and will increase in importance in the forthcoming years.

References

[1] Irretier, O.: Energieeffizienz in Industrieofenbau

und Wärmebehandlung – Maßnahmen und Po-

tentiale. elektrowärme international (2010) [1]

Fig. 5 Energy balance with (r.) and without cogeneration