Increasing energy costs and environ-mental obligations force manufac-turers of industrial kiln plant and theceramic industry in general to ex -plore all available potential energysaving methods. One of our cus-tomers’ main selection criteria bySACMI/IT when considering invest-ment in new plant is energy effi-ciency and Riedhammer GmbH/DEoffers cutting-edge innovation andspecific technical solutions to meetcurrent challenges in this regard.The principal measures for enhancedenergy efficiency in new plant asalready presented in detail in variouspublications by Riedhammer GmbHcomprise of the following:• energy-efficient engineering (EEE);• energy-management-system

(EMS) and Reko burner system;• integrated process control;• internal heat re-use;• combined re-use of thermal en -

ergy. Using the examples of a tunnel kilnand a shuttle kiln for firing sanitaryceramics the following sections willdescribe possible technical alter-ations to existing kiln plant whichcan be realized with varying invest-ment costs and effort to achievehigher energy efficiency.

Technical options for continuous kilnsWhen using tunnel kilns the cus-tomer can achieve very good energyefficiency without any alterations tothe kilns themselves by ensuring thata high product setting density isachieved, the kiln cars are uniformlyloaded and an optimal use of theavailable cross section as well asshort cycle times are realized.As a first additional step which re-quires some alterations to be madeto the kiln the waste heat from thecooling zone of the kiln can bedirectly re-used, which for this stephas an efficiency of 100 % despitelow investment costs and simpletechnology which can easily beinstalled on existing kiln plants.As a second additional step heatexchangers can be fitted to usewaste air from the cooling zone orwaste gases from the kiln exhaust forthe generation of hot water.

If hot air is required it is possible touse clean hot air directly from thecooling zone of the kiln without anyheat exchanger, if the exhaust gasesare to be used for producing hot airthen a heat exchanger would beneeded to be able to provide cleanhot air. These steps are relatively easyto carry out and have a short termreturn on investment. The use of theenergy contained in the flue gases isvery much dependent on the actualflue gas temperature that is avail-able; the level of feasibility can bedescribed as follows:• temperature >180 °C a good feasi-

bility;• temperature <180 °C a reduced

feasibility.The retro-fitting of equipment forthe use of flue gas energy on existingtunnel kilns can in most cases be rela tively simple.The 3rd step that is possible is theimplementation of the use of pre-heated combustion air in the burnersystem. This can be realised via thedirect use of waste hot air from thecooling zone combined with a regu-lated air gas ratio. This type of wasteheat usage is characterised by:• high investment costs;• medium reduction of energy con-

sumption.The direct use of waste hot air canhowever also be used as combustionair for burner systems that have afixed combustion air (EMS 250). Thismethod of waste heat usage is char-acterised by:• cost efficient investment; • medium reduction of energy con-

sumption.A further step forward is the use ofadditional heating of the waste airby using an indirect cooling heatexchanger (EMS 400/600). Thismethod of waste heat usage is char-acterised by:• high end solution with high en-

ergy savings;• high quality gas-air ratio control

system.

Technical options forintermittent kilnsAs with the continuous kilns thathave been described above there arealso certain measures that can be

cfi/Ber. DKG 90 (2013) No. 5 E 51

taken to increase an intermittentkiln’s efficiency without makingalterations to the kiln itself. Some ofthese actions are to increase the set-ting density in the kiln to the max -imum that is feasible, optimise theuse of the loading space in the kiln,take out the most complicated prod-ucts so that they can be fired sep -arately with their own firing pro-gram. This will avoid having to firethe simpler products on longercycles which would increase theenergy usage unnecessarily, which inturn will enable shorter firing cycles.Regarding energy saving methodsthat require some alterations to bemade to the kiln, one of the firstthings that can be done is to carryout an evaluation of the practicalityof using exhaust gases directly in thekiln as diffusion or secondary “air”. Additionally the use of waste gasescan be considered via a heat ex -changer that is fitted into the ex -haust system. This is characterisedby the following:• technical feasibility;• large difference in volumes and

temperature;• discontinuous supply;• technically advanced system.A heat exchanger that can be fitteddirectly into the exhaust system sothat the combustion air can be heat-ed to a suitable temperature has thefollowing characteristics:• works well only for high tempera-

ture applications;• technically advanced system.Further to the use of waste heat newfiring systems can be fitted to thekiln which increase efficiency andimprove temperature distributionwithin the kiln. The first of these systems that areavailable is the pulse firing systemwhich as the name implies usesburners that are either switched onand off according to the energyrequirement of the kiln or burners

Process Engineering

Energy Reduction for Kilns Usedin the Sanitaryware Production

SACMI 40026 Imola (BO), Italywww.sacmi.com

Riedhammer GmbH90411 Nuremberg, Germanywww.riedhammer.de

• heat exchange takes place in theburner – cold combustion air pip-ing;

• uniform flue gas extraction – verygood temperature uniformity;

• shorter firing cycles due to largecooling volumes for final cooling.

The technical measures that are pre-sented under point 1 and 2 have tobe investigated for technical andeconomic feasibility in each individ-ual case. Riedhammer GmbH’s expertise alsocomprises new and alternative solu-tions for generating power fromwaste heat which can be used with-in the production system for sani-taryware and other products. Thesepossibilities are defined under theterm cogeneration.One process that is described as fol-lows is the use of kiln waste heat forpower generation by means of the

Organic Rankine Cycle (ORC). Themain features of the ORC processare:• The conversion of heat, first into

mechanical and then into electricalenergy according to the functionaldiagram in Fig. 1.

• The working fluid of the ORC is anorganic liquid.

• The heat exchanger uses dia -thermic oil.

• The cooling medium is water.The main application for the ORC isgeneration of power from wasteheat. There are factors that influencewhether or not the ORC is a suitabletechnology for a specific application.The efficiency of the ORC is depend -ent on the volume and temperatureof the waste heat flow that is avail-able. ORC equipment is available forvarying temperatures and volumesat varying efficiencies and as sucheach case must be looked at individ-ually. ORC equipment is moving towardsbeing a standard type of equipmentwhich will result in higher produc-tion levels that will in turn, as manu-facturers produce more ORC equip-ment, help to reduce productioncosts and thus investment costs. A second process is the generation ofpower and usable waste heat bymeans of a micro-gas turbine whichentails the following advantages(Fig. 2):• production of electrical power for

independence from the electricalgrid;

• production of electrical power for areduction in the amount of pur-chased electricity;

• production of electrical power foran increased efficiency by usingthe waste gases;

• production of electrical power forthe decentralization of the entiresystem.

The main features and the function-al diagram of the micro-gas turbineare shown in Fig. 3. The use of amicro-gas turbine in cogenerationcan result in an overall efficiency ofup to 86 %. Higher efficiencies de -pend on the optimization of the heatexchanger and on the specific plantparameters.

SummaryThe main objective of the develop-ments presented under the termsEMS, Reko system and cogenerationconsists of the following: significantenergy savings combined with CO2emission reduction and improvedglaze quality on continuously oper-

E 52 cfi/Ber. DKG 90 (2013) No. 5

that are fired in a high – low mode.The characteristics of this type of fir-ing system are:• reduction in energy consumption

by elimination of secondary air;• increased temperature uniformity

due to an impulse in the kiln;• wide range of energy supply via

the burners.A second firing system that is highlyeffective is the use of recuperativeburners which use the exhaust gasesof the kiln to directly heat the com-bustion air within the burner itself,this being realised by exhausting thekiln through secondary externalburner tubes that are fitted aroundthe actual burner nozzle. The Rekofiring system’s characteristics are:• technically the most efficient solu-

tion;• high reduction of energy con-

sumption;

Process Engineering

Fig. 1 Functional diagram of the ORC process

Fig. 2 Power plant without cogeneration vs. power plant with cogeneration

ated kiln plants for sanitaryware production thanks to theEnergy Management System (EMS). Apart from the possi-bility of using the waste heat from the kiln plant for otherpurposes to improve the energy balance of the factory, theEMS presents the latest technology for optimizing the useof resources such as gas and electrical power which alsocontributes to an increase in product quality. Due to vari-ous hardware and software tools contained within the sys-tem which interact with the state-of-the-art kiln compo-nents, an extremely high performance level can beachieved to meet our customers’ demand for ecologicaland economical production plants for firing sanitaryware.Reko is synonymous for enormous energy savings com-bined with CO2 emission reduction on intermittently oper-ated kiln plants.The state-of-the-art combustion system with self-recuper-ating burners presents a new milestone in advanced firingsystems for sanitaryware production plants. This burner system with preheated combustion air andpreheated combustion gas installed in the kiln chamberensures a high level of flexibility and economic efficiencycombined with first-class product quality. Due to the high-er consumption of resources in intermittently oper -ated kiln plants compared to con tinuously operated kilnplants, the Reko burner system represents an im portantstep forward for production plants in the sanitaryware in -dustry. Cogeneration stands for flexibility and high efficiency inthe use of available energy sources and recovery of wasteen ergy from the firing process.

cfi/Ber. DKG 90 (2013) No. 5

Fig. 3 Functional diagram of the micro-gas turbine