Energy-Efficient Firing of Ceramic Sanitaryware Technology Update J. Ridder In recent years, the issue of energy effi ciency has become fi rmly established in the production process of ceramic sanitaryware, especially 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. programs and the ever-growing capacity of modern computer systems have made the simulation of thermal processes attractive for kiln engineering too. Although a complete 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 within the scope of pre-engineering. Introduction Over the last 30 years, the global consumption 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 hydrocarbons leads to the formation of nitrogen oxides and especially to carbon dioxide gases. gas is associated with the term greenhouse gas, characterizing the damage effects on the environment. As a result of the absorption of the infrared 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, longterm goals were defi ned, like, for instance, halving emissions by 2050, which is not pos sible without an increase in energy effi ciency (World Energy Outlook 2014). The emission of is related directly to fuel consumption. Low percentages in the exhaust gas are not an indication of a low 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 saving The above-mentioned requirements are leading to new developments that have been realized by GmbH and can be summarized as follows: Energy-effi cient engineering (EEE) Energy Management System (EMS) in the new generation for all continuously operated kilns Reko shuttle kilns Combined heat utilization of the fi ring equipment with energy consumers in a plant. Energy-efficient engineering (EEE) Another milestone in the development of thermal process equipment is the introduction of 3D-based design systems. Today, it is possible to represent the plant as an integrated model, as a result of which collisions can be reliably avoided at the installation site. The key advantage here is the representation of the design of a plant with every inter esting detail such that all necessary sections can be viewed from every perspective. Such a view, complemented with available calculation and simulation techniques, enables the designer to perfect detail solutions. The interconnection of 3D design The new generation of the Energy Management System (EMS Based on the continuous kilns which have been successfully operated in the market for years, has concentrated its amassed experience and integrated this into a new generation of EMS systems as follows (Fig. 1 2). In this new EMS version, the same results are achieved in respect of energy saving and reduction, but with half the investment costs for this system compared to the previous EMS400. This new 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 preheated to 400 C. Electronic gas/air ratio control Combined heat-related operation with the relief and waste heat systems. Jörg Ridder GmbH 90411 Nuremberg, Germany E-mail: joerg.ridder@riedhammer.de www.riedhammer.de Keywords: energy effi ciency, resource conservation, emissions reduction, EEE, EMS, combined heat utilization, cogeneration cfi/ber. DKG 93 (2016) No. 1-2 E 1
Fig. 1 Tunnel kiln with EMS Fig. 2 Model of a tunnel kiln with EMS Tab. 1 and 2 show a consumption/cost and emission breakdown for a tunnel kiln and roller kiln with 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 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 firing zone with combustion air preheated 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 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. 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 emissions were much higher than for continuous 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 temperature. Kiln wall and kiln car insulation in modern kilns are designed and optimized according to the principles of transient heat conduction with the latest computer technology. With special computer programs, the flow conditions in the kiln chamber can be determined so that optimum burner positions and burner operating modes can be defined, 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-mentioned methods are compared with those of a conventional shuttle kiln. Already with the measures described, energy savings and emission reductions of around 45 % can be achieved. As a basis for the calculation, here a price of 0,3 EUR/m³ n fuel gas was used. This enables the plant operator to achieve an enormous reduction in production costs and certainly gives him advantages over the global competition. In the Reko shuttle kiln, with consideration of the results of the above-mentioned calculation 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 E 2 cfi/ber. DKG 93 (2016) No. 1-2
Tab. 1 Comparison of energy and emission data of tunnel kilns with and tunnel kilns without EMS Tunnel Kiln with Energy consumption [kcal/kg net] 660 1260 Energy consumption [kcal/kg charge] 315 599 Total fuel cost [EUR/year] 420 132 802 326 Total -emission [kg/year] 2 800 882 5 348 837 Difference +90 % Tab. 2 Comparison of energy and emission data of roller kilns with and tunnel kilns without EMS Roller Kiln with Energy consumption [kcal/kg net] 543 1260 Energy consumption [kcal/kg charge] 435 599 Total fuel cost [EUR/year] 206 700 481 395 Total -emission [kg/year] 1 378 000 3 209 302 Difference +126 % Tab. 3 Comparison of energy and emission data of tunnel kilns with EMS700-Cyber and tunnel kilns without EMS Tab. 4 Comparison of energy and emission data of roller kilns with EMS700-Cyber and tunnel kilns without EMS Tunnel Kiln with EMS700-Cyber Roller Kiln with EMS700- Cyber Energy consumption [kcal/kg net] 545 1260 Energy consumption [kcal/kg charge] 259 599 Total fuel cost [EUR/year] 346 927 802 326 Total -emission [kg/year] 2 312 850 5 348 837 Difference +131 % Energy consumption [kcal/kg net] 462 1260 Energy consumption [kcal/kg charge] 370 599 Total fuel cost [EUR/year] 175 866 481 395 Total -emission [kg/year] 1 172 443 3 209 302 Difference +173 % 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 common 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 improvement in energy efficiency is achieved. The goal of the developments presented is primarily to save energy and minimize emissions. As an optimum combustion of fuels according to physical laws is associated with a very extreme reaction, the 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. Fig. 3 Latest-generation Reko shuttle kiln cfi/ber. DKG 93 (2016) No. 1-2 E 3
Tab. 5 Comparison of energy and emission data of shuttle kilns with and without new recuperator burners Fig. 4 ORC scheme This has been accomplished outstandingly with the new developments presented, as the results in the tables show... and development 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 temperatures <80 C in a relatively short zone. The heat must be transferred with high convective heat transfer coefficients, which Shuttle Kiln with New Recuperator Burners (Reko 2.0) Shuttle Kilns Energy consumption [kcal/kg net] 995 2500 Energy consumption [kcal/kg charge] 582 1460 Total fuel cost [EUR/year] 254 535 638 372 Total -emission [kg/year] 1 696 898 4 244 186 Difference +249 % demands considerable cooling air rates and accordingly huge volume flows, which have considerable enthalpy but a low temperature. The volumes of cooling air are too large to be used completely as combustion air, but the volume and temperature level are suitable for use in dryers, spray towers, heating, etc. As the specific energy demand and the emissions for the individual units are not inconsiderable, a combined heat utilization 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 amount. There are very many variations for the operation and control of the various units in a combined heat utilization system. It goes without saying that the plant engineering company discusses the specific requirements 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 seldom 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. GmbH has the expertise needed to integrate new or alternative possibilities 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 mechanical and then into electrical energy, according 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 evaluated from case to case. Feasibility will, however, increase in the forthcoming years on account of the improved efficiency of ORC machines. More and more firms are switching to series manufacture, which can lead to a cost reduction for the ORC machines. The second process describes the production 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 suppliers to obtain electricity more economically to obtain high economic efficiency with the utilization of exhaust gases to obtain a decentralized system. E 4 cfi/ber. DKG 93 (2016) No. 1-2
Conclusion The efficient and environmentally compatible use of energy has gained significantly in importance in process of ceramic sanitaryware production. Possibilities for improved energy efficiency result first from the optimization of individual kiln functional groups, e.g. the combustion system, and secondly from the no lesser potential of the linked processes, e.g. utilization of waste heat. Energy efficiency in the process has now a significant influence on the economic effi ciency and competitiveness of the manufacturers of ceramic sanitaryware and will increase in importance in the forthcoming years. References [1] Irretier, O.: Energieeffizienz in Industrieofenbau und Wärmebehandlung Maßnahmen und Potentiale. elektrowärme international (2010) [1] Fig. 5 Energy balance with (r.) and without cogeneration [2] Ridder, J.; Lindl, D.: /Sacmi: Kilns [4] Hajduk, A.: Moderne Trends in der Wärmebehandlung von hochentwickelten Materialien. cfi/ber. latest developments for sanitaryware. cfi/ber. DKG 89 (2012) [5] E128 E134 DKG 92 (2015) [4] D15 D18 [3] Energy reduction for kilns used in the sanitaryware production. cfi/ber. DKG 90 (2013) [5] E51 E53 cfi/ber. DKG 93 (2016) No. 1-2 E 5