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Thermal energy storage (TES) systems using heat from waste
Thermal energy storage (TES) systems using heat from waste
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A. I. Fernández1, C. Barreneche1, L. Miró2, S. Brückner3, L. F. Cabeza2 Universitat de Barcelona, Spain; 2Universitat de Lleida, Spain; 3Bavarian Center for Applied Energy Research (ZAE Bayern), Germany 1
19.1 Introduction As shown in Figure 19.1, the global energy consumption of the planet has been increasing during the last 20 years. This effect was previously observed in OECD countries but the energy consumption trend in developed countries is now showing a 2–3% annual increment [1]. The production of energy for domestic consumption in each region of the world is one of the most important points that government leaders have to deal with when seeking alternatives to generate energy or to reduce energy consumption. One of the sectors with a higher impact in the worldwide energy consumption is the industrial sector, which accounts for 31% of the global energy consumption reported by the International Energy Agency (IEA) [1]. Alternatives to change this scenario are recently emerging to stop the effects from the increasing global energy consumption, the CO2 emissions, greenhouse gas emissions, and global warming. The energy consumption of the industry sector was around 76.5 EJ in 2011 according to data services of the IEA [2] and it had an important weight in the total energy consumption distribution as Figure 19.2 shows. This figure is divided into three sectors: industry, transportation and other, which includes the energy consumption from buildings, power generation, etc. Total energy consumption
Industry sector
Energy consumption (Mtoe)
10000 8000 6000 4000 2000 0 1990
1995
2000
2005
2010
2011
Figure 19.1 Global energy consumption over time vs. industrial energy consumption [1]. Advances in Thermal Energy Storage Systems. http://dx.doi.org/10.1533/9781782420965.4.479 Copyright © 2015 Elsevier Ltd. All rights reserved.
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Industry sector (76.2 EJ) Transport
(66.4 EJ)
Other sectors (101.7 EJ)
Figure 19.2 Worldwide energy consumption distribution divided by sector for 2011 [2].
Europe’s situation is similar. Industry accounts for around 33% [3] of all the energy used in Europe, the major part of which is accounted for by materials processing industries. As stated in the Worldwide Trends in Energy Use and Efficiency report from the IEA [3], applying ‘the best available technology (BAT) or best practice technology (BPT) on a global basis could save between 25 EJ and 37 EJ of energy per year (on a primary energy equivalent basis), which represents 18% to 26% of current energy use in industry. The associated CO 2 savings would be between 1.9 Gt CO2 and 3.2 Gt CO2 per year’. The industry sector has put a major effort into becoming more energy efficient, but this effort must be redoubled to achieve the time horizon of 2020 across all these materials processing industries [4]. Energy consumption is increasing, which is a major issue. Several alternatives have been proposed to stop this increase and even to reverse it. In fact, the energy consumed in the industry sector is not completely exploited and several processes are supplying heat which gets wasted in the form of hot gas, vapour, hot water, etc. Part of this energy is wasted as heat in several components of the system or the final parts of processes. Recovery of this waste heat should be considered to improve the energy requirements in these processes. Using the definition from the report Waste Heat Recovery: Technology and Opportunities in US Industry, [5], industrial waste heat refers to energy that is generated in industrial processes without being put to practical use. Recovering industrial waste heat can be achieved via numerous methods and it can be reused (in the same industry or can be transported to another use), stored using storage technologies or transformed into another type of heat, cold or power [6]. It is estimated that somewhere between 20 and 50% of industrial energy input is lost as waste heat in the form of hot exhaust gases, cooling water, and heat lost from hot equipment surfaces and heated products [5]. Waste heat is becoming an important issue and there are several studies on the measures to recover this heat, though often these measures are not justifiable from
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the point of view of cost. Due to cost considerations, different alternatives are gaining importance that will reinforce the reuse of waste heat. The scheme showed in Figure 19.3 presents a possible flux diagram of the waste heat recovery process: a hot gas crosses the burner and it is heated up. Then, the heated gas crosses the water heat exchanger and part of the gas is slightly cooled and the water inside the heat exchanger can be used, for instance, to activate the cooling equipment. The industrial process showed in Figure 19.3 could represent a chemical plant process, petroleum refinery, bio-refinery, pulp and paper mill, etc. Another method to take advantage of the unconsumed energy in the industry sector is thermal energy storage (TES). TES systems can store energy following three different methods: first, the sensible heat generated when a temperature gradient is applied to a material, which is directly proportional to the heat capacity of the material; second, the use of the latent heat produced during a change of state from solid–solid, liquid–solid, solid–gas, liquid–liquid, etc.; finally, the use of a thermochemical reactor, in which a thermochemical material (TCM) can store energy in a reversible chemical reaction which releases heat [7,8]. These two methods to improve the energy requirements and energy efficiency of industry (waste heat recovery and TES) can be combined in order to decrease the industrial energy consumption. Thereby, a TES system could allow the charge/ discharge of the system when thermal conditions are favorable for the process. In addition, the energy stored by the TES system can be kept and this energy can be used whenever the industry process needs it. ZAE Bayern eV, Küttner GmbH and Giesserei Heunisch GmbH, started a new project in 2013 where industrial waste heat is used by new thermal storage and heat transformation technologies. At Giesserei Heunisch GmbH, industrial waste heat from an iron melting kiln (approximately 3 MW at 230°C) is available. The project aims to demonstrate an economically and ecologically efficient energy system to use industrial waste heat (high temperature thermal storage in combination with absorption heat pump/chiller) under real life conditions [9].
Hot water/steam to heating or thermally activate the cooling
Heat exhaust gas
Heat recovery
Heat recovery unit
Spent exhaust gas
Water source return
Figure 19.3 Scheme: flux diagram of the waste heat recovery process.
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19.2 Generation of waste process heat in different industries Waste heat sources are being mapped in several parts of the world because they are free sources that could be taken advantage of or they could be interesting to other neighboring industry companies and/or a nearby town where this heat could be used [10]. The Netherlands is one example. The waste heat points available in the Netherlands from industry are indicated on the map shown in Figure 19.4 as black circles where the size represents the amount of waste heat. The information of outlet temperatures, CO2 emissions, etc., is detailed in the website from Agendschap [11]. In industrial processes there are several individual parts of the processes where waste heat is located. Some examples of the outlet temperature data of several industrial processes from the literature are listed in Table 19.1 [5,12]. In addition, several components of systems able to recover waste heat have been identified [6]. The classification diagram of the components where waste heat was recognized is presented in Figure 19.5 [13]. In order to recover this waste heat from an industrial process, several technologies have been developed in order to reuse this heat in the same industry (heat exchangers), to produce heat (mechanical vapor compressors (MVC) or absorption heat pumps),
Concentration Waste heat points
Figure 19.4 Waste heat points located in the Netherlands (data adapted from [11]).
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Outlet temperatures of component systems from several industrial processes
Table 19.1
Process
Exhaust gas Reference temperature (°C)
Steel electric arc furnace Glass melting furnace Aluminum reverberatory furnace Steel heating furnace Copper reverberatory furnace Gas oven without regenerator Hydrogen plants Fume incinerators Coke oven Cement kiln Melting oven Steam boiler exhaust Steam boiler Ceramic kiln Cooling water from internal combustion engines Exhaust gases exiting recovery devices in gas-fired boilers, ethylene furnaces, etc. Conventional hot water boiler Cooling water from air conditioning and refrigeration condensers
1370–1650 1300–1540 1100–1200 930–1040 900–1090 900–1300 650–980 650–143 650–100 450–620 400–700 230–480 200–300 150–1000 70–120 70–230
[5] [5] [5] [5] [5] [11] [5] [5] [5] [5] [11] [5] [11] [11] [5] [5]
60–230 30–40
[11] [5]
Source: Bayerisches Landesamt für Umwelt (2012) [12]
Heat exchangers Storage technologies
Waste heat technologies
Sorption systems
Absorption chillers Absorption heat pump
MVC SRC, ORC, Kalina cycles
Figure 19.5 Classification diagram of components able to recover waste heat [13].
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to produce cold (absorption chillers), or to produce power (Steam Rankine cycles (SRC), organic Rankine cycles (ORC), Kalina cycle, etc.). The utilization of one of these technologies will depend on the interests or requirements of the industry. In the review of the scientific literature on industrial waste heat recovery, the use of thermoelectric devices is being intensively investigated for waste heat harvesting in a wide range of temperatures and sectors. Kajikawa [14] reported the status of the research and development on thermoelectric power generation technology in Japan. Demonstration system tests and feasibility studies have been achieved by private companies using practical heat sources such as industrial furnaces, motorcycles, solid waste incinerators, and solar thermal systems. The research on different types of thermoelectric materials carried out by universities and national research institutes is also described. Another example is given by Hocheng et al. [15] who report a thermoelectric prototype generating 300 W at 12 V with a temperature difference of 150°C. For selecting thermoelectric materials, a decision matrix is defined by Homm and Klar [16] that analyzes the potential of the thermoelectric materials SiGe, PbTe, Bi2Te3, and FeSi2 in four types of applications, classified by mobile vs. stationary and specialized vs. mass application. The selection criteria comprise energy efficiency, materials availability, costs, environmental friendliness and toxicity.
19.3 Application of thermal energy storage (TES) for valorization of waste process heat Thermal energy storage is also proposed as a promising method to be implemented in waste heat recovery systems. Already in the early 1980s there were references in the literature to the potential of using heat storage technologies for waste heat management in different industries, mainly materials primary production [17], also identifying technologies for low-level to high-level heat storage [18]. Within these technologies, the use of fluidized bed heat exchangers was evaluated for a cement rotary kiln and electric arc furnace steel plant [19]. Some design and evaluation case studies are reported implementing some kind of storage concept. For instance, the design and cost evaluation of a latent heat storage unit with HDPE for the utilization of waste heat from an incinerator operated for 8 hours at a constant thermal energy output into the waste heat recovery system: 582 kW is feasible and the storage unit can be operated with constant inlet temperature and with a thermal input/output which matches the heat supply/demand by changing the flow rate [20]. Focusing on the materials with potential to be implemented in TES systems for waste heat recovery, sensible heat storage systems are described using either concrete [21] or basalt stone [22]. Research on latent heat storage materials has increased significantly during the last 20 years, and recent trends in new hybrid materials and combined systems identify the recovery of waste heat as a potential application [23–27]. Sharma and Sagara [28] reviewed latent heat storage materials and systems paying attention to reported designs for waste heat recovery. However, few cases
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have been implemented as real cases. Nomura et al. [29] reported recent trends in technologies using PCM for waste heat recovery systems. These are summarized in Table 19.2. In this section several cases where a TES system was successfully implemented to an industrial waste heat recovery process are presented.
19.3.1 District heating versus transportation of waste heat from steel industry In 2006, a pre-study was conducted on the transportation of waste heat from the steelmaking industry in Sweden. Three different methods for transporting the heat were compared. The first one was a conventional district heating process and its main downside was the requirement for new underground piping to cover the 30 km distance. The second one was transportation of heat by train using phase change material (PCM) storage. finally, the last method was the transportation of heat by train using zeolite sorption technology used as thermochemical storage. The converter gas was used in this study and it gave a potential to be transported of 60 GWh/year. Therefore, the costs for the three different options were estimated and the results are shown in Figure 19.6. The results indicated that the last method using zeolites was the most promising with regard to cost effectiveness. The main reason was the high energy density from the zeolites in comparison with the other alternatives. This example of thermal energy storage applied in a waste heat recovery case studied was framed in Annex 18 of the ECES IA of the International Energy Agency [30].
Table 19.2
Recovery waste heat characteristics of PCM studies
PCM
Heat source
Pb (Tm = 328°C)
High temperature gas exhausted (<727°C)
Magnesium nitrate hexahydrate/ magnesium chloride hexahydrate
Urban waste heat from emerged co-generation system (<60–100°C)
Copper (Tm: 1083°C)
High temperature gas exhausted from steelmaking converter (<1600°C)
Various sugars (Tm: 93-172°C)
Industrial waste heat at low temperature (<200°C)
Sodium acetate trihydrate (Tm: 58°C) Erythtitol (Tm: 118°C)
Industrial waste heat at low temperature (<200°C)
Erythtitol (Tm: 118°C)
Industrial waste heat at low temperature (<200°C)
Sodium acetate trihydrate (Tm: 58°C) Erythtitol (Tm: 119°C) Source: Nomura et al. (2010) [29]
Industrial waste heat at low temperature (<200°C)
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Train - zeolites
Train - PCM
District heating
0
10
20
30 40 Cost (7/MWh)
50
60
Figure 19.6 Cost of three different methods to implement waste heat recovery.
19.3.2 District cooling There are some areas where there are local cooling sources which may be wasted. This source can be included in a high-efficient alternative to the traditional cooling solutions when it is connected to a district cooling system provided by pipes. As stated in the Euroheat project: ‘the centralization of cooling production is a prerequisite to reach a high efficiency, as it makes possible to use free cooling or waste heat sources’ [31]. In addition, a district cooling system can reach an efficiency of 5–10 times higher than traditional local cooling systems. The cold could be from different free sources: deep sea, lakes, rivers or aquifers; industrial cooling sources where absorption chillers are used, e.g. waste heat from industry, CHP, waste to energy plants, etc. District cooling systems are considered a win-win solution for society as the Euroheat project mentions [31]. Furthermore, this type of cooling system can include an extra system for seasonal thermal storage and the configuration is shown in Figure 19.7.
19.3.3 Waste incineration plant/PVC sludge drying The system presented in the study presented in this section consisted of one charging station at the site of a waste heat source, providing energy for one or several consumers. This study was also included in Annex 18 of ECES IA of the IEA [30]. A thermochemical mobile storage is charged at a waste incineration plant and discharged at a PVC drying facility. German regulations do not permit more than one storage unit per truck as total weight for truck–trailer combinations is limited to 40 tons. For similar reasons, considerations have been limited to a charging station dealing with only one storage unit at a time. The system presented here is a sorption storage unit with 14 t of zeolite as storage material situated within fixed beds in a wedge-shaped configuration
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Customers Storage
Production cooling
Waste heat or “free cooling” source
Sub-station (heat exchanger)
Distribution network
Figure 19.7 District cooling system connected between free cooling source and consumers where a storage system is installed for seasonal thermal storage [31].
Figure 19.8 ZAE Bayern sorption storage module based on zeolite sorption process [30].
as shown in Figure 19.8. The unit is charged by applying a hot air stream to the system: the zeolite is dried and water released to the air. During the discharging process a moist air stream is used. The containing water is absorbed by the sorbent bed releasing heat. Thereby, the air stream is dried and heated up. The scheme of this process is presented in Figure 19.9.
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Discharging
Heat of condensation
Air + water
Zeolite
Desorption heat
Air
Air
Absorption heat
Figure 19.9 Charging/discharging zeolite process: water sorption.
(a)
(b)
Figure 19.10 Charging/discharging waste heat recovery configuration process.
The configuration during the charging/discharging process in the waste incineration plant is shown in Figure 19.10. The charging station of the pilot storage is installed in Hamm at the local waste incineration plant (MVA Hamm). Due to the heat extraction, the electricity production of the plant is reduced by approximately 10%. The discharging takes place ca 7 km away at Fa. Jäckering, a pvc sludge drying plant. For zeolite storage the capacity of the storage depends on the charging temperature. For this storage it is 200–308 kWh/t at 135–250°C respectively, leading to 2.4–3.7 MWh for the 14 t storage used in this project. The sorption system provides dry, hot air being compatible with industrial drying processes: exhaust air from the system is normally moist and can be used directly in the sorption unit. In this case, the exhaust air from a drying process is used at approximately 65°C and 65% relative humidity [32].
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An economic analysis revealed that a heat production price of round about 750/ MWh is feasible. A sensibility analysis showed that the crucial parameters for the cost effectiveness of such a storage system are high energy density, short transportation and transit times, and a high utilization rate [32].
19.3.4 Glass furnace Furnaces are used in the glass industry as reactors where the glass-forming process occurs at high temperature. there are two types of furnace: intermittent work furnace and continuous working furnace. The sources of energy used for heating have changed over time: wood, coal, fuel oil, natural gas and the newest fuels are low oxygen-rich mixtures. However, electrical energy is a safe alternative source that assists as a heat source or as a support for heating. One of the furnaces used in glass forming is the raft furnace. This type of furnace incorporated a thermal regeneration system since 1857 (developed by Siemens) that allowed its continuous use. The thermal regeneration system is based on the use of two cameras which operate alternately as heat exchangers, and each has a grid of refractory material which is able store thermal energy as sensible heat (Fig. 19.11). As hot gases from the combustion pass through a chamber and cool the refractory material along the way, the combustion air enters through the other chamber, preheated during its journey. This is an application that has been using sensible heat that has been stored and exchanged, and which was actually implemented in the mid-nineteenth century!
Figure 19.11 Thermal regeneration system inside glass furnace with two cameras used as heat exchangers (adapted from [33]).
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19.4 Conclusions Waste heat is an energy source that needs to be taken into account within the new energy consumption scenario in Europe, because it is an alternative energy supply which can be implemented in the same place where it is produced or it can be transported to the required place. Some examples shown in this chapter show the storage of waste heat as one way to reduce energy consumption in the industry sector, which is the major energy consumer in developed countries. Therefore, reutilization, recovery and storage of waste heat should be a key point to take into consideration for future energy saving plans from policy makers.
References 1. IEA. Energy Technology Perspectives 2012 – Pathways to a Clean Energy System. Available from: http://www.iea.org/etp/etp2012/ 2. IEA. Data Services – International Energy Agency (IEA). Available from: http://wds. iea.org/WDS/Common/Login/login.aspx 3. IEA. Worldwide Trends in Energy Use and Efficiency: Key Insights from IEA Indicator Analysis. Energy Indicators. International Energy Agency (IEA). Available from: http:// www.iea.org/publications/freepublications/publication/Indicators_2008-1.pdf 4. J.M. Allwood and J.M. Cullen. Sustainable materials with both eyes open: Future Buildings, Vehicles, Products and Equipment – Made Efficiently and Made with Less New Material. Cambridge: UIT Cambridge (2012). 5. US Department of Energy. Waste Heat Recovery: Technology and Opportunities in US Industry. Industrial Technology Program. BCS. Available from: http://www1.eere. energy.gov/manufacturing/intensiveprocesses/pdfs/waste_heat_recovery.pdf 6. IEA. Industrial Energy-related Technologies and Systems. Industrial excess heat recovery technologies and applications (2010). 7. J.C. Hadorn. Thermal energy storage for solar and low temperature buildings – State of the art by IEA Solar Heating and Cooling Task 32. Chapter 8: a brief history of PCMs for heat storage. Servei de publicacions, University of Lleida (2005). 8. L.F. Cabeza, A. Castell, C. Barreneche, A. de Gracia and A.I. Fernández. Materials used as PCM in thermal energy storage in buildings: a review. Renewable and Sustainable Energy Reviews 15, 1675–1695, (2011). 9. Waste heat recovery in a foundry with a high temperature thermal storage in combination with an absorption chiller. Available from: www.zae-bayern.de and http://doku.uba.de/ aDISWeb/ 10. Euroheat & Power. Heat Roadmap Europe 2050 Second Pre-study for the EU27. Available from: http://www.euroheat.org/Heat-Roadmap-Europe-165.aspx 11. Agendschap, Ministerie van Economische Zaken. Available from: http://www.saena.de/ angebete/abwaermeatlas.html 12. Bayerisches Landesamt für Umwelt (LfU). Abwärmenutzung im Bretrieb, Klima schützen - Kosten senken, 2012. Available from: http://www.lfu.bayern.de/energie/ co2_minderung/doc/leitfaden_abwaermenutzung_betrieb.pdf 13. L. Miró, C. Barreneche, S. Brückner, A. I. Fernandez and, L. F. Cabeza. Recovering waste heat using thermal energy storage technologies. Proceedings from Eurotherm Seminar #99: Advances in Thermal Energy Storage. Lleida (2014)
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14. T. Kajikawa. Status of research and development on thermoelectric power generation technology in Japan. Journal of Thermoelectricity 1, 18–29 (2009). 15. H. Hocheng, C.S. Tan, C.A. Lin, C.H. Lai, M.C. Yip, C.C. Hu and C.N. Liao. Advanced energy research of college of engineering at National Tsing Hua University. Proceedings of the International Conference on Energy and Sustainable Development: Issues and Strategies, Chiang Mai, Thailand, 201–205 (2010). 16. G. Homm and P. Klar. Compromising between high efficiency and materials abundance. Journal of thermoelectric materials. Physica Status Solidi RRL: Rapid Research Letters 5(9), 324–331 (2011). 17. H.W. Hoffman, R.J. Kedl and R.A. Duscha. Thermal energy storage for industrial waste heat recovery. NASA Tech. Memo. (NASA-TM-78953, DOE/NASA/1034-78/2, E-9702) (1978). 18. W.J. Yang. Recovery and storage of waste heat. NATO ASI Series, Series E: Applied Sciences, 167, 525–537 (1989). 19. T.E. Weast, L.J. Shannon and K.P. Ananth. Study of thermal energy storage using fluidized bed heat exchangers. Proceedings of the 15th Intersociety Energy Conversion Engineering Conference, 619–623 (1980). 20. M. Kamimoto, Y. Abe, S. Sawata, T. Tani and T. Ozawa. Design and cost evaluations of solar energy and waste heat utilization systems with latent thermal storage unit using form-stable high-density polyethylene. Journal of Chemical Engineering of Japan 19(4), 287–293 (1986). 21. D. Laing, D. Lehmann, M. Fiss and C. Bahl. Test results of concrete thermal energy storage for parabolic trough power plants. Journal of Solar Energy Engineering 131(4), 041007/1-041007/6 (2009). 22. H. Gunerhan and A. Hepbasli. Utilization of basalt stone as a sensible heat storage material. Energy Sources 27(14), 1357–1366, (2005). 23. G. Fang, H. Li and X. Liu. Preparation and properties of lauric acid/silicon dioxide composites as form-stable phase change materials for thermal energy storage. Materials Chemistry and Physics 122(2–3), 533–536 (2010). 24. V. Pandiyarajan, M. Chinna Pandian, E. Malan, R. Velraj and R.V. Seeniraj. Experimental investigation on heat recovery from diesel engine exhaust using finned shell and tube heat exchanger and thermal storage system. Applied Energy 88(1), 77–87 (2011). 25. Y. Zhang. Physical property and thermal physical property of microencapsulated phase change material slurry. Applied Mechanics and Materials 110–116, 571–576. (2012). 26. S. Jesumathy, M. Udayakumar and S. Suresh. Experimental study of enhanced heat transfer by addition of CuO nanoparticle. Heat and Mass Transfer 48(6), 965–978 (2012). 27. H. Sugo, E. Kisi and D. Cuskelly. Miscibility gap alloys with inverse microstructures and high thermal conductivity for high energy density thermal storage applications. Applied Thermal Engineering 51(1–2), 1345–1350 (2013). 28. S.D. Sharma and K. Sagara. Latent heat storage materials and systems: a review. International Journal of Green Energy 2(1), 1–56 (2005). 29. T. Nomura, N. Okinaka and T. Akiyama. Technology of latent heat storage for high temperature application: a review. Iron and Steel Institute of Japan International 50(9), 1229–1239 (2010). 30. Transportation of Energy by Utilization of Thermal Energy Storage Technology: Final Report. Annex 18 – ECES. International Energy Agency (IEA), 2010. Available from: http://www.iea-eces.org/files/annex18_final_rept_october_2010.pdf
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31. Ecoheatcool: a Euroheat & Power initiative. Supported by Energy Europe. Available from: www.ecoheatcool.org 32. A. Hauer, S. Hiebler and M. Reuß. Bine Fachbuch. Wärmespeicher. Available from: http://www.bine.info/fileadmin/content/Produkte-im-Shop/Buchreihe/Leseprobe_ Waermespeicher.pdf 33. J.M. Fernández Navarro. El vidrio, 3rd edn. CSIC, Sociedad Espa–ola de Cerámica y vidrio, Spain (2003).
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A. I. Fernández1, C. Barreneche1, L. Miró2, S. Brückner3, L. F. Cabeza2 Universitat de Barcelona, Spain; 2Universitat de Lleida, Spain; 3Bavarian Center for Applied Energy Research (ZAE Bayern), Germany 1
19.1 Introduction As shown in Figure 19.1, the global energy consumption of the planet has been increasing during the last 20 years. This effect was previously observed in OECD countries but the energy consumption trend in developed countries is now showing a 2–3% annual increment [1]. The production of energy for domestic consumption in each region of the world is one of the most important points that government leaders have to deal with when seeking alternatives to generate energy or to reduce energy consumption. One of the sectors with a higher impact in the worldwide energy consumption is the industrial sector, which accounts for 31% of the global energy consumption reported by the International Energy Agency (IEA) [1]. Alternatives to change this scenario are recently emerging to stop the effects from the increasing global energy consumption, the CO2 emissions, greenhouse gas emissions, and global warming. The energy consumption of the industry sector was around 76.5 EJ in 2011 according to data services of the IEA [2] and it had an important weight in the total energy consumption distribution as Figure 19.2 shows. This figure is divided into three sectors: industry, transportation and other, which includes the energy consumption from buildings, power generation, etc. Total energy consumption
Industry sector
Energy consumption (Mtoe)
10000 8000 6000 4000 2000 0 1990
1995
2000
2005
2010
2011
Figure 19.1 Global energy consumption over time vs. industrial energy consumption [1]. Advances in Thermal Energy Storage Systems. http://dx.doi.org/10.1533/9781782420965.4.479 Copyright © 2015 Elsevier Ltd. All rights reserved.
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Industry sector (76.2 EJ) Transport
(66.4 EJ)
Other sectors (101.7 EJ)
Figure 19.2 Worldwide energy consumption distribution divided by sector for 2011 [2].
Europe’s situation is similar. Industry accounts for around 33% [3] of all the energy used in Europe, the major part of which is accounted for by materials processing industries. As stated in the Worldwide Trends in Energy Use and Efficiency report from the IEA [3], applying ‘the best available technology (BAT) or best practice technology (BPT) on a global basis could save between 25 EJ and 37 EJ of energy per year (on a primary energy equivalent basis), which represents 18% to 26% of current energy use in industry. The associated CO 2 savings would be between 1.9 Gt CO2 and 3.2 Gt CO2 per year’. The industry sector has put a major effort into becoming more energy efficient, but this effort must be redoubled to achieve the time horizon of 2020 across all these materials processing industries [4]. Energy consumption is increasing, which is a major issue. Several alternatives have been proposed to stop this increase and even to reverse it. In fact, the energy consumed in the industry sector is not completely exploited and several processes are supplying heat which gets wasted in the form of hot gas, vapour, hot water, etc. Part of this energy is wasted as heat in several components of the system or the final parts of processes. Recovery of this waste heat should be considered to improve the energy requirements in these processes. Using the definition from the report Waste Heat Recovery: Technology and Opportunities in US Industry, [5], industrial waste heat refers to energy that is generated in industrial processes without being put to practical use. Recovering industrial waste heat can be achieved via numerous methods and it can be reused (in the same industry or can be transported to another use), stored using storage technologies or transformed into another type of heat, cold or power [6]. It is estimated that somewhere between 20 and 50% of industrial energy input is lost as waste heat in the form of hot exhaust gases, cooling water, and heat lost from hot equipment surfaces and heated products [5]. Waste heat is becoming an important issue and there are several studies on the measures to recover this heat, though often these measures are not justifiable from
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the point of view of cost. Due to cost considerations, different alternatives are gaining importance that will reinforce the reuse of waste heat. The scheme showed in Figure 19.3 presents a possible flux diagram of the waste heat recovery process: a hot gas crosses the burner and it is heated up. Then, the heated gas crosses the water heat exchanger and part of the gas is slightly cooled and the water inside the heat exchanger can be used, for instance, to activate the cooling equipment. The industrial process showed in Figure 19.3 could represent a chemical plant process, petroleum refinery, bio-refinery, pulp and paper mill, etc. Another method to take advantage of the unconsumed energy in the industry sector is thermal energy storage (TES). TES systems can store energy following three different methods: first, the sensible heat generated when a temperature gradient is applied to a material, which is directly proportional to the heat capacity of the material; second, the use of the latent heat produced during a change of state from solid–solid, liquid–solid, solid–gas, liquid–liquid, etc.; finally, the use of a thermochemical reactor, in which a thermochemical material (TCM) can store energy in a reversible chemical reaction which releases heat [7,8]. These two methods to improve the energy requirements and energy efficiency of industry (waste heat recovery and TES) can be combined in order to decrease the industrial energy consumption. Thereby, a TES system could allow the charge/ discharge of the system when thermal conditions are favorable for the process. In addition, the energy stored by the TES system can be kept and this energy can be used whenever the industry process needs it. ZAE Bayern eV, Küttner GmbH and Giesserei Heunisch GmbH, started a new project in 2013 where industrial waste heat is used by new thermal storage and heat transformation technologies. At Giesserei Heunisch GmbH, industrial waste heat from an iron melting kiln (approximately 3 MW at 230°C) is available. The project aims to demonstrate an economically and ecologically efficient energy system to use industrial waste heat (high temperature thermal storage in combination with absorption heat pump/chiller) under real life conditions [9].
Hot water/steam to heating or thermally activate the cooling
Heat exhaust gas
Heat recovery
Heat recovery unit
Spent exhaust gas
Water source return
Figure 19.3 Scheme: flux diagram of the waste heat recovery process.
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19.2 Generation of waste process heat in different industries Waste heat sources are being mapped in several parts of the world because they are free sources that could be taken advantage of or they could be interesting to other neighboring industry companies and/or a nearby town where this heat could be used [10]. The Netherlands is one example. The waste heat points available in the Netherlands from industry are indicated on the map shown in Figure 19.4 as black circles where the size represents the amount of waste heat. The information of outlet temperatures, CO2 emissions, etc., is detailed in the website from Agendschap [11]. In industrial processes there are several individual parts of the processes where waste heat is located. Some examples of the outlet temperature data of several industrial processes from the literature are listed in Table 19.1 [5,12]. In addition, several components of systems able to recover waste heat have been identified [6]. The classification diagram of the components where waste heat was recognized is presented in Figure 19.5 [13]. In order to recover this waste heat from an industrial process, several technologies have been developed in order to reuse this heat in the same industry (heat exchangers), to produce heat (mechanical vapor compressors (MVC) or absorption heat pumps),
Concentration Waste heat points
Figure 19.4 Waste heat points located in the Netherlands (data adapted from [11]).
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Outlet temperatures of component systems from several industrial processes
Table 19.1
Process
Exhaust gas Reference temperature (°C)
Steel electric arc furnace Glass melting furnace Aluminum reverberatory furnace Steel heating furnace Copper reverberatory furnace Gas oven without regenerator Hydrogen plants Fume incinerators Coke oven Cement kiln Melting oven Steam boiler exhaust Steam boiler Ceramic kiln Cooling water from internal combustion engines Exhaust gases exiting recovery devices in gas-fired boilers, ethylene furnaces, etc. Conventional hot water boiler Cooling water from air conditioning and refrigeration condensers
1370–1650 1300–1540 1100–1200 930–1040 900–1090 900–1300 650–980 650–143 650–100 450–620 400–700 230–480 200–300 150–1000 70–120 70–230
[5] [5] [5] [5] [5] [11] [5] [5] [5] [5] [11] [5] [11] [11] [5] [5]
60–230 30–40
[11] [5]
Source: Bayerisches Landesamt für Umwelt (2012) [12]
Heat exchangers Storage technologies
Waste heat technologies
Sorption systems
Absorption chillers Absorption heat pump
MVC SRC, ORC, Kalina cycles
Figure 19.5 Classification diagram of components able to recover waste heat [13].
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to produce cold (absorption chillers), or to produce power (Steam Rankine cycles (SRC), organic Rankine cycles (ORC), Kalina cycle, etc.). The utilization of one of these technologies will depend on the interests or requirements of the industry. In the review of the scientific literature on industrial waste heat recovery, the use of thermoelectric devices is being intensively investigated for waste heat harvesting in a wide range of temperatures and sectors. Kajikawa [14] reported the status of the research and development on thermoelectric power generation technology in Japan. Demonstration system tests and feasibility studies have been achieved by private companies using practical heat sources such as industrial furnaces, motorcycles, solid waste incinerators, and solar thermal systems. The research on different types of thermoelectric materials carried out by universities and national research institutes is also described. Another example is given by Hocheng et al. [15] who report a thermoelectric prototype generating 300 W at 12 V with a temperature difference of 150°C. For selecting thermoelectric materials, a decision matrix is defined by Homm and Klar [16] that analyzes the potential of the thermoelectric materials SiGe, PbTe, Bi2Te3, and FeSi2 in four types of applications, classified by mobile vs. stationary and specialized vs. mass application. The selection criteria comprise energy efficiency, materials availability, costs, environmental friendliness and toxicity.
19.3 Application of thermal energy storage (TES) for valorization of waste process heat Thermal energy storage is also proposed as a promising method to be implemented in waste heat recovery systems. Already in the early 1980s there were references in the literature to the potential of using heat storage technologies for waste heat management in different industries, mainly materials primary production [17], also identifying technologies for low-level to high-level heat storage [18]. Within these technologies, the use of fluidized bed heat exchangers was evaluated for a cement rotary kiln and electric arc furnace steel plant [19]. Some design and evaluation case studies are reported implementing some kind of storage concept. For instance, the design and cost evaluation of a latent heat storage unit with HDPE for the utilization of waste heat from an incinerator operated for 8 hours at a constant thermal energy output into the waste heat recovery system: 582 kW is feasible and the storage unit can be operated with constant inlet temperature and with a thermal input/output which matches the heat supply/demand by changing the flow rate [20]. Focusing on the materials with potential to be implemented in TES systems for waste heat recovery, sensible heat storage systems are described using either concrete [21] or basalt stone [22]. Research on latent heat storage materials has increased significantly during the last 20 years, and recent trends in new hybrid materials and combined systems identify the recovery of waste heat as a potential application [23–27]. Sharma and Sagara [28] reviewed latent heat storage materials and systems paying attention to reported designs for waste heat recovery. However, few cases
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have been implemented as real cases. Nomura et al. [29] reported recent trends in technologies using PCM for waste heat recovery systems. These are summarized in Table 19.2. In this section several cases where a TES system was successfully implemented to an industrial waste heat recovery process are presented.
19.3.1 District heating versus transportation of waste heat from steel industry In 2006, a pre-study was conducted on the transportation of waste heat from the steelmaking industry in Sweden. Three different methods for transporting the heat were compared. The first one was a conventional district heating process and its main downside was the requirement for new underground piping to cover the 30 km distance. The second one was transportation of heat by train using phase change material (PCM) storage. finally, the last method was the transportation of heat by train using zeolite sorption technology used as thermochemical storage. The converter gas was used in this study and it gave a potential to be transported of 60 GWh/year. Therefore, the costs for the three different options were estimated and the results are shown in Figure 19.6. The results indicated that the last method using zeolites was the most promising with regard to cost effectiveness. The main reason was the high energy density from the zeolites in comparison with the other alternatives. This example of thermal energy storage applied in a waste heat recovery case studied was framed in Annex 18 of the ECES IA of the International Energy Agency [30].
Table 19.2
Recovery waste heat characteristics of PCM studies
PCM
Heat source
Pb (Tm = 328°C)
High temperature gas exhausted (<727°C)
Magnesium nitrate hexahydrate/ magnesium chloride hexahydrate
Urban waste heat from emerged co-generation system (<60–100°C)
Copper (Tm: 1083°C)
High temperature gas exhausted from steelmaking converter (<1600°C)
Various sugars (Tm: 93-172°C)
Industrial waste heat at low temperature (<200°C)
Sodium acetate trihydrate (Tm: 58°C) Erythtitol (Tm: 118°C)
Industrial waste heat at low temperature (<200°C)
Erythtitol (Tm: 118°C)
Industrial waste heat at low temperature (<200°C)
Sodium acetate trihydrate (Tm: 58°C) Erythtitol (Tm: 119°C) Source: Nomura et al. (2010) [29]
Industrial waste heat at low temperature (<200°C)
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Train - zeolites
Train - PCM
District heating
0
10
20
30 40 Cost (7/MWh)
50
60
Figure 19.6 Cost of three different methods to implement waste heat recovery.
19.3.2 District cooling There are some areas where there are local cooling sources which may be wasted. This source can be included in a high-efficient alternative to the traditional cooling solutions when it is connected to a district cooling system provided by pipes. As stated in the Euroheat project: ‘the centralization of cooling production is a prerequisite to reach a high efficiency, as it makes possible to use free cooling or waste heat sources’ [31]. In addition, a district cooling system can reach an efficiency of 5–10 times higher than traditional local cooling systems. The cold could be from different free sources: deep sea, lakes, rivers or aquifers; industrial cooling sources where absorption chillers are used, e.g. waste heat from industry, CHP, waste to energy plants, etc. District cooling systems are considered a win-win solution for society as the Euroheat project mentions [31]. Furthermore, this type of cooling system can include an extra system for seasonal thermal storage and the configuration is shown in Figure 19.7.
19.3.3 Waste incineration plant/PVC sludge drying The system presented in the study presented in this section consisted of one charging station at the site of a waste heat source, providing energy for one or several consumers. This study was also included in Annex 18 of ECES IA of the IEA [30]. A thermochemical mobile storage is charged at a waste incineration plant and discharged at a PVC drying facility. German regulations do not permit more than one storage unit per truck as total weight for truck–trailer combinations is limited to 40 tons. For similar reasons, considerations have been limited to a charging station dealing with only one storage unit at a time. The system presented here is a sorption storage unit with 14 t of zeolite as storage material situated within fixed beds in a wedge-shaped configuration
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Customers Storage
Production cooling
Waste heat or “free cooling” source
Sub-station (heat exchanger)
Distribution network
Figure 19.7 District cooling system connected between free cooling source and consumers where a storage system is installed for seasonal thermal storage [31].
Figure 19.8 ZAE Bayern sorption storage module based on zeolite sorption process [30].
as shown in Figure 19.8. The unit is charged by applying a hot air stream to the system: the zeolite is dried and water released to the air. During the discharging process a moist air stream is used. The containing water is absorbed by the sorbent bed releasing heat. Thereby, the air stream is dried and heated up. The scheme of this process is presented in Figure 19.9.
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Discharging
Heat of condensation
Air + water
Zeolite
Desorption heat
Air
Air
Absorption heat
Figure 19.9 Charging/discharging zeolite process: water sorption.
(a)
(b)
Figure 19.10 Charging/discharging waste heat recovery configuration process.
The configuration during the charging/discharging process in the waste incineration plant is shown in Figure 19.10. The charging station of the pilot storage is installed in Hamm at the local waste incineration plant (MVA Hamm). Due to the heat extraction, the electricity production of the plant is reduced by approximately 10%. The discharging takes place ca 7 km away at Fa. Jäckering, a pvc sludge drying plant. For zeolite storage the capacity of the storage depends on the charging temperature. For this storage it is 200–308 kWh/t at 135–250°C respectively, leading to 2.4–3.7 MWh for the 14 t storage used in this project. The sorption system provides dry, hot air being compatible with industrial drying processes: exhaust air from the system is normally moist and can be used directly in the sorption unit. In this case, the exhaust air from a drying process is used at approximately 65°C and 65% relative humidity [32].
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An economic analysis revealed that a heat production price of round about 750/ MWh is feasible. A sensibility analysis showed that the crucial parameters for the cost effectiveness of such a storage system are high energy density, short transportation and transit times, and a high utilization rate [32].
19.3.4 Glass furnace Furnaces are used in the glass industry as reactors where the glass-forming process occurs at high temperature. there are two types of furnace: intermittent work furnace and continuous working furnace. The sources of energy used for heating have changed over time: wood, coal, fuel oil, natural gas and the newest fuels are low oxygen-rich mixtures. However, electrical energy is a safe alternative source that assists as a heat source or as a support for heating. One of the furnaces used in glass forming is the raft furnace. This type of furnace incorporated a thermal regeneration system since 1857 (developed by Siemens) that allowed its continuous use. The thermal regeneration system is based on the use of two cameras which operate alternately as heat exchangers, and each has a grid of refractory material which is able store thermal energy as sensible heat (Fig. 19.11). As hot gases from the combustion pass through a chamber and cool the refractory material along the way, the combustion air enters through the other chamber, preheated during its journey. This is an application that has been using sensible heat that has been stored and exchanged, and which was actually implemented in the mid-nineteenth century!
Figure 19.11 Thermal regeneration system inside glass furnace with two cameras used as heat exchangers (adapted from [33]).
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19.4 Conclusions Waste heat is an energy source that needs to be taken into account within the new energy consumption scenario in Europe, because it is an alternative energy supply which can be implemented in the same place where it is produced or it can be transported to the required place. Some examples shown in this chapter show the storage of waste heat as one way to reduce energy consumption in the industry sector, which is the major energy consumer in developed countries. Therefore, reutilization, recovery and storage of waste heat should be a key point to take into consideration for future energy saving plans from policy makers.
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31. Ecoheatcool: a Euroheat & Power initiative. Supported by Energy Europe. Available from: www.ecoheatcool.org 32. A. Hauer, S. Hiebler and M. Reuß. Bine Fachbuch. Wärmespeicher. Available from: http://www.bine.info/fileadmin/content/Produkte-im-Shop/Buchreihe/Leseprobe_ Waermespeicher.pdf 33. J.M. Fernández Navarro. El vidrio, 3rd edn. CSIC, Sociedad Espa–ola de Cerámica y vidrio, Spain (2003).