Estimating the waste heat recovery in the European Union Industry
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Industrial processes are currently responsible for nearly 26% of European primary energy consumptions and are characterized by a multitude of energy losses. Among them, the ones that occur as heat streams rejected to the environment in the form of exhausts or effluents take place at different temperature levels. The reduction or recovery of such types of energy flows will undoubtedly contribute to the achievement of improved environmental performance as well as to reduce the overall manufacturing costs of goods. In this scenario, the current work aims at outlining the prospects of potential for industrial waste heat recovery in the European Union (EU) upon identification and quantification of primary energy consumptions among the major industrial sectors and their related waste streams and temperature levels. The paper introduces a new approach toward estimating the waste heat recovery in the European Union industry, using the Carnot efficiency in relation to the temperature levels of the processes involved. The assessment is carried out using EU statistical energy databases. The overall EU thermal energy waste is quantified at 920 TWh theoretical potential and 279 TWh Carnot potential.
KeywordsWaste heat recovery WHR potential estimation Carnot potential WHR Europe Energy statistics Energy recovery Heat to power conversion
The European Union (EU), with twenty-eight (28) member states, over 4 million km2 and over 512 million inhabitants, is currently responsible for about 12% of the world final energy consumptions (1122 Mtoe in 2017) and for about 11% of the world final CO2 emissions (8.7 greenhouse gas emissions tonnes per capita in 2016) (European C 2016a, b; International Energy Agency 2016). Industry in the EU accounts for about 26% of the final energy consumption and for about 48% of the final CO2 emissions (European C 2016b). EU, being at the forefront of awareness and involvement in global environmental issues, has contributed in the reduction of greenhouse gas emissions by about 23% compared to the ones in 1990. One of the key EU-related targets for 2030 is to reach a reduction of at least 40% with respect to the same reference year (European C 2016a), through energy savings and a more intensive usage of renewable energy sources.
To this end, recovery actions from existing energetic systems can offer substantial primary energy savings with simultaneous equally important greenhouse gas emission reductions. One such example is the industrial processes that are characterized by a multitude of waste heat streams at different temperature levels. In this context, the process of waste heat recovery (WHR) is the capturing of heat from such waste streams and its direct utilization, through its upgrading into a more useful temperature and/or its conversion into electrical power or cooling. The energy generated from heat recovery can either be used for the needs of the same industrial site or exported to neighboring facilities or to electrical or heat distribution networks.
Through the rising concerns over the cost of energy and energy security as well as general environmental and sustainability considerations, there is nowadays increased global interest in the development and application of WHR systems, motivated even by government regulatory requirements on emissions reduction targets. The Global WHR market is expected to surpass $65 billion by the end of 2021 with a compound annual growth rate (CAGR) of 6.9% (Markets 2018). Newer report suggests a compound annual growth rate of 4.8% by the end of 2025 (QYResearch G 2018). Europe leads the market related to WHR equipment with a 38% share of the global market as of 2012 (Markets 2018).
The Asia–Pacific region has been experiencing the highest growth rate in the last few years, of about 10% per annum, with China and India accounting for the highest number of installations of heat recovery units. For these figures to insist and expand in the future, however, and for the European manufacturing and user industry to benefit from these developments, technological improvements and innovations should take place aimed at improving the energy efficiency of heat recovery equipment and reducing installed costs [see, for example, Agathokleous et al. (2019) and Jouhara et al.(2018)].
Depending on their nature, waste heat streams may be valued through different approaches. For instance, high-pressure effluents are suitable for direct expansion, while low-temperature flue gases can be exploited through condensing economizers that aim at recovering the latent heat of the water vapors. Other WHR techniques include the mechanical or thermal recompression of vapors as well as the usage of industrial heat pumps (Ommen et al. 2015). Some energy systems, for example the internal combustion engines for road transportation or power generation, are suitable for novel technologies such as the six-stroke internal combustion engine cycle or the thermoelectric generators that perform a conversion of heat into direct current electricity without involving any additional equipment (Yang et al. 2019; Merienne et al. 2019).
In industrial scenarios, the most common WHR approaches are the ones based on sensible preheating as well as the waste heat to power generation via bottoming thermodynamic cycles. In the first case, heat exchangers and heat transfer fluids are employed to recover the energy from the waste heat source and either to import it back to the same industrial process or to export it over the fence, i.e., in near industrial sites or in residential areas for domestic heating. In the latter, the working fluid that performs an enthalpy gain during the heat recovery process undergoes a series of thermodynamic transformations that produce a net positive power output. Unlike heat recovery, which requires a heat demand in the industrial site or in the nearby ones, an electrical energy recovery is undoubtedly more favorable in terms of energy management since the surplus of electricity due to the recovery process can interact with the electrical grid and its larger capacity. Furthermore, the nobler nature of electric energy implies greater economic and emission savings. For instance, if the recovery occurred via thermal form as if it was resulting from a combustion of natural gas, 1 MWh of thermal energy recovered would avoid 0.202 tons of CO2 emitted in the atmosphere, while the same energy recovery but in electrical form would have an emission factor of 0.460 tCO2/MWhe (Markets 2018). On the other hand, conversion efficiencies of heat to power approaches are lower than the ones that characterize heat recovery devices. The reference cycles for these energy recovery technologies have been extensively investigated by the scientific and industrial communities. In particular, plenty of research has been performed on organic Rankine cycles (ORC) using pure fluids or zeotropic mixtures as well as different machinery and heat transfer equipments (Liu et al. 2004; Wei et al. 2007; Li et al. 2014).
A comprehensive review of the convectional WHR technologies was introduced by Jouhara et al. (2018), where various technologies were discussed, such as recuperators, regenerators, furnace regenerators and rotary regenerators or heat wheels, passive air preheaters, regenerative and recuperative burners, plate heat exchangers, economizers, as well as units of waste heat boilers and run-around coil (RAC). Among the available technologies, thermal energy storage (TES) (in particular when using phase change materials) offers the possibility of solving the problem of matching the discontinuous waste heat supply with the heat demand and achieving a better capacity factor (Miró et al. 2016; Elias and Stathopoulos 2019). In addition to the convectional WHR approaches, new technologies have been proposed by Agathokleous et al. (2019), including trilateral flash cycle, Joule-Brayton cycle working with supercritical carbon dioxide, flat heat pipes and condensing economizer for acidic effluents.
The main aim of the current paper is to present the industrial WHR potential available in the member states of the European Union. In Sect. 2, the calculation methodology is introduced. It is based on the use of the Carnot efficiency through the identification of the WHR processes in different temperature levels. An assessment of the WHR potential in EU industry is given in Sect. 3, where results are detailed by temperature levels, country and industrial sectors. We conclude in Sect. 4 with suggestions for future work.
Several studies have addressed the estimation of waste heat potential as well as the environmental effect. For example, Papapetrou et al. (2018) have proposed a new methodology on estimating the WHR potential, presenting results as per temperature level and per industrial sector for the EU region. The authors have exploited results from 425 UK industrial sites in the years 2000–2003 to calculate the waste heat fractions, where they then adjusted the waste heat fraction for the EU countries and consequently alternating for the year 2015. The estimation of the technical WHR potential in the UK industry was also described by Hammond and Norman (2014). Emphasis has been given on that the savings estimation with technical potential will be lower than the maximum theoretical potential, but also higher than the economic potential. Forman et al. (2016) have presented a novel—at the time—approach for the estimation of the global WHR potential through the calculation of the Carnot potential. The approach above was used to estimate the waste heat emissions from the power generation industry, transport industry and construction industry on a global scale. The authors have gone a step further to investigate the environmental impact with potential savings on the emissions by using the WHR theoretical potential.
The constraints above establish the technical potential, which naturally depends on the technologies considered. An important technical constraint is the required minimum temperature. The technical potential to use waste heat is ruled by two key constraints: the boundary conditions of the technology itself and a heating or cooling demand that is necessary.
In the present work, going a step further, the technical potential is separated into technical potential (theoretical) and technical potential (applicable). These are distinguishable through the fact that the former can be calculated using a theoretical/generic process-related analysis, while the latter can be calculated using onsite data with all plant specific parameters taken into consideration (see proposed Fig. 1b). Accordingly, the feasibility of the technology considered can be eventually analyzed by means of economic criteria.
In the current study, the theoretical WHR potential (simply referred to as theoretical potential from this point onward) has been estimated through the methodology proposed by Forman et al. (2016), applied to the energy statistics (reference year 2014) for the European Union. According to the classification made by Brueckner et al. (2014), on what concerns the data collection and the application of input parameters, Forman’s methodology is a top-down approach, while on what concerns the usage of literature data, coefficients and estimation, the calculation method used is of medium accuracy.
The database for the primary energy consumptions can be found in Panayiotou et al. (2017), while both loss and temperature-level coefficients can be found in Brueckner et al. (2014). Note that, when multiple loss coefficients were listed for the same primary energy source, the parameter used in the estimations was the weighted average of the listed ones.
The use of WHRP in Eq. (2) in Eq. (3) improves the accuracy of the calculations, giving more reliable values for both the theoretical WHRP and the Carnot WHRP, as these are presented in Sect. 3 below.
2.1 Identification of the processes with WHR potential in each industrial sector
Identification of the WHR processes is the key parameter to evaluate the potential of WHR based on the methodology described above. A previous research on the available processes and temperatures has been presented by Panayiotou et al. (2017). Therein, information of the available processes that implicate waste heat in the process is outlined by industry. There are 18 industries where WHR can be achieved, namely (1) the iron and steel industry, (2) the large combustion plants, (3) large volume inorganic chemicals: ammonia, acids and fertilizers, (4) large volume inorganic chemicals: solids and others industry, (5) food and tobacco, (6) production of glass, (7) production of organic fine chemicals, (8) production of nonferrous metals, (9) production of cement, lime and magnesium oxide, (10) production of polymers, (11) ferrous metals processing, (12) production of pulp, paper and board, (13) surface treatment using organic solvents, (14) tanning of hides and skins, (15) textiles industry, (16) waste incineration, (17) waste treatment and (18) wood-based panel production.
The main processes and their temperature levels (important for coefficient σijk in Eq. (2) above) that implicate waste heat in each of the industries above are summarized in Table 1 of the “Appendix.”
Although identification of the processes for WHR exists in the literature, it is not straightforward within the manufacturing facilities to isolate the most suitable waste heat sources and processes. To overcome this issue and standardize the procedure, Simeone et al. (2016) have presented a decision support tool for the WHR options based on a framework (Woolley et al. 2018) that consists of four stages: waste heat survey, waste heat assessment, technology selection and decision support.
3 Calculation of the waste heat recovery potential
Based on the methodology described in Sect. 2, the calculations of the WHR potential per EU member state and per industrial sector are performed.
3.1 Aggregated waste heat recovery potentials and EU member states
3.2 Detailed waste heat recovery potentials per industrial sector
The results above indicate the difference of the theoretical and the Carnot potential, with the temperature levels being accountable. These results, based on the newly presented Eq. (2) above, constitute a significant improvement on the accuracy of calculations, compared to previous studies [see, e.g., Forman et al. (2016) and Panayiotou et al. (2017)].
In the current study, the WHR potential of the EU industry has been “revisited” through a more elegant methodology that takes into consideration the temperature levels of the process. Both the theoretical potential and the Carnot potential have been addressed. Results have been given for EU countries as well as EU industries. These verify that the potential is high, of the order of 300 TWh/year, even for the conservative estimation used here (as opposed to the less accurate (Panayiotou et al. 2017), less detailed (Forman et al. 2016) or less conservative methods (Papapetrou et al. 2018) used).
With insight information into the different processes, together with their temperature ranges, used in all industrial sectors in the EU having been identified [see Agathokleous et al. (2019), Jouhara et al. (2018), Papapetrou et al. (2018) and Panayiotou et al. (2017)], the next step is to assess the potential market of the most intensive industrial sectors in relation to old and “new” technologies and their COPs and how to improve recovery techniques (Agathokleous et al. 2019). It is also important to obtain further knowledge on barriers (e.g., financial, technological, legislative) to the adoption of WHR technologies and see how these can be overcome.
The research presented in this paper has received funding from: (1) the European Union’s Horizon 2020 research and innovation program under Grant agreement No. 680599, (2) Innovate UK (Project No. 61995-431253, (3) Engineering and Physical Sciences Research Council UK (EPSRC), Grant No. EP/P510294/1; (4) Research Councils UK (RCUK), Grant No. EP/K011820/1. The authors would like to acknowledge the financial support from these organizations as well as contributions from industry partners: Spirax Sarco Engineering PLC, Howden Compressors Ltd, Tata Steel, Arctic Circle Ltd, Cooper Tires Ltd and Industrial Power Units Ltd.
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