Introduction

The WtE technologies have become a keystone and are increasingly interesting as viewed from both an energy supply perspective and waste management. Globally, energy-intensive industries still emit the largest share of industrial greenhouse gas (GHG) emissions (IEA 2008b). WtE combines several ways of reducing GHG emissions. The term WtE is often used in reference to the incineration of municipal waste. However, in this article, WtE refers to all technologies that convert, transport, manage, and recover or reuse energy from any type of waste (solid, liquid, gas, and heat) in a continuous industrial process. In addition, these technologies have the potential for increasing heat recovery, emissions reduction, electric efficiency, transportation fuel substitution, and storing energy and fuel (Münster and Lund 2009). To our knowledge, no work has been reported in the open literature on WtE technologies in continuous process industries.

On the one hand, the global crisis has shown the importance of sustainable development. Tomorrow’s industries must simultaneously address economic, social, and ecological dimensions, with processes that are as lean and clean as possible. In the medium and long term, “zero waste” and “zero emissions” will be the goals for the “factories of the future”. On the other hand, under the pressure of rising world population and increasing lifestyle aspirations, global energy consumption is expected to double from the present level of 15 TW by 2050, and to triple by 2100. Thus, this will put a massive strain on Earth’s resources (EU 2010).

The overall objective of the work presented was to investigate synergies between large energy consumers to achieve environmental and energy-saving technologies. In other words, the focus of this article was the analysis of the optimal use of WtE technologies in continuous process industries. The core of the first part of the article is the application of WtE technologies in the steel sector. The second section presents a summary of WtE technologies for a branch of general manufacturing industries with continuous processes. Finally, this study brings about a synergetic interaction in a matrix analysis among energy-intensive industries and identifies potentially energy-saving R&D areas of new WtE technologies.

Iron and steel industry

The iron and steel industry provides the backbone for construction, transportation, and manufacturing, and has become the material of choice for a variety of consumer products. Moreover, markets for iron and steel are expanding. As a result, this sector is critical to the worldwide economy.

The production process for manufacturing iron and steel is energy-intensive and requires a large amount of natural resources. The iron and steel industry accounted for 19% of final energy use and about a quarter of direct CO2 emissions from the industry sector (IEA 2007). Energy constitutes a significant portion of the cost of iron and steel production, up to 40% in some countries. The majority of emissions generated by iron and steel production are due to coal use and other energy resources as a key process input, which means that increasing energy efficiency is the most cost-effective way to improve environmental performance (APP 2008). The aggregate carbon dioxide (CO2) emissions from the global iron and steel industry have reached roughly two billion tons annually, accounting for approximately 5% of global anthropogenic CO2 emissions (APP 2007).

The sector is divided into two basic types of production. First, standard processes with coke-making, iron-making, steel-making, and subsequent forming and finishing operations, which are referred to as “fully integrated production”. Alternatively, a second type of production without coke-making or iron-making operations is mainly associated to metal scrap by applying electric arc furnace (EAF) technology, and is commonly referred to as “mini-mills” (EPA 2011). The integrated mill accounts for two-thirds of steel production (IEA 2007).

The production of steel requires a number of steps which can include: agglomeration processes (sintering, pelletizing, and briquetting), coke-making, iron-making (blast furnace, direct reduction, and direct iron-making), steel-making (basic oxygen furnace or BOF, EAF), and forming and finishing processes (ladle refining, casting, rolling, forming and finishing) (APP 2007).

Coke, which is the fuel and carbon source at integrated mills, is produced by heating coal in the absence of oxygen at high temperatures in coke ovens. Pig iron is then produced by heating the coke, iron ore, and limestone in a blast furnace. In a BOF, molten iron from the blast furnace is combined with flux and scrap steel where high-purity oxygen is injected. Moreover, in an EAF the input material is primarily scrap steel, which is melted and refined by passing an electric current from the electrodes through the scrap.

The sector has multi-media impacts, including air emissions (carbon oxide or COx, nitrogen oxide or NOx, sulfur oxide or SOx, and particulate matter or PMx), wastewater contaminants, hazardous wastes, and solid wastes. The major environmental impacts from integrated steel mills are from coke-making and iron-making. Furthermore, the energy used by “mini-mills” generates GHG from power generation (EPA 2011).

WtE technologies in the iron and steel industry

The iron and steel industry is faced with a wide range of environmental concerns that are fundamentally related to the high energy requirements, material usage, and the by-products associated with generating enormous quantities of steel (Manning and Fruehan 2001).

Figure 1 presents a layout of the current state-of-the-art in WtE technology in the iron and steel industry as collected from Asia Pacific Partnership (2007) and ArcelorMittal (2011).

Fig. 1
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Layout of WtE technologies in the iron and steel production processes

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Table 1 describes one by one these WtE technologies (showed in Fig. 1) in terms of iron and steel processes, typical uses and key factors (energy saving, environmental emission, commercial status, and other benefits). Fundamentally, the data have been gathered from Asia Pacific Partnership (2007).

Table 1 Matrix of WtE technologies, uses and benefits in the iron and steel industry
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Continuous process industries

Cement industry

Cement is an essential material for social infrastructure and has played a vital role in economic development around the world. The nonmetallic mineral sub-sector accounts for about 9% of global industrial energy use, of which 70–80% is used in cement production. The cement industry uses energy-intensive production processes and energy typically represents 20–40% of the total production costs (IEA 2007). Fossil fuels (e.g. coal, oil, or natural gas) are the predominant fuels used in the cement industry. Consequently, the aggregate amount of CO2 emitted from the global cement industry has reached about 2.2 billion tons, accounting for approximately 5% of global man-made CO2 emissions. However, alternative fossil fuels such as natural gas and biomass fuels have been increasingly used as a key factor to reduce CO2 emissions in the recent years (IEA 2009).

The production of cement involves four steps: preparation of a material mixture, thermal formation of clinker in the cement kiln, clinker cooling, and finally grinding and mixing with additives to the cement quality required (Bolwerk 2005). Dry process kilns produce almost 80% of cement manufactured in Europe (EHS 2007). Table 2 exhibits the particular WtE technologies in the cement industry, which have mainly been obtained from International Energy Agency (2009).

Table 2 Summary of WtE technologies in the cement industry
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Primary aluminum production industry

More than half of the energy used in nonferrous metals is for primary aluminum production (IEA 2007). Aluminum is the third most abundant element (following oxygen and silicon) and represents 8% of the Earth’s crust (Balomenos et al. 2009). Because of its chemical reactivity, aluminum is never found in nature as an isolated element but always in its oxidized form as a component of a variety of minerals. The steps for primary aluminum production are: bauxite mining, production of alumina from bauxite, production of carbon anodes, electrolysis, and rolling. Electrolysis is the most energy-intensive step in the production of aluminum (IEA 2007) and is responsible for the generation of large amounts of CO2 (Balomenos et al. 2009). The pre-eminent WtE technologies are outlined in Table 3.

Table 3 Main WtE technologies in the primary aluminum production industry
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Metal-casting industry

The metal-casting industry produces both simple and complex parts that meet a wide variety of manufacturing needs. Metal-casting foundries range in size from small job shops to large manufacturing plants that turn out thousands of tons of castings each day (ITP 2005). Cast metal products are found in 90% of manufactured goods and equipment, from critical components for aircraft, automobiles, defense equipment to power generation equipment, industrial machinery, and construction materials (Eppich and Naranjo 2007).

The most common process used for casting is green sand molding, accounting for approximately 60% of castings produced. The major energy-consuming processes in metal casting include melting metal (about 55% of energy consumption), core making, heat treating, and post-casting operations (Eppich and Naranjo 2007). Generation of waste is directly related to the type of material melted (cast iron, steel, brass/bronze, or aluminum) (ITP 2005). Major information (Table 4) has been collected from Industrial Technologies Program (2005).

Table 4 WtE technologies in metal casting process
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Glass industry

The glass industry consists of five segments: flat glass, glass containers, pressed and blown glass, wool fiberglass, and products of purchased glass. Approximately, 57% of all glass melted is produced by the glass container segment. The remaining glass melting is roughly divided between the flat glass (24%) and pressed and blown glass (19%) segments (SOTA 1997).

More than half of energy consumption in the glass production process corresponds to the melting process. The main production steps found in virtually all glass plants are: raw materials selection, batch preparation (weighing and mixing raw materials), melting and refining, conditioning and forming, and post-processing—annealing, tempering, polishing or coating (IEA 2007). WtE technologies related to glass process are shown in Table 5.

Table 5 WtE technologies related to glass industry
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Applications

Waste heat recovery technologies in energy-intensive industries

Between 20 and 50% of industrial energy input is estimated to be lost as waste heat in the form of hot exhaust gases, cooling water, and heat lost from hot equipment surfaces and heated products (ITP 2008). In fact, heating is considered to be the second largest energy-consuming operation (EERE 2007).

Table 6 presents a current state of WHR practices in a variety of applications in energy-intensive industries as collected from International Technologies Program in U.S. industry (2008). The results from this investigation serve as a basis for understanding the current state of WHR in terms of commercialization status, technical, and economic feasibility in the U.S. industry.

Table 6 WHR in the U.S. energy-intensive industries
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New technologies are emerging as options for heat recovery such as the kalina cycle for low temperature power generation and thermoelectric devices (direct conversion technologies) (ITP 2008).

Case study in the steel sector

A case study for solid recovery using WHR in sintering process is illustrated (Fig. 2) as a real-world example.

Fig. 2
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Case study in the steel sector using WHR

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The key points for solid recovery are: two hoods with two air/water tubular heat exchangers (50% of the cooler is covered), one bag filter for the dedusting of gas and two blowers. There is a reduction of 250 t/h of sinter from 500 to 50°C => 30 MW (theory) and emission reduction of 92% of the diffuse dust (ArcelorMittal 2010).

A first conclusion is that heat recovery can be used alone or with dedusting and good synergy exists between cooler dedusting and heat recovery. Moreover, heat can be used for district heating, but other applications are possible, such as preheating combustion air or sinter raw mix. Finally, heat recovery can lead to CO2 emission reduction.

Synergetic interaction between continuous process industries

Table 7 describes the interaction between continuous process industries in terms of synergy (inter-industry collaboration), typical uses, and key factors.

Table 7 Synergetic interaction between continuous process industries
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R&D areas of new WtE technologies

Literature searches were conducted to obtain available information on R&D areas of new WtE technologies. The U.S.A. appears to be the top country in terms of relative amount of annual R&D intensities and number of scientists and engineers per million people (WBCSD 2010). Based on the report of the World Business Council for Sustainable Development (2010), which lists a wide range of WtE technologies in continuous industrial processes, there are two issues on R&D:

  • The first issue is focusing on industrial reactions & separations related to: advanced water removal (500 TBtu), low-water-use industrial processes, advanced gas separations (60 TBtu), hybrid distillation (240 TBtu), energy-intensive conversion processes (200 TBtu), and is projected in the long-term (2030) savings of 1,000 TBtu and 75 MMTCO2 (Chan 2010; Glatt 2010).

  • The second issue is waste heat minimization & recovery related to: super Boiler (350 TBtu), ultra-high efficiency furnace (90 TBtu), waste heat recovery systems (260 TBtu), and is projected savings in 2030 of 700 TBtu and 50 MMTCO2 (Chan 2010; Glatt 2010).

Top three R&D areas of new WtE technologies are: low-temperature waste heat recovery (steam generation, heat utilization), high efficiency thermoelectric for low temperature heat recovery, and combined heat & power (CHP): systems recover waste heat to generate electricity and heat at >80% efficiency.

Conclusions

This research has been conducted on the field of “WtE technologies”, which represents an emerging technology group for energy-intensive industries apart from the wide concept of “clean energy technologies”. The current state of WtE technologies has been investigated for five representative sectors in continuous industrial processes: iron and steel, cement, primary aluminum production, metal casting, and glass industry. Goals for the “factories of the future” in all of those sectors are “zero emissions” and “zero material waste” (clean energy technologies) plus maximum efficiency in energy consumption, which requires the best specific technologies for waste energy recovery.

This new group of WtE technologies in continuous process industries has been analyzed in terms of conversion, transportation, management, and recovery or reuse energy from any type of waste (solid, liquid, gas, and heat). Such technologies have the potential for increasing heat recovery, emissions reduction, electric efficiency, transportation fuel substitution, and storing energy and fuel.

This article outlines the potential for technological advancement in the continuous industrial processes of the five sectors studied, as well as inter-industry energy-efficiency opportunities. The aim of the study has been to provide a practical classification of the typical uses and key factors of current WtE technologies. As an application, some synergetic interactions between continuous process industries have been identified, mostly related to WHR technologies, in addition to potentially energy-saving R&D areas of new WtE technologies.

WtE technologies for industrial processes represent a challenge that requires scientific innovation, process development, and manufacturing scale-up required to accelerate the commercialization of WtE technologies with potential cross-industry collaboration. In conclusion, WtE technologies are the key to success as energy-efficiency technologies to reduce energy use and GHG emissions in medium- and long-term approach.