Waste energy recovery and energy efficiency improvement in China’s iron and steel industry

Applied Energy 191 (2017) 502–520

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Applied Energy journal homepage: www.elsevier.com/locate/apenergy

Waste energy recovery and energy efficiency improvement in China’s iron and steel industry Qi Zhang a,⇑, Xiaoyu Zhao a, Hongyou Lu b, Tuanjie Ni a, Yu Li a a b

SEPA Key Laboratory on Eco-industry, Northeastern University, Shenyang 110819, Liaoning, China China Energy Group, Energy Analysis and Environmental Impacts Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA

h i g h l i g h t s
Three WERU potentials were thermodynamic, technical, and economic potentials.
A techno-economic model was proposed to quantify the available waste energy potential.
Various types of waste energy in the steel production process were examined.
Evaluated the energy benefit and cost effectiveness of energy saving technology.
Four scenarios were established to evaluate future energy consumption reduction.

a r t i c l e

i n f o

Article history: Received 30 August 2016 Received in revised form 10 January 2017 Accepted 27 January 2017

Keywords: Waste energy potential Energy saving technology Iron and steel industry Techno-economic model Energy conservation supply curve

a b s t r a c t Waste energy recovery and utilization presents a crucial opportunity in primary energy reduction and energy efficiency improvement for the global iron and steel industry. However, lack of comprehensive and practical methodology, the exact quantity of waste energy is often poorly quantified. This paper develops an innovative techno-economic model to quantify this opportunity that links theoretical, technical, and economic potential with the characteristics of waste energy resources and waste recycling technologies. Various forms of waste energy, such as sensible heat, pressure energy, and chemical energy, were examined. In addition, four scenarios were established to evaluate future energy saving potential and energy consumption reduction under the synergistic effect of technology promotion and structure adjustment. Findings show that the proportion of practical potential is less than 20% when considering the technical implementation rate for the average industry value. The selected 35 energy-saving technologies contribute to 3.08 GJ/t crude steel of cumulative energy savings, and technology implementation plays a significant role in energy consumption reduction. A sensitivity analysis indicates that energy price and discount rate are the most sensitive factors. Ó 2017 Elsevier Ltd. All rights reserved.

1. Introduction Recently, there has been global concern on the climate change and energy resource depletion. As one of the most significant contributors to fossil fuel consumption and related severe environmental pollution, iron and steel industry in differing countries around the world faced the common challenge that is energysaving and emission reduction. This can be achieved by improving energy efficiency, as well as by efficient recovery of waste energy. Improving energy efficiency covers numerous energy reducing options including fuel switching, improved process control, and increasing the thermodynamic efficiency of specific production ⇑ Corresponding author. E-mail address: [email protected] (Q. Zhang). http://dx.doi.org/10.1016/j.apenergy.2017.01.072 0306-2619/Ó 2017 Elsevier Ltd. All rights reserved.

processes [1]. Enhancing waste energy recovery and utilization (WERU) contributes not only to the reduction of primary energy consumption but also to the mitigation of pollutant emissions and the achievement of associated economic benefits [2]. Many industrial processes generate waste energy during manufacturing production processes. The United States Department of Energy (US DOE) [2] stated that as much as 20–50% of primary energy inputs in industry sector is ultimately discharged as waste heat in some forms of heat energy at the temperature range from 1500 °C to near ambient temperature, but the exact quantity of industrial waste heat is poorly quantified. Meanwhile, the lack of standardized methodology and full understanding of technical benefits and cost effectiveness have created barriers against clearly identifying WERU potential. Therefore, the current quantification

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Nomenclature Abbreviation BAU business-as-usual BF-BOF blast furnace and basic oxygen furnace BFG blast furnace gas BOFG basic oxygen furnace gas CCPP combined cycle power plant CDQ coke dry quenching CHP combined heating and power CMC coal moisture control COG coke oven gas CISA China Iron and Steel Association CISI China’s iron and steel industry EAF electric arc furnace ECSC energy conservation supply curve ESTs energy saving technologies G-ESTs general energy saving technologies HBS hot blast stove IEA International Energy Agency kgce kilograms of coal equivalent LT-PR LT process for purification and recovery MIIT Ministry of Industry and Information Technology NDRC National Development and Reform Commission O&M operation and maintenance PCI pulverized coal injection PP-ESTs production-process energy saving technologies RD&D research, development and demonstration SH sensible heat TIS Turkish industrial sector

of waste energy resource and its effects on energy efficiency improvement need to be evaluated. China’s iron and steel industry (CISI) is an important basic industry of the national economy and is characterized by energyintensive manufacturing processes. In 2014, China’s crude steel production reached 822 million tonnes, accounting for nearly 49.5% of the world’s crude steel production [3]. The rapid growth of crude steel production has resulted in excess capacity, high energy consumption and severe environmental pollution. The energy consumption of CISI accounts for approximately 15% of the total domestic energy consumption in recent years [4,5]. However, if small- and medium-sized steel enterprises1 are taken into consideration, then a 10–20% gap of specific energy consumption and a 25–30% higher steel production cost exist compared with international advanced level [6,7]. To enhance energy conservation and emission reduction, and promote construction of energy-efficient systems, a series of measures and multiple binding targets have been identified in China’s national development strategy plan [6,8–11]. For example, the Ministry of Industry and Information Technology (MIIT) issued the 12th Five-Year Development Plan for CISI [8] and the Guidebook of Advanced and Applicable Energy Savings and Emission Reduction Technologies for CISI [9] (hereinafter referred to as ‘the Plan’ and ‘the Guidebook’). The Guidebook provided comprehensive data, such as energy savings, capital costs, and current technology implementation situation, which are crucial in evaluating energy saving potential and cost effectiveness of the selected technologies. The Plan specified the development objectives and the main tasks

1 In this paper, small- and medium-sized steel enterprises represent the workforce and the total assets of steel enterprises less than 2000 people and 400 million yuan, respectively.

TRT top-pressure recovery turbines US DOE United States Department of Energy WER-ESTs waste energy recovery saving technologies WERU waste energy recovery and utilization WSA World Steel Association Symbols ACC AEB CCE cp d h n T TES

annualized capital cost annual energy benefit cost of conserved energy specific heat capacity at constant pressure discount rate specific enthalpy lifetime temperature typical energy saving

Subscript ce i j k pe ref te y

chemical energy steel production procedure j-th item technology or measure waste energy pressure energy reference temperature or year thermal energy t-th year

to reduce comprehensive energy consumption per tonne of crude steel from 605 kg of coal equivalent (kgce)/t in 2010 to 580 kgce/ t in 2015; it highlighted the strategic significance of popularizing waste recycling technology, strengthening management and improving efficiency, and supporting development and technological innovation. Numerous studies evaluated the WERU potential for different sectors in different countries. Through a bottom-up approach, the US DOE [2] evaluated waste heat quantity, quality, current recovery practices, research, development and demonstration (RD&D) needs and barriers for implementing waste energy recovery options in US manufacturing. They found that the work potential of investigated waste heat is approximately 600 TBtu/year, but roughly 60% of unrecovered waste heat is of low quality and has poor thermal and economic efficiency. Lu et al. [12] presented that the practical waste heat potential in CISI is 1 GW. However, these studies focused solely on exhaust gas without considering large amounts of sensible heat (SH) from product and slag. In accordance with the study scale, data collection, and chosen approach, Brückner et al. [13,14] categorized different methods to estimate the waste heat potential of regions and further investigated the potential of industrial waste heat for heating and cooling applications, as well as the technical and economic potentials of heat transformation technologies. Miró et al. [15] proposed a methodology to confirm the reliability and feasibility of data in reference to industrial waste heat quantities from different countries. The results indicated that without a transparent or standardized methodology, China’s technical or practical potential for WERU is unclear. However, these studies did not estimate industry-specific potential, as well as not address any discussion of the potential in China. In this paper, waste energy is considered as all forms of waste heat (SH of industrial exhaust gas, product, melting slag and cooling water) as

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well as pressure energy, and chemical energy that released from system due to residues. Oluleye et al. [16] developed a mathematical method to identify WERU potential by considering the temperature and quantity in process sites using a case study of a petroleum refinery. Findings indicated that site energy efficiency increased by 10% when the demand for recovered energy is taken into account; combining technologies into the system increased the waste heat potential. However, the methodology of the applicability for other industrial sectors, regional, or countries has not to be verified. Through a hybrid material and energy flow analysis approach at plant level, Zhang et al. [17] quantified waste heat recovery and carbon emission mitigation potential in CISI and found that the case plant has 4.87 GJ/t crude steel waste heat potential, equal to 26.08% of the total energy consumption; reducing metallurgy gas dissipation and recycling waste heat are the main ways of improving system energy efficiency. However, this paper did not consider the economic conditions or environment constraints. Chen et al. [18] presented that recycling waste energy plays an important role in energy savings and carbon emission reduction, and highlighted that a critical issue for the low efficiency of WERU is the lack of thermodynamic optimization, while this paper’s intention was not to quantify waste heat potential. Other studies investigated WERU potential from the standpoint of thermodynamic assessment. Utlu [19] created a consistent basis for determining system efficiency and reliability at low-, mediumand high-temperature on the basis of real data from 1990 to 2011 for the Turkish industrial sector. Results indicated that the iron and steel subsector has the highest technical potential for WERU because of the use of high-quality energy resources for hightemperature applications. Ammar et al. [20] addressed the potential for low-grade heat recovery with regard to new incentives and technological advances and found that the benefit of recycling and utilizing low-grade thermal energy is highly dependent on the qualities and properties of the waste streams heat. Shigaki et al. [21] developed a simulation model and applied exergy analysis to optimize steel production and recycling system from various viewpoints. Results indicated that sensible heat (SH) recovery is effective for the improvement of overall energy efficiency in the steelmaking process, and the electric arc furnace (EAF) process is more effective in exergy utilization than the blast furnace and basic oxygen furnace (BF-BOF) process in terms of exergy efficiency, although they have almost the same exergy loss. Cai et al. [22] analyzed WERU potential based on real production data for CISI and found that the current energy consumption of per tonne steel for the investigated large- and medium-sized enterprises is 9.9– 17.2% higher than the international advanced level, and the quantity of waste energy resources is 455.1 kgce/t, equal to 13.32 GJ/t crude steel. Therefore, reducing specific energy consumption, improving energy efficiency, and strengthening the waste heat recovery are the main orientation of future energy conservation in CISI. The aforementioned studies applied the thermodynamics method to analyze WERU rationality and potential, and have increased widespread public awareness about the usefulness and desirability of recycling waste energy. However, little attention has been devoted to evaluating industry-specific potentials or considering the economic conditions and environment constraints, especially the financial parameters of energy-saving technologies (ESTs). Numerous studies presented quantitative analyses of ESTs for various industrial sectors worldwide. Napp et al. [23] provided a comprehensive overview of the process improvements, technologies and economics for achieving energy saving and reducing emissions in the industrial sector, and addressed the effectiveness of policy instruments to promote the implementation of those tech-

nologies and discussed other cost-effective ESTs to achieve further decarbonization. Viklund et al. [24] reviewed different measures for the recovery and utilization of industrial waste heat, and further applied energy systems modeling tool reMIND to quantify the potential for waste energy recovery and to investigate the effect of related technologies on carbon emission mitigation in Gävleborg County in Sweden [25]. Chen et al. [26] applied the TIMES model to analyze future steel demand, scrap consumption, energy consumption, and carbon emissions from 2010 to 2050. Wen et al. [27] constructed an AIM model and Lin et al. [28] used a multivariate regression model combined with risk analysis to evaluate the future energy saving potential and carbon emission reduction in CISI. With the use of a bottom-up model, Fleiter et al. [29] assessed 17 ESTs to improve energy efficiency in the German pulp and paper industry up to 2035. Moya et al. [30] investigated the cost effectiveness of the best available technologies and innovative technologies in the EU27 iron and steel industry up to 2030 under different payback periods. Flues et al. [31] analyzed the effects of EST attributes, energy prices, policy factors, and total steel productions on the reduction in specific energy consumption in the iron and steel industry. Another significant quantitative analysis method for ESTs is the energy conservation supply curve (ECSC) from both the technical and the economic perspectives. Meier [32] first introduced the ECSC to provide an accounting framework for the treatment of conservation potentials and guidance on predicting the effect of changes in assumptions. Moreover, ECSC has proven to be an excellent tool for establishing energy policy. The consequences of energy conservation policy are described with respect to the marginal energy savings and costs of ESTs. Subsequently, ECSC has been widely applied in energy system analysis and models, especially those by the Lawrence Berkeley National Laboratory. With the use of a bottom-up ECSC model, Worrell et al. [33,34] assessed the energy saving potential and carbon emission reduction opportunities, as well as productivity benefits of energy efficiency investments in the US iron and steel industry based on the basis of data from numerous historical industrial case studies. Hasanbeigi et al. [35,36] estimated the energy saving potential and cost effectiveness of different ESTs for the Thai cement and iron and steel industries. Morrow et al. [37] analyzed 22 and 25 applicable ESTs for India’s cement and iron and steel industries, respectively. Kong et al. [38] assessed the technical and economic aspects of energy conservation and analyzed future steel demand and steel scrap consumption. Li et al. [39] estimated the energy saving and cost effectiveness of 41 ESTs that are widely used or popular in CISI. Zhang et al. [40] analyzed the co-benefits of energy efficiency improvement and air pollution abatement in CISI. Ma et al. [41] developed a new evaluation framework to quantify the energy and environmental benefits, and evaluate the cost effectiveness of 36 ESTs under different scenarios. Many studies have dealt specifically with the techno-economic analysis for different scopes. In the field of renewable energy, Davis [42] and Wright [43] examined biomass for fuel production, and Yang [44] optimized a hybrid solar-wind power generation system using techno-economic analysis. Techno-economic analysis was also conducted on a mixed biogas, solar, and (or) ground source heat pump system to investigate technical feasibility of greenhouse heating [45] or economic performance of space heating [46]. For the power plant, techno-economic analysis and optimization of the heat recovery system using boiler flue gas were carried out based on the principles of thermodynamic, heat transfer, and hydrodynamics [47]; and the economic feasibility of three different configurations of a woodchips power plant via circulating fluidized-bed gasification were performed [48]. Moving beyond equipment and to systems optimization, technically feasible energy saving potentials and associated costs of implementation

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of energy efficiency measure for industrial coal-fired steam systems in China were quantified [49]. Merei [50] presented technoeconomic analysis and sensitivity analysis of PV-battery system to demonstrate the influence of battery storage to reduce electricity cost. From the perspective of environmental performance, Bellqvist [51] applied a process integration approach to evaluate the potential benefits of energy- and cost-saving, and CO2 mitigation, with considering the low-temperature waste heat recovery technologies of an integrated steel plant in Sweden. Through technoeconomic system analysis, Fischedick [52] analyzed the technical and economical long-term potential for viable greenhouse gas emission reduction of innovative primary steel production technologies in Germany up to 2100. Up to now, the previous studies focused solely on a few sectors in China, little attention has been devoted to evaluating energy-saving potential technically and economically, especially insufficient understanding of the benefits and cost effectiveness of waste recycling technologies for CISI. These studies conducted in-depth quantitative analyses by considering the economic factors of the ESTs and emphasized the importance of energy efficiency improvement for energy savings. However, other forms of waste energy, such as SH of product, melting slag, and cooling water as well as pressure energy and chemical energy, were rarely mentioned or quantified. Furthermore, little attention was paid to the influence of technology promotion on energy saving potential and energy consumption reduction. As a result of these shortcomings, fully understanding WERU and energy efficiency improvement via technology promotion is difficult for decision makers. This paper aims to fill the research gaps by identifying WERU potential in the iron and steel industry (A case study in China) through a comprehensive and practical methodology, which involves the creation of an innovative techno-economic model that links theoretical, technical, and economic potential with the characteristics of waste energy resources and waste recycling technologies. The energy benefits and cost effectiveness of implementing energy-saving technology that can be implemented to improve energy efficiency are evaluated based on the quantitative approach of conservation supply curve and technical attributes analysis. Specifically, in addition to focusing on the common objective of industrial exhaust gas, this paper focuses on other forms of waste energy, such as sensible heat (SH), pressure energy, and chemical energy in CISI. The methodology, which considers the synergistic effect of technology promotion and structure adjustment on energy efficiency improvement as well as other forms of waste energy that are often neglected, could be further applied to other energy-intensive industries or countries. The remainder of this paper is organized as follows: Section 2 briefly introduces iron and steelmaking processes, defines waste energy resources, and describes key waste recycling technology. Section 3 addresses the research methods used in this paper and sets four scenarios to evaluate the energy saving potential and energy consumption reduction associated with future ESTs promotion. Section 4 presents the results and key findings of the technoeconomic model. An overall discussion and recommendation are presented in Section 5. Section 6 concludes this paper.

2. Overview of WERU in CISI 2.1. Brief introduction of iron and steelmaking processes In China, two main routes are used in the production of crude steel: blast furnace and basic oxygen furnace (BF-BOF) process, which uses primarily iron ore; and electric arc furnace (EAF) process, which uses scrap as raw material. The BF-BOF route is the dominant steel production method in CISI and accounts for

505

approximately 90% of the total crude steel production, which is higher than the worldwide level [17,53]. EAF steel production route is also commonly used throughout the world, accounting for approximately 30% of the total crude steel production; in China, it accounts for only 10% [36]. Fig. 1 presents a schematic of the main iron and steel production routes and processes, which defines the system boundary in this study. The BF-BOF route consists of many processes, such as sintering, coking, iron making, steelmaking, and rolling processes. In the sintering process, iron ore is agglomerated to sinter in sinter plants or in pellet plants. The sintering process mainly uses solid fossil fuels (e.g., coke breeze) and electricity. In this process, iron ore and coke breeze are mixed and baked at temperatures of approximately 1000 °C after ignition in a gas-fired furnace [54]. Controlling the ignition temperature, changing the material conditions, optimizing sintering mixture, controlling the sintering layer thickness and ventilate rate of sintering machine could be performed to reduce the sintering process’s energy consumption [39,55]. In the coking process, cleaned coal is converted to coke by removing volatile substances in coke ovens and coke oven gas (COG) and tar recovery as by-product. In the iron-making process, sinter ore, coke, and other substances (mainly limestone) are carried to the top into the blast furnace, and hot wind from a hot blast stove (HBS) with pulverized coal injection (PCI) is blasted into the bottom of the blast furnace, from which oxygen combusts with the coke. Carbon monoxide is then formed and flows up through the blast furnace. It removes oxygen from the iron ores on its way down, thereby leaving molten iron as a by-product. Blast furnace gas (BFG) leaves the blast furnace at the top and is used in other furnaces in steelworks, such as coke oven, HBS, and rolling furnaces. The hot metal is fed to the basic oxygen furnace (BOF), where very pure oxygen is blown at high pressure and carbon is removed by an exothermic reaction with oxygen, thereby producing crude steel. Basic oxygen furnace gas (BOFG) is recovered and is used in power generation [54]. Continuous casting is mainly a casting process that occupies a 99.8% share in CISI in 2010 [49]. In hot rolling mills, semi-finished steel products, such as billets, blooms, or slabs, are rolled into sheets or long products after heating in the rolling furnace. Cold rolling is a reheating process to produce high-quality products. Compared with the BF-BOF route, the EAF route is less energyintensive and uses higher levels of ore-based iron, direct reduced iron, iron carbide, or scrap as raw material and uses electricity as heat source. Significant energy savings can be achieved by switching from BF-BOF to EAF production, but such changes may be limited by barriers such as the availability of scrap and the demand for higher grades of steel [56]. 2.2. Definition of waste energy resource In this study, waste energy resource is the heat carrier that can releases valuable heat and other forms of energy including pressure and chemical energy. In the iron and steel manufacturing process, many waste energy resources are produced, such as waste heat (i.e., SH of coke, sintering ore, melting slag, by-product gas, flue gas, and cooling water), pressure of the blast furnace roof, and chemical energy of metallurgical gas. More detailed information of investigated waste energy sources and types is given in Fig. 1. The chemical energy of BFG and COG is not taken into consideration because it is used in the iron and steel production processes. In addition, heat released diffusively, for example by radiation, is usually not involved. Nonetheless, in previous studies, only waste energy generated in a process as a heat carrier medium, such as exhaust gas or air, cooling water, is considered. WERU is one of the crucial opportunities that focus particularly on energy savings and energy efficiency improvements in CISI.

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Fig. 1. Simplified scheme of iron and steel production routes, processes, and main waste energy resources (Note: The different colors of the blocks in the figure represent the waste energy resources categorized by type, such as blue, dark red, purple, green, light blue, orange, and yellow blocks, which represent the main product, metallurgical byproduct gas, flue gas, slag, cooling water, chemical energy, and pressure energy, respectively.)

Understanding the availability of waste energy temperature, type, and quality is important to achieve rational energy use. Heat carrier temperature levels are categorized in this study by dividing temperature ranges into high-temperature (>650 °C), mediumtemperature (300–650 °C) and low-temperature (<300 °C). Generally, a high temperature of waste heat corresponds to high quality and increased economic efficiency of the heat no matter the method used in any study. In addition, matching supply with demand is essential in achieving an effective implementation of waste energy from the view of technical and economical feasibilities [16]. 2.3. Waste energy recovery technologies or measures Three methods are generally applied in waste heat utilization: heat delivery to district heating or cooling (namely directly utilizing), heat recovery for electricity generation (namely power utilizing), and cascade utilization by combined cooling, heating, and power or CHP systems in CISI [7,19,22,25]. A series of national policies and measures have been formulated to curb excess capacity in CISI and encourage enterprises to use new technology for improving energy efficiency [9–11]. As shown in Table 1, different technologies or measures are available to recover and utilize waste energy resource, such as SH of coke via coke dry quenching (CDQ) for high pressure steam production, SH of coke oven flue gas via coal moisture control (CMC) for preheating mixture, and pressure of top in BF via top-pressure recovery turbines (TRT) for electricity generation. Some works indicated that waste recycling technologies usually reduce operation and maintenance (O&M) cost by increasing the productivity of the process [19]. Various technologies have been widely promoted since the 11th FiveYear Plan, but the implementation rate of those technologies is different [36,39]; the waste energy resource is not fully utilized as

well. Constrained by technical and economic barriers, no effective technologies exist for utilizing SH of high-temperature slag, lowtemperature flue gas, and cooling water. Some measures, such as evaporated uptake cooling, thermal powdered slag, foamy slag practices listed in this study, represent only the current state of widely and typically available in CISI. 3. Methodology General speaking, three different kinds of potentials for WERU should be distinguished: the theoretical potential, the technical potential and the economically feasible potential [13,57]. To quantify the energy saving potential and the energy benefits of implementing technology, as well as to evaluate the factor impacts on cost effectiveness in CISI, a novel approach was developed, which involves an techno-economic model that includes thermodynamic assessment, energy consumption, and ECSC. The main structure of the inputs, outputs, and the techno-economic model is shown in Fig. 2. 3.1. Techno-economic model In this section, the theoretical, practical, and economic considerations of recovery and utilization of waste energy resources are examined. 3.1.1. Thermodynamic assessment modeling A thermodynamic assessment modeling tool was applied to calculate the quantity of waste energy resource. The theoretical potential is quantified by thermal enthalpy analysis, which is a function of the source and sink temperatures of waste heat [2,12,22,24] as shown in Eq. (1). Other waste energy potentials,

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Table 1 Main information of waste energy resource and related recovery technology in CISI. Source: Data are from investigated practices in China’s iron and steel works, and represent only the average value of the industry. Process

Source

Type

Parameter

Recovery technology or measure

Coking

Coke Oven

SH of coke SH of COG SH of flue gas

1000 °C (high T) 800 °C (high T) 200 °C (low T)

1 Coke dry quenching (CDQ) 2 Evaporated uptake cooling 3 Coal moisture control (CMC)

Sintering

Ring Cold Machine Sintering Machine

SH of sinter ore SH of flue gas

800 °C(high T) 300 °C (low T)

4 Heat recovery from sinter cooler 5 Preheating mixture

Iron-making

Blast Furnace

SH of BFG Pressure of top in BF SH of BF slag SH of flue gas

200 °C (low T) 0.25 MPa 1500 °C (high T) 400 °C (middle T)

6 7 8 9

HBS

Under RD&D Top-pressure recovery turbines (TRT) Slag heat recovery* Preheating of fuel and air for HBS

Steelmaking-BOF

Converter

SH of BOFG Chemical heat of BOFG SH of BOF slag

1500 °C (high T) 2000 kcal/m3 1550 °C (high T)

10 Recovery of BOF gas and SH 11 LT-PR of converter gas 12 Thermal powdered slag*

Steelmaking-EAF

Electric Arc Furnaces

SH of flue gas SH of EAF slag

1200 °C (high T) 1500 °C (high T)

13 Flue gas waste heat recovery 14 Foamy slag practices*

Rolling

Casting-Rolling Workshop Heating Furnace Heating Furnace Hearth

SH of Billet SH of flue gas SH of cooling water

900 °C (high T) 900 °C (high T) 200 °C (low T)

15 Hot delivery and hot charging of casting billet 16 Recuperative or regenerative burner 17 Waste heat recovery from cooling water

Note: SH short for sensible heat; ‘‘*” represents emerging waste recycling technology.

Fig. 2. Main structure of the inputs, outputs, and techno-economic models.

including pressure and chemical energy potentials, could be quantified as shown in Eqs. (2) and (3).

Q te ¼ cp;k  mk  ðT wh;k  T ref ;k Þ ¼ mk  hk ðtÞ

ð1Þ

Q pe ¼ mk  ðpwe;k  pref ;k Þ

ð2Þ

Q ce ¼ mk  Q g;k

ð3Þ

where Q te , Q pe , and Q ce represent the quantity of thermal energy, pressure energy, and chemical energy in waste energy resource,

respectively; cp;k is the specific heat capacity at constant pressure of waste energy k; mk is the mass of waste energy k; T wh;k is the temperature of waste energy k when heat carrier is discharged from the source; T ref ;k is the reference temperature of waste energy k; hk ðtÞ represents specific enthalpy of waste energy k; t is the temperature difference between the heat source and reference temperatures; pwe;k is the pressure of waste energy k; pref ;k is the reference pressure of waste energy k assumed at standard atmospheric pressure in this study; and Q g;k represents the gross calorific value of waste energy k.

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In the calculation of the theoretical quantity of waste heat resource, two different reference temperatures were considered as the prescribed minimum temperatures: in Case (1), the ambient reference temperature (T ref ;k = 20 °C), which represents the maximum theoretical waste heat resource and is typically fixed by the environment, is assumed. On the basis of the thermodynamic analysis method, various reports studied industrial waste heat resource and evaluated energy saving potential in reference to the ambient temperature because WERU is subject to thermodynamic or absolute theoretical limit [13,22,57]. However, the physical potential cannot be achieved in practice. Technological performance imposes a technical limit on the availability of WERU; therefore, a practical reference temperature is defined. In Case (2), the modified reference temperature with current technical recovery level (T solid ref ;k = 200 °C, T liquid ref ;k = 20 °C and T gaseous ref ;k = 180 °C, respectively) [2,12,58,59] is assumed, which is different owing to the different type and working condition of waste heat, as well as technical attributes [58]. Nevertheless, GB/T 102820002 [58] is no longer applied for the recovery level now. Thus, a reference temperature is modified according to the current technical level [9,60]. The current study does not use the conventional method to calculate the quantity of waste energy. Moreover, the recovered energy has a significant effect on the energy saving potential and the cost effectiveness of ESTs. This study is different from other similar studies because it provides a detailed and in-depth calculation of energy saving potential and the cost effectiveness of ESTs. 3.1.2. Energy consumption modeling Energy consumption is the energy consumed per unit of product output. This study estimated the influence of the implementation rate of the selected ESTs on energy consumption according to Eqs. (4) and (5).

TESj;y ¼ REj;y  ðIRj;y  IRj;y¼ref Þ EC i;y ¼ EC i;y¼ref 

X TESj;y

ð4Þ ð5Þ

j

where TESj;y represents the typical energy saving per unit of product due to the implementation technology j in year y and REj;y refers to the waste energy which is recovered via technology j in year y where its calculation formula can be obtained from Calculating methods of energy saved for enterprise (GB/T 13234-2009) [61]. IRj;y and IRj;y¼ref represent the implementation rate of technology j in target year y and in the reference year, respectively; EC i;y and EC i;y¼ref represent the energy consumption per unit of product in procedure i due to the implementation of the corresponding technology j in target year y and in the reference year, respectively. 3.1.3. Energy conservation supply curve modeling An assessment index for evaluating the economic viability of ESTs in this study is ECSC modeling, which is used to estimate the energy benefit and cost effectiveness of the selected technology [36–40]. The cost of conserved energy (CCE), annualized capital costs (ACC), and annual energy benefits (AEB) are required for the development of ECSC, as shown in Eqs. (6)–(8), respectively.

2 Based on the principle of technically and economically feasible, this standard (GB/ T 1028-2000), released by Chinese State Quality and Technology Supervision Bureau in the year 2000, specifies the prescribed minimum temperature of industrial waste heat carrier when calculating the quantity of waste heat resources. However, the standard is no longer applied for the recovery level now because medium discharge temperature of waste heat utilization equipment is lower than the prescribed minimum temperature of heat carrier. Therefore, we give a modified reference temperature according to current technical recovery level.

CCEj ¼

Pi  ðACC j þ DO&M j Þ  AEBj  PE AEBj

ACC ¼ Capital Cost 

d n ð1  ð1 þ dÞ Þ

AEBj ¼ Pi  TESj

ð6Þ

ð7Þ ð8Þ

where CCEj , ACC j , and AEBj represent the cost of conserved energy, annualized capital costs, and annual energy benefits of technology j, respectively; Pi is the production of procedure i; DO&Mj is annual change in O&M cost of technology j; PE is the future energy price; d is the discount rate; and n is the lifetime of technology j. Another common assessment index to calculate economic viability of ESTs is simple payback period [57,62], which is the ratio of ACC to AEB, as shown in Eq. (9).

Payback Period ¼

Annualized capital costs Annual energy benefits

ð9Þ

3.2. Data collection and basic assumption To analyze the energy benefits of implementing ESTs in CISI, 35 available ESTs were selected for this study, including most waste recycling technologies based on the principle of advancement, applicability, and economic viability, which are categorized by process and are almost already popularized and technically proven. The assumption is that no interaction exists between all the selected technologies. Table 2 provides typical energy savings (TES), capital cost, O&M cost, lifetime, and current implementation rate of the technology. Data listed in the table represent only the average value of the industry because of the heterogeneity of different technologies. Data used in this study were provided by expert interviews and investigated practices in China’s iron and steel works, and small- and medium-sized steel enterprises are not taken into consideration. Although Chinese government agencies including MIIT [9] and NDRC [11] have proposed numerous energy saving and emission reduction technologies for the iron and steel industry collectively, insufficient comprehensive qualitative analysis of technical potential has created barriers for technology application and promotion. Therefore, qualitative analysis is needed on the technical implementation and cost effectiveness of the ESTs by dividing them into the following three groups based on their technical attributes: 20 waste energy recovery energy-saving technologies (WER-ESTs), 10 production-process energy saving technologies (PP-ESTs), and 5 general energy saving technologies (G-ESTs). In this study, the analyzed period was 2010–2050, with 2010 as the base year. Data of ESTs were obtained from Ref. [9,11,36,39,4 0,60,63–66], and expert interviews and practices in China’s iron and steel works. The production of each processes for CISI in reference year 2010 were obtained from WSA [3] and CISA [5]. The energy price of the base year given by IMF [67] was calculated by the weighted average price of power coal and coke (CNY 31.31 yuan/GJ). Waste energy resource is discontinuous or dispersive in the actual manufacturing process, but we assumed that it is continuous and reliable in this study. The production of COG, BFG, and BOFG is 400 m3/t coke, 1700 m3/t hot metal, and 100 m3/t steel, respectively. The chemical composition of COG is 60% hydrogen, 25% methane, 8% carbon monoxide, and 7% nitrogen. The chemical composition of BOG is 60% nitrogen, 30% carbon monoxide, 8% carbon dioxide, and 2% hydrogen. The chemical composition of BOFG is 65% carbon monoxide, 20% carbon dioxide, 10% nitrogen, and 5% hydrogen. The discount rate used in the calculation is 15%, which is

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Q. Zhang et al. / Applied Energy 191 (2017) 502–520 Table 2 Data of the selected available energy saving technologies in CISI. Typical energy saving (GJ/t)

Annualized capital costs (yuan/t)

Annual O&M cost change (yuan/t)

Lifetime (year)

Current implementation rate (%)

Source

Coke making T1 Coke dry quenching (CDQ)

0.37

9.97

1.87

20

85%

T2

0.06

14.60

4.40

15

9%

Ref. [9,11,39,54] Ref. [9,11,39,51]

0.35

2.39

0

10

20%

0.08

0.48

0

10

80%

0.18 0.35

0.16 0.24

0 0

10 10

70% 60%

Ref. [9,11,36,51] Ref. [9,36,51] Ref. [9] Ref. [9]

0.70

1.70

-17.29

20

40%

Ref. [6,36]

0.12

0.96

0

15

83%

Ref. [9]

0.25

1.69

0

20

5%

Ref. [9]

0.01

1.52

0

20

94%

0.18 0.39

26.63 2.59

0 0

20 20

1% 0%

Ref. [9,11,39,40] Ref. [9,51] Ref. [9,36]

0.10

1.32

0

20

3%

Ref. [9,39]

0.12

1.99

0

10

40%

0.14

4.14

0

15

20%

Ref. [9,36,55] Ref. [9]

0.09 0.69 0.06

4.23 0.24 27.32

0.65 3.5 -4.85

10 15 20

15% 20% 5%

Ref. [9] Ref. [9,39] Ref. [9]

Steelmaking - electric arc furnace (EAF) T19 Scrap preheating T20 Optimization of power supply T21 Flue gas waste heat recovery T22 Foamy Slag Practices*

0.02 0.01 0.06 0.01

2.06 0.08 2.85 4.04

0 0 0 0

30 30 30 30

10% 15% 10% 30%

Ref. [9,36] Ref. [9] Ref. [9,39] Ref. [39,49,56]

Casting and refining T23 Continuous casting T24 Efficient ladle preheating

0.39 0.02

2.26 1.66

-6.8 0

20 20

75% 15%

Ref. [9] Ref. [39,40]

0.28

253.11

-148.93

30

20%

0.15

2.03

0

10

40%

0.28

20.32

0

10

80%

0.04

23.09

2

15

20%

Ref. [9,49,56] Ref. [9,36,55] Ref. [9,36,39,49] Ref. [9,49]

0.23

0.42

1.95

10

80%

Ref. [9,55,56]

0.11

55.25

0

10

55%

0.20

21.92

0

10

55%

Ref. [9,49,56] Ref. [9,49,56]

0.45 0.12

4.28 2.06

0 0

15 10

40% 50%

Ref. [9,39] Ref. [9,56]

0.38 0.51

57.51 0.21

0 0.27

20 15

90% 15%

Ref. [9,39] Ref. [9]

No

Energy saving technologies

Coal moisture control(CMC)

Sintering T3 Heat recovery from sintering and sinter cooler T4 Increasing bed depth T5 T6

Reduction of air leakage Low-temperature sintering tech.

Iron making - Blast furnace T7 Pulverized coal injection (130 kg/t) T8 Top-pressure recovery turbines (TRT) T9 Preheating of fuel and air for hot blast stove T10 Recovery of blast furnace gas* T11 T12 T13

Slag heat recovery* Pulverized coke oven gas injection* Pulverized waste plastic injection*

Steelmaking - basic oxygen furnace(BOF) T14 Recovery of BOF gas and sensible heat T15 Dry gas cleaning system (wet to dry) T16 Flue gas waste heat recovery T17 LT-PR of converter gas T18 Slag heat recovery*

Hot rolling T25 Integrated casting and rolling (strip casting)* T26 Recuperative or regenerative burner T27 Process control in hot strip mill T28 T29

Waste heat recovery from cooling water Hot delivery and hot charging of casting billet

Cold rolling T30 Heat recovery on the annealing line T31 Automated monitoring and targeting systems General technologies T32 Preventative maintenance T33 Energy monitoring and management systems T34 Cogeneration T35 Combined cycle power plantCCPP Note: ‘‘*” represents emerging technology.

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a typical rate that is accepted by both the enterprises and decision makers [31]. The steel ratio coefficient is a conversion factor. For the iron and steelmaking processes in CISI, 0.34 tonnes of coke and 1.36 tonnes of sinter (excluding pellet) are required to produce 1 tonne of pig iron, 0.91 tonnes of pig iron is required to produce 1 tonne crude steel, which contains 90% BOF steel and 10% EAF steel, and 1.09 tonnes of crude steel is required to produce 1 tonne of hot rolled steel [7,17,22]. 3.3. Scenarios design IEA [56] pointed out that the implementation of currently available low-cost energy saving and emission reduction technologies is essential to achieve short-term cost-effective energy consumption reduction. The implementation of selected ESTs is the key driver of energy efficiency improvement in the near future. However, structural change will be far more effective from a long-term perspective with the increasing share of EAF steel production [26,68]. Given the uncertainties about the future market promotion of ESTs, four scenarios were developed to forecast future energy saving potential and energy consumption reduction under the synergistic effect of ESTs promotion and structure adjustment, as shown in Table 3. The following provides an idea of the effect of future changes in the steel production structure from BF-BOF to EAF for energy efficiency improvement: the proportion of EAF steel was 10% in 2010 and will increase by 15%, 25%, 35% and 45% from 2010 to 2020, 2020 to 2030, 2030 to 2040, and 2040 to 2050, respectively. BF-BOF will reduce correspondingly. The aforementioned methodology, which considers other forms of waste energy that are often neglected in industrial facilities as well as evaluates industry-specific potentials from theoretical, practical, and economic aspects, could be further applied to other energy-intensive industries or countries. In addition, applying a comprehensive and practical methodology across sectors that well quantify the exact quantity of waste energy and analyze the synergistic effect of technology promotion and structure adjustment on energy efficiency improvement, is helpful for researches and decision makers to fully understand the international potential for waste energy recovery and utilization. 4. Results 4.1. Thermodynamic, technical, and economic analysis for WERU in CISI Fig. 3 shows the results of the thermodynamics assessment of waste energy resources in CISI under theoretical and practical considerations. Approximately 62% of the total waste energy poten-

Table 3 Key attribute of different scenarios. Scenarios

Scenario description

Business-asusual (BAU)

The implementation rate of ESTs will increase 2.0% and 3.0% per year during 2010–2030 and 2030–2050, respectively.

Cost-effective

The implementation rate of all cost-effective technologies will increase 3.0% and 4% per year during 2010–2030 and 2030–2050, respectively; Nevertheless, not cost-effective technologies will follow the path above mentioned BAU scenario.

Technicalmoderate

The implementation rate of ESTs will increase 3% and 4% per year during 2010–2030 and 2030–2050, respectively.

Technicaladvanced

The implementation rate of ESTs will increase 4% and 5% per year during 2010–2030 and 2030–2050, respectively.

tials come from the iron-making, rolling, and steelmaking (BOF) processes. The technical potentials account for 42.5% and 56.3% of the theoretical potential under the ambient and modified reference temperatures, respectively, and the remaining potentials are 3.76 GJ/t and 2.16 GJ/t crude steel, accordingly. The iron and steel industry has more high-temperature waste heat (>650 °C), which are recovered via numerous available technologies to generate electricity or high pressure steam, than other manufacturing industries. Most of the medium-temperature waste heat (300– 650 °C) is recovered to preheat or dry materials. For instance, the SH of HBS flue gas is recovered to preheat fuel and air. The technical potentials of medium-high temperature waste heat are 42.6% and 54.4% of the total waste heat potential under the ambient and modified reference temperatures, respectively. Heat exchangers, heat pipes, heat pumps, thermoelectric conversions, and refrigeration cycles can be used to utilize low-temperature waste heat (<300 °C) [20,24]. However, the technical potential of lowtemperature waste heat is only 14.3% under ambient reference temperature, the SH of which is not available in CISI at present because of poor thermodynamic performance and economic efficiency of waste heat, such as coking flue gas, sintering flue gas, BFG, and cooling water. Therefore, a reasonable approach to address the WERU issue, particularly for low-temperature waste heat, will improve the energy efficiency and achieve wide-scale application. The SH of products (i.e., coke, sinter ore, and billet) is a hightemperature waste heat resource, and the technical potential is approximately 30% of the total waste heat potential. The SH of flue gas (i.e., coking, sintering, and HBS flue gases) is low-medium temperature waste heat, accounting for a relatively high proportion of total waste heat potential. However, the SH of COG, BOG, and BOFG is unavailable (Fig. 4). The recovered energy of the SH of coking fuel gas is higher than the total quantity of waste heat resources under the modified reference temperature, thereby indicating that the technical recovery level exceeded the prescribed minimum temperature limitation. The low WERU level of the EAF process may be associated with the small proportion and low investment in the EAF steel production route in CISI. We develop the ECSC to quantify the benefits and evaluate the cost effectiveness of waste recycling technology, as shown in Fig. 5. Seven cost-effective technologies exist when the discount rate is 15%, and the cumulative energy savings are 0.61 GJ/t. However, different enterprises have different production conditions, capital costs, and O&M costs. The collected data in this study represent only an average value of the industry, which could mask the heterogeneity of technologies [39]. Thus, considering a CCE below 20 yuan/GJ, ten cost-effective waste recycling technologies exist, and the cumulative energy savings are 0.94 GJ/t, which accounts for 97% of the total energy savings. The analysis indicates that some technologies or measures, such as CMC, evaporated uptake cooling, thermal powdered slag, foamy slag practices and waste heat recovery from cooling water, will not be treated as the preferred investment object from the perspective of the enterprise decision makers because of poor economic efficiency. Therefore, the most economically attractive technologies are prioritized in utilizing waste energy resource. The techno-economic model results, including the calculated thermodynamic, technical, and economic potentials for the WERU and benefits of implementing waste recycling technology in CISI under each constraint, are shown in Fig. 6. Two cases of theoretical potential are shown: the quantities of waste energy sources under ambient and modified reference temperatures are 6.54 GJ/t and 4.94 GJ/t, respectively. The technical potential, with and without considering the technology implementation rate for the average value of industry, is examined. Results indicate that the implementation rate of waste recycling technology has a significant effect on

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WERU potentials (GJ/t)

7.00

6.54

Theoretical potential under the ambient reference temperature

6.00

Theoretical potential under the modified reference temperature

5.00

Technical potential

4.94

4.00 2.78

3.00

1.76

2.00 1.18 1.00

0.82

1.11 0.80 0.44

0.55 0.45

1.28

1.11 1.07 0.85

0.55

1.11 0.42

0.39 0.30 0.08

0.00 Coking

Sintering

Iron making

Steel making(BOF)

Steel making(EAF)

Rolling

Total

Fig. 3. Quantity of waste energy resources under two cases and the technical recovered energy (categorized by process).

0.23 , 4%

0.40 , 6%

0.23 , 5%

0.74 , 11%

Product 0.74 , 15%

1.85 , 29%

Gas(COG,BFG,BOFG)

1.50 , 30%

Slag 0.40 , 8% Flue Gas 0.74 , 11%

1.84 , 28%

0.36 , 7%

1.07 , 22%

Cooling Water Chemical energy

0.74 , 11%

0.64 , 13%

Pressure energy

Fig. 4. Quantity of waste energy resources under two cases: (a) and (b) (categorized by type) ((a) under the ambient reference temperature; (b) under the modified reference temperature).

Cost of Conserved Energy (yuan/GJ)

Technical energy saving potential:

700

17

0.97GJ/t

600 14

500 400 Cost-effective energy

300

12 3

saving potential: 0.61GJ/t

200

62 8

100 0

11

9 4

7

15

16 10

13 5

1

-100

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Cumulative energy saving (GJ/t) Fig. 5. ECSC of the waste energy recovery technologies or measures.

the technical potential, and the potential for WERU regarding technology implementation only accounting for approximately 35% of the total available recovered waste energy. Although numerous technologies are already well developed and technically proven, some applications still exist in which waste energy is unavailable

and not recovered in practice because of financial strains and technical barriers. Therefore, policy incentives are necessary to encourage ESTs to save more energy [62]. Two cases of economic potential are shown: whether the payback period of the equipment would be within 3 years and whether the CCE data of the waste recycling

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WERU potentials (GJ/t)

8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 Thermodynamic

Technical

Economic

Fig. 6. Theoretical, technical, and economical potentials for WERU based on the techno-economic model.

technology will be below 0 yuan/GJ. Results indicate that the economic potentials for WERU under two constraints are 2.41 GJ/t and 1.90 GJ/t, respectively. This implies that some waste recycling technologies in CISI are already economically proven, while the effectiveness that is not realized by decision makers, and hence cost effective technology popularization and promotion approaches need to be enhanced for the average industry in the near future. The findings are sensitive to the input parameters, and the error bars represent the standard deviation of uncertainty under the best and worst case scenarios. 4.2. Assessment of ESTs in iron and steel industry Detailed information of the 35 available ESTs selected for the analysis and the result are presented in Table 2. The ECSC was established to evaluate the cost effectiveness and energy benefits for the energy efficiency improvement in CISI. Fig. 7 indicates that the total energy savings are 3.08 GJ/t. Nineteen technologies are cost effective, and the cumulative energy savings are 1.93 GJ/t, when the discount rate is 15%. For individual technologies, PCI (T7) has the lowest cost of conserved energy and has relatively higher energy savings. Furthermore, continuous casting (T23), low-temperature sintering technology (T6), preventative maintenance (T32), and hot delivery and hot charging of casting billet (T29) have similar effects. Among all the non-cost-effective

technologies, except for CDQ (T1), the process controls in hot strip mill (T27) and cogeneration (T34) share the common characteristic of low energy savings but high capital costs. In addition, the implementation of ESTs has important effects on the energy benefits. The implementation rate is presented with the cost effectiveness and payback period of ESTs in a four-quadrant diagram based on the quantitative analysis. Fig. 8 shows that the implementation rate served as the horizontal axis and 50% was chosen as the experiential demarcation line (IR > 50% is considered the comparative maturity or benignant promotion). The cost effectiveness of ESTs served as the vertical axis (CCE < 0 yuan/GJ is considered good economic efficiency). Six technologies in the first quadrant have a high implementation rate but not cost effectiveness. Ten technologies, including eight WER-ESTs and two PP-ESTs in the second quadrant, have low implementation rates and poor economic efficiencies, which are the major barriers for wider promotion, thereby requiring policy support or economic motivation to break through the threshold of technology popularization. Twelve technologies in the third quadrant have good economic efficiencies but low implementation rate. Of the 20 WER-ESTs, 75% of those distributed in the second and third quadrants with implementation rates lower than 50% should focus more on promotion. Almost all seven technologies in the fourth quadrant are PP-ESTs, which not only have a high implementation rate but are also cost effective. This finding shows that the PP-ESTs are implemented more than the WER-ESTs even though some of them are also cost effective. The reason may be the national policy or measures proposed by the Chinese government in the past two decades, such as production structure adjustment and process optimization. However, inadequate attention has been paid to WER-ESTs until the 11th Five-Year Plan because of technical and economic barriers. The implementation rate of 50% and simple payback period of three years serve as the demarcation lines (Fig. 9). Four technologies in the first quadrant have high implementation rates but long payback periods. It is inseparable from the support of national measures for strengthening energy saving management in energy-intensive industrial sectors. In the second quadrant, six technologies have low implementation rates and long payback periods. Emerging technologies, including slag heat recovery (T18), foamy slag practices (T22), and integrated casting and rolling (strip casting) (T25), which are the most typical representatives,

700 T28

Cost of Conserved Energy (yuan/GJ)

600 T22 500

T30

400

T25 T18 T2

300 200

T11 T19

100 0

T14 T17 T26 T15 T8 T5 T35 T4 T3 T32 T29

T7

T23

T6

-100 0.0

0.5

1.0

T1 T21 T27 T31 T24

T13 T33

T9 T20 1.5

T34

T16

T12

2.0

2.5

Cumulave energy saving(GJ/t) Fig. 7. ECSC of the selected available energy saving technologies in CISI.

T10 3.0

3.5

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700 WHR-ESTs PP-ESTs G-ESTs

T28 600 T22 500 Cost-effecveness yuan/GJ

T30

400 T25

T18

300

T2

200

T10

T34

T11

100 T31

T19 T24

T27 T21

T16 T15 T20 T3 T35 T17

T1 3 T12 T9

T14 T26 T32

0

T1

T33 T6

T5

T29

T23

T7

T8

Implementation rate (%)

T4

-100 0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Fig. 8. Cost effectiveness of selected available energy saving technologies in CISI.

and waste heat recovery from cooling water (T28) have poor economic efficiency and low market awareness. Of the 25 WER-ESTs and PP-ESTs, 88% are distributed in the third and fourth quadrants with payback periods shorter than three years. Therefore, we proposed that the promotion of emerging technologies, such as pulverized coke oven gas injection (T12), and pulverized waste plastic injection (T13), should be strengthened. 4.3. Estimated potential of energy savings under different scenarios during 2010–2050 The increase in the implementation rate of ESTs and change of steel production structure from BF-BOF to EAF has a synergistic effect on energy saving potential. The results show an upward trend regardless of the scenario. The energy saving potentials on the process level under four scenarios are estimated to identify which processes have the largest contributions to the energy savings of the entire industry, as shown in Fig. 10. In the BAU scenario, the energy saving potential will gradually increase from 0.88 GJ/t in 2020 to 2.98 GJ/t in 2050, with an average annual growth rate of 4%. In the cost-effective scenario, the energy saving potential will increase from 37.5% in 2020 to 14.8% in 2050 compared with that in the BAU scenario, and nearly half of all cost-effective technologies are distributed in the sintering and iron-making (BF) processes. In the technical-moderate scenario, the energy saving potential will increase from 8.3% in 2020 to 5.6% in 2050 compared with that in the cost-effective scenario. The gap between the costeffective and technical-moderate scenarios is comparatively small

because 54% of the selected ESTs in the table are cost effective. By 2050, almost 94% of the ESTs would be implemented in CISI under the technical-advanced scenario, and the energy saving potential will increase to 3.95 GJ/t. It should be mentioned that the increase rate of energy saving potential has seen gradually downward trend, as the increase of technology implementation rate. On the process level, iron-making, steelmaking (BOF), rolling, and general technologies have relatively larger contributions to the total energy savings. Among the individual technologies, 20 WER-ESTs and 10 PP-ESTs account for 53.9% and 25.6% of the energy savings, respectively, while four technologies, namely, LT process for purification and recovery (LT-PR) of converter gas, combined cycle power plant (CCPP), pulverized coal injection, and pulverized coke oven gas injection, have the largest contributions, with the proportion of cumulative energy savings to the total energy saving potential accounting for 29.3%. This finding indicates that ESTs will become more cost effective from 2010 to 2050. The larger energy saving potential is due to the higher implementation rate. However, the implementation of ESTs will be gradually saturated in the future, and room for further tapping net energy savings will be limited. The future energy consumption reduction potential caused by implementing ESTs in CISI under different scenarios is shown in Fig. 11. From 2010 to 2050, energy consumption will decrease from 17.72 GJ/t to 14.74 GJ/t, 14.30 GJ/t, 14.14 GJ/t and 13.77 GJ/t under the BAU, cost-effective, technical-moderate, and technicaladvanced scenarios with corresponding average annual decline rates of 0.46%, 0.54%, 0.57%, and 0.64%, respectively. However,

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33 WHR- ESTs PP-ESTs G-ESTs

30 T25 27

Simple payback time (year)

24

21 T28 T22

18 T30 15

T18 12

9 T2 6 T34

T11 T19 T24

T31

3

0%

10% 20% T16 T13 T21 T15 T20 T3 T35 T17 T12 T9

30%

40% T14 T26 T32 T7

T10

50% 0

60% T33

T6

80% T27

70%

T29

T5

90% 100% T1 Implementation rate (%)

T23 T4 T8

3.50

Energy saving potential, GJ/t

Energy saving potential, GJ/t

Fig. 9. Simple payback period of selected available energy saving technologies in CISI.

a)

3.00 2.50 2.00 1.50 1.00 0.50 0.00 2030

2 2040

b)

3.00 2.50 2.00 1.50 1.00 0.50

2050 Year

Energy saving potential, GJ/t

Energy saving potential, GJ/t

3.50

3.50

0.00 2020

4.00

4.00

c)

3.00 2.50 2.00 1.50 1.00 0.50

4.50 4.00

2020

2030

2040

2050 Year

2020

2030

2040

2050 Year

d)

3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00

0.00 2020 Coking

2030 Sintering

2 2040 Ironmaking(BF)

2050 Year Steelmaking(BOF)

Steelmaking(EAF)

Rolling

General technologies

Fig. 10. Future energy saving potential under the BAU scenario (a), cost-effective scenario (b), technical-moderate scenario (c), and technical-advanced scenario (d).

515

Energy consumpon (GJ/t)

Q. Zhang et al. / Applied Energy 191 (2017) 502–520

19.00 BAU Scenario

18.00 17.00

Cost-effecve Scenario

16.00 15.00

Technical-moderate scenario

14.00

Technical-advanced scenario

13.00 12.00 2010

2020

2030

2040

2050

Year Fig. 11. Energy consumption reduction potential under different scenarios during 2010–2050.

the downward trend will be reduced with the implementation of ESTs and adjustment of steel production structure. In addition, it shows that technology promotion is the main driving force of the reduction of energy consumption, and limited potential exists for energy savings and energy consumption reduction because of industry structure adjustment. In summary, the reduction of energy consumption will rely more on energy efficiency improvement from the popularization and promotion of ESTs. The induced effect of steel structure adjustment with a proportion of EAF steel energy efficiency improvement from 10% in 2010 to 45% in 2050 is not obvious. However, EAF steel has been attracting increased attention for its high energy efficiency and because it is much less energy intensive and produces low environmental pollution. Therefore, the adjustment of steel production structure from a long-term perspective will be important with the development of the circular economy [26]. 4.4. Comparison with other studies Previous studies have also conducted the similar subject mainly focusing on WERU and energy efficiency improvement. For example, the maximum available waste heat potential from the blast furnace stove in CISI is calculated to be 2.9 GW, and the practical potential is evaluated to be 1 GW [7]. The waste heat potential of a case plant in CISI is estimated to be 4.87 GJ/t crude steel [17]. The total waste energy in Turkish iron and steel industry is calculated to be 14.73 PJ/year, and the technical potential is estimated to be 65% of these values [19]. Differing in scope and boundary, comparing these studies is not straightforward. Hence, some similar results, obtained by using a quantitative analysis method from both the technical and the economic perspectives, comparison with the results of previous studies are given in Table 4. Hasanbeigi [36] analyzed 23 applicable ESTs for CISI and found that the total fuel savings and electricity savings are 12,139 PJ and 416 TW h, respectively. When the discount rate is 15%, the cumulative cost-effective savings are 11,999 PJ and 251 TW h accordingly. Comparing cumulative energy savings with our results is made difficult because different categories and incompatible units

of the results. Li [39] pointed out that the total energy savings of 41 ESTs for CISI are 4.63 GJ/t. Twenty-five technologies are cost effective, and the cumulative energy savings are 3.89 GJ/t, when the discount rate is 20%. The results are higher mainly due to the inclusion of more ESTs from steelmaking-EAF, rolling and finishing processes. Ma et al. [41] calculated the total fuel savings and electricity savings of 36 ESTs for CISI are 36.5 Mtce and 78,659 GWh, which equal to 1071 PJ and 78.7 TW h, respectively. When the discount rate is 15%, the cumulative cost-effective savings are 19.6 Mtce and 67,249 GW h, which equal to 574.5 PJ and 67.2 TW h accordingly. In general, compared to conventional analysis of WERU, this study also consider comprehensive and numerous forms of waste energy in CISI, as well as technical and economic potential for waste energy resources by using waste recycling technologies. Energy benefits and cost effectiveness of implementing technology are also quantified based on ECSC model. 5. Discussion and recommendations This study provides a comprehensive and detailed assessment of the waste energy resource and related recovery technology from the perspectives of thermodynamic, technical and economic potentials. In this section, efficient measures to recover and utilize waste energy need to be considered, and factors, such as discount rate, energy price, capital cost, and subsidy, will be emphatically discussed based on the sensitivity analysis. Subsequently, the research limitations will be discussed, and recommendations will be presented. 5.1. Determination of waste energy recovery potential and ESTs in CISI The study reveals that the existence of approximately 56% and 43% of total waste energy potential is available under different reference conditions in CISI. However, the technical potential is less than 20% when the implementation rate of ESTs for the entire industry is considered. On the basis of the thermodynamic analysis model, Utlu [19] estimated that the available waste heat potential from total energy use is 36–40% in Turkish industrial sector, and the technical potential is 55–65% of these values, respectively. Ammar et al. [20] highlighted that three criteria are particularly significant, namely, matching heat supply and demand, government incentives for poor economic efficiency project, and economic transportation from the heat source to sink. Long-distance transportation was commonly used in traditional waste energy recovery projects, thereby resulting in high energy consumption and considerable transportation losses. The availability of demand for recovered energy improved the energy efficiency of process sites by 10% [16]. The WERU potential is influenced by multiple factors, including the characteristics of waste energy resources (i.e., quantity, temperature, and type), the compatibility of the sources and the sinks, and the available ESTs (efficiency, capital costs, and related policy

Table 4 Results obtained comparison with the results of previous studies.

Scope Amount of ESTs Cumulative energy savings Discount rate Base year Cost-effective energy savings

Hasanbeigi et al. [36]

Li et al. [39]

Ma et al. [41]

This study

CISI (2013) 23 Fuel: 12,139 PJ Electricity: 416 TW h 15% 2010 Fuel: 11,999 PJ Electricity: 251 TW h

CISI (2014) 41 4.63 GJ/t steel

CISI (2015) 36 Fuel: 1071 PJ Electricity: 78.7 TW h 15% 2012 Fuel: 574.5 PJ Electricity: 67.2 TW h

CISI 35 3.08 GJ/t steel

20% 2010 3.89 GJ/t steel

15% 2010 1.93 GJ/t steel

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instruments). Barriers, such as thermal load instability, corrosive and unclean flue gas, and equipment size limitations, have created many difficulties for the recovery of waste energy. The above analyses indicate the need for a balanced and efficient approach to sustainable and effective recovery and utilization of waste energy in which energy grade recovery and cascade utilization are the basic principles. 5.2. Sensitivity analysis The energy benefits and cost effectiveness of implementing ESTs or measures are influenced by the discount rate and energy price factors. We conducted a sensitivity analysis with different discount rates (5%, 10%, 15%, 20%, 25% and 30%), considering that investment decision makers always use higher discount rates, while energy modelers and policymakers typically choose lower discount rates. The cost effectiveness of ESTs gradually worsens with the increase of discount rates (Fig. 12). Twenty-two ESTs are cost effective and the cumulative energy savings are 2.3 GJ/t when the discount rate is 5%, whereas 18 ESTs are cost effective and the cumulative energy savings are 1.9 GJ/t when the discount rate is 30%, which is higher than the base discount rate of 15% with cost effectiveness of 19 ESTs and cumulative energy savings of 1.93 GJ/t. The emerging technology of integrated casting and rolling (strip casting), as the most typical example influenced by discount rate, possesses excellent economic benefits with a discount rate of 5%. However, it would not be cost effective when the discount rate is 30%. The main reason might be the high level of annual change in O&M cost (Data from Ref. [36]). The subtle variation of discount rate has a limited influence on the cost effectiveness of technologies, and the cumulative energy savings of total ESTs remain unchanged under different discount rates.

We performed a sensitivity analysis with different energy price increase rates (20%, 10%, 10%, 20%, and 30%). Fig. 13 shows that a higher energy price leads to higher energy benefits and greater cost-effective potentials of ESTs. The two technologies of dry gas cleaning system (wet to dry) and CDQ will become cost effective when the energy price increase rate changes from 20% to 30%, that is, from CNY 25.06 yuan/GJ to CNY 40.72 yuan/GJ. The performance of most technologies will improve by increasing the implementation rate and decreasing the capital cost to increase energy conservation. Fig. 14 shows that ESTs will become more cost effective when capital costs are reduced from 10% to 15%. The cost of subsidies is a financial incentive factor that aims to improve the competitiveness of ESTs and the implementation of technology. Practical experience indicates that the common subsidy rate ranges from 10% to 50%. Fig. 15 shows that 23 ESTs will be cost effective and cumulative energy savings will be 2.32 GJ/t when the subsidy rate is 50% compared with the baseline (without subsidy) with cost effectiveness of 19 ESTs and cumulative energy savings of 1.93 GJ/t. The cost of subsidies can increase the implementation rate, but the variation tendency of technology promotion remains unchanged under different cost subsidies. In summary, the sensitivity analysis demonstrates that discount rate and energy price have a greater significant influence on the cost effectiveness of ESTs, but energy benefits and cost effective are less sensitive to the capital cost and subsidy. 5.3. Research limitations and recommendations First, the matching of waste energy supply and demand, which would likely be essential in achieving an effective supply chain to the rational use of energy in practical production from the perspective of technical and economic feasibilities, was not discussed in

Fig. 12. Sensitivity on ECSC with different discount rates.

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Fig. 13. Sensitivity on ECSC with different energy prices.

Fig. 14. Sensitivity on ECSC with different capital costs.

detail in this study. Second, the total energy saving potential might be underestimated because of the selected technologies that are not representative of the entire industry and the shortcomings of ECSC based on existing technologies only. Some assumptions might affect the research result, such as the interactions and co-

benefits between ESTs. Therefore, presenting all the methodological assumptions and conducting a sensitivity analysis on crucial factors are necessary. Third, the accuracy of data poses limitations in understanding the true energy savings because of unavailable data, system boundaries, statistical specifications, and difference

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Fig. 15. Sensitivity on ECSC with different subsidies.

between the research methods of previous research papers. To address all these issues, we collected as much official public authoritative information as possible to serve as main data sources and performed a more detailed calculation of TES at the technical level. Further work should focus on updating data for a more recent period, providing a more in-depth assessment of low-medium temperature waste heat utilization potential in CISI and policy analysis with respect to drives of and barriers to the promotion of ESTs. In addition, technical attribute analysis of the declining performance over the lifetime of ESTs is necessary. Technical issues and insufficient capital are the main barriers to the effective recovery of industrial waste energy. In the short-term perspective, the most urgent task is to maximize waste recycling technology with the short payback period and low implementation rate that is mainly based on the economically feasible index. Meanwhile, in the long-term perspective should focus on the rationality of energy end use and availability of technology options. RD&D needs to focus on the wide-scale utilization of waste energy to improve energy efficiency in CISI. Meanwhile, the importance of structural change in steel production industry cannot be ignored. Although steelmaking (EAF) has a limited contribution to the total energy savings and energy consumption reduction on the process level in this study because of the low technology implementation, it will make a difference with the increasing proportion of EAF steel production. 6. Conclusions Iron and steel industry is one of the most energy intensive manufacturing industries. It consumes large amounts of primary energy as waste energy. The literature review shows that the exact quantity of waste energy is poorly quantified in practice. The Chinese government has released a series of measures and multiple binding targets to improve energy efficiency and enhance energy conservation. However, the technical potentials for waste energy recovery and utilization (WERU) have not been identified clearly because of the absence of a standardized methodology. In addition,

insufficient understanding of the benefits and cost effectiveness of technology has created barriers to the wide promotion of energysaving technologies (ESTs). In this study, a novel approach that involves the creation of a techno-economic model was developed to analyze the WERU and energy efficiency improvement in CISI. A quantitative analysis of the theoretical, technical, and economic potentials of waste energy resources was performed based on thermodynamic assessment, energy consumption, and ECSC model, respectively. This study attempted to quantify thermodynamic waste energy potential from the perspectives of absolute theoretical limit and current technical recovery limits by adopting two cases of the prescribed minimum temperature. Two cases of technical potential, with and without considering the technology implementation rate for the average value of the industry, were addressed. We evaluated the cost effectiveness of the waste recycling technology on the basis of two cases of CCE data (below 0 yuan/GJ and payback period within three years) when calculating the economic potential, and then calculated the data of typical energy savings for the specific destination through expert interviews and investigation of practices in CISI to acquire accurate results. Subsequently, the ECSC model was established to analyze the energy benefits and cost effectiveness of implementing 35 ESTs in CISI. Four scenarios were developed to estimate future energy saving potential and energy consumption reduction by considering technology promotion and structural change with the increasing share of EAF steel production. Results of the techno-economic model suggest that technology application and promotion approaches can recover approximately 44% of available waste heat. However, the technical potential is less than 20% of the total waste energy resources at the current average value of CISI. Opportunity areas for utilizing the waste energy or increasing the value of available energy are supported by the optimization of the existing waste heat recovery systems. Recovery of high-temperature waste heat in hot slag, where the technology exists but is too difficult to implement, is constrained by technical and economic barriers. Furthermore, no technology

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