1. Introduction
In light of the Paris agreement goals [
1] for global temperature control, countries around the world need to take all achievable actions to reduce greenhouse gas emissions (GHG) from every sector [
2]. Many countries have set timetables for peaking carbon emissions and have adopted broader policies and practical measures. Additionally, countries are under considerable pressure to improve their air quality as they develop green, low-carbon economies and energy systems. Although the prevention and control of air pollutants has been somewhat successful [
3], controlling total societal pollution remains a long-term task [
4]. As typical energy-intensive industries, the iron and steel industries are under great pressure to reduce its emissions [
5].
In developing countries, especially in China, the pattern of energy use favors a raw approach. Specifically, China has a rather typical steel industry, with steel production having expanded over the past decade and its share of crude steel production having increased from 15% to 56%. It has become the world’s largest steel producer [
6]; consequently, the associated increases in energy consumption and pollution emissions have become a serious problem [
7]. In China, 90% of steel production is based on the blast furnace–alkaline oxygen furnace (BF–BOF) process, which involves the use of iron ore. Unlike iron ore, which is a limited natural resource, scrap is a renewable and recyclable resource. Improving scrap recycling saves resources and makes production more sustainable, while the use of scrap in crude steel smelting results in much lower CO
2 emissions than those when using iron ore. The scrap-based electric arc furnace (EAF) process accounts for 10% of the steel production capacity [
8]. Because the EAF process produces 50% less carbon emissions than those produced by the BF–BOF process [
9], the promotion of the EAF process is widely considered an important measure for achieving emission reductions in the steel industry. Rational modelling is needed to assess the carbon reduction benefits of steel scrap recycling.
In recent years, carbon emissions have attracted the attention of many researchers. To reduce carbon emissions, the steel industry can impose direct restrictions on steel production; however, these come at the expense of socioeconomic development. Researchers have analyzed CO
2 reduction options for the steel industry. For example, research has been conducted on low-carbon processes and the use of energy sources (e.g., fuels) with low CO
2 emissions [
10,
11,
12]. The first topic involves reducing carbon along the 14 process steps of steel smelting [
13], increasing the smelting temperature to reduce CO
2 emissions from the pellet ore in the blast furnace, or developing slag-free, low-energy-consumption pellet bonding technologies. The second topic involves developing large coking reactors and non-recycling furnaces to improve the coking efficiency [
14]. There are also technologies that use carbon-neutral materials, such as recycled waste plastics and biomass, as reducing agents in kilns to reduce the use of fuel and coke, thereby allowing waste to be recycled and reducing resource consumption and greenhouse gas emissions [
15]. There is also a category of technologies that use carbon capture and sequestration technologies [
10].
Nevertheless, the development and deployment of efficient carbon abatement technologies is expected to take decades, and alternative pathways to carbon abatement in the steel industry are necessary for the short to medium term [
16]. Existing studies on the production structure suggest that future carbon reduction in the steel industry will largely depend on the coverage of electric arc furnaces (EAFs) [
16]. Xuan (2017) emphasized that increasing the proportion of the EAF route in production can contribute to the sustainable performance of the steel industry in many ways, while saving iron ore and other energy sources [
17]. However, the use of EAFs is inseparable from scrap, and researchers have focused on the integral role of scrap recycling in promoting the management of pollutant emissions in the steel industry [
18]. The recycling of waste resources is an important way forward for the green development of society, and many scholars are exploring methods of waste resource utilization [
19,
20], with some scholars exploring policy support for the rational use of waste resources [
21,
22]. The recycling value of steel scrap is even greater, and many studies have focused on predicting scrap inventory demand and recycling. For example, Zhang (2015) used econometric analysis to analyze future scrap trends by forecasting steel demand in terms of gross domestic product (GDP) and GDP per capita [
23]. Based on an input–output model, Xuan (2017) indicated that China can still achieve great improvements regarding its scrap ratio compared to those that the United States or many European countries can achieve [
17]. Ryan (2020) used a dynamic material flow model to determine the range of steel inventories and available scrap based on changes in per capita steel inventories and recycling rates in the United States [
24]. To further investigate scrap recycling, Sahoo (2019) developed an Life Cycle Assessment (LCA) model-based approach to evaluate the optimal utilization scenario for scrap steel [
25]. Numerous other studies have investigated the technical processes of scrap melting in EAFs in different ways [
26,
27,
28,
29,
30].
The manner in which scrap is recycled in China does not differ from those in developed countries. Many steel mills in China commonly use a method involving iron plus scrap combinations. This method is very different from the all-scrap EAF melting method used in developed countries and is known as the Chinese-style short-process steelmaking method [
31,
32,
33]. The use of iron plus scrap in China is mainly motivated by the economy rather than carbon emission reductions [
34]. There is also a direct correlation between the slow establishment of EAFs in the steel industry and high scrap prices [
35]. Many studies have analyzed the economic benefits and environmental indicators of using iron plus scrap based on economic cost considerations for specific situations. For example, Duan (2009) showed that increasing the amount of iron in an electric furnace leads to decreased electricity consumption and increased oxygen and lime consumptions [
35]. Conversely, the emission reduction benefits of electric furnace production are also outstanding. Burchart-Korol (2013) compared the life-cycle greenhouse gas (GHG) emissions of the Polish blast furnace-converter and scrap-based electric furnace routes [
36]. The results showed that the GHG emissions of one ton of steel produced in an EAF were 913 kg CO
2, i.e., much lower than the 2459 kg CO
2 produced in a blast furnace. Ryberg (2018) studied the GHG emissions of three typical steelmaking processes: the sinter-converter, roasting-electric furnace, and scrap-electric furnace routes [
37]. The results showed that the scrap-electric furnace route results in an emission reduction of 1 kg per 1 kg of finished steel produced. However, these carbon emission studies do not provide good assessments of the melting patterns of ferrous scrap in China.
The Chinese-style, short-process steelmaking method is based on the social reality. Developing countries have insufficient scrap resources and high steel smelting costs; therefore, they use a combination of small amounts of scrap and large amounts of iron to reduce costs and remove impurities. Developing countries cannot achieve the all-scrap smelting patterns of developed countries [
38,
39,
40]. China’s short-process steelmaking model is of interest to developing countries, with countries such as Brazil and India having adopted this model to smelt steel [
31]. However, the large amount of iron used will inevitably result in carbon emissions and will not allow the carbon reduction effect of scrap steel to be realized. Therefore, there is a need to establish a carbon emission reduction index to assess the impact of scrap recycling on carbon emissions in developing countries.
This study builds on the above literature by first defining the system boundary and calculation method of CO2 emissions in scrap steel recycling. By selecting the typical iron and steel melting processes in China, this study calculates and analyzes the carbon emissions of the “Chinese-style” long- and short-process steelmaking. Many factors of scrap recycling were combined to calculate carbon emissions, design an evaluation method for the carbon emission reduction index of scrap recycling, and establish a carbon emission reduction index model. Furthermore, the carbon emission reduction effect of scrap recycling was evaluated in China in recent years; this study analyzes and compares the current role of scrap steel in carbon emission reduction in the iron and steel industry, and offers realistic suggestions.
This study helps to enrich the theoretical system of carbon emission calculation in the steel production process. It also provides theoretical references for determining the boundary and content of carbon emission reduction, accounting for the recycling of steel scrap. By studying the composition of actual carbon emissions under different smelting modes of iron and steel enterprises, it provides reference significance for the government and enterprises to explore the low-carbon transition path. This study innovatively applies an index to demonstrate the carbon emission reduction effect of steel scrap, providing a new way of expressing carbon emission reduction in the iron and steel industry.
5. Conclusions
This study established a model for evaluating the CO2 emission reduction effect of scrap recycling. The construction of the emission reduction evaluation model focused on the calculation of carbon emissions from iron and steel smelting processes. Based on the dynamic changes in the values of raw materials, scrap ratios, and fuels in different years, we calculated and analyzed the changes in the carbon emission reduction index of the iron and steel industry under the influence of scrap recycling. The carbon reduction index for scrap recycling established in this paper is suitable for steel enterprises to assess the carbon emissions in the process of scrap utilization and adjust the related material usage. It can also help government departments to assess the carbon emission situation of the steel industry at different moments and formulate relevant policies in a timely manner. The limitation lies in the fact that the data collected are too short to assess the changes of the index from a long-term historical perspective.
In this study, the use of steel scrap is divided into two main categories, namely long process steelmaking and short process steelmaking. Both types require iron to be melted in a blast furnace. Smelting iron in a blast furnace requires various fuels, electricity and raw materials. The highest carbon emissions are from fuels, which emit 1.42 tonnes of carbon dioxide per tonne of iron, electricity, which emits 0.038 tonnes of carbon dioxide, and raw materials, which emit 0.22 tonnes of carbon dioxide. The molten iron is used to make steel in either a converter or an electric arc furnace. The carbon dioxide emissions per tonne of steel in converter mode are 1.58 tonnes (based on 2022 figures) and 0.996 tonnes per tonne of steel in electric arc furnace mode (based on 2022 figures). This is close to what Sahoo calculated, but a little lower [
25]. The result is also lower than the 2.15 tonnes of CO
2 mentioned by Hasanbeigi [
52]. Emissions vary from year to year due to the different proportions of materials used.
The results showed that the carbon emission reduction index per ton of steel has increased in recent years, considering a fixed reference year. This finding confirms from an academic research perspective that the existing smelting processes can effectively reduce carbon emissions by increasing the use of scrap steel. In recent years, only 20% of scrap has been used. Xuan and Yue (2016) believe that full utilization of scrap can only be achieved when the scrap ratio reaches 36.6% [
53]. By covering scrap steel with molten iron during the smelting process, the purity of the steel can be improved while maintaining cost efficiency. However, because of the consistent use of a low fixed proportion of scrap steel over the years, this method has resulted in relatively high carbon emissions from smelting, resulting in a weak carbon emission reduction effect.
The results calculated from the model show that the years with the highest fluctuations in the carbon emission reduction index for scrap recycling, with 2013 as the base year, were 2015 and 2016. However, in the subsequent years, the index showed minimal changes. Furthermore, the pattern of change in the scrap recycling rate was very similar to the index fluctuations, indicating a significant emission reduction effect of scrap recycling. Similarly, calculations have shown that the EAF mode with pure scrap steel can achieve an emission reduction of up to 80% compared with the traditional mode. The same Sirintip study calculated that increasing the use of steel scrap could reduce carbon emissions by more than 60 percent [
54]. Given the current situation in China, although the Chinese-style short-cycle steelmaking can produce high-quality steel at a low cost, it cannot effectively and sustainably reduce carbon emissions from the steel industry and has failed to meet the emission reduction targets on time. To address this issue, companies must shift their focus from cost considerations to carbon reduction. Increasing the use of scrap steel is key for meeting the environmental targets of the steel industry.