The significance of biochar in steel industrial sustainability
The iron and steel industries (ISI) play a significant role in global economic growth and are known for their high energy consumption. As presented in Fig. 1, around 26% of the energy used by industries worldwide is consumed by the ISI, with coal and coke playing a key role (Mousa et al. 2016; Safarian 2023b). Fossil fuels are primarily used to generate heat and as reducing agents in the steel-making process, which results in significant worldwide CO2 emissions (Ibitoye 2018; Osman et al. 2022; Sundberg et al. 2020). Studies have shown that using fossil-based carbon during steel-making is responsible for about 60–70% of the CO2 emitted in steel production via electric arc furnaces (EAF) and reheating furnaces (Robinson et al. 2021). Also, the dwindling fossil fuel supply is unfavorable to the ISI. These situations motivate the search for reliable, sustainable, and environmentally friendly fuels to replace coal and coke. Biomass sources seem to be one of the promising solutions (Adekunle et al. 2019; Hu et al. 2019; Suopajärvi et al. 2018). The carbon contents of lignocellulose biomasses are high and could be converted into usable energy. Therefore, biomass and biomass residues are thermo-chemically transformed into bio-oil, syngas, and biochar to improve their fuel qualities for various applications in the ISI (Zakaria et al. 2023).
Biochar has recently been considered a potential replacement for coal/coke since it can be easily adapted and has qualities equivalent to coal and coke in the metallurgical process. However, the factors limiting biochar application in ISI include cost-effectiveness in large-scale biochar production, challenges in ensuring consistent biochar quality, and integration of biochar into complex processes of iron and steel production (Mousa et al. 2016a).
Biochar is a porous black solid derived from the thermochemical transformation of biomass materials. It is characterized by a high surface area, possessing exceptional physical and chemical attributes that facilitate long-term environmental carbon storage (Reddy et al. 2019; Safarian 2023a). The distinctive characteristics of biochar, encompassing a notable adsorption capacity and ion exchange capability, extend its utility to various applications (Amer et al. 2022; Cho et al. 2023; Majumder et al. 2023). Employing biochar for iron and steel production holds considerable attraction, especially for nations endowed with ample and sustainable biomass resources (Ye et al. 2019; Zaini et al. 2023). This is underpinned by its renewable nature, widespread availability, and versatile applicability (Hamidzadeh et al. 2023; Tan 2023).
Pursuing sustainable industrial practices incorporating innovation and environmental responsibility has recently become popular (Chang et al. 2023; Simmou et al. 2023). These two imperatives have sparked research into cutting-edge approaches that improve the efficiency and efficacy of industrial processes while reducing their adverse environmental effects (Le 2022). Biochar comprehensively addresses climate change, ranging from its function in soil enrichment to its potential integration inside the steel industry, a classic sector distinguished by its significant carbon footprint and complex manufacturing methods (Abhi et al. 2023; Azzi et al. 2022).
In light of this context, the steel sector is a top prospect for creative biochar integration. The steel industry seeks solutions to coordinate its operations with sustainable practices because it contributes significantly to global carbon emissions. The ability of biochar to sequester carbon, as shown by its use in land recovery operations, presents an attractive opportunity for the sector. The potential use of biochar as a reducing agent in steel-making processes is another interesting direction to pursue (Gan et al. 2023; Zhang et al. 2022). The renewable nature of biochar and its ability to operate as a reducing agent provides a solution to lessen dependency on fossil-based reducing agents, promoting a more environmentally friendly steel production cycle.
Biochar production from biomass feedstock is another method of managing biomass waste and the problems associated with its disposal. This aligns with the circular economy of converting wastes into usable products (Adeniyi et al. 2023; Chaturvedi et al. 2023; Ismail et al. 2023).
Biochar production techniques
This study examines diverse biochar production methods, observing the possible interactions between the technical and economic practicality of integrating biochar into ISI. Moreover, the technological advancements and real-world implications of integrating biochar in the ISI were examined.
A thorough search strategy was formulated to discover studies that were pertinent to the review process. This strategy primarily involved searching the ScienceDirect and SpringerLink databases for articles related to biochar production techniques and their applications in the ISI. Additionally, some articles obtained through Google Scholar searches, which were directly relevant but not available in ScienceDirect and SpringerLink, were also considered. The search strategy encompassed a wide range of keywords and combinations to ensure thorough coverage of the subject.
The criteria for inclusion and exclusion of studies were developed based on the subject of the review, drawing from guidelines outlined by Vlachokostas et al. (2021) and Balali et al. (2023). The inclusion criteria include studies published in peer-reviewed journals, studies conducted on the application of biochar in the ISI, studies identifying different biochar production methods and applications, papers investigating the impact of production methods on the properties of biochar, and studies related to iron and steel production. Conversely, the exclusion criteria encompassed investigations that did not meet the inclusion criteria, papers not written in English, manuscripts not available in full text, and studies not carried out in the last seven years. However, some articles published later than 2018, which were directly relevant to the subject, were still included in the review.
Biochar production methods
Various cutting-edge technologies are used to manufacture biochar, including pyrolysis (Mishra and Mohanty 2021), gasification (Ibitoye et al. 2021b), hydrothermal carbonization (HTC) (Ibitoye et al., 2022; Ibitoye et al. 2023b), torrefaction (Ibitoye et al. 2021c), and even innovative methods like microwave pyrolysis (Gabhane et al. 2020), and plasma pyrolysis (Bhatt et al. 2022). The viability of these methods is influenced by several parameters, including the type of feedstock, catalysts utilized, temperature, heating rates, and the configuration of the reactor (Alahakoon et al. 2022; Panwar et al. 2019; Uday et al. 2022; Zhang et al. 2022). The assessment of their effectiveness considers factors such as energy usage, product yield, and overall environmental impact (Karthik et al. 2021; Zhou et al. 2021). A detailed summary of the various biochar production methods is provided in Table 2.
Each method for producing biochar has merits and demerits, making it appropriate for various uses depending on the intended product output, energy needs, feedstock accessibility, and environmental considerations. The optimum way to produce biochar for use in steel industry applications will rely on several variables, including the demands of the ISI, the intended application of the biochar, cost, and the overall characteristics of biochar required for steel making.
Analysis of the characteristics displayed in Table 2; Fig. 5 (data extracted from Ercan et al. (2023)) revealed that slow pyrolysis stands out as a potential approach for producing biochar in the context of the steel industry. Compared to other processes like fast pyrolysis and gasification, which may prioritize the generation of bio-oil or syngas, hydrothermal carbonization, and slow pyrolysis are recognized for generating larger biochar yields (Salimbeni et al. 2023). These results aligned with the reports of Abhi et al. (2023); Safarian (2023a), which revealed that slow pyrolysis and HTC are the most effective techniques for producing high-yielding biochar, with yields that vary from 25 to 90 weight%, and even more subject to the reactor type, feedstock, and operating circumstances.
The potential need for enormous quantities of biochar for iron and steel industrial use as a reducing agent is in line with this improved biochar yield. This is because of the extended dwelling time at lower temperatures during slow pyrolysis. The biochar generated is characteristically more stable and rich in carbon (Nega et al. 2023; Rathod et al. 2023). Further, the lower energy required and improved properties of biochar produced are desirable features for large-scale industrial utilizations and may reduce operating costs. It recurrently results in biochar with more structural stability and less volatile material (Premchand et al. 2023a). This can result in better biochar properties and transportation qualities, which are essential when considering integrating biochar into ISI (Liu et al. 2023; Safarian 2023b).
Technical viability and adaptation challenges
The integration of biochar into the steel-making process is not without its challenges. The primary challenge is guaranteeing that the integration of biochar in the steel-making process is consistent with traditional steel production methods (Abhi et al. 2023). Different operating conditions, heating rates, temperature ranges, and materials specifications exist for various steel-making processes- blast furnaces, electric arc furnaces, and direct reduction steel-making. Biochar’s chemical and physical properties must suit these methods to ensure a smooth integration.
The commercial viability of biochar generation is hindered by costs related to biomass collection, feedstock handling, transport, drying, etc., rendering biochar products less competitive compared to coal. A report has highlighted that implementing a carbon tax will be crucial in alleviating costs associated with biomass adoption in the ISI (Mousa et al. 2016a).
Another challenge is the vital high-temperature characteristics of coke, essential for sizeable modern BFs, commonly assessed through CSR and CRI values. Coke with high CSR (above 460%) and low CRI (below 23%) is preferred for optimal performance. These properties enhance penetrability in the upper part of the shaft and improve combustion, demonstrating the necessity of high-strength coke to prevent degradation and maintain permeability in the BF skeleton (Mousa et al. 2016a).
The AC significantly affects the calorific value of biochar and the heat balance and slag-forming reactions in the BF. Different biomass sources have unique ash compositions; for instance, agricultural biomass often contains K2O and SiO2, whereas a higher CaO content characterizes woody biomass. Effectively managing components like zinc, lead, alkalis, phosphorus, and sulfur is vital in the BF to prevent operational challenges and ensure steel quality, with sulfur and phosphorus posing specific risks (Abhi et al. 2023). Therefore, addressing ash-related concerns is crucial for the seamless integration and implementation of the process.
It may be essential to make significant technological changes to adapt steel manufacturing processes to accommodate biochar production and consumption. Rebuilding gear, improving temperature profiles, establishing biochar manufacturing units, and ensuring proper handling practices are just a few of the challenges that may occur. Management of biochar feed rates, distribution, and burning may necessitate the development of new apparatus or control systems.
The potential for CO to be produced by biochar during heating or combustion needs to be appropriately controlled. It is crucial to comprehend the CO generation capability of biochar and how it interacts with the steel-making reactions in processes where CO is a valuable reducing agent. The optimal use of CO must be achieved while averting unfavorable results. Hence, appropriate control methods must be in place.
Biochar production often leads to the generation of byproducts, including ash and VM (Lin et al. 2023; Premchand et al. 2023a). It is vital to manage and dispose of these byproducts in an environmentally-friendly manner. The complete process design must include techniques for collecting VMs or gases, treating the resulting ash, and eliminating possible emissions.
Continuous R&D efforts are required to solve technical issues. The suitability of biochar characteristics in iron and steel production should be studied in detail, including its impact on product quality, emissions, and process optimization. To develop novel solutions, it is essential that experts in process engineering, biochar technology, and iron and steel manufacturing work together.
Any variations to current iron and steel manufacturing methods may impact operational efficiency. Evaluating the possible effects of biochar integration on process and energy efficiency and product quality is vital. Cautious planning is necessary to minimize process disruptions and avoid unexpected consequences such as increased energy consumption, product output, and quality reduction.
Cost implications, scalability, and long-term sustainability
The cost implications like start-up costs, recurring costs, possible cost savings, and financial incentives like tax breaks and subsidies impact the biochar production and applications in ISI. Variables that affect the scalability and long-term sustainability of biochar utilization are also discussed in this section.
The design and construction of a biomass conversion plant, such as pyrolysis setup and other biochar production technologies and processes to establish biochar production facilities that can match ISI demand are capital intensive (Alias et al. 2014). The initial cost of modifying the existing ISI facilities is another significant expense (Gu et al. 2023). This can entail making modifications to feedstock handling systems, furnaces, and storage facilities. Nonetheless, these costs might be lessened using an integrated approach to cost reduction in steel production planning, especially in marginally profitable operations (Pelser et al. 2022). Furthermore, research and development cost implications are necessary to develop and optimize the biochar production technique that is appropriate for large-scale industrial uses (de Jong et al. 2017; Purohit et al. 2018).
The biomass availability and cost of collection depend on factors including location, season, and competing applications (Berry and Sessions 2018). For instance, the cost of transportation of biomass feedstock from collection site to biochar production facility, and transporting biochar to iron and steel plants contribute to the overall operational cost of the ISI (Berry and Sessions 2018). These costs can be substantial, especially when the feedstock collection location, biomass production facilities, and iron and steel plants are far from one another (Cheng et al. 2020b). The energy required for biochar production contributes to the industrial operational costs. In addition, the control of biomass feedstock supply chains, running and maintaining biochar production facilities, and integration of biochar into iron and steel industry processes require professional personnel. To ensure continuing and efficient output, industrial equipment has to be constantly monitored and maintained. This is especially crucial given the competitive nature of the global iron and steel market and the requirement for effective manufacturing methods. These actions can greatly raise the entire cost of maintenance, repairs, and part replacement.
Biochar has the prospect of earning carbon credits under several carbon trading programs because it minimizes the emission of greenhouse gases (Salma et al. 2024). The organization can generate revenue by selling these credits or using them to offset carbon taxes. In addition, an organization may escape sanctions and improve its corporate sustainability reputation by using biochar as an alternative to traditional carbon, thus reducing emissions and complying with environmental regulations (Salma et al. 2024). Furthermore, the conversion of industrial wastes into biochar reduces the cost of disposing of industrial wastes and residues (Ghosh et al. 2023; Gunarathne et al. 2019).
Governments and financial institutions may provide subsidies, grants, or low-interest loans to encourage the adoption and implementation of sustainable practices like biochar production as an alternative to fossil fuels. The start-up and operational costs of biochar production and implementation in ISI can be reduced considerably via governmental support.
The scalability of biochar production and use in ISI depends on factors like feedstock availability, technology advancement and innovations, market demand, and compatibility with the existing industrial processes. Mapping and identifying biomass resources through regional evaluations might aid in feedstock supply chain optimization (Hogland et al. 2018). The utilization of advanced technologies, which are efficient, and able to handle a variety of biomass, is crucial for scalability. These include but are not limited to advanced automation design engineering, and process control.
The adoption of biochar on a larger scale in ISI depends on the ability of the biochar producer to manufacture biochar comparable with coal and coke (creation of value-added products). This involves setting and maintaining biochar of high-quality standards, and sensitizing ISI to the benefit of biochar utilization are necessary to create a stable market and demand for biochar by iron and steel producers (Ye et al. 2019).
The long-term sustainability impacts of biochar production and use in ISI are related to their environmental, economic, and social consequences. The use of biochar as an alternative to fossil fuels and other traditional carbon-intensive sources can help minimize the emissions from the ISI. More so, agricultural applications of biochar include improve soil nutrient retention, soil structure, and water-holding capacity, enhancing crop yields and facilitating climate change mitigation. The conversion of agricultural wastes into biochar alleviates the environmental challenges resulting from the dumping and burning of agricultural and forest wastes in an open field (Ibitoye et al. 2021a, b). This creates valuable products from waste, promoting a
