Life cycle assessment of sintering process for carbon footprint and cost reduction: A comparative study for coke and biomass-derived sintering process (2023)

In order to solve the utilization problem of dry quenching coke dust removal ash (DRA) and high-temperature exhaust gas (HTEG) at the same time, this study proposes a new technology that combines DRA and high-temperature exhaust gas to produce energy gas CO and realize the removal of heavy metals in dust removal ash. The reaction properties of DRA and high-temperature exhaust gases, as well as the migration law of heavy metals, are preliminarily evaluated using thermodynamic simulation software (FactSage) and a combination of thermogravimetric mass spectrometry (TG-MS). The dropper furnace (DF) experiments are used to verify the feasibility of the new technology by simulating the high-temperature flue gas environment. The findings reveal that as pressure rises, the content of gas products namely CO₂ and CH₄ rises while the content of gas products CO and H₂ falls. At the same time, when the temperature rises, the CO and H₂ contents rise. Heavy metals such as Cd, Pb, and Zn are also more volatile, whereas heavy metals such as Ni, Cr, and Cu, require higher temperatures to volatilize. As the temperature increases from 800 to 1200°C, the Pb removal rate climbs from 34.6% to 92.5%, the Cd removal rate increases from 46.5% to 95.6%, and the Zn removal rate increases from 13.4% to 80.5%. The new technology captures CO₂ from high-temperature exhaust gases and converts them into CO energy gases, simultaneously realizing the removal of heavy metals. This provides an innovative solution for the treatment of organic solid waste.

Electric arc furnace (EAF) steelmaking process is an important way to realize recycling of scrap resources and sustainable development of iron and steel industry, which is orderly guided and major promoted during the 14th Five-Year Plan for achieving the carbon neutrality goal before 2060. The smelting modes with full scrap and hot metal added are two main methods in EAF steelmaking process in China, and there is still a lack of effective quantitative means and consensus on the smelting mode of lower carbon emissions. In this paper, based on the function unit of 1000kg of molten steel, the life cycle carbon footprint (CF) of EAF steelmaking process under 13 current smelting modes were comprehensively analyzed and quantized. The results showed that with the hot metal ratio increased by 80.29%, the life cycle CF increased by 962.718 (45.85%) kg CO₂ eq, the upstream CF of blast furnace ironmaking and sintering increased by 1944.544 (63.50%) and 674.194 (22.02%) kg CO₂ eq. Reducing the hot metal ratio or indirect CF of hot metal production will rapidly lower the total CF of EAF steelmaking process. With the mass of carbon powder and natural gas increased by 24.82 and 9.84kg, the life cycle CF decreased by 52.81 and 82.03kg CO₂ eq, respectively. Adopting full scrap smelting mode with appropriate amount of carbon powder and natural gas, or applying clean energy power production and low-carbon materials will be the best choice of future EAF steelmaking process.

Engineering muck represents a typical, large output construction waste. However, the comprehensive utilisation rate of engineering muck is typically low. Large quantities of engineering muck accumulate in the open air, exerting a pressure on scarce land resources and exacerbating the risk of landslides. There is an urgent need for the efficient waste management techniques to improve the long-term utilisation of engineering muck. In this study, a low-carbon, low-cost, and innovative approach to recycling engineering muck to produce non-sintering lightweight aggregates (NSLWA) is reported. NSLWA was successfully prepared by a bonding granulation technique, and a systematic investigation on the physico-mechanical properties, microstructure, and corresponding reaction mechanism of NSLWA was conducted. The experimental results indicated that the prepared NSLWA, possessing a loose bulk density of 0.91–1.16g/cm³ and a cylinder strength of 1.22–11.7MPa, met the performance requirements of lightweight aggregates (GB/T17431.1 2010). The mechanistic analysis demonstrated that the cylinder strength of NSLWA could mainly be attributed to two factors: 1) the cementation effect of hydration products and 2) cohesive forces between clay particles. Finally, the environmental impact was analysed by life cycle assessment. The global warming potential (GWP) was in the range of 47.4–201.2kg CO₂-eq/t NSLWA; Processing NSLWA by engineering muck could enable a reduction of GWP by 31–84% relative to that a landfill disposal process following chemical stabilisation. Compared with the lightweight aggregates obtained after sintering processes, the GWP of NSLWA was reduced by 11.7–79.2%. The total costs of NSLWA processing were in the range of 8.1–20.9 $/t NSLWA, bringing about an economic benefit of 9.0–21.8 $/t NSLWA compared with the traditional artificial aggregates. The findings of this work will guide the eco-friendly and economical management of engineering muck to support the sustainable development of the aggregate manufacturing industry.

The iron and steel industry are expanding to meet the steel demand. Raw materials used in steel manufacturing gradually degrade in quality and quantity over time. Heating and power needs in this sector are primarily met by coal. Sintering is regulated and impacts overall gas emissions (including CO and CO₂). Iron-making plants, particularly those engaged in agglomeration processes like sintering; require alternative fuels to limit their CO₂ emissions to the environment. This review focuses on explaining the role that various reductants/fuels play in the sintering of iron ore and how those choices affect product quality and the surrounding ecosystem. Coke breeze is used as primary fuel source. Still, alternative, less expensive options such as coal, charcoal, biomass, and wastes from iron and steel-making units offer great promise as partial or complete replacements for coke breeze. This work primarily focuses on the impact of fuel characteristics, particle size distribution, and sintering parameters with associated emissions.

Fuel combustion provides the essential energy required for the iron ore sintering process, this process results in tremendous carbon dioxide emissions. Therefore, it is vital to develop innovative strategies to reduce fossil fuel consumption by effectively utilizing the heat storage effect in packed beds. Herein, an innovative double-layered fuel segregation method with return fines embedded in the lower layer was proposed and validated, and a goal of intensively reducing fuel consumption by 16% was achieved. Specifically, the oxygen concentration in the flue gas decreased from 16.7% to 11.5%, whereas the carbon dioxide and carbon monoxide concentrations increased from 5.5% and 0.3% to 13.4% and 1.3%, respectively. Moreover, the tumbler and shatter indices increased by 1.7% and 3.2%, respectively, indicating an increase in the sinter quality. In addition to optimizing the parameters of the proposed technology, the mechanisms for intensifying fuel combustion by applying the proposed technology were elucidated. The narrow thicknesses of the combustion and over-wet zones were found to significantly contribute to the improved permeability of the sintering bed.

Due to the combined effects of carbon emission and carbon sink, agriculture is acknowledged as an essential contributor to achieve the Chinese government's carbon neutrality goal of 2060, and carbon footprint (CF) and carbon footprint intensity are substantial indicators to reveal the carbon emission level. For these reasons, the Theil index technique and extended STIRPAT model were employed to evaluate their spatiotemporal heterogeneity and influencing factors using panel data from 31 provinces for the period 1997–2019. The findings revealed that the CF showed an increasing trend with an annual growth rate of 24.6 %. The carbon footprint intensity (CFI) indicated an evident spatiotemporal heterogeneity and transferred over time, with an average growth rate of 19.82 %. The CFI Theil index and its contribution rate both confirmed that intra-regional difference is the main source of the overall difference, among which, the CFI Theil index displayed the distribution feature of “western (11.50 %) > central (11.12 %) > eastern (10.56 %) > northeast (6.61 %). The contribution rate of CFI illustrated the spatial pattern of “eastern (33.74 %) > central (21.07 %) > western (19.87 %) > northeast (5.24 %). Furthermore, the influencing effects of GDP per capita, planting structure, population density and urbanization level on CF and CFI also demonstrate evident spatiotemporal heterogeneity.

Applied Thermal Engineering, Volume 102, 2016, pp. 648-660

A relatively more comprehensive 1D mathematical model, compared to previous models, is proposed for flue gas recirculation sintering (FGRS). The proposed model considers multiphase theory, eight major reactions significantly affected by the input gas conditions, and various heat transfer processes within/between different solid and gas phases. Characteristic size distributions of materials including coke, limestone and dolomite are used to correct the reaction rates of key sub-models, as well as specific kinetic parameters determined via thermogravimetric analysis instead of empirical values. Geometric changes caused by the reactive and melting factors are described in improved manners. This model is validated by contrasting the modeling results and the measured data from sinter pot tests. Parametric studies show FGRS technology can significantly enhance combustion characteristic within sinter bed, meaning to increase maximum temperature and melt fraction, improve the uneven distribution of heat. Therefore, the quality of sintered ore can be improved. However, the slightly reduced flame front speed deserves further attention. The velocity of input flue gas exerts the most significant effect, followed by O₂ concentration, and then, temperature. The operating parameters of FGRS must be carefully determined. Three measures, which still require further investigations, can be proposed to optimize the process.

Applied Energy, Volume 207, 2017, pp. 230-242

It has been widely reported that the sinter strength and heat pattern would be weakened when adopting the low grade solid fuels, such as biomass, semi-coke and anthracite. Moreover, the imbalance of heat distribution in the sintering bed is considered to be problematic on the energy efficiency. To solve the above problems simultaneously, the gaseous fuel segregation method was firstly proposed in this paper. The gaseous fuel was injected to the melting zone from the top and auto-ignited near the solid fuel combustion zone. Firstly, methane concentrations of 0.0% and 0.5% vol. were tested, keeping the total calorific heat input unchanged. The heat pattern in melting zone was recorded by both contact thermocouples and non-contact thermal infrared imager. The results indicated that the methane injection could significantly extend the melting zone from the upstream and raise the sinter strength higher than that of coke sintering, without increasing the energy consumption. Then, the energy saving potential of the novel method was evaluated by reducing the calorific heat input 4, 6 and 8%. Furthermore, in the segregation case, the gaseous fuel injecting concentration was increased in the upper bed to enhance the weak heat pattern, and decreased in the lower bed to avoid the energy waste. It was observed that the melting zone became much more uniform in the infrared images. Finally, the optimum segregation degree of 1.0%/mm was recommended, where the sinter strength grew 2.31%. The present study provides an effective way for optimizing the energy efficiency in the sintering process.

Journal of Cleaner Production, Volume 166, 2017, pp. 66-80

This study proposed three optimization strategies for metallurgical plants and compared their effects on energy conservation and cost saving in China's metallurgical industry. These strategies include 1) the complete outsourcing of the coking process, 2) the decrease of the iron/steel ratio and 3) substitution of BF/BOF (Blast Furnace/Basic Oxygen Furnace) with DR/EAF (Direct Reduction/Electric Arc Furnace). The simulation was accomplished by constructing a system dynamics model that included cost, energy consumption and production sub-systems. The result indicated that DR/EAF is the fundamental solution for energy conservation and cost control, but the huge demand by this process for scrap will limit its development into the near future. Therefore, at present, establishment of large-scaled independent coking plants and control of the iron/steel ratio by technical means are more suitable. In addition, policy advice was given.

Journal of Cleaner Production, Volume 101, 2015, pp. 387-394

A study was carried out into the use of charcoal as a supplementary fuel in the iron-ore sintering process. The primary fuel was coke breeze and anthracite with 0, 10, 25, 50 and 100% replacement of the energy input with charcoal to produce sinter. This was achieved by considering the carbon content of each fuel and its corresponding participation on fuel blending, in order to have the same carbon input in each test run. An extensive analysis of the environmental impact was carried out regarding the atmospheric pollutants characterization (dust, sulphur dioxide, nitrogen oxides, carbon monoxide, carbon dioxide, methane, total hydrocarbons, and dioxins and furans). Experimental results indicate that fuel blending where 50% of the heat input was provided by charcoal may be comparable with those using 100% coke, under normal sintering conditions, and may result in a 50% reduction on greenhouse gas emission. It was also observed that while dust, methane and hydrocarbons emissions increased, the total dioxins and furans, expressed as polychlorinated dibenzodioxins/furans, decreased approximately 50% when compared with operation with 100% coke.

Journal of the Energy Institute, Volume 93, Issue 5, 2020, pp. 1934-1941

To thoroughly understand the combustion behaviors of coke and biomass char based on its physiochemical characteristics and distribution states in iron ore sintering, three types of single, composite and pellet quasi-granules of coke and biomass char were prepared carefully, catalytic potential of Cu_0.1Ce_0.9O₂ to increase quasi-granule combustion efficiency defined by the extent of CO destruction in flue gas was investigated. The results showed that biomass char is combusted at relative low temperature in the range of 350–800°C because it has higher volatiles and porosity, exhibiting high reactivity compared to coke which combusts from 650°C to 1030°C. Pellet type has an intrinsic high combustion efficiency due to its fine fuel size and the neighboring compounds effect. Single coarse type granules have a high CO concentration in flue gas and have the highest combustion efficiency improvement by Cu_0.1Ce_0.9O₂ loading among all the types, which is mainly attributed to CO catalytic oxidation following Mars-van Krevelen path rather than the carbon oxidation. Through intentionally producing more coarse single type and composite type granules with 3wt% Cu_0.1Ce_0.9O₂ in granulation, substitution ratio of biomass for coke can be increased, leading to improved combustion efficiency of ~98% without deterioration of sintering performance.

Journal of Cleaner Production, Volume 161, 2017, pp. 1374-1384

Using biomass for partial replacement of coke breeze in iron-ore sintering process is an effective technique as a countermeasure against global warming. However, the sinter strength would be weakened due to the damaged heat pattern at high biomass proportion. In this paper, the gaseous fuel injection method was experimentally investigated with the aim at solving this problem. Eleven cases were arranged to examine the ultra-low concentration of methane combustion and its effect on the improvement of heat pattern at high charcoal proportion. The temperature in the sintering bed was recorded by both thermocouples and infrared thermography. The thermocouple data indicated that the melt quantity index was significantly increased by employing the gaseous fuel injection method. Moreover, the infrared images show that the red-hot region was expanded at each moment in the methane injection cases. The influencing mechanism of gaseous fuel injection on the heat pattern in sintering process was revealed in this paper. As the premixed methane/air approaching to the solid fuel combustion zone, it was preheated by the hot sintered ores, then ignited and self-sustained near the solid fuel combustion zone. A newly generated gaseous fuel combustion zone coupled with the solid fuel combustion zone was used to control the heat pattern in sintering bed. The results showed that the heat pattern and sinter strength kept increasing until the methane concentration increased to 0.4–0.5% under the lab conditions. The stable interval of secondary combustion zone in the sintering bed was also analyzed. Finally, comprehensively considering the sinter strength, yield, productivity and sintering time, the recommended equivalent methane concentration at high charcoal proportion was 0.5% where the shatter strength grew 3.78% and solid fuel rate reduced 7.52%, compared with 100% coke sintering case. Generally, the gaseous fuel injection offers a technical support for the iron ore sinter production using cheap or carbon neutral solid fuel. More importantly, this method can also reduce solid fuels (the main contributor of contamination dust during the production, transportation and storage) consumption by partial substitution of cleaner gaseous fuel.