АР14972699 – «Investigation of the Influence of High-ash Coals on the Technological Parameters of Smelting Carbon Ferrochromium Grades»

Ferrochromium production has grown rapidly over the past fifty years as it is used in alloyed, corrosion resistant steel grades. A significant increase in the consumption of ferrochromium is due to many specific properties of chromium, which is close in density to iron. In structural steels with a chromium content of up to 0.5%, wear resistance increases. The concentration of chromium in bearing steel is in the range of 1.30-1.65%. It is known that the introduction of 5-10% chromium into steels increases their heat resistance, and 4% chromium increases their hardness. Steels containing more than 11% chromium are classified as corrosion-resistant due to the formation of protective films that are insoluble in water and many acids, and at a content of 23-28% chromium, the alloys become heat-resistant.

Ferroalloy production, as one of the largest industries, is experiencing an acute shortage of high-quality carbon-containing reducing agents necessary to obtain metals that meet international standards. The smelting of carbonaceous ferrochromium is carried out by the carbothermal method, while the need for carbonaceous reducing agents, especially coke, is covered by its import from abroad. In Kazakhstan, there are deposits of high-ash hard coals, characterized by a low content of harmful impurities, and open-pit mining, which are a potential feedstock for the production of carbonaceous ferrochromium.

In this regard, the task of finding new domestic reducing agents with optimal physical and chemical properties and low cost, as well as a comprehensive assessment of the suitability of the studied materials as reducing agents, is of particular importance. Carbon-containing materials used as reducing agents in the ore reduction process must have high reactivity and electrical resistance, good gas permeability, sufficient mechanical strength and heat resistance, as well as a low content of harmful impurities and a high content of useful impurities.

1) Kuatbay Yerbol – Doctor of Philosophy (PhD), senior researcher at the Department of Science, Innovation and International Cooperation, project manager.

Scopus ID: 57218196966  

Researcher ID: ABE-5679-2021 

https://orcid.org/0000-0002-8400-3537

2) Nurumgaliyev Assylbek – Doctor of Technical Sciences, Professor of the Department of Metallurgy and Materials Science, domestic scientific consultant.

Scopus ID: 10042501900 

Researcher ID: AAF-9195-2021 

https://orcid.org/0000-0002-8782-9975

The results of the study are promising from the point of view of improving the technological process of smelting carbonaceous ferrochromium with a lower cost of the final alloy.

To date, the Republic of Kazakhstan has not established the production of carbonaceous ferrochromium using high-ash coal due to the lack of a rational technology for their production. The social and economic effect of the project implementation will be significant: by reducing the consumption of expensive metallurgical coke, the cost of the final alloy, ferrochromium, will be approximately 15% lower. According to preliminary estimates of the technical and economic indicators of experimental and basic options for the technology of smelting carbonaceous ferrochromium, it shows that when high-ash coal is used in the charge, the productivity of the furnace increases by 1.3%; specific power consumption is reduced by 4.6%; chromium recovery increases by 5.29%.

The environmental effect of the project will be from the implementation of the technology, where unsuitable high-ash coals stored in dumps will be involved in the process, thereby improving the ecological situation in the region. The scientific and technical effectiveness of the project is aimed at solving the national project of the Republic of Kazakhstan “Technological breakthrough through digitalization, science and innovation” and at improving the production of high-quality metal products.

The results of scientific research will be disseminated at international conferences, symposiums, various international technology exhibitions, publication of articles in peer-reviewed foreign or domestic publications recommended by CQAFES in this field and therefore will be available to scientists. The test results will be validated, a package of documents will be transferred directly to the scientific and technical department of ArcelorMittal Temirtau JSC, which co-finances this project, and other production organizations, and recommendations will be issued, as necessary, on the introduction of carbon ferrochromium production technology in TNC Kazchrome JSC.

1) A complete thermodynamic modeling of the process of smelting carbon ferrochrome was carried out. As a result, 521 phases were identified, of which 150 were the gas phase, 241 were the oxide and (or) slag phase, and 130 were the metal phase. Metallic phases are formed from intermetallic compounds, phosphides, sulfides, carbides and pure metals: Cr3C2 (7.2÷16.1), Cr4C (49.8÷52.4), Cr7C3 (5.7÷7.7), Fe2C (0.9÷7.8), Fe3C (0.3÷1.8), Cr (1.5÷6.3), Fe (11.2÷17.4). The maximum content of chromium-containing phases was found in the temperature range of 1700-1800°C, indicating that this temperature range is optimal for melting. The slag phase consists of magnesium chromate (MgCr2O4), chromium oxide (Cr2O3) and mullite (Al2O3·SiO2), as well as compounds based on Al2O3, MgO and SiO2: Al2O3 (2.3÷3.6); Al2O3·SiO2 (3.4÷10.9); (CaMg)0.5·SiO3 (1.1÷1.8); CaO·MgO·SiO2 (0.7÷1.1); MgAl2O4 (4.7÷6.2); MgCr2O4 (0.01÷2.5); MgO (23.5÷32.2); MgO Al2O3 (5.9÷8.8); MgSiO3 (23.3÷26.9); Mg2SiO4 (8.3÷13.5); SiO2 (10÷12.8). Laboratory tests were carried out on the Tamman furnace. The resulting ferrochrome meets the requirements of the standard. Analysis of the obtained results of thermodynamic modeling showed that when replacing coke with coal by 10, 20, 30 and 40%, 30-40% is more positive options at a given SiO2 content in the slag of 32%. Replacing coke with coal leads to a shift in the melting zone from the periclase and forsterite zones towards the sapphirine and spinel zones and a decrease in the melting temperature of the slag to ~1750°C.

2) A complete thermodynamic modeling of the process of smelting carbon ferrochrome was carried out. As a result, 521 phases were identified, of which 150 were the gas phase, 241 were the oxide and (or) slag phase, and 130 were the metal phase. Metallic phases are formed from intermetallic compounds, phosphides, sulfides, carbides and pure metals: Cr3C2 (7.2÷16.1), Cr4C (49.8÷52.4), Cr7C3 (5.7÷7.7), Fe2C (0.9÷7.8), Fe3C (0.3÷1.8), Cr (1.5÷6.3), Fe (11.2÷17.4). The maximum content of chromium-containing phases was found in the temperature range of 1700-1800°C, indicating that this temperature range is optimal for melting. The slag phase consists of magnesium chromate (MgCr2O4), chromium oxide (Cr2O3) and mullite (Al2O3·SiO2), as well as compounds based on Al2O3, MgO and SiO2: Al2O3 (2.3÷3.6); Al2O3·SiO2 (3.4÷10.9); (CaMg)0.5·SiO3 (1.1÷1.8); CaO·MgO·SiO2 (0.7÷1.1); MgAl2O4 (4.7÷6.2); MgCr2O4 (0.01÷2.5); MgO (23.5÷32.2); MgO Al2O3 (5.9÷8.8); MgSiO3 (23.3÷26.9); Mg2SiO4 (8.3÷13.5); SiO2 (10÷12.8). Laboratory tests were carried out on the Tamman furnace. The resulting ferrochrome meets the requirements of the standard. Analysis of the obtained results of thermodynamic modeling showed that when replacing coke with coal by 10, 20, 30 and 40%, 30-40% is more positive options at a given SiO2 content in the slag of 32%. Replacing coke with coal leads to a shift in the melting zone from the periclase and forsterite zones towards the sapphirine and spinel zones and a decrease in the melting temperature of the slag to ~1750°C.

3) A metallurgical assessment of the qualities of high-ash coals from the Saryadyr and Borly deposits used for the smelting of carbon ferrochrome was carried out. The technical composition of coals was determined, %: A 45-56, V 12-17, W 5-10, St. 38-45 and chemical composition of ash,%: SiO2 55-65, Al2O3 22-35, CaO 2-5, Fetot. up to 5. A study was carried out to measure the electrical resistivity of coal during heating. It was determined that at equal ash content values ​​(50%) in the temperature range 700-990°C, the electrical resistivity of Saryadyr coal is higher than Borly (by 20-30%). The electrical resistivity value is 2.5-0.5 Ohm cm. The phase transformations of high-ash bituminous coals when heated by differential thermal analysis (DTA) to a temperature of 1500°C in an oxidizing atmosphere were studied. According to DTA, high-ash coals have several pronounced thermal effects, which are associated with the removal of moisture, the release of volatiles, and an increase in the thermal conductivity of coal during its transition to a plastic state. An exothermic effect at a temperature of 1395°C characterizes the formation of mullite. The optimal composition of the charge mixture for smelting carbon ferrochrome, %, was selected: high-ash coal – 26, chrome ore – 57, metallurgical coke – 17.

4) The technical composition of coals was determined, %: A 45-56, V 12-17, W 5-10, St. 38-45 and chemical composition of ash,%: SiO2 55-65, Al2O3 22-35, CaO 2-5, Fetot. up to 5. A study was carried out to measure the electrical resistivity of coal during heating. It was determined that at equal ash content values ​​(50%) in the temperature range 700-990°C, the electrical resistivity of Saryadyr coal is higher than Borly (by 20-30%). According to DTA, high-ash coals have several pronounced thermal effects, which are associated with the removal of moisture, the release of volatiles, and an increase in the thermal conductivity of coal during its transition to a plastic state. An exothermic effect at a temperature of 1395°C characterizes the formation of mullite. The optimal composition of the charge mixture for smelting carbon ferrochrome, %: high-ash coal – 26, chrome ore – 57, metallurgical coke – 17.