Kinetics of SiC Formation on Graphite Using N 2 -CO-SiO and N 2 -CO-H 2 -SiO Gas Mixtures
- PDF / 3,105,076 Bytes
- 6 Pages / 593.972 x 792 pts Page_size
- 68 Downloads / 305 Views
INTRODUCTION
DURING the past few decades, ironmaking industries have been confronted with the significant challenges of reducing the CO2 emission and increasing the energy efficiency in blast furnace (BF) operations. The utilization of H2 gas as a reducing agent in BF operation has been considered a promising solution.[1,2] With the increasing H2 gas utilization, the consumption rate of coke as fuel and reductant would decrease. However, as the consumption rate of coke decreases, the thickness of the coke layer in BF operation would decrease, which may cause process instability owing to the mixing of coke and ore particles in the cohesive zone.[3] Furthermore, the liquid slag-formation temperature increases owing to the fast reduction of iron oxides. As the local slag holdup in the coke bed increases, it is expected that the temperature may be distributed unevenly in the coke bed.[4] Consequently, slag holdup should be properly controlled to obtain a stable operating condition. Slag holdup is known to be strongly influenced by the wettability of coke by molten slag.[5,6] In general, molten slag shows poor wettability on the coke surface, whereas the formation of SiC on the coke surface improves the JOON SEOK OH and JOONHO LEE are with the Department of Materials Science and Engineering, Korea University, Anam-ro 145, Seongbuk-gu, Seoul, 02841, Republic of Korea. Contact e-mail: [email protected] Manuscript submitted December 3, 2018. Article published online May 8, 2019. 1808—VOLUME 50B, AUGUST 2019
wettability.[6–8] From the sampling tests in the conventional BF, SiC was mainly observed in the bosh and raceway cokes.[9,10] Accordingly, it is expected that the formation of SiC on the coke surface may improve the slag permeability through the coke layers. In the H2-enriched BF operation, the formation of SiC and the corresponding change in wettability of coke by molten slag have not been studied. Therefore, in this study, the formation rates of SiC on the graphite surface were investigated at 1843 K, 1873 K, and 1903 K (1570 °C, 1600 °C, and 1630 °C) under N2-CO-SiO or N2-CO-H2-SiO gas mixture atmosphere. Based on the experimental results, the temperature dependence of the rate constant is presented, and the effect of the introduction of H2 gas is discussed.
II.
EXPERIMENTAL
A. Materials A mixture of SiO2 (99 pct purity, Samchun) and SiC (97.5 pct purity, Aldrich) powders was obtained by homogeneously mixing via ball-milling at 300 rpm for 12 hours using zirconia balls as the milling medium. Approximately, 2.5 g of the powder mixture was thereafter pressed into a tablet in a steel die of diameter 10 mm with three droplets of distilled water under the pressure of 250 MPa for 1 minute. The tablet was sintered in an alumina crucible in a high-frequency induction furnace (20 kW, 35 kHz) at 1873 K (1600 °C) for 30 minutes under an Ar atmosphere (99.9999 pct METALLURGICAL AND MATERIALS TRANSACTIONS B
Table I. Fe
Ti
V
Chemical Composition and Physical Properties of Graphite Ni
Al
Mg
Zn
Etc.
ppm 38.49
19.10
10
Data Loading...
