Coke Minerals Research Articles

Transformation of minerals at the boundary of magma-coal contact zone: case study from Wolonghu Coal Mine, Huaibei Coalfield, China

Mesozoic and Cenozoic magma activity in the Wolong Lake mining area of Huaibei is frequent, and the degree of magma intrusion into coal seams remarkable. On the one hand, magma intrusion affects the utilization of coal resources; on the other hand, the macro and trace elements in coal are redistributed to form new mineral types. This study uses the Wolong Lake magma intrusion coal seam as a research object. The mineral paragenesis for igneous rock, coke, and thermally-altered coal in an igneous intrusion zone is studied using SEM, XRD, and Raman spectroscopy. During igneous intrusion, the temperature and pressure of igneous rock metamorphose ambient low-rank coal to high-rank coal and coke. The response mechanism of minerals and trace elements to magmatic intrusion is discussed. The results are: ① SEM analysis shows that ankerite and pyrite are formed from magma intrusion. Both minerals are strongly developed in the magma-coal contact zone, and less well developed in thermally-altered coal. ② XRD analysis shows that igneous intrusion strongly influences the types and content of minerals in coke and thermally-altered coal. In addition to the increase amounts of ankerite and pyrite, chlorite, serpentine, and muscovite, and other secondary minerals, are generated following igneous intrusion. ③ Raman analysis suggests that thermally-altered coal possesses the characteristics of both pyrite and coke. Coke from the magma-coal boundary zone possesses the typical characteristics of pyrite. Igneous rock contains a mineral similar to pyrite, confirmed by both having similar Raman peaks. The scattering intensity of Ag indicates that the formation pressure of pyrite increases from thermally-altered coal via the boundary between the coke zone and the igneous rock.

Influence of SiO2 reduction on the local structural order and fluidity of molten coke ash in the high temperature zone of a blast furnace. A molecular dynamics simulation investigation

An in-depth understanding about the transformation of molten coke ash is significant to uncover the mechanism of coke reaction at high temperature inside a blast furnace. The evolution of local structural order and fluidity of molten coke ash (SiO2-Al2O3-CaO) with the reduction of SiO2 at a fixed Al2O3/CaO ratio was investigated by means of molecular dynamics (MD) simulation. While [SiO4] tetrahedral was the main structural units forming Si-O network, due to the high levels of Al2O3 in coke minerals [AlO4] and a small amount of [AlO5] were the two key structural units forming the Al-O network. The effect of chemical composition on the bond length of Si-O, Al-O and Ca-O is very weak, while the coordination number of Al-O can be slightly influenced by the reduction of SiO2 due to the unstable structure of Al-centered polyhedron compared with [SiO4]. The concentration of bridging oxygen decreases, while that of tricluster oxygen increases with the reduction of SiO2 from the system. Al-centered polyhedrons prefer to be connected by O triclusters, while Si-centered polyhedron favor a link by bridging oxygen. With the decrease of SiO2, more [AlO4] will change from edge-sharing to corner-sharing with similar units. The angular distribution of Si-O-Si exhibits an asymmetric shape with the average value around 151°, while two peaks were observed in the Al-O-Al angular distribution because of the edge-sharing (∼90°) and corner-sharing (∼122°) features in Al-centered polyhedrons. With the reduction of SiO2 from the system, the diffusivity of all atoms increase considerably since the amount of strong Si-O bond decreases. Viscosity estimated from MD simulation decrease with the reduction of SiO2. The good agreement between MD simulated data and experimental data indicates that MD simulation can be adopted to estimate the property change of molten coke ash at high temperature.

Influence of alkaline (Na, K) vapors on carbon and mineral behavior in blast furnace cokes

A series of adsorption–alkalization experiments were conducted in a muffle furnace on two types of blast furnace cokes at 1300°C in the presence of alkali vapors. Coke textures were found to peel off layer by layer after the alkalization process by potassium vapor, and macro fissures were observed for K/Coke ratios higher than 3/100. This phenomenon was not observed in the coke samples alkalized by sodium vapor. A number of additional potassium-bearing and sodium-bearing phases were detected with scanning electron microscope and energy dispersive spectrometer after the alkalization process. The formation of kalsilite or potassium aluminum silicate (KAlSiO4) and sodium alumina silicates (Na6Al4Si4O17) was confirmed through X-ray diffraction, however the formation of intercalation compounds that were expected to form in the alkalized coke samples could not be confirmed. The catalytic effect of sodium and potassium-bearing minerals appeared to be quite similar; the degradation of coke strength by sodium was however found to be stronger than that caused by potassium. The severe degradation of coke quality caused by alkali vapors was attributed to their strong influence on the coke carbon matrix, coke minerals, as well as their catalytic effect on the carbon gasification reaction.

Zinc Accumulation and Behavior in Tuyere Coke

A case study of zinc oxide, which represents the first report on the occurrence, crystalline features, formation mechanism, and influence of this mineral in tuyere coke, was conducted in this study. A number of zinc oxides, some of which were in hexagonal wurtzite habit, were observed to distribute mainly in coke pores, cracks, surfaces, and around coke minerals. The accumulation of zinc in tuyere coke may enhance the degradation of coke and increase the generation and accumulation of coke fine in a blast furnace, which would cause bad effect on blast furnace operation. Investigations into zinc behavior in tuyere coke can be important for further interpretations of coke degradation in the high temperature zone of a blast furnace.

Flow of Molten Slag through a Coke Packed Bed

The productivity and performance of the ironmaking blast furnace is significantly affected by the flow behaviour in the lower zone. The flow of reducing gas and liquids (iron and slag) through coke particles is often characterised as flow through a packed bed. To improve understanding of the flow in the lower zone of the blast furnace, an investigation has been carried out, where the primary aim was to obtain a physical description of the high temperature flow phenomena of liquid slag through a coke packed bed, based on characterisation of laboratory scale packed bed systems.A synthetic slag in the CaO–SiO2–MgO–Al2O3 system was fed at a controlled rate to pass through a coke packed bed heated to 1500–1600°C. The mass of slag passing through the bed was logged. The bed was packed using synthetic coke to minimise the experimental uncertainty associated with the heterogeneity of industrial coke. Slag supply-drain curves, liquid holdup and residence time have been characterised. The effects of bed packing density, temperature and mineral content of the coke were tested.Increasing the packing density or decreasing the temperature of the packed coke bed was found to increase the total liquid holdup and residence time of the slag. Increasing coke mineral content from 4.4% to 12% resulted in a decrease in the total holdup and the residence time. Mathematical models from the literature based on cold packed beds were used to predict the liquid holdup for the experiments, but were found to not adequately describe the results.

Behaviors of NH4HSO4 in SCR of NO by NH3 over different cokes

Deposition of ammonium sulfates over catalysts is often observed during selective catalytic reduction (SCR) of NOX by NH3 in the presence of SO2 and H2O, especially at temperatures lower than 350°C, which results in catalyst deactivation and equipment erosion. Activated coke was reported to be a support effective in reducing accumulation of ammonium sulfates on the catalyst surface. However, detailed information on stability of ammonium sulfates and the properties of coke affecting the stability have not been explored. This work studies decomposition behavior of NH4HSO4 deposited on different cokes in a TG-MS system. It shows that NH4HSO4 on coke decomposes in two steps: formation of NH3 and H2SO4 starting at about 170°C and reduction of H2SO4 by coke to form SO2 at higher temperatures, regardless of the presence of NO. The decreased NH4HSO4 poisoning is attributed to reduction of H2SO4 because it frees the pores of coke. The BET surface area and pore volume of coke do not affect the reduction behavior of H2SO4 if only they are high enough; the oxygen and nitrogen containing functional groups in coke promote the reduction of H2SO4; the minerals in coke may interact with H2SO4 to form stable sulfates; V2O5 on coke and NO in the gas elevate the reduction temperature of H2SO4.

Effect of Thermal Treatment on Coke Reactivity and Catalytic Iron Mineralogy

Iron minerals in coke can catalyze its gasification and may affect coke behavior in the blast furnace. The catalytic behavior of iron depends largely upon the nature of the iron-bearing minerals. To determine the mineralogical changes that iron could undergo in the blast furnace, cokes made from three coals containing iron present in different mineral forms (clays, carbonates, and pyrite) were examined. All coke samples were heat-treated in a horizontal furnace at 1373, 1573, and 1773 K and then gasified with CO{sub 2} at 1173 K in a fixed bed reactor (FBR). Coke mineralogy was characterized using quantitative X-ray diffraction (XRD) analysis of coke mineral matter prepared by low-temperature ashing (LTA) and field emission scanning electron microscopy combined with energy dispersive X-ray analysis (FESEM/EDS). The mineralogy of the three cokes was most notably distinguished by differing proportions of iron-bearing phases. During heat treatment and subsequent gasification, iron-containing minerals transformed to a range of minerals but predominantly iron-silicides and iron oxides, the relative amounts of which varied with heat treatment temperature and gasification conditions. The relationship between initial apparent reaction rate and the amount of catalytic iron minerals - pyrrhotite, metallic iron, and iron oxides - was linear and independent ofmore » heat treatment temperature at total catalyst levels below 1 wt %. The study showed that the coke reactivity decreased with increasing temperature of heat treatment due to decreased levels of catalytic iron minerals (largely due to formation of iron silicides) as well as increased ordering of the carbon structure. The study also showed that the importance of catalytic mineral matter in determining reactivity declines as gasification proceeds. 37 refs., 13 figs., 7 tabs.« less

Effect of CO2 Gasification on the Transformations of Coke Minerals at High Temperatures

Mineral phases of three metallurgical cokes were characterized after reactions with CO2 at 1373 and 1773 K in a horizontal furnace for 2 h using X-ray diffraction (XRD) and scanning electron microscope/energy dispersive spectroscopy (SEM/EDS). After reaction at 1373 K, all cokes displayed an increased degree of mineral decomposition, dissemination within the carbon matrix, and inclusions in pores such that the intensity of transformation varied with coke types. As for the original cokes, XRD analysis of the reacted cokes indicated the presence of quartz, mullite, and high melting point aluminosilicate as the major refractory phases while pyrrhotite, triolite, iron oxides, and metallic iron phases were the main reactive phases. Framboidal sulfide appeared to diminish after CO2 reactions. Iron-spinel was the common reaction product while olivine was observed in only one coke. All minerals occurred in a wide variety of sizes and distributions such that fine minerals occurred mainly within or close to pores and were comprised of iron sulfide and Al2O3. At 1773 K, aggregates of Al-silicates decomposed further to form mullite and cristobalite while low melting point Al-silicates transformed to running slag in coke. Iron was observed to occur in many forms including metallic iron, silicates, and oxides but less frequently as sulfides and appeared to occur within or in close proximity to pores. At 1773 K, pore inclusions were the prominent features of the reacted cokes, particularly a high proportion of Al2O3 (corundum). Calcium was observed as silicates as well as thermally stable phosphate and sulfides. This study demonstrated that characteristics of coke minerals after reactions at standard coke strength after reaction (CSR) test temperatures of 1373 and 1773 K were significantly different in terms of phase distribution which would influence coke strength and reactivity accordingly. This study implies that coke properties measured at relatively lower temperatures in the conventional tests may not provide a true assessment of coke performance in an operating blast furnace.

Characterization of the Origin and Distribution of the Minerals and Phases in Metallurgical Cokes

Three industrial metallurgical cokes were examined using X-ray diffraction (XRD) and scanning electron microscopy combined with energy dispersive X-ray analysis (SEM/EDS). The study highlighted the difficulties and implications of identifying the inherent crystalline mineral phases in cokes using XRD such that increasing the ashing temperature led to the formation of anhydrite and destruction of metallic iron: microwave plasma ashing resulted in minimal alteration of the original coke mineralogy apart from the formation of bassanite and possibly jarosite. A preliminary scheme to characterize coke minerals is presented such that, physically, minerals can be classified as fine (<50 μm), coarse (50−100 μm), and agglomerate (>1000 μm); chemically, minerals can be grouped as refractory, semirefractory, and reactive, while on the basis of distribution they can be described as discrete, disseminated, or pore inclusions. Quartz, cristobalite, mullite, and high melting point Al-silicates were found to be the predominant refractory phases while low melting point Al-silicates, e.g., containing high fluxing elements such as K, and Fe were the main semirefractory phases present in all cokes. A variety of iron containing phases including pyrrhotite, troilite, iron oxides, metallic iron, and iron silicates were also invariably present in all cokes while calcium phases were found to occur as sulfide, silicates, and phosphates. In general, iron and calcium phases can be categorized as reactive phases with few exceptions such as oldhamite (CaS). The study highlighted that most of the cokes possess a similar mineralogy, with the main distinction being in their relative abundance, particle size, and nature of distribution in the coke matrix. The study provides a basis to develop a mechanistic understanding of the influence of minerals on coke reactivity and strength at high temperatures.

Application of the unterzaucher method to the determination of oxygen in coke

The Unterzaucher method, used for the determination of oxygen in organic compounds and coal, has been adapted to the determination of oxygen in coke. Modifications were made to the conventional apparatus in order to eliminate any contribution made by the coke moisture to the determined oxygen content. The carbon dioxide produced from the combustion of the oxygen in the coke was estimated by a sensitive conductimetric method. Evidence is presented which indicates that additional liberation of oxygen from the coke mineral matter does not make a significant contribution to the total oxygen determined under the prescribed experimental conditions. The error of the determination is approximately 0.1%. A comparison is made between results obtained for a series of cokes and chars by the direct method and by an independent determination, based on neutron activation.