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Thermoanalysis was used in this research to produce a comparative study on the combustion and gasification characteristics of semi-coke prepared under pyrolytic atmospheres rich in CH4 and H2 at different proportions. Distinctions of different semi-coke in terms of carbon chemical structure, functional groups, and micropore structure were examined. The results indicated that adding some reducing gases during pyrolysis could inhibit semi-coke reactivity, the inhibitory effect of the composite gas of H2 and CH4 was the most observable, and the effect of H2 was higher than that of CH4; moreover, increasing the proportion of reducing gas increased its inhibitory effect. X-ray diffractometer and Fourier-transform infrared spectrometer results indicated that adding reducing gases in the atmosphere elevated the disordering degree of carbon microcrystalline structures, boosted the removal of hydroxyl- and oxygen-containing functional groups, decreased the unsaturated side chains, and improved condensation degree of macromolecular networks. The nitrogen adsorption experiment revealed that the types of pore structure of semi-coke are mainly micropore and mesopore, and the influence of pyrolytic atmosphere on micropores was not of strong regularity but could inhibit mesopore development. Aromatic lamellar stack height of semi-coke, specific surface area of mesopore, and pore volume had a favorable linear correlation with semi-coke reactivity indexes.

Various metallurgical dust contains Fe2O3 and CaO, which catalyze the carbon–oxygen reaction and exhibit variable distributions and relative contents. Herein, we probe the interactions between Fe2O...

Pyrolytic chars are a potential high-quality fuel for use in iron ore sintering and pulverized coal injection (PCI) operations of blast furnace. In this study, industrial char produced from a moving-bed pyrolyzer was screened into four particle size ranges and compared with coke used in an industrial sintering process and a PCI coal used in an industrial blast furnace, and their basic compositions, micropore structures, functional group distributions, carbonaceous structures, reactivities, and gas release behaviors during combustion were analyzed. Furthermore, the mechanism underlying the particle size-dependent properties of the char was analyzed by comparing it with a char prepared under laboratory-simulation conditions. Results demonstrate that char particles larger and smaller than 3 mm (the turning point) have different structures and properties. More specifically, particles larger than 3 mm have stable properties, better developed pore structures, carbonaceous structures that are more ordered, superior reactivities, and lower releases of SO2 and NOx. Therefore, they represent a desirable option for use in fueling sintering and PCI operations. Char particles smaller than 3 mm were further investigated by screening them into particle size ranges, and results showed that they had significantly varied compositions and structures, which further confirmed their unsuitability for use in the two operations. Finally, the particle-size-dependent properties of the char can be explained by the differing residence times, the radial variations in pyrolysis degrees, and the mechanical (or thermal) stresses experienced by the different raw coal particles within the pyrolyzer.

Herein, the pyrolysis characteristics of low-rank coal under a CO-containing atmosphere was studied via thermogravimetry coupled with mass spectrometry and Fourier transform infrared analysis. Furt...

Nickel slags can be produced through ferronickel preparation by the pyrometallurgical processing of laterite nickel ores, however, such techniques are underutilized at present, and serious environmental problems arise from the stockpiling of such nickel ores. In this study, a modification to the process of ferronickel preparation by the direct reduction of carbon bases in laterite nickel ores is proposed. The gangue from the ore is used as a raw material to prepare a cementitious material, with the main components of tricalcium silicate and tricalcium aluminate. By using FactSage software, thermodynamic calculations are performed to analyze the reduction of nickel and iron and the effect of reduction on the formation of tricalcium silicate and tricalcium aluminate. The feasibility of a coupled process to prepare ferronickel and cementitious materials by the direct reduction of laterite nickel ore and gangue calcination, respectively, is discussed under varying thermodynamic conditions. Different warming strategies are applied to experimentally verify the coupled reactions. The coupled preparation of ferronickel and cementitious materials with calcium silicate and calcium aluminate as the main phases in the same experimental process is realized.

To realize the efficient and comprehensive utilization of specularite resources, combined with the cement clinker production technology of rotary kilns, the coupling process of the direct reduction of specularite by lignite and the preparation of cementitious material was proposed, with the additional aim of achieving the reduction of iron oxide and transforming the gangue component into cementitious material. Thermodynamic software was used to calculate the product composition when the reaction reached equilibrium under the set conditions. By analyzing the influence of the ratio of C/O, basicity, temperature, and other parameters on the reduction of iron oxide and cementitious material generation, the feasibility of the process was judged and experimentally verified. The results showed that the coupling process of the direct reduction of specularite and the preparation of cementitious material was thermodynamically feasible when using highly volatile lignite with added calcium oxide. The optimal C/O ratio of the reducing agent was 1.2 for the complete reduction of iron oxide (Fe2O3, Fe3O4, FeO) without the gangue fraction; reduced iron could stably coexist with the cementitious material components, but the unreduced FeO would result in a substantial reduction in tricalcium silicate generation. Using lignite as a reducing agent, the hydrogen-rich volatiles in coal created a good reducing atmosphere, strengthened the reduction process of iron oxide, and provided favorable conditions for the generation of cementitious material. A two-stage heating system must be adopted to realize the reduction of iron oxide and the generation of cementitious material. The process parameters conducive to the reduction of specularite and cementitious materials were determined, the basicity range of the system was regulated to 2.4–3.3, the reasonable reduction temperature was close to and not higher than 1137 °C, and the optimal temperature of cementitious material generation was 1450 °C.

Oxy-fuel combustion of coal pyrolysis gas has recently been proposed to serve as internal heat source of a vertical low-temperature pyrolysis furnace, in order to make the output pyrolysis gas nearly free of nitrogen and widely useful. To keep the pyrolysis temperature and the heat carrier gas volume unchanged from air combustion to oxy-fuel combustion, the equivalence ratio has to be increased up to 8. To explore the flame temperature and species variation at this ultra-rich condition, freely propagating premixed oxy-fuel flames of a typical coal pyrolysis gas at equivalence ratios of 0.5–10 are numerically studied with detailed chemistry. It is found that super-adiabatic flame temperatures (SAFT) occur at equivalence ratios larger than 3 for the considered pyrolysis gas and the SAFT magnitude is 294 K at equivalence ratio of 8. Due to the high H2 mole fraction (46%) in the pyrolysis gas, preferential diffusion plays a negligible role in the SAFT feature. Global net production of CO and H2 by the rich combustion only occurs at moderate equivalence ratio ranges, which are 1.5–8 and 3–5.5 respectively for the two species. At equivalence ratio of 8, the three fuel components are all net consumed following the mole ratio of CH4:CO:H2 = 1:0.07:0.84. Kinetic analysis reveals three factors responsible for the reaction mechanism change with the increase in equivalence ratio. Firstly, the lack of H-radical and the decrease in temperature result in the disappearance of the H2 production peak in the initial stage. Secondly, HO2 attack to CO prevails and hence contribution of CO oxidation in the initial stage increases. Thirdly, the long lasting OH attack to CO and H2 leads to the weakened CO and H2 production rate in the final stage.

Large quantities of residual slag with high Fe content are left behind in pyrometallurgical nickel processing. How to separate and recover iron from the high fayalite residue is still a problem because iron mainly exists as iron-magnesium silicate in slag. This article suggests that the slag for nickel smelting is adjusted by increasing the amount of lime, partly instead of quartz, to form liable reduction compounds for subsequent Fe extraction. Based on the thermodynamic analysis and phase diagram of the FeO-SiO2-CaO-MgO slag system, the new slag composition was chosen, the suitable melting point of relevant slags was measured, and the phase change was observed. The new slag with a composition of 7 to 9 pct MgO, 10 to 15 pct CaO and 1.5 to 1.8 Fe/SiO2 was found to work well for nickel matte smelting. With the increase of CaO and decrease of SiO2 content in slag, Ca(Fe, Mg)Si2O6 and Mg(Ca)Fe2O4 are the main existing phases instead of (Fe, Mg)2SiO4 in the residual smelting slag. More than 50 pct of Fe-containing phases are in the form of MgFe2O4 when 15 pct CaO is added, which is what we want because the MgFe2O4 is much better for magnetic separation and reduction than the original (Fe, Mg)2SiO4. In this way, Fe can be much more easily extracted from residual slag and have multipurpose benefits.

The devolatilization characteristics and non-isothermal kinetics of gaseous volatile evolution of bituminous coal were investigated through simultaneous thermogravimetry-mass spectrometry (TG-MS). The TG-MS results indicated that the three types of coals possess similar devolatilization characteristics in terms of mass loss and gas evolution. A high heating rate slightly shifted the TG, derivative thermogravimetric analysis (DTG), and MS curves to a high temperature range and promoted the release of evolved gases. The kinetic parameters of gaseous volatile evolution were determined through a novel procedure. In this procedure, the kinetic model function f (α) was identified using the Malek method, and the activation energy E and the pre-exponential factor A were calculated with common isoconversional methods or a distributed activation energy model (DAEM). With the Malek method, the reaction order model (n = 2) was the most probable mechanism to describe the gaseous formation of H 2 and C 2 H 2 . This finding implied that chemical reaction is a limiting factor of gas evolution. The evolved rate curve of CO 2 and CO could be fitted and identified by subjecting the spectral peaks to multi-Gaussian analysis. A JMA model (n = 3) and a standard Z-T-L model were applied to describe various kinetic stages. Results revealed that the evolved CO 2 and CO were mainly controlled by diffusion. All of the standard models failed to fit the gaseous evolution of CH 4 and H 2 O. Therefore, CH 4 and H 2 O possibly underwent a complex process involving different reactions and stages.

The interaction mechanism between the combustion products of pulverized coal injected and coke in the raceway of blast furnace was studied through thermodynamic calculation and experiments. The results indicated that additives significantly affected the melting property of coal ash in high temperature zone. Although the unburnt char, raw coal ash, and catalyzed coal ash failed to wet the coke surface, the wettability of the catalyzed coal ash on the coke was greater than that of the raw coal ash. Since the unburnt char had weak reaction with the coke surface, it showed little influence on the surface morphology of the coke. The interaction between the raw coal ash and the coke gave rise to the increase in the pore size on the coke surface. However, the raw coal ash only affected the coke surface and the entrances of the pores owing to its poor fluidity. After being melted, the catalyzed coal ash was expected to immerge into the inside part of the coke and then react with the coke, resulting in an expansion and increase of coke cavities. The raw coal ash and the unburnt char reduced the coke reactivity, while the catalyzed coal ash improved the coke reactivity. Thereinto, the coal ash containing Fe2O3 exhibited a larger influence on the reactivity than that containing CaO.

An industrial experiment was carried out by classifying the waste cathodes of aluminum electrolytic cells in Shanxi Province and investigating the effect of particle size and temperature on the leaching of soluble fluoride. It was discovered that NaF was the main dissolvent and could be effectively dissolved by four-stage leaching at 348 K and that the soluble fluorine could be decreased to the limit for hazardous solid waste. After the leaching of discarded water, the fluoride concentration in the final water was enriched to 17.69 g/L, and the effective enrichment of fluoride ion was realized.

The effects of CaO, Fe2O3, and MnO2 on the combustion reactivity of anthracite and coal char with low combustibility were investigated using thermogravimetric analysis (TG) and a drop tube furnace (DTF) under an oxygen-rich atmosphere. TG results showed that catalysts exhibited different effects on the combustion characteristics of fuels. For ignition temperature, it was found that, with increasing addition, the ignition temperature first decreased and then increased. For combustion rate, the positive effect of the catalyst on combustion rate was significantly enhanced with the increasing amount of additive. For burnout behaviour, at an equal additive dose, the effects of the three catalysts on burnout behaviour of two fuels varied greatly. The DTF results showed that the combustion reactivity of coal char was improved even more than that of anthracite. Eventually, the effects of three factors, including properties of the catalysts, fuel properties, and combustion conditions, on the catalytic combustion, were discussed.

The reduction of iron in hematite and process coupling of cementing material generated from gangue components are explored in this paper, and a technical proposal for preparing directly reduced iron and cementing materials considering the processes of energy and material flows is proposed. An experimental study preparing cementing materials, such as tricalcium silicate and dicalcium silicate, by roasting the components, was performed. In this study, hematite was used as the raw material and powdered carbon was added, as the reducing agent, with CaO, at the same time, the gangue components of iron ore were used as the principal raw materials for the process of directly reduced iron preparation by direct reduction of iron ore. The FactSage software package was used to perform thermodynamic calculations of the reduction of iron and its influence on the formation of tricalcium silicate and dicalcium silicate. The feasibility of the direct reduction of iron to elemental iron and preparation of cementing materials by roasting of gangue components under the studied thermodynamic conditions was discussed. Different temperature control strategies were used to verify the reaction coupling test. The results showed that zero-valent iron could be produced by roasting and reducing hematite under certain experimental conditions, and cementing materials, such as tricalcium silicate and dicalcium silicate, could be produced simultaneously by reacting the gangue components with CaO. Fe2O3 exerted an adverse effect on the formation of tricalcium silicate, and sufficient reduction of the iron was a precondition for the formation and stability of tricalcium silicate.

When applied for desulfurization in the coal combustion process, traditional sulfur sorbents have very low sorbent utilization and normally have a negative effect on combustion efficiency. A new type of sulfur sorbent, calcium peroxide (CaO2), synthesized from natural limestone, is proposed and its effects on desulfurization and combustion efficiency are investigated in this paper. The first series of experiments were carried out in a drop tube furnace (DTF). The results showed that CaO2 captured more sulfur than limestone and improved the burnout behavior of coal. To investigate the sulfur removal efficiency of CaO2, the second experiment was carried out in a fixed bed. The results indicated that the sulfur capture capability of CaO2 definitely exceeds that of limestone no matter whether in a low or high temperature range. Moreover, the combustion behavior of coal with and without CaO2 addition was investigated using thermogravity (TG) and differential scanning calorimetric (DSC) analysis. An inc...

This paper presents a new method to calculate accurately the composition of the mineralogical phase in iron ore sinter, especially the minor phases. This model is based on the combined model of gray-level distribution for a multi-phase system. The composition of the mineralogical phase is calculated by minimizing the difference between the theoretical gray-level histogram and the actual gray-level histogram of a micrograph of the iron ore sinter. A genetic algorithm and an improved genetic algorithm are introduced to solve this extreme value problem. Suitable parameters for the algorithm were determined by comparing the solutions for each of several cases. The example provided demonstrates that this model is valid, especially for the minor phases, and the solution is credible.