The resistivity of carbonaceous reducing agents critically influences the current and thermal distribution in submerged arc furnaces (SAF). A sharp decline in resistivity causes secondary current instability and frequent electrode adjustments, resulting in furnace temperature decline, reaction zone shrinkage, increased energy consumption, and reduced productivity. This study investigated the causes of the significant decline in the resistivity of semi-coke derived from low-rank coal in the SAF by measuring the ambient temperature resistivity of heat-treated samples and analyzing the irreversible physicochemical evolution of the apparent characteristics (volatile matter, bulk density, pore structure) and micro-chemical structure (functional group structure, microcrystalline structure) of semi-coke during the heating process. The results show that the resistivity of semicoke drops sharply between 500 degrees C and 900 degrees C, which is strongly correlated with devolatilization (specifically CO and CO2 release). The decomposition of C-O functional groups is responsible for the differences in the resistivity decrease rates of semi-coke, significantly enhancing carrier mobility by reducing charge scattering centers. Concurrently, the carbon microcrystalline structure undergoes preferential growth, leading to an increase in the microcrystal diameter and an optimization of the stacking mode. The results imply that the resistivity fluctuation of semi-coke can be mitigated by regulating the transformation and extent of such microstructures during the coal pyrolysis process.

Excessive accumulation of unburned char (UBC) in the blast furnace can impair permeability and constrain further increases in the pulverized-coal injection (PCI) rate unless UBC is effectively consumed, primarily through subsequent gasification. Nine high-volatile bituminous coals with comparable properties were rapidly combusted in a drop tube furnace to produce UBCs with different burnout levels. Their thermal conversion and CO2 gasification behaviors were investigated using simultaneous thermal analysis, complemented by pore-structure, microcrystalline, and mineralogical characterization. UBC gasification reactivity showed no direct correlation with parent-coal burnout but remained strongly related to parent-coal reactivity at burnout levels below 80% (R2 > 0.92). Increasing burnout decreased both the specific surface area and aromatic interlayer spacing d002; however, neither parameter showed a consistently positive correlation with UBC gasification reactivity. Instead, Ca-bearing minerals in the UBC ash promoted gasification through low-temperature carbonation followed by high-temperature carbonate decomposition, thereby generating or regenerating catalytically active CaO, while carbonate decomposition may also contribute to local pore development. The associated mass-gain and decomposition features in the TG-DTG-DTA curves reflected the catalytic contribution of discrete Ca-bearing species. As burnout increased, mineral catalysis progressively outweighed the adverse effects of pore deterioration and increasing carbon structural order, ultimately becoming a dominant factor governing UBC gasification reactivity. These findings reveal the coupled effects of parent-coal properties, UBC microstructure, and ash-mineral transformations on the thermal conversion and CO2 gasification reactivity of UBC.

To address the kinetic constraints inherent in the catalytic combustion of pulverized coal injection under low heating-rate conditions within conventional air atmospheres, a drop tube furnace was utilized to simulate the catalytic combustion of pulverized coal (PC). The effects of gas composition, oxygen concentration, the type, and the content of catalysts on the combustion reactivity were systematically analyzed. Furthermore, the structural changes of unburned pulverized coal were also examined. Experimental results indicate that as the oxygen concentration increased from 21% to 79%, compared with the O2/N2 condition, the increment in the burnout rate of PC under the O2/CO2 condition increased from 3% to 23%. After the addition of catalysts, including hematite, metallurgical oil sludge, and light-burnt dolomite (LBD), under the condition of 21% oxygen concentration, the effects of the three catalysts under the O2/CO2 condition were superior to those under the O2/N2 condition. This trend was reversed under the conditions of 38% and 79% oxygen concentrations. In all atmospheres, the three catalysts can enhance the burnout rate of PC. Among them, LBD exhibits the most favorable effect, and there exists an optimal dosage. Mechanistic analysis through scanning electron microscopy, X-ray diffraction, and N2 adsorption-desorption reveals that under 21% O2/79% CO2 conditions, high-concentration CO2 leads to the formation of pores, and additives accelerate the oxidation of C and the gasification of CO2 through oxygen transfer, thereby enhancing the burnout rate of PC.

Low grindability of semicoke is the key factor restraining its large-scale application in boiler power generation, blast furnace injection and other fields. In this paper, the differences of particle size distribution, surface morphology, microstructure and mineral phases of semicoke and anthracite following ball milling are studied. The results indicate that under the same grinding process, more semicoke particles are concentrated in large particle size intervals, whereas anthracite shows a more uniform distribution across different particle size interval. In terms of composition, the enrichment phenomenon of ash and volatiles in anthracite is obvious. Compared to anthracite, semicoke has a rough morphology and developed pore structure. The carbon matrix with disordered microcrystalline structure is prone to be broken up. Mineralogical research indicates that the difficult-to-grind mineral phases significantly influences the grindability of semicoke. Semicoke is characterized by a surface abrasion requires that higher energy consumption, whereas anthracite follows a volume crushing.

Semi-coke prepared by pyrolyzing low-rank coal can be a potential fuel for utilization in blast furnaces (BFs). To investigate the effects of coal properties and pyrolysis conditions on semi-coke characteristics, the properties and structures of low ash-content coal from 20 coal mines in Shenfu coalfield and the semi-coke produced from it were studied. The composition, tar yield, and thermal stability of the coals showed clear differences. Pyrolysis rates are mainly affected by the total hydrogen and oxygen contents of coals. The pyrolysis temperature appropriate for preparing high-performance semi-coke was determined to be close to the initiation of polycondensation reaction. At this temperature, sufficient tar can be obtained, the semi-coke has an appropriate volatile content, well-developed pore structure, and disordered microcrystalline structure. The main factors affecting the combustion reactivity of semi-coke are the C/O ratio of coal and volatile content in semi-coke. A prediction formula of the calorific value of semi-coke is proposed based on the composition of coal and semi-coke. Semi-coke with good combustion reactivity, high calorific value, and stable performance can be produced by controlling pyrolysis conditions. The application of pyrolyzed semi-coke in a BF to replace anthracite for injection showed that BF operation was optimized, and fuel consumption was reduced.

This study investigated the effect of temperature and atmosphere on the grindability of the semicoke prepared via a mid-low temperature pyrolysis of low-rank Shenmu coal, analyzed the variation in its grinding characteristics with the increase of ball grinding duration, and explored the influence mechanism of the pyrolysis conditions on the grindability of semicoke based on the pyrolysis process and semicoke structure evolution. The results show that as the pyrolysis temperature increases (400-700 degrees C), grindability and grinding mechanism of the semicoke change significantly; the grindability first increases and then decreases with the increase of the pyrolysis temperature. As the grinding duration increased, high-Hardgrove grindability index (HGI) semicoke underwent intensive bulk grinding at a specific grinding time. Additionally, the varying contents of the proximate analysis during devolatilization are not the main cause of the varying HGI during pyrolysis. Using thermogravimetric and thermomechanical analyses, the optimal grindability of the semicoke was found to occur at the transition stage of the pyrolysis to pyrocondensation reactions (approximately 600 degrees C). During the transition, the intense pyrolysis reaction led the semicoke to have abundant pores and cracks, a highly disordered chemical structure, and low matrix hardness. The porous semicoke which has high grindability first underwent surface grinding; subsequently, the loose cores were more prone to bulk grinding, whereby the optimal grindability was obtained. HGIs of the semicoke prepared in the reductive atmospheres such as H2, CO and CH4 are lower than that of the semicoke prepared in N2 atmosphere at the same pyrolysis temperature. Moreover, the reductive atmospheres inhibited pore development in the semicoke and made its carbon structure more ordered, which densified the structure and decreased the grindability of the semicoke.

Using semicoke instead of anthracite for pulverized coal injection (PCI) in a blast furnace can greatly reduce the cost of iron making, but the combustion performance of semicoke first needs to be accurately predicted. In this study, the combustion performances of different fuels were compared and analyzed in a drop tube furnace (DTF) and under isothermal and nonisothermal conditions. The results showed that semicoke had a better combustion performance than coal in the DTF. Isothermal combustion provided a more consistent performance evaluation of the fuels because the effect of volatiles was eliminated. Nonisothermal combustion significantly differed from the DTF results because of the influence of volatiles; after the fuels received high-temperature treatment for devolatilization, the combustion performance was consistent with the DTF results. The influencing factors for the fuel combustion performance differed according to the combustion conditions. For the DTF, the burnout rate was correlated with the pore structure and microcrystalline structure, especially the latter. For isothermal combustion, the combustion characteristic parameter and microcrystalline structure d(002) and L-c after high-temperature treatment were strongly correlated. For nonisothermal combustion, the combustion characteristic parameters were strongly correlated with the volatile content. The above results can serve as a reference for evaluating the combustion performance of different fuels in a blast furnace using PCI.

Semi-coke is a product of low-temperature pyrolysis by low-rank coal, with a composition similar to that of anthracite for pulverized coal injection (PCI). Herein, we investigated the differences in grindability and combustibility between semi-coke and anthracite, analyzed the compositional and microstructural characteristics related to the performance of semi-coke, and assessed the impacts on grinding efficiency and blast furnace operation after replacing anthracite for injection with two types of semi-coke. Semi-coke is rich in high-hardness quartz that is tightly bound to the carbon matrix, making the semi-coke particles very hard, with a high Hardgrove grindability index (HGI) and high abrasion index. The addition of semi-coke reduced the grinding efficiency of the mill and afforded large-sized milled particles. The developed pore structure of semi-coke can enhance kinetic diffusion, and semi-coke is less ordered than coal, thereby providing more reactive sites for combustion reactions. These two reasons cause the ignition temperature of semi-coke to be significantly lower than that of coal. The addition of semi-coke increased the PCI ratio, decreased the fuel ratio, improved the permeability of the blast furnace, decreased the sulfur content in pig iron and carbon content in blast furnace dust. The difference in grinding productivity between semi-coke and coal widens as grinding time increases, suggesting that the HGI method may overestimate the actual grindability of semi-coke. The feasibility of reducing the grinding energy by optimizing particle sizes of semi-coke and improving the grindability of semi-coke by using selected pyrolytic coal and adjusting the pyrolysis temperature was proposed.

文章研究了高炉制粉车间在使用哈氏可磨指数为 100 左右的煤种时出现中速磨机排渣口吐料问题.通过对该煤种的哈氏可磨指数、工业分析、制粉产物形态、岩相分析等结果的研究发现,不同批次煤样的变质程度改变造成了煤体硬度的差异.在相同的哈氏可磨指数和工业分析条件下,因高可磨性煤硬度低,在受到垂直方向碾压后易形成饼状形态并在辊缝之间难以翻转,在进一步粉碎过程中又因表面结构差异产生"黏磨"现象,进而造成中速磨机间断性排渣.

可磨性差是制约兰炭在高炉中喷吹应用的关键问题,在调研大样本量工业兰炭的可磨性指数基础上,分别采用SEM、XRF、FTIR、XRD、N2吸附法表征了兰炭的表面形貌、矿物元素、官能团、微晶结构及孔隙结构,探究了热解条件和微观结构对兰炭可磨性指数的影响机制,开展了制备高可磨兰炭的工业试验.结果表明,超过50％的工业兰炭表现出较差的可磨性能(可磨性指数＜52);灰分中ω(Si+Al)/ω(Ca)越小,兰炭可磨性指数越高;灰分中硅和铝主要以氧化物的形式呈现出点状聚集式分布,对可磨表现出明显的抑制作用;钙元素表现出弥散分布的特性,对可磨表现出积极的促进作用.热解过程存在最佳可磨性指数对应的热解温度,但不同煤种的热解温度存在差异.当热解温度低于转变温度时,比表面积和芳香层层间距d002的增大以及颗粒内部的分解、解聚对基质强度的弱化共同促进可磨性指数的提高;当热解温度高于转变温度时,缩聚反应导致的兰炭基质强度增强是可磨性指数降低的主要原因.基硅研究和工业试验研究均表明,以优选原煤作为热解原料煤种并调控其热解条件,可制备出高可磨性且组成稳定、热值较高、燃烧性能优良的高炉喷吹用高性能兰炭.

采用井式炉干馏装置分别对兰炭进行不同温度热处理,并以此模拟兰炭在硅铁炉上部区域下行过程中的状态.利用氮气吸附、拉曼光谱、热重分析等方法研究了不同热处理温度下入炉兰炭的理化结构和性能变化,结合工业实验结果分析兰炭影响炉况的关键环节.结果表明,随热处理温度升高,兰炭比表面积和孔容呈先增大后减小再增大直至稳定的变化规律,碳化学结构中缺陷和无定型结构逐渐转变为有序碳结构,兰炭反应性能变差,电阻率呈阶段性降低.热处理温度大于1600℃后,不同兰炭间的孔隙结构、碳化学结构、反应性能和电阻率性能变化趋于稳定.孔隙结构发达及反应性能较好的兰炭入炉后在料面的过度烧损导致兰炭机械强度恶化和炭耗增加,这是影响不同品质兰炭入炉冶炼效果存在差异的主要因素.

采用热分析仪并借助等转化率的FOW(Flynn-Wall-Ozawa)方法和Malek方法(非等温燃烧)以及模式配合法(等温燃烧)比较研究了喷吹用兰炭和煤粉在非等温燃烧和等温燃烧条件下的燃烧特性、动力学参数和机理模型,其中非等温燃烧实验是在50 mL/min的空气气氛下,在升温速率分别为5℃/min,10℃/min,20℃/min条件下升温至900℃;等温燃烧实验需预先将炉腔抽成真空,随后通入Ar,在分别达到预设温度1000℃,1100℃,1200℃之后切换成空气进行反应.结果表明:非等温燃烧与等温燃烧条件下两者的燃烧反应性顺序存在显著差异,非等温燃烧条件下燃烧反应性与挥发分含量关系密切,表现为挥发分含量高的Char 1#和Coal 1#的燃烧性能较好;等温燃烧条件下兰炭粉的燃烧性能优于喷吹煤粉的燃烧性能;非等温燃烧过程的机理模型较为复杂,反应级数与扩散模型能较好地模拟燃烧动力学过程;等温燃烧过程兰炭和喷吹煤粉均以扩散为动力学模型,传质成为燃烧过程的控速环节;等温燃烧表观活化能明显小于非等温燃烧表观活化能,表明以扩散为限制性环节的等温燃烧过程更容易发生;整体上看,兰炭燃烧反应的活化能普遍低于喷吹煤粉燃烧反应的活化能.

利用煤焦显微分析系统测定了不同温度热解兰炭、纯工业兰炭及其所用原煤的反射率分布,并进行了兰炭掺煤实验.结果表明,通过镜质组随机反射率分布可辨别兰炭中掺混煤粉情况.通过测定兰炭的镜质组反射率分布区间可以判断兰炭的热解程度均匀性,分布区间越大,热解程度越不均匀.