浅析焦炭反应性与高炉冶炼

总结了焦炭反应性与高炉冶炼关系的认知历程,阐述了不同反应性焦炭对高炉冶炼过程的影响以及不同反应性焦炭生产的技术手段和研究现状。通过对不同反应性焦炭与高炉冶炼过程适用性的讨论,提出了应根据高炉的冶炼条件和矿石的还原性能来规定适宜的焦炭反应性。     

Influence of coal preparation and coking conditions on coke reactivity

The influence of various technological factors on the high-temperature properties of coke is investigated. It is found that factors facilitating an orderly organic structure of the coke (fine grinding and compaction of the batch, increased conditioning of the coke, dry slaking, the introduction of lubricant additives in the batch) reduce the reactivity of the coke; by contrast, introducing coke fines, intermediate product, and red mud in the batch increases the reactivity.     

Effect of pore diffusion on reactivity of lump coke

The gasification of fine-grained and lump coke in CO₂ atmosphere was measured in a laboratory reactor. Owing to the effect of pore diffusion, the reactivity of lump coke at 1050 °C was found to be considerably lower than that of fine-grained coke at otherwise the same conditions. The diffusion effect is more significant for cokes produced by a stamping method than for cokes from top charges. To express the gasification of lump coke, a simplified mathematical model considering the effect of pore diffusion on gasification rate was adopted. Kinetic parameters were determined from experiments with fine-grained coke, while effective diffusivity was evaluated from experiments with a single coke particle. The model fits experimental data of lump coke well. The relation between reactivity and textural characteristics was also examined: the correlation between effective diffusivity and the fraction of largest pore volume was found.     

碳溶反应温度对高反应性焦炭热态性能的影响

以钢渣为催化剂添加至焦煤中制备高反应性焦炭,研究碳溶反应温度对焦炭热态性能的影响及焦炭反应后的结构变化。结果表明,添加钢渣后,焦炭的反应性提高;随着碳溶反应温度的升高,焦炭的反应性呈线性增加,而反应后强度先缓慢降低然后迅速劣化;焦炭反应后的比表面积先增大而后减小。     

Influence of the reactivity of coke on blast-furnace performance

The cold strength M ₂₅₍₄₀₎ and M ₁₀ of the coke determines the gas permeability of the batch bed in the blast furnace down to the viscoplastic zone of the ore and the coke windows in that zone. The hot characteristics CRI and CSR determine the mechanical strength of the coke in the lower part of the furnace batch, in and below the viscoplastic zone, including the furnace well. It is wrong to regard the hot and cold characteristics as alternatives, since they describe different conditions; the significance of each one should be acknowledged. The coke consumption may be reduced with increase in reactivity of the coke, so long as the high initial strength of the coke is maintained. The minimum permissible reactivity of the coke without clogging of the hearth depends on the operating conditions in the specific blast furnace.     

Information content of methods of determining coke reactivity

The reactivity of coke plays an important role in blast-furnace smelting. The reaction of carbon in coke with oxygen generates the heat required for various chemical reactions in the blast furnace. The reaction of carbon in coke with carbon dioxide and water vapor forms carbon monoxide and hydrogen, which reduce the iron and alloying elements from their oxides. As a result of these reactions, the strength of the coke pieces in the blast furnace is reduced, and they break down more as they move in the furnace batch, with consequent decrease in gas permeability of the batch column.     

不同尾气处理方式对焦炭热反应性的影响

研究了3种不同的尾气处理方式对焦炭热反应性和反应后强度的影响,结果表明,尾气在炉盖处大火烧掉时焦炭热反应性最高,反应后强度最低;尾气导出用酒精灯烧掉次之;尾气放散时焦炭的热反应性最低,反应后强度最高。在相同的尾气处理方式下,热电偶冷端温度66℃时焦炭的热反应性高于36℃;热电偶冷端温度36℃和66℃的焦炭热反应后强度规律趋于一致。     

炼焦工艺条件对焦炭反应性和反应后强度的影响

通过40 kg焦炉炼焦实验,研究了加热速率、焦饼终温、焖炉时间、入炉煤堆密度及入炉煤细度等对焦炭的CRI(焦炭反应性)、CSR(反应后强度)的影响。结果表明:为保证焦炭成熟和获得较低的CRI值,较高的CSR值,焦饼终温应控制在1000～1050℃范围内。炼焦时焖炉时间应控制在3 h以上。提高入炉煤堆密度,可显著改善焦炭的热性质。入炉煤细度控制在90%左右时,CRI、CSR值较佳。提高加热速率,特别是粘结阶段的升温速率,有利于改善焦炭的热性质。     

Correlation of reactivity and electrical resistivity of coke

A correlation between the reactivity and electrical resistivity of a series of cokes was determined using cokes prepared from blends of medium- and high-volatile coals. After correcting for the ash yield of the coke and the density of the resistivity specimen, a statistically significant relation between reactivity and resistivity was established. As the resistivity test requires much less time to perform than the reactivity test, it can be considered as an alternative approach to reactivity testing currently performed for quality control purposes.     

典型碱金属、碱土金属对不同变质程度煤焦溶损反应的催化作用

试验研究发现,添加碱金属、碱土金属对低变质程度煤焦反应性的催化作用小于焦煤等中等变质程度煤焦反应性。它们对焦炭溶损反应的催化作用顺序为：K〉Na〉Ca〉Mg,且随着添加量的增加,催化作用越强。随反应时间和典型金属添加量的增加,以及温度的升高,焦炭转化率越大。     

New insights into the reactivity of blast-furnace coke

The factors most responsible for the reactivity of metallurgical coke—the structure of the carbon matrix and the catalytic action of the inorganic components—are considered in the light of new data regarding the relation between CRI and the anisotropy of the reflectance ΔR _o and data regarding the variable composition of the mineral components during the high-temperature reaction of CO₂ with coke. New literature data regarding the transformations of coke samples within special metal baskets in a prototype blast furnace are also discussed.     

Quality comparison of coke nuts

The strength, reactivity, and technical analysis of coke nuts are discussed. Nuts from gross coke contain 20% more of the (19?C25)-mm size class than for blast-furnace siftings. Compared to wet-slaked coke nuts, dry-slaked coke nuts are characterized by higher hot and cold strength, higher carbon content, and reduced reactivity.     

Quality assessment of foundry coke

Possible methods for quality assessment of foundry coke are evaluated with a view to predicting the smelting characteristics and the properties of the cast iron produced. This involves defining what is meant by the quality assessment of foundry coke; a literature review of existing methods of coke assessment; and the identification of possible methods for the quality assessment of foundry coke. Analysis in terms of the macrostructure, the electrical resistance, the structure of the cast iron in a cupola furnace, and the coke consumption indicates that compliance with State Standard GOST 3340-88 does not ensure satisfactory quality of foundry coke. The quality of foundry coke may be assessed in terms of the yield of volatiles, the reactivity, the mean piece size, the macroporosity, and the electrical resistance. The resistance is greatest for samples in the size class 40–60 mm and is least for the size class 60–80 mm. It increases with increase in the moisture, ash, and sulfur content. Quality assessment may be based on the content of <0.1 mm and 0.1–0.2 mm pores in unit length of the coke surface or on the wall thickness of the pores (<0.05 mm, >0.3 mm, and 0.2–0.3 mm), and also on the structural parameters of the cast iron: the shape and size of the graphite inclusions, which depend on the ash content, total sulfur content, and total moisture content in the coke. Voluntary certification may be used for the quality assessment of foundry coke.     

Influence of mass transfer on thermogravimetric analysis of combustion and gasification reactivity of coke

Non-isothermal TG/DTG measurements are widely used to determine kinetic parameters of oxidation and gasification of carbons, e.g. by multi-heating rate methods. Thereby it is important to avoid spurious effects due to diffusion limitations. In this work, TG/DTG experiments with activated carbon were conducted under isothermal and non-isothermal conditions. The agreement of the experimental results with results of simulations based on the intrinsic kinetics, pore diffusion and external diffusion in/to the sample (crucible) is very good. The simulations show that mass transfer has an unwanted influence on TG measurements, if the concentration of the gaseous reactant (O₂ and CO₂) is too low and/or the heating rate is too high. Based on literature data, the simulation was extended to blast furnace coke with a very low reactivity and to highly reactive coke from pyrolysis of miscanthussinensis. The simulations and theoretical considerations lead to a criterion to exclude the influence of mass transfer on TG measurements a priori. This criterion is valid for combustion as well as for gasification with steam or carbon dioxide.     

添加剂对焦粉型焦性能的影响

分析了热压成型及冷压成型方法的优劣。选择增强剂、固化防水剂等添加剂对水玻璃粘合剂进行改性,研究了添加剂对型焦性能的影响。实验结果表明,焦粉成型添加剂加入量为:水玻璃粘合剂12%,增强剂0.2%,固化防水剂0.3%,成型焦球生(干)型焦落下强度、生(干)型焦压缩强度、耐水性、热稳定性、反应活性等性能可满足工业生产的工艺要求。     

Production of coke with ore additives in coke furnaces

Coke with ore additive may be produced from Zarechnaya DG coal (Kuznets Basin) and high-sulfur Zh coal (from Samsonovskaya and Krasnolimanskaya enrichment facilities, Donets Basin), which is of low technological value and is used in small quantities in batch for the production of blast-furnace coke. The ore additive employed is dust from the dry gas purifiers in the production of commercial silicomanganese, manganese-carbonate concentrate, and manganese-oxide concentrate of the first and second kinds. In experimental batches, the content of the ore additive is adjusted in 5% increments over the range 0–15%. On introducing the ore additive in the batch, the corresponding quantity of G coal is removed, with constant content (40%) of Zh coal. Experimental batches are coked in a 5-kg laboratory furnace (designed by Ukrainian Coal-Chemistry Institute). The coke obtained is tested by methods including technical analysis and determination of the electrical resistivity, the reactivity, and the structural and mechanical strength. In the production of highly reactive coke with high electrical resistivity, the best ore additive is 10–15% manganese-oxide concentrate. The coke is suitable for transportation, transfer, sorting, and crushing to the required size.     

Assessing the metallurgical coke produced at OAO NLMK

Up-to-date methods of assessing coal and coke quality have been introduced at OAO NLMK. Industrial coking tests using high-quality Russian and imported coal have been conducted to boost coke quality. Algorithms are proposed for predicting the postreactive strength (CSR) and reactivity (CRI) of coke as a function of the batch characteristics.     

氧化铁对焦炭溶损反应的影响

在井式硅钼棒电炉中对焦炭溶损反应性进行研究,考察了反应条件(CO₂流量、反应时间)并重点研究负载氧化铁对焦炭溶损反应性的影响;通过扫描电子显微镜(SEM)和电子能谱(EDS)对反应前后负载氧化铁的焦炭进行分析,探究氧化铁负载方式对焦炭溶损反应影响差异的原因,并进一步分析比较其影响机理。结果表明:焦炭溶损反应性随CO₂流量和反应时间的增加而增大;以吸附法和添加法负载氧化铁对焦炭溶损反应均有促进作用,氧化铁吸附负载量存在一个饱和点(1%),超过该点后氧化铁吸附负载量对焦炭溶损反应性影响甚微;吸附法负载氧化铁对焦炭溶损反应性的影响大于添加法。SEM分析表明:添加法的部分铁氧化物被焦炭气孔壁基质包裹而无法发挥作用,吸附法的氧化铁均匀分布在焦炭表面使其能提供更多有效催化活性中心;且添加氧化铁时铁氧化物参与成焦,影响焦炭结构从而对焦炭溶损反应产生影响,吸附氧化铁则是影响焦炭溶损反应的催化作用,两种负载方式下氧化铁的影响机理不同。     

Catalytic gasification of metallurgical coke by carbon dioxide using potassium salts

The catalytic gasification of metallurgical coke by carbon dioxide with potassium salts is studied from the view-point of the catalytic activity of the salts, the optical texture of the coke and its reactivity, monitoring weight losses and the detail of topographical change induced in the coke surface by gasification. The activity of the catalyst and the reactivity of the coke were found to be dependent upon the anion of the salt and optical texture of the coke. Potassium metal may be produced in situ in the gasification reactions and has a significant role in the mechanism of catalytic gasification. The reactivity of a coke and its performance in a blast furnace must be associated both with extents of gasification and development of pits and fissures which could promote a weakening of the coke.     

Predicting the reactivity and hot strength of coke on the basis of ash basicity

Models for predicting the reactivity and hot strength of coke are analyzed. The models take account, for example, of the genetic characteristics of the coal and the ash composition. Predictive formulas for CSR and CRI are proposed on the basis of the ash basicity in the coal batch.