Evaluation of coal and its influence on coke quality and the coking process

The evaluation of coal batch is considered, along with its influence on coke quality and the coking properties. The quality of the coal available for coking at OAO Zapadno-Sibirskii Metallurgicheskii Kombinat is declining. Given the shortage of coking coal, coal ranks that are not of equivalent coking and enrichment characteristics are being added to the batch. In some cases, mixtures with energy coals are prepared. The ash content of the batch sent for enrichment is rising, and the concentrate yield is falling. With decrease in the content of bituminous coal in the coking batch, the strength of the coke is declining. Improving the performance of the coke-production and blast-furnace shops depends on access to coal of satisfactory structure and quality.     

Optimal preparation of oxidized coal

The oxidation index is an important characteristic of coal and coal batch, indicating the change in coking properties on oxidation. The coke obtained from coal batch containing poorly clinkering oxidized coal has a higher content of isotropic carbon and a lower content of anisotropic carbon. That explains its increased reactivity and impaired mechanical and postreactive strength. The oxidation on storage is greatest for small coal classes (<0.5 mm). Preliminary removal of <0.5 mm oxidized coal markedly improves the reactivity and also the mechanical and postreactive strength. A method of preparing oxidized coal for coking is proposed: finer grinding (until the content of the ≤1 mm class is 100%). That considerably reduces the influence of the oxidized coal on the quality of the coke produced.     

Technological value of coal used for coking

The technological value of coal used for coking is analyzed, with particular attention to clinkering coal, the coke group, and lean additives, as well as G and GZhO coal. A relation is established between the technological value of the coal components and their permissible content in coking batch so as to produce coke of constant strength (M ₂₅ = 87%). The precision in determining the technological value of coal is assessed.     

Influence of the Crushing of Bituminous Batch on Coke Quality

Laboratory and industrial research confirms that decrease in the clinkering properties of bituminous coal when it is present to excess in the coking batch improves the strength of blast-furnace coke. If coal batch containing >70% bituminous coal is crushed until its content of the ≤3 mm class is 90%, the crushability Π₂₅ may be increased by 1.8%, with decrease in the susceptibility to wear И₁₀ by 0.8%. This behavior may be explained in that increase in the specific surface of the coal particles reduces the fluidity of the plastic mass and hence increases its viscosity. Consequently, the residence time of the gaseous products in the plastic zone increases. That results in the formation of a large quantity high-molecular gas, creating higher expansion pressure. The overall outcome is greater utilization of the destruction products as plasticizers; the formation of additional liquid from the gaseous products within the grains; and improvement in the contact conditions.     

Modifying <Emphasis Type="Italic">CRI</Emphasis> and <Emphasis Type="Italic">CSR</Emphasis> values of coke

The influence of the following factors on the reactivity CRI and hot strength CSR in industrial coking is studied: eliminating bituminous coal from the coal batch; considerably increasing the coking periods; and significantly reducing the ash content of the batch. Batch composition such that the coke quality meets the needs of export customers (including requirements regarding CRI and CSR) is identified. Sharp deterioration in CRI and CSR is seen when the batch includes coal with high ash basicity and coal concentrate that is heavily contaminated with intermediate products.     

Preparation of coking batch

With steady decline in quality of the coal available for coking, particular care must be taken in batch preparation. Correct choice of the degree of coal crushing in accordance with the actual proportions of bituminous and coke-grade coal maintains the petrographic composition of the batch and prevents a predominance of lean components.     

Modification of poorly clinkering coal for use in coking

If coal is modified by the volatile products formed in pyrolysis, high-quality blast-furnace coke may be produced from batch with a smaller proportion of expensive clinkering coal. In such coking, the batch is modified in the coking chamber; its clinkering properties are improved as a result of partial hydrogenation. New parameters are proposed to describe the modification of the batch; the variation in clinkering properties is established as a function of these parameters. The quality of the coke obtained from modified coal batch is assessed. The relationship between coke quality and the batch composition is determined. The formulas obtained may be used to predict coke quality. Tests show that partial hydrogenation improves coke quality     

Producing high-quality coke from blends of domestic and imported coal at PAO Zaporozhkoks

The evolution of quality requirements on blast-furnace coke indicates the need to use low-sulfur imported coal of the required quality. The best performance characteristics of European blast furnaces are noted. At such furnaces, with the injection of pulverized coal, the consumption of low-reactivity blast-furnace coke is 280.9–355.8 kg/t of hot metal. On the basis of the requirements imposed on coal used in the production of low-reactivity, low-sulfur, high-strength coke, an industrial coking method has been developed and tested at PAO Zaporozhkoks on the basis of Ukrainian, Russian, and United States coal of the required quality. The coke produced is tested in blast furnace 5 at PAO Zaporozhstal’. The results show that coke of improved quality may be obtained from batch containing 50% Ukrainian coal, 30% Russian coal, and 15% United States coal at PAO Zaporozhkoks. Thus, in the first 11 months of 2013, the quality of the blast-furnace coke produced was as follows: moisture content 3.6%; ash content 11.0%; sulfur content 0.78%; M ₁₀ = 6.3%; content of the >80 mm class 4.1%; content of the <25 mm class 3.1%; CRI = 31.8%; CSR = 51.9%.     

Influence of the coking properties of coal batch on coke properties

At OAO Zapadno-Sibirskii Metallurgicheskii Kombinat (ZSMK), research is undertaken to improve the optimization of coking batch. The basic approach, proposed by specialists from OAO Nizhne-tagil’skii Metallurgicheskii Kombinat, employs the coefficient K _opt, which characterizes the deviation of the batch from its optimal composition. The coking properties of the OAO ZSMK coal batch over the last few years are analyzed. After laboratory and industrial coking of batch with different K _opt, the strength and reactivity of the resulting coke is investigated. Evaluation of coke-grade coal in terms of its rank according to State Standard GOST 25543-88 proves inadequate, since coal of the same rank may differ markedly in coking properties. A method is established for assessing the optimality of the coal batch at OAO ZSMK.     

Coking properties of coal pitch in coal batch

The coking properties of coal pitch depend significantly on its fractional composition, which determines the set of structural components involved in meso-phase formation. The optimal combination of high-molecular aromatic compounds, polycyclic compounds of intermediate molecular mass, and hydrogen-donor hydroaromatic components corresponds to a ratio of pitch fractions α: β: γ = 1: 2: 2. This is typical of coal pitch with a softening temperature of 75–85°C. Such pitch is the best clinkering additive to coking batch, resulting in the production of coke of maximum strength.     

炼焦单种煤最佳粉碎粒度研究

为研究炼焦煤在不同粒度下的性质,对肥煤、1/3焦煤、焦煤、贫瘦煤进行了不同筛分粒级的煤岩显微组分及煤质分析,进行了单种煤在不同粉碎粒度下的坩埚焦实验,分析了粒度对焦炭冷热态强度的影响。筛分结果表明:随筛分粒级的减小,镜质组含量增加,惰质组含量减少;灰分主要集中在-1 mm的细粒部分与+10 mm的粗粒部分,硫分主要集中在-1 mm的细粒部分,粒度对煤挥发分影响不大,黏结指数在1～5 mm时优于其它粒级。坩埚焦实验表明:肥煤、1/3焦煤、焦煤等强黏结性煤粉碎到1 mm以下时,热态性能劣化;贫瘦煤配入量多时,细粉碎后没有足够的活性物质包裹惰性组分,焦炭强度急剧下降。     

Assessing the value of coking coal in terms of coking properties and genetic compatibility

On the basis of new research by the Sapozhnikov method (State Standard GOST 1186), as well as data on the yield of volatiles (State Standard GOST 6382) and the petrological characteristics, new definitions are proposed in assessing the clinkering and coking of coal for bed coking. Under that proposal, clinkering properties and coking properties would refer exclusively to samples of individual coals; clinkering ability and coking ability would apply to coal blends and coal batch. As is shown, data for the petrographic composition and vitrinite reflection coefficient permit assessment of the genetic compatibility of coal, which may be used as a behavioral characteristic of coal in batch for blast-furnace coke production.     

Elegest coal in coking batch at OAO EVRAZ ZSMK

The coking of batch with different proportions of Elegest coal from the Ulug-Khemsk Basin is investigated in laboratory and production conditions. The mechanical strength of the coke is improved when such coal is used in the batch. At the same time, CSR falls, while CRI rises.     

Determining the coking properties and technological value of coal and coal mixtures

A method is developed for determining the coking properties and technological value of coal from newly identified beds or new sections of existing mines. The coking properties are assessed on the basis of predictions of the strength and reactivity of coke obtained from batch containing coal from single beds and coal blends. The prediction of coke quality is based on the chemical and petrographic characteristics of the coal.     

Technological value of coal. 1. Clinkering coal

The concept of technological value is discussed. On that basis, a method of assessing the technological value of coal is recommended. The technological value of the basic clinkering coal in coking batch (Zh, GZh coal) is assessed. Similar estimates are presented for poorly coking GZhO and Zh coal, with somewhat inferior clinkering properties. Three levels of technological value are identified for clinkering coal: the first level includes Zh and GZh coal from enterprises in the Kuznets and Pechorsk basins; the second includes GZhO coal from the Raspadskaya and Vorgashorskaya mines; and the third includes G coal from the Kirov mine. GZhO and G coal from other enterprises in the Kuznets Basin does not function as clinkering coal.     

Using coke-battery flue gas to dry coal batch before coking

The utilization of heat from coke-battery flue gases and other potential secondary energy resources in drying coal batch prior to coking is considered. The main factors that influence the thermal potential of the flue gases as a drying agent are identified. The reduction in moisture content of the coal batch prior to coking thanks to the coke-battery flue gases is calculated for different battery operating conditions. Technological principles for combining the drying of coal batch with its preparation by selective crushing and pneumomechanical separation are considered.     

Effect of coal soluble constituents on caking property of coal

Three cokemaking bituminous coals were extracted by the CS₂/NMP mixed solvents with different content of NMP, and the effect of the amount and the component of coal soluble constituents on the caking property of the extracted residues of coals were investigated in this study. The CS₂/NMP mixed solvent (1:1 by volume) was found to give the maximal extraction yields for the three coals, and the fat coal gave the highest extraction yield of 78.6% (daf) corresponding to its highest caking index of 101. It was found that for coking coal, when the extraction yield got to the maximum of 25.3% in the 1:1 by volume of CS₂/NMP mixed solvent, the residue extracted still had caking property with the caking index of 19. This means parts of the caking constituents of coal are un-extractible because of covalent bonding or strong associative cross-links. The soluble components extracted by the CS₂/NMP mixed solvent and their effects on the caking indexes of the residues at a similar extraction yield quite differed depending on the NMP content in the mixed solvent. The coal solubles extracted by the CS₂/NMP mixed solvent with NMP less than 50% contained less light constituents with less of oxygen groups. This may lead to the decrease in the caking indexes for the residues obtained at the similar extraction yields compared to those of the CS₂/NMP mixed solvent with NMP more than 50%.     

Oil agglomeration as a pretreatment for coal liquefaction

Laboratory experiments demonstrated that a variety of distillate coal liquefaction recycle oils were satisfactory agents for cleaning Illinois no. 6 bituminous coal by oil agglomeration. Ash rejection up to 41% with 98% organic recovery was attained with conventionally cleaned coal, and ash rejection up to 67% with 90% organic recovery with run-of-mine coal. Agglomerates of > 1 mm average diameter were produced under a variety of conditions. Similar results were obtained in the scaled-up production of 268 kg of agglomerates. Oils with lower hydrogen aromaticities and higher hydrogen contents performed better than more aromatic oils. Fe, Ti and Mg were selectively enriched in the ash of the product coal, while Ca, Si, and Al were selectively rejected. The mineral pyrite was rejected only ≈ 30–40% as extensively as the bulk of the ashforming minerals. The coal cleaned by oil agglomeration performed similarly to the feed coal in batch donor liquefaction tests. In continuous hydroliquefaction tests, run-of-mine coal cleaned by oil agglomeration performed substantially better than coal cleaned to the same ash level by conventional means, because of the selective enrichment of catalytic iron minerals.     

Calculating the relative value of coal in Russian coking-coal markets

In order to improve the pricing of Russian coking coal, a method is proposed for calculating the relative technological value of purchased coking-coal batches. The basic idea is to compare the parameters of optimal coking batch and coking batch that includes the purchased coking-coal concentrate and other coals available to a particular buyer. It is shown that the relative technological value of a particular batch of coking-coal concentrate will depend on the parameters of the other coals included in the coking batch at a particular coke plant.     

Coking theory: Internal stress in the coal batch

The development of local internal stress in the coal batch is analyzed on the basis of recent theoretical and experimental data. Its influence on coke quality is demonstrated. The influence of mineralized rock particles and large hard-to-crush particles of highly metamorphic coal (including petrographically uniform coal) is considered. The results of appropriate preparation of coal batch for coking are described.