Group chemical composition of coal batch and reactivity of coke. Part 2

The dependence of CRI and CSR on the group chemical composition of coal and coal batch is investigated. This dependence is associated with change in the coal properties in the plastic state.     

Preparation of coal batch for top loading: Experimental research

The packing density is an important parameter of coal batch in the top loading of coke ovens. By careful adjustment of the packing density, the coke quality may be maximized and the productivity of the coke battery may be enhanced. Various methods of compacting coal batch for top loading are considered. The influence of batch preparation on the charge density and quality of the coke produced (CRI and CSR) is assessed.     

Influence of the high content of Zh coal in coking batch on the coke quality

Industrial tests show that the enrichment of coal batch containing more than 70% Zh coal must be increased in order to boost coke strength. However, it makes more sense to replace some of the Zh coal in the batch with an optimal quantity of G coal, and to reduce the degree of crushing, so as to ensure coke quality consistent with blast-furnace requirements (minimum strength M ₂₅ = 90%, M ₁₀ = 6%).     

Relation between the coking properties and quality of coke

On the basis of laboratory data for production batch employed at AO Evraz NTMK and AO Evraz ZSMK, including batch that contains Ulug-Khem coal, a coking characteristic is proposed. This characteristic permits relatively precise prediction of CSR and CRI. Its relation with the quality of coke produced by the classical method and from rammed coal batch is analyzed.     

Optimizing the preparation of coal batch for coking at ChAO Makeevkoks

The expediency of introducing up-to-date systems in the preparation of coal batch for coking at ChAO Makeevkoks is evident if the quality of the coal concentrates employed is assessed in terms of technical, plastometric, petrographic, and granulometric characteristics. Coking trials indicate that separating out the small coal classes prior to final crushing significantly improves the technological characteristics (M ₂₅, M ₁₀) and structural parameters (the Ginzburg abrasive hardness and Gryaznov structural strength) of the blastfurnace coke produced. Introducing hydrocarbon briquets in the coal batch permits the utilization of coking waste without impairing the coke strength.     

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.     

Optimizing the batch composition at OAO Moskoks

A multiple-regression equation is derived to describe the change in hot strength CSR of coke as a function of the coal quality in the batch and the coking parameters. The influence of these parameters on the hot strength of coke is analyzed. A computer program is written for calculating the optimal batch composition on the basis of the available coal.     

Predicting CSR and CRI of coke on the basis of the chemical and petrographic parameters of the coal batch and the coking conditions

A model is developed for predicting the postreactive strength CSR and reactivity CRI of coke. The model adequately reflects the dependence of these characteristics on the chemical and petrographic parameters of the coal batch, taking account of the batch preparation and coking period, as well as the slaking method.     

Influence of batch composition and clinkering properties on the hot strength of coke and blast-furnace operation

The relation of the basic characteristics of coking batch to the hot strength CSR and reactivity CRI of coke is established. The plastic layer of the batch components influences CRI and CSR. The relation of the batch composition to CSR and CRI is determined. When using enrichment batch that contains ～50.4% cokeforming coal, the best results are obtained: CSR = 61.8–62.3% and CRI = 26.4–26.7%.     

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.     

Improving the Preparation of Coking Batch

Currently, the most promising blast-furnace technology involves pulverized-coal injection, and the most promising blast-furnace technology for coke production involves ramming the coal batch before delivery to the coke ovens, so as to ensure high packing density. In classic bed coking, the packing density of the coal batch is also of great importance. In the absence of mechanical methods (such as ramming or partial briquetting), the packing density mainly depends on the ash and moisture content and the degree of crushing of the batch. It follows from industrial tests in the coke plant at PAO ArcelorMittal Krivoy Rog and analysis of the multifactorial correlation of the strength M₂₅ and wear resistance M₁₀ with the packing density of the batch that, with decrease in packing density, the coke strength and wear resistance decline. That increases coke consumption and considerably complicates blast-furnace operation. Since improvement in coke quality entails decreasing the moisture content of the coal batch, a method has been developed for decreasing the moisture content directly in the silo, on the basis of osmosis and vacuum, that permits decrease in the coal’s moisture content to the optimal value, thereby boosting coke quality and improving blast-furnace performance. For example, it has been established that, in the blast-furnace shops at PAO ArcelorMittal Krivoy Rog, 1% decrease in M₁₀ lowers the mean coke consumption by 5.5%. With increase in M₂₅ by 1%, the mean coke consumption falls by 2.1%, on average.     

Optimizing coke production at OAO EVRAZ ZSMK on the basis of the available coal

A model is proposed for predicting the coke strength (M ₄₀ and M ₁₀) and its NSC parameters CSR and CRI on the basis of the chemical and petrographic parameters of the coal. The model takes account of the chemical composition of the ash, the duration of coking, and the coke-slaking technology. On the basis of this model, the technological value of the coal types used at OAO EVRAZ ZSMK is assessed, and the batch composition is optimized to produce coke of elevated quality.     

Influence of the batch’s ash content on coke quality (CRI and CSR)

To permit more precise assessment of Russia’s coal reserves, the influence of the batch’s ash content on the reactivity (CRI) and postreactive strength (CSR) of the coke produced is analyzed.     

Environmental impact of polymer-waste disposal

The laboratory carbonization of well-known polymers to 850°C is studied, in order to determine the benzo[a]pyrene emissions. In carbonization, the exhaust gases from all the polymers contain benzo[a]pyrene in levels far exceeding workplace air standards. The levels are higher for carbon-chain polymers than for heterochain polymers. The utilization of polymer wastes with the coal batch in coke ovens is investigated. It is found that the yield of gas and its content of benzo[a]pyrene are several times higher than for industrial coke ovens. This means that, in the industrial coking of coal batch with added carbon-chain polymers, elevated expansion pressure should be expected in the coke oven, along with increased atmospheric emissions of benzo[a]pyrene.     

Industrial utilization of spent ion-exchange resin in the coke battery

Experimental coking with spent ion-exchange resins as an additive in the coal batch is considered; rammed batch is employed. Both box coking and large-scale coking are considered; the resin content in the batch is 1–5 wt %. The influence of the resins on coke quality is assessed. The coal blend used in industrial coke production is employed. Adding small quantities of resin (<5 wt %) to the batch improves the coke’s cold strength M ₈₀ and M ₄₀, without impairment of CRI and CSR. The quality of the coal tar and the organized gas emission remains unchanged. Hence, spent ion-exchange resins may be recycled by adding small quantities (3%) to the coal batch in coke production.     

Determining the petrographic inhomogeneity of mixed-rank coal

It is shown that the inhomogeneity of coal mixtures (enrichment-plant concentrates) differing in vitrinite reflection coefficient and the content of clinkering components (i.e., in the deviation of these parameters S _R and S _CC ) may only be objectively estimated on the basis of refractogram and petrographic analysis of bed samples of the coal from the mines that supply the enrichment plant. A method and corresponding program for calculating S _R and S _CC is proposed. This program permits correct determination of the petrographic inhomogeneity of coal batch, which is important in evaluating the influence of this factor on coal quality.     

Hydroliquefaction of Yallourn coal catalysed by organotin compounds

The hydroliquefaction of Yallourn coal was investigated in a batch micro autoclave, using halogen free organotin compounds as a catalyst precursor. The catalytic activities of tin compounds were compared as a function of reaction time, initial hydrogen pressure and catalyst concentration. All the organotin compounds studied showed moderate to good catalytic activity in the liquefaction of Yallourn coal. In the presence of 1 wt% of tetra-n-butyl tin (n-Bu₄Sn) as Sn, at 698 K under an initial hydrogen pressure of 5.0 MPa in a non-hydrogen donating solvent, 1-methyl-naphthalene, coal conversion was increased from 36.7% to 78.6% with catalyst. An amount of hydrogen transferred to coal from the gas phase also increased from 0.8 to 1.6 wt% of d.a.f. coal with the 1 wt% of n-Bu₄Sn. An increase in the catalyst concentration of more than 2 wt% did not show any remarkable change in coal conversion or the amount of hydrogen absorbed. After the reaction time of 20 min, coal conversion, yield of asphaltene and yield of oil fraction levelled off. An increase in the initial hydrogen pressure substantially affected the catalytic activity of n-Bu₄Sn. Catalytically active species derived from n-Bu₄Sn seem to activate molecular hydrogen and may transfer hydrogen directly to coal fragment radicals to stabilize them.     

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.     

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.     

Influence of batch properties and its preparation and coking conditions on the characteristics of coke

The influence of batch preparation on the properties of blast-furnace coke is considered for OAO Zapadno-Sibirskii Metallurgicheskii Kombinat. In particular, the influence of the batch composition and its preparation and heating conditions on the strength of blast-furnace coke is investigated. It is found that increasing the moisture content of the batch from 7.3 to 12.6% impairs coke strength: M ₁₀ changes from 7.8 to 9.4%. The mechanical strength is also reduced by increasing the ash content and reducing the piece size of K, OS, and KS coal.