Statistical analyses and prediction of coking properties of coal

Using regression analyses between the properties of coals and the strengths of their cokes several significant correlations are derived, which are useful to evaluate coals in the making of metallurgical coke. Slight but significant modification was necessary for their application to coal blends. For example, plasticities of the coal blends required a different equation from that derived for the single coals. The region of high coke-strength in the diagram of volatile matter vs. total dilatation was expanded considerably towards coals of lower caking properties by blending of coals, suggesting that the blending may serve to increase the coking properties of component coals. The coke strength, especially after the gasification was found to increase with the increasing inert maceral content in the parent coals up to 30 wt %. The high level of strength was maintained even above 35 wt % of inert content.     

Correlation of microstrength and industrial drum strength indices of metallurgical cokes

Correlations between microstrength and industrial drum strength indices of metallurgical cokes were obtained using a 230 kg coke oven. Twelve coking coals from different countries, and ranging in ASTM rank from hvA to Iv bituminous, were carbonized singly and in blends. Microstrength, JIS Drum and ASTM Drum tests were performed on the cokes produced. The results indicated that the relationship between the Dl¹⁵⁰₁₅ index and microstrength was non-linear. Correlation coefficients increased when highly fluid US hvA bituminous coals were excluded. The relationship between ASTM hardness and microstrength was less defined. Results of this study indicate that thermoplasticity is an important consideration when correlating microstrengths with industrial drum strengths.     

Modification of sub-bituminous coal by steam treatment: Caking and coking properties

A Chinese sub-bituminous Shenfu (SF) coal was steam treated under atmospheric pressure and the caking and coking properties of the treated coals were evaluated by caking indexes (G_RI) and crucible coking characterizations. The results show that steam treatment can obviously increase the G_RI of SF coal. When the steam treated coals were used in the coal blends instead of SF raw coal, the micro-strength index (MSI) and particle coke strength after reaction (PSR) of the coke increased, and particle coke reactivity index (PRI) decreased, which are beneficial for metallurgical coke to increase the gas permeability in blast furnace. The quality of the coke obtained from 8% of 200 °C steam treated SF coal in coal blends gets to that of the coke obtained from the standard coal blends, in which there was no SF coal addition in the coal blends. The removal of oxygen groups, especially hydroxyl group thus favoring the breakage of the coal macromolecules and allowing the treated coal formation of much more amount of hydrocarbons, may be responsible for the modified results. The mechanism of the steam treatment was proposed based on the elemental analysis, thermo gravimetric (TG) and FTIR spectrometer characterizations of the steam treated coal.     

Gas permeability and mechanical properties of polystyrene–polypropylene blends

Permeability to water vapor and oxygen, elastic modulus, tensile strength, and impact strength of polystyrene–polypropylene and high-impact polystyrene–polypropylene blends were determined as functions of blend composition and morphology. Three types of styrene–butadiene block copolymers were tested as compatibilizers and found to improve mechanical properties of blends. The experimental data on permeability and modulus were compared with the predictions for the studied binary and ternary blends. The predictive scheme employs a two-parameter equivalent box model and the data on phase continuity of constituents calculated using general equations derived from percolation theory. Blends with decreased permeability and plausible mechanical properties were proposed with regard to intended applications in food packaging. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 69: 2615–2623, 1998     

Oil-cum-gas-fired experimental coke oven developed at CFRI and the correlation studies of its coke with commercial oven coke

Assessment of the coking behaviour of coals and blends by conducting coking tests in experimental coke ovens still continues to be the most reliable method and is extensively used all over the world. The oil-cum-gas fired experimental coke oven developed at CFRI has a coal charging capacity of 1100 kg and simulates industrial carbonising conditions. The oven is capable of intermittent operation and can be brought up to working temperature within 36 hours.Correlation studies of coke quality were carried out by conducting a series of coking tests on the same blend, carbonised under similar conditions in the CFRI experimental coke oven and the commercial coke ovens of Bokaro Steel Plant. The study has revealed that the physical strength of the CFRI oven coke compares favourably with the Bokaro oven coke. M₄₀ and M₁₀ indices of the commercial oven coke can be predicted fairly accurately from the results of CFRI oven coke.T-tests performed on the shatter results showed that at 5% probability level there was no significant variation between the shatter indices of both cokes. The quality of the gas produced from the CFRI test oven was very similar to that of the gas produced from the Bokaro ovens.     

Comparison of the associative structure of two different types of rich coals and their coking properties

Solvent extractions of two different types of Chinese rich coals i.e. Aiweiergou coal (AG) and Zaozhuang coal (ZZ) using the mixed solvent of carbon disulfide/N-methyl-2-pyrrolidinone (CS₂/NMP) with different mixing ratios were carried out and the caking indexes of the extracted residues were measured. It was found that the extracted residues from the two types of coals showed different changing tendencies of the caking indexes with the extraction yield. When the extraction yield attained about 50% for ZZ coal, the extracted residue had no caking property. However for AG coal, when the extraction yield reached the maximum of 63.5%, the corresponding extracted residue still had considerable caking property with the caking index of 25. This difference indicated the different associative structure of the two coals although they are of the same coalification. Hydro-thermal treatment of the two rich coals gave different extract fractionation distributions for the treated coals compared to those of raw coals respectively. The coking property evaluations of the two coals and their hydro-thermally treated ones were carried out in a crucible coking determination. The results showed that the hydro-thermal treatment could greatly improve the micro-strengths of the resulting coke from the two coals, and the improvement was more significant for the more aggregated AG coal. The reactivities of hydro-thermally treated AG coal blends were almost the same as those of raw coal blends. The higher coke reactivities of AG raw coal and its hydro-thermally treated ones than those of ZZ coal might be attributed to its special ash composition.     

Possible CO2 mitigation via addition of charcoal to coking coal blends

Processes involving biomass oxidation are considered to be CO₂ neutral since the replenishing of the biomass by normal growth will remove CO₂ from the atmosphere. Thus the use of charcoal in the production of metallurgical coke, to be used as a reducing agent in the formation of iron, would be a strategy for the reduction of CO₂ in the overall ironmaking process. This paper describes experimental attempts to produce industrial grade coke from coking coal blends to which are added amounts of charcoal up to 10%. Coking experiments were carried out partly in a 30 lb coke oven and partly in a sole heated oven. The influence of blend composition, heating rates and charcoal particle size was investigated. Cokes made using fine charcoal addition (− 60 mesh) were considerably weaker than cokes made from the base blend. This is interpreted to be the effect of the ash constituents in the charcoal which, among other things, contains much higher calcium than the coals used. However, carefully sized fractions of coarse charcoal (− 3/8 + 1/4 in) produced much higher quality coke, possibly the result of a different dispersion of the charcoal mineral components.     

Simultaneous prediction of the modulus and yield strength of binary polymer blends

A new scheme is proposed for the simultaneous prediction of the modulus and yield (or tensile) strength of binary blends, which employs a two-parameter equivalent box model and the data on the continuity of constituents acquired from the percolation theory. Prediction of the elastic modulus in the linear stress-strain region assumes “perfect” interfacial adhesion; at yielding (or breaking), the upper and lower bounds have to be distinguished, those bounds being related, respectively, to the interfacial adhesion sufficient and insufficient for the transmission of the acting stress. The modulus and the upper bound of yield (or tensile) strength are monotonic functions of the blend composition within the interval delimited by the values characterizing the components. The lower bound of strengths passes through a minimum (close to the 50/50 composition) linked to the minimum sum of the continuity parameters of the constituents. Predicted dependences of the modulus and of the yield (or tensile) strength on the blend composition are in a good accord with experimental data selected from literature.     

The strength of industrial cokes: Part 4. The influence of carbonizing conditions on the tensile strength

The objective of this study was to ascertain if the observed differences in strength behaviour of blast-furnace and foundry cokes could be attributed to the different carbonizing conditions used in their production. Two coal blends, one being representative for blast-furnace coke production and the other for foundry coke production, were carbonized in a small-scale test oven using a wide range of heating conditions which included those used in the industrial production of the two types of coke. Coke tensile strengths were determined by the diametrical-compression test and a small-scale drum test was used to derive strength indices comparable to standard micum indices. The tensile strengths and material constants obtained by Weibull statistical analysis, when related to those drum-test indices which assess the resistance of coke to attrition and to corresponding data for equivalent commercial cokes, demonstrated that the cokes fell into two distinct sets according to the coal blend used. It was concluded that changes in coke strength caused by different carbonizing conditions could not account for the different strength behaviour of blast-furnace and foundry cokes. The alternative hypothesis that the nature of the coal blend is the predominant factor is supported by the correlations established for each of the coal blends.     

Pitch and petroleum coke additions to coke oven charges

Several pitch materials and a petroleum coke were added to coke oven charges in an attempt to make good metallurgical coke from Canadian coal of poor coking quality. Coal and petroleum pitches were added to a low fluid western Canadian coal of medium volatile bituminous rank, and the blends coked in a technical-scale moveable wall test oven having a 230-kg charge capacity. Pitches improved coke tumble test indices, the principal coke quality parameter related to blast furnace performance. Varying levels of petroleum coke were added to an eastern Canadian coal of high volatile bituminous rank, and the blends, some partially briquetted, were carbonized in a test oven. Tumble indices of coke from the partially briquetted charges approached an acceptable level. These investigations confirm that petroleum products as well as coal derivative can play a useful part in the production of a metallurgical strength coke from poor or non-coking coals.     

A scanning electron microscope study of fractured and etched metallurgical coke surfaces

The object of this work was to attempt to link more closely coke strength and structure by establishing whether features visible on fracture surfaces could be identified with coke carbon textural constituents revealed either by polarized light microscopy of polished surfaces or by scanning electron microscopy of atomic oxygen-etched surfaces. The cokes used were produced in a laboratory furnace from coals covering the whole range or rank normally encountered in metallurgical coke production in the UK. Fracture surfaces were created by tensile fracture during diametral compression. In all three surfaces examined, the appearance of components derived from reactive coal constituents varied with the rank of the coal carbonized. A clear similarity was evident between features visible in the etched and fracture surfaces. The marked variation of fracture features imply that the textural composition of the coke carbon may make some contribution, as yet unquantified, to the variation in strength among cokes.     

Carbonization of coal blends: mesophase formation and coke properties

Laboratory investigations of strength of cokes from blends of coals incorporating pitch were supported by 7 kg trials. The stronger cokes showed a greater interaction between coal and pitch to produce an interface component of anisotropic mozaics which is relatively resistant to crack propagation. The process whereby coal is transformed into coke includes the formation of a fluid zone in which develop nematic liquid crystals and anisotropic carbon which is an essential component of metallurgical coke. Strength, thermal and oxidation resistance of coke can be discussed in terms of the size and shape of the anisotropic carbon which constitutes the optical texture of pore-wall material of coke. Coals of different rank form cokes with different optical textures. Blending procedures of non-caking, caking and coking coals involve the interactions of components of the blend to form mesophase and optical texture. Petroleum pitches used as additives are effective in modifying the carbonization process because of an ability to participate in hydrogen transfer reactions.     

A three-dimensional numerical study of the combustion of coal blends in blast furnace

The practice of blending coals for pulverized coal combustion is widely used in ironmaking blast furnace. It is desirable to characterize the combustion behaviour of coal blends and their component coals. A three-dimensional numerical model is described to simulate the flow and combustion of binary coal blends under simplified blast furnace conditions. The model is validated against the experimental results from a pilot-scale combustion test rig for a range of conditions, which features an inclined co-axial lance. The overall performance of coal blend and the individual behaviours of their component coals are analysed, with special reference to the influences of particle size and coal type. The synergistic effect of coal blending on overall burnout is examined. The results show that the interactions between component coals, in terms of particle temperature and volatile content, are responsible for the synergistic effect. Such synergistic effect can be optimized by adjusting the blending fraction. The model provides an effective tool for the design of coal blends.     

Influence of gas composition on the reactivity of cokes

The NSC reactivity test is often criticised for not being able to accurately predict the performance of cokes in the blast furnace. One explanation proposed for this inaccuracy is that the gas used in the NSC test, pure carbon dioxide, is different to the gas that coke is exposed to in blast furnaces, which is a complex mixture including carbon monoxide, carbon dioxide and nitrogen. The aim of this work was to see to what extent different cokes behaved differently during the NSC test under different gases.Nine Australian coals, used in coking blends, were selected to cover a wide range of rank, maceral composition and elemental composition of the mineral matter. These coals were coked and their relative reactivities in a series of gas mixtures were compared. The time for the reaction of the coke in a 30% CO₂/70% CO mixture was set to eight hours to give about the same weight loss as two hours exposure to 100% CO₂.The main conclusion of this study was that gas composition (using mixtures of CO, CO₂ and N₂) had little effect on the relative rate of gasification of cokes over a wide compositional range of gas and of coke (although of course the absolute reaction rate decreased with decreasing CO₂ levels). The previous studies that suggested changes in gas composition affect the relative reaction rate of different cokes were misleading because they performed the studies at constant burnoff time (2 h) rather than ensuring the cokes were reacted to about the same weight loss.Thus any differences between the behaviour of cokes in the NSC test and in the blast furnace are not due to differences in gas composition between the two.The CSR value was found to be a combination of strength and reactivity: for the data in this study, CSR was determined by a two-component fit involving CRI and the I600/10 index (the strength of the unreacted coke as measured by the CSR tumble test).     

An approach to blast furnace coke quality prediction

Although coke cold drum mechanical strength has historically been the most relevant coke quality parameter, currently coke reactivity and post-reaction strength (CRI/CSR) are the most important parameters used to assess blast-furnace coke quality. Many models of coke quality prediction have been proposed, most of which are based on coal characteristics and limited to the same coal geographic origin, but as yet there is no universally applicable prediction formula. The present work describes a simple model of coke CRI/CSR prediction based on the assumption that the CSR of a coke produced from a blend of coals can be predicted from the CSR obtained from the cokes of the individual coals through the application of the additivity law. The additivity law was also applied to the coke cold mechanical strength indices derived from the Irsid test, which are widely employed by the European coke industry as complementary coke quality indicators.     

Effects of additions of petroleum coke in coals upon strengths of resultant cokes

Coals of NCB rank 301, 401 and 502 were co-carbonized with pitch-coke breeze pre-carbonized to temperatures between 900–1200 K, in the ratio 9:1. The objective was to provide fundamental information concerning the effect of inert components upon strength of metallurgical coke; these inert components occur naturally in coals and may also be added to coking blends as coke breeze. Polished surfaces of resultant cokes were examined by optical microscopy and fracture surfaces were examined by SEM to investigate the coal-coke/pitch-coke interface for bonding between components and fissure propagation across the interface. Strengths of cokes were measured using a micro-strength apparatus. For three coals, pitch-coke breeze (900 K and highest volatile content) bonded best to the surrounding coal-coke. The interface became increasingly fissured with increasing pre-carbonization temperature of pitch-coke.     

单种煤结焦性能评价与焦炭质量预测

根据11种单种煤的性质,在实验室20kg小焦炉上进行了11种单种煤和8种配煤方案的炼焦实验,并对焦炭进行了筛分组成、冷态强度、焦炭热性质等分析,初步建立了焦炭质量预测模型。实验结果表明:单一的煤质指标与焦炭强度的关系不是很明显,选用煤质多因素指标进行焦炭质量预测,其预测效果较好;单一的煤质指标(Vd、R0max、Ad)与焦炭反应性之间有较好的关系,且焦炭的反应性随反应温度的升高而增大。     

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.     

Bond strength of steel deformed rebars embedded in artificial lightweight aggregate concrete

The recycling of industrial waste such as bottom ash from furnaces is an important issue in construction industry, since it enables reduction in construction cost and has beneficial effect on the environment. In this study, we have investigated the bond characteristics of steel deformed bars embedded in artificial lightweight aggregate concrete which is manufactured from bottom ash. A pullout test was performed on 144 lightweight aggregate concrete specimens to measure the bond strengths. In this test, the parameters included the compressive strength of the concrete and embedment length of rebar. The pullout load vs. slip responses and modes of failure of the specimens were identified during the test. A bond strength equation for lightweight concrete is formulated by performing a regression analysis on the test results and compared with the predictions by the existing equations such as ACI 408, Orangun’s, and Darwin’s. The comparison shows that the existing bond strength equations cannot be directly applied to the design of lightweight concrete structures and the proposed equation is able to provide a more accurate estimation of the bond strength of lightweight concrete than the existing equations.     

Upgrading lignites via thermal reduction with coke-oven gas

Three Turkish lignites of varying rank were processed by using coke-oven gas under various processing conditions. Proximate and ultimate analyses and microscopic investigations with a polarized-reflected light microscope were carried out for all of these samples. Gaseous products were also determined after each process. Blends of processed lignites with coking coals were subjected to dilatation tests and cokes were produced in a laboratory scale coke oven using the same blends. The tensile strengths of the cokes produced were determined. The chemical and physical data showed that there are useful changes in lignite structures upon treatment with coke-oven gas under certain processing conditions. The dilatation and tensile-strength results showed that it would be possible to blend processed lignites with coking coals in significant proportions to produce metallurgical grade cokes.