Coal Charge Research Articles

Contribution to the study of carbon deposition in coke ovens

The formation of carbon deposits from coal pyrolysis in a two-stage reactor has been studied for several cracking temperatures from 850 to 1000 °C. The weight of the carbon deposit was monitored continuously during pyrolysis by a thermogravimetric balance. Four successive periods of deposition can be distinguished: 1. (1) no weight uptake; 2. (2) a slow increase in weight; 3. (3) a sharp increase in weight; 4. (4) constant weight. From the data, three distinct deposition rates have been calculated at different cracking temperatures: germination rate, growth rate and overall deposition rate. The general tendency is an increase in all three deposition rates with temperature. Scanning electron and polarized light micrographs of these deposits show that they have a laminar structure. There are two (sometimes three) cone layers, the first being formed during the liberation of water contained in the coal charge, indicating that water plays the role of an inhibitor in the formation of carbon deposits. The structure of the deposits is independent of the temperature at which deposition takes place. The mechanism of this carbon formation is discussed.

Effect of preheating in carbonization on the nature of resultant coal tars and pitches

The tars and resultant pitches produced by normal (wet) and preheated carbonization of a high-volatile bituminous coal in a semi-industrial scale coke oven have been compared using a combination of liquid chromatographic (LC) and nuclear magnetic resonance (NMR) spectroscopic methods. The toluene-soluble (TS) and quinoline- (QI) and toluene-insoluble (TI) fractions were selected to assess the differences in composition. HPLC revealed that preheating gave rise to tars containing lower proportions of substituted polynuclear aromatic compounds (PACs) than those produced from the wet coal charge. Pitches derived from the tars obtained with preheating contain more higher molecular weight species as reflected in the higher QI, TI, and asphaltene contents, together with a higher proportion of peri-condensed PACs in the TS fractions

Analysis of steam flow in coke oven chamber by test coke ovens and a two-dimensional mathematical model.

The deviation in the carbonization rate in the coke oven chamber has been investigated with the use of test coke ovens and a 2-dimensional mathematical model.In the measurement using a 250 kg test coke oven, in the case of using a wet coal charge, there were several points of delay in the carbonization rate at random times, but in the case of a dry coal charge, there were no points of delay and the carbonization progressed uniformly. It was confirmed that the deviation in the carbonization rate was affected by the moisture content of the charged coal.In order to evaluate flow pattern and heat transfer caused by the steam and the decomposition gas during carbonization, a 2-dimensional gas flow mathematical model was developed. This model consists of mass, energy involving terms of convection and momentum balance equations in both the gas and solid phases. It was confirmed that temperature change, changes in gas pressure and steam flow pattern in a test coke oven with the heating wall at the upper portion were estimated by this model. In the model calculation, the coke fissures and a local distribution of the bulk density affected the steam flow and caused a deviation in the carbonization rate.

Effects of the conditioning of coal charges on the tensile strength and Young's modulus as well as on the structure of semi-coke and coke

To define the mechanical strength and deformability of semi-coke and coke from seam coals and of binary and ternary blends of coals the so-called Brazilian test has been selected. The pore structure of semi-coke and coke, which influences directly the mechanical properties tensile strength and Young's modulus in defined by means of image analysis.

Progress on the Investigation of Coal-Water Slurry Fuel Combustion in a Medium Speed Diesel Engine: Part 2—Preliminary Full Load Test

Full load (186 kW/cyl) operation using CWS fuel at 1050 rpm has been achieved on a single-cylinder GE-7FDL test engine. No major changes in engine parameters were made. With normal inlet air conditions, 3–5 percent pilot diesel fuel, separately injected or stratified into the main coal charge, was used. Inlet air temperature had to be raised about 40°C if no pilot diesel fuel was used. The coal burnout was about 95 percent and the cycle efficiency was comparable to using diesel fuel. The NOx and CO emissions were about 1/2 of those obtained normally with diesel fuel. The maximum heat release rate was higher than diesel fuel operation which resulted in higher maximum cylinder firing pressure. The combustion characteristic and its dependence on some fuel characteristics and inlet air parameters are discussed. Increasing coal burnout while limiting maximum cylinder firing pressure is the main objective of near future studies.

Resins and asphaltenes in sintering petroleum coke

One of the directions in utilization of sintering coke breeze that may be effective is its addition to a coal or coal briquet charge to coke ovens in place of sintering and weakly sintering coals in coal-tar chemical production. For their investigation they took commercial samples of petroleum coke breeze (0-25 mm) obtained from different types of raw material: (1) a semitar (medium straight-run resid) produced from mixed Perm' and West Siberian crudes by the Industrial Association Permnefteorgsintez; (2) a blend of vacuum resid and tar from cracking atmospheric resid (1:1), from the Krasnovodsk refinery; (3) a blend of cracked tars from processing vacuum resid and thermal gasoil (1:1.5), from the Novo-Ufa refinery. The dependence of the yield of resins and asphaltenes in thermal breakdown of coke as a function of the calcination temperature and the coke size distribution was investigated with continuous heating (2-4/sup 0/C/min) and isothermal (high-speed) heating.

Laboratory coal carbonization oven

A laboratory coal carbonization oven has been described which simulates the carbonization of coal in a commercial slot-type oven. Essentially a cylinder of packed, crushed coal is inserted at a controlled rate into a long furnace so that a plastic layer moves progressively along the cylinder. Widely varying coal charges and carbonization conditions can be employed. The tensile strength and pore structural data of the cokes produced under standard conditions lie within the range of values obtained for commercial cokes.

Coke reactivity: Effect of Fe 2O 3 and K 2CO 3 addition to the coal charge before carbonization

Six individual coals and one blended metallurgical coal were used in this investigation, and two additives, Fe 2O 3 (up to 1%) and K 2CO 3 (0.5%), were added to each coal before carbonization. Results showed that the additives strongly increase CRI (coke reactivity index) and decrease CSR (coke strength after reaction) of each coke, but there are no significant changes in coke microstructure.

Preliminary studies of the relation between the carbon texture and the strength of metallurgical coke

Preliminary attempts to relate the carbon texture to the tensile strength of metallurgical cokes are described. Two series of cokes made by carbonizing blended coal charges in pilot scale ovens were examined. The diametral compression test was used to determine the tensile strength of the cokes and the composition of the coke carbon was measured by applying a point-counting technique to the examination of atomic-oxygen etched surfaces. The strengths and textural compositions could be related by a single equation derived by multi-linear regression analysis.

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. M 40 and M 10 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.

石炭および石油ピッチの物性と付着カーボン量の関係

The deposition of carbon on the chamber wall brings many prob-lems to the coke oven operation. In the present paper the amounts of carbon deposi-tion of 24 coals and petroleum pitches were determined by the weight increase of alumina ball in the secondary pyrolitic furnace above the coking furnace with 300g coal charge. The factor affecting the carbon deposition was studied and the following results were obtained.(1) The amounts of carbon deposition of coals and petroleum pitches could not be explained by quantity of volatile matter alone, but proportional to the multi-plied products of that and quality parameter as indicated by carbon contents in volatile matter except CO and CO2.(2) The main source of carbon deposition in volatile matter was considered to be tar, but partially formed from hydrocarbon gas.(3) When coal and petroleum pitch was blended, a similar value of carbon depo-sition was obtained with that calculated from each coal and petroleum pitch.

Co-carbonization of selected American coals with commercial additives

Because of the short supply of high-quality coking coals in certain areas of the world, many methods of improving the coking characteristics of poorly coking or noncoking coals have been examined as alternatives to importing more expensive, better quality coals. Co-carbonization, or the addition of coal-derived or petroleum-derived materials to the coal charge prior to carbonization, has been used on a commercial basis in the Japanese coking industry. These additives have been used in both solid and liquid form as binders in coal briquettes or as direct additions to the coal blend. In this study three different coal lithotypes were sampled from each of three United States bituminous coal seams: (1) a marginally coking high-volatile B-rank Illinois No. 6 Seam; (2) a highly fluid, good coking quality, high-volatile A-rank Pittsburgh Seam; and (3) a strongly coking low-volatile Blue Creek Seam. Each lithotype sample was carbonized in small-scale (50 g) charges with each of three additives at 0, 2, 5, and 10% additive by weight. The additives included ASP, an asphalt pitch; KRP, a petroleum residue pitch; and SRC, a solvent-refined coal product. The different lithotypes were sampled to examine the effects of coal type as well as rank. A micro-tumbler test was used to give at least a relative coke-strength value for the cokes produced. In addition, all the cokes produced were examined microscopically to determine the effects of co-carbonization on the coke structure. The Illinois No. 6, Pittsburgh, and Blue Creek Seam coals all showed substantial strength increases when co-carbonized with 2, 5, and 10% of each of the three additives, particularly at the 5 and 10% levels. The SRC appears to be the best additive overall for the three ranks of coal, as judged by its ability to combine with the coal to make a higher strength coke. There appear to be no conclusive coke-strength differences among lithotype samples for any of the three coals, probably because of the small scale of the tests and the relatively small differences in inert maceral content among the lithotypes. Five percent by weight of additive appears to be sufficient, if properly blended with the coal charge, to produce higher strength cokes. This is also probably the maximum economically viable level, particularly in the United States coking industry. Two percent is probably the minimum additive level for adequate mixing on a commercial scale.

Investigation of Two-stage, Closed-circuit Crushing System (CPC Process) for Size Control of Coal Charge

The crushing conditions of coal in a closed circuit with a vertical centrifugal screen and the effect of this closed-circuit crushing were studied, and the CPC process was newly proposed. To commercially apply the CPC process, the vertical centrifugal screen was improved for screening a large amount of wet coal, and test operations with an actual coke oven were conducted to examine the effectiveness of this process by the use of the improved screen. The following practical effects of the CPC process were confirmed.(1) As coke quality indices, DI15015and CSR can be respectively improved by 1 to 2 and 1 to 4.(2) The coke breeze yield can be reduced by 2%.(3) About 10% American hard-coking coal can be replaced by Australian soft-coking coal.(4) About 5-10% noncaking and poorly caking coals can be used in the coal blend.The mechanism for the improvement of coke strength by this process was also investigated. Lastly, it is also mentioned that the CPC process can be assessed as basic coal preparation technique, on the basis of the experimental data in comparison with other technologies and the combination of the CPC process with the other pretreating techniques (coking process with briquette-blend and process with the addition of caking substance).

Clay–coal charge transfer and beneficiation by dry mineral removal

Most coal requires upgrading (beneficiation) prior to burning to reduce the amount of ash left after combustion. Normal washing techniques may produce large amounts of clayey sludge requiring expensive storage behind dykes and dams.Dry coal powder, pulverized to 150 μm for burning, is suitable for dry beneficiation using electrostatic techniques. Such a process would eliminate clay sludge. Agitation of the powdered coal and its mineral wastes results in a charge transfer on contact, the coal becoming positive and the mineral matter negative. Separation in an electrostatic tower produces high quality coal and dry clay mineral waste.Clay minerals form the main component of the ash in most Canadian coals; kaolinite in eastern coals and montmorillonite in western coals. The cumulative amount of charge transfer controls the efficiency of separation. The test results show that the cumulative amount of charge transfer increases with increasing number of contacts, montmorillonite generating four times more charge than kaolinite at a given dry density. Typical values of cumulative charge after 100 contacts on montmorillonite and kaolinite pellets of 1.9 g/cm3 dry density are 0.3 × 10−10 and 0.07 × 10−10 C, respectively.

Size Control of Coal Charge (III)

The CPC-process proposed previously, a technique for pretreating the coal charge of coke ovens, and the effect of combining the CPC-process with the briquette-blend coking process and the addition of caking additives were investigated in order to broaden the possible applications of the CPC-process. The investigation yielded the following results:1) By applying the CPC-process, it was possible to improve the strength, DI15015, of coke even when a high-quality coal charge is used. The other processes cannot produce as great a relative improvement as the CPC-process.2) An excellent composite effect can be expected by combining CPC-process with either of the other processes. Therefore, the CPC-process has been established as a fundamental prerequisite in techniques for pretreating the coal charge for coke ovens.3) The CPC-process is a method which reinforces the structural strength of coke, and cannot be expected to improve the quality of coke carbon. Therefore, it is not reaso-nable to expect an improvement in strength after CO2 reaction through combining this process with other processes.

統計理論のコークス炉装入炭粒度調整技術への応用

For the purpose of obtaining the maximum coke strength by optimum size preparation of coal charge, a mathematical theory is developed, which clarifies the relation between coke strength, inhomogeneity of charge and grain size structure of charge.Inhomogeneity of charge is represented by variance (V) of caking property parameter (X) and of coal rank parameter (Y), and related to observed coke strength (S) by the following equation, S=S+1/2 ∂2S/∂X2 Vxx+∂2S/∂X∂Y Vxy+1/2 ∂2S/∂Y2 Vyywhere S is coke strength of homogeneous charge. Furthermore the mathematical solution is derived for each variance, which is expressed by volume and coking properties of each coal particle.The preliminary analysis of coke strength shows that the second derivatives are always negative. The mathematical solution shows that the variance is effectively lowered by the selective fine crushing of coal.The validity of theory is examined by experiments. For practical purposes, the theoretical equation is approximated based on the experimental results.

Size Control of Coal Charge (II)

In the application of the CPC-Process to commercial ovens, the vertical cylindrical screen was scaled up and improved for wet coal screening. As the result of commercial oven tests, the findings disclosed in the previous report on fundamental research were confirmed and the following merits of the process were realized:(1) improvement of coke strength; DI15015+1-2, CSR (coke strength after CO2 reaction) +1-4, (2) reduction of yield of coke breeze; -2%, (3) 10% of good American hard coking coal could be replaced with Australian soft coking coal, (4) it was possible to use 5-10% non or poor caking coal in the coal charge.

Size Control of Coal Charge (I)

The CPC-process proposed previously, a technique for pretreating the coal charge of coke ovens, and the effect of combining the CPC-process with the briquette-blend coking process and the addition of caking additives were investigated in order to broaden the possible applications of the CPC-process. The investigation yielded the following results:1) By applying the CPC-process, it was possible to improve the strength, DI15015, of coke even when a high-quality coal charge is used. The other processes cannot produce as great a relative improvement as the CPC-process.2) An excellent composite effect can be expected by combining CPC-process with either of the other processes. Therefore, the CPC-process has been established as a fundamental prerequisite in techniques for pretreating the coal charge for coke ovens.3) The CPC-process is a method which reinforces the structural strength of coke, and cannot be expected to improve the quality of coke carbon. Therefore, it is not reaso-nable to expect an improvement in strength after CO2 reaction through combining this process with other processes.

Coal Blending Theory-Retrospect and Prospect

This paper summarizes a series of experimental studies conducted by the author et al., on coal blending theory which is a basic condition for the production of coke. A brief history is given of the condition of coking coal supply and past studies undertaken in Japan ranging from the establishment of basic concepts of coal blending in the period immediately after World War II to recent trends in the search for blending standards aiming at the improvement of hot properties of coke. The essential point in coal blending is to obtain uniform, strong-textured coke as a composite material by an optimum combination of various grades of coal having different heating properties, i.e., thermal transformation temperatures. With the above-mentioned in mind, the paper describes the classification of single coal on the basis of the blending theory, the estimation of coke strength, and the theory for size control of coal charge. Finally, the relation among coal blending, coke texture, reactivity with CO2, and strength after the reaction with CO2 is described, indicating the importance of future efforts for the improvement of hot properties of coke by the addition of caking additive.

Coke breakage behaviour in relation to its structure

Coke for blast-furnace use must meet specified quality criteria as defined in terms of its measured breakage characteristics in a revolving flew drum. An assessment of the relationship between coke macrostructure and volumetric (coarse) breakage behaviour is made and the manner in which both features are affected by the coal charge composition is made. In particular, coke degradation studies have revealed a heterogeneous pattern of volumetric breakage in so far as: (i) coke pieces which are extensively fissured fail spontaneously after only a few revolutions in the drum; (ii) coke pieces which are less fissured require an extended treatment in the drum and finally fail in a manner consistent with that of fatigue crack growth induced by repeated impact. This heterogeneity in breakage behaviour was demonstrated in terms of an abrupt change in gradient of the Weibull distribution function for the coke. Heterogeneity may be removed by fully stabilising the coke or by the use of a more energetic test method. The role of fatigue crack growth in coke breakage was studied.