Caking Coal Research Articles

Enhancement of Caking Property of Slightly Caking Coal by Addition of Hydrogen Donor

In this study, relation between the amount of transferable hydrogen of coal tar pitch (CP) and fluidity of the slightly caking coal adding CP was discussed in order to enhance fluidity of the slightly caking coal. In particular, additive effects of two constituents (toluene soluble but hexane insoluble; TSHI and pyridine soluble but toluene insoluble; PSTI) separated from solvent extraction of CP were estimated. As a result, an amount of transferable hydrogen of these constituents increased slightly by high temperature (360–420°C) hydrogenation. Fluidity of Enshu coal (slightly caking coal) increased by addition of these hydrogenated constituents (TSHI and PSTI). Because retrogressive reaction among the molecules in Enshu coal was suppressed by hydrogen donation from the increased transferable hydrogen in TSHI or PSTI to the molecules in Enshu coal. Further, additive effect of fluoranthene (FL) was estimated. For all tested coals, maximum fluidity of coal adding hydrogenated FL (HFL) was larger than that adding FL. The difference was large for coals containing much of oxygen. Accordingly, retrogressive reaction among the oxygen containing groups in the coal molecules was suppressed by hydrogen donation from the transferable hydrogen in HFL. Estimating from the polarizing micrographs of cokes from coal adding HFL, it was clarified that thermal plasticity of coal was enhanced by addition of HFL, not by thermal plasticity of HFL itself.

Stamped coal cakes in cokemaking technology: Part 2 – The investigation of cake strength

Coking of coal blends using high volatile coals with poor caking properties to produce a high quality coke for blast furnace application can be achieved by compacting the whole coal blend before the pyrolysis in the so called stamp charge operation. Using stamp charging not only improves the flexibility of the cokemaking plant using cost efficient raw materials, but also increases oven throughput. Therefore, in recent years, densification of coals has been introduced even to coals with good carbonisation properties when heat recovery ovens are used. At the Department for Mechanical Process Engineering and Solids Processing of the Technical University Berlin, the two subprocesses, densification and strengthening during stamping, were theoretically and experimentally investigated. The research work aims on the development of an integrated mathematical model, allowing the calculation of cake density and strength of the coal cake for a given coal blend and as a function of the stamping energy. In the first part of the paper, investigations on the stampability of coal blends were reported. In this paper, the development of a new strength test device for the systematic investigation of mechanical strength of coal compacts produced by stamping is described. Results from compressive strength tests indicate an elastic–plastic behaviour with failure by plastic fracture. Shear test results show similarity to the yield limit description in soil mechanics.

Stamped coal cakes in cokemaking technology: Part 1 – A parameter study on stampability

Coking of coal blends using high volatile coals with poor caking properties to produce a high quality coke for blast furnace application can be achieved by compacting the whole coal blend before pyrolysis in the so called stamp charge operation. Using stamp charging not only improves the flexibility of the coke making plant using cost efficient raw materials, but oven throughput is also increased. Therefore, in recent years, densification of coals has been introduced even to coals with good carbonisation properties when heat recovery ovens are used. At the Department for Mechanical Process Engineering and Solids Processing of the Technical University Berlin, the two subprocesses, densification and strengthening during stamping, were theoretically and experimentally investigated. The research work aims on the development of an integrated mathematical model, allowing the calculation of cake density and strength of the coal cake for a given coal blend depending on the stamping energy. The first part of this paper defines the overall process objectives and presents results from systematic investigations of the effects of several coal properties on the so called stampability as the integral model parameter for compacting. Surface moisture, coal granulometry and mechanical properties have significant influence on the densification. The incorporation of these parameters into the model allows the differentiated calculation of the cake density.

Investigation of co-combustion of coal and olive cake in a bubbling fluidized bed with secondary air injection

In this study, a bubbling fluidized bed of 102 mm inside diameter and 900 mm height was used to burn olive cake and coal mixtures. Tunçbilek lignite coal was used together with olive cake for the co-combustion tests. Combustion performances and emission characteristics of olive cake and coal mixtures were investigated. Various co-combustion tests of coal with olive cake were conducted with mixing ratios of 25%, 50%, and 75% of olive cake by weight in the mixture. Operational parameters (excess air ratio, secondary air injection) were changed and variation of pollutant concentrations and combustion efficiency with these operational parameters were studied. The results were compared with that of the combustion of olive cake and coal. Flue gas concentrations of O 2, CO, SO 2, NO x , and total hydrocarbons (C m H n ) were measured during combustion tests. For the setup used in this study, the optimum operating conditions with respect to NO x and SO 2 emissions were found to be 1.35 for excess air ratio, and 30 L/min for secondary air flowrate for the combustion of 75 wt% olive cake and 25 wt% coal mixture. The highest combustion efficiency of 99.8% was obtained with an excess air ratio of 1.7, secondary air flow rate of 40 L/min for the combustion of 25 wt% olive cake and 75 wt% coal mixture.

Effects of HyperCoal Addition on Coke Strength and Thermoplasticity of Coal Blends

Ashless coal, also known as HyperCoal (HPC), was produced by thermal extraction of three coals of different ranks (Gregory caking coal, Warkworth steam coal, and Pasir subbituminous coal) with 1-me...

Some Fundamental Aspects of Highly Reactive Iron Coke Production

It is important to develop the production and utilization technology of highly reactive coke in order to improve the efficiency of blast furnace reactions. In this study, some fundamental aspects of highly reactive iron coke produced in a coke oven chamber were investigated. First, the effects of catalytic Fe powder addition to coal before carbonization on coke strength were investigated. The addition of Fe powder decreased the coal caking property and hence the resultant coke drum index (DI15015). On the other hand it increased coke reactivity (JIS coke reactivity index and CRI) to a great extent. This means that the caking property of blended coals needs to be adjusted higher to produce iron coke with proper strength and high reactivity. Secondly, it was shown that the iron ore reacts with silica brick at 1200°C in a condition similar to that in a coke oven chamber. The iron ore and silica reacted to produce fayalite (2FeO·SiO2) and the brick was damaged. On the other hand, it was proven that the iron ore does not react with silica brick at 1100°C in the above condition. Based on this fundamental study, iron coke with proper strength and high reactivity was successfully produced in a coke oven chamber on a commercial scale by adjusting the coal blend composition and the coke oven temperature. Furthermore it was revealed that about 70% of iron in iron ore powder added to coal was reduced to metallic iron during carbonization.

被覆造粒炭添加による新コークス製造法の開発

New cokemaking by blending of agglomerated coal particles was developed for making high strength and high reactivity coke. Agglomerated coal particles were produced by coating the slightly caking coal particles with caking coal particles. In the case of conventional cokemaking process, at the high blending ratio of the slightly caking coal, coke reactivity is raised, however, coke strength reduces. Cracks can be easily generated at the interface between coke textures, because the slightly caking coal particles have low fluidity at the carbonization and the semi-coke has high contraction.The slightly caking coal particles (1-5 mm) coated with the caking coal were carbonized in coal blend. From microfocus X ray CT images, the generation of the cracks at the interface between coke textures was not observed. When the -0.5 mm of Ro =1.1% caking coal was used as a coating coal and the slightly caking coal (MF value; 2 ddpm) was used as a central coal, coke strength and coke size were enhanced. At 1373-1773K, the CO2 reaction rate of the coke blended with 20% agglomerated particles was higher than that of coke without adding agglomerated particles.

高反応性フェロコークス製造技術の基礎検討

The development of production and utilization technology of highly reactive coke is significant in order to improve blast furnace reaction efficiency. In this report, some fundamental aspects of highly reactive iron coke produced in a coke oven chamber were investigated. First, the effects of catalytic Fe powder addition to coal before carbonization on coke strength were investigated. The addition of Fe powder decreased coal caking property and hence resultant coke drum index (DI15015). On the other hand it increased coke reactivity (JIS coke reactivity index and CRI) to a great extent. This means that caking property of blended coals needs to be adjusted higher to produce the iron coke with properstrength and high reactivity. Secondly, it was shown that the iron ore reacts with silica brick at 1200°C in a condition similar to that in a cokeoven chamber. The iron ore and silica reacted to produce fayalite (2FeO·SiO2) and the brick was damaged. On the other hand, it was proved that the iron ore does not react with silica brick at 1 100°C in the above condition. Based on this fundamental study, the iron coke with proper strength and high reactivity was successfully produced in coke ovens on a commercial scale by adjusting the coal blend composition and the coke oven temperature. Furthermore it was revealed that about 70% of iron in iron ore powder added to coal was reduced to metallic iron during carbonization in coke ovens.

05/02403 X-ray investigation of transformation in coal organic mass during heating. Part 2. Influence of coal charge density and heating rate on structural transformation in organic mass of poor caking coals

05/02403 X-ray investigation of transformation in coal organic mass during heating. Part 2. Influence of coal charge density and heating rate on structural transformation in organic mass of poor caking coals

Laboratory Scale Investigation to Improve the Productivity of Stamp Charge Coke Oven through Optimisation of Bulk Density of Coal Cake

In the recent past, it was realised that the gross coke yield was going down as a result of lower oven throughput in the stamp charged batteries of Tata Steel. The basic reason for this being the net reduction in the ash content of the coal blend used due to the incorporation of higher percentage of low ash imported coals and reduction in the ash content of captive coals through washing. The coals having higher ash content improves the bulk density, as the specific gravity of ash is higher than that of pure coal. Moreover, the ash components have affinity for water and pure coal repels water, which in case of pure coal, works against the holding together of the blend. Hence, lower the ash content, less is the bulk density of cake under identical stamping energy and lower the bulk density, less is the oven throughput. In order to maximise the oven throughput and productivity, a study was conducted in the laboratory mainly to assess the effect of various blend constituents and their ash content on the bulk density of coal charge. The effect of ash content on the coal cake stability has also been dealt with. This study, in short, is a useful tool for selecting the right type of coals and designing the optimum blend for stamp charging to achieve maximum throughput and productivity.In addition, studies were also carried out to assess the effect of addition of various binders on coal cake stability at lower moisture level which would also help in achieving higher throughput and productivity.

X-ray investigation of transformation in coal organic mass during heating. Part 2. Influence of coal charge density and heating rate on structural transformation in organic mass of poor caking coals

The influence of density and heating rate on the processes occurring during carbonization of low rank and high rank coals was investigated using X-ray technique. X-ray pictures have shown that an increase in charge density has no or little effect on decreasing its volume during carbonization. A rapid heating results in increasing the volume of solid residues obtained after carbonization. The results of X-ray analyses have shown that the increase in charge density tends to increase the quantity of the ordered phase largely due to growth of the crystallites present. During rapid heating processes of crystallite growth also take place, however, the main contribution to the increase in the ordered phase is made by the processes of occurrence and growth of new crystallites.

04/02267 A novel process for stationary hydrogen production: the reformer sponge iron cycle (RESC): Hacker, V. Journal of Power Sources, 2003, 118, (1–2), 311–314

Hot-compaction behaviour of semi-anthracite, low-, medium- and high-volatile caking, oxidized medium-volatile, sub-bituminous and lignite coals was studied under a constant load of 3.45 MPa. Generally, total compaction decreased and initial compaction temperatures increased with increasing coal rank. Initial compaction of the caking coals was noted at temperatures below their Ruhr dilatometer softening temperatures. For the high-volatile sample, this softening temperature was low enough, at about 250 °C, to imply possible thermal breakdown of such coals in preheating processes used before coke-making. The visco-elastic behaviour of coals of different rank over a range of temperature was examined. Densification mechanisms are suggested and the rate-controlling steps are discussed. Devolatilization is an important factor in particle-flow and shrinkage/dilatation mechanisms, as inferred from the similarities of the activation energies associated with these mechanisms and the reported values for devolatilization processes. Non-caking coals exhibit visco-elasticity at temperatures where they are expected to be semi-chars, in contrast with the caking coals.

XRD analysis of carbon stacking structure in coal during heat treatment

The fraction of the stacking structure ( P s) and the average number of aromatic layers ( N ave) in several raw coals were estimated by X-ray diffraction analysis (Standard Analysis of Coal by XRD: STAC-XRD). STAC-XRD is more appropriate for analyzing coal with low crystallinity than the classical XRD analysis method by using the interlayer spacing of aromatic layers ( d 002) and the mean crystallite size along the c axis ( L c ). STAC-XRD was also used to compare the development of the stacking structure in caking coal during heat treatment with that in non-caking coal. After heat treatment at 920 °C, N ave of the caking coals was larger than that of the non-caking coals. The stacking of the aromatic layers in the caking coal temporarily developed at the fluidity stage at 400–440 °C, but in the 440–600 °C range, the release of volatile components partially disordered the stacked layers. The influence of heat-treatment conditions on carbon stacking structure in several kinds of coal was investigated by means of STAC-XRD. The heating rate required for the development of stacking structure in lower-rank coals was slower than that required for higher-rank coals.

04/01196 The effect of plastic addition on coal caking properties during carbonization: Nomura, S. et al. Fuel, 2003, 82, (14), 1775–1782

04/01196 The effect of plastic addition on coal caking properties during carbonization: Nomura, S. et al. Fuel, 2003, 82, (14), 1775–1782

Coal blending theory for dry coal charging process

Nippon Steel has successfully developed dry coal charging processes such as CMC and DAPS for cokemaking. In this report, the fundamental aspects of the coal blending theory for dry coal charging processes are investigated. The investigation has made it clear that even in cases of high coal bulk density due to dry coal charging processes, it is possible to control coking pressure by adjusting the blending ratio of a slightly caking and low rank coal; and it is also possible to produce high quality coke by adjusting the total dilatation of the blended coal at a suitable level.

Some peculiarities of formation mechanism of metallurgical coke from polish coals

The carbonisation of two Polish coals of different caking capacity was studied in a laboratory unit using X-rays. Based on the X-ray pictures of a coal charge being heated with some markers a dynamic pattern was constructed for a coking process of well caking coals. It is shown that a displacement of the non-volatile mass of the coal charge takes place causing a change in the charge volume and forming porosity in the solid residues. On the basis of the marker trajectory during heating it is shown that on coking good caking coals the volume change of the charge proceeds stepwise. A relationship was established between a compaction of the foamy mass in the plastic layer of good caking coals and the thickness of the gas-saturated zone in it. The X-ray data have been confirmed by experimental data using scanning electron microscopy.

Application of Binder in Stamp Charge Coke Making

Successful and sustainable implementation of Stamp Charging Technology in Tata Steel has given it an edge over conventional Top Charging Technology in terms of production of superior quality of Blast Furnace grade coke from a wide range of coal base, even permitting use of inferior coals. But, the stability of stamped coal cake and the additional thermal energy necessary to drive the extra quantity of water (3-4 %), added intentionally to the coal blend to impart requisite coal cake strength, have always been the two haunting issues associated with this technology. This paper describes the role of coal tar pitch, used as a binder to the coal blend that not only imparts required strength and stability to the coal cake even at lower moisture level and thereby, reducing energy consumption, but also improves the rheological properties of coal blend that contributes to the quality of coke produced from inferior coals. This paper also describes the laboratory scale experimentation and its results followed by commercial plant-scale trials that confirmed the R & D findings on the use of coal tar pitch.

The effect of plastic addition on coal caking properties during carbonization ☆

The recycling process of waste plastics using coke ovens is now being studied. The effect of plastic addition on coal caking property was investigated. It was revealed that thermal decomposition products of plastics interacted with bituminous coal during carbonization in coke ovens. The effect of plastic addition on coal caking property varied with types of plastics. The addition of aliphatic polymers such as polyethylene (PE), polypropylene (PP) and poly(vinyl chloride) (PVC) had only a small effect on coal caking property and coke strength and in some cases PE addition increased coke strength. On the other hand, the addition of polystyrene (PS), poly(ethylene terephthalate) (PET) and terephtalic acid (TFA) inhibited coal expansion and fusion, decreased maximum fluidity and total dilatation, and deteriorated the coke strength. These differences were discussed from the viewpoint of the interaction between thermal decomposition products of plastics and hydrogen in coal. It was suggested that the radical formed as a result of PS or PET thermal decomposition abstracted hydrogen from coal, which resulted in the decrease in coal caking property.

Oxidation Behavior and Caking Property of Coal under the Atmosphere at Low Oxygen Concentration.

Eight coals ranging from bituminous coal to brown coal were oxidized in a thermo-balance or a fixed bed reactor using 5 vol% of oxygen at 100-380°C for 10-400 min. The effects of coal particle size, coal rank, oxidation temperature and oxygen concentration on the oxidation behavior of coal were investigated. The caking property, FT-IR spectrum and pyrolysis behavior of sample oxidized were measured. The oxidation behavior strongly depended on the coal rank. The oxidation reaction of highly caking coal was controlled by the rate of internal gaseous diffusion. The caking property of bituminous coal decreases by the oxidation in the oxidative atmosphere of low oxygen concentration of 5 vol%, which corresponds to that in a flue gas. The aliphatic C-H groups in highly caking coals are easily oxidized during oxidation and remained in coal structure as relatively stable forms. The differences in chemical structure and caking property between the exterior part and the central part of oxidized coal particle was investigated. In the case of highly caking coal, the chemical structure and some properties of oxidized coal depends on the position of the coal particle because the mild oxidation reaction of coal proceeds from the exterior part of coal particle.

Study of the mechanism of changes in electrical resistance when heating caking and noncaking coals

Electrical resistivity, permittivity and X-ray structural characteristics are determined for solid residues after thermal destruction of caking and noncaking coals within a temperature range of 200–800 °C. The run of curves for changes of electrical resistivity depending on temperature is explained by analogy with the mechanism for changes of electrical resistance in high-molecular compounds. From peculiarities of structure of solid carbonised residues, it is shown that transport of electrical charges through a sample consists of several steps.