Coke Blend Research Articles

Interfacial Reactions between Coke/HDPE Blends and High Carbon Ferromanganese Slag

The reduction of MnO in slag by blends of coke with high density polyethylene (HDPE) was investigated by the sessile drop method at 1500°C in this study. The results show improved wettability and extents of reduction are realised with the use of an HDPE/coke blend in this system by comparison to reduction by pure coke, whereby increasing HDPE content resulted in further improvement in extent of reduction and increased wettability. The extensive devolatilisation from HDPE samples is the primary cause for these improvements, whereby the gasified HDPE created both CH4 and H2 reducing gases. Additionally, increased sample porosity allowed for improved wetting, and thus improved reduction capabilities. The dynamic contact angle between the carbon substrate and the slag varied, with HDPE samples ranging between 140°–60°, whilst the coke samples ranged between 160°–120°. The addition of HDPE allowed for the near complete reduction of MnO and partial reduction of SiO2 from the slag with distinct metallic regions of Mn–Si formed in the sample; regions containing pure Si were also found.

Study on reducing and melting behavior of mill scale/petroleum coke blend

Study on reducing and melting behavior of mill scale/petroleum coke blend

A novel technique for assessing the coking potential of coals/coal blends for non-recovery coke making process

In an effort to broaden the scope of coal selection, the authors have developed a novel procedure based on a coefficient, named as Composite Coking Potential (CCP). CCP value assesses the suitability of a coal/coal blend for producing coke of desired quality; measured by the parameter coke strength after reaction (CSR). The coking potential takes into account of various properties of the coals and their proportions in a given coal blend and convert them into a single value. This technique is having advantage since each of these parameters represents different aspects of the coking phenomena along with inter dependence of some of these parameters also exists. This makes the coal selection process extremely difficult and in majority of the cases, decision is taken based on experience.In this investigation, CCP model has been used for selecting the least expensive coal blends which will comply with the minimum coke quality requirements of blast furnace. The study confirms the inter relations between the CCP and the hot strength of coke i.e. CSR. Actual plant data of a non-recovery coke oven have been used for developing and validation of the model. The technique was successfully used in identifying cheaper coals for producing coke with desired quality.

Hydrothermal Treatment of a Sub-bituminous Coal and Its Use in Coking Blends

The demand for metallurgical coke for blast furnaces is forcing the coke-making industry to look for new sources of coking coals. Noncoking coals are attractive for use in the coke-making coal blends, because they are cheaper and more available. In this study, a Chinese sub-bituminous coal with noncaking property was hydrothermally treated in order to modify its caking and coking properties to be used in coke-making coal blends as much as possible. The caking and coking properties of the hydrothermally treated coals were characterized by solvent extraction, caking index (GRI) measurement, and crucible coking determination. The results show that the solvent extraction yield and GRI of the sub-bituminous coal can be greatly increased by hydrothermal treatment at proper conditions and the removal of oxygen functional groups, especially the hydroxyl group, thus dissociating the aggregated structure of coal is responsible for the modification results. Crucible coking determinations suggest that hydrothermal treatment can greatly increase the coke strength and the particle coke strength after reaction toward CO2 and decrease the coke reactivity when the hydrothermally treated coals were used in the coal blends instead of the raw coal. Therefore, hydrothermal treatment is an effective method to modify the caking and coking properties of the sub-bituminous coal.

Interactions of vanadium-rich slags with crucible materials during viscosity measurements

Slag chemistry is important for the assessment of flow behaviour of slags produced during gasification of coal and coal–petroleum coke blends. Slags containing vanadium species react readily with the crucible and spindle materials used for viscosity measurements. Interaction of vanadium-rich slags with various materials has been investigated in order to obtain a better understanding of the impact of containment materials on the resulting slag chemistry and viscosity. The bulk and phase compositions of two petroleum coke slags in Al2O3, Mo, Pt and Ni crucibles produced under different laboratory conditions were analysed, and kinetics of slag composition changes at 1400 °C were determined. Mechanisms of the slag interactions with crucibles are described. They involve exchanging of crucible and slag constituents, formation of interfaces with distinct compositions, and continuously changing phase equilibria in the system. For slag processed in Ni and Pt crucibles, reduction of Fe and Ni from oxide to metallic form occurs and is followed by dissolution into the crucible materials. Viscosity of slags with Mo, Ni and Al2O3 crucibles are determined in the temperature range 1200–1500 °C. Resulting changes in the bulk composition of the processed slag has an impact on the slag viscosity. At given temperatures, viscosities of the slags produced in different crucibles are different. The impact of crucible materials and their applicability in viscosity measurements of high vanadium-containing slags are also discussed in order to define the optimal conditions.

Reduction of FeO in EAF Steelmaking Slag by Blends of Metallurgical Coke and End‐of‐Life Tyre

AbstractThe reduction of FeO‐containing slag by blends of metallurgical coke and end‐of‐life tyres (RT) have been investigated through experiments conducted in a laboratory‐scale horizontal tube furnace. Composite pellets of EAF slag (47.1% FeO) with coke, RT, and blends of coke/RT (in four different proportions) were rapidly heated at 1550°C under high purity argon gas and the off gas was continuously analyzed for CO and CO2using an online infrared (IR) gas analyzer. The extent of reduction after 10 min, level of carburization and desulfurization, and the total amount of CO2 emissions were determined for each carbonaceous reductant. The results indicate that the extent of reduction, level of carburization and desulfurization of the reduced metal are significantly improved when coke is blended with RT. Blending of coke with RT resulted in a decrease in direct CO2 emissions from the reduction reactions.

Combustion of Agricultural Waste and Coke Blends during High Temperature Processes: Effect of Physical, Chemical and Surface Properties

Combustion of Agricultural Waste and Coke Blends during High Temperature Processes: Effect of Physical, Chemical and Surface Properties

The Effect of Biomass on Fluidity Development in Coking Blends Using High-Temperature SAOS Rheometry

The addition of biomass to coking blends has the potential benefits of reducing the amount of expensive coking coals and reducing carbon emissions. However, there is little research in the use of biomass as additive in coking blends. The easily available biomass samples pine wood, sugar beet, and miscanthus have been chosen to study the effect of these additives on the fluidity properties of coal. High-temperature small-amplitude oscillatory-shear (SAOS) rheometry was used to determine the fluidity of the samples as a function of temperature. TGA and solid-state 13C NMR were also used to determine the thermal stability and compositional changes in the samples during pyrolysis. Sugar beet can be added in coking blends up to 5 wt % without altering the viscoelastic properties of the coal, whereas pine wood and miscanthus reduce the fluidity even with 2 wt % additions. No solid–solid interactions were observed in the blends, but there were differences in viscoelastic behavior that were attributed to gas–solid interactions. Fast heating (i.e., 180 °C/min) can facilitate the incorporation of pine wood and miscanthus in coking blends. The use of fast heating increases the fluidity of the coal and preserves the fluid material in the biomass at higher temperatures. As a result, the biomass acts as a regulator of fluid material development in the coal, and the viscoelastic properties of the blend are identical to those of prime coking coals. Although fast heating could also be used to produce good coking blends by combining biomass with high volatile matter, high fluidity coals, the amount of biomass required (>5 wt %) is expected to be detrimental for coke strength.

Recycling Waste Polymers in EAF Steelmaking: Influence of Polymer Composition on Carbon/Slag Interactions

Interactions between blends of metallurgical coke and polymers with EAF slag (30.5% FeO) at 1550°C have been investigated using a sessile drop arrangement to determine the influence the polymer and its chemical composition on carbon/slag interactions. Two polymers, namely polyethylene terephthalate (PET) and polyurethane (PU), were used in this study. The CO emissions during carbon/slag interactions for PET/Coke and PU/Coke blends were lower as compared to corresponding emissions from metallurgical coke. An improvement in slag foaming, as determined by the dynamic changes in the volume of the slag droplet, was observed when PET/Coke and PU/Coke blends were used compared to the coke alone. Relatively greater number of gas bubbles was found to be entrapped in the slag droplet along with reduced iron droplets. Higher level of H2O formation was also seen in the case of PET/Coke and PU/Coke blends as a result of FeO reduction by H2. These results indicate that volatiles (H2 and CH4) released from the polymer/coke blends can influence the interactions between carbon and slag (in addition to reduction reactions by solid carbon). This study shows that a variety of waste polymers can be utilised as a carbon resource in EAF steelmaking processes.

Recycling End-of-Life Polymers in an Electric Arc Furnace Steelmaking Process: Fundamentals of Polymer Reactions with Slag and Metal

Research on the use of waste polymeric materials is one of the solutions for developing environmentally friendly recycling processes for steelmaking. Different polymeric materials [i.e., rubber, high-density polyethylene (HDPE), polyethylene therephtalate (PET), and Bakelite], which have different chemical structures and compositions, were selected for this study as carbon resources. The rapid heating to high temperatures provided during steelmaking will break down the polymeric chains and reactions with liquid slag, enabling gas formation. The dynamic changes in the volume of the slag droplet while in contact with the coke/polymer substrates are measured. Significant levels of gas generation and entrapment are present, leading to an improved performance over coke. Carbon/metal reactions were studied by measuring carbon and sulfur pick-up by liquid metal as well as the formation of reaction products at the metal/carbon interface. The measured carbon pick-up value after 2 min of reaction for metallurgical coke was approximately 0.08 wt %, whereas 100% polymers, such as PET and HDPE, showed an increased value of >2 wt %. The proportion of sulfur pick-up was very similar. The formation of interfacial products, in the case of Bakelite–coke blends, was studied, and the presence of CaCO3 used as a filler was seen to influence the chemical properties of the carbonaceous substrate. This study has established fundamentals of the interaction of waste polymers with slag and metal in the steelmaking process.

Recycling Rubber Tyres and Waste Plastics in EAF Steelmaking

AbstractElectric Arc Furnace (EAF) steelmaking uses different carbon based materials as foaming agents. Depending on cost and availability, anthracite and metallurgical coke are among the conventional injecting materials. Considering the energy and green house gas emissions requirements, alternative carbon sources are put on the spot to replace, at least partially, the conventional materials, i.e. waste materials such as rubber and high density polyethylene (HDPE) plastics may react with gas and slag phases resulting in devolatilization, combustion and iron oxide reduction reactions. The addition of waste tyres and waste plastics in EAF steelmaking has been studied in detail by our groups at UNSW and OneSteel is developing a method for EAFs to use blends of different proportions of rubber/HDPE plastics and coke as a slag foaming agent. Initially, laboratory investigations were carried out to establish the feasibility of carbon and polymer blends as foaming agents. The enhanced slag foaming performance compared to coke was found to be in good accordance with the results obtained in the laboratory indicating an increased slag volume when using polymeric blends. Following the successful installation of materials handling systems at both plants, the use of a rubber and coke blend is no longer considered a trial and is instead standard practice.

Co-gasification performance of coal and petroleum coke blends in a pilot-scale pressurized entrained-flow gasifier

Co-gasification performance of coal and petroleum coke (petcoke) blends in a pilot-scale pressurized entrained-flow gasifier was studied experimentally. Two different coals, including a subbituminous coal (Coal A) and a bituminous coal (Coal B), individually blended with a petcoke in the gasifier were considered. The experimental results suggested that, when the petcoke was mixed with Coal A over 70%, the slagging problem, which could shorten the operational period due to high ash content in the coal, was improved. It was found that increasing O2/C tended to decrease the syngas concentration and better operational conditions of O2/C were between 0.6 and 0.65 Nm3 kg−1. For the blends of Coal B and the petcoke, the slagging problem was encountered no more, as a result of low ash content in both Coal B and the petcoke. The better co-gasification performance could be achieved if the blending ratio of the two fuels was 50%, perhaps resulting from the synergistic effect of the blends. With the aforementioned blending ratio, the optimal condition of O2/C was located at around 0.65 Nm3 kg−1. The co-gasification was also simulated using Aspen Plus. It revealed that the simulation could provide a useful insight into the practical operation of co-gasification. Copyright © 2011 John Wiley & Sons, Ltd.

Reduction of FeO in EAF Steelmaking Slag by Metallurgical Coke and Waste Plastics Blends

In Australia, the use of plastics has increased tremendously over the last few decades, but less than 20% of the waste plastics are recycled. The rest is usually landfilled, which poses major environmental problems. The solution to this problem involves the development of novel environmentally-benign technologies that would utilise these waste materials. This work investigates the reduction of EAF slags (47% FeO) by blends of metallurgical coke with High-Density Polyethylene (HDPE) plastics at 1550°C. The experiments were conducted in a laboratory-scale horizontal tube furnace, and were coupled with off-gas analysis using an infrared gas analyser and a multiple gas chromatographic analyser. The results indicate that the rate of FeO reduction in slags is significantly higher when the coke/plastics blends were used compared to pure coke, with the maximum rate of reduction (Blend 4) being over twice that of coke. Moreover, the CO2 content in the off-gas was observed to decrease (by ~75%) with increase in the polymer content of the blend. Additionally, the degree of carburisation and the removal of sulphur from the metal improved considerably when the coke was blended with plastics. The observed improvements in the rates of reduction, carburisation and desulphurisation are attributed to the reactions of hydrogen evolved from the waste plastics at these high temperatures.

Co-Gasification of Biomass Wastes and Coal−Coke Blends in an Entrained Flow Gasifier: An Experimental Study

An experimental study of entrained flow, air-blown cogasification of biomass and a coal−coke mixture has been performed in order to evaluate the effect of the relative fuel/air ratio (ranging between 2.5 and 7.5), the reaction temperature (ranging between 750 and 1150 °C), and the biomass content in the fuel blend on the producer gas composition and the process performance. Dealcoholized grape marc, a waste coming from the wine industry and with high potential in the south-central regions of Spain, has been chosen as biomass fuel. On the other hand, the coal−coke blend (composed of a low-rank autochthonous coal and a solid residue from refineries) is an abundant fossil fuel which is used in a commercial IGCC power plant. The results obtained show that an increase of the biomass content in the fuel blend upgrades the producer gas quality and improves the cold gas efficiency. Some hints of synergy between biomass and coal−coke have been found, especially at low fuel/air ratios and low reaction temperatures,...

Gasification of biomass wastes in an entrained flow gasifier: Effect of the particle size and the residence time

Experimental tests in an entrained flow gasifier have been carried out in order to evaluate the effect of the biomass particle size and the space residence time on the gasifier performance and the producer gas quality. Three types of biomass fuels (grapevine pruning and sawdust wastes, and marc of grape) and a fossil fuel (a coal–coke blend) have been tested. The results obtained show that a reduction in the fuel particle size leads to a significant improvement in the gasification parameters. The thermochemical characterisation of the resulting char–ash residue shows a sharp increase in the fuel conversion for particles below 1 mm diameter, which could be adequate to be used in conventional entrained flow gasifiers. Significant differences in the thermochemical behaviour of the biomass fuels and the coal–coke blend have been found, especially in the evolution of the H 2/CO ratio with the space time, mainly due to the catalytic effect of the coal–coke ash. The reaction temperature and the space time have a significant effect on the H 2/CO ratio (the relative importance of each of these parameters depending on the temperature), this value being independent of the fuel particle size.

Recycling Plastics as a Resource for Electric Arc Furnace (EAF) Steelmaking: Combustion and Structural Transformations of Metallurgical Coke and Plastic Blends

Recycling end of life products, such as waste tires and waste plastics in iron- and steelmaking permits their use as energy and material resources. The current paper discusses the combustion efficiencies of blends of metallurgical coke (MC) with plastics for electric arc furnace (EAF) steelmaking. Laboratory tests involved the combustion in a drop tube furnace (DTF) at 1473 K of MC premixed with different proportions of plastics, polypropylene (PP), and high-density polyethylene (HDPE) (10−30%) under a 20% O2 and 80% N2 gas mixture. In the tested conditions, coke−plastic blends indicated higher combustion efficiencies compared to coke. The gas-phase reactions appear to be influenced by the amount of volatile matter present in the carbonaceous matrix and its subsequent effect on the structural transformation of the particles because of the release of volatiles. The surface area of the coke−polymeric mixtures before and after combustion was found to be higher than the surface area of coke alone. The residual chars collected after the reaction in the DTF were characterized as a function of pore volumes and surface area of the particles. A previous study has demonstrated the possibility of partially replacing conventional coke in EAF steelmaking with end of life rubber tires. The present paper studies the potential replacement of MC with waste materials, such as PP and HDPE, as auxiliary fuels in EAF steelmaking. A comparison to previously reported combustion efficiencies for rubber blends is also provided.

Non-isothermal combustion behaviour of coal blends in a thermobalance as seen by optical microscopy

Combustion at programmed temperature in a thermobalance is a common test for the rapid assessment of coal combustibility. In this study two series of blends (low rank/medium rank coal-AB and low rank/petroleum coke-AC) with the low rank coal in three different proportions (1/4, 2/4 and 3/4) have been tested. Samples have been ground and sieved to 20–75 μm after blend preparation. The combustion profiles indicated different behaviour for the two series of samples: the AB series showed wide curves with the presence of shoulders whereas the AC series showed two maxima corresponding to the component fuels. The comparison of the calculated and experimental curves indicated different effects of blending on the relevant temperatures and reactivity of the blends. In the AB blend most relevant parameters were similar than expected and only a slight reduction of burnout temperature was observed. In the AC series the difference between calculated and experimental values was large with higher initiation temperatures, lower burnout temperatures and higher reactivity in the experimental curves. This indicates synergistic effects for the combination of subbituminous/petroleum coke blends. In order to visualize the relative combustibility of the coals the reaction was stopped at 50% conversion and the samples were examined through the microscope. The combustion of the particles followed a shrinking core pattern in which the core of the low rank particles remained isotropic whereas anisotropy development was observed in the medium rank coal. The reflectance of the coals increased with increasing the temperature at which the reaction was stopped regardless the rank of the parent coal following a linear trend. The consumption rate of the low rank coal increased with temperature rise.

Micro-finite element modelling of coke blends using X-ray microtomography

X-ray micro-computed tomography (microCT) is a non-destructive method of visualising specimens in three dimensions at the micrometer scale. Finite element analysis (FEA) is a method for approximating the structural response of systems to mechanical loading. The two methods are readily combined in micro-finite element analysis (microFEA). The microCT image, already in the discretized form of voxels, can be directly converted into a finite element mesh allowing materials with complex microstructures to be modelled. In this paper we present an example of microFEA model construction and use in the study of coke, a porous mineral. MicroCT datasets of different coke blends were used to create finite element models. The models were used to examine the material’s structural response to compressive loading by studying the resultant stress distributions and material deformation. MicroFEA can be used to advance our understanding of the relationship between porous materials’ microstructure and their bulk properties.

Influence of the co-firing on the leaching of trace pollutants from coal fly ash

The (co)-firing of low-cost alternative fuels is expected to increase in the forthcoming years in the EU because of the economic and environmental benefits provided by this technology. This study deals with the impact of the different coal/waste fuel ratio of the feed blend on the mineralogy, the chemical composition and especially on the leaching properties of fly ash. Different blends of coal, petroleum coke, sewage sludge, wood pellets, coal tailings and other minor biomass fuels were tested in PCC (pulverised coal combustion) and FBC (fluidized bed combustion) power plants. The co-firing of the studied blends did not drastically modify the mineralogy, bulk composition or the overall leaching of the fly ash obtained. This suggests that the co-firing process using the alternative fuels studied does not entail significant limitations in the re-use or management strategies of fly ash.

Effect of Rapid Preheating on the Coking Behavior of Bituminous Coals: Retrogressive Reactions and Extract Yields

Mechanisms underlying observed changes in the plastic properties and swelling ability of weakly coking coals, induced by rapid heating to 400−450 °C, have been investigated. The enhanced softening would allow the shifting of coke blend compositions toward weakly coking coals. A surge in extractables content was observed at heating rates of >500 °C/s. After rapid heating, 25%−28% more of the mass of the weakly coking coal could be extracted. At these low temperatures (∼400−450 °C), repolymerization rates of solvent-extractables seem to be negligible. Increases in the extractables content that were determined by rapid heating clearly improve coke strengths via the related increase in thermoplasticity. However, when a “prime coking coal” was tested under similar conditions, no measurable effect of heating rate on the extractable contents was observed. A third “coking” coal showed behavior that was intermediate between these two cases. Taken together, the data strongly suggest the sequential occurrence of (i) fast retrogressive recombinations between reactive free radicals formed during thermally induced covalent bond cleavage reactions during the heat-up process, and (ii) slower repolymerization/recombination reactions occurring between the more-stable free radicals, observable at >450 °C. The example of the prime coking coal suggests that more of the reactive free radicals might be stabilized (quenched) by locally available hydrogen, irrespective of the heating rate. Liquefaction in the presence of hydrogen donors shows that high conversions to extractables are possible during slow heating. However, for transitional coals (between weakly coking coal and prime coking coals), pyrolysis yields are clearly sensitive to changes in heating rate. Transitional coals thus seem to be those that are marginally deficient in donatable hydrogen.