Coking Behavior Research Articles

コークスガス化反応のその場観察と灰分の挙動

コークスガス化反応のその場観察と灰分の挙動

Coke, char and organic waste behaviour in the blast furnace with high injection rate

Blast furnace operation with low coke rate, high amount of auxiliary hydrocarbons and use of nut coke causes a change in coke quality requirements. In particular, not burned in the raceway residues of injected substances (char and ash) can influence the coke behaviour. Therefore combustion efficiency of various organic wastes with and without pulverized coal injection (PCI) and coal char has been investigated under the raceway simulation conditions. Mixing of various substances improves their combustion efficiency. Study on coke gasification by carbon dioxide in the presence of char showed that with the increase of char concentration, coke strength reduction becomes smaller. The reactivity of char with CO 2 is higher than that of coke. Therefore char is consumed preferentially. In presence of injected char, total pore volume in coke and its wear resistance were increased. Coke reactivity and microstructure in the presence of various kinds of ash has been studied. Many ash spheres were observed on the surface of coke matrix and its size was dependent on ash properties.

Coking kinetics on the catalyst during alkylation of fcc off-gas with benzene to ethylbenzene

The production of ethylbenzene from the alkylation of dilute ethylene in fcc off-gases with benzene has been commercialized in China over a newly developed catalyst composed of ZSM-5/ZSM-11 co-crystallized zeolite. The duration of an operation cycle of the commercial catalyst could be as long as 180 days. The conversion of ethylene could attain higher than 95%, while the amount of coke deposited on the catalyst was only about 10 wt.%. Thermogravimetry (TG) was used to study the coking behavior of the catalyst during the alkylation of fcc off-gas with benzene to ethylbenzene. Based on effects of reaction time, reaction temperature, reactants and products on coking during the alkylation process, it is found that the coking rate during the alkylation procedure follows the order: ethylbenzene>ethylene>propylene>benzene for single component, and benzene–ethylene>benzene–propylene for bi-components under the same reaction condition. Furthermore, the coking kinetic equations for benzene–ethylene, benzene–propylene and ethylbenzene were established.

Consistency of Asphaltene Chemical Structures with Pyrolysis and Coking Behavior

Molecular representations of asphaltenes have been proposed from a variety of analytical methods; however, any useful representation must also consider the behavior of these mixtures upon processing. Mild thermal cracking of asphaltenes gives products that have a wide range of boiling points and contain many chemical types, including a range of aromatic, heteroatomic, and aliphatic components. Under severe cracking, the content of aromatic carbon correlates with the yield of solid residue, which can range from 35% to 75%. These process observations are most consistent with representations of asphaltenes as a variety of aromatic groups joined by bridges and substituted by aliphatic groups.

Devolatilisation behaviour of petroleum coke under pulverised fuel combustion conditions

The combustion of petroleum coke in large scale facilities has been limited due to its high sulphur content, but the increasing installation of flue-gas desulphurisation units makes possible the firing of petroleum coke either as a primary fuel or blended with coals. This study focuses on the behaviour of three fuel-grade petroleum cokes of different provenance under pulverised fuel combustion conditions. These cokes, ground and sieved 125–20 μm were fed to a drop tube reactor operating at 1300 °C under different atmospheres to produce chars with different combustion degrees. Char reactivity assessment was performed isothermally in a thermobalance at 550 °C and morphology and optical texture of the chars were studied by optical and scanning electron microscopy. Petroleum coke chars are composed of two main types of particles: (i) porous anisotropic particles that passed through a plastic stage and generated either cenospheric or network-like chars and (ii) angular particles with fine-mosaic optical texture that did not swell and show abundant contraction cleats. The relative proportions of both types of particles were very different in the three petroleum coke chars indicating significant differences in their devolatilisation patterns. The morphology and optical texture of the petroleum coke chars were related to their reactivity (as measured in a thermobalance) and to the characteristics (chemical composition and optical texture) of the parent petroleum cokes, in an attempt to understand the implications of their different devolatilisation behaviours on the combustion efficiency.

Comparison of different catalysts in the membrane-supported dehydrogenation of propane

Dehydrogenation of propane is studied in a high temperature packed bed catalytic membrane reactor with a hydrogen-selective silica membrane. The silica membrane is prepared by a two-step sol–gel process. The removal of hydrogen in the membrane reactor results in higher propane conversion and higher propene yields in comparison to an equivalent fixed-bed reactor. Unfortunately, as a result of the H 2 removal coking is favoured in the membrane reactor. Therefore, the higher propene yields are found only for the first 100–120 min time on stream. However, the lower selectivity of the membrane reactor due to coking is compensated to some extend by a reduced hydrogenolysis. Two commercial dehydrogenation catalysts of different activity were tested in the membrane reactor: Cr 2O 3/Al 2O 3 and Pt–Sn/Al 2O 3. The two catalysts show a different activity, coking, and regeneration behaviour in the membrane-supported propane dehydrogenation.

Thermogravimetric investigations in prediction of coking behaviour and coke properties derived from inertinite rich coals

The coal quality, temperature, pressure, heating rate, various processes and reactor type affect coking behaviour of coal and resulting coke properties. Several petrographic and chemical methods were proposed earlier for prediction of coking behaviour of coals. Inertinite rich coal samples ( I mmf>30 vol%) having different petrographic compositions were selected for thermogravimetric investigations (DTA, DTG and TGA) and their coking behaviour was studied. The petrographic build up, micro-structural properties (porosity and cell wall thickness) and mechanical strength of the resulted cokes were also investigated. Δ H and Δ H max (the main endothermic area of heat absorption and fast absorbing main endothermic area, respectively) were distinguished in DTA curves. Δ A and Δ A max (the main decomposition area and fast disintegrating main decomposition area) under DTG curves were identified. Δ H max/Δ A max shows good correlation with Roga's indices (RI, caking properties) as well as with petrographic caking ratio (PCR). The coarse mosaic content of cokes seem to depend on LΔ T max/Δ T max (ratio of weight loss during fast decomposing main reaction to temperature difference) under DTG. L mΔ T/Δ T (ratio of weight loss during main decomposing reaction to temperature difference) under DTG exhibits correlation with p 1 (mean pore size) and t 1 (mean cell wall thickness) of cokes. Δ A max/( L mΔ T max) also indicates good relationship with mechanical strength of cokes. ( L mΔ T A− T B)/( L mΔ T) (i.e. ratio of weight loss during main endothermic reaction under DTA to weight loss during main decomposing reaction) appears to have relationship with DD (compactness) of cokes. The course of main endothermic reaction/main decomposition reaction under DTA, DTG and TGA seems to govern coking behaviour and the resulting coke strength, which in turn is controlled by microlithotypes.

Influence of coal blending ratio on the high-temperature behavior of coke

The influence of coal blending ratio on high - temperature behavior of coke has been studied. Theresults showd that it was important for improving coke quality by blending with 10% lean coal under theindustrial blending ratio of Magang. There were some structural and composition differences between thedifferent coal well in the same coal group, this would lead to distinct influence on coke quality.

Deactivation Behavior of Bifunctional Pt/H-Zeolite Catalysts during Cyclopentane Hydroconversion

Cyclopentane hydroconversion was used as a probe reaction to study the coking behavior of selected large-pore zeolites loaded with 0.5% Pt under identical conditions. The zeolites studied, namely, Y zeolite, zeolite beta, mordenite, LTL, and ZSM-12, were also tested at several different Si/Al ratios. The zeolite pore structure was the most important factor determining the deactivation behavior. Zeolites like Y and L that possess large cavities connected to smaller pore openings allow polyaromatic molecules to form and also trap these coke molecules to a great extent, resulting in rapid deactivation. This was confirmed by the analysis of soluble coke, which revealed the presence of large amounts of benzoperylene and coronene. Zeolite beta, which possesses an intersecting three-dimensional pore system, but no large cages, was the most stable. Apart from its pore structure, the excellent stability of the zeolite beta catalysts could also be partly attributed to the electronic state of platinum in the catalyst. The absence of aromatic compounds in the product stream and the aliphatic nature of coke indicated that the platinum in zeolite beta selectively opened the cyclopentane ring and did not dehydrogenate it, preventing the formation of cyclopentadiene that condenses via a Diels–Alder mechanism into polyaromatic coke. Mordenite and ZSM-12 showed reasonably good stability. Interestingly, the soluble coke in mordenite consisted of both polyaromatic and long-chain aliphatic compounds, indicating that the selectivity of the metal function changes with time. The amount of “hard coke” deposited in the zeolites was strongly related to the initial activity of the acid function, with the more active catalysts having a larger amount of coke. However, this trend was not followed in ZSM-12 which showed a shape-selective behavior that restricted the deposition of hard coke to a great extent. Apart from pore structure, variation of the acid site density (Si/Al ratio) affected metal dispersion and metal/acid balance and caused significant differences in the catalytic performance within a particular type of zeolite. However, the nature of the acid sites (Brønsted or Lewis) did not have a significant effect. Catalysts that had Si/Al ratios in the range 15 to 40 showed a minimum in the C1/C3 ratio indicating a good balance between the metallic and acidic functions and showed good time stability.

Quality of selected coal seams from Indiana: implications for carbonization

The chemical properties of two high-volatile bituminous coals, the Danville Coal Member of the Dugger Formation and the Lower Block Coal Member of the Brazil Formation from southern Indiana, were compared to understand the differences in their coking behavior. It was determined that of the two, the Lower Block has better characteristics for coking. Observed factors that contribute to the differences in the coking behavior of the coals include carbon content, organic sulfur content, and oxygen/carbon (O/C) ratios. The Lower Block coal has greater carbon content than the Danville coal, leading to a lower O/C ratio, which is more favorable for coking. Organic sulfur content is higher in the Lower Block coal, and a strong correlation was found between organic sulfur and plasticity. The majority of the data for both seams plot in the Type III zone on a van Krevelen diagram, and several samples from the Lower Block coal plot into the Type II zone, suggesting a perhydrous character for those samples. This divergence in properties between the Lower Block and Danville coals may account for the superior coking behavior of the Lower Block coal.

Effects of thermal treatment on the composition and properties of air-blown anthracene oils

Eight parent samples, obtained from a commercial anthracene oil by air-blowing under different conditions, were thermally treated in nitrogen between 350 and 390°C for 3–8 h. Changes in the composition, pyrolysis behaviour and microstructure of the resultant cokes were studied by standard procedures (i.e. elemental analysis, softening point, etc.), Fourier transformed infrared spectroscopy, size exclusion chromatography, thermogravimetric analysis, mass spectrometry and optical microscopy. The results show that thermal treatment causes the removal of hydrogen (mainly aliphatic) and a considerable amount of the oxygenated functionalities created during the air-blowing treatment. As a result, H 2O, CO and CO 2 are removed and new C–C bonds are formed producing larger molecules with a higher degree of condensation. Consequently, the toluene insolubles, softening point and carbon yield of the treated samples substantially increase their values. Thermal treatment also improves the quality of samples as carbon precursors and increases graphitisability and resistance of the derived cokes to oxidation.

コークスの剪断応力による粉化挙動解析

To clarify the generation behavior of fine coke by shear stress in the lower part of blast furnace, coke degradation behavior was investigated using the shear stress tester. Furthermore the theory of tribology was applied to estimate the resistance of wear. The main results obtained are as follows;1) The generation rate of coke fine was basically proportional to sliding distance. Shear conditions (shear rate and vertical stress) had a great effect on coke deterioration behavior.2) The coke fine ratio increased rapidly with the vertical pressure or the decrease of coke strength. It was assumed that plastic deformation of coke surface layer resulted in the expand of real contact area among lump coke.3) The wear resistance of coke could be described by the specific wear rate and breaking energy which were approximately 0.1kJ-1 and 200 kJ/kg respectively for normal metallurgical coke.

高温域における球形コークスの反応にともなう組織変化と粉発生挙動

高温域における球形コークスの反応にともなう組織変化と粉発生挙動

Deactivation of MoS2/Al2O3 in Thiophene Hydrodesulfurization: An Infrared Spectroscopic Analysis by Adsorbed CO

Fourier transform infrared spectroscopy on adsorbed carbon monoxide was used to study the deactivation and rejuvenation of a MoS2/γ-Al2O3 catalyst during hydrodesulfurization (HDS) of thiophene. The study covered several sample pretreatment steps, each resembling a stage in the catalyst life. The number of active sites on the sulfided sample was correlated to the intensity of CO-stretch absorption bands in the infrared spectrum. It was concluded that with increasing HDS time on stream the intensity of bands correlated to CO adsorbed on edge and corner sites decreases, while simultaneously those in the carbon–carbon stretch region (1800–1200 cm−1) increase in intensity. Rejuvenation of a spent catalyst under H2S/H2 at 673 K revealed an increase in the number of gas-phase exposed edge and corner sites of the MoS2 slabs, while concurrently the intensities of bands correlated to carbon–carbon stretch vibrations decreased. Thus, it was concluded that catalyst deactivation was caused by preferential coke deposition on the active sites, which can be removed under H2S/H2. No differences were found in the coking behavior of edge and corner sites.

The anomalous behaviour of properties of seams at the Plessey (M) horizon of the Northumberland and Durham coalfields

The Plessey (M) coal in the Northumberland and Durham coalfields has never had the economic significance of many other coal seams in the region because of its variable thickness and its sporadic occurrence as several thin seams. Where mined, the seam has been long known to display aberrant coking properties compared with coals above and below in the succession. Samples of Plessey coals were analysed from nine offshore boreholes, three opencast prospecting boreholes and three collieries. Vitrinite-reflectance measurements consistently suggest that the seams have an anomalously lower degree of coalification than would be expected from their position in the geological succession. Higher volatile-matter yields from “whole-coal” samples of the Plessey seam, compared with the volatile-matter contents of coals immediately above and below in the succession, confirm this view. The suppressed vitrinite reflectances of the Plessey coals cannot be attributed to particular geothermal conditions and overlying seam lithologies, as other reduced reflectances of certain seams in the Durham coalfield have been in the past. Neither is the suppression caused by the now familiar close association that sometimes occurs between vitrinites and liptinitic macerals. The suppression and the raised volatile-matter yields are more likely to be caused by the original conditions under which the Plessey coals were deposited. The behaviour of the Plessey seam parallels that of the Katharina seam of the Ruhr coalfield, which, at the time of its deposition, was marine-influenced. Although no direct evidence exists that the Plessey seam was similarily affected, the close association of leaves of the Plessey seam in several boreholes with the Harvey Marine Band suggests that marine, near-marine or calcium-rich conditions, possibly aided by a high liptinite content in the marine band, are the most likely explanation for the production of the perhydrous coals. Bitumen exudates would have been generated early during the coalification process, so causing the aberrant properties and unexpectedly strong coking behaviour of the Plessey coals.

99/02731 The influence of pitch quality on anode carbon gasification

The objective of this research is to investigate the gasification, in air and carbon dioxide, of anode carbons used in the aluminium industry, to identify any differences in the behaviour of filler coke and the coke from the coal-tar binder pitch, and to study the effect of pitch quality, especially the type and proportion of quinoline insolubles (QI) and the sodium content, on those processes which contribute to excess anode consumption. [Continues.]

Coke quality and behavior of coke in the blast furnace

In spite of the great progress made by the blast furnace process and the increased use of other forms of thermal and chemical energy sources, significant amounts of coke remain essential for hot metal production. Most blast furnace coke is presently produced in regenerative horizontal chamber ovens. As illustrated by the most recently built coke plants in Europe, the multichamber cokemaking system has reached a very high state of development. This does not prevent to take innovative steps in various directions in order to be able to meet the wishes for an environment friendly coke production in the next century.

Influence of lithium salts on the behaviour of a petroleum coke in organic carbonate solutions

We studied the influence of the anion of lithium salts dissolved in a solution based on propylene carbonate (PC), ethylene carbonate (EC) and dimethyl carbonate (DMC) on the electrochemical properties of a petroleum coke (LONZA) and on the petroleum coke/electrolyte interface. We explored a correlation between the electrochemical properties and the surface chemistry of this coke using infrared spectroscopy, Rutherford backscattering spectrometry, fluoride selective electrode and standard electrochemical techniques. The different techniques show that LiF is a major product of the reduction of LiAsF 6 and LiBF 4 and a minor product of the reduction of LiCF 3SO 3 and LiTFSI. Alkyl carbonates are generated by reductions of the carbonate solvents to an extent which is independent of the anion of the lithium salt. Electrochemical behaviour of the coke is discussed with regard to the composition of the passivating layer. We found better cycling behaviour and greater lithium stability with LiCF 3SO 3 and LiTFSI.

Effect of polymeric additives to coal tar pitch on carbonization behaviour and optical texture of resultant cokes

Homogeneous compositions of coal tar pitch with 10% addition of various polymers were prepared under relatively mild conditions. The effect of a polymer on properties of composition and yield and optical texture of resultant semi-coke was assessed. There was no correlation between softening point or toluene insoluble content and carbonization yield. The addition of cumarone-indene resin, polystyrene, poly(ethylene-terephthalate), polypropylene and polysaccharide resulted in an increase in carbonization yield by 5–3%. Pitch-polymer compositions gave semi-coke of less homogeneous optical texture compared to parent coal tar pitch coke. Poly(vinyl chloride) was the only polymer which clearly improved the development of anisotropy on carbonization. The addition of polypropylene, polysaccharide and butadiene–styrene copolymer contributed to the deterioration of the optical texture.

98/03557 Oxidative semicoking of coal in fluidized bed

Coke Strength after Reaction (CSR) and the concomitant Coke Reactivity Index (CRI) are useful parameters for assessing the behavior of coke in blast furnace. To measure CSR and CRI of the resultant coke from a particular metallurgical coal or blend, a pilot scale oven test for producing appropriate industrial grade coke for measurements is unavoidable. If the quantity of coal sample available is not sufficient for pilot scale oven test, CSR measurement of the resultant coke is normally not possible. CanmetENERGY has developed a procedure for producing coke to allow CSR measurement involving relatively small amounts of coal sample (∼15 kg). The procedure involves producing semi-coke using the Sole Heated Oven in accordance with ASTM standard D2014-97 (2004). In the Sole Heated Oven test the coal sample is heated only from the bottom (the sole) up to 950 °C with the top of the oven charge rising to 500 °C over a period of 6–7 h. The resulting semi-coke is quenched (either wet or dry) and subsequently reheated to 1100 °C under nitrogen for 1 h. CSR and CRI are measured using the coke produced using this procedure. To demonstrate the validity of CSR and CRI measured using this approach, identical coal blends were carbonized concurrently using the CanmetENERGY pilot scale moveable wall oven (460 mm wide, 350 kg capacity) and the procedures mentioned above. CSR and CRI of the cokes produced by these two approaches were compared. Statistical analysis and coke textual analysis were performed to demonstrate the relevance of this novel approach on CSR determination.