Properties Of Coke Research Articles

Effect of composition of coke deposited in delayed coker furnace tubes on on-line spalling

Delayed coking is one of the most widely used residue upgradation process in crude oil refining where vacuum residue is thermally cracked and converted into distillates and petroleum coke. During heating of vacuum residue in coker furnace, coke is continuously deposited in furnace tubes which is removed at regular intervals by one of the three methods namely (i) pigging, (ii) steam air decoking or (iii) online spalling (OLS). OLS is one of the preferred methods of coke removal from coker furnace tubes. We have noticed very effective as well as “not so effective” OLS in a commercial delayed coker furnace. In present article, the changes in composition and properties of furnace coke during effective and ineffective OLS were systematically analyzed by various analytical tools such as Dilatometer, TGA, HRSEM, SEM-EDX and XRD. Based on these analyses, it was found that inorganic deposits such as iron sulphides and tube metal corrosion products play a major role in failure of OLS. Higher total acid number (TAN) of vacuum residue may be promoting the formation of iron sulfide deposits in furnace tube.

Study Relationship Between the Coal Thermoplastic Factor With Its Organic and Inorganic Properties by the Support Vector Regression Method

ABSTRACT Metallurgical cokes, as fuel for blast furnaces, have certain properties which are directly related to their blended parental coal characters. The maximum fluidity (MF) of coal as an energy index is typically used to estimate the coke properties. In this investigation, Support Vector Regression (SVR), as an intelligent method, has been applied to link characteristics and pyrolysis properties of coal samples with their representative MFs. SVR variable importance measurement (VIM) through a wide range of coal properties indicated that volatile matter (VM) and maximum vitrinite reflectance (Rmax) are the most effective parameters for the MF prediction. The results indicated that low rank coal samples (VM>45% and Rmax>0.7) have log(MF) higher than 14 and high rank ones (VM<35% and Rmax<0.6) have log(MF) less than 4. The evaluation of the SVR model trained with these two selected input variables showed that SVR can predict MF quite accurately where the coefficient of determination (R 2) between actual MF and SVR predicted was 0.86. According to these results, generation of SVR models which can predict and measure variable importance dependently, potentially may be applied for the scaling up of laboratory coal thermoplastic behavior to industrial levels, helping to sustainable development, and satisfactorily estimating coal consumption in the steel-making plants.

Effects of iron compounds on pyrolysis behavior of coals and metallurgical properties of resultant cokes

The utilization of highly reactive and high-strength coke can enhance the efficiency of blast furnace by promoting indirect reduction of iron oxides. Iron compounds, as the main constituent in iron-bearing minerals, have aroused wide interest in preparation of highly reactive iron coke. However, the effects of iron compounds on pyrolysis behavior of coal and metallurgical properties of resultant cokes are still unclear. Thus, three iron compounds, i. e., Fe3O4, Fe2O3 and FeC2O4 · 2H2O, were adopted to investigate their effects on coal pyrolysis behavior and metallurgical properties of the resultant cokes. The results show that iron compounds have slight effects on the thermal behavior of coal blend originated from thermogravimetric and differential thermogravimetric curves. The apparent activation energy varies with different iron compounds ranging from 94. 85 to 110. 11 kJ/mol in the primary pyrolysis process, while lower apparent activation energy is required for the secondary pyrolysis process. Iron compounds have an adverse influence on the mechanical properties and carbon structure of cokes. Strong correlations exist among coke reactivity, coke strength after reaction, and the content of metallic iron in cokes or the values of crystallite stacking height, which reflect the dependency of thermal property on metallic iron content and carbon structure of cokes.

Investigation into the effects of ash-free coal binder and torrefied biomass addition on coke strength and reactivity

The effects of adding ash-free coal (AFC) as a binder on the physical and chemical properties of coke were investigated to understand the mechanism of coke strength increase and to measure CO conversion reactivity. Two AFC samples (AFC_P and AFC_E) were first extracted from Indonesian low-rank coal. Torrefied biomass was also produced from woody biomass for use as an additive to AFC samples. Coke samples were then prepared by adding 3% AFC and 3% AFC + torrefied fuel. The coke strength was investigated by performing indirect tensile tests and 13C NMR analyses. Coke reactivity was examined using thermogravimetric analysis and a coke reactivity test apparatus. The use of AFC as a binder increased the tensile strength of coke between 39% and 48%. Specifically, coke tensile strength was 2.32 MPa with AFC_P and 2.16 MPa with AFC_P + torrefied fuel; and 2.17 MPa with AFC_E and 2.10 MPa with AFC_E + torrefied fuel. The reactivity of the coke containing AFC + torrefied fuel was higher than that of the coke containing AFC alone. The coke produced with AFC_E + torrefied fuel had the highest reaction rate and average CO emission of 257,543 ppm.

No.1-21 乾留過程におけるコークスの性状が亀裂の形成に及ぼす影響の数値解析的検討

No.1-21 乾留過程におけるコークスの性状が亀裂の形成に及ぼす影響の数値解析的検討

A comparative study on different regeneration processes of Pt-Sn/γ-Al2O3 catalysts for propane dehydrogenation

Three different regeneration processes including hydrogen or nitrogen purging and coke-burning treatment were used to restore the Pt-Sn/γ-Al2O3 catalysts, through which propane dehydrogenation reaction was performed in a consecutive reaction-regeneration mode. It was found that the catalyst using hydrogen regeneration showed the best stability compared with those regenerated by nitrogen purging and coke-burning treatment, suggesting that hydrogen regeneration is an effective approach for maintaining the performance of Pt-Sn/γ-Al2O3 catalysts in propane dehydrogenation reaction. The effect of different regeneration atmospheres on the metal active center and the coke deposition was investigated by XRD, TEM, N2-physisorption, TPO, TG and Raman technologies, and the results revealed that hydrogen or nitrogen regeneration resulted in little impact on the size and structure of metal active center, retaining the effective PtSn phase over the catalyst. Moreover, hydrogen regeneration not only removed the low dense components of the coke, but also altered the property of the residual coke through hydrogenation, leading to a higher mobility of coke, and thus a higher accessibility of the metal active centers. Whereas nitrogen regeneration only removed the low dense components of the coke. Although coke-burning regeneration caused a thorough coke removal, the catalyst subjected to repeated redox exhibited poor stability due to metal agglomeration, phase segregation and the resulting large Pt3Sn particle and core-shell structure with a Sn-rich surface.

Relating coke formation and characteristics to deactivation of ZSM-5 zeolite in methanol to gasoline conversion

Two ZSM-5 catalysts, differing only in their crystal size, viz, nanocrystal at∼100nm and microcrystal at 13μm, respectively, were synthesised and tested in methanol to gasoline (MTG) conversion, with a focus on the formation and characteristics of coke deposits. Over time periods when methanol conversion decreased to 50%, herein termed as the service lifespan of the catalyst, the nanocrystal catalyst incurred 31.1wt% coke deposition, while the microcrystal counterpart had 14.1wt% coke. The nanocrystal catalyst showed a service lifespan almost seven times longer than the microcrystal catalyst. The difference in the catalytic service lifespans was examined in terms of the rate of formation of internal coke and structural properties of external coke, as determined using nitrogen physisorption, TGA and TEM. It was found that the internal coke was quickly formed in the microcrystal catalyst leading to rapid coverage of the active sites and blockage of the pores, resulting in fast deactivation. In contrast, coke formed preferentially on the external surface in the case of the nanocrystal catalyst. This external coke was of porous graphitic structures, and thus was not detrimental to the catalytic performance. The coke fouled nanocrystal catalyst was regenerated and the activity of the regenerated catalyst was evaluated under the same reaction conditions. An increase in catalytic service lifespan compared to the pristine nanocrystal catalyst was observed, due to the effect of decreased Al concentration on the catalytic performance.

Beneficial changes in coke properties with alkaline treatment on aluminum-rich mordenite

The impact of the textural properties of mordenite zeolites on the growth and toxicity of coke formed at 350°C during propene transformation is investigated. The addition of intracrystal mesopores by alkaline treatment to a unidimensional zeolite is a simple tool for changing its classical deactivation mode, pore blocking, to a mode more usual on zeolites with a three-dimensional framework, poisoning. This change requires that the zeolite possess a high hierarchy factor, as a result of severe alkaline conditions generating a lot of intracrystal mesopores. Desilication treatment removes part of the Brønsted acid sites and generates extra-framework aluminum species that can block access to the protonic sites and/or enhance their strength, which increases the coking rate. A mild acid leaching is enough to dissolve them. The presence of a few mesopores is sufficient to enhance the access of oxygen to coke, which favor its combustion.

Effect of coal blending ratio on CO2 coke gasification

Coke gasification is largely influenced by the raw coal, catalyst, and blending ratios, pore structure, and specific surface area of the raw coal. In this study, several properties of cokes related to their reactivity were measured using coke reactivity test apparatus (CRTA), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Brunauer-Emmet-Teller (BET) surface area analysis, and energy dispersive X-ray spectroscopy (EDS) to investigate the characteristics of coke gasification. The results indicated that the reactivity of coke in the temperature range from 950 to 1,050 °C was affected by the type of coke and its specific surface area rather than the general properties of the coke, although the overall reactivities at the other temperatures were uniform. EDS analysis showed that the catalyst acted on the reactivity of cokes at low temperatures, whereas the BET analysis indicated that the reactivity at high temperature was influenced by the specific surface area.

Effects of kaolinite addition on the thermoplastic behaviour of coking coal during low temperature pyrolysis

The presence of kaolinite as mineral in coal may significantly influence coking properties of coal, therefore affects quality of coke that is produced from such coals. In this paper, the effect of kaolinite addition on pyrolysis behaviour of coal was examined by blending kaolinite with a medium rank, high vitrinite, low ash coal. Thermoplasticity of coal was characterised by using a Gieseler Plastometer. Char and tar samples were collected through pyrolysis at 450°C in a Gray-King apparatus. The functional groups of the char samples were measured using FT-IR spectroscopy, while tar compositions were characterised using GC/MS. The results indicated that under the test conditions, addition of up to 5wt% of kaolinite could increase the coal fluidity, attributed to the decrease in CH3/CH2 ratio in the residual char. The proportion of CO/CC bonds affected the plastic range. Furthermore, the results showed that kaolinite addition suppresses the evolution of low molecular compounds in tar phase. This study provides useful information for optimising coal blending in cokemaking industry.

Characterization of microstructure and strength of coke particles and their dependence on coal properties

Microstructural features of coke particles are crucial for determining the performance of cokes in ironmaking blast furnaces. An analytical study was carried out to examine coke microstructure using image analysis. The microstructure parameters were correlated to the tensile strength of cokes. Coke properties were related to coal fluidity data based on Gieseler Plastometer measurements and other coal properties including quantitative mineralogy of coals using SIROQUANT analysis. Based on the microstructural data, a new modified microstructural parameter (S+) is proposed to characterize the heterogeneous nature of the physical structure of coke particles. The modified parameter was shown to have a good correlation with the tensile strength of coke as well as with the plastic range of the parent coals. Coal rank was shown to have a strong influence on the thermo-plasticity, with the results showing that there is an increase in both the maximum fluidity and plastic range of coals with increasing volatile matters of coal. The study highlighted the significance of coal mineral chemistry on coke particle characteristics from the observation that kaolinite-rich coals displayed a better correlation with the proposed modified parameter as well as the coke strength under the tested conditions. Stamp charging is also shown to have a positive impact on the microstructure as well as mechanical strength of cokes. This study has implications for the optimisation of the impact of coal chemistry and process conditions on coke quality.

Coking propensity during hydroprocessing of vacuum residues, deasphalted oils, and asphaltenes

Residue hydroprocessing is one of the important processes in refinery to get maximum benefit. Coke deposition on the catalyst and on the interior of parts of the unit is a major challenge to process the residue having high concentration of metals and micro carbon residues. In this regard, three vacuum residues of different refineries are used to study the hydroprocessing activities on NiMo/Al2O3 catalyst. Asphaltenes and deasphalted oils are extracted and their hydroprocessing activities are compared with that of vacuum residues. It is noticed that the hydrocracking activity of the deasphalted oil is easier than that of the respective vacuum residue. The result also shows that the hydrocracking of asphaltene is very difficult particularly at low temperature like 410°C. However, this temperature is sufficient for coke formation by free radical mechanism. It is also observed that the deasphalted oils also yield coke though the feeds do not content asphaltene. It suggests that resin and aromatic hydrocarbons contribute microcarbon residue and hence finally to coke formation. Microcarbon residue of a feed is a very important factor to determine the coking tendency of a feed. The combustion property of coke measured by TGA shows that the cokes deposited on spent catalysts have similar combustion property irrespective of the origin: whether it is from aromatic, resin or asphaltene.

How coke optical texture became a relevant tool for understanding coal blending and coke quality

The scope of this work was to examine the cause-effect relationships between the characteristics of coking coals and blends, and the optical texture and the quality parameters of the resultant cokes. Although a detailed quantitative analysis of the several anisotropic carbon forms, according to size and shape, was carried out, the data used for the calculation of optical texture index (OTI) were compiled into only five microtextural categories: isotropic, incipient anisotropy, circular or mosaics, lenticular and ribbon. Considering the optical texture components of the carbon matrix of the cokes obtained from individual coals, a simple mathematical model is presented on the basis of the additivity law in order to estimate each optical texture component within the matrix of the cokes produced from coal blends. When looking at the good linear relationship between experimental and calculated data, it can be concluded that the proposed model is a useful way of describing the optical texture of cokes from coking blends. As an additional top objective of this study, the coal blends were made for the purpose of lowering the amount of high-cost coking coals. The individual coals and their blends were carbonized in a pilot scale coke oven and, then, the resultant cokes were evaluated in terms of mechanical strength before and after partial gasification with CO2. The degree of coke anisotropy clearly increased with the coal rank and it is correlated to coke reactivity and strength after reaction. From coke characteristics, the optimum quantity of each low-cost coal in the blends to avoid a deterioration of coke properties and structure was established.

Comparative study on calcination of weight loss for coking and calcined coke properties used for aluminum anode –grade

The aim of the present paper consists in the evaluation of the physical-chemical characteristics of some petroleum coke, before and after thermal treatment, which was used to observe the alterations which took place over the coke’s quality. The impact of heat treatment (temperature, heat-soak time and heating rate) on petroleum coke properties were examined. Investigated coke produced from feedstock with different compositions. the sulphur content, volatile matter, density value and ash content before and after heat treatment to 1100 °C were analysed. These properties along with low metals and ash contents make calcined petroleum coke the best material currently available for making carbon anodes.

5-10.石炭物性値とコークス化特性との関連(Session(5)石炭構造と反応性の関連)

5-10.石炭物性値とコークス化特性との関連(Session(5)石炭構造と反応性の関連)

No.9 褐炭を原料とする改質炭のコークス化性に関する基礎的研究

No.9 褐炭を原料とする改質炭のコークス化性に関する基礎的研究

Effect of pore structure and matrix reactivity on coke reactivity and post-reaction strength

Metallurgical coke accounts for a significant portion of the costs associated with blast furnace operations. The coke reactivity index (CRI) and coke strength after reaction (CSR), determined via the Nippon Steel Corporation test, are the most popular indexes for estimating the high-temperature properties of coke. Multiple factors affect the coke solution-loss reaction, and the CRI and CSR depend on the composition and structure of the coke. The pore structure is one of the most important factors affecting this reaction. The effect of the pore structure on the coke reactivity was determined by quantitatively evaluating the CRI and CSR of 10 types of coke. In each case, the corresponding structure was determined via image analysis. Furthermore, the initial reaction rate of the coke matrix was determined via thermogravimetric analysis of the fine grains. Mathematical models, quantitatively describing the CRI and CSR, were formulated via multiple linear regression, and the fit of the results to the experimental data was verified via the regression coefficient and a significance test. The models indicated that pores with sizes of 60–120 µm have a strong positive impact on CRI. In the case of invariant CRI, the high reactivity of the matrix has a positive impact on the post-reaction strength of the coke.

Effect of Grinding on Chemical and Coking Properties of a Highly Volatile Bituminous Coal and Its Size Fractions

ABSTRACTCoal is a highly nonhomogenous material. Owing to the different inherent hardness of its various components, the weaker component has a tendency to segregate in the finer fractions and the others in the coarser fractions. These varied fractions would be expected to have different physical, rheological, and chemical properties. A high volatile U.S. coal when crushed and separated into six fractions using laboratory sieves showed varied properties. Noticeably, both the coarser (> 3.15 mm) and finer (< 0.5 mm) fractions have a higher ash % than the composite sample. The volatile-matter content shows a 3–6% variation. But the notable variation is observed in the total dilatation of the fractions. First the total dilatation increases with decreasing particle size then suddenly falls to a surprisingly low value (9%) compared to the composite sample. This may be due to the fact that with decreasing particle size, volatile matter escapes the matrix without sufficiently imparting swelling to the coal particle.

Experimental Simulation of the Interaction of Slag and Hot Metal with Coke at the Bosh Region of Blast Furnace

Coke is the only raw material which remains solid even in the lowest zone of a blast furnace. The bed-permeability in the bosh zone of the blast furnace is maintained by the solid coke structure. The wetting behaviour of slags in the coke bed of the bosh region in a blast furnace plays a very important role in the process by directly influencing the free movement of the burden and furnace gas and thereby affecting the fuel consumption. Cokes of unsuitable quality will lead to lower permeability in the bosh zone and hinder the furnace operation. In this work, various industrial coke samples are treated with slags of different basicities in a drop-shape analysis facility at a high temperature similar to process conditions. The coke samples have been treated under standard CRI (Coke Reactivity Index) test conditions beforehand in order to simulate the process more closely. The results display the variations in wetting behaviour, temperature, and time for different coke and slag combinations as a function of coke properties and slag compositions. The wetting behaviour at the coke/hot metal interface has also been investigated. The results provide a better understanding of the solid-liquid interaction which takes place in the bosh region of the blast furnace.

Improving the properties of high volatile coking coals by controlled mild oxidation

Four bituminous coals of the same rank but with different thermoplastic properties were oxidized at 40 and 50°C for one month. The chemical changes due to oxidation were studied by applying Gieseler plastometry, the free-swelling index (FSI), thermogravimetric analysis and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). In general, oxidation at 50°C produced a greater impairment of coking properties, the different responses to oxidation depending on the parent coal. The main effects caused by oxidation were a loss of thermoplastic properties, a decrease in aliphatic hydrogen and a slight increase in groups with oxygen functionalities.Both the fresh and oxidized coals were carbonized in a movable-wall oven of 17kg capacity and the quality of the resulting cokes was tested by means of the JIS and ASTM standard methods. The results showed that, in certain cases, mild oxidation produced an improvement in coke quality. Oxidation also affected the porosity of the cokes, which may be related to the coke quality. It was found that the higher quality cokes had less macroporosity, whereas the lower quality cokes had a higher pore volume.