Coke Pore Structure Research Articles

Pore structure evolution during the coke graphitization process in a blast furnace

Pore structure is an important factor influencing coke strength, while the property of coke is essential to maintaining gas and liquid permeability in a blast furnace. Therefore, an in-depth understanding of the pore structure evolution during the graphitization process can reveal the coke size degradation behavior during its descent in a blast furnace. Coke graphitization was simulated at different heating temperatures from 1100 to 1600°C at intervals of 100°C. The quantitative evaluation of the coke pore structure with different graphitization degree was determined by vacuum drainage method and nitrogen adsorption method. Results show that the adsorption and desorption curves of graphitized coke have intersection points, and the two curves did not coincide, instead forming a “hysteresis loop.” Based on the hysteresis loop analysis, the porous structure of the graphitized coke mostly appeared in the shape of a “hair follicle.” Furthermore, with an increase in heating temperature, the apparent porosity, specific surface area, total pore volume, and amount of micropores showed good correlation and can divided into three stages: 1100–1200, 1200–1400, and 1400–1600°C. When the temperature was less than 1400°C, ash migration from the inner part mainly led to changes in the coke pore structure. When the temperature was greater than 1400°C, the pore structure evolution was mainly affected by the coke graphitization degree. The results of scanning electron microscopy, energy dispersive spectrometry, and ash content analyses also confirmed that the migration of the internal ash to the surface of the matrix during the graphitization process up to 1400°C contributed to these changes.

Effect of carbon solution-loss reaction on properties of coke in blast furnace

The pore structure of coke under CO2 atmosphere was investigated by the carbon solution-loss reaction experiment. The results show that the pore size distribution of coke gradually changes from dispersion to relative concentration with the increase in carbon loss rate, but it tends to be dispersed again in the late stage of the reaction, and the pore volume and specific surface area also increase first and then decrease with the increase in carbon loss rate. Scanning electron microscopy results show that the evolution of coke pores is from the formation of micropores to the expansion of micropores, and finally the micropore and mesopores collapse to form a large number of string holes. The chemical bonds and functional groups of different reacted cokes were analyzed by Fourier-transform infrared spectroscopy. Furthermore, the microstructure of reacted cokes was analyzed by optical microscopy, and then the ordering of the affinity of different microstructures with CO2 was given. The volume hypothesis which was the theory about energy size of comminution was adopted to analyze the degradation behavior of reacted cokes. The breakage energy of reacted cokes was calculated by volume hypothesis, and the power consumption coefficient CK of different reacted cokes was determined by drum experiment, and then the degradation behavior of reacted cokes under different power consumptions was predicted.

Characteristics of coke pore formation and its effect on solution loss degradation

Pore structure is an important factor that affects coke thermal properties. In order to reveal the formation regularity of coke pore structure, high temperature carbonization experiment of blending coals was carried out in 40 kg test coke oven. The pore structure of different regions and different orientations of the obtained coke was detected by microscope. The ratio of the average pore diameter of the coke to the average wall thickness was highly correlated with the square of porosity. The relationship shows that during coking, the development of the wall thickness is restricted by pore coalescence and coal expansion. The softened coal can form a thicker wall structure only after the pores have coalesced fully without excessive expansion. The four coke pore size distribution curves and pore-wall-thickness distribution curves reflect the quality change of the coal blending. Therefore, the adjustment of a coal blending scheme according to the pore structure distribution curve provides a promising, accurate coal blending method.

Fractal description and adsorption-desorption behaviour of coke treated by benzene pyrolysis carbons

For explaining why benzene pyrolysis carbons could inhibit coke deterioration in blast furnace, the adsorption-desorption data of coke sample treated by benzene pyrolysis carbons were obtained to establish adsorption-desorption isotherms and to fit fractal description model with Frenkel-Halsey-Hill equation. The SEM photographs of coke revealed that the pores of the infiltrated coke were almost filled with pyrolysis carbon particles. The fitted curves showed that the types of isotherms were similar to 'type II' of IUPAC classification, and the hysteresis loops belonged to type H3 which represents a typical multilayer adsorption. Model tests indicated that the pore structure of the coke samples have obvious fractal feature and the fractal dimensions of coke sample treated by benzene pyrolysis carbons were smaller than that of original coke sample. So, it explained that benzene pyrolysis carbons can effectively inhibit coke deterioration by infiltrating into the pore structure of coke and reducing pore roughness.

Numerical Analysis of Reaction Degradation for Three-dimensional Coke Pore Structure

Numerical Analysis of Reaction Degradation for Three-dimensional Coke Pore Structure

Effect of Meso-scale Pore Structure on Coke Strength

To explore the factors that affect coke strength in the meso-scale pore structure of coke, we investigated the relationship between the strength and meso-scale pore structure of the polished surface of coke sample. Coke was fractured using diametral-compression tests, and the tensile strength of coke was measured. Furthermore, we observed the polished surface of coke and obtained combined images with a size of 10 mm × 10 mm. The size and roundness of the pores were evaluated by image analysis. The pores were classified according to the pore size, and the strength of coke with many pores with a diameter of more than 1000 µm was indicated to be low. Moreover, the roundness of pores with a diameter of more than 1000 µm was low. Therefore, pores with diameter of more than 1000 µm and low roundness are considered to greatly affect the strength of coke in a meso-scale structure.

Microscopic study on the interior and exterior reactions of coke with CO2 and H2O

The interior and exterior reactions of coke with H2O and CO2 were studied at 950–1250°C by self-made gas–solid reacting apparatus, including the particle diameter, apparent porosity, relative volume density distribution and pore structure of coke after reaction. It was obtained that the porcoke in the interior and exterior parts were all eroded after reacting with CO2 or H2O. However, compared with CO2, the reaction of coke with H2O occurred at the coke exterior more strongly, but in the coke interior occurred more weakly, indicating the reaction area of coke with H2O was much closer to the coke exterior. Therefore, injecting hydrogen fuel into blast furnace can increase the coke particle size, so as to make coke playing a better role as skeleton in blast furnace. In addition, increasing the temperature can reduce the amount of solution loss in the coke interior, in particular for the reaction with H2O.

Effects of coking coal properties on coke pore structure: Prediction models

The porosity, pore size, and specific surface area of coke significantly affects its strength and thermal properties. To investigate the factors affecting the pore structure during the carbonization of coking coal, experimental studies were performed using 18 types of single and mixed coals. Based on the experimental results of the structure and properties of coke pores, regression equations were developed to predict the structural parameters. The structural parameters include porosity, average pore size, volume ratio of pores with diameters >150 ¯m, volume ratio of pores with diameters <30 ¯m, and specific surface area. The regression equations indicate that the maximum volatile release rate, Gieseler fluidity, and vitrinite maximum reflectance are the main factors affecting the formation of micron-size pores. The surface area of coke dominated by nanoscale micropores was significantly affected by volatiles released during 800−950 °C.

Changes in Pore Structure of Metallurgical Cokes under Blast Furnace Conditions

Metallurgical cokes were subjected to gasification by CO–CO2–N2 gas with blast-furnace-like composition–temperature profile to 1673 K (1400 °C) and annealing under N2 at temperature up to 2273 K (2000 °C). Pore structure of cokes was examined using image analysis. Porosity and pore size were both enlarged under gasification and annealing conditions. The pore structure change during gasification was mainly a result of the Boudouard reaction; the pore structure development upon annealing was attributed to the reactions of mineral matters with carbon and further devolatilization. Annealing and gasification caused a decrease in average pore roundness, an increase in the fraction of low roundness pores and the increase of coalescence points in the pore area. The degradation of coke strength following reaction and annealing was characterized using tensile testing. Both gasification and annealing decreased the mechanical strength of coke. Degradation of more reactive cokes (cokes C and D) by gasification at 1673...

Observation of the Coal Thermoplastic Layer Using μ-focus X-ray CT and Sole-heated Oven

The pore structure of coke is one of the factors governing coke strength. As a step toward technology development to control the coke pore structure, we observed the behavior of coal thermoplastic layers in which coke pores are formed using our newly developed technique with sole-heated oven and μ-focus X-ray CT.Coal packed bed was heated in the sole-heated oven, and then cooled rapidly after the sample temperature reached 350°C at the top and 550°C at the bottom. Next, many cross-section images of the coal and coke layers were observed nondestructively and continuously by the μ-focus X-ray CT. As a result, the following knowledge was obtained.The thermoplastic layer of coal goes through the following four processes: 1) initial process of pore formation, 2) initial softening process whereby the growth of pores, expansion of coal, filling of voids between coal particles, and decrease in porosity occur, 3) intermediate softening process whereby the porosity becomes maximum, and 4) final softening process (resolidification process) whereby the pore size and porosity decrease.With a given type of coal, firstly pores are formed inside the particles over 1 mm in diameter, while the pore formation inside the particles less than 1 mm occurs at approximately 10°C temperature higher than the temperature at which pore formation inside large particles.

コークス気孔構造解析に基づいた石炭軟化溶融膨張挙動の評価

コークス気孔構造解析に基づいた石炭軟化溶融膨張挙動の評価

Evaluation of Coal Thermoplastic and Dilatation Behavior with Coke Pore Structure Analysis

Evaluation of Coal Thermoplastic and Dilatation Behavior with Coke Pore Structure Analysis

Influence of coke particle size on pore structural determination by optical microscopy

Coke produced from a commercial oven was ground into various particle size ranges as a method to investigate the effect of coke particle size on pore structural parameters. The prepared samples were studied using reflected-light optical microscopy coupled with computerized and manual image analyses. Helium density and surface area measurements were performed on the prepared samples. Results showed that the use of smaller coke particle sizes for sample preparation leads to a loss of larger pores, thus, leading to an inaccurate description of the coke pore structure. This was shown by a decrease in volume porosity and average pore area; and an increase in average cell-wall thickness, coke density, and surface area that accompanied a decrease in the coke particle size. Moreover, a decrease in the ratio between pore area and cell-wall thickness, and a decrease in the ratio between pore long and short axial lengths (Feret's ratio) indicated a loss of large and elongated pores as the coke particle size decreased. However, a comparison of coke particle size ranges of 2.8–4.7mm and 15–16mm indicated that a particle size in a range of 2.8–4.7mm can be employed without compromising pore structural characteristics, yet still enabling representative sampling.

1-1-2 低炭化度非微粘結炭配合時のコークス欠陥構造変化(1-1 反応性,コークス,Session 1 石炭・重質油等)

1-1-2 低炭化度非微粘結炭配合時のコークス欠陥構造変化(1-1 反応性,コークス,Session 1 石炭・重質油等)

Quantitative Evaluation for Relationship between Development of Pore Structure and Swelling of Coal in Carbonization of Single Coal Particle

The objective of this paper are to study the formation process of coke pore structure in relation to the swelling of coke during the thermoplastic stage and the pore structure at the initial carbonization. The swelling ratio, changes in pore structure and growth behavior of pore which originally present in the coal were evaluated. Two kinds of caking coals were carbonized in nitrogen-atmosphere with an infrared furnace. The swelling ratios were measured, and the cross-sectional images of coal particles at different heating temperatures were observed with an optical microscope. Before carbonization, all pores in both coals were a diameter of less than 100 μm. When the temperature increased up to the level at which the swelling started, the pores with greater than 100 μm-diameters were formed, and they had also simultaneously coalesced. However, each coal had a different temperature for starting swelling and observing the generation and coalescence of pores with a diameter of more than 100 μm. At this point, the formation of pores were expressed with Laplace equations. The results showed the volatile matter inflow affected the change of pore structure. Furthermore, the pore structures within coal particles before and after carbonization were compared by micro-X-ray Computed Tomography. Carbonization up to the temperature for the softening stage increased pore diameters, which provided evidence that the proportion of pores existing within post-carbonized coal had grown based on the pores already existing in pre-carbonized coal.

No.31 コークス気孔構造に及ぼす粘結材粉砕粒度の影響(熱分解・コークス(2),構造・物性(1),コプロセッシング)

No.31 コークス気孔構造に及ぼす粘結材粉砕粒度の影響(熱分解・コークス(2),構造・物性(1),コプロセッシング)

コークスの表面破壊強度およびCO&lt;SUB&gt;2&lt;/SUB&gt; 反応前後での引張強度に及ぼす気孔構造の影響

コークスの表面破壊強度およびCO&lt;SUB&gt;2&lt;/SUB&gt; 反応前後での引張強度に及ぼす気孔構造の影響

04/00048 Application of image analysis in the determining of coke pore structure parameters: Ren, S.-B. et al. Anhui Gongye Daxue Xuebao, Ziran Kexueban, 2003, 20, (1), 66–68. (In Chinese)

With Optimas 6.5(the image analyzing and processing s oftware),many images of 7factories' coke were segmented and counted and the best th reshold value was gotten.Segmented and identified the image of coke pore structure with the value,it was achi eved to determine the parameters of c oke pore structure with the method of image analysis.Comparing with the t rade methods,this method has the advantages with more precise and more representative etc.

コークス気孔構造の反応粉化に及ぼす影響

Improvement in coke strength against abrasion is needed for a stable operation of blast furnace. Pore structure of coke (e.g. pore size distribution and tortuosity) is important for an improvement of coke abrasion strength, because its effect influences CO2 diffusion coefficient and coke strength after CO2 reaction. In this study, production of coke samples having different pore structure was attempted by blending different size of slightly caking coal to coal blend. The effect of pore structure on CO2 reactivity and abrasion after CO2 reaction was investigated.In case that larger size (2-3 mm) slightly caking coal was added to coal blend and carbonized (Coke A), the pore size distribution of coke became wider and contained larger pore which had higher value of tortuosity than the coke produced by adding smaller size (1-2 mm) slightly caking coal particles (Coke B). Difference in pore structure is considered to be originated by bubble size generated during softening of coal particles. Relationship between pore size and tortuosity is caused by the quantity of bottle-neck type pores in coke.The reactivity of Coke A was higher and the extent of the reaction at inner part of coke lump analyzed by X-ray computerized tomography was larger, compared with the Coke B. These differences are considered to be based on the fact that large pore enhances diffusion of CO2 into inner part of the coke, and that concentration of shear stress easily occurs around large pores.

NMRガスイメージング法によるコークス気孔での反応解析

The pore structure is very critical and sensitive to react with CO2 in the case of cokes. But it is very difficult to detect the pore structure of cokes with nondestructive and high resolution because conventional porosimeter method can't detect macro pore (over 400 μm), and at the same time with destructive. We are at first demonstrating 3D-SPRITE imaging to detect the pore structure using SF4 gas, before and after CO2 reaction, (over 1 μm) with non destructive and the same pores, and then clarify the reaction mechanism. We found that the reaction rate of the cokes with CO2 depends on the pore size and the critical pore size is over 100 μm.