Gasification reactivities of optical textures of metallurgical cokes

Optical textures of ten typical cokes before and after gasification in CO₂ were quantified by point counting under a polarized microscope to quantify the reactivities of each type of optical texture. Although absolute values of gasification rate for each texture varied considerably from coke to coke, their relative values were constant regardless of the origin of the cokes. The relative reactivities of flow, mosaic, isotropic and inert textures were 1,1.8,2.8 and 3.0, respectively. The relative reactivity of a single coke calculated from a knowledge of optical textures, was monotonicly correlated with the mean maximum reflectance ($\text{R}\text{?}{}_0$) of the parent coal. This indicates that the high reactivity of coke from a high-rank coal ($\text{r}\text{?}{}_0\text{= 1.8\%}$) is due to factors other than its optical texture. The crystallite height, L_c(002)' of the coke correlated with $\text{R}\text{?}{}_0$ of the parent coal, although the values of L_c(002) varied only from 1.5 to 2.1 nm.     

Gasification reactivities of cokes derived from athabasca bitumen

Gasification reactivities of cokes obtained from Athabasca bitumen by delayed coking and fluid coking were compared in fixed and fluidized bed systems. In both systems the C + O₂ reaction accounted for the most of converted carbon. The C + H₂O reaction proceeded to a smaller extent. The bulk reactivity of the fluid coke was higher than that of delayed coke, when comparing ?20 to +60 mesh particles in fluidized bed and ?14 to +20 mesh particles in fixed bed, respectively. However, the reactivity of the delayed coke expressed per unit of surface area was markedly higher than that of the fluid coke.     

Catalytic gasification of carbon with steam,carbon dioxide and hydrogen

Nine transition metals in Group VIII were examined as catalysts for the carbon gasification with steam, carbon dioxide and hydrogen. Metal-doped carbons were heated up to 950°C at a constant rate of 200°C/hr in a flowing reactant gas. The relative activities of metal catalysts are nearly the same for all gases regardless of their quite different chemical nature. Metals like Ru, Rh, Ir and Pt are invariably active, whereas Fe, Co and Pd have small activities. The reaction pattern differs from catalyst to catalyst. Only four metals (e.g. Ni, Ru, Rh and Os) exhibit the maximum reactivity in the low-temperature region, and this behavior is common to three gases. It is speculated from these observations that the metal-carbon interaction is more important than the metal-gas interaction in determining the reaction profile.     

Adsorption of hydrogen sulfide,carbon dioxide,methane, and their mixtures on activated carbon

Abstract

H₂S and CO₂ are acid contaminants of natural gas and biogas, which removal have been studied using adsorption data for monocomponent and binary mixtures. However, equilibrium adsorption data for H₂S?+?CO₂ + CH₄ mixture has not been investigated yet. In this work, H₂S and CO₂ partition coefficients (K) and activated carbon (AC) selectivity (S) for H₂S?+?CO₂ + CH₄ mixture separation at high-pressure and different temperatures were determined. To reach this goal, monocomponent isotherms for H₂S, CO₂ and CH₄ on Brazilian babassu coconut hush AC were experimentally determined at different temperatures and pressures. Then, obtained data were correlated by Langmuir and Tóth models, and multicomponent adsorption was predicted using Extended Langmuir, Extended Tóth and Ideal Adsorption Solution Theory (IAST) methods. Results indicate AC captures approximately 26?wt% of H₂S or CO₂. K values for CO₂ and H₂S reached more than 3 and 26, respectively, depending on the predictive model utilized and were higher for diluted mixtures (high CH₄ content in gas phase). S values for CO₂ and H₂S can reach values greater than 25 for Tóth?+?IAST. Furthermore, selectivity toward H₂S is approximately 5.6 times greater than CO₂. The effect of temperature on multicomponent results indicate K and S values decrease as temperature increases. Therefore, results obtained herein show that is possible to separate H₂S and CO₂ from mixture containing CH₄ using this AC as adsorbent and better separation performance was observed for low H₂S and CO₂ concentrations and lower temperatures.     

Reaction kinetics of pulverized coal-chars derived from inertinite-rich coal discards: Gasification with carbon dioxide and steam

An investigation was undertaken to determine the kinetics of gasification of coal-chars (pulverized) derived from typical South African inertinite-rich (high-ash) coals involving char reactions with carbon dioxide and steam and the effects of carbon monoxide and hydrogen. The chars used were characterized with respect to structural, chemical, mineralogical and petrographic (maceral content) properties and gasification experiments were conducted in a TGA at atmospheric pressure with different gas mixtures within a temperature range of 1073–1223 K. The shrinking core model with a controlling surface reaction was shown to be applicable for the gasification of pulverized coal-chars consisting of essentially of carbon-rich particles. The validity of this model can be attributed to the core having an exceptional low porosity (high inertinite parent coal) and consequently negligible penetration of the gases. It was found that the gasification intrinsic reaction rates could be adequately described by Langmuir–Hinshelwood type rate equations and that established equations have been validated with corresponding constants according to new data processing procedures. It was found that the reaction rate constants for coal-chars derived from inertinite-rich (76–80%) coal discards were different to results published in the literature and that the intrinsic reaction rates differed only slightly (order of magnitude) for coal-chars with similar maceral (inertinite) compositions and different total ash contents. The marked inhibiting effect of the carbon monoxide and hydrogen on the carbon dioxide/carbon monoxide and steam/hydrogen gasification reactions is shown and relevant constants are reported. Experiments were done and models evaluated for a multi-component gasification mixture consisting of a feed mixture of carbon dioxide, carbon monoxide, steam and hydrogen. Reaction constants determined with results from binary mixtures were used to predict results and it was found that the overall rate is best described with the assumption that the important reactions proceed on separate sites.     

Properties and structure of metallurgical formed cokes

Properties and structure of formed cokes obtained from various raw materials using different technologies and changes of properties and structure of formed and conventional cokes occurring in the blast-furnace process were investigated. In formed cokes, in distinction from conventional cokes, there are many types of structure depending on the kind of raw materials used and on the technology of formed cokes production. Formed fuels have shown a lower degree of homogeneity and arrangement of structure in comparison with conventional cokes. In the blast furnace process a gradual arrangement of coke structure takes place. The process of structure arranging is more intensive in conventional coke. The petrographic composition of original coals has a great effect on the quality of the formed cokes. Based on the results of structural investigations, changes in the technological process can be introduced, to obtain a product of the desired quality.     

Interaction of a porous carbon particle with steam and carbon dioxide

As part of a diffusion-kinetic model of gasification of a porous carbon particle in steam and carbon dioxide, this paper presents a study of heat- and mass-transfer processes both inside the porous particle and in the gas phase above its surface. The radiation heat transfer between the particle and the walls of the furnace is taken into account. Heterogeneous reactions of carbon with steam and carbon dioxide and the homogeneous reaction of carbon monoxide with steam. are considered. In addition, allowance is made for pressure variation in the porous particle due to an increase in gas mass during heterogeneous reactions. Dependences of the gasification rate on the composition of the reaction mixture, pressure, furnace temperature, and particle size, and the inner surface area of the porous carbon particle.     

Adsorption of methane, nitrogen, carbon dioxide and their mixtures on wet Tiffany coal

Gas adsorption was measured for methane, nitrogen, CO₂ and their binary and ternary mixtures on a wet Tiffany coal sample. The measurements were conducted at 327.6 K (130.0 F) at pressures to 13.8 MPa (2000 psia). The expected uncertainties in the amounts adsorbed vary with pressure and composition. In general, average uncertainties are about 5% (0.01–0.08 mmol/g) for the total adsorption; however, the expected percentage uncertainties in the amount of individual-component adsorption are significantly higher for the lesser-adsorbed gas at lower molar feed concentrations (e.g. nitrogen in the 20/80 nitrogen/CO₂ system).

The Langmuir/loading ratio correlation (LRC) and the Zhou–Gasem–Robinson (ZGR) two-dimensional equation of state (EOS) are capable of representing the total adsorption for the pure, binary and ternary systems within their expected experimental uncertainties. However, the quality of fit for the individual-component adsorption varies significantly, ranging from 3% (0.01 mmol/g) for the more-adsorbed methane or CO₂ to 32% (0.01 mmol/g) for the lesser-adsorbed nitrogen. Further, the LRC and ZGR EOS predict binary adsorption isotherms, based solely on pure-fluid adsorption parameters, within twice their experimental uncertainties.     

Gasification of Irsha-Borodin coal coke by carbon dioxide

Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 25, No. 2, pp. 63–67, March–April, 1989.     

Non-isothermal kinetics of metallurgical coke gasification by carbon dioxide

Under non-isothermal conditions, thermogravimetric analysis was applied to study carbon dioxide gasification of three metallurgical cokes. The cokes selected for the study were named Coke A, Coke B and Coke C. The experimental data are fitted using four common gas-solid kinetic models: the homogeneous model, the sharp interface model, the traditional model and the random pore model. It is found that the random pore model most closely reflects the kinetic behavior of coke gasification characteristics. Using the random pore model, the apparent activation energies for gasification of Coke A, Coke B, and Coke C were calculated to be 139.08, 127.78, and 116.32 kJ mol^–1, respectively.     

Correlation of microstrength and industrial drum strength indices of metallurgical cokes

Correlations between microstrength and industrial drum strength indices of metallurgical cokes were obtained using a 230 kg coke oven. Twelve coking coals from different countries, and ranging in ASTM rank from hvA to Iv bituminous, were carbonized singly and in blends. Microstrength, JIS Drum and ASTM Drum tests were performed on the cokes produced. The results indicated that the relationship between the Dl¹⁵⁰₁₅ index and microstrength was non-linear. Correlation coefficients increased when highly fluid US hvA bituminous coals were excluded. The relationship between ASTM hardness and microstrength was less defined. Results of this study indicate that thermoplasticity is an important consideration when correlating microstrengths with industrial drum strengths.     

Gas hydrate formation from hydrogen/carbon dioxide and nitrogen/carbon dioxide gas mixtures

Gas hydrates from CO₂/N₂ and CO₂/H₂ gas mixtures were formed in a semi-batch stirred vessel at constant pressure and temperature of 273.7 K. These mixtures are of interest to CO₂ separation and recovery from flue gas and fuel gas, respectively. During hydrate formation the gas uptake was determined and the composition changes in the gas phase were obtained by gas chromatography. The rate of hydrate growth from CO₂/H₂ mixtures was found to be the fastest. In both mixtures CO₂ was found to be preferentially incorporated into the hydrate phase. The observed fractionation effect is desirable and provides the basis for CO₂ capture from flue gas or fuel gas mixtures. The separation from fuel gas is also a source of H₂. The impact of tetrahydrofuran (THF) on hydrate formation from the CO₂/N₂ mixture was also observed. THF is known to substantially reduce the equilibrium formation conditions enabling hydrate formation at much lower pressures. THF was found to reduce the induction time and the rate of hydrate growth.     

The characterization of interfaces between textural components in metallurgical cokes

Six coals, representing the rank range normally encountered in commercial coking, were carbonized in a small oven to give dense cokes, of tensile strength comparable with that of good-quality blast-furnace coke. Interfaces between the different textural components in the cokes were studied by polarized-light microscopy. It proved possible to classify interfaces according to their perceived quality, to quantify their occurrence by point-counting and to calculate interface quality indices for the coke as a whole or for interfaces involving individual textural components. Interfaces between vitrinite-derived reactive coke components were superior to those involving inerts, but the inerts content of a coke did not have a marked influence on the coke interface quality index. The highest coke interface quality index was observed for the coke from the coal with the highest dilatation. No clear evidence of an influence of interface quality on coke tensile strength is apparent from the present data.     

The excess enthalpy of gaseous mixtures of carbon dioxide with methane

Excess enthalpies (heats of mixing) of mixtures of methane and carbon dioxide have been measured in a flow calorimeter at temperatures between 10°C and 80°C and pressures up to 100 atmospheres. All measurements were for the mixing of two gas phases. The results were compared with various predictions based on equations of state and the principle of corresponding states.     

Catalytic gasification of metallurgical coke by carbon dioxide using potassium salts

The catalytic gasification of metallurgical coke by carbon dioxide with potassium salts is studied from the view-point of the catalytic activity of the salts, the optical texture of the coke and its reactivity, monitoring weight losses and the detail of topographical change induced in the coke surface by gasification. The activity of the catalyst and the reactivity of the coke were found to be dependent upon the anion of the salt and optical texture of the coke. Potassium metal may be produced in situ in the gasification reactions and has a significant role in the mechanism of catalytic gasification. The reactivity of a coke and its performance in a blast furnace must be associated both with extents of gasification and development of pits and fissures which could promote a weakening of the coke.     

Permeability of dense (homogeneous) cellulose acetate membranes to methane,carbon dioxide,and their mixtures at elevated pressures

Mean permeability coefficients for CH₄ and CO₂ (P̄ and P̄) in cellulose acetate (CA, DS = 2.45) were determined at 35°C (95°F) and at pressures up to about 54 atm (800 psia). The measurements were made with pure CH₄ and CO₂ as well as with CH₄/CO₂ mixtures containing 9.7, 24.0, and 46.1 mol % CO₂. In the measurements with the pure gases, P̄ was found to decrease with increasing pressure, as expected from the “dual-mode” sorption model. By contrast, P̄ passes through a minimum and then increases with increasing pressure, probably due to the plasticization (swelling) of CA by CO₂. The values of P̄ and P̄ determined with the mixtures containing 9.7 and 24.0 mol % CO₂ decrease with increasing total pressure; this behavior is adequately described by the extended “dual-mode” sorption model for mixtures. By contrast, the values of P̄ and P̄ obtained with the mixture containing 46.1 mol % CO₂ pass through a minimum and then increase as the total pressure is raised, probably also due to the plasticization of CA by CO₂. The CO₂/CH₄ selectivity (≡P̄/P̄) of the CA membrances decreases with increasing total pressure and, at constant pressure, decreases with increasing CO₂ concentration in the feed mixture. The effects of exposing the CA membranes to high-pressure CO₂ prior to the permeability measurements (“conditioning” effects) on P̄ and P̄ have also been studied. © 1996 John Wiley & Sons, Inc.     

煤焦与CO2及水蒸气气化特性研究进展

为了深入系统的研究煤焦与CO2及水蒸气的气化反应特性,综述了国内外对煤气化的主要影响因素、煤焦与CO2及水蒸气气化反应动力学、煤的结构特性在气化过程中的变化及CO2气化与水蒸气气化反应活性对比等方面的研究进展,并进行了总结。     

On the intrinsic reaction rate of biomass char gasification with carbon dioxide and steam

The gasification of beech wood char and oil palm shell char with carbon dioxide and steam was studied. To avoid heat and mass transport limitations during gasification, the amount of char, particle size and flow rate were varied in isothermal experiments. A rate expression of the Langmuir–Hinshelwood-type was applied to match the experimental data at different partial pressures and reaction temperatures in the intrinsic regime. Furthermore, the reactive surface area (RSA) of the biomass chars was determined as a function of the degree of conversion by the temperature-programmed desorption technique (TPD). The results show that the reaction rate is in general proportional to the RSA. The surface related reaction rates for the studied biomass chars are comparable to surface related reaction rates for coal chars at similar reaction temperatures.