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.     

Effect of potassium and sodium carbonate catalysts on the rate of gasification of metallurgical coke

The catalytic effects of potassium and sodium carbonates on the rate of gasification of metallurgical coke with carbon dioxide have been investigated by the thermogravimetric method. The experiments were carried out using metallurgical coke fines mixed with 5 wt% catalyst, the mixture pressed into disc-shaped pellets from which a small specimen (23 mg) was cut and used. The reaction was carried out at temperatures ranging from 725 to 900°C using pure CO₂ at 1 atm.The rates were measured for uncatalyzed coke-CO₂ reaction and with K₂CO₃, Na₂CO₃ and mixed (K, Na)₂CO₃ catalysts. Potassium carbonate exhibited the greatest catalytic activity closely followed by the mixed catalyst and sodium carbonate. For the K₂CO₃-catalyzed reaction, an activation energy of 41.74 (±3.13) kcal/mole was found; and for the Na₂CO₃-catalyzed reaction the figure was 40.27 (± 5.05) kcal/mole.The catalysis is thought to occur by the “vapor cycle” mechanism. It consists of reduction (M₂CO₃→2M) followed by oxidation (2M → M₂CO₃). When CO₂ is present in the system the alkali vapor (M) quickly gets reconverted to the carbonate.     

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.     

冶炼烟气中二氧化硫的催化还原

自热熔炼镍冶炼工艺产生的烟气ψ(SO2)为20％或更高,可用于生产元素硫。该技术的基本原理是用天然气还原二氧化硫,在还原阶段采用催化剂有可能大大提高效率。     

Catalytic gasification of coal using eutectic salts: identification of eutectics

Different eutectic salt mixture catalysts for the gasification of Illinois No. 6 coal were identified and various impregnation or catalyst addition methods to improve catalyst dispersion were evaluated in this study. In addition, the effects of major process variables such as temperature, pressure, and steam/carbon ratio were investigated in a thermogravimetric analyzer (TGA) and fixed-bed bench scale reactor systems. The TGA studies showed that the eutectic catalysts increased CO₂ gasification rate significantly. The methods of catalyst preparation and addition had significant effect on the catalytic activity and coal gasification. Based on the TGA studies of several eutectic systems, the 43.5% Li₂CO₃-31.5% Na₂CO₃-25% K₂CO₃ and 39% Li₂CO₃-38.5% Na₂CO₃-22.5% Rb₂CO₃ ternary eutectics, the 29% Na₂CO₃-71% K₂CO₃ binary eutectic and the K₂CO₃ single salt catalysts were selected for the fixed-bed studies. The catalyst loading increased the gasification rate and almost complete conversion of carbon was observed when 10 wt.% of catalyst was added to the coal. Upon further increasing the catalyst amount to 20 wt.% and above, there was no significant rise in gasification rate.     

Catalytic reduction of carbon dioxide. 1. Reduction of carbon dioxide with carbon carrying potassium carbonate

The catalytic behaviour of potassium carbonate doped onto active carbon was investigated with respect to reduction of carbon dioxide. The distribution of potassium on the carbon surface was found by an X-ray microanalyzer to be uniform. The amount of oxygen trapped on the carbon surface during reaction was nearly proportional to the surface concentration of potassium. The catalytic activity with carbon doped with less than 2% potassium carbonate was proportional to the amount of trapped oxygen, while excessive doping by potassium was found to form trapped oxygen independently of the gasification of carbon. Disproportionation of carbon monoxide into carbon dioxide and carbon was found to take place readily at 700 °C, with carbon doped with 4.0 wt % potassium carbonate.     

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.     

The influence of potassium carbonate on surface area development and reactivity during gasification of activated carbon by carbon dioxide

In this study it is shown that the uncatalysed gasification of activated peat char can be described by a reaction temperature independent increase of the specific surface area with increasing burn-off and a constant reactivity per unit surface area up to 60% burn off. Unlike nickel catalysis, potassium catalysis causes an increased microporosity due to microchanneling. Above ca. 0.6 atoms per nm² the increase of the reactivity per unit surface area with increasing burn-off can be described by a first order dependency with respect to the number of potassium atoms per unit surface area. This can be explained by assuming potassium intercalate formation to be an essential step. The development of microporosity appears to be more pronounced at higher reactivities and, consequently, at higher effective catalyst loadings and higher reaction pressures.     

Theoretical work on reaction sequences in the gasification of coke by carbon dioxide and by steam in conditions remote from equilibrium

The theory of the kinetics of gasification at atmospheric pressure expounded principally by Ergun is extended to reinterpret the experimental results obtained at pressures up to 5 MPa and temperatures up to 870 °C by Blackwood and his co-workers. The reaction sequences that are proposed enable a rate equation to be put forward for the general case of gasification in any mixture of carbon dioxide, carbon monoxide, steam and hydrogen at any pressure and temperature within the range of the original data. An equation for the rate of formation of methane during gasification in mixutres of steam and hydrogen is offered and some other consequences of the theory are mentioned.     

The gasification of carbon by carbon dioxide at high temperatures and pressures

Presented is the analysis of experimental data on the interaction of carbon with CO₂ + N₂ mixtures at temperatures up to 3400 K and pressures up to 40 atm. The influence of pressure and roles of different stages of the reaction multistage mechanism are determined.     

Fluidised bed gasification of a metallurgical coke with CO2/N2 Mixtures

The gasification of a metallurgical coke with CO₂/N₂ mixtures in a 0.1 m diameter fluidised bed has been studied over the temperature range 810–1050°C. The rate of gasification was found to be essentially kinetically controlled, with negligible influence of fluidisation parameters below 1000°C. A number of flow models were assessed. The plug flow model was found to be the simplest model which could predict the experimental results, giving similar results to the more complex two-phase flow model of Davidson and Harrison (1963). For the range of conditions studied, the simple nth order reaction model was used to determine a best value of the reaction order of 0.8. For this combination of flow and reaction models, an activation energy of 197 kJ/mol was deduced from the experiments, in agreement with packed bed results and literature data. Very simple models can be used to predict the experimental results within the range studied.     

Kinetic study of Argentinean asphaltite gasification using carbon dioxide as gasifying agent

The kinetics of Argentinean asphaltite char gasification using carbon dioxide as gasifying agent was studied between 1048 and 1223 K. The chars were obtained by pyrolysis of an asphaltite in a fixed bed reactor. The relative mass change during the gasification reaction was continuously monitored using a high resolution thermogravimetric system. The starting temperature for the reaction of the char with carbon dioxide was determined at about 800 K. The influence of gaseous flow rate, sample mass, carbon dioxide partial pressure and temperature in the reaction rate was analyzed. The experimental condition under which the progress of gasification reaction is chemically controlled was established. In those conditions, an activation energy of 185 kJ mol⁻¹ was obtained with an isoconversional method. Concerning the influence of carbon dioxide partial pressure, it was determined that pressures greater than 50 kPa do not alter the kinetics regime. Finally a reaction order of 0.5 for carbon dioxide partial pressure was determined and a global rate equation that includes these parameters was developed.

     

Form coke reaction processes in carbon dioxide

Uncertainty in metallurgical coke supplies has prompted development of form coke from low quality coals and fines. Reaction rates have been measured and mechanisms identified that control carbonaceous briquette reaction rate in CO₂. Three briquette formulations were prepared, characterized and coked in an inert atmosphere at high temperature. A given weight of each formulation was then reacted in a packed bed with CO₂ at 1373 K for 0.5–2 h. Partially reacted briquettes contained a solid core with some internal reaction surrounded by a loosely adhering layer of carbon-containing ash. The reaction rate of briquettes with CO₂ was affected by diffusion of CO₂ through the bulk gas and the ash-carbon layer to the core surface, as well as CO₂–carbon reaction. Key variables governing briquette reaction rate included CO₂ mole fraction and briquette void fraction.     

Hydrogen production from coal by separating carbon dioxide during gasification

Hydrogen generation during the reaction of a coal/CaO mixture with high pressure steam was investigated using a flow-type reactor. Coal, CaO and CO reactions with steam, and CO₂ absorption by Ca(OH)₂ or CaO occurred simultaneously in the experiment. It was found that H₂ was the primary resultant gas, comprising about 85% of the reaction products. CO₂ was fixed into CaCO₃ and CO was completely converted to H₂. Pyrolysis of the coal/CaO mixture carried out in N₂ was also examined. The pyrolysis gases were compared with gases produced by general coal pyrolysis. While general coal pyrolysis produced about 14.7% H₂, 50.5% CH₄, 12.0% CO and 12.0% CO₂, the gases produced from coal/CaO mixture pyrolysis were 84.8% H₂, 9.6% CH₄, 1.6% CO₂ and 1.1% CO.     

Catalytic coal gasification: use of calcium versus potassium

A comparative study is made of the relative catalytic effects of potassium and calcium on the gasification in air and 3.1 kPa steam of North Dakota lignitic chars prepared under slow and rapid pyrolysis conditions. It is indicated that potassium achieves relatively high catalytic activity by chemical interaction with the carbonaceous support, no matter how it is added to the lignite or its char. Deactivation of the catalytic potassium is brought about by interaction with inherent aluminosilicates. However, deactivation of calcium is related to its sintering via crystallite growth.     

Coal gasification at pressure by mixtures of carbon dioxide and oxygen

This Paper discusses results obtained from experiments on coal gasification by mixtures of carbon dioxide and oxygen under pressure. This research was carried out at the INIEX pilot station as part of the Belgian-German programme for the development of underground gasification. Tests were carried out to study the influence of the ratio of carbon dioxide to injected oxygen on the composition and the heating value of the gas obtained, the gasification efficiency and the consumption of the gasification medium. The experimental results can be satisfactorily explained by means of a model based on thermodynamic equilibria, assuming that gasification is brought about by an internal gasification agent formed by the volatile components of the coal and by an external gasification agent consisting of injected carbon dioxide and oxygen.     

冶金焦粉的综合利用

为了更好地利用冶金焦粉,分析了其来源和性质。详细分析了其在配煤炼焦、气化型焦、活性炭、分子筛、电极材料以及其它领域的应用。通过分析其在这些领域的应用,发现冶金焦粉可以降低生产成本,同时实现资源的合理利用。最后对焦粉的利用前景进行了评述。     

Thermal degradation of metallurgical coke

To understand the drastic deterioration of coke at the 3–5 m level above the tuyeres in the blast furnace, studies were made of the tensile strength in relation to the JIS drum strength, and measurements were made of the tensile strength of coke at high temperatures (maximum 2300 °C). Plastic deformation was observed above 2000 °C and this could be estimated from the microstrength and the porosity of coke. It was concluded that the factors affecting the resistivity to plastic deformation were the coke bonding between inerts and reactives and the existence of amorphous texture, and that the thermal degradation of the matrix strength must contribute, to some extent, to the drastic reduction in drum strength in the lower part of blast furnace.     

Catalytic gasification of coal using eutectic salts: reaction kinetics with binary and ternary eutectic catalysts

Kinetic studies of the catalytic steam gasification of Illinois No. 6 coal were carried out using binary and ternary eutectic salt mixtures in a fixed-bed reactor. The effects of major process variables such as temperature, pressure, catalyst loading and steam flow rate were evaluated for the binary 29% Na₂CO₃-71% K₂CO₃ and ternary 43.5% Li₂CO₃-31.5% Na₂CO₃-25% K₂CO₃ eutectic catalyst systems. A Langmuir-Hinshelwood rate expression was developed to explain the reaction mechanism for steam gasification using the binary and ternary catalysts. The activation energy of the ternary catalyst (98 kJ/mol) was less than that of the binary catalyst (201 kJ/mol) or single salt such as K₂CO₃ (170 kJ/mol). The molar heats of adsorption for the ternary and binary catalysts were exothermic and about 180 and 92 kJ/mol, respectively. The molten nature of the ternary eutectic at the gasification temperatures and its lower activation energy favored higher gasification rates compared to the single and binary alkali metal salts.