Progress Of Gasification Research Articles

Changes in the Biochar Chemical Structure during the Low-Temperature Gasification of Mallee Biochar in Air as Revealed with Fourier Transform Infrared/Raman and X-ray Photoelectron Spectroscopies

Structural changes in partially gasified char during low-temperature gasification in air were investigated using Fourier transform infrared/Raman and X-ray photoelectron spectroscopies. Two kinds of chars prepared from the gasification of mallee wood in 15% H2O–Ar at 600 and 900 °C were gasified in air at 375 °C in a thermogravimetric analyzer, separately. The breakage of large aromatic ring systems, the consumption of cross-linking structures, and the formation of dangling structures indicated the destruction of the aromatic ring systems of char with the progress of gasification in air. In addition, the oxidation of char was very significant at the initial stage (char conversion of <10%) of gasification in air, which was mainly due to the newly formed aromatic C–O structures. The newly formed aromatic C–O structure was also mainly responsible for the continuously increased total oxygen content, the total Raman intensity, and the total infrared (IR) intensity of char with the progress of gasification in a...

The Effect of Metallic Iron Particle on Coke-Matrix after Coke CO2 Gasification Reaction

In order to prevent pulverization and fracture of metallurgical coke, control of gasification reaction part in coke lump and embrittlement behavior is important. Addition of catalyst particle is an effective and a simple method for enhancement of the CO2 gasification reactivity. However, the effect of the catalyst particle on coke-matrix and gasification part of coke lump after gasification reaction has not been investigated. In this study, the effect of iron particles on coke-matrix state after gasification reaction is investigated experimentally. Coke-matrix vanishing is evaluated by spatial distribution of lump porosity and microscopic observation. Elastic modulus of coke-matrix is evaluated by nano-indentation method. Coke lumps with and without iron-particles (ferrous coke and formed coke, respectively) were used. These coke lumps were gasified by CO2-containing gas. Reaction temperature was set at 1173 K. Reaction gas compositions were set at 100/0 and 50/50 in ratio of CO2/CO. In each reaction gas composition, in ferrous coke, a decrease in the elastic modulus of coke-matrix with progress of gasification is smaller than that in formed coke and coke-matrix vanishing occurred. It is suggested that the iron particle promotes gasification reaction of coke-matrix selectively around itself (and coke-matrix in that part is rapidly vanished). It is also suggested that this reaction mechanism maintains elastic modulus of coke-matrix because of the local rapid gasification reaction around the iron particle.

Effect of pressure on gasification reactivity of three Chinese coals with different ranks

The gasification reactivities of three kinds of different coal ranks (Huolinhe lignite, Shenmu bituminous coal, and Jincheng anthracite) with CO2 and H2O was carried out on a self-made pressurized fixed-bed reactor at increased pressures (up to 1.0 MPa). The physicochemical characteristics of the chars at various levels of carbon conversion were studied via scanning electron microscopy (SEM), X-ray diffraction (XRD), and BET surface area. Results show that the char gasification reactivity increases with increasing partial pressure. The gasification reaction is controlled by pore diffusion, the rate decreases with increasing total system pressure, and under chemical kinetic control there is no pressure dependence. In general, gasification rates decrease for coals of progressively higher rank. The experimental results could be well described by the shrinking core model for three chars during steam and CO2 gasification. The values of reaction order n with steam were 0.49, 0.46, 0.43, respectively. Meanwhile, the values of reaction order n with CO2 were 0.31, 0.28, 0.26, respectively. With the coal rank increasing, the pressure order m is higher, the activation energies increase slightly with steam, and the activation energy with CO2 increases noticeably. As the carbon conversion increases, the degree of graphitization is enhanced. The surface area of the gasified char increases rapidly with the progress of gasification and peaks at about 40% of char gasification.

Behavior of Inherent Metallic Species as a Crucial Factor for Kinetics of Steam Gasification of Char from Coal Pyrolysis

Four pairs of raw and acid-washed brown coals were subjected to pyrolysis and in-situ steam gasification at 900 °C in fixed-bed reactors with or without forced gas flow through the bed of char particles. The chars from the acid-washed coals were gasified obeying a first-order kinetics with respect to the fraction of unconverted char regardless of the presence/absence of forced gas flow. Its presence/absence considerably influenced the gasification kinetics of the chars from the raw coals, even altering the manner of change in the rate of gasification with time and the char conversion, such as the apparent order of reaction. It was found that alkali and alkaline earth metallic (AAEM) species were allowed to stay in/on the char in the absence of the forced gas flow but volatilized extensively in its presence. Thus, the catalysis of AAEM species diminished in the presence of forced gas flow much quicker than in its absence, in which the catalysis was lost exclusively by intraparticle deactivation of AAEM species. The char conversion was quantitatively described as a function of time by a kinetic model that considered the progress of catalytic and noncatalytic gasification in parallel and also the loss of catalysis along with the progress of gasification.

Gasification rate analysis of coal char with a pressurized drop tube furnace

Two coal chars were gasified with carbon dioxide or steam using a Pressurized Drop Tube Furnace (PDTF) at high temperature and pressurized conditions to simulate the inside of an air-blown two-stage entrained flow coal gasifier. Chars were produced by rapid pyrolysis of pulverized coals using a DTF in a nitrogen gas flow at 1400°C. Gasification temperatures were from 1100 to 1500°C and pressures were from 0.2 to 2 MPa. As a result, the surface area of the gasified char increased rapidly with the progress of gasification up to about six times the size of initial surface area and peaked at about 40% of char gasification. These changes of surface area and reaction rate could be described with a random pore model and a gasification reaction rate equation was derived. Reaction order was 0.73 for gasification of the coal char with carbon dioxide and 0.86 for that with steam. Activation energy was 163 kJ/mol for gasification with carbon dioxide and 214 kJ/mol for that with steam. At high temperature as the reaction rate with carbon dioxide is about 0.03 s −1, the reaction rate of the coal char was controlled by pore diffusion, while that of another coal char was controlled by surface reaction where reaction order was 0.49 and activation energy was 261 kJ/mol.

灰分融点制御を目的とした石炭気流層ガス化実験に関する研究（ＩＩ） フラックス添加による灰分融点の降下効果

A laboratory scale entrained bed coal gasifier was used to study ash melting behavior and the effect of flux addition on the ash melting behavior. Blair Athol coal, Taiheiyo coal and limestone as a flux were used in this study.Ashes produced by char gasification, mostly adhere to the surface of unreacted char particle, and flow together with char in gases flow. Ash adhension to the gasifier wall, ηa, w was increased with the progress of gasification, and was mostly increased around at the exit of gasifier, where char gasification was in the final stage.By the flux addtion, slag (Blair Athol coal, FT > 1873K) melting temperature was reduced to 1613K, when CaO content is about 40wt% in slag. The ratio of flux in slag to the flux added, η was found to about 0.65 in this work.Melting temperature change of slag with flux addition can be explained by the mineral change in slag with a phase diagram for CaO-Al2O3-SiO2 compositions.

Disintegration of Coke by mechanical impact under gasification reaction.

In order to elucidate the behavior of coke fines in blast furnace, fundamental experiments were carried out on the disintegration of coke during gasification reaction accompanied by mechanical impact.The following results were obtained:(1) Coke fines of high ash content are generated with the progress of gasification, which suggests the close correlation between generation of coke fines and gasification.(2) Coke fines generate increasingly when the mechanical impact strength is beyond a critical value.(3) Reaction temperature, gas composition and coke size also affect the generation of coke fines causing a different rate of gasification.A mathematical model was introduced using the rate equation of coke fine generation based on the experimental results. The calculation results by this model agree very well with the experimental results. The model, therefore, is supposed to be applied for the investigation of the behavior of coke fines in blast furnaces.

A quantitative evaluation of active site number for CO2 gasification of various coal chars by temperature-programmed desorption method.

A temperature-programmed desorption (TPD) method was applied to the characterization of CO2 gasification of coal chars obtained by pyrolysis of coals of various ranks ranging from brown to sub-bituminous coals. Gasification was carried out at temperatures of 1073 and 1273 K and pressures from 0.4 to 1.6 MPa, using a high-pressure TGA apparatus. For all chars employed, the rate constant based on the initial char weight, kv, decreased with the progress of gasification. This variation of kv was unexplained in terms of the change in the BET surface area of the chars obtained at different conversions; in general, the rate constant based upon the surface area, ks, decreased with char conversion lower than about 0.2 and then remained constant before decreasing again at the conversion of 0.8 towards the completion of the reaction. The active site number, NCO, was evaluated on the basis of the amount of CO desorbed in TPD runs after CO2 was adsorbed. Thus, the rate constant per unit number of active sites, ka, was estimated on the basis of the NCO and the Kv values for chars having different conversion levels. The values of ka obtained at 1073 and 1173 K were found to be invariable for conversions up to about 0.8 to 0.9 and to be of the same order of the magnitude for all chars at a given temperature. However, in all cases they decreased with conversion in the range higher than 0.9. This decrease in char reactivity was attributed to variation in the carbon structure of the char. X-ray diffraction spectra indicated an appreciable growth of the graphite peak at the final stage of gasification.