Coal Gasification Reaction Research Articles

The Reactivity and Kinetics of Yanzhou Coal Chars from Elevated Pyrolysis Temperatures During Gasification in Steam at 900–1200°C

This paper studied on the steam gasification reactivity and kinetics for Yanzhou coal chars prepared at elevated pyrolysis temperatures, using a fixed-bed reactor at the atmospheric pressure and gasification temperature ranging from 900°C to 1200°C. The following conclusions were reached mainly. The effect of gasification temperatures on the gasification reactivity was stronger than that of pyrolysis temperatures under the condition of elevated pyrolysis temperatures. Changes of reaction rate and surface area had a similar trend, but the relationship between the change of surface area and that of reaction rate was not proportional during the reaction process. While simulating the steam gasification reaction of Yanzhou coal chars at the temperatures of 900–1200°C, the shrinking un-reacted core model (SUCM) was superior to the volume reaction model (VRM) and the reaction–diffusion model based on the shrinking un-reaction core model was more favourable, which suggested that the diffusion had an effect on the reaction process, but its effect was not rather strong. Therefore, it may be considered that the reaction process was mainly controlled by the chemical reaction. Apparent activation energies obtained for the steam gasification of Yanzhou coal chars ranged from 127.17 kJ mol −1 to 196.55 kJ mol −1 . Moreover, it was also found that kinetic parameters were in accord with the isokinetic relationship, according to which the calculated isokinetic temperature for all the reactions was 1197°C.

Numerical simulation of coal gasification in entrained flow coal gasifier

This paper presents modeling of a coal gasification reaction, and prediction of gasification performance for an entrained flow coal gasifier. The purposes of this study are to develop an evaluation technique for design and performance optimization of coal gasifiers using a numerical simulation technique, and to confirm the validity of the model. The coal gasification model suggested in this paper is composed of a pyrolysis model, char gasification model, and gas phase reaction model. A numerical simulation with the coal gasification model is performed on the CRIEPI 2 tons/day (T/D) research scale coal gasifier. Influence of the air ratio on gasification performance, such as a per pass carbon conversion efficiency, amount of product char, a heating value of the product gas, and cold gas efficiency is presented with regard to the 2 T/D gasifier. Gas temperature distribution and product gas composition are also presented. A comparison between the calculation and experimental data shows that most features of the gasification performance were identified accurately by the numerical simulation, confirming the validity of the current model.

Brazing as a means of sealing ceramic membranes for use in advanced coal gasification processes

Coal is potentially a very inexpensive source of clean hydrogen fuel for use in fuel cells, turbines, and various process applications. To realize its potential however, efficient low-cost gas separation systems are needed to provide high purity oxygen that will enhance the coal gasification reaction and to extract hydrogen from the resulting gas product stream. Several types of inorganic membranes are being developed for hydrogen or oxygen separation, including porous alumina, transition metal oxide perovskites, and zirconia. Because they form the heart of the working device, numerous advances have been made in the fabrication and performance of these membrane materials. However, less emphasis has been placed on the materials that will be used in the balance of the device; in particular, the seals that bond the functional ceramic to the metallic structural component. In an effort to begin addressing this issue, we have examined ceramic-to-metal brazing as a method of sealing a model set of gas separation component materials: yttria-stabilized zirconia and stainless steel. In comparative high-temperature exposure testing of joints prepared using commercial brazes and a newly conceived braze alloy, the commercial material proved to be unsuitable due to excessive oxidation. On the other hand, the new material not only displayed superior oxidation resistance, but also excellent hermeticity in prototypic membrane testing.

Development of Numerical Simulation Technique for Coal Gasification on Entrained Flow Coal Gasifier (Modeling of Coal Gasification Reaction and Prediction of Gasifier Performance)

A modeling of a coal gasification reaction and prediction of gasification performance of an entrained flow coal gasifier are presented in this paper. The purposes of this study are to develop an evaluation technique for a design and performance optimization of the coal gasifier using a numerical simulation technique and to confirm the validity of the model. The coal gasification model suggested in this paper is composed by a pyrolysis model, char gasification model and gas phase reaction model. A numerical simulation with the coal gasification model was carried out on the CRIEPI 2 tons/day bench scale coal gasifier. Influence of air ratio on gasification performance, such as a per pass carbon conversion efficiency, amount of the product char, a heating value of the product gas and cold gas efficiency, is presented on the 2 t/d coal gasifier. Gas temperature distribution and product gas composition are also presented. Comparison between the computation and the experimental data shows that most features of the gasification performance have been captured accurately by the numerical procedure and the validity of the current model was confirmed.

Gasification of Seven Coals in Carbon Dioxide at Elevated Temperatures and High Heating Rates: Unification Approach of Reactivity.

Studies on coal gasification in CO 2 at elevated temperatures and high heating rates are necessary to develop IGCC technology. Coal gasification is a very complicated phenomenon, which makes a generalized understanding and description of gasification reactivity of a coal highly important. With a unique fluidized bed, the reactivity of seven coals was investigated at elevated temperatures and high heating rates. A modified random pore model was proposed to unify the gasification reactivity of coals obtained by us. It was identified that the coal reactivity can be unified with a master curve described by the new model for all the coals, temperatures and heating rates examined in this work. This model can also satisfactorily unify the experimental gasification data in literature. The modified random pore model can predict the experimental data with an error within about 5%. The error of the prediction by the modified random pore model is about one-third smaller than that of the prediction by the random pore model. It is recommended as a sub-model for simulation of coal gasification in practical gasifiers.

E208 PREDICTION OF INFLUENCE OF OPERATING CONDITIONS ON GASIFICATION PERFORMANCE OF ENTRAINED FLOW AIR BLOWN COAL GASIFIER

Deeply understanding of phenomena in a coal gasifier is very useful for an assessment gasifier performance and for an optimization of a design and operation parameters. In this paper, influence of operating conditions, such as oxygen concentration in oxygen enriched air as a gasifying agent and steam flow rate, on gasification performance of an entrained flow air blown coal gasifier is discussed. A numerical simulation, three-dimensional gas-particles reacting flow calculations were carried out to predict gasification performance of the gasifier. As a target of this simulation, the 2 tons/day (T/D) coal gasifier of CRIEPI was selected. The gas phase properties are calculated by three dimensional time-mean Eulerian conservation equations. The turbulent flow field is determined by the κ-ε two equations model. Radiative energy transfer is calculated by the discrete transfer radiation model. The pulverized coal and ash particle behavior is modeled via a Lagrangian manner. Coal gasification reaction model is constited by three chemical processes in the current model; a pyrolysis, a char gasification and gas phase reactions. Per pass gasification performance were only taken into account in the calculation (without unburnt char recycle system). The model result of the per pass carbon conversion efficiency increases as the oxygen concentration in gasifying agent increases. The per pass carbon conversion efficiency hardly changes even if the steam flow rate increases in the same oxygen concentration condition. The current model is potentially powerful tool for the evaluation of gasification performance.

H∞ control of gasification plant

The design and simulation of an H∞ control system for an experimental 87 MW fluidizedbed coal gasification reactor (‘gasifier’) are described. This is a highly coupled multivariable system that produces fuel gas by reacting coal, air and steam at a high temperature and pressure. H∞ optimization is used to design a robust controller that attenuates the effect of a pressure disturbance on four key outputs. The initial design was fairly robust to changes in load condition and to input non-linearities, but the performance was only moderate; it violated nine out of 48 limits given in a tentative specification, including some at nominal conditions. A redesign led to a 20-state controller that essentially met the specification, bar the transient violation of a lower pressure limit at the extreme operating point. This is shown to be due to the effect of input rate limits.

00/02111 Study on gasification reaction of coal and char in circulation fluidized bed (CFB). II. Effect of temperature and oxygen concentration on gasi

00/02111 Study on gasification reaction of coal and char in circulation fluidized bed (CFB). II. Effect of temperature and oxygen concentration on gasi

00/02110 Study on gasification reaction of coal and char in circulating fluidized bed (CFB). III. Comparison on gasification reaction between bubble fl

00/02110 Study on gasification reaction of coal and char in circulating fluidized bed (CFB). III. Comparison on gasification reaction between bubble fl

00/00641 Gasification reaction of coal and char in the circulating fluidized bed (CFB) I. Effect of operating gas velocity and solid circulating rate on gasification reaction in CFB

00/00641 Gasification reaction of coal and char in the circulating fluidized bed (CFB) I. Effect of operating gas velocity and solid circulating rate on gasification reaction in CFB

Coal-gasification kinetics derived from pyrolysis in a fluidized-bed reactor

Coal pyrolysis and gasification reactions were carried out in a fluidized-bed reactor (0.1 m i.d. by 1.6 m height) over a temperature range from 1023 to 1173 K at atmospheric pressure. The overall gasification kinetics for the steam–char and oxygen–char reactions were determined in a thermobalance reactor. The compositions of the product gases from the coal-gasification reactions are 30–40% H 2, 23–28% CO, 27–35% CO 2 and 6–9% CH 4 with heating values of 2000–3750 kJ m −3. The heating value increases with increasing temperature and steam/coal ratio but decreases with increasing air/coal ratio. Our kinetic data derived from the two-phase theory on coal gasification in a thermobalance reactor and coal pyrolysis in a fluidized bed may be used to predict the product-gas compositions.

Development of Pressurized Coal Partial Combustor. Characteristics of 7T/d Gasifier with Various Coal-Feed Ratios.

A pressurized coal partial combustor (P-CPC) with two-stage coal supply was tested to elucidate the characteristics of a 7T-coal/d air-blown coal gasifier. As the secondary coal-feed ratio (2ry coal/total coal) was increased, the following phenomena were observed, indicating depression of the coal gasification reaction ; (1) decrease of CO and H2 concentrations, (2) decrease of calorific value of product gas, (3) increase of hydrocarbon (CH4 + C2H6) content, (4) decrease of carbon conversion efficiency. Secondary coal supply is effective for stable slag discharge and the prevention of the slagging problem in a reductor due to the rapid temperature drop of molten slag. In conclusion, as long as stable slag discharge is obtained, it is effective to lower the 2ry coal-feed ratio to promote the coal gasification reaction, resulting in, for example, higher calorific value of the product gas.

硫酸処理石炭のガス化活性

Five coals (C:76-88 wt%,daf) were treated with sulfuric acid, hydrochloric acid and nitric acid. The treated coal and the char were gasified with a H 2 O (24%)-N2 mixture and an O 2 (2%)-N 2 mixture at constant rates or 2 o C/min and 20 o C/min, and their reactivities were analyzed with our modified volume reaction (MVR) model. With nitric and hydrochloric acids, differences in coal properties and gasification rates among coals persisted alter acid treatment. By contrast, after sulfuric acid treatment all or the coals showed similar levels or fixed carbon content and or moisture-holding capacity. These treated coals and chars show similar gasification reactivity

4-5.高温下における石炭チャーのガス化反応性(Session(4)資源変換)

4-5.高温下における石炭チャーのガス化反応性(Session(4)資源変換)

脱灰炭ＣＯ２ガス化反応速度のマセラルによる統一的評価

In the study of coal gasification, it's necessary to analyze the diffe-rent reactivity for coals. Then we estimated coal gasification reaction in point of macer-al, which was a component of coal, uniformly tried to evaluate the reactivity.We prepared four demineralized coals (Taiheiyo, Datong, Wandoan, Plateau) by the HF-HCl treatment to remove the catalytic effect of ash and carried out density separa-tion of these coals by the ZnCl2 solution (density range; 1.20-1.50) to have some sam-ples with concentrated maceral from same coal. Every fractions were gasified in a CO2 stream under 850°C, using a thermobalance and measured the reaction rate and reaction order from TG-curve. Futhermore, some fractions were characterized by ultimate and proximate analysis, CO2 surface area, chemisorbed oxygen, 13C-NMR, maceral analysis, which showed different values. Apparently, the initial reaction rate based on CO2 sur-face area was proportional to acertain maceral ratio, the rate corrected by CO2 surface area and maceral ratio had an exponential relation to H/C ratio. Also the reaction order was proportional to the vitrinite ratio in maceral groups.Consequently, it was possible that the reaction rate constant and reaction order were estimated uniformly with H/C ratio, CO2 surface area, and maceral ratio.

Oxidative Reforming of Coal Liquefaction Residues

Oxidative reforming of coal liquefaction residues was performed for two samples (Illinois No.6 and Yallourn coal liquefaction residues) at 150-290°C to change some physical constants to adequate values for the gasification in a coal gasification reactor. These physical constants (softening point and fluidity) and reactivities (pyrolysis and reaction with CO2) were also investigated. As the oxidation proceeded, softening points increased gradually and fluidities decreased for both samples. Adhesion forces decreased with oxidation and reached the value of original coal at 290°C for 0.5h for both samples. Pyrolysis reactivity was decreased by oxidation. Reactivity with CO2 increased for the Illinois No.6 liquefaction residue and decreased for the Yallourn liquefaction residue. To obtain information on structural changes during oxidation and their relation to properties and reactivities, FT-IR spectra of the samples were taken. Aliphatic and aromatic structures in the Illinois No.6 liquefaction residue decomposed and some carbonylic and hydroxylic functionalities were formed. Aliphatic structures in the Yallourn liquefaction residue decomposed and some carbonylic, ester and ethereal crosslinks were formed. Properties and pyrolysis reactivities were changed by formation of oxygen-containing functional groups. The difference of reactivity with CO2 in the two samples was due to the difference in structural change caused by oxidation.

石炭地下ガス化による水素製造に関する基礎研究

Underground coal gasification was examined to be a new system for hydrogen production. For this purpose, a packed bed of coal in a quartz glass tube was used to simulate experimentally an underground coal gasification system. Carbonization of coal and char gasification reactions were investigated for discussion of the process of hydrogen production with H2O as a gasifier.Results are summarized as follows.(1) Combustion reaction rate of the packed bed of coal was obtained from the propagation speed of flame front. Apparent activation energy for combustion reaction of coal in oxygen was 33 kJ/mol, which implies that mass transfer process may affect the combustion reaction. This means that the reaction rate and combustion temperature can be controlled by the flow rate of oxygen.(2) Production of hydrogen increased with combustion temperature and partial pressure of steam in the range of experiment. In the present study, 60 percent increment of hydrogen was attained in comparison with experiment of 02 as a gasifier.(3) Reaction, CO+H2O H2+CO2 was the most important for the increase of hydrogen production in a case of 600°C of combustion temperature, and both reactions, C+H2O H2+CO and CO +H2O-H2+CO2 contributed to the hydrogen production in the case of combustion temperatures higher than 750°C.

High temperature gasification reactivity of coal under severely product inhibited conditions

Analagous to the widely used burning profiles coal samples were characterised by their “gasification profiles”. From isothermal, fully chemically controlled, gasification experiments in a thermobalance, reaction times for complete gasification were obtained. The reaction times were extrapolated to higher temperatures using the Arrhenius equation (E a = 250 kJ/mole). Verification of extrapolated reaction times up to 1373 K was performed in an entrained flow reactor. Reaction times for gasification in a severely product inhibited gas phase were predicted.

A novel fused metal anode solid electrolyte fuel cell for direct coal gasification: a steady-state model

The simultaneous gasification of coal and the generation of electrical current in a high-temperature solid electrolyte fuel cell of the form C, O/sub 2/, fused metal/ZrO/sub 2/ (8 mol % Y/sub 2/O/sub 3/)/Pt, O/sub 2/ with a fused metal anode is a promising new concept. This process utilizes part of the Gibbs energy change of the coal gasification reaction to generate electricity with the high thermodynamic efficiency characteristic of fuel cells. The authors present a lumped parameter model that describes the steady-state behavior of this novel fuel cell and discuss the effect of operating conditions upon cell performance. The electrochemical cell reactor is capable of producing very high current and power densities and exhibits steady-state multiplicity over a wide range of operating conditions.

Evolution of hydrogen sulfide in a fluidized bed coal gasification reactor

The rates of evolution of hydrogen sulfide have been measured for the steam/oxygen gasification of a devolatilized Western Kentucky bituminous coal, a New Mexico subbituminous coal, and a Texas lignite in a pilot-scale fluidized bed reactor, and a phenomenological model has been formulated to correlate the results. The model assumes instantaneous devolatilization and partial combustion of the coal followed by rate-limited gasification of the char in a single well-mixed stage and includes kinetic correlations for the water gas shift reaction and char hydrodesulfurization. Estimated char reactivities agree well with results obtained in other studies, and the model predictions are generally satisfactory, especially considering the relative simplicity of the model. The results indicate that sulfur present in the coal as pyrite, mercaptans, aliphatic sulfides, and disulfides is converted completely, while sulfur in aryl sulfides and thiophenes is only partially converted. A substantial fraction of the sulfur converted during gasification is released in pyrolysis - 50-70% for the subbituminous coal and 35-45% for the lignite.