Steam Gasification Rate Research Articles

Graphite and Graphite Oxide: New Models to Analyze the Calcium Catalytic Effect on Steam Gasification of Lignite and Char

Graphite oxide (GO) and graphite (G) were used as Shengli lignite (SL) and char (SL⁺-T) models to study gasification reactivity for the first time. The steam gasification performance of SL⁺, SL⁺-T, G, GO and the corresponding Ca-added samples was evaluated in a fixed bed reactor equipped and linked with a downstream GC system. The samples were comprehensively characterized by Fourier transform infrared, XRD, Raman, X-ray photoelectron spectroscopy, and ¹³C NMR. Results show that calcium exerted a significant catalytic effect on the steam gasification of SL⁺ and GO but had a limited impact on high-temperature char and G. Once the char was oxidized using a similar liquid oxidation method to prepare GO, the steam gasification rate of the oxidized Ca-added char presented higher reactivity at low temperature, which was similar to the gasification behavior of GO with calcium addition. Characterization results show that the oxygen-containing functional group of SL is similar to GO. By comparing the catalytic effect of calcium of oxidized char and GO with that of char and G, it was further demonstrated that the oxygen-containing functional group was the key structure for Ca-catalyzed coal gasification. These results suggest that GO is similar to SL not only in terms of its oxygen structure but also in its steam gasification reactivity. Thus, GO is an excellent model of lignite. This study provides a new lignite modeling approach with a more accurate structure than reported lignite models and is suitable for precise investigations of the structural evolution of lignite as well as the catalytic mechanism of calcium in steam gasification.

Characteristics and kinetics of coal char steam gasification under microwave heating

The behavior and kinetics of coal char steam gasification under microwave heating are investigated. The influence of the coal char particle size, water injection rate, and reaction temperature on the carbon conversion rate and gas product evolution during microwave heating gasification are considered and compared to the results from coal char steam gasification using conventional heating under the same conditions. The results show that microwave heating can accelerate the reaction rate of coal char steam gasification and improve the quality of the gas product. It was found that at temperatures varying from 600 to 900 °C, the coal char steam gasification reaction was well described using the shrinking core model (SCM). Activation energies of 82.8 kJ/mol and 114.3 kJ/mol were obtained for microwave heating and conventional electric heating, respectively.

Impacts of Bed Material Activation and Fuel Moisture Content on the Gasification Rate of Biomass Char in a Fluidized Bed

The use of certain bed materials has been Activated found to increase the steam gasification rate of biomass char. olivine The present work investigates how this phenomenon is influenced by different parameters (e.g., temperature, fuel type, and fuel moisture content), using a laboratory-scale bubbling fluidized bed gasifier. Silica sand, fresh olivine, and activated olivine were employed as bed materials, and three biomass fuels (wood chips, wood pellets, and forest residue pellets) were considered. Switching the bed material from silica sand to activated olivine resulted in a significant increase in the char gasification rate for all three fuels, with further increases noted as the fuel particle size was decreased. The observed effect was strongest (up to 4-fold) during the initial conversion phase (char gasification degrees < 20%) when the temperature was relatively low (<= 800 degrees C). The moisture content of the wood chips (0-40%) had no significant effect on the char gasification rate.

Direct production of high hydrogen syngas by steam gasification of Shengli lignite/chars: Significant catalytic effect of calcium and its possible active intermediate complexes

The catalytic effect of calcium on the steam gasification of Shengli chars was studied in this work. The calcium-added chars were prepared by pyrolysis under argon atmosphere from calcium oxide added demineralized Shengli lignite. The chars were characterized in detail by SEM-EDX, XRD, Raman, FTIR and XPS and were tested on a fixed-bed reactor to evaluate its performances steam gasification. Calcium was found to have significantly promotional effect on the steam gasification of char samples with reduces of activation energy. It was observed the presences of 5wt% or above in the char significantly enhanced H2 productions, which resulted in high H2/CO ratio of syngas. The SEM-EDS and XRD results suggested calcium was highly dispersed within the char particles, CaO and CaS presented in the char samples, but the hydrochloric acid treatment of the char caused significant loss of these calcium compounds. The steam gasification rate of the acid-treated samples was still much higher than that of the no-calcium-added char, which elucidates that superior steam gasification performance of the Ca-added chars was not the simple CaO species in the char, instead, a special calcium lignite intermediate complex “R1-O-Ca-O-R2” (R representing aromatic or aliphatic constituents), formed within char during the pyrolysis. Thus the crosslink-like intermediate complexes “R1-O-Ca-O-R2” structure between calcium and chars was postulated to be the decisive factor to promote the steam gasification of Shengli chars with more production of high hydrogen syngas.

3-75p 熱分解charの加圧水蒸気ガス化速度向上に関する研究(バイオマス等,研究発表(ポスター発表))

3-75p 熱分解charの加圧水蒸気ガス化速度向上に関する研究(バイオマス等,研究発表(ポスター発表))

A theoretical model to estimate steam and CO2 gasification rates based on feedstock characterization properties

An improved model for the estimation of gasification rate constants using CO2 and steam as gasifying agents is presented in this work. The theoretically deduced model only considers the micropore surface area and catalyst (alkali) content of the raw feedstock as inputs for the gasification rate estimation. The main advantage compared with other models is its simplicity in determining the rate constant with only one regression parameter, which is a result of introducing, for the first time, theoretical limits to the activation energy of the main gasification reactions (steam gasification and Boudouard reactions).Experiments were carried out in a setup that reduces the most common problems associated with laboratory gasification procedures, such as misinterpretation of a maximum gasification rate, adverse effects on the char properties during the pyrolysis phase, and interparticle diffusion. Statistical analysis showed that the model fitted well with experimental data, since the determination coefficient was higher than 0.96 for 13 coal samples with a broad range of ash contents (6.4% to 74.8%).The new model gives an accurate mixing rule that is useful in determining gasification rates of different feedstock mixtures. The new concepts presented in this research can be used for simulating and determining suitable process conditions for industrial gasifiers operating with different feed mixtures.

Catalytic Gasification Activity of Na2CO3 and Comparison with K2CO3 for a High-Aluminum Coal Char

The catalytic performance of Na2CO3 for high-aluminum coal gasification was specially investigated, and the effect of the ash constituents in Sunjiahao (SJH) high-aluminum coal char on the catalytic activity of Na2CO3 and a comparison with that of K2CO3 were also studied through steam gasification experiments of SJH char catalyzed by Na2CO3 or K2CO3 carried out using a thermogravimetric analyzer and a fixed-bed reactor at 800 °C, respectively. The results indicate that the steam gasification rates of SJH char and acid-treated SJH char catalyzed by Na2CO3 are higher than those by K2CO3 with equal masses of catalyst. Na2CO3 can be used as the catalyst for high-aluminum coal gasification at 800 °C. The effect of the ash components on the catalytic activity of Na2CO3 is larger than that of K2CO3 in the catalytic steam gasification of SJH high-aluminum coal char at 800 °C. The X-ray diffraction (XRD) patterns of the steam gasification ashes of SJH char impregnated with Na2CO3 or K2CO3 reveal that the main comp...

Production of High H2/CO Syngas by Steam Gasification of Shengli Lignite: Catalytic Effect of Inherent Minerals

The steam gasification of Shengli lignite (SL-raw) and demineralized samples (SL-HCl and SL-HF) obtained by sequential leaching with hydrochloric acid and hydrofluoric acid aqueous solutions was conducted using fixed-bed microreactor equipment. The high steam gasification rate of Shengli lignite was achieved at a lower temperature range of 616–750 °C compared to the demineralized lignite SL-HCl and SL-HF, indicating that the inherent minerals within Shengli lignite had a distinguished catalytic effect on the steam gasification. The initiating temperature for the steam gasification of SL-raw was 616 °C, which was about 140 °C lower compared to the initiating temperature of demineralized lignite samples SL-HCl and SL-HF at 756 °C. On the basis of the very similar characteristics of steam gasification of SL-HCl and SL-HF, it was indeed confirmed that the principal component of inherent minerals that played a catalytic effect on the steam gasification reaction was calcium ion, which can be readily eluted by h...

Clarifying the influence of moisture on the ignition and combustion of wet Victorian brown coal in air-firing and oxy-fuel modes: Part 2: Contribution of gasification reaction to char oxidation rate

This paper is the second part of the study to clarify the influence of moisture in Victorian brown coal oxy-fuel combustion, with a focus on char oxidation and gasification reaction through experimental and modelling efforts. An in-situ high-speed two-colour pyrometer with the wavelength band of 0.85–1.05μm was employed to measure particle temperature in the flat flame burner reactor. The combustion stage of carbon particle was simulated for the transient phenomena with particle heating and radiative heat transfer. The multiple surface reaction single-film approach, including char–O2, char–CO2 and char–steam reactions, was employed and the contribution of individual reactions to carbon consumption rate was determined via matching with the measured particle temperature. Irrespective of the initial moisture content, the extent of char–steam gasification reaction was found to account for ~15% in the air-firing case. This reaction was mainly triggered by the external steam in the reactor, rather than the inherent moisture that resided preferentially as volatile cloud on char particle surface. The combined effect of both char–CO2 and char–steam gasification was significant in oxy-fuel combustion mode, especially for the wet coal. In the oxy-21 case, these two reactions have a total extent of around 8% and 18% on the burning char surface of dried and wet coal, respectively. The char–CO2 gasification is insignificant, because the char particle temperature was low. Increasing the oxygen percentage to 31% in CO2 enhanced the total extent of these two gasification reactions to 28%, based on the mass of total carbon. Such an extent is comparable with the literature. However, the steam gasification rate for brown coal char was far higher, ~26% relative to ~10% for high-rank bituminous coal reported in the literature. This substantiates the strong steam gasification reactivity of Victorian brown coal char. The contribution of inherent moisture to char–steam gasification reaction is crucial in the combustion of wet coal in the oxy-21 case, accounting for ~10%. This is due to the long residence of the unevaporated steam as a thick cloud on the char surface. Increasing the oxygen concentration in CO2 enhanced the char–O2 reaction, the release rate of volatiles and inherent moisture. Therefore, the char–steam reaction caused by the inherent moisture within coal matrix was minimised and eventually diminished in the oxy-31 case.

Effects of titanium dioxide as direct causticization agent on the pyrolysis and steam gasification characteristics of straw black liquor solid

Black liquor gasification process with direct causticization using titanium dioxide (TiO2) is considered a promising technology for black liquor recovery in the future. In this study, laboratory-scale pyrolysis and steam gasification experiments with direct causticization using TiO2 for straw black liquor solid were performed in a thermogravimetric analyzer and a tube furnace, respectively. Effects of TiO2 on the pyrolysis and steam gasification characteristics are discussed on the basis of product analysis. The results show that after adding TiO2 at temperature higher than 550°C, the direct causticization reactions happened, while the thermogravimetric behavior of the black liquor solid along with releasing pattern of carbon dioxide and carbon monoxide was changed. In the presence of TiO2, swelling and agglomeration were prevented during the pyrolysis process. Meanwhile, sodium emission was significantly decreased and the steam gasification rate of the black liquor char at 850°C was substantially improved. The melting process during gasification was suppressed with direct causticization. Moreover, the yield of hydrogen was kept constant while the yields of carbon dioxide and carbon monoxide were increased during the steam gasification process with direct causticization.

Kinetics of steam and CO 2 gasification of high ash coal–char produced under various heating rates

Abstract Char particles of high ash Indian coal with different sizes are produced using thermogravimetric method at different heating rates. Particle diameter and porosity changes during devolatilization significantly affect char gasification rates. The effect of coal particle size on char production under various heating rates is reviewed. Char gasification is affected by operating conditions such as reaction temperature, char production method, and particle size in addition to chemical composition and physical structure of char. The measurements of the steam and CO2 gasification rate of the produced chars are performed by an isothermal thermo-gravimetric analysis at the temperatures of 900, 950, and 1000 °C under ambient pressure conditions. It is found that the reactivity of char gasification is increased along with heating rate of char. Three kinetic models are applied to describe the varying conversion rate: volumetric model, grain model, and random pore model. The activation energy of the gasification is varied based on the char generation method and particle sizes. The activation energy is varying from 122 to 177 kJ mol−1 for steam gasification and 130 to 214 kJ mol−1 for CO2 gasification to different sized char particles. The effect of char heating rate on gasification is more pronounced in the activation energies of smaller sized particles.

Steam Gasification Rates of Three Bituminous Coal Chars in an Entrained-Flow Reactor at Pressurized Conditions

Three bituminous coal chars (Illinois #6, Utah Skyline, and Pittsburgh #8) were gasified separately at total pressures of 10 and 15 atm in an entrained-flow reactor using gas temperatures up to 1830 K and particle residence times <240 ms. Most of the experiments were performed at conditions where the majority of particle mass release was due to H2O gasification, although select experiments were performed at conditions where significant mass release was due to gasification by both H2O and CO2. The measured coal data were fit to three char gasification models including a simple first-order global model, as well as the CCKN and CCK models that stem from the CBK model. The optimal kinetic parameters for each of the three models are reported, and the steam reactivity of the coal chars at the studied conditions is as follows: Pittsburgh #8 > Utah Skyline > Illinois #6.

Effect of char generation method on steam, CO2 and blended mixture gasification of high ash Turkish coals

Char particles of high ash Turkish coal of two sizes were produced by pyrolysis in an atmospheric pressure thermo-gravimetric apparatus using 3 heating rates (100K/min, 500K/min and 800K/min). It is observed that the particle size (for particles between 0.8 and 3mm) did not change the pyrolysis process results. Char gasification rates in CO2, steam and mixture of CO2+steam are investigated in the same TGA system over the temperature range of 850–950°C. The pyrolysis heating rate for char formation is observed to have a marked influence on the subsequent gasification reactivity of the char. The results indicate that the char produced from high heating rates show improved gasification rates. Smaller particles exhibit higher char–CO2 and char–steam gasification rates. Increasing the temperature from 850 to 950°C, leads to a significant reduction of the time required for 50% char conversion both for small and large particles. The maximum reaction rate is shifted to higher conversion degrees when the chars are produced from high heating rates. The gasification rate of char–H2O strongly depends on the H2O partial pressure. Gasification rates in CO2 ambiance are much lower than those in steam. For CO2–steam blended ambiance, no obvious CO2 inhibition effect is observed. But this topic requires more investigation. Kinetic parameters of the char particles are estimated using three different kinetic models. The obtained activation energies for char gasification essentially depend on the particle size and the three kinetic models give very close activation energy values for all the tested conditions.

Gasification of pyrolysis chars from sewage sludge

Gasification of char derived from sewage sludge was studied by using the TG–MS system. Experiments were carried out at different temperatures and steam concentrations. The temperatures of 700–900°C were necessary to complete the conversion in reasonable time. Three reaction rate models for gas–solid reaction were applied to describe the effect of char conversion on the reaction rate. In comparison to the shrinking core model for reaction-controlled regime and random pore distribution models, simple pseudo-homogeneous first-order kinetics was found to be the best for predicting the rate of char steam gasification. Kinetic parameters estimated from the experimental data are in accordance with the literature for lignocellulosic char gasification and are the first ones published for sewage sludge char gasification.

Influences of heating rate during coal char preparation and AAEMs on volatile–char interaction with different sources of biomass volatile

Volatile–char interaction is important for the operation of co-gasification of coal and biomass. Biomass generally produces large amount of volatiles while char is mainly produced from coal. Hence, in this study, the interaction between coal char and volatiles from biomass samples (xylan, cellulose and rice straw) was examined using a rapid-heating thermobalance reactor. Three types of coal char, consisting of slow pyrolyzed-coal char (Ex-char), fast pyrolyzed-coal char (In-char), and acid washed-coal char (Ac-char), were employed to reveal influences of heating rate during char preparation and retention of alkali and alkaline earth metallic (AAEM) species on char surface. The steam gasification rates of all coal chars in both cases with and without volatile contacting were investigated from the gas evolution rate and remaining char analyses. The results indicate that the steam gasification rates of Ex-char and In-char were significantly diminished by the volatiles derived from all sources, especially rice straw. However, in the case of Ac-char, the reduction of steam gasification rate was less important. Moreover, the Ex-char exhibited the catalyst for the decomposition of biomass volatiles, resulting in the increase in gas production rate. Porous structure and the AAEM over char play crucial roles on the volatile–char interaction.

Effect of catalysts on the reactivity and structure evolution of char in petroleum coke steam gasification

Petroleum coke was gasified using non-isothermal thermogravimetric analysis (TGA). The catalytic effects of FeCl3, CaCl2, KCl, K2CO3, K2SO4, KAC and KNO3 were studied. It was found that the gasification of petroleum coke was inefficient at temperature <1000°C. However, with the addition of catalysts, the efficiency greatly improved. In particular, with the addition of K2CO3, gasification was completed quickly in 10min and the final temperature was about 900°C. To further uncover the catalytic mechanism, the structures of char samples at various conversions were investigated with Raman spectra (Raman) and X-ray diffractometry (XRD). The Raman spectra showed that with K2CO3 catalyst, the formation of active intermediates C(O) and M–C–O were enhanced by the relatively small aromatic ring systems with 3–5 fused benzene rings, alkyl–aryl C–C structures and methyl carbon dangling onto an aromatic ring. K2CO3 could stimulate the crackdown of big aromatic ring systems into small aromatic ring systems. Thereby, the addition of K2CO3 could increase the steam gasification rate of petroleum coke. XRD analysis indicated that with char conversion increasing, char structure became more ordered with a large amount of aromatic ring formed in original samples, while the degree of graphitization was lowered with K2CO3 addition, which is favorable for char gasification.

Kinetic analysis of catalytic coal gasification process in fixed bed condition using Aspen Plus

Coal is one of the energy resources useful for solving the energy crisis. It has met nearly half of the rise in global energy demand over the last decade, growing even faster than total renewables. Catalytic coal gasification is useful technology in SNG (Substitute Natural Gas) and IGFC (Integrated Gasification Fuel Cell) plants that use coal. The Catalytic Coal Gasification Process developed by Exxon in 1978 was simulated with Aspen Plus in the fixed bed type reactor. The purpose of this study is to derive kinetic parameters from experimental results in literature and compare them using the catalytic coal gasification model in Aspen Plus. Carbon–Steam reaction is an important reaction in catalytic gasification reaction since steam is only an oxidant feeding in the system. Mainly, alkali metal gasification catalysts like potassium carbonate increase the rate of steam gasification. The kinetic values calculated from the experimental data are 0.30126, 0.09204, and 0.076995 (cc mol−1 h−1). Obtained kinetic value kf determines ko and E values compared with Arrhenius equation to input Aspen Plus simulation. Another major focus is on low-rank coal because upgrading low-rank coal is very useful for energy efficiency and environmental aspects. Upgrading coal means removing moisture from low-rank coal. Boiler efficiency is decreased because a lot of moisture content and CO2 emissions are increased. Carbon dioxide and the flue gas emissions for the same energy level can be reduced by about 30%. Low-rank coal will be increased energy requirement for removing carbon dioxide. The investigation of the drying characteristics of low-rank coal is performed in our laboratory. The experimental results based on the drying characteristics are reflected in this simulation process.

Intrinsic reactivity of biomass-derived char under steam gasification conditions-potential of wood ash as catalyst

The influence of ash on the steam gasification rate of pine wood derived char particles in the temperature range 600–800°C is investigated. Ash derived from pine wood or specific ash components were added to the pine-wood (before pyrolysis) or to the produced char (after pyrolysis) via physical mixing or impregnation. The addition method and the amount and type of ash/ash component have been studied and the obtained gasification rates are compared. Impregnation of ash/ash components by ∼10wt% or more (in the original pine wood) always resulted in a significant increase in the (initial) gasification rate. At 700°C, e.g., impregnating 9.5wt% KOH in pine wood resulted in complete char conversion within 12min, corresponding to an increase in (initial) gasification rate by a factor 30 compared to char without impregnation. SEM images of the chars showed that impregnating the wood with concentrations up to 14wt% resulted in unevenly distributed ash (components) in the particles. Based on this, the hypothesis is that besides the overall amount of ash also its distribution among and inside the char particles is important for enhancement of the reaction rate. A biomass gasification concept in which the steam gasification reaction of char is catalyzed by concentrating the ashes in the biomass is feasible.

A novel technique for measuring the kinetics of high-temperature gasification of biomass char with steam

Solar thermal gasification of biomass is a promising technology that allows for operation at high temperature without burning a large portion of the biomass feedstock. Additionally, the process allows for solar energy to be stored and transported in chemical form. In order to design efficient solar reactors, a kinetic rate expression for high-temperature steam gasification is needed. Various methods have been used to measure the steam gasification rate of coal and biomass char at temperatures up to 1000°C. These conventional techniques often fail to collect accurate kinetic data at temperatures above 1000°C due to heat and mass transfer resistance, and the time constants associated with the analysis system. In this paper we discuss a novel kinetics measurement technique based on a modified fixed bed and data collected solely from a gas flow meter. The technique was used to collect kinetic rate data for switchgrass char over a range of reaction conditions between 1000°C and 1150°C. An empirical expression to predict the kinetic rate as a function of the degree of conversion, temperature, steam concentration, and hydrogen concentration was developed. The random pore model was used to predict the reaction rate as a function of conversion, and the initial kinetic rate was fit using a Langmuir–Hinshelwood type expression.

Use of manganese ore in chemical-looping combustion (CLC)—Effect on steam gasification

The chemical-looping combustion (CLC) process is a novel solution for efficient combustion with direct separation of carbon dioxide. The process uses a metal oxide as an oxygen carrier to transfer oxygen from an air to a fuel reactor, where the fuel reacts with the solid oxygen carrier. When solid fuel is used in CLC, the char needs to be gasified by e.g. steam to form H2 and CO that can be subsequently oxidized to H2O and CO2 by the oxygen carrier. In this work, the influence of the oxygen carrier on the rate of steam gasification is studied, by comparing the conversion of petcoke in the presence of manganese ore to that of ilmenite. The experiments were carried out in a fluidized-bed reactor at 970°C using a fluidization gas of 50% steam in nitrogen. The manganese ore shows an increase by a factor five in the rate of steam gasification of char as compared to ilmenite. The dramatic increase in rate of steam gasification, in combination with potentially low costs of this material suggests that manganese ore could be an interesting material for CLC with solid fuels.