Enhanced Carbon Conversion Research Articles

Steam reforming of different biomass tar model compounds over Ni/Al2O3 catalysts

This work focuses on the removal of the tar derived from biomass gasification by catalytic steam reforming on Ni/Al2O3 catalysts. Different tar model compounds (phenol, toluene, methyl naphthalene, indene, anisole and furfural) were individually steam reformed (after dissolving each one in methanol), as well as a mixture of all of them, at 700°C under a steam/carbon (S/C) ratio of 3 and 60min on stream. The highest conversions and H2 potential were attained for anisole and furfural, while methyl naphthalene presented the lowest reactivity. Nevertheless, the higher reactivity of oxygenates compared to aromatic hydrocarbons promoted carbon deposition on the catalyst (in the 1.5–2.8 wt.% range). When the concentration of methanol is decreased in the feedstock and that of toluene or anisole is increased, the selectivity to CO is favoured in the gaseous products, thus increasing coke deposition on the catalyst and decreasing catalyst activity for the steam reforming reaction. Moreover, an increase in Ni loading in the catalyst from 5 to 20% enhances carbon conversion and H2 formation in the steam reforming of a mixture of all the model compounds studied, but these values decrease for a Ni content of 40%. Coke formation also increased by increasing Ni loading, attaining its maximum value for 40% Ni (6.5 wt.%).

Synthesis and characteristics of BaSrCoFe-based perovskite as a functional material for chemical looping gasification of coal

Perovskite-type oxides have attracted considerable attention as advanced materials with redox stability. In this study, four different types of perovskite oxides were used in chemical looping gasification (CLG) to enhance carbon conversion and gas production. The performances of perovskites for CLG were investigated in a fixed-bed reactor. The perovskite oxides were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy (SEM). Results demonstrated that all of the perovskites could improve both the yield and the quality of gas production. Particularly, Ba0.5Sr0.5Co0.8Fe0.2O3-δ perovskite (BSCF) exhibited the best performance. Moreover, the gas production in the CLG process was improved by increasing the reaction temperature and using steam/hydrogen mixed atmosphere. The optimal gasification temperature and steam/hydrogen ratio for BSCF were approximately 850 °C and 0.641, respectively. The performance of BSCF stabilized after six cyclic experiments. Moreover, XRD, XRF, and SEM results showed that BSCF is capable of structural recovery and exhibits stable elemental composition in mixed atmosphere. BSCF has good cyclic performance and is a promising oxygen-carrier material for gasification.

Effect of Ternary Eutectic Salt on the Calcium Sulfate Oxygen Carrier for Chemical Looping Combustion of Coal Char

AbstractThe effect of a ternary eutectic salt (43.5 % Li2CO3–31.5 % Na2CO3–25 % K2CO3) on the CaSO4 oxygen carrier for chemical looping combustion (CLC) of coal char is experimentally investigated in a bench‐scale fluidized‐bed reactor with steam as the gasification agent at atmospheric pressure and 925 °C. The ternary eutectic catalyst is added to the CaSO4 oxygen carrier by physical mixing and impregnation, respectively. The enhanced carbon conversion and shortened reaction time in the fluidized bed reactor, coupled with the high weight loss rate of CaSO4 reduction with CO in the thermogravimetric analyzer (TGA), suggest that the reactions of coal char gasification and CaSO4 reduction are synergistically catalyzed in the presence of the ternary eutectic salt. The modified oxygen carriers prepared by physical mixing and impregnation show no significant difference in carbon conversion and gasification rates according to the experimental results. The sample with catalyst impregnated into the mixture of anhydrite and coal char gives higher activity compared to the samples with catalyst impregnated into the coal char or anhydrite solely, due to the more uniform distribution of the catalyst.

Experimental investigation on biomass gasification using chemical looping in a batch reactor and a continuous dual reactor

Biomass gasification using chemical looping (BGCL) is an innovative biomass gasification technique using lattice oxygen from oxygen carrier. The present work selected natural hematite as oxygen carrier, and experimental results from batch reactor and continuous reactor were compared in this work. The results showed that the presence of hematite would accelerate the process of biomass gasification and enhance carbon conversion rate, and hematite could increase the heat-carrier capacity of bed materials in the continuous reactor. In the batch reactor, carbon conversion efficiency and fraction of CO+H2 increased within the temperature range of 750–900°C. However, syngas yield in the continuous reactor reached the maximum of 0.64Nm3kg−1 at 850°C. Besides, the effect of hematite fraction on the gasification performance was similar between the batch reactor and the continuous reactor. When hematite fraction was exceed 40wt.%, higher hematite fraction resulted in higher carbon conversion efficiency and lower syngas production. At last, the phase characterization of reduced hematite was investigated. Fe3O4 were the main reduced phases of hematite in the batch reactor, while FeO might be existed in the continuous reactor.

Thermodynamic analysis of biomass gasification for biomethane production

A thermodynamic analysis has been performed to predict the biomass gasification performance on the basis of the minimization of Gibbs free energy. The theoretical methane yield was further predicted based on the equilibrium in the downstream processes. A C–H–O ternary diagram is proposed to predict the boundary for the formation of carbon deposit. Three zones, namely carbon deposit, carbon-free and intermediate zone, are defined, with possible carbon formation or elimination mechanisms being postulated. The biomass gasification performance using different gasifying agents, namely H2O, CO2, O2 or air, was then analyzed. Results showed that the steam addition is conductive to enhance carbon conversion and shrink the carbon deposit zone, but the use of air, O2 and CO2 will impose a negative impact on the methane yield and H2/CO ratio. The maximum methane yield can be achieved at the temperature at which carbon is completely converted. The effects of pressure are dependent on whether or not solid carbon is absent. Based on the analysis on thermodynamic and exergetic efficiencies, it is concluded that steam gasification is the preferred conversion scheme for biomethane production.

Simulation Research on Performance of IGCC System with Brown Coal/Liquid CO<sub>2</sub> Slurry Feed

A simulation research on IGCC process adopting the technique of coal/liquid CO2 (CO2(l)) slurry was proposed. A model of a brown coal slurry fed IGCC system with CO2 capture unit was developed in ASPEN Plus. This model was used to investigate the thermal performance of the IGCC process under different operating conditions. Three kinds of Chinese brown coal were employed in this work. The simulation results show excellent performance of IGCC system when brown coal/CO2(l) slurry feed in gasification system. Enhanced carbon conversion rate and net plant efficiency can be observed with less coal consumption meanwhile. H2O/CO ratio decreases because of more CO and less H2O in the syngas with brown coal /CO2(l) slurry feeding. The net CO2 output from IGCC system also decreases as the advantage of CO2 capture and reuse in coal/CO2(l) slurry.

The Effect of Biomass Contents with Heavy Metal on Gasification Efficiency during Fluidized Bed Gasification Process

Catalysis was used to increase the H2 production, syngas heating value, enhanced carbon conversion efficiency and cold gas efficiency during gasification. Due to Cu and Zn were abundant in waste according to previous researches, this research discussed the effect of Cu and Zn on artificial waste gasification. The syngas composition and total lower heating value (LHV) were determined in this study. The results showed that the existence of Cu and Zn increased production of H2 and CO. However, the production of CH4 and CO2 decreased. At same time, total LHV was also increased. Additionally, the different Cu concentration affected gas composition and LHV, but the effect of Zn concentration was not significant.

Double CO 2 fixation in photosynthesis–fermentation model enhances algal lipid synthesis for biodiesel production

In this study, a photosynthesis–fermentation model was proposed to merge the positive aspects of autotrophs and heterotrophs. Microalga Chlorella protothecoides was grown autotrophically for CO 2 fixation and then metabolized heterotrophically for oil accumulation. Compared to typical heterotrophic metabolism, 69% higher lipid yield on glucose was achieved at the fermentation stage in the photosynthesis–fermentation model. An elementary flux mode study suggested that the enzyme Rubisco-catalyzed CO 2 re-fixation, enhancing carbon efficiency from sugar to oil. This result may explain the higher lipid yield. In this new model, 61.5% less CO 2 was released compared with typical heterotrophic metabolism. Immunoblotting and activity assay further showed that Rubisco functioned in sugar-bleaching cells at the fermentation stage. Overall, the photosynthesis–fermentation model with double CO 2 fixation in both photosynthesis and fermentation stages, enhances carbon conversion ratio of sugar to oil and thus provides an efficient approach for the production of algal lipid.

Simulation of biomass gasification in fluidized bed reactor using ASPEN PLUS

Abstract A comprehensive process model is developed for biomass gasification in an atmospheric fluidized bed gasifier using the ASPEN PLUS simulator. The proposed model addresses both hydrodynamic parameters and reaction kinetic modeling. Governing hydrodynamic equations for a bubbling bed and kinetic expressions for the char combustion are adopted from the literature. Four ASPEN PLUS reactor models and external FORTRAN subroutines for hydrodynamics and kinetics nested in ASPEN PLUS simulate the gasification process. Different sets of operating conditions for a lab-scale pine gasifier are used to demonstrate validation of the model. Temperature increases the production of hydrogen and enhances carbon conversion efficiency. Equivalence ratio is directly proportional to carbon dioxide production and carbon conversion efficiency. Increasing steam-to-biomass ratio increases hydrogen and carbon monoxide production and decreases carbon dioxide and carbon conversion efficiency. Particle average size in the range of 0.25–0.75 mm does not seem to contribute significantly to the composition of product gases.

Theoretical Study of Coal Gasification in a 50 ton/day HYCOL Entrained Flow Gasifier. II. Effects of Operating Conditions and Comparison with Pilot-Scale Experiments

The sensitivity of our three-dimensional simulator was studied under various operating conditions. It was clarified that, in addition to coal properties, this simulator also has satisfactory sensitivity, with respect to the change in operating conditions. O2 partition between the lower and upper burners significantly influenced the temperature distribution in a gasifier. Staged gasification not only enhanced carbon conversion and cold gas efficiency, but also led to favorable temperature distribution that suppresses ash slagging in the gasifier. The carbon conversion increased as the O2/coal ratio increased, whereas the cold gas efficiency reached a maximum value as the O2/coal ratio increased. The carbon conversion and cold gas efficiency decreased as the load ratio of a gasifier increased, but with a limited magnitude. The predicted results were in good agreement with the experimental data obtained from a 50 ton/day hydrogen-from-coal (HYCOL) pilot-scale gasifier. The results obtained in this research may be useful information for the designing and operation of gasifiers. This simulator can be applied to predict the gasification characteristics of an oxygen-blown HYCOL gasifier.

Experimental study and theoretical analysis of fixed-bed biomass pyrolysis

A comprehensive process model is developed for biomass gasification in an atmospheric fluidized bed gasifier using the ASPEN PLUS simulator. The proposed model addresses both hydrodynamic parameters and reaction kinetic modeling. Governing hydrodynamic equations for a bubbling bed and kinetic expressions for the char combustion are adopted from the literature. Four ASPEN PLUS reactor models and external FORTRAN subroutines for hydrodynamics and kinetics nested in ASPEN PLUS simulate the gasification process. Different sets of operating conditions for a lab-scale pine gasifier are used to demonstrate validation of the model.Temperature increases the production of hydrogen and enhances carbon conversion efficiency. Equivalence ratio is directly proportional to carbon dioxide production and carbon conversion efficiency. Increasing steam-to-biomass ratio increases hydrogen and carbon monoxide production and decreases carbon dioxide and carbon conversion efficiency. Particle average size in the range of 0.25–0.75 mm does not seem to contribute significantly to the composition of product gases.

Pyrolysis and hydropyrolysis of two carbonaceous Australian oil shales in supercritical toluene and tetralin

Two carbonaceous Australian oil shales from the Yaamba and Nagoorin deposits have been pyrolysed in a batch micro-autoclave tubing bomb reactor at a heating rate of ≈ 1000 K min −1. The shale samples were pyrolysed under reactive (hydrogen) and non-reactive (helium) gases, and in the presence and absence of an added reactive or non-reactive fluid phase consisting of either tetralin or toluene. Limited screening of the effect of impregnated molybdenum and platinum catalysts has also been carried out. Experiments were conducted at 450 °C and ≈ 15.2 MPa, at which conditions the added liquids were present in the reactor as supercritical fluids. Data on organic carbon conversion to oil plus gas have been obtained for residence times ranging from 2 to 30 min. Application of rapid heating under helium coupled with the presence of a non-reactive supercritical fluid phase (toluene) enhances carbon conversion to oil plus gas relative to rapid pyrolysis in the absence of supercritical toluene. Hydrogen gas in the presence of supercritical toluene is effective in increasing yields even further for the more aromatic shale, while the effect of hydrogen partial pressure is minimal for the aliphatic shale. Use of a hydrogen transfer agent as the supercritical fluid greatly enhances organic carbon conversion with yields of over 1100% of Fischer Assay achieved for the aromatic (Yaamba) oil shale. Application of impregnated molybdenum and platinum catalysts also enhances carbon conversion and oil yield, but only at elevated hydrogen partial pressures.