•Devolatilization characteristics of coal in oxy-steam combustion were studied.•Char characteristics during devolatilization in H2O/CO2 differ from those in N2.•High concentration of H2O greatly ...decreases the char yields and condenses the char.•CO2 in H2O/CO2 affects char yield little but leads a less condensed char.•A relationship between the char structural features and char reactivity was set up.
Oxy-steam combustion is considered as one of promising technologies for the next generation oxy-fuel combustion, in which coal mainly burns in O2/H2O atmosphere. This work aims to investigate the devolatilization characteristics of coal in oxy-steam combustion and clarify the potential effects of steam and CO2 on the char characteristics. Chars of a Chinese lignite were prepared in a fixed-bed reactor at 1050°C under various steam/CO2/N2 atmospheres and characterized by a FT-IR/Raman spectrometer and thermogravimetric analyzer. The results indicate the char yield during devolatilization in oxy-steam combustion was lower than that in N2 atmosphere, and the steam gasification reaction played the key role. The high concentration of steam would significantly accelerate the condensation of aromatic rings in the char, and more condensed char would form during devolatilization in oxy-steam combustion compared to that in N2 atmosphere. CO2 in high concentration of steam had little effects on the char yields but it could participate in the cross-linking reactions on the char surface and partly reduce the condensation of the chars during devolatilization. Steam and CO2 gasification reactions can not only speed up the consumption of the original O-containing functional groups in the coal but also bring some additional O-containing functional groups in the char. The reactivity of the char formed during devolatilization in oxy-steam combustion was lower than that in N2. A good linear relationship between the Raman band area ratio I(Gr+Vl+Vr)/ID and char reactivity confirmed the decrease of the char reactivity was mainly attributed to the condensation of the char.
•Investigate the inter-conversion of the four classes of alkali during cofiring.•Assess the release characteristics of sodium and potassium during the cofiring.•Observe eutectic melting phenomenon ...due to the interaction in cofiring.
Solvent fractionation, Laser induced breakdown spectroscopy (LIBS), X-ray Diffraction (XRD) and chemical analysis were applied to binary fuel mixtures of Zhundong coal and cornstalk agricultural class to investigate the release characteristics of alkali species during co-firing of coal and biomass. As the biomass proportion increases, the water-soluble, NH4Ac-soluble and HCl-soluble alkali species interconvert; the extent of the conversion depends on the composition of the blend. From LIBS measurements, it was found that adding the biomass accelerates combustion and outgassing processes. The higher the proportion of the biomass in the blend, the earlier the peak concentrations of alkali appear, and the magnitude of peak concentrations of sodium and potassium decrease and increase, respectively. Furthermore, the interaction between coal and biomass can generate crystals causing the eutectic melting phenomenon (similar to feldspar in XRD results), which results in a sharp decline of the ash fusion temperatures (AFTs). The results not only provide the information of fundamental transformation but also guide industrial co-firing applications of lignite and agricultural class biomass to reduce the risk of ash deposition.
In the present work CO2 adsorption isotherms of a commercially available activated carbon, Norit Darco type obtained from lignite granular material, were measured. Adsorption isotherms were measured ...at different temperatures 298 K, 308 K, 318 K and 338 K and over a pressure range of 0–45 bar using Sievert's type experimental setup. Experimental data of CO2 adsorption isotherms were modelled using Langmuir and Dubinin–Astakhov (D–A) isotherm models. Based on coefficient of correlation and normalized standard deviation it was found that D–A isotherm model was well suited with the experimental data of CO2 adsorption isotherms. The important thermodynamic properties viz., limiting heat of adsorption at zero coverage, entropy, Gibbs free energy and isosteric heat of adsorption as a function of surface coverage were evaluated using van't Hoff and Clausius–Clapeyron equations. These thermodynamic properties were indicating that CO2 uptake by activated carbon is a physisorption phenomenon. The adsorption isotherms data and the thermodynamic parameters estimated in the present study are useful for designing of an adsorption based gas storage systems.
Pyrolysis conditions greatly affect the structure-reactivity relationship of char during coal gasification. This work investigated the effect of temperature and microwave heating on the structural ...properties of the chars generated during pyrolysis, as well as gaseous and tar products. Results showed that microwave pyrolysis of Mississippi coal produced more gaseous products and less tars compared to conventional pyrolysis. Higher CO/CO2 ratio (>1) was observed under microwave pyrolysis compared to conventional pyrolysis (CO/CO2 < 1), which may be explained by a greater extent of gasification between solid carbon and the CO2 formed during microwave pyrolysis. Additionally, in microwave pyrolysis, the oil tars generated exhibited lower concentrations of polar oxygenates, while the wax tars showed higher concentrations of non-polar alkanes, as observed from the intensity of CH vibrations in FTIR. The product compositions and FTIR analysis of the tars (oils and waxes) suggest that the microwave interacted preferentially with these polar species, which have relatively higher dielectric properties compared to alkanes. The structure–reactivity relationship of the chars produced was also investigated using a variety of characterization tools such as XRD, BET, SEM, EDS, and FTIR. Finally, the char reactivity towards combustion suggested that microwave-produced chars have a higher thermal stability, likely due to lower O/C ratios, and could be utilized in the metallurgical industry.
This work is aimed to study in situ upgrading of Shengli lignite pyrolysis vapors over different metal-loaded HZSM-5 in a drop tube reactor. Co/HZSM-5, Mo/HZSM-5 and Ni/HZSM-5 (5.0wt%) were prepared ...by wet impregnation and characterized by N2 adsorption-desorption analyzer, X-ray diffraction, transmission electron microscope, Fourier transform infrared spectrometer and temperature programmed desorption of ammonia. The effects of temperature and catalyst on product yields and tar properties were investigated. The results show that the optimal temperature for liquid product was 600°C and aromatics can be directly produced from solid lignite by catalytic fast pyrolysis over metal-loaded HZSM-5 under such mild condition. Due to the participation of metal and acid sites, the bifunctional metal-loaded HZSM-5 showed comparable catalytic activity for deoxygenation reaction in the valorization of oxygen content below 7.1%. The introduction of metal causes the increase of aromatics and the decrease of organic oxygen species in upgraded tar remarkably. Among the catalysts, Ni/HZSM-5 exhibited the best performance for production of high quality tars with highest aromatics content of 94.2% (area%), which can be used as a potential candidate for catalytic upgrading of pyrolysis oil.
•Metal-loaded HZSM-5 was prepared for conversion of lignite to light aromatics.•The BTEXN formation was enhanced by metal-loaded HZSM-5.•Oxygen content in pyrolysis tar is remarkably decreased by metal-loaded HZSM-5.•Ni-loaded HZSM-5 is a potential candidate in catalytic upgrading of pyrolysis oil.
In this work, co-pyrolysis of Miscanthus Sacchariflorus (MS) and three ranks of coal, namely lignite (LC), bituminous coal (BC), and anthracite (AC), was performed at the analytical scale. The ...co-pyrolysis kinetic and products were analysed and compared theoretically and experimentally. The results revealed the synergistic effects of the coal characterstics and biomass blend ratio (BBR) on the thermal decomposition and the products in gaseous phase.
The co-pyrolysis of MS-LC and MS-BC samples was characterised by three distinct stages, which were sequentially dominated by moisture removal, decomposition of MS and decomposition of coal. The activation energies of the co-pyrolysis process were different from the activation energies of the pyrolysis of individual MS and coal samples. The kinetics analysis showed that increasing the BBR increased the activation energies of the MS-coal blends up to 25% at the temperatures below 350 °C. However, at the higher temperature range, it decreased the activation energies of MS-LC and MS-BC blends but increased those of MS-AC blends. Both of the coal rank and BBR had noticeable impacts on the thermal behaviour during co-pyrolysis. The optimum positive synergistic effects were obtained on MS-LC blend with a BBR of 1:1. The FTIR analysis results showed the evolution profiles of CH4, CO, CO2, water, formic acid, phenol and xylene. All the products analysed showed L-peaks (250–400 °C) corresponding to MS decomposition. Increasing the BBR promoted the release of all the analysed products from MS-LC and MS-BC, indicating the synergistic effect of the co-pyrolysis.
As a possible new focus of oxy-fuel work, O2/H2O combustion has many advantages over O2/CO2 combustion, and has gradually gained increasing attention. The unique physicochemical properties (thermal ...capacity, diffusivity, reactivity) of H2O significantly influence the char combustion characteristics. In the present work, the combustion and kinetics characteristics of lignite char particle were studied in a fluidized bed (FB) reactor under N2, CO2 and H2O atmospheres with different O2 concentrations (15%–27%) and bed temperatures (Tb, 837–937 °C). Results indicated that the average reaction rate (raverage) and the peak reaction rate (rpeak) of lignite char in H2O atmospheres were slower than those in CO2 atmospheres at low O2 concentrations. However, as the O2 concentration increases, the rpeak and raverage of lignite char in H2O atmospheres significantly improved and exceeded those under CO2 atmospheres. The calculation result for the activation energy based on the shrinking-core model showed that the order of activation energy under different atmospheres is: O2/CO2 (28.96 kJ/mol) > O2/H2O (26.11 kJ/mol) > O2/N2 (23.31 kJ/mol). Furthermore, gasification reactions play an important role in both O2/CO2 and O2/H2O combustion, and should not be ignored. As the Tb increased, the active sites occupied by gasification agent were significantly increased, while the active sites occupied by oxygen decreased correspondingly.
•Combustion characteristics of char were studied in a FB under O2/H2O atmosphere.•Char combustion reaction kinetics were analyzed in different atmospheres.•The effects of CO2 and H2O on lignite char combustion process were studied.•The proportion of gasification in O2/H2O atmosphere were quantitatively analyzed.
•A novel evaluating method was proposed to determinate the spontaneous combustion of coal.•Variations of the indexes of spontaneous combustion from three rank coal were obtained.•The prediction ...accuracy of this method can be set according to the actual requirements of coal mine site.•The evaluating method is simple and applicable to the coal of different ranks.
Coal spontaneous combustion has always been a worldwide problem, which causes waste of coal resources, greenhouse gas emissions and other atmospheric environmental pollution problems. Although coal temperature monitoring is the most direct and accurate means of predicting the spontaneous combustion of coal, the coal temperature often cannot be directly measured owing to various physical restrictions. As an alternative, the present study assessed the qualitative and quantitative analysis of the CO and C2H4 formation rates, as well as various gas ratios such as the CO/CO2 ratio and fire coefficient R2 (R2 = 100×ΔCO/ΔO2), to predict spontaneous combustion. This method was established based on the temperature-programmed experiments of three different coal rank (including lignite, bituminous coal and anthracite), and was verified using data obtained from on-site monitoring at an actual mine. The results show that the method accuracy is as high as 97% when predicting the coal temperature to within 15 °C (allowable error range of the predicted value). This degree of accuracy should be sufficient for on-site fire prevention and control. This new technique is not only accurate and reliable but also has theoretical significance with regard to the identification of coal spontaneous combustion in goaf and for the development of fire prevention and suppression technologies.
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•Diclofenac sodium removal by low-cost lignite activated cokes (LACs) was reported for the first time.•DCF was quickly removed by LAC-2, with qm of 224 mg/g at pH 6.5.•Macro/micropore ...structure and phenolic groups obviously enhanced adsorption capacity.•TEM images revealed the turbostratic and graphite-like structure on LAC-2 were clogged by DCF after adsorption.
Activated cokes have attracted great interest inwater treatment to remove organic pollutants due to their low cost and specific textural properties. In this study, adsorptive removal of diclofenac sodium (DCF) from neutral aqueous solution by available lignite activated cokes (LACs) was reported for the first time. Diclofenac sodium could be quickly removed from aqueous solution by LAC-2, with the maximum Langmuir adsorption capacity qm of 224 mg/g at pH 6.5. Characterization results (including scanning electron microscopy, transmission electron microscopy, elemental analyses, Boehm titrations, N2 adsorption-desorption isotherms and Fourier transform infrared spectroscopy) and a series of adsorption kinetics, adsorption isotherms model studies revealed that high porosity with developed macro- and micropore structures on LAC-2, as well as high content of phenolic groups, could obviously enhance the DCF adsorption capacity and rate. Moreover, LAC-2 showed high affinity towards DCF at low concentrations, as well as good reusability after three adsorption-desorption cycles. pH effect studies revealed that hydrogen-bonding interaction plays an important role during adsorption, accompanied with certain contribution from electrostatic interaction and π-π interaction. This study indicates the promising potential of LAC-2 as an efficient, low-cost and recyclable material for DCF removal from water bodies.
•Using disposable Ca(OH)2 for steam/oxygen gasification of coal could produce high quality syngas.•Adding Ca(OH)2 promoted carbon conversion and improved syngas quality.•Lower ER and gasification ...temperature and higher S/C helped to improve H2/CO mole ratio.•Pressure favored CH4 formation and H2/CO mole ratio, especially in the presence of Ca(OH)2.
This study works on the production of high H2/CO mole ratio and CH4-rich syngas suitable for methane synthesis from catalytic coal gasification using inexpensive and disposable Ca(OH)2 in a fluidized bed with a continuous coal feeding rate of 1.2kg/h. Experiments conducted at atmospheric pressure demonstrated that carbon conversion and gas yield increased markedly after loading Ca(OH)2 into lignite, while CH4 yield was almost constant. Increasing excess oxygen ratio (ER), steam to carbon mole ratio (S/C) and catalytic gasification temperature could increase carbon conversion but went against CH4 production. At atmosphere pressure, CH4 was mainly derived from coal pyrolysis and raising carbon conversion thus led to the reduction of CH4 content in syngas. Elevating gasification pressure exhibited a significant effect in raising carbon conversion and encouraging CH4 formation. Increasing S/C and pressure as well as reducing ER and gasification temperature were beneficial to raise H2/CO mole ratio in syngas. At 1.5MPa, under conditions of ER=0.050, S/C=1.00 and gasification temperature of 800°C, catalytic coal gasification achieved good results with carbon conversion of about 70.0% and CH4 yield of 0.142Nm3/kg–coal. And its producer gas, with the best H2/CO mole ratio of about 3.0, was highly rich in CH4 with its content of 10.1vol.% well matched in terms of SNG production.
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