•Ash deposition (AD) characteristics of four straws were investigated.•Effects of lignite on the AD mass ratio variation of straws were explored.•Mad variation by lignite addition mainly results from their potassium oxide content.•Ca2+ replacing K+ in semi-molten alumino-silicate leads to the formation of anorthite.•FactSage calculation is an effective method to explain the variation of Mad.The ash-deposition (AD) characteristics of straws (corn stalk [CS], wheat straw [WS], cotton stems [CCS], and soybean stalk [SS]), and the effects of lignite (Husheng [HS], Huolinhe [HLH]) on the characteristics were investigated. Under the same conditions, the AD mass ratio (Mad) decreases as WS > CS > CCS > SS, and the Mad of the four straws decreases more obviously with HS addition than that for HLH addition. The Mad of SS and CSS increases slowly before 1000 °C and then increases rapidly; whereas for CS and WS, the change occurs at 950 °C. The differences result mostly from the higher potassium-oxide contents in CS (26.34%) and WS (30.04%) over those in CCS (11.63%) and SS (10.25%). Ca2+ replaces K+ in semi-molten alumino-silicate (orthoclase and leucite) and results in the formation of a high melting-point anorthite. This, together with the generation of high melting-point mullite, leads to a decrease in Mad of the mixed ashes with an increase in lignite mass ratio. The position changes of the ash composition in the ternary phase diagrams and their variation in liquid-phase content with increasing temperature based on the FactSage software calculation may explain the variation in Mad.

•Different particle size distributions (PSDs) were studied at elevated pressure.•Wide PSDs have smaller Umf than the narrow PSD at the pressures above 0.3 MPa.•The types of wide PSDs have little effect on the Umf at pressures above 0.9 MPa.•Correlations to predict Umf and bed expansion at elevated pressures were proposed.This paper presents an experimental study on the effects of elevated pressure and particle size distribution (PSD) on the minimum fluidization velocity (Umf) and the bed expansion. It was developed with Geldart B and D-type polystyrene particles. Four wide PSDs and five narrow PSDs were investigated. The four wide PSDs studied included a Gaussian distribution, a flat distribution, a ternary mixture, and a binary mixture, all with the same mean diameters. Operation pressure ranged from 0.1 MPa (absolute pressure) to 2.7 MPa. The results revealed that the Umfs of the wide PSDs were lower than that of the reference narrow PSD with the same diameter at pressures exceeding 0.3 MPa. The segregation tendency of wide PSDs decreases with the increase in the operating pressure. The four wide PSDs had obviously different Umfs at pressures below 0.9 MPa; however, this difference in the Umfs was gradually reducing with a further increase in the pressure (> 0.9 MPa). The bed expansion increased with increasing the pressure at same excess fluidized gas velocity. Correlations basing on experimental data were proposed in order to predict the Umf and bed expansion for the narrow PSD at elevated pressures, and three correlations were investigated for predicting the Umf of wide PSD.Download high-res image (171KB)Download full-size image

•Deposition mass ratios of different low rank coal ashes are different.•Iron content and valence mainly result in the differences in ash deposition characteristics.•Possible formation mechanism of ash deposition was proposed.The ash adhesion and deposition (AD)characteristics of three low-rank coal (LRC) were investigated by self-made AD analyzer, X-ray fluorescence spectrometry, scanning electron microscopy equipped with energy dispersive X-ray detector, and X-ray diffraction. Under a given condition, the deposition mass ratios of different LRC ashes are different, which mainly due to the difference in iron content. The mass ratios of ash deposition under oxidizing atmospheres are higher than those under reducing atmospheres because of the effects of different valence of iron. The mass ratio of AD increases with the increase of temperature, while it decreases with gas velocity increases. The possible formation mechanism of AD is proposed by adhesive amorphous matter formation, iron enrichment and the generation of ferro-aluminate and ferro-alumino silicate, substitution of Fe2 + by Ca2 +, and mullite adhesion.

This paper investigated the distribution of secondary air after injection into a multi-stage conversion fluidized bed (MFB) cold model. Carbon dioxide (CO2) was used as the tracer and its concentration was tested. The effects of the velocity of the primary air and secondary air, the particle circulating rate, and the diameter, number and included angle with the central line of the riser of injectors on the distribution of CO2 were studied. Single- and multi-injector systems were applied, in which different designs of the secondary-air injectors were used. The radial gas dispersion coefficient was calculated by the dispersed plug flow model (DPFM). The concentration profile of the tracer and calculated radial gas dispersion coefficients indicated that lower velocity of primary air, higher velocity of secondary air and particle circulating rate, bigger size of injectors and smaller included angles of injectors helped the gas mixing of the secondary air in the MFB. The tangential injection of secondary air would induce a gathering of gasification agents in the region near the wall, which was undesirable for the operation of the MFB gasifier. The variation of the penetration depth of the secondary air indicated that the penetration depth under multi-injector system was smaller than that under single-injector system when other operational parameters were uniform. Thus, according to numbers of injectors, taking the included angles between injectors and the central line of the riser into consideration, the penetration depth of the secondary air was correlated with operational parameters.

β-Mo2C and Ni/β-Mo2C catalysts were prepared by a single-step thermal decomposition method using hexamethylenetetramine (HMT) as a reducing agent and carbon source. The synthesized carbides were detailedly characterized and their catalytic performances in methanation were evaluated. The results showed that serious carbon deposition was observed in β-Mo2C, while for Ni/β-Mo2C, the carbon content was insufficient and Ni3Mo3N was produced. With respect to catalytic performances in methanation, the β-Mo2C catalyst exhibited a high CO conversion, but its CH4 selectivity was low and its activity was not stable due to hydrogenation of the carbidic carbon. While the Ni/β-Mo2C catalyst exhibited excellent activity and stability, the CO conversion and CH4 selectivity increased from 67.41% and 33.54% on β-Mo2C to 92.51% and 52.73% on Ni/β-Mo2C. This is ascribed to Ni3Mo3N in Ni/β-Mo2C, which is more active and stable during methanation.

Four slag samples of Shenmu bituminite and Huolinhe lignite (SSM(A), SSM(B), SHLH(A), and SHLH(B)) selected from two upper parts of a multistage conversion integrated fluidized bed (MFB) were analyzed by X-ray fluorescence spectrometry, scanning electron microscopy, and X-ray diffraction analyses. The results show that the ash sintering temperature and ash fusion temperature of slag samples are below those of the raw coal ashes and increase in the order SSM(A) < SSM(B) < SHLH(A) < SHLH(B) because of differences in acid/base composition. The slag samples are composed of amorphous matter and some crystals, and the crystal content of the two SHLH samples are higher than that of the two SSM samples. The section of the MFB above the site of oxygen injection may be divided into three zones based on particle movement. Fine mineral particles contain much more iron and calcium than other particles. The possible mechanism of slag formation may involve mineral exposure by char gasification, interaction of minerals, formation of particles of different sizes, formation of an initial adhesive layer, and emergence of slag.

The fusion characteristics of ash mixtures of two lignites (Husheng and Xiaolongtan) and three biomasses (peanut hull, corn straw, and pine sawdust) were investigated by measurements using ash fusion temperature (AFT) detector, X-ray diffraction, normalized reference intensity ratio, analysis using Rietveld-based SIROQUANT software, and scanning electron microscopy. AFT modification of lignite mixed ashes is not the same as the addition of different biomasses at the same mass ratio, which depends upon their ash compositions, especially on the mineral arising from mineral evolution with the temperature increase. The formation of high-melting-point (MP) mullite and change in its content might be the main reason for AFT fluctuation of the lignite mixed ashes. With the increase in mass ratio of biomass, the amount of low-MP minerals and their eutectic increases at a high temperature, leading to the decrease in AFT of the mixed ashes.

•The CO affects the generation of CH4.•The polarity of CO can facilitate the cracking of chemical bonds in coal/char.•The CO disproportionation reaction contributes the lower CH4 yield.The fast pyrolysis of Huolinhe lignite in the atmosphere of CO/N2 and CO/H2/N2 atmospheres were carried out in a fixed bed reactor, and the evolution characteristics of CH4, the influence of CO and H2 on the process of pyrolysis and their mechanisms were investigated by the blank experiments and comparative analyses of IR spectra, element content and surface structure property. The results show that the CO and H2 can influence the evolution of CH4 and these influences are affected by the pyrolytic temperature: the CO and H2 can improve CH4 yield before 600 °C, but it reduced the CH4 yield at higher temperature (above 700 °C). The reason for this may be that the polarity of CO can facilitate the cracking of the aromatic ring, side chain, ether linkages and aliphatic chain in the coal/nascent char, and these cracking can generate smaller molecular fragments and free radicals, for example, CH3, CH2 and H. These induced-smaller free radicals can stabilize other molecular fragments produced during coal pyrolysis and convert them into volatile and CH4. Above 700 °C, however, the disproportionation reaction of CO and the carbon-deposition produced from the CO disproportionation reaction may partly cover the surface of char or block the pore entrance of the char so that some volatiles cannot diffuse out fast enough to avoid secondary reaction, resulting in lower specific surface area, lower pore volume, higher carbon content but less evolution amount of CH4 and gaseous products.

•A novel Multi-stage conversion fluidized bed has been introduced and studied.•A solid distribution ratio was proposed to quantify increased-solid distribution.•The transition gas velocity of MFB, uM,tr, was defined.•A qualitative and quantitative flow regime “phase diagram” of MFB was proposed.A novel multi-stage conversion fluidized bed (MFB) gasifier which coupled an ash agglomerated fluidized bed gasifier (AFB, cold model as jetting fluidized bed, JFB) with a riser has been introduced and studied. The new gasifier aimed to independently control solid and gas retention times and to achieve high solids concentration, which was essential to raise the coal gasification efficiency. The hydrodynamic characteristics of MFB were investigated in a cold model apparatus (JFB 1.5 m in height and 0.3 m inner diameter, riser 8 m in height and 0.15 m inner diameter) with silica gel particles. Experimental results showed that under suitable operating conditions, MFB could successfully couple JFB with a riser, in which the solids that entered could form three-level step-by-step supplement entrainment and multi-flow regimes formed. A solid distribution ratio was proposed to quantify increased-solid distribution relationship between JFB and the riser, and the transition velocity of the MFB, uM,tr, was defined and its physical significance was explained. Finally, a qualitative and quantitative “phase diagram” describing the existence of different flow regimes of MFB as a function of the dimensionless parameters Gs/(ρpvt) and Reynolds was proposed and MFB ought to be operated in JF-FF flow regime. This phase diagram was indispensable for the design, operation and scale-up of the MFB gasifier.

Chemical looping combustion (CLC) of coal has received increasing interest in recent years. However, few attempts have been made to examine the effects of CO2 atmosphere and K2CO3 addition on the reduction rate, the oxygen transport capacity (OTC), and the sintering of the oxygen carrier when coal is used directly in CLC. In this work, these issues for Fe2O3 and the CuO oxygen carriers were investigated by thermogravimetric analysis (TGA), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and inductively coupled plasma–atomic emission spectrometry (ICP-AES). The TGA results indicate that the reduction rates can be increased by either the CO2 atmosphere or the K2CO3 additive due to the enhanced CO2 gasification of coal char. Detailed analyses demonstrate that the CO2 atmosphere affects the OTC and the sintering of the oxygen carrier by thermodynamic restrictions. The CO2 atmosphere has no effect on the OTC of the CuO oxygen carrier, and there are no significant differences in sintering between the residues obtained under CO2 and N2 atmospheres. However, the CO2 atmosphere limits the OTC of the Fe2O3 oxygen carrier within the transformation Fe2O3–Fe3O4, and the sintering could be moderated because of the higher sintering resistance of Fe3O4. The K2CO3 addition does not affect the OTC because the catalyst has no impact on the equilibrium but promotes the sintering of the oxygen carrier due to its low Tammann temperature. Although severe sintering could be caused by the K2CO3 addition, the catalytic effect can be observed during several redox cycles.

The CO2 gasification behaviors of two fine chars separated from a pilot-scale fluidized-bed gasifier were studied in a thermogravimetric analyzer (TGA) within the temperature range of 1000–1300 °C. The physical properties of fine chars were examined by scanning electron microscopy (SEM), N2 adsorption, and X-ray diffraction (XRD). The differences in gasification reactivity and related properties between the fine chars and the corresponding experimental-produced coal chars were also compared. The results show that the fine chars have higher ash content, larger Brunauer–Emmett–Teller (BET) surface area, and better gasification reactivity than the corresponding coal chars. The gasification reactivity of fine chars was promoted by the catalytic alkali and alkaline earth metals (AAEMs) but inhibited by the enrichment of the ash layer in a higher carbon conversion range or the ash melting at a higher temperature. In addition to the AAEMs, the reactivity of different fine chars is mainly influenced by their pore and carbon crystalline structures. The kinetic investigation reveals that the modified random pore model (MRPM) and shifted-modified random pore model (S-MRPM) perform more reasonably than the random pore model (RPM) in some special conditions. Moreover, the reactivity of fine chars increases, and the reaction shifts from chemical reaction control to gas diffusion control as the gasification temperature increases.

The isothermal and non-isothermal CO2 gasification of eight different coal rank chars was conducted by a thermogravimetric analyzer (TGA), and the reactivity index and peak temperature were obtained to express the gasification reactivity. In addition, the physicochemical properties of these chars, such as the alkali index, Brunauer–Emmett–Teller surface area (SBET), micropore area (Smic), and carbon crystalline structure, were examined by an inductively coupled plasma (ICP) spectrometer, N2 adsorption, and X-ray diffraction (XRD). The CO2 chemisorption was also measured by a TGA, and the total, strong, and weak chemisorbed volumes (Ctotal, Cstr, and Cwea) were obtained. All of these properties were used to evaluate the CO2 gasification reactivity of these chars. The results show that the gasification reactivity of chars decreases with an increasing coal rank. In comparison to the other properties, the Ctotal and Cstr are the best parameters for predicting the gasification reactivity, and the linear correlation coefficients between Ctotal/Cstr and gasification reactivity can reach up to 0.90 or even 0.98. It suggests that the CO2 chemisorption can be used to evaluate the gasification reactivity of different coal rank chars.

To investigate the mineral behavior of lignite ashes under gasification conditions, 450 °C Xiaolongtan lignite ash samples (XLT-LTA) treated at different temperatures or pressures under reducing atmosphere (H2/CO2=1: 1, volume ratio) have been examined by means of an SC-444 apparatus, a scanning electron microscope with an energy dispersive X-ray detector (SEM-EDX), and by X-ray diffraction (XRD). The results showed the sulfur content in the XLT-LTA to be much higher than that in ashes prepared at 815 °C, as a result of the release of sulfur dioxide during the oxidization of pyrite. With increasing temperature, the XLT-LTA particles gradually agglomerate and form partially molten surface entities with obvious apertures, and the content of iron and calcium in the congeries or molten parts increases due to the fusion of fine ash particles with the enrichment of iron and the formation of low-temperature eutectics of calcium and iron. An increase of pressure restrains the decomposition of calcite and muscovite, and promotes the formation of iron minerals (e.g., hercynite, cordierite, and sekaninaite) and orthoclase. The content of amorphous material also increases with increasing pressure.

A model of a pilot scale pressurized Ash Agglomerating Fluidized Bed (AFB) Gasifier has been developed using ASPEN PLUS. The model is based on a sequential modular method with a recycle loop. Both hydrodynamics and reaction kinetics are considered simultaneously through FORTRAN codes if necessary. The physical properties of related gas and solid substance are calculated dynamically by the Peng–Robinson equation of state with Boston-Mathias alpha function (PR-BM) with in-line powerful physical property database in ASPEN PLUS, and then the calculated results are passed immediately to the fluid-dynamic correlations for space division. Therefore, only a few parameters are needed in this model. Different sets of pilot-scale experimental data are used to validate this model. The model predictions are in good agreement with experimental data at gas composition, carbon conversion, high heat value, cold gas efficiency, and dry gas yield. In addition, the effects of oxygen/coal ratio and steam/coal ratio on the gasification performance have been studied by this model. Within the calculation range, the oxygen/coal ratio should be lower than 0.55 N m3/kg. According to the intended final use, it is possible to have a molar H2/CO ratio of two to one in the synthesis gas by controlling the suitable ratios of oxygen/coal and steam/coal.

Chemical looping combustion (CLC) has been suggested as an energetically efficient approach for coal combustion with CO2 sequestration. An iron oxide oxygen carrier is an attractive option because of its low cost and environmental compatibility. However, the low reactivity between iron oxide and coal is a challenge for its application. In this paper, the effects of the C/Fe2O3 molar ratio and alkali carbonate addition on the reduction rate of coal char with an Fe2O3 oxygen carrier and the feasibility of coal char direct CLC with an alkali-carbonate-impregnated Fe2O3 oxygen carrier were investigated using thermogravimetric analysis coupled with a mass spectrometer (TGA–MS), an X-ray diffractometer (XRD), scanning electron microscopy (SEM), and carbon content tests. Results indicate that, on the premise of full consumption of C by an Fe2O3 oxygen carrier, higher C/Fe2O3 molar ratios are not only beneficial to the oxygen transport capacity but also to reduction kinetics. The kinetics enhancement by higher C/Fe2O3 molar ratios could be attributed to more iron oxide/carbon contacts, which improves the char gasification rate and, in turn, enhances the reduction rate. The reduction rate also increases with the increase of alkali carbonate addition, which could be ascribed to the synergistic effects of alkali carbonates and iron on char gasification. The catalytic activities of K2CO3, Na2CO3, and Li2CO3 decrease in the order of K2CO3 > Na2CO3 > Li2CO3. Overall, a high reduction rate of coal char with an Fe2O3 oxygen carrier can be achieved with the appropriate C/Fe2O3 molar ratio and alkali carbonate addition. Catalytic CLC by alkali carbonates appears to be an effective way to combust coal directly with an Fe2O3 oxygen carrier.

To investigate fusibility characteristics of residual ash from Xiaolongtan lignite (XLT) pressurized fluidized-bed ash agglomerate (PFBA) gasification and its formation mechanism, the ash samples were examined by press-drop sintering technique, scanning electron microscope with energy-dispersive X-ray detector (SEM–EDX), and X-ray diffraction (XRD) analyses. The results show that both sintering temperatures and ash fusion temperatures (AFTs) of ash samples decrease from the gangue ashes to agglomerates to slag, because of the increase of the total base content and the differences in their mineral compositions accordingly. The surfaces of the slag were obviously molten; the agglomerates were covered with some small spheres and large particle aggregates, and the gangue ashes were composed of some irregular prismatic particles. During XLT PFBA gasification, the agglomerates originate from the collision and reunification of low-melting minerals under the dragging force of rising gases and the gangue ashes result from some thermally stable mineral particles with a high-melting point. When the PFBA gasification deviates from the suitable operation parameters (e.g., the gas velocity of the distribution plate is low, the gas velocity of the tubular loop is high, or the steam/oxygen ratio is low), the slag might be formed in the gasifier.

The co-gasification behavior of meat and bone meal (MBM) char and two types of coal (Jincheng anthracite (JC) and Huolinhe lignite (HLH)) char was investigated using a thermogravimetric analyzer (TGA). The effects of coal type, mineral matter in MBM, gasification temperatures and contacting conditions between MBM char and coal char on the gasification behavior were studied. The results show that the gasification behavior of MBM char and HLH char can be well described by ash diffusion controlled shrinking core model, while that of JC char can be described by chemical reaction controlled shrinking core model. The co-gasification rate of MBM/JC chars at 950 °C is approximately 1.5 times faster than that calculated from independent behavior. The mineral matter in MBM may play as a catalyst during co-gasification. However, the analogous effect observed in the blends of HLH/MBM chars is smaller, suggesting that the coal types play a great role. Furthermore, as the gasification temperature increased from 850 to 1000 °C, the maximum synergistic effect is observed at 900 °C. The lower temperature is not conducive to transferring the mineral matters of MBM to the coal char, while the higher temperature makes Na and Ca react with minerals of coal, leading to a loss of catalytic activity.

To investigate the formation mechanism of slag and prevent its occurrence during lignite fluid-bed gasification, mixed samples of graphite and 450 °C Xiaolongtan (XLT) ashes (1:19, mass ratio, MA) treated with different temperatures were prepared. The samples and the block slag formed during the tests of XLT ash agglomeration fluid-bed (AFB) pilot-scale gasification were examined by chemical composition, scanning electron microscope with energy dispersive X-ray detector (SEM-EDX), and X-ray diffraction (XRD) analyses. The results show the elements of iron and silicon are enriched in the slag due to the adherence of low-melting-point ferro-silicate. The interactions of the mineral matter in MA formed the same kinds of mineral crystals as those in the slag under reducing atmosphere (CO2/H2 = 1:1) at 950 °C. The formation mechanism of slag is proposed by the generation of adhesive glassy material, the formation of partial melting entities, the substitution of the iron in liquid aluminate or aluminosilicate by calcium and the mergence of individual particles. Pilot-scale AFB tests indicate that the reduction of operating temperature to 850−930 °C by increasing steam/oxygen ratio can successfully prevent slag problems during XLT AFB gasification.

Experiments have been conducted with Huolinhe (HLH), Xiaolongtan (XLT), and Ethiopian (ET) lignites to investigate the effects of washing with water, acid-leaching, and floatation on their ash fusion temperatures (AFTs). The results show that the AFTs of XLT and ET are elevated by washing with water and floatation, but the AFT of HLH is decreased. The AFTs of all three lignites are increased markedly by acid leaching. A decrease in the total basic composition in ash increases its AFT, and vice versa. Changes in the mineral contents of the coals after treatment contribute to the variations in their AFTs. After washing with water, the lower AFT of HLH is brought about by the increases in the amounts of cordierite and anhydrite, whereas the higher AFT of XLT is caused by the decreases in the amounts of anhydrite and calcite. For the floatation treatment, the decrease of AFT for HLH is due to the reduction in the amount of kaolinite, but the elevation of AFT for XLT or ET is caused by the decrease in the amount of pyrite and the reductions in the amounts of gypsum and xanthoxenite, respectively. For the acid-leaching treatment, a decrease in the amount of pyrite and an increase in the amount of kaolinite result in increases in AFTs for HLH and XLT. Increases in the amounts of kaolinite and cristobalite in FET (ET after floatation), WET (ET after washing with water), and AET (ET after acid-leaching) lead to corresponding increases in the AFTs.Highlights► The effects of leaching and floatation on the AFTs of three lignites were investigated. ► The AFTs of XLT and ET are elevated by water-washing and floatation. ► At the same condition, the AFT of HLH is decreased. ► The AFTs of all three lignites are increased markedly by acid leaching.

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.

The pressurized fast pyrolysis of three typical Chinese coals with different coal ranks (Huolinhe lignite, Shenmu bituminous coal, and Jincheng anthracite) was conducted on a self-made pressurized fixed-bed reactor. The physicochemical characteristics of the chars were studied via scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). In addition, thermogravimetric analysis (TGA) at ambient pressure has been used to study the influence of the residence time, the pyrolysis temperature, and pressure on the gasification reactivity of residual chars. The results show that the change in char yield and reactivity with pressure, at a residence time of 1 min, is different from that at longer residence time. This is related to the changing impacts of the rapid primary release of volatiles and the slower secondary cracking reactions of the evolved tars and the graphitization of the char structure. Furthermore, as the coal rank, pyrolysis pressure, temperature, and residence time increase, the surface structure of the char becomes much denser, the degree of graphitization is enhanced, and the number of the functional groups is reduced, which lead to the decrease in the gasification reactivity of the coal char.

The ash fusion characteristics, particle-size distribution and gasification reactivity of Shenmu coal (SM) fine chars from ash agglomerate fluidized bed gasification were explored by ash fusion point analyzer, scanning electron microscopy equipped with energy dispersive X-ray analysis (SEM-EDX), and thermo-gravimetric analyzer. The results show that the decrease in basic ingredients (e.g. iron and calcium) and the increase in acidic ingredients make the ash fusion temperature (AFT) of SM fine chars lower than that of SM. There is a wide particle-size distribution in SM fine chars, which shows a significant multi-peak distribution, and a large difference of the elemental distribution in fine char particles with different sizes. The moisture content is lower and ash content is higher in fine power than that in SM, respectively. SM fine char has higher surface area than that of SM char, and relatively rich in meso-pores and macro-pores, which results in its higher gasification reactivity than SM char.

The catalytic deoxygenating experiment of oxygen-bearing coal mine methane (CMM) was carried out in a bench-scale fluidized bed reactor with the spherical Cu-based catalyst. The effects of the bed temperature, the particle size and the space velocity were investigated on the oxygen removal efficiency and CO2 selectivity. The rise of bed temperature could promote the oxygen conversion due to the high activity of the catalyst. The O2 conversion could reach more than 95% when the temperature was above 450°C. The smaller particle size was beneficial to the CO2 selectivity of the catalyst because of the decrease in inner diffusion resistance. The lower space velocity also could improve the oxygen removal efficiency when the bed temperature was below 450°C although the improvement almost disappears above 450°C due to the increase catalytic combustion rate. Additionally, by adjusting the CH4/Air ratio, the catalytic deoxygenation adaptability of the fluidized bed reactor and the catalyst were evaluated for the variable oxygen content in CMM. The results indicate that the process has a perfect oxygen removal performance with the O2 concentration less than 0.2% and the CO2 selectivity more than 98% for the O2 content from 5% to 15% in the simulated CMM.

The pyrolysis of Huolinhe lignite under CO2 atmosphere was carried out in a thermobalance and a fast heating-up fixed bed reactor. The distribution of gases, char yield and its property such as element, surface structure, FT-IR spectra were analyzed. By this, the effect of CO2 on the pyrolysis behaviors was studied. The results show that CO2 gasification of the nascent char, which destroys the hydrogen-containing char structure, not only promotes cracking of benzene ring and fracture of hydroxyl, methyl and methylene groups etc., but also weakens the interaction between H and char matrix and increases the H fluidity, leading to the increase in the generation of H radicals. These H radicals can combine with other free radical fragments generated from fracture of the coal macromolecules to produce more volatiles. This will produce the char with a high specific surface and high pore volume and porosity. The introduction of CO2 promotes the coal pyrolysis and generation of volatile, resulting in decrease in char yield and increase in the evolution amount of H2, CO, CH4 and other small molecules hydrocarbons.

•The β-Mo2C and Co/β-Mo2C were prepared by the one-step thermal decomposition.•The prepared catalysts showed high performance for methanation.•The catalytic activity and stability were significantly improved by the addition of Co.•The Co3Mo3C might be responsible for the high catalytic activity.β-Mo2C and Co/β-Mo2C catalysts were prepared by a single-step thermal decomposition method. The synthesized carbides were characterized and their catalytic performances on methanation were evaluated. The results showed that the β-Mo2C exhibited high CO conversion (XCO), but its CH4 selectivity (SCH4) was low and the activity was not stable due to the hydrogenation of carbidic carbon in the β-Mo2C. While the Co/β-Mo2C exhibited an excellent activity and stability, this is ascribed to the Co3Mo3C in Co–Mo carbide, which was more active and stable during methanation.Download high-res image (381KB)Download full-size image