Zhongqing Yang

Catalytic combustion of low-concentration coal bed methane over CuO/γ-Al2O3 catalyst: effect of SO2

The purpose of this work is to report the results of an experimental study devoted to investigate the effects of SO2 in feed gas on the catalytic combustion of low-concentration coal bed methane (1 vol%) over CuO/γ-Al2O3 catalyst with 10 wt% Cu prepared by incipient wetness impregnation in a fix-bed reactor. The study deals with researching a regular low-concentration coal bed methane combustion with lean SO2, which is vital in utilizing low-concentration coal bed methane and in eliminating greenhouse emissions. The concentration of SO2 varied from 0 ppm to 200 ppm, and the accumulation of sulfur on the catalyst surface was examined by X-ray fluorescence (XRF) and Scanning electron microscopy (SEM). The reaction temperature was in the range of 450–700 °C controlled by an electric heater, and at two key reaction temperatures (550 °C and 650 °C), the effect of altering SO2 concentration on low-concentration coal bed methane combustion was studied experimentally. A sulfur poisoning mechanism of CuO/γ-Al2O3 catalyst was proposed. The results showed that the presence of SO2 in feed gas led to the phenomena of sulfur poisoning over CuO/γ-Al2O3 catalyst, and the effect of sulfur poisoning aggravated with increased SO2 concentration. Meanwhile, it had significant influence when temperature was below 575 °C due to the faster decomposition of sulfates at higher temperatures. A high reaction temperature promoted the decomposition of sulfates produced simultaneously, which provided more activating sites on the catalyst for methane catalytic combustion. Sulfates (CuSO4 and Al2(SO4)3) were detected by Fourier transform-infrared spectroscopy (FT-IR) and X-ray diffraction (XRD), resulting in both the reduction of activating sites and specific surface area of the catalyst. The absorption of methane molecules on activated sites was hindered and the catalyst activity decreased.

Effect of bauxite additives on ash sintering characteristics during the K2CO3-catalyzed steam gasification of lignite

We report here the ash sintering characteristics of LLI lignite with added bauxite during K2CO3-catalyzed steam gasification. The ash samples were prepared using a catalytic gasification system at 1123 K under a steam atmosphere with a carrier gas of N2. The ash sintering temperature was determined using a pressure-drop sintering device in inert N2. The ash mineralogy and morphology were determined by X-ray diffraction and energy-dispersive X-ray spectrometry-scanning electron microscopy. The K2CO3 catalyst decreased the sintering temperature of the ash samples and increased the amount of melting of the ash. The presence of kaliophilite facilitated the formation of the liquid phases and triggered the start of sintering, resulting in a lower ash sintering temperature. The addition of bauxite reduced the degree of melting of the ash and led to a higher ash sintering temperature. The main reason for this is that bauxite containing sufficient SiO2 and Al2O3 reacts with other minerals to generate more refractory silicon oxide and decreases the amount of arcanite (which acts a flux) and amorphous material in the ash. The addition of bauxite also decreased the rate of gasification of lignite by reacting with K to generate water-insoluble kaliophilite, which deactivated the K catalyst.

Pyrolysis behavior of biomass with different Ca-based additives

CaO is an important catalyst in biomass gasification and pyrolysis. However, CaO can stem from many precursors. And, the effect between different precursors has still not been studied. Calcined natural limestone, natural dolomite, calcium oxide, calcium carbonate, calcium acetate, and calcium propionate were used to investigate their pyrolysis reactivity of biomass (peanut shells and pine sawdust) at high temperature (>800 °C). Experiments were conducted using a thermogravimetric apparatus and a fixed-bed pyrolysis system. Pine sawdust displayed higher pyrolysis reactivity than peanut shells. During pyrolysis, Ca-based additives fixed carbon dioxide mainly in the temperature range of 300–700 °C. By addition of Ca-based additives, the concentrations of hydrogen and carbon monoxide were increased and the concentrations of methane and carbon dioxide (over 18 vol%) were decreased. De-carbonation started around 700 °C. The emission of CO2 by de-carbonation promoted the reduction of char by the Boudouard reaction and methane by the dry reforming reaction. The total pyrolysis conversion decreased as PI-Dol > PI-CaA > PI-Lime > PI-Ca > PI-CaP > PI Raw > PI-CaC. The excellent pyrolysis reactivity of biomass in the presence of calcined calcium acetate can be ascribed to its preeminent physical structure. Addition of Ca-based additives increased the activation energy of the main devolatilization region. The activation energy of biomass with calcined natural dolomite, about 110 kJ mol−1, was much lower than that of other Ca-based additives studied at high temperatures. Pyrolysis of the pure biomass sample can be simply hypothesized as a first order reaction, but it varied significantly with the addition of additives.

Low-concentration methane combustion over a Cu/γ-Al2O3 catalyst: effects of water

The influence of water on low-concentration methane oxidation over a Cu/γ-Al2O3 catalyst was investigated in a fixed bed reactor. This paper studied the effect of water on the activity of methane combustion, using parameters such as water reversible adsorption, regeneration of the activity and surface characteristics of the catalyst. Apparent activation energy was found by experiments, and water surface coverage was calculated using the Langmuir equation. It was found that the activity of methane combustion over a Cu/γ-Al2O3 catalyst decreased with time due to water adsorption. The inhibitory effect generated by water weakened as the temperature rose above 550 °C. Reactivity could be refreshed if the catalyst particles were scavenged by N2. Kinetic experiments showed that, if water was added into the feed, apparent activation energy (Ea) increased noticeably (81.4 kJ mol−1 → 153.0 kJ mol−1) and the reaction order with respect to water was −0.6 to −1. Using the Langmuir equation, it could be concluded that the coverage of water adsorption on catalytic active sites increased noticeably as vapor was introduced into the feed. If the temperature increased, water coverage went down and tended towards 0% above 625 °C.

Investigation of low concentration methane combustion in a fluidized bed with Pd/Al2O3 as catalytic particles

The catalytic combustion characteristics of low concentration (0.15–3 vol%) methane combustion in a lab-scale fluidized bed with 0.5 wt% Pd/Al2O3 as catalytic particles were studied experimentally. A mathematical model was developed according to the flow and reaction characteristics of the fluidized bed. The effects of bed temperature and inlet methane concentration on combustion were investigated and the kinetic characteristics were analyzed. The results show that methane conversion increases with increasing bed temperature, while it decreases slightly as the inlet methane concentration increases. The reaction order was evaluated as 0.608, and the activation energy was determined to be 96185 J mol−1 during low-concentration methane catalytic combustion in the fluidized bed. It was also found that the reaction in the fluidized bed was controlled by kinetics when the temperature was below 450 °C. When the temperature exceeded 450 °C, the reaction kinetic constant increased with increasing temperature, and the reaction was eventually controlled by kinetics, mass transfer and diffusion. A comparison of the results showed that the values calculated by the mathematical model agreed well with the experimental data.

Effects of non-catalytic surface reactions on the CH4–air premixed flame within micro-channels

The non-catalytic surface of a micro-combustor plays a significant role in flame propagation. For the purpose of investigating the effects of surface reactions on the combustion process, this paper presents a numerical 2D simulation of a CH4–air premixed flame within a micro planar channel with detailed gas-phase and non-catalytic surface reaction mechanisms. In this paper, we focus on numerically examining the effects of surface reactions on the flame structure. The simulation results show that surface reactions affect the temperature distribution in three controlling regimes, distinguished according to the inlet velocity. Besides, radicals suffer sharper declines near the active surface than those near the inert surface due to the radical removing effect. Moreover, as the temperature increases, the difference will become more remarkable especially in the vicinity of the wall. Among the radicals, the mass fractions of H, O, and OH & CH3 near the surface experience the largest, mediate and smallest decay, respectively, when changing the inert surface to the active surface. The adsorption of H should be of the greatest concern. The OH radical has a similar distribution profile to the O radical for both kinds of surfaces.

Planar Laser-Induced Fluorescence Research on Flame Quenching and OH Radical Behavior Near the Walls

AbstractThis paper details a quantitative joint Reynolds number, equivalence ratio, wall material, and quenching distance imaging experiment designed to investigate OH radical behavior near the wal...

Effect of catalytic cylinders on autothermal reforming of methane for hydrogen production in a microchamber reactor.

A new multicylinder microchamber reactor is designed on autothermal reforming of methane for hydrogen production, and its performance and thermal behavior, that is, based on the reaction mechanism, is numerically investigated by varying the cylinder radius, cylinder spacing, and cylinder layout. The results show that larger cylinder radius can promote reforming reaction; the mass fraction of methane decreased from 26% to 21% with cylinder radius from 0.25 mm to 0.75 mm; compact cylinder spacing corresponds to more catalytic surface and the time to steady state is decreased from 40 s to 20 s; alteration of staggered and aligned cylinder layout at constant inlet flow rates does not result in significant difference in reactor performance and it can be neglected. The results provide an indication and optimize performance of reactor; it achieves higher conversion compared with other reforming reactors.

Numerical analysis on the characteristics of carbon deposition of catalytic partial oxidation of methane in micro-chamber

In order to get the characteristics of catalytic partial oxidation of methane in micro-scale, the numerical study is used to investigate the effects of component changing and wall temperature changing on conversion of methane and oxygen and on the selectivity of H2, CO, CO2, carbon deposition on the surface along the flow direction is also investigated. The results show that the selectivity of H2 can achieve a maximum 91.05% when the wall temperature is 1300K, at this time the selectivity of CO is high and the selectivity of CO2 is low, the carbon deposition is little on the wall; there is just a little carbon deposition on the wall and a higher selectivity of H2 and CO, meanwhile there is a lower selectivity of CO2; comprehensive consideration of conversion of CH4 and O2 and of selectivity of H2 and CO and CO2 and of the life of reactor and catalysts, the most suitable reaction conditions should be the wall temperature for 1300K and the C/O for 2.0.