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Direct methanol fuel cells (DMFCs) have bright prospects because of their high energy density, simple structure, small fuel cartridge, instant recharging, and ease of storage and transport. Noble m...

Soot formed during high temperature pyrolysis or incomplete combustion, has strong effects on human health and the environment, as well as radiation heat transfer during combustion. Most studies on soot formation are focused on gas combustion, while the studies of soot formation during solid fuel combustion are rarely reported. In this study, the formation and properties of soot particles from coal pyrolysis are investigated in a drop tube furnace at 1000–1300 °C. The soot morphology, number size distribution, ignition characteristics, gas composition and soot-ash composition were characterized with transmission electron microscopy, scanning mobility particle sizer, thermogravimetric analyzer, gas chromatography, and energy disperse spectroscopy. The effect of coal rank on soot formation and yield is mainly discussed. The results show that with the increase of pyrolysis temperature, the soot yield increases. The soot yields show no dependent relationship with the coal ranks. Among the five kinds of coal tested (anthracite, lean coal, bituminous coal, lignite, and high sodium coal), bituminous coal has a much higher soot yield (>7.5%) than that of other coals (0.5–2%). The oxidation reactivity of soot particles from high sodium coal pyrolysis is much higher than that from other coals, because of the high contents of alkali and alkaline earth metals in soot particles.

Pressurized oxy-combustion is a promising technology that can significantly re-duce the energy penalty associated with first generation oxy-combustion for CO2 capture in coal-fired power plants. However, higher pressure enhances the production of strong acid gases, including NO2 and SO3, aggravating the corrosion threat during flue gas re-circulation. In the flame region, high temperature NOx exists mainly as NO, while conversion from NO to NO2 happened in post-flame region. In this study, the conversion of NO ? NO2 has been kinetically evaluated under representative post-flame conditions of pressurized oxy-combustion after validating the mechanism (80 species and 464 reactions), which includes nitrogen and sulfur chemistry based on GRI-MECH 3.0. The effects of residence time, temperature, pressure, major species (O2/H2O), and minor or trace species (CO/SOx) on NO2 formation are studied. The calculation results show that when pressure is increased from 1 to 15 bar, NO2 is increased from 1 to 60 ppm, and the acid dew point increases by over 80?C. Higher pressure and temperature greatly reduce the time required to reach equilibrium. With increasing pressure and decreasing temperature, O plays a much more important role than HO2 in the oxidation of NO. A higher water vapor content accelerates NO2 formation in all cases by providing more O and HO2 radicals. The addition of CO or SO2 also promotes the formation of NO2. The NO2 formation in a pressurized oxy-combustion furnace can be over 10 times that of an atmospheric air-combustion furnace.

Oxy-combustion is one of the most prominent solutions for reducing CO2 emissions from coal- fired power plants using carbon-capture-and- utilization technology. However, when compared to air combustion at atmospheric pressure, oxy- combustion is very expensive, owing to the significant efficiency penalties associated with air separation, flue gas recirculation (FGR), treatment, compression, and storage or transit of CO2. In comparison, pressurized oxy-combustion (POC) is more efficient as it recovers a significant amount of heat energy from the flue gas moistures. Nevertheless, CO2 derived from pressurized oxy coal combustion has impurities, e.g., acid gases (NOX and SOX) that can corrode the plant equipment, transport lines as well as deteriorating effect on the environment. Fortunately, in pressurized combustion systems, both NOX and SOX can be scrubbed by a single- column direct contact cooler (DCC), but this requires a minimum ratio of NOX to SOX at the inlet to be efficiently removed. Therefore, NOx is one of the important hindering parameters in commercializing the pressurized oxy-combustion. Although NOx evolution during oxy-coal combustion has been explored extensively at 1 atm, higher pressure studies are rare. Much still needs to be done to better understand the NOX mechanism and the effects of different parameters on NOX emissions under these conditions. This paper reviews the published literature on nitrogen evolution, NOX formation and reduction in pressurized oxy-coal combustion. At higher pressures, the NOX from fuel-bound nitrogen is generated through volatiles, tar and char, all of which are discussed. Where literature is not available, the effect of pressure on NOx evolution in different stages of coal combustion is predicted through CHEMKIN simulation. Homogeneous and heterogeneous pathways of NOX formation and their destruction in pressurized oxy-coal combustion are evaluated. Additionally, the effect of pressure on a few mature and commercialized NOx abatement methods is explored. In the last, the future perspective and recommendation are given. This review will aid in the provision of basic knowledge about NOx evolution and control in pressurized fuel combustion, as well as the identification of new research areas to pursue.

Oxy-combustion is one of the most promising technology for CO2 capture in coal-fired power plants. However, under oxy-combustion conditions, the concentrations of acid gas species are significantly increased due to the introduction of the flue gas recycle, which aggravates the high-temperature corrosion of heat exchanger materials in boilers. In this study, the early-stage high-temperature corrosion (0–16 h) of two representative water-wall tube materials (20G, 12Cr1MoV) is experimentally tested in a lab-scale furnace with the simulated oxy-combustion atmosphere. The effects of material, temperature, CO2, H2O, SO2, H2S and CO atmospheres on high-temperature corrosion behaviors is investigated. The micro-morphologies and compositions of corrosion layers are characterized by scanning electron microscope with energy dispersive X-ray spectra (SEM-EDS) and X-ray diffraction (XRD). Kinetic analysis shows that the high concentration of CO2 accelerates high-temperature corrosion of water wall materials. In the simulated oxy-fuel combustion atmosphere (CO2/O2/SO2), the mass gain rate can be enhanced by 10%–30% compared to the conventional air combustion atmosphere (N2/O2/SO2), and the major composition of oxide scale is magnetite. In a reducing oxy-fuel atmosphere (CO2/CO/SO2/H2S), the major components of oxide scale are magnetite and ferrous sulfide. The high concentration of moisture in the atmosphere accelerated the corrosion rate by 10–30%. For both model alloys, the corrosion kinetics obey the parabolic law. Water-wall tube material 12Cr1MoV appears superiority in corrosion resistance compared with 20G material.

The fine slag produced from the entrained flow gasifier in coal chemical industry contains a high amount of unburned carbon content, which can reach more than 40%. The coal gasification fine slag is dissipated just by land filling which occupies a lot of land. Consequently, it causes the pollution of soil, water and wastes the combustible carbon in coal gasification fine slag. It is crucial to develop an environmental friendly and economical scheme for the utilization of coal gasification fine slag. To achieve this aim, it is significant to investigate the combustibility of coal gasification fine slag and then propose a comprehensive utilization technology. In this study, the physical and chemical properties of the raw bituminous coal and the produced coal gasification fine slag, including proximate and ultimate analysis, particle size distribution, ash composition, morphology, and specific area were investigated. The combustion and co-combustion characteristics of coal gasification fine slag were analyzed by a thermo-gravimetric analyzer. A drop tube furnace and a fluidized bed reactor were employed to test the combustibility of coal gasification fine slag in a pulverized furnace and a fluidized bed furnace, respectively. Results show that the carbon content in dried coal gasification fine slag is >40% with a heating value > 16 MJ kg-1. Further, thermo-gravimetric analyzer test showed that the combustion property of coal gasification fine slag is worse than that of anthracite and close to that of high ash coal, and there is a non-negligible synergistic effect for raw bituminous coal and coal gasification fine slag co-firing. The combustibility test in drop tube furnace and fluidized bed reactor showed that coal gasification fine slag can be well burned in a pulverized furnace requiring combustion temperature >900 °C and oxygen concentration >10 vol%. However, the fluidized bed furnace was not appropriate for high efficiency coal gasification fine slag burning, because the unburned carbon content of fly ash after coal gasification fine slag combustion is still >14%, even at 900 °C, 21% oxygen concentration and a low fluidization number. It is suggested that coal gasification fine slag will be better to burned it in a pulverized furnace rather than fluidized furnace.

Sulfur trioxide (SO3) is not only environmentally harmful but also highly corrosive, taking a great threat to the safe operation of coal-fired power plants. A dominant pathway of SO3 formation in coal-fired power plant is through the catalytic oxidation of SO2 (SO2+1/2O2→SO3) on the surfaces of ash particles containing Fe2O3. The catalytic formation of SO3 could be affected by complex atmosphere, where the effect from H2O is still debatable. In this paper, density functional theory (DFT) is employed to explore the reaction pathway of SO3 formation catalyzed by α-Fe2O3 in complex atmosphere containing O, O2, SO2 and H2O. In order to get the stable adsorption sites of these species, the adsorption energy of potential adsorption configurations on the α-Fe2O3 (001) surface is calculated. The dissociations of O2 molecule on complete and defect α-Fe2O3 (001) surfaces with O vacancy are calculated, and the Langmuir-Hinshelwood and Eley-Rideal mechanisms for the O(ads) reaction with SO2(ads) or SO2 are compared. The effect of H2O besides of SO2 and O2 on the formation of SO3 is especially discussed. The DFT calculation results show that for the formation of SO3 in gas phase, the energy barrier of ‘SO2+1/2O2→SO3’ is 436.75 kJ mol−1, in contrast, for the catalytic formation of SO3 on α-Fe2O3 surfaces, this energy barrier becomes an order of magnitude smaller, 24.82 kJ mol−1. O2 molecules can dissociate on the defect α-Fe2O3 (001) surface with O vacancy spontaneously, indicating that the defect α-Fe2O3 is favorable for the dissociation of O2, thereby promotes the formation of SO3. The energy barrier of ‘SO2(ads)+O(ads)→SO3(ads)’ through Langmuir-Hinshelwood mechanism is much higher than that of ‘SO2+O(ads)→SO3(ads)’ through Eley-Rideal mechanism. The adsorption energy on the α-Fe2O3 (001) surface of H2O is much smaller than that of SO2 and O2, indicating that H2O has little effect on the adsorption of O, O2, SO2 and eventually the heterogeneous formation of SO3. The DFT analysis results in this study provide a deep understanding on the reaction pathway of SO3 catalytic formation by Fe2O3.

At present, large amounts of high-carbon-ash (HCA), a waste by-product from chemical industry, are landfilled each year across China. Because of its small particulate size, HCA particles from open landfills are easily suspended in air and are a major source of air particulate pollution. Soil and ground water contamination with heavy metals is the second negative effect of HCA landfilling. As inappropriate disposal of the HCA may lead to serious environmental and human health impacts, alternative ways for its safe disposal are studied. One of the options is the co-firing of HCA and coal in a cement calciner. Energy recovery of HCA in cement combustion units has two major advantages over landfilling. First one is that after the carbon content in HCA is combusted the leftover ash, reach in silica, reacts with the raw material and exits the rotary kiln as clinker, so there is no solid residue to contend with. The second benefit from using HCA in existing pulverized coal cement combustion units is the preservation of space in existing landfills. However, due to different fuel properties, HCA has a direct impact on the performance of existing pulverized coal fired furnaces. Therefore, special care needs to be taken into account when such waste fuel is used. The aim of this paper is to present a numerical analysis of co- firing HCA and pulverized coal inside a cement calciner. Numerical model of pulverized HCA combustion was developed and implemented into a commercial computational fluid dynamics (CFD) code AVL FIRE®, which was then used for the analysis. To benchmark the HCA combustion numerical model, drop tube tests were performed. The drop tube tests datum together with the experimental analysis of HCA properties is also given in this paper. A real industrial cement calciner geometry was used for the numerical analysis. Four cases of which three different co-firing cases were analysed. As different co-firing modes have a different effect on the cement calciner’s performance, where the rate of calcium carbonate decomposition is an important indicator for evaluating the performance of a cement calciner, this study brings added value to the investigations related to HCA use as an alternative fuel inside a cement calciner.