Single-particle coal ignition and alkali metal radiation characteristics based on optical diagnosis technology

Study on the ignition characteristics of coal is the theoretical basis for realizing the high-efficient and clean utilization of coal. The alkali metals such as K and Na in coal are released into the gas phase during combustion and enter the system, which can easily cause high temperature corrosion of the reactor, fouling of the heating surface and slagging in the furnace. Based on the single-particle coal ignition detection platform, the ignition and alkali metal Na* and K* radiation characteristics of single-particle Yangchangwan (YCW) bituminous coal and Naomaohu (NMH) lignite during combustion were investigated under different oxygen volume flow rates. High-speed camera technology was used to capture the flame evolution process during single-particle coal ignition, and hyperspectral imaging technology was used to measure the spontaneous emission spectra of alkali metals Na* and K* in the flame to obtain the spatial release behavior of alkali metals. The results show that the ignition process of different types of coal is different. The enveloping flame is formed in the combustion process of volatile matter in the YCW coal particles, while the ignition reaction of the NMH coal is more intense without enveloping phenomenon due to its high volatile matter content, and the flame brightness in the whole ignition process is stronger than that of the YCW coal. The increase of oxygen can promote the ignition of coal particles, with the increase of oxygen volume flow, the ignition delay time of the YCW coal and the NMH coal decreases, and the ignition delay time of the NMH coal is smaller than that of the YCW coal. When the fire occurs, the flame brightness is the brightest, and the flame shape is relatively smooth and stable. The radiation characteristics of alkali metals Na* and K* in single-particle YCW coal and NMH coal during ignition and combustion are different from that in coke combustion process, in which the radiation intensity of Na* and K* is the strongest. Na* has a release peak both in the volatile reaction process and coke reaction process, but K* radiation intensity does not have an obvious release peak in the volatile reaction process and coke combustion process. When oxygen content increases, the release time of alkali metals from the YCW coal and the NMH coal is gradually advanced, and the beginning time of alkali metal radiation from the NMH coal is less than that from the YCW coal. In addition, the analysis of the ignition process of single-particle coal shows that the release intensity of alkali metals Na* and K* in the peripheral position of the combustion flame is stronger than that in the central position

Preparation and toughening mechanism of Al2O3 composite ceramic toughened by B4C@TiB2 core–shell units

In this paper, the concept of incorporating core–shell structured units as secondary phases to toughen Al2O3 ceramics is proposed. Al2O3 composite ceramics toughened by B4C@TiB2 core–shell units are successfully synthesized using a combination of molten salt methodology and spark plasma sintering. The synthesis of B4C@TiB2 core–shell toughening units stems from the prior production of core–shell structural B4C@TiB2 powders, and this core–shell structure is effectively preserved within the Al2O3 matrix after sintering. The B4C@TiB2 core–shell toughening unit consists of a micron-sized B4C core enclosed by a shell approximately 500 nm in thickness, composed of numerous nanosized TiB2 grains. The regions surrounding these core–shell units exhibit distinct geometric structures and encompass multidimensional variations in phase composition, grain dimensions, and thermal expansion coefficients. Consequently, intricate stress distributions emerge, fostering the propagation of cracks in multiple dimensions. This behavior consumes a considerable amount of crack propagation energy, thereby enhancing the fracture toughness of the Al2O3 matrix. The resulting Al2O3 composite ceramics display relative density of 99.7%±0.2%, Vickers hardness of 21.5±0.8 GPa, and fracture toughness 6.92±0.22 MPa·m1/2

Gasification under CO2–Steam Mixture: Kinetic Model Study Based on Shared Active Sites

In this work, char gasification of two coals (i.e., Shenfu bituminous coal and Zunyi anthracite) and a petroleum coke under a steam and CO2 mixture (steam/CO2 partial pressures, 0.025–0.075 MPa; total pressures, 0.100 MPa) and CO2/steam chemisorption of char samples were conducted in a Thermogravimetric Analyzer (TGA). Two conventional kinetic models exhibited difficulties in exactly fitting the experimental data of char–steam–CO2 gasification. Hence, a modified model based on Langmuir–Hinshelwood model and assuming that char–CO2 and char–steam reactions partially shared active sites was proposed and had indicated high accuracy for estimating the interactions in char–steam–CO2 reaction. Moreover, it was found that two new model parameters (respectively characterized as the amount ratio of shared active sites to total active sites in char–CO2 and char–steam reactions) in the modified model hardly varied with gasification conditions, and the results of chemisorption indicate that these two new model parameters mainly depended on the carbon active sites in char samples

Experimental investigations on temperature distributions of flame sections in a bench-scale opposed multi-burner gasifier

Based on a flame image processing technique, the temperature distributions of flame sections in a bench-scale opposed multi-burner (OMB) gasifier is visualized. With the assumption of the gray radiation, a charge-coupled device camera installed on the top of the gasifier is used to capture the approximately monochromatic radiant images under the visible wavelengths. To reduce the errors, the camera is calibrated by a blackbody cavity. By using the two-color method, the radiant intensity captured by the camera is calculated from the pair of red/green with reference to the calibration data. Based on the assumption of rotational symmetry, the temperature distributions of flame sections are reconstructed by the Filtered back-projection method. The results show that the temperature distributions of flame sections are consistent with the flame structure. The flame temperature distribution at the burner plane ranges from 1700 to 2100 °C. The section is farther from the burner plane, the temperature is lower. The relative errors between the calculated temperatures and the measured temperatures by a B-type thermocouple are no greater than ±6.4%. The research results establish the foundation for understanding the flame internal structure and temperature distribution in the OMB gasifier.Entrained-flow gasification Temperature distribution Flame image Two-color method Filtered back-projection method

Oxygen Vacancy-Mediated Selective H₂S Oxidation over Co-Doped LaFe_xCo_1−xO₃ Perovskite

Compared to the Claus process, selective H2S catalytic oxidation to sulfur is a promising reaction, as it is not subject to thermodynamic limitations and could theoretically achieve ~100% H2S conversion to sulfur. In this study, we investigated the effects of Co and Fe co-doping in ABO3 perovskite on H2S selective catalytic oxidation. A series of LaFexCo1−xO3 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) perovskites were synthesized by the sol-gel method. Compared to LaFeO3 and LaCoO3, co-doped LaFexCo1−xO3 significantly improved the H2S conversion and sulfur selectivity at a lower reaction temperature. Nearly 100% sulfur yield was achieved on LaFe0.4Co0.6O3 under 220 °C with exceptional catalyst stability (above 95% sulfur yield after 77 h). The catalysts were characterized by XRD, BET, FTIR, XPS, and H2-TPR. The characterization results showed that the structure of LaFexCo1−xO3 changed from the rhombic phase of LaCoO3 to the cubic phase of LaFeO3 with Fe substitution. Doping with appropriate iron (x = 0.4) facilitates the reduction of Co ions in the catalyst, thereby promoting the H2S selective oxidation. This study demonstrates a promising approach for low-temperature H2S combustion with ~100% sulfur yield

Experimental Study on the Atomization and Chemiluminescence Characteristics of Ethanol Flame

The breakup regime in ethanol diffusion flame under different conditions was studied by the high speed camera system combined with the UV camera system. Spray angle and Weber number (We) were used to represent the change of breakup regime. With the increases of spray angle and We, the breakup mode changes from the Rayleigh-type breakup regime to the superpulsating regime. The reaction area and intensity of ethanol flames under different breakup regimes could be discussed by the OH⁎ distribution. From Rayleigh-type breakup regime to superpulsating breakup regime, the OH⁎ distribution increased and the oxidation-reduction reaction area expanded. At the condition of superpulsating breakup mode, the intensity of OH⁎ was significantly higher than that of other modes. The flame luminous length can be obtained by the OH⁎ emission, and OH⁎ distribution reflects the structure of flame. When the breakup regime changes from the fiber-type breakup regime to the superpulsating regime, the flame luminous length increases suddenly