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This investigation aims to understand the enhancement characteristics of plasma-assisted combustion in oxy-coal combustion. A 1064 nm Nd:YAG laser was added into a laminar flow reactor to produce laser-induced plasmas (LIPs). The high-speed visualization of the coal flame was used to reveal combustion's progress and evolution following laser-induced breakdown. To the best of our knowledge, this is the first time LIP has been applied to the optimization of pulverized coal combustion. The optical emission spectroscopy (OES) demonstrats that LIPs can generate adequate free electrons and ions during combustion. When the laser's pulse interval exceeds 60 ms, the LIP has a beneficial impact on combustion. For the heterogeneous reaction, the thermal effect generated by LIP only improves the intensity of flame radiation by 11–33 %. In contrast, the combination of chemical and thermal effects of plasma can result in significant enhancements of radiation intensity for high-volatile coals, with improvements of 76–203 %. Following laser-induced breakdown, the ignition delay time also decreases from lignite to anthracite, and the flame's peak intensity occurs earlier. [ABSTRACT FROM AUTHOR]

One of the major challenges regarding measuring chemical structures with laser-induced breakdown spectroscopy (LIBS) is that, it is difficult to track the source of organic components from atomic spectra since these structures have a similar elemental composition. However, LIBS molecular emissions (C 2 , CN, etc.) provide a possibility to investigate these similar compositions. In the present study, an experimental investigation was conducted to diagnose the structural evolution during coal combustion. The structural evolution of char particles was also evaluated as a reference using offline Raman spectroscopy. The significance of minerals on plasma emission was investigated based on plasmas of raw and demineralized coals. As combustion progresses, coal particles show the overall dissipation of active structures such as G r , V L , and V r bands, and the aromatization of char structures. The minerals in coal may increase the free–free bremsstrahlung and free–bound recombination events, resulting in a significant continuous baseline. Presence of minerals also reduces the breakdown threshold and enhances the LIBS's emissions. The char's structural transformation is regarded to be correlated with the rotational temperature (T rot) of CN molecules of LIBS's emissions. The mathematical correlations of linear fitting (R 2: 0.94) and exponential fitting (R 2: 0.99) exist between the drift coefficient and the T rot. This structural transformation might change the LIP's CN formation mechanism and lead to the T rot reduction. [ABSTRACT FROM AUTHOR]

The rapid development of measurement technology has created possibilities for the advancement of intelligent combustion diagnostics. The high-speed OH-PLIF was used to investigate homogeneous ignition and combustion characteristics of gas-solid two-phase flame in a laminar flow reactor of oxy-coal combustion. The primary focus is to investigate the physico-chemical processes of gas-solid interaction during the early stages of combustion. The image processing was employed to analyze the flame features and then obtain the ignition mechanism, OH distribution, species radiations, and fluctuation frequency. Results show that the homogeneous reaction dominates the ignition and volatile combustion at the early stages of oxy-coal flame. The ignition delay time and volatile burning time decrease with the increasing gas temperatures and oxygen concentrations. The fluctuation dominant frequency increases from 190.5 Hz to 243.2 Hz at the ambient temperature from 1200 to 1800 K. The dominant frequency stabilizes between 243.2 Hz and 243.5 Hz at the ambient temperature from 1500 to 1800 K. The dominant frequency undergoes a shift to a maximum limit of 243.5 Hz from 1200 to 1800 K. When the oxygen concentration increases from 20 % to 40 %, the dominant frequency continues to rise from 244.8 Hz to 268.7 Hz. • Homogeneous reaction dominates the early stages of oxy-coal flame. • Fluctuation dominant frequency is closely related to ignition processes. • Dominant frequency shifts to a maximum limit with the increasing temperatures. [ABSTRACT FROM AUTHOR]

The use of a coal-based energy structure generates a large amount of CO2 and NOx. The numerous emissions from these agents result in acid rain, photochemical smog, and haze. This environmental problem is considered one of the greatest challenges facing humankind in this century. Preheating combustion technology is considered an essential method for lowering the emissions of CO2 and NO. In this research, the char prepared from O2/CO2 and O2/H2O atmospheres was employed to reveal the effects of the addition of an oxidizing agent on the combustion characteristics of char. The structural features and combustion characteristics of preheated chars were determined by Raman, temperature-programmed desorption (TPD), and non-isothermal, thermo-gravimetric (TGA) experiments. According to the experimental results, the addition of oxidizing agents promoted the generation of smaller aromatic ring structures and oxygen-containing functional groups. The improvement in the surface physicochemical properties enhanced the reactivity of char and lowered its combustion activation energy. Furthermore, the combustion mechanisms of the char prepared from the O2/CO2 and O2/H2O atmospheres were investigated using the density functional theory (DFT). The simulation results illustrated that the combustion essence of char could be attributed to the migration of active atoms, the fracture of the benzene ring structure, and the reorganization of new systems. The addition of oxidizing agents weakened the conjugated components of the aromatic ring systems, promoting the successive decomposition of CO and NO. The results of this study can provide a theoretical basis for regulating the reaction atmosphere in the preheating process and promoting the development of clean combustion for high-rank coals. [ABSTRACT FROM AUTHOR]

[Display omitted] • O 2 /H 2 O pretreatment with Na participation accelerated the formation of micropores. • Sodium addition enhanced the reactivity of semichar via the structure of C-O-Na. • Increasing the quantity of small aromatic rings could accelerate the emission of CN/C 2. • The addition of O 2 , H 2 O, and Na could synergistically increase the NO reduction ability of semichar. • Na promoted the reduction of NO by attenuating the conjugated components of the aromatic system. The surface physicochemical features of semichar play a crucial role in determining its reactivity, dominating the subsequent reaction between semichar and NO. Therefore, the synergistic effect of O 2 /H 2 O pretreatment and Na addition on the microstructural characteristics of semichar and NO reduction characteristics is revealed through experimental and density functional theory (DFT) methods. Experimental results indicate that O 2 /H 2 O pretreatments with Na addition promote the development of pores. Micropores are considered the major pore structures in semichar. Based on Raman and laser-induced breakdown spectroscopy (LIBS) results, the combined effect of O 2 /H 2 O pretreatments and Na promotes the formation of small aromatic rings, exhibiting a positive correlation with molecular emissions. Temperature-programmed reduction experiments (TPR) demonstrate that the inclusion of Na in O 2 /H 2 O pretreatments enhances the reduction ability of NO. The reduction mechanism of NO-semichar is determined using the DFT method. The simulation results indicate that the adsorption of H 2 O during O 2 /H 2 O pretreatment is chemisorption and independent of Na atom. The additional Na reduces the energy gap of the NO-semichar, facilitating the decomposition of N 2 by weakening the conjugated components of the aromatic structures. [ABSTRACT FROM AUTHOR]

N -glycosylation has been revealed to be tightly associated with cancer metastasis. As a key transferase that catalyzes the formation of β1,4 N -acetylglucosamine (β1,4GlcNAc) branches on the mannose core of N -glycans, N -acetylglucosaminyltransferase IVa (GnT-IVa) has been reported to be involved in hepatocellular carcinoma (HCC) metastasis by forming N -glycans; however, the underlying mechanisms are largely unknown. In the current study, we found that GnT-IVa was upregulated in HCC tissues and positively correlated with worse outcomes in HCC patients. We found that GnT-IVa could promote tumor growth in mice; notably, this effect was attenuated after mutating the enzymatic site (D445A) of GnT-IVa, suggesting that GnT-IVa regulated HCC progression by forming β1,4GlcNAc branches. To mechanistically investigate the role of GnT-IVa in HCC, we conducted GSEA and GO functional analysis as well as in vitro experiments. The results showed that GnT-IVa could enhance HCC cell migration, invasion and adhesion ability and increase β1,4GlcNAc branch glycans on integrin β1 (ITGB1), a tumor-associated glycoprotein that is closely involved in cell motility by interacting with vimentin. Interruption of β1,4GlcNAc branch glycan modification on ITGB1 could suppress the interaction of ITGB1 with vimentin and inhibit cell motility. These results revealed that GnT-IVa could promote HCC cell motility by affecting the biological functions of ITGB1 through N -glycosylation. In summary, our results revealed that GnT-IVa is highly expressed in HCC and can form β1,4GlcNAc branches on ITGB1, which are essential for interactions with vimentin to promote HCC cell motility. These findings not only proposed a novel mechanism for GnT-IVa in HCC progression but also revealed the significance of N -glycosylation on ITGB1 during the process, which may provide a novel target for future HCC therapy. • GnT-IVa enhances cell motility and correlates with poor outcomes of HCC. • GnT-IVa increases β1,4GlcNAc branches on ITGB1 to promote cell motility of HCC. • β1,4GlcNAc branches on ITGB1 affect interactions with vimentin in HCC. [ABSTRACT FROM AUTHOR]

• CN and C 2 emissions were positively correlated to the amounts of small aromatic rings. • The synergetic effects of O 2 /Ar and sodium salt enhanced the combustibility index of semichar. • O 2 /Ar pretreatments and sodium salt addition altered the distribution of charge in semichar. • Additional Na during O 2 /Ar pretreatment decreased the combustion barrier of semichar. Using Raman spectroscopy, temperature-programmed desorption (TPD) and laser-induced breakdown spectroscopy (LIBS), the relationship between microstructural characteristics and molecular emissions was determined. It can be concluded that the enhancement of C 2 and CN emissions was related to the generation of small aromatic rings and C(O) groups. Compared with the Ar preheating treatment, the presence of additional amount of O 2 and sodium salt accelerated the dissociation of the large aromatic ring skeleton, leading to the significant enhancement of small aromatic rings, C(O) and C O Na groups. Subsequently, the combustion performance of preheated semichar was investigated by the TG-DTG method. The experimental results demonstrated that pretreatment under oxidizing atmospheres (without and with sodium salt addition) enhanced the comprehensive combustion index (S) and the combustion stability (R w) of semichars. The corresponding combustion activation energy (E) was weakened. Furthermore, the DFT method was used to analyse the combustion behaviours of semichars. This result demonstrated that preheating treatment (with or without sodium participation) altered the distribution of the Hirshfeld atomic charge (ADCH) of preheated samples, and the combustion essence of semichar was the fracture and recombination of aromatic clusters. For the semichar preheated in the O 2 /Ar atmosphere, the energy gap of the most optimized pathway was 436.26 kJ/mol. When sodium participated in the oxidizing pretreatment, the energy gap of the most optimized pathway was 413.80 kJ/mol. The positive effect of sodium on the combustion performance of semichar was identified, which was in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

• Homo-/heterogeneous Damkhöler numbers are adopted to characterize the MILD regime. • A low O 2 content and a CO 2 environment promote the homo-MILD regime while hetero-MILD regime is inhibited. • An ideal hetero-MILD combustion can be realized by increasing O 2 content. • Reduced effect of char-O 2 reaction share and promoted effect of char-CO 2 reaction share with increasing X O2 are weakened. • The surface behavior of char and NO x emission are affected by X O2 and CO 2 dilution. The present study numerically investigates the effects of the O 2 content (X O2) in the oxidizer on the MILD combustion behaviours of large-proportion semicoke mixtures, such as those involving temperature, MILD regime recognition, char surface consumption, homo/heterogeneous Damkhöler number, and NO x emission, under O 2 /N 2 and O 2 /CO 2 atmospheres. The results indicate that by increasing X O2 from 15 % to 30 %, the peak temperature increases significantly due to the increased char consumption rate, the high temperature region shrinks, and the axial length of the MILD regime region slightly increases from ∼1 to ∼1.4 m because of enhanced flue gas recirculation under O 2 /N 2 or O 2 /CO 2 atmosphere. The reduction effects of the char-O 2 reaction proportions and the promoted effects of the char-CO 2 reaction proportions due to the increased XO 2 are both obviously weakened when N 2 is substituted for CO 2. A high O 2 content and an O 2 /N 2 atmosphere reduce the char burnout time. With increasing XO 2 , the maximum value of the turbulent Damkhöler number Dat increases from 6.79 to 10.16 under the O 2 /N 2 atmosphere and from 3.99 to 10.6 under the O 2 /CO 2 atmosphere, implying that a low O 2 dilution and a CO 2 environment promote the establishment of the homo-MILD regime. The maximum values of the surface Damkhöler number (Das-CO 2 and Das-H 2 O) of the two gasification reactions (Char-CO 2 and Char-H 2 O) have the same order of magnitude and are much lower than those of the surface Damkhöler number (Das-O 2) of the Char-O 2 oxidation reaction, i.e., Das-H 2 O < Das-CO 2 ≪ Das-O 2 < 1. The maximum values of the three surface Damkhöler numbers all increase with increasing XO 2 , while they decrease with the replacement of N 2 by CO 2 , indicating that a high O 2 content and an O 2 /N 2 atmosphere could facilitate the establishment of an ideal hetero-MILD combustion regime to some extent. Low NO x emissions can be realized under moderate O 2 and CO 2 dilution conditions by regulating the oxy-MILD combustion regime of semicoke blends. [ABSTRACT FROM AUTHOR]

A novel application of multi-point LIBS was used to investigate the mineral release for dispersed-particle streams during coal combustion in an enclosed laminar flow reactor. A 1064 nm Nd: YAG laser was used to ablate the pulverized coal in air-like combustion environments at atmospheric pressure. The electron temperature (T e) and electron density (N e) were calculated to evaluate the characteristics of the laser-induced plasma along the height from the burner surface, and LS -coupling method was further used to distinguish whether self-absorption occurred. The particle temperature was measured by a two-color pyrometer, and the time-resolved behaviors of Na, Ca and Fe along with the combustion process were measured by LIBS. Results show that the T e and N e of laser-induced plasmas decreased with the flow of coal flame upon devolatilization, and became relatively stable during char combustion. There was little atomic self-absorption during char-combustion process, which provided theoretical support for quantitative combustion analysis. The Na release, mainly atomic forms, decreased with the particle flow upon devolatilization and showed a trend from rise to decline following devolatilization. The Fe and Ca was rarely released upon devolatilization. During char combustion, the Ca have a similar behavior to Na release, while the Fe increased and then remained constant. The temperature dependent kinetics of the Na and Ca release rate was found to obey an Arrhenius expression. The kinetics of Na and Ca atomic release determined by a first-order model had the pre-exponential factor of 101.16 and 102.67 s −1 and the activation energy of 87.2 and 150.8 kJ/mol, respectively. [ABSTRACT FROM AUTHOR]

To study the combination of fuel-rich/lean combustion with oxy-MILD (moderate and intense low-oxygen dilution) combustion for the reduction of NO x emissions by adopting carbon capture and storage, this paper numerically investigates the turbulence−chemistry interactions and NO x emission behaviours of semicoke mixtures under different secondary velocities V sec (from air-fuel combustion to air-MILD combustion) and under different CO 2 dilution levels (oxy-MILD combustion). The bias concentration ratio (BCR) hardly affects the establishment of air-MILD combustion, which is obtained at V sec = 158.6 m/s. The oxy-MILD combustion, which is composed of small flamelets diffusing in large-scale eddies (turbulent Damköhler number Da t = 0.1–1), is enhanced, and the ignition and char burnout times are prolonged by increasing CO 2 from 0 vol% to 79 vol%. The char oxidation reaction in the diffusion/kinetics-controlled regime and the char gasification reactions in the kinetics-controlled regime both shift towards the kinetics-controlled regime with increasing velocities and CO 2 dilution, thus leading to lower burnout rates. The heterogeneous MILD regime of the fuel-lean side is more easily established for the air-MILD combustion, while that of the fuel-rich side is more easily established for oxy-MILD combustion. This is because the intensive turbulence increases the O 2 dilution level in the fuel-lean jet, while a high concentration of CO 2 reduces the oxygen diffusivity in the fuel-rich jet, which also leads to a larger X NO in the fuel-lean jet compared to the fuel-lean jet. The NO x concentration at the furnace outlet decreases significantly from air-fuel combustion to air-MILD combustion and further decreases as the oxy-MILD combustion is enhanced, along with relatively lower homogeneous and heterogeneous Da. • Integrating fuel-rich/lean technology with oxy-MILD combustion is introduced for semicoke co-combustion. • CO 2 dilution is adopted to further enhance the oxy-MILD combustion. • Air-MILD combustion facilitates MILD regimeof fuel-lean jet, while oxy-MILD combustion promotes that of fuel-rich jet. • Low NO x emissions can be achieved in air-MILD combustion and is further promoted under enhanced oxy-MILD combustion. [ABSTRACT FROM AUTHOR]

Laser-induced breakdown spectroscopy (LIBS) was employed to study the spectral characteristics of the C 2 and CN emissions of three types of coal and their pyrolysis char samples. By analysing the atomic and molecular emissions, the electron temperature, electron density and rotational temperature were calculated to evaluate the characteristics of the laser-induced plasma. The correlation between the molecular emissions and coal combustion characteristics was also investigated, which was explained from the aspect of microstructural evolution obtained by Raman spectroscopy. The molecular emissions were gradually inhibited with increasing pyrolysis temperatures, however the molecules tended to distribute at a higher equilibrium temperature. The rotational temperatures increase by 1000–3300 K relative to the raw coal for chars prepared at pyrolysis temperatures of 293–1173 K. The reduction of C 2 and CN emissions, which are thought to be mainly caused by small aromatic rings and amorphous carbon structures, is consistent with the Raman spectroscopy results in that the microstructures evolve towards a more stable large aromatic-ring skeleton after pyrolysis. When the carbon conversion ratio is X c = 50% for three kinds of coal, the R 2 values of the exponential fitting between C 2 emission and carbon conversion rate are all higher than 0.99. • The presence of KBr binder has improved the rotation temperature of plasmas of the coal and char samples. • LIBS molecular emissions of char were inhibited with the increasing pyrolysis temperature. • The reduction of C 2 and CN emissions is consistent with microstructure evolution upon pyrolysis. • The C 2 emissions has a positive correlation with the carbon conversion rate during combustion. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fuel-rich/lean technology is used for large-proportion semicoke co-combustion. • Adding bluff bodies at the fuel-rich side facilitates fuel-rich/lean technology. • Turbulence-chemistry interaction behaviour is featured by Damköhler number. • Low NO x formation is due to a local homogeneous MILD regime at the fuel-rich side. Fuel-rich/lean combustion is considered as a novel combustion technology due to its enhanced ignition performance and low NO x emissions. To further improve the poor performance of large-proportion semicoke and bituminous coal blended combustion and reduce NO x emissions, under a bias concentration ratio (BCR) of 2:1, an addition of bluff bodies at the fuel-rich side is proposed to numerically and experimentally investigate the turbulence-chemistry interaction behaviours of the fuel-rich/lean combustion regime in a 0.3 kW pilot-scale bias combustion furnace for various bluff body blockage ratios (BR = 0%, 11% and 21%). The results show that, increasing the blockage ratio evidently shortens the ignition delay time and burnout time of bituminous coal and semicoke, and the promotive effect of triangular bluff-body (BR = 21%) is greater. The turbulent Damköhler number Da t maximums decrease from 194 to 113 with increasing BR, denoting the regime is traditional combustion mode controlled by mixing. On the fuel-rich side, a local homogeneous MILD combustion zone (Da t <10) extends with increasing BR. For the heterogeneous combustion, the char-O 2 reaction determined by diffusion/kinetics and the char gasification reaction controlled by kinetics both show a kinetically controlled trend with increasing BR. Moreover, with increasing BR, a decreasing in the NO concentration in the main reaction zone can be attributed to an enhanced recirculation rate K v. There is a strong correlation between the maximum NO and the local homogeneous/heterogeneous Damkhöler number on the fuel-rich/lean side in the plane of maximum K v. Increasing BR can evidently decrease the maximum NO concentration on the fuel-rich side due to the enhanced local MILD combustion regime, and thus reducing NOx exit emissions. Considering temperature, ignition, burnout, turbulence-chemistry interactions and NO x emissions, a triangular-shaped bluff body on the fuel-rich side (BR = 21%) is recommended rather than a cubic bluff body in the fuel-rich/lean co-combustion of semicoke. [ABSTRACT FROM AUTHOR]

During large-scale semicoke and bituminous coal co-combustion, the behaviors of turbulence-chemistry interactions were experimentally and numerically used to investigate the effects of char burnout and NOx emissions in a pilot-scale bias combustor at different bluff-body cone angles (α). The results show that with increasing α the main reaction zone moves upstream significantly, and a widened flame and uniform temperature profile are obtained due to enhancing the internal flue gas recirculation. An increase in α can improve the char-oxidation reaction, and further results in increased pore structures and char burnout ratios. For all cases, the Da t (homogeneous Damköhler number) maximum values are below 0.50. The Da , O 2 , Da , CO 2 and Da , H 2 O (heterogeneous Damköhler numbers) values are within 0.670–1.207, 0.004–0.017 and 0.001–0.004, indicating that the char oxidation reaction is dominated by diffusion/kinetics, while the char gasification reactions are controlled by chemical kinetics. However, both reactions tend to be kinetically-controlled with increasing α. The NOx emissions decrease by 27% at the α = 34° value, because a large cone angle can enlarge the combustion reduction zone and enhance the oxygen diffusion rate. The findings can provide deep insight into the turbulence-chemistry interactions and its effect on NOx emission characteristics of semicoke co-combustion in a bluff-body tangential burner. [Display omitted] • Bluff-body with different cone angle is used for semicoke and bituminous coal large-scale co-combustion. • The behaviors of turbulence-chemistry interaction are characterized by the Damköhler number. • NOx formation can be controlled by achieving a moderate kinetic rate and preferable O 2 diffusivity regime. • As the cone angle increases, more uniform and lower temperature profiles, as well as extended reduction zone are captured. [ABSTRACT FROM AUTHOR]

• The ignition and combustion of co-combustion is studied using OH-PLIF. • The synergistic effect on blends ignition is volatile content and K, Na, and Ca. • The high flame temperature and Na/ Fe promote the fixed carbon burnout of blends. • The promotion on ignition and burnout is dominant at 20% pyrolyzed char in blends. This work studies the ignition behavior and combustion characteristics of pulverized pyrolyzed bituminous (PB) char blended with pulverized bituminous coal at different mass fractions. Experimental studies were conducted with OH planar laser-induced fluorescence (OH-PLIF) diagnosis technology in a flat-flame optical entrained flow reactor for pulverized coal/char. An interaction occurs between pyrolyzed char and bituminous coal, which is indicated by the relationship observed between the pyrolyzed char mass fraction mean values (MFMVs) and the combustion properties of the blended fuels. The addition of bituminous coal enhances the competitive effects of the two fuels on ignition and burnout. The synergistic effect observed upon ignition of the blends is mainly attributed to the high volatile contents and the potential catalysis effects from the alkali and alkaline earth metal species in the blends. The important factor leading to this synergistic effect is that the alkali and alkaline earth metal species in the ash can reduce the ignition temperature and accelerate the release of volatiles, thereby shortening the ignition delay. The high flame temperature and the potential catalysis effects from the alkali metal and transition metal species promote blended fuel burnout. Considering both the ignition delay and the residual char burnout, the optimal blending ratio of pyrolyzed char is approximately 20% because the fixed carbon burnout of the blends is considerably promoted and the ignition delay is significantly shortened. In comparison with PB char, the ignition delay decreased by 28.95% and the burnout ratio increased by 39% at the 20% PB char blending ratio. [ABSTRACT FROM AUTHOR]