Pressurized coal gasification fine slag (PGFS) contains residual carbon and mineral-rich ash, but its combustion utilization is limited by poor apparent reactivity. In this study, raw coal (RC), PGFS, and acid-leached PGFS-CFN were investigated using sequential acid leaching and multi-scale characterization, including SEM–EDS, TEM, N2 adsorption, XRD, Raman, XPS, and TG/DTG analysis. The results show that pressurized gasification forms a carbon–ash composite structure with high ash content, mineral-rich surface coverage, and a more ordered residual carbon skeleton. These structural features are associated with delayed ignition, a broader combustion temperature range, and a lower maximum mass-loss rate of PGFS. After sequential HCl–HF–HNO3 acid leaching, the ash content decreased from 66.27 wt% to 0.83 wt%, while the specific surface area and total pore volume increased from 134.90 m2·g−1 and 0.140 cm3·g−1 to 412.56 m2·g−1 and 0.263 cm3·g−1, respectively. The acid-leached sample exhibited lower ignition and burnout temperatures, a higher maximum mass-loss rate, and a markedly increased comprehensive combustion index under the same TG conditions. The combined structural and combustion results suggest that ash-related shielding, pore accessibility, residual carbon ordering, and surface chemistry jointly regulate the apparent combustion behavior of PGFS. This study provides structural insight into the combustion inertness of PGFS and may support future optimization of combustion-oriented utilization strategies.

Pressurized coal gasification fine slag (PGFS) shows low combustion reactivity due to ash encapsulation. Using gravity separation, high-carbon PGFS-HC was obtained with ash content reduced to 10.73 wt% and SBET increased to 253 m2·g−1. Its comprehensive combustion index S increased from 0.09 × 10−8 to 14.84 × 10−8. TG-MS analysis shows that the CO2 release peak in PGFS-HC coincides with the DTG peak, whereas it is delayed in raw PGFS, indicating that mass transfer limitation rather than carbon graphitization dominates combustion inertness. These results demonstrate that targeted removal of the physical ash barrier is key to improving PGFS combustion and enables cascade utilization of high-carbon and high-ash fractions.

Current swirl combustion technology for low-grade coal lacks flexibility in peak regulation without auxiliary combustion-supporting measures, which can hardly meet the deep peak shaving requirements of thermal power units. Therefore, it is urgent to develop novel low-load stable combustion technologies. In this study, the existing Low NOx Axial Swirl Burner (LNASB) of a 350 MW boiler was taken as the research object. The influence law of central air velocity on the gas-particle two-phase flow characteristics of the burner was systematically investigated, and a structure optimization scheme with minor modification was proposed, namely eliminating the central air passage, pulverized coal collector and combustion stabilization ring in the primary air duct of the original burner. On this basis, a 1:7 scale cold-flow modeling test bench was built in accordance with the similarity criterion, and scheme verification and characteristic tests were completed using a three-dimensional Phase Doppler Anemometry (PDA). The research results show that although the gas-particle two-phase swirl intensity of the original LNASB burner increases slightly with the rise of central air velocity, the flow field is dominated by high-speed primary air. As a result, a stable central recirculation zone (CRZ) cannot be formed at the burner outlet, and the radial diffusion capacity of pulverized coal particles is severely limited, which ultimately leads to difficult ignition of pulverized coal and insufficient low-load stable combustion performance. For the improved LNASB burner, increasing the primary air velocity can significantly raise the particle concentration near the wall of the primary air duct and extend the axial transport distance of particles, thereby improving the furnace flame fullness and pulverized coal burnout characteristics. However, excessively high primary air velocity will weaken the radial diffusion capacity of particles and deteriorate the uniformity of gas-particle mixing. Based on the test results under multiple working conditions, the recommended primary air velocity is 13.5 m/s. The improved LNASB burner can form a stable central recirculation zone at the nozzle outlet under the full load range of 20% similar to 100%. When the load drops to 20%, the length and width of the recirculation zone can still reach 0.4d and 0.1d respectively, where d represents the diameter of the outer secondary-air outlet, i.e. the characteristic diameter of the burner outlet (d = 0.200 m), with a recirculation ratio of 0.561. This recirculation zone is conducive to the recirculation of high-temperature flue gas and promotes the transport of pulverized coal from the central injection zone to the radial periphery, thereby providing a more favorable flow field basis for the mixing of pulverized coal and secondary air and for low-load stable combustion. These results can provide a theoretical basis and technical support for the low-load stable combustion retrofitting of the same type of LNASB burners.

To solve the problems of upward movement of flame center, slagging, and NOx emissions in traditional down fired boilers when burning high volatile bituminous coal, this study proposes an innovative coupling strategy based on primary air bias combustion technology (PABCT): primary air biased technology coupled with precise furnace gas port tuning (PAFPT). However, the core mechanism of how the position of the vent air position regulates the spatiotemporal evolution of the gas solid two phase of the biased primary air jet is not yet clear, and there is a lack of quantitative optimization basis. Therefore, a 1:20 cold state gas solid two phase modeling test bench was established to systematically study the flow characteristics under different vent air nozzle positions (55 mm, 95 mm, 145 mm, 195 mm), with precise measurements conducted using 3D-Phase Doppler Particle Anemometer (PDA). For the first time, this study combines main effect and interaction effect analysis to quantitatively reveal the core mechanism of vent air position. The results show that vent air position is the key to controlling the timing of gas-solid mixing and entrainment intensity: the high-position arrangement at 55 mm leads to premature mixing, which is unfavorable for stable combustion and NOx control; the low-position arrangement at 195 mm causes premature particle deflection and insufficient downward momentum. Multi-index joint optimization analysis identifies 145 mm as the global optimal operating condition. Under this condition, the peak particle volume flow rate in the cold ash hopper area reaches 1.64-2.25 times that of other conditions, and the gas-solid velocity and pulsation characteristics achieve the best synergy. This can effectively delay pulverized coal ignition, reconstruct the "W"-shaped flame, thereby improving the lower furnace utilization rate and pulverized coal burnout rate, and laying a flow field foundation for reducing NOx generation at the source. Through a data-driven optimization method, this study provides a solid theoretical basis and universal optimization strategy for the design and operation of down fire boilers, contributing to the clean and efficient utilization of coal.

Deep peak-shaving compels units to operate far below design load, tightening the coupling among combustion kinetics, pollutant formation, safety, efficiency, and cost. This study quantifies these interactions via full-scale tests on a 660 MW opposed wall-fired boiler under coal-only operation from 180 to 600 MW (27-91% boiler rated load). Multi-point near-burner profiling, near-sidewall sampling, and infrared pyrometry were integrated. A secondary-to-primary air momentum-flux ratio (J) was utilized to diagnose aerodynamic transitions, while a Relative Corrosion Propensity Index (RCPI) was developed to assess gas-phase corrosion aggressiveness. The layer-D reference burner exhibits an ignition transition with J approximate to 0.77: as load decreases, ignition shifts from similar to 0.3 m to >2.3 m, whereas the layer-A and layer-C burners maintain ignition distance <1.4 m across all loads. Infrared reconstruction indicates that at 180 MW the high-temperature core is confined near the lower burner elevation (similar to 21 m). At 495 MW, a severe near-wall reducing hotspot (CO > 3.5 & times; 10(4) ppm) is identified at the layer-A sidewall, yielding an RCPI similar to 50 times the baseline. At minimum load, a high-excess-air stabilization strategy incurs efficiency and cost penalties, with NOx (6% O-2) rising to 491.9 mg m(-3), specific heat-loss cost increasing by 27.8%, and exhaust temperature falling below the acid dew point. Overall, the results delineate a transition from an efficiency-driven regime at high loads to a safety-constrained regime at low loads, supporting flexibility retrofits and model validation for similar utility boilers.

Against the background of deep peak shaving requirements and severe slagging and burnout issues of swirl burners in Zhundong coal-fired boilers, an improved Inner-Pulverized-Coal-Concentration (IIPCC) burner is proposed in this study. The flow and combustion characteristics of the original Outer-Pulverized-Coal-Concentration (OPCC) burner and the IIPCC burner are systematically investigated via a 1:6 cold-state gas-solid two-phase test and 600 MW industrial experiments. The results show that central air significantly suppresses the recirculation zone and delays ignition of the OPCC burner; reducing central air opening advances ignition only slightly, and the minimum stable combustion load remains as high as 60% rated load. Compared with the OPCC burner, the IIPCC burner removes central air, adds swirling slit air and three-stage concentration rings, and optimizes the secondary air nozzle. It forms a larger recirculation zone (max height from 0.22d to 0.33d), weakens the near-nozzle recirculation intensity (recirculation ratio from 24.10% to 18.36%), and achieves obvious internal-rich and external-lean pulverized coal distribution. These changes effectively improve the low-load combustion stability and reduce the risk of burner slagging and burnout. The IIPCC burner exhibits a high engineering value, with simple modification and low cost, providing a feasible technical solution for deep peak shaving and anti-slagging retrofit of Zhundong coal-fired boilers.

Based on an MW-scale coal-NH3 co-combustion pilot facility, this study systematically investigated the effects of four inner-to-outer secondary air ratios (RSA, defined as the mass flow ratio of inner secondary air to outer secondary air) on the in-furnace temperature field, key species distributions (O2, CO, NH3, NOx), and final emissions. The results indicate that RSA is a critical parameter controlling the atmosphere structure in the main combustion zone and the fuel nitrogen conversion pathways. As RSA increased from 0.11 to 0.57, the preferential oxygen consumption by pulverized coal was enhanced, and the main combustion zone gradually shifted from a relatively oxidizing to a strongly reducing environment, effectively suppressing fuel nitrogen conversion to NOx. Under the RSA = 0.57 condition, NOx emissions decreased to 432 mg/m3, approximately 14.5% lower than those at RSA = 0.11, while the tail-end CO concentration remained low at 14 ppm, and the combustible content in fly ash was only 5.01% (achieving a burnout rate of 99.53%). These findings demonstrate that appropriately configuring the radial secondary air ratio can balance "high combustion efficiency" and "ultra-low emissions" in coal-NH3 co-combustion, providing an experimental basis for the optimized design of coal-NH3 burners.

Abstract Pressurized coal gasification fine slag exhibits poor combustion reactivity due to the coupled effects of mineral encapsulation and highly ordered residual carbon. In this study, sequential HCl → HF → HNO3 demineralization was employed as a mechanistic probe to distinguish the predominant contributions of mineral shielding and carbon-structure inertness to combustion behavior. The ash content decreased from 66.27 wt % to 0.83 wt %, while the carbon content increased to 93.82 wt %. HCl and HF primarily removed mineral barriers and opened oxygen-accessible pore networks, increasing the specific surface area and pore volume. In contrast, HNO3 oxidation increased carbon disorder and redistributed surface oxygen species toward a higher relative abundance of carbonyl/quinone-like structures. The comprehensive combustion index increased from 0.09 × 10–8 to a maximum of 13.95 × 10–8 %2·min–2·°C–3 after HCl → HF treatment. Subsequent HNO3 oxidation increased the maximum mass-loss rate from 5.42 to 6.21%·min–1 but decreased the mean mass-loss rate from 3.64 to 2.95%·min–1, resulting in a slightly lower S value of 13.20 × 10–8 %2·min–2·°C–3. These results demonstrate that mineral shielding removal and pore accessibility dominate the overall combustion improvement, whereas HNO3-induced defects and surface-oxygen redistribution mainly enhance localized oxidation reactivity.

The gasification agent's flow rate has a significant impact on gasification performance. However, current research has only examined the effect of material balance on syngas composition. No studies have investigated the impact of gasification agent flow rate on mixing characteristics and flow field in the gasifier. To enhance the gasification performance of the gasifier, this study employs two cold-flow experiments. A 0.75: 1 single-phase flow experiment shows that at a gasification agent flow rate of 75%, mixing between the airflows is dominated by flow diffusion, resulting in a low mixing degree. At 100% flow rate, axial mixing is intense. At 125% flow rate, the central flow must overcome shear resistance to maintain motion, resulting in weakened diffusion capacity. A 1: 2.5 air-particle two-phase flow experiment shows that in the upper chamber, an increase in gasifier agent flow rate can significantly enhance the tangential average velocity and improve the gas-solid two-phase mixing degree. In the lower chamber, under the three flow rates, the particles all move downward along the wall with the rotating gas flow, and the formed slag layer can protect the membrane wall from ablation.

Pressurized gasification plays a significant role in clean coal technology, but the by-product, coal gasification fine ash (CGFA), exhibits a year-on-year increase in emission volumes, which severely constrains the healthy development of the coal gasification industry. In this study, CGFA with ultra-low calorific value and ultra-low volatile content was utilized as a substitute fuel for coal and was consumed via chamber combustion. By constructing a MW-scale swirl combustion system, the combustion characteristics of pressurized coal gasification fine ash (calorific value: 8660.01 kJ/kg, volatile matter content: 3.52%) blended with bituminous coal at different blending ratios (pressurized CGFA blending ratio: 0-40%) were investigated. Comprehensive measurements were conducted on in-furnace parameters such as temperature, flue gas composition, and fly ash burnout rate. Stable ignition and efficient burnout of pressurized CGFA were achieved. At a 30% blending ratio, the furnace flame remained bright and stable, with the maximum temperature in the main combustion zone exceeding 1300 degrees C. The burnout rate reached as high as 99.24%, while NOx emissions at the furnace outlet were measured at 290.93 mg/m3, a 32.19% decrease from the 429.03 mg/m3 observed in pure coal combustion.

This study systematically investigated the co-combustion characteristics of coal and NH3 at different ammonia blending ratios (0%, 5%, 15%, and 20%) on a MW-scale pilot platform. The effects on in-furnace temperature fields, key species distributions, and burnout behavior were analyzed to reveal the synergistic influence of ammonia addition on combustion and pollutant formation. A staged combustion strategy was implemented to achieve stable combustion and coordinated emission control. Results show that a 5% NH3 blending ratio weakened the initial coal ignition and combustion intensity, while promoting NOx formation. With increasing NH3 proportion, the main combustion zone gradually shifted toward a strongly reducing atmosphere. NOx emissions exhibited a non-monotonic trend, increasing first and then decreasing with higher NH3 blending ratios. Under the 15% NH3 condition, NOx concentration was 489 mg/m3, NH3 slip remained below 78 ppm, CO was only 9 ppm, and burnout reached 99.39%. The 15% NH3 condition achieved a balance between emission reduction, combustion stability, and engineering feasibility, providing experimental evidence for low-carbon combustion and low-NOx synergistic control.

This study evaluates how the primary-zone excess air ratio (alpha) dictates in-furnace combustion dynamics and NOx emissions during coal-ammonia (NH3) co-firing. Results show that under all tested alpha conditions, the primary combustion zone exhibits a radially stratified structure, with a fuel-rich core surrounded by an oxygen-rich outer annulus. The oxidation-reduction conditions in the core, however, change significantly with alpha. Decreasing the primary-zone excess air ratio (alpha) from 0.97 to 0.70 shifts the core atmosphere from mildly oxidizing to strongly reducing. This causes substantial accumulation of CO and NH3 both axially and radially, while elongating the flame downstream. NO(x )emissions decrease monotonically from 735 mg/m(3) (alpha = 0.97, NH3 slip 69 ppm), 663 mg/m(3) (alpha = 0.88, 45 ppm), 489 mg/m(3) (alpha = 0.80, 78 ppm), to 350 mg/m(3) (alpha = 0.70, 342 ppm), all with >98.4% coal burnout; alpha = 0.80-0.88 provides optimal balance. These findings indicate that the excess air ratio in the primary combustion zone is a key parameter for controlling NOx formation during coal-NH3 co-firing.

The co-biased burner arrangement has the advantages of generating swirling flow and enhancing gas-solid mixing. The deviation of the burner deflection angle from the design value is a common occurrence, yet relevant research on it is uncommon. This study investigates the changes in gas-solid two-phase flow and flame deflection in the gasifier when the burner deflection angle deviates from the design value, using Particle Dynamic Analyzer (PDA) experiments and numerical simulation. When the burner deflection angle is smaller than the design value, the swirling flow in the gasifier tilts. When the deflection angles of A1 and A2 are 0 degrees, 4 degrees, the temperature at the furnace top reaches above 1900 degrees C. When the burner deflection angle is larger than the design value, the carbon conversion rate reaches the highest at 85%, but the swirling flow expands, and the hightemperature zone is close to the wall. The results explore the typical characteristics and potential hazards of burner flame deviation, providing a reference for the optimal operation of entrained-flow gasifiers.

The production of fine slag from gasification results in a significant waste of resources and environmental problems. To address this issue, a feasible option is to use fine slag as a feedstock for gasification. This study proposes a new gasifier with burners that are suitable for fine slag gasification. The burner structure was optimized through airflow experiments. This helped to demonstrate the superiority of the novel burner in mixing feedstock and gasification agents. Simulations were then used to verify the gasification performance of this optimized burner. The results of the airflow experiment suggest that the mixed temperature near the outlet of the fine slag burner was relatively high. Furthermore, the mixing distance was short. The simulation results show that the gasification agents from the fine slag burner, convergent burner, and parallel channel burner were all accelerated to approximately 90-94 m/s in 10,000 Nm3/h entrained flow gasifiers. However, the gasification agent and fine slag from the fine slag burner were better mixed due to the deflection angle of the two airflow channels. The highest carbon conversion rate of 80% was achieved when using the fine slag burner. The effective syngas concentration was 62%.

To address the randomness and volatility of new energy sources, reducing the minimum stable combustion load of thermal power units is critical. We studied an improved swirl burner has the potential to achieve stable combustion without auxiliary combustion support under ultra-low load (20% rated load), which has been applied to a 350 MW boiler firing Zhundong coal. The novelty of this work lies in the systematic characterization of this new burner through a rigorous combination of laboratory-scale gas-solid two-phase flow measurements and full-scale industrial trials under different loads. A 1:6 scaled experimental platform utilizing Phase Doppler Anemometry (PDA) was established to measure three-dimensional velocity, turbulence intensity, and particle volume flux at varying loads. Industrial experiments revealed the distribution laws of flue gas temperature and component concentration of the improved burner under different loads. Results reveal that the improved burner forms an annular recirculation zone under all load conditions. As the load decreases, the reflux rate increases and the primary air mass flow decreases, demonstrating its potential for stable combustion at 20% rated load. When the load rates decrease from 246 MW to 165 MW, the ignition distance decreases from 0.9 m to 0.3 m. The distribution of flue gas composition concentrations shows a similar pattern. The ignition distance at 165 MW also shows an excellent low-load stable combustion ability of the improved burner.

Coal gasification fine ash is an industrial solid waste with high carbon content that cannot be directly utilized. To address the large-scale disposal of coal gasification fine ash, this paper proposes a combustion technology route and develops a novel burner equipped with a pre-combustion chamber and a radial staged combustion arrangement, thereby enhancing combustion stability and reducing NOx emissions. A MW-scale pilot-scale combustion test rig is constructed to conduct combustion tests on CGFA, SC, and BC. The flue gas temperature and composition are measured at different positions in the combustion system, as well as the flue gas composition and burnout rate at the furnace outlet. The results indicate that the new PCC burner can achieve stable ignition and combustion for all three fuels tested, with temperature rise rates exceeding 2000 degrees C/m and the peak furnace temperature reaching above 1300 degrees C. When burning CGFA with ultra-low volatile content, the burnout rate reaches 92.68%, achieving excellent burnout performance and meeting the high-efficiency decarbonization target of CGFA. The NOx emissions at the furnace outlet are only 147.16 mg/m3 (@6%O2). The test results indicate that the combustion of CGFA by chamber combustion method proposed in this paper is feasible.

Existing faulty coal-fired units generally achieve oil-free stable combustion only at loads over 30%, failing to meet low load regulation demands. To address the insufficient flexibility of boilers, a novel flame-stabilization theory was developed for retrofitting a 350 MW faulty coal-fired unit boiler. Based on the actual burner dimensions of the 350 MW unit boiler, a geometric scaling ratio of 1:7 between model and actual burners was established. Phase Doppler Anemometry (PDA) was employed to conduct gas particle flow experiments on the model burner, revealing the impact of different primary air velocities on the gas particle flow characteristics of the novel stabilized flow burner. The analysis of experimental results suggests that, When the primary air velocity is 9 m/s, a central recirculation zone forms at the burner outlet. At a primary air velocity of 10 m/s, an annular recirculation zone develops with a relatively large coverage area. When the primary air velocity increases to 11 m/s, the extent of the annular recirculation zone diminishes. At a primary air velocity of 10 m/s, an extensive annular recirculation zone forms at the burner outlet, which appears to provide sufficient energy for the ignition of pulverized coal. Elevated pulverized coal concentration near the burner centerline facilitates the formation of a high-temperature oxygen-lean reducing atmosphere, suppressing fuel-based NOx generation. Therefore, it is recommended to set the actual operating parameters of the novel stabilized flow burner based on the 10 m/s primary air velocity condition in the gas particle flow experiments.

Existing swirl burners faced issues such as bluff body wear, insufficient understanding of concentration ring, and limitations of numerical simulation conditions, making it difficult to support stable combustion under deep peak-shaving. To address this issue in boilers firing faulty coal, the novel swirl stable combustion technology was developed. It was applied to prototype swirl burners used in a 700 MW utility boiler. Cold-state gas-particle experiments using phase doppler anemometry (PDA) and full-scale numerical simulations were conducted on the novel burner. With three-stage CR, the recirculation zone (RZ) was annular, measuring 2.5d in length and 0.50d in diameter, where d denoted the burner outlet inner diameter. With two-stage CR, it shortened to 1.5d and 0.46d, respectively. Without CR, the RZ became a heart-shaped central zone, 2.5d long and 0.70d in diameter, originating 1.0d downstream of burner outlet. Burner with three-stage CR exhibited a higher recirculation ratio, stronger turbulence kinetic energy, and better particle confinement near centerline compared to the two-stage CR case. r denoted the radial distance measured from a given point to the centerline. Compared to the two-stage CR case, the three-stage CR case also produced a broader and stronger region of negative particle volumetric flux at r/d = 0.2-0.4. Numerical simulations showed that the new burner could raise the gas temperature to 1000 degrees C within 0.25 m. Compared to the original design, the retrofitted boiler, where the middle and lower burner layers were replaced with new burners, showed an overall increase in furnace temperature, about 25 % reduction in fly ash unburned carbon and 70 mg/m3@6%O2 reduction in NOx emissions. Even at 30 % load, the new burners alone maintained temperatures above 1300 degrees C at the main combustion zone.

The entrained-flow gasifier for fine slag can be applied for large-scale industrial use of gasification fine slag. The gas-solid two-phase flow characteristics of a 10000 Nm3/h fine slag entrained-flow gasifier were studied using a cold flow experiment system and a PDA (Phase Doppler Anemometry) measurement system to improve the gasifier's gasification performance. The flow field in the gasifier was compared in detail with various burner bias angles. The results reveal that when the burner is arranged biased in the same direction, there is an obvious central tangent circle in the velocity field of the horizontal section where the burner is positioned. When the burner's bias angle is 2°, the tangential area is the smallest, the upward movement of particles is the greatest, the particle updraft rate is up to 0.47, and the turbulence intensity is more than when the bias angle is 4° or 6°. When the bias angle is 2° in the vertical section of the upper gasifier, the downward-moving particle velocity is the largest, the downward-moving particle concentration is the greatest, the airflow swirl intensity is the smallest, and the swirl is the weakest, which is not conducive to the formation of slag layer on the membrane wall. When the bias angle is 6° in the vertical section of the lower gasifier, the tangential velocity of the airflow is the greatest, the swirl intensity is the highest, and the axial velocity is greater than the axial velocity of 4° and 2°. The particles' residence time in the gasifier gets shorter, which hinders the complete reaction of the fine slag.