Chang Xing

Accurate prediction of NO emissions is important for the development of low-emission gas turbine combustors. This study evaluates several NO formation models for a 78 MW F-class gas turbine using a decoupled post-processing framework. Steady RANS simulations were performed with a partially premixed flamelet/PDF combustion model. Thermal NO, prompt NO, the N₂O intermediate pathway, and turbulence–chemistry interaction were assessed at 50% and 100% load. Thermal NO was the dominant pathway and showed strong load dependence. Using partial equilibrium for O radicals increased outlet NO by 16.46% at 50% load and 43.69% at 100% load. Including partial-equilibrium OH further increased NO by 8.67% at 50% load but had little effect at full load. Prompt NO remained on the order of 10⁻³ ppm. The N₂O pathway and turbulence–chemistry interaction also affected the prediction, especially at full load. The selected model was further compared with field measurements during load ramping and pilot-ratio variation. Most load-ramping predictions agreed with measurements within 18%. The results demonstrate the applicability of the proposed framework for engineering NO emission prediction while also identifying limitations under transitional operating conditions.

This study investigated the effect of replacing N₂ with CO₂ on the pyrolysis behavior, char structure evolution, and kinetics of Fushun (FS) and Changji (CJ) oil shales. Non-isothermal thermogravimetric experiments were conducted at 5, 10, 20, and 40 °C·min⁻¹ under N₂ and CO₂ atmospheres, and the resulting chars were characterized by FTIR, XPS, BET, and SEM. Kinetic parameters were evaluated using Friedman, FWO, KAS, Starink, and Vyazovkin iso-conversional methods. Both oil shales underwent three stages: moisture release, main organic-matter pyrolysis, and high-temperature mineral decomposition. Increasing the heating rate shifted T_s and T_max to higher temperatures and intensified volatile release. At 40 °C·min⁻¹, replacing N₂ with CO₂ increased T_s from 322.6 to 399.3 °C for FS and from 368.1 to 377.3 °C for CJ, while reducing the maximum mass-loss rates to 6.81 and 8.66%·min⁻¹, respectively. N₂ favored pore development, increasing the specific surface areas of FS and CJ chars to 14.1402 and 6.1464 m²·g⁻¹, whereas CO₂ caused pore blockage in FS char and reduced its surface area to 2.7783 m²·g⁻¹. XPS showed that CO₂ promoted the formation or preservation of oxygen-containing surface carbon, especially C=O and O–C=O groups. The E_α values first decreased and then increased with conversion and were generally lower in CO₂ than in N₂. The average activation-energy differences between the two atmospheres were 23.5 and 43.2 kJ·mol⁻¹ for FS and CJ, respectively. These results provide experimental and kinetic data for modeling primary oil shale pyrolysis and subsequent char combustion and gasification under CO₂-rich conditions.

This study investigates how O₂ concentration affects the combustion performance and kinetic response of Changji and Fushun oil shales under CO₂-based oxy-fuel atmospheres. Coupled TGA–DSC–MS analysis was performed to characterize thermal decomposition, heat release and absorption, gaseous product evolution, and apparent kinetic parameters. The results show that raising the O₂ concentration facilitates oil shale combustion. The TG–DTG and heat flow profiles move to lower-temperature regions as O₂ concentration increases. At 20 °C·min⁻¹, increasing the O₂ concentration from 35% to 100% reduced T_p1 and T_p2 from 357.3 and 519.7 °C to 331.2 and 491.5 °C for CJ oil shale, and from 352.3 and 484.0 °C to 326.6 and 429.7 °C for FS oil shale, respectively. These shifts were accompanied by decreases in ignition and burnout temperatures and an increase in the comprehensive combustion index. Fushun oil shale shows a more concentrated main mass-loss and heat-release region than Changji oil shale. It also exhibits lower ignition and burnout temperatures, indicating stronger overall combustion reactivity. By contrast, Changji oil shale displays more evident mass loss and thermal responses at high temperatures, suggesting a greater contribution from carbonate mineral decomposition in the later reaction stage. MS results further show that CO₂, H₂O, SO₂, and NO₂ release mainly occurs within 300–600 °C. Their release peaks shift toward lower temperatures as the O₂ concentration increases, indicating that oxygen-enriched atmospheres promote the oxidative conversion of organic carbon, hydrogen-containing structures, and S- and N-containing functional groups. The Vyazovkin nonlinear iso-conversional analysis provides conversion-dependent apparent activation energies rather than a single global kinetic parameter. The substantial variation in E_α with conversion highlights the overlapping and multi-stage nature of oil shale combustion. When the O₂ concentration is raised from 21% to 75%, E_α generally follows an upward trend; under pure O₂, however, it drops sharply. This non-monotonic variation suggests that O₂ concentration changes not only the combustion rate but also the dominant reaction routes at different conversion stages. These findings provide experimental support for selecting suitable oxy-fuel combustion conditions and improving the clean and efficient utilization of oil shale.

To elucidate the combustion behavior and molecular-scale reaction mechanisms of Fushun oil shale kerogen under oxy-fuel atmospheres, ReaxFF molecular dynamics simulations were performed based on a previously constructed kerogen model. Five reaction systems were established: 21% O₂/79% N₂, 21% O₂/79% CO₂, 35% O₂/65% CO₂, 55% O₂/45% CO₂, and 75% O₂/25% CO₂. Under programmed heating, the evolution of chemical bonds, gaseous products, char, tar and gas transformation, and system potential energy was systematically analyzed. The results show that, at the same O₂ concentration, CO₂ delays low-temperature oxidation, shifting C–C and C–H bond cleavage and O₂ consumption to higher temperatures. At elevated temperatures, however, CO₂-related pathways promote carbon skeleton fragmentation and CO formation. Increasing O₂ concentration from 21% to 75% advances O₂ participation and H₂O formation, suppresses low-temperature CO accumulation, accelerates char consumption, and drives the system toward complete oxidation dominated by small-molecule gases. Potential energy analysis further indicates that higher O₂ concentrations advance the intense exothermic oxidation stage. A four-stage oxy-fuel combustion mechanism is proposed, providing molecular-level insight into the coupled effects of CO₂ and O₂ concentration.