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387 results on '"Ma, Lun"'

19. Aerodynamic analysis of large wind farms using two-scale coupled modelling approaches

Author

Ma, Lun, Tsoutsanis, Panagiotis, and Antoniadis, Antonis

Subjects
ABL, actuator disc, CFD, DES, full-resolved turbine, LES, numerical weather prediction model, support structure, theoretical model, URANS, wind energy, wind farm, wind turbine
Abstract

The effects of turbine aerodynamics and response characteristics of the atmospheric boundary layer on the overall wind farm efficiency are investigated in this research. Various wind farm modelling strategies, which include a theoretical and several CFD models, are presented. This study consists of three main parts: (i) improve and validate an existing theoretical wind farm model, (ii) infinitely large wind farm modelling with actuator-disc and fully-resolved turbine models, and (iii) finite-size wind farm modelling with a numerical weather prediction model. In the first part, an extended theoretical model based on a two-scale coupled momentum balance method is proposed to estimate aerodynamic effects of wind turbine towers on the performance of large wind farms. The modified theoretical model predicts that the optimal turbine spacing should increase with the value of normalised support-structure drag, as well as additional parameters describing the response characteristics of the atmospheric boundary layer to the total farm drag. The Detached-Eddy simulations of a periodic array of fully staggered actuator discs (AD) show a reasonably good agreement (within 10% in the prediction of power) with the modified theoretical model. In the second part, a fully resolved (FR) NREL 5MW turbine model is employed in two URANS simulations (with and without the turbine tower) of a fully developed wind farm boundary layer. The FR-URANS results show stronger tower effects than both AD-RANS and theoretical model predictions, which is a strong indication of the necessity of considering turbine support structure within large wind farm models. The possibility of performing DDES is also investigated with the same FR turbine model and periodic domain setup. The results show complex turbulent flow characteristics within a large wind farm, where typical hairpin and hub vortices have been clearly captured. In addition, the computational cost of DDES has been found to be similar to URANS (for a given number of rotations), which is a positive sign for conducting DDES in future studies. In the third part, a numerical weather prediction model is used as a realistic farm-scale flow model to investigate how the streamwise pressure gradient, Coriolis force and acceleration/deceleration terms in the farm-scale momentum balance equation tend to change in time. The results suggest that the streamwise pressure gradient may be enhanced substantially by the resistance caused by the wind farm, whereas its influence on the other two terms appears to be relatively minor. These results suggest the importance of modelling the farm-induced pressure gradient accurately for various weather conditions in future studies of large wind farms.

Published
2021

35. A novel low-NOxswirl burner with coal-ammonia co-firing: Effect of ammonia ratio in the dual channels on combustion and NOxformation

Author

Ma, Lun, Fang, Qingyan, Zhang, Cheng, Chen, Gang, and Li, Kaiyuan

Abstract

Coal-ammonia co-firing is a promising technology for reducing CO2emissions in coal-fired boilers. However, coal-ammonia co-firing may cause significant NOxowing to the high nitrogen in ammonia. This study proposes a novel low-NOxswirl burner with a scalable dual-channel ammonia pipe for coal-ammonia co-firing, and evaluates the combustion and NOxformation under different ammonia ratios of the dual channels (i.e.,inner and outer channels). The results show that the ammonia is injected into the low-oxygen and high-CO environment behind the internal recirculation zone, contributing to the ammonia pyrolysis and inhibiting the ammonia oxidation reaction. Low NOxis successfully achieved with high combustion efficiency. In addition, it is observed that the effect of the ammonia ratio of the dual channels on the combustion and NOxformation is slight for the high ammonia blending ratio (20 %), while it is prominent for the low ammonia blending ratio (10 %). Especially, for the low ammonia blending ratio, lower ammonia ratio in the outer channel can obtain high velocity of ammonia stream in the inner channel, contributing to NOxreduction. Overall, the cases with lower ROC(0.1, 0.2) are suggested with low NOx(below 120 ppm) and carbon content in fly ash (below 3.50 %) for the low ammonia blending ratio in this study.

Published
2024
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40. A novel swirl burner with coal co-firing ammonia: Effect of extension length of the dual-channel ammonia pipe on combustion and NOx formation.

Author

Ma, Lun, Li, Kaiyuan, Fang, Qingyan, Chen, Gang, and Zhang, Cheng

Subjects
*COAL ash, *CARBON emissions, *CO-combustion, *AMMONIA, *FLY ash, *COMBUSTION
Abstract

The coal/ammonia co-firing technology for thermal power generation is a feasible method to effectively reduce CO 2 emissions. However, the easy formation of NO x is one of the challenges faced by this technology owing to the high nitrogen content in ammonia. This study proposes a novel swirl burner with a scalable dual-channel ammonia pipe, and evaluates the combustion and NO x formation under different extension lengths of the dual-channel ammonia pipe (i.e., 0 m, 0.4 m, 0.8 m, 1.0 m, 1.2 m). The results show that the extension length of the dual-channel ammonia pipe significantly affects the flow, combustion, and NO x formation. When the extension length of the dual-channel ammonia pipe is above 0.8 m, the ammonia stream can completely penetrate the internal recirculation zone into the high CO environment, which contributes to promoting the ammonia pyrolysis and inhibiting the ammonia oxidation to form NO x. NO x emissions significantly decrease from 846 ppm to 146 ppm as the extension length of the dual-channel ammonia pipe from 0 m to 0.8 m, but change slightly as further increases from 0.8 m to 1.2 m. The carbon content in fly ash decreases from 4.53% to 3.40% as the extension length of the dual-channel ammonia pipe increases from 0 m to 1.0 m. Still, it increases from 3.40% to 3.70% as the extension length of the dual-channel ammonia pipe rises to 1.2 m. Overall, it is reasonable to set the extension length of the dual-channel ammonia pipe at 1.0 m in this studied condition, which can obtain low NO x and low carbon content in fly ash. [Display omitted] • A novel swirl burner with a scalable dual-channel NH 3 pipe is proposed. • Effect of NH 3 pipe extension length on combustion and NO x formation is investigated. • NH 3 pipe extension length significantly affects flow, combustion, and NO x formation. • 1.0 m for NH 3 pipe extension length is reasonable with good performance. [ABSTRACT FROM AUTHOR]

Published
2024
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