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Influence of nozzle height to width ratio on ignition and NOx emission characteristics of semicoke/bituminous coal blends in a 300 kW pulverized coal-fired furnace

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Abstract

To improve the ignition behavior and to reduce the high NOx emissions of blended pulverized fuels (PF) of semicoke (SC), large-scale experiments were conducted in a 300 kW fired furnace at various nozzle settings, i.e., ratios (denoted by hf/b) of the height of the rectangular burner nozzle to its width of 1.65, 2.32, and 3.22. The combustion tests indicate that the flame stability, ignition performance, and fuel burnout ratio were significantly improved at a nozzle setting of hf/b = 2.32. The smaller hf/b delayed ignition and caused the flame to concentrate excessively on the axis of the furnace, while the larger hf/b easily caused the deflection of the pulverized coal flame, and a high-temperature flame zone emerged close to the furnace wall. NOx emissions at the outlet of the primary zone decreased from 447 to 354 mg/m3 (O2 = 6%), and the ignition distance decreased from 420 to 246 mm when the hf/b varied from 1.65 to 3.22. Furthermore, the ratio (denoted by SR/SC) of the strong reduction zone area to the combustion reaction zone area was defined experimentally by the CO concentration to evaluate the reduction zone. The SR/SC rose monotonously, but its restraining effects on NOx formation decreased as hf/b increased. The results suggested that in a test furnace, regulating the nozzle hf/b conditions sharply reduces NOx emissions and improves the combustion efficiency of SC blends possessing an appropriate jet rigidity.

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Abbreviations

PF:

Pulverized fuels

SC:

Semicoke

PA:

Primary air

SA:

Secondary air

NOx :

Nitrogen oxides

O2 :

Oxygen

CO:

Carbon monoxide

HCN:

Hydrogen cyanide

BCR:

Bias concentration ratio

CFD:

Computational fluid dynamics

DTFs:

Drop tube furnaces

PBCS:

Pilot-scale bias combustion simulator

FTIR:

Fourier transform infrared

NELRECC:

National Engineering Laboratory for Reducing Emissions from Coal Combustion

HIT:

Harbin Institute of Technology

x :

Distance between the measuring point and the burner outlet for the axial direction/mm

r :

Distance between the measuring point and the burner outlet for the radial direction/mm

h f :

Burner’s primary-air nozzle height/mm

b :

Total burner’s primary-air nozzle width without nozzle distance/mm

h f/b :

Height to width ratio

S R :

The high reduction zone area/mm

S C :

The combustion zone area/mm

S R/S C :

The high reduction zone area to combustion zone area ratio

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Acknowledgements

This work was supported by the National Key Research and Development Program of China (No. 2017YFB0602002) and National Natural Science Foundation of China (Grant No. 51536002).

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Authors and Affiliations

  1. School of Energy Science and Engineering, Harbin Institute of Technology, Harbin, 150001, China

    Liutao Sun, Yonghong Yan, Rui Sun, Zhengkang Peng, Chunli Xing & Jiangquan Wu

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  1. Liutao Sun
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  2. Yonghong Yan
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  3. Rui Sun
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Correspondence to Rui Sun.

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Sun, L., Yan, Y., Sun, R. et al. Influence of nozzle height to width ratio on ignition and NOx emission characteristics of semicoke/bituminous coal blends in a 300 kW pulverized coal-fired furnace. Front. Energy 15, 431–448 (2021). https://doi.org/10.1007/s11708-021-0726-3

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