An experimental study on ignition of single coal particles at low oxygen concentrations

doi:10.1007/s11708-020-0692-1

Front. Energy

2021, Vol. 15

Issue (1) : 38-45 https://doi.org/10.1007/s11708-020-0692-1

RESEARCH ARTICLE

An experimental study on ignition of single coal particles at low oxygen concentrations

Wantao YANG, Yang ZHANG, Lilin HU, Junfu LYU, Hai ZHANG(

)

Key Laboratory for Thermal Science and Power Engineering of the Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China

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Abstract

An experimental study on the ignition of single coal particles at low oxygen concentrations ( $X O 2$ <21%) was conducted using a tube furnace. The surface temperature (T_s) and the center temperature (T_c) of the coal particles were obtained from the images taken by an infrared camera and thermocouples respectively. The ignition processes were recorded by a high-speed camera at different $X O 2$ values and furnace temperatures T_w. Compared with literature experimental data obtained at a high $X O 2$ value, the ignition delay time t_i decreases more rapidly as $X O 2$ increases at the low $X O 2$ region. The responses of T_s and T_c to the variation of $X O 2$ are different: T_s decreases while T_c remains nearly constant with increasing $X O 2$ at a low $X O 2$ value. In addition, t_i is less sensitive to T_w while the ignition temperature T_i is more sensitive to T_w at a low $X O 2$ value than in air. Observations of the position of flame front evolution illustrate that the ignition of a coal particle may change from a homogeneous mode to a heterogeneous or combined ignition mode as $X O 2$ decreases. At a low $X O 2$ value, buoyancy plays a more significant role in sweeping away the released volatiles during the ignition process.

Keywords coal particles low oxygen concentration ignition ignition temperature ignition modes

Corresponding Author(s): Hai ZHANG

Online First Date: 08 September 2020 Issue Date: 19 March 2021

Cite this article:

Wantao YANG,Yang ZHANG,Lilin HU, et al. An experimental study on ignition of single coal particles at low oxygen concentrations[J]. Front. Energy, 2021, 15(1): 38-45.

URL:

https://academic.hep.com.cn/fie/EN/10.1007/s11708-020-0692-1
https://academic.hep.com.cn/fie/EN/Y2021/V15/I1/38

Fig.1 Schematic of experimental system.

Tab.1 Properties of tested coal

Fig.2 Measurement of the center temperature of a single coal particle (d_p≈ 2 mm).

Fig.3 Typical images for temperature calibration.

Fig.4 Comparison of dimensionless ignition delay time t* (t_i/t_i,air) versus

X O 2

at a low

X O 2

values of this paper with experimental data obtained at both low and high

X O 2

values from references.

Fig.5 Ignition delay time (t_i) versus furnace temperature (T_w) at different

X O 2

values.

Fig.6 Comparison of dimensionless ignition temperature T* (T_i/T_i,air) versus

X O 2

with experimental results obtained at both low and high

X O 2

values from references.

Fig.7 Ignition temperature (T_i) versus furnace temperature (T_w) in air and low

X O 2

conditions.

Fig.8 Typical images of volatile flames at different times after ignition for DTC particles at low oxygen concentrations (

X O 2

) and different furnace temperatures (T_w) (d_p ≈ 2 mm).

Fig.9 Dimensionless standoff distance (r*) at a low

X O 2

value and air at different furnace temperatures (T_w).

Fig.10 Ignition modes for single coal particle at different

X O 2

values and furnace temperatures (T_w) (d_p ≈ 2 mm).

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