A combined experimental and theoretical study of micronized coal reburning

doi:10.1007/s11708-012-0226-6

Front Energ

2013, Vol. 7

Issue (1) : 119-126 https://doi.org/10.1007/s11708-012-0226-6

RESEARCH ARTICLE

A combined experimental and theoretical study of micronized coal reburning

Hai ZHANG, Jiaxun LIU(

), Jun SHEN, Xiumin JIANG

Institute of Thermal Energr Engineering, School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China

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Abstract

Micronized coal reburning (MCR) can not only reduce carbon in fly ash but also reduce NO_x emissions as compared to the conventional coal reburning. However, it has two major kinetic barriers in minimizing NO_x emission. The first is the conversion of NO into hydrogen cyanide (HCN) by conjunction with various hydrocarbon fragments. The second is the oxidation of HCN by association with oxygen-containing groups. To elucidate the advantages of MCR, a combination of Diffuse Reflection Fourier Transform Infrared (FTIR) experimental studies with Density Functional Theory (DFT) theoretical calculations is conducted in terms of the second kinetic barrier.

FTIR studies based on Chinese Tiefa coal show that there are five hydroxide groups such as OH-π, OH-N, OH-OR₂, self-associated OH and free OH. The hydroxide groups increase as the mean particle size decreases expect for free OH. DFT calculations at the B3LYP/6-31 G(d) level indicate that HCN can be oxidized by hydroxide groups in three paths, HCN+OH→HOCN+H (path 1), HCN+OH→HNCO+H (path 2), and HCN+OH→CN+H₂O (path 3). The rate limiting steps for path 1, path 2 and path 3 are IM2→P1+H (170.66 kJ/mol activated energy), IM1→IM3 (231.04 kJ/mol activated energy), and R1+OH→P3+H₂O (97.14 kJ/mol activated energy), respectively. The present study of MCR will provide insight into its lower NO_x emission and guidance for further studies.

Keywords hydroxyl radicals Fourier transform infrared spectroscopy (FTIR) density functional theory (DFT) homogeneous reaction mechanism NO_x

Corresponding Author(s): LIU Jiaxun,Email:ljxpk01@163.com

Issue Date: 05 March 2013

Cite this article:

Hai ZHANG,Jiaxun LIU,Jun SHEN, et al. A combined experimental and theoretical study of micronized coal reburning[J]. Front Energ, 2013, 7(1): 119-126.

URL:

https://academic.hep.com.cn/fie/EN/10.1007/s11708-012-0226-6
https://academic.hep.com.cn/fie/EN/Y2013/V7/I1/119

Fig.1 Schematic of the reburning system

Tab.1 Analysis of coal samples

Fig.2 (a) 400–2000 cmwave number; (b) 2000–4000 cmwave number

Tab.2 Various OH peak assignments in the present study and the study of Miura et al.

Fig.3 Curve-fitted FTIR spectrum of the hydroxide groups stretching bands for coal samples
(a) TF_6 82; (b) TF_10 21; (c) TF_15 55; (d) TF_25 10

Fig.4 Effect of coal particle size on hydroxide groups

Fig.5 Optimized geometries of all reactants intermediates transition states and products (Bond lengths are in angstroms and angles are in degrees)

Fig.6 Imaginary vibration model of each transition state

Fig.7 HCN oxidation mechanism

Fig.8 Energetic sketch of the stationary points for HCN oxidation

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