Coal ash inevitably forms deposits as combustion residue on the walls and heat transfer surfaces of coal-fired boilers. Ash deposits decrease the boiler efficiency, reduce the generating capacity, and cause unscheduled outages. The radiative heat transfer is the major heat transfer mechanism in utility boilers; thus, the ash deposit emissivity is critical to boiler efficiency and safety. This paper presents a radiative transfer model to predict the spectral emissivities of coal ash deposits. The model includes the effects of the microstructure, chemical composition, and temperature. Typical ash deposit microstructures are generated using diffusion-limited aggregation (DLA). The radiative properties are then calculated using the generalized multiparticle Mie-solution (GMM). The combined GMM and DLA model predicts spectral emissivity better than the original Mie theory and Tien's dependent scattering theory with the average relative difference between predicted results and experimental data decreasing from 17.8% to 9.1% for sample 1 and from 18.6% to 4.2% for sample 2. Maxwell-Garnett (MG) effective medium theory is used to calculate the ash deposit optical constants based on the chemical compositions to include the effect of chemical composition. Increasing temperatures increase the particle diameters and particle volume fractions and, thus, the spectral emissivities. The spectral emissivity ultimately remains constant and less than one. The homogeneous slab model gives the upper limit of the ash deposit spectral emissivity.

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Engineering of Ministry of Education,

Beijing Key Laboratory for CO

and Reduction Technology,

Tsinghua University,

e-mail: liu-d10@mails.tsinghua.edu.cn

Engineering of Ministry of Education,

Beijing Key Laboratory for CO

and Reduction Technology,

Tsinghua University,

e-mail: yyduan@tsinghua.edu.cn

Engineering of Ministry of Education,

Beijing Key Laboratory for CO

and Reduction Technology,

Tsinghua University,

e-mail: zhenyang@tsinghua.edu.cn

Engineering of Ministry of Education,

Beijing Key Laboratory for CO

and Reduction Technology,

Tsinghua University,

e-mail: yht09@mails.tsinghua.edu.cn

Article navigation

Research-Article

# Theoretical Predictions of Spectral Emissivity for Coal Ash Deposits

Dong Liu,

Engineering of Ministry of Education,

Beijing Key Laboratory for CO

and Reduction Technology,

Tsinghua University,

e-mail: liu-d10@mails.tsinghua.edu.cn

Dong Liu

Key Laboratory of Thermal Science and Power

Engineering of Ministry of Education,

Beijing Key Laboratory for CO

_{2}Utilization

and Reduction Technology,

Tsinghua University,

Beijing 100084

, China

e-mail: liu-d10@mails.tsinghua.edu.cn

Search for other works by this author on:

Yuan-Yuan Duan,

Engineering of Ministry of Education,

Beijing Key Laboratory for CO

and Reduction Technology,

Tsinghua University,

e-mail: yyduan@tsinghua.edu.cn

Yuan-Yuan Duan
1

Key Laboratory of Thermal Science and Power

Engineering of Ministry of Education,

Beijing Key Laboratory for CO

_{2}Utilization

and Reduction Technology,

Tsinghua University,

Beijing 100084

, China

e-mail: yyduan@tsinghua.edu.cn

1Corresponding author.

Search for other works by this author on:

Zhen Yang,

Engineering of Ministry of Education,

Beijing Key Laboratory for CO

and Reduction Technology,

Tsinghua University,

e-mail: zhenyang@tsinghua.edu.cn

Zhen Yang

Key Laboratory of Thermal Science and Power

Engineering of Ministry of Education,

Beijing Key Laboratory for CO

_{2}Utilization

and Reduction Technology,

Tsinghua University,

Beijing 100084

, China

e-mail: zhenyang@tsinghua.edu.cn

Search for other works by this author on:

Hai-Tong Yu

Engineering of Ministry of Education,

Beijing Key Laboratory for CO

and Reduction Technology,

Tsinghua University,

e-mail: yht09@mails.tsinghua.edu.cn

Hai-Tong Yu

Key Laboratory of Thermal Science and Power

Engineering of Ministry of Education,

Beijing Key Laboratory for CO

_{2}Utilization

and Reduction Technology,

Tsinghua University,

Beijing 100084

, China

e-mail: yht09@mails.tsinghua.edu.cn

Search for other works by this author on:

Dong Liu

Key Laboratory of Thermal Science and Power

Engineering of Ministry of Education,

Beijing Key Laboratory for CO

_{2}Utilization

and Reduction Technology,

Tsinghua University,

Beijing 100084

, China

e-mail: liu-d10@mails.tsinghua.edu.cn

Yuan-Yuan Duan

Key Laboratory of Thermal Science and Power

Engineering of Ministry of Education,

Beijing Key Laboratory for CO

_{2}Utilization

and Reduction Technology,

Tsinghua University,

Beijing 100084

, China

e-mail: yyduan@tsinghua.edu.cn

Zhen Yang

Key Laboratory of Thermal Science and Power

Engineering of Ministry of Education,

Beijing Key Laboratory for CO

_{2}Utilization

and Reduction Technology,

Tsinghua University,

Beijing 100084

, China

e-mail: zhenyang@tsinghua.edu.cn

Hai-Tong Yu

Key Laboratory of Thermal Science and Power

Engineering of Ministry of Education,

Beijing Key Laboratory for CO

_{2}Utilization

and Reduction Technology,

Tsinghua University,

Beijing 100084

, China

e-mail: yht09@mails.tsinghua.edu.cn

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received March 23, 2013; final manuscript received July 11, 2013; published online March 17, 2014. Assoc. Editor: Zhixiong Guo.

*J. Heat Transfer*. Jul 2014, 136(7): 072701 (7 pages)

**Published Online:**March 17, 2014

Article history

Received:

March 23, 2013

Revision Received:

July 11, 2013

Citation

Liu, D., Duan, Y., Yang, Z., and Yu, H. (March 17, 2014). "Theoretical Predictions of Spectral Emissivity for Coal Ash Deposits." ASME. *J. Heat Transfer*. July 2014; 136(7): 072701. https://doi.org/10.1115/1.4026907

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