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浙江大学学报(工学版)
Journal of ZheJiang University (Engineering Science)  2019, Vol. 53 Issue (6): 1139-1147    DOI: 10.3785/j.issn.1008-973X.2019.06.013
Mechanical and Energy Engineering     
Numerical simulation of fly ash deposition in coal and corn stalk co-combustion with dynamic mesh technique
Hao ZHOU(),Kun ZHANG,Ya-wei LI,Jia-kai ZHANG
Zhejiang University, Institute for Thermal Power Engineering, State Key Laboratory of Clean Energy Utilization, Hangzhou 310027, China
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Abstract  

The computational fluid dynamics (CFD) model based on dynamic mesh technique was used to simulate the slagging experiment of pulverized coal-corn stalk blended combustion (the proportion of corn straw is 0, 5% and 10%, respectively) in order to investigate the slagging characteristics of pulverized coal and biomass blended combustion. The thermal conductivity of the slag and the surface temperature of the slag were considered in the simulation; the simulation results were compared with the experimental results. The simulation results show that the mass flow rate of fly ash impacting decreases with the deposition because the deposition (leading to the dynamic mesh) changes the flow field near the probe. In the three conditions, the deposition efficiency of the fly ash on the probe surface was 75%, 80% and 87%, respectively, at 100 min, which indicates that the corn-blended condition is easier to slag. Real-time variation of deposition can be realized by the dynamic mesh technique. In terms of the heat transfer characteristics, the modelling values of slag surface temperature and the heat flux through the deposit are in agreement with experimental ones. The reduction rate of heat flux within 100 min for the three cases was 52.13%, 46.96% and 53.25%, respectively.

Key words： ash deposition      computational fluid dynamics (CFD)      dynamic mesh technique      biomass      surface temperature      effective thermal conductivity     
Received: 07 November 2018      Published: 22 May 2019
CLC:  TK 16  
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Hao ZHOU
Kun ZHANG
Ya-wei LI
Jia-kai ZHANG
Cite this article:

Hao ZHOU,Kun ZHANG,Ya-wei LI,Jia-kai ZHANG. Numerical simulation of fly ash deposition in coal and corn stalk co-combustion with dynamic mesh technique. Journal of ZheJiang University (Engineering Science), 2019, 53(6): 1139-1147.

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http://www.zjujournals.com/eng/10.3785/j.issn.1008-973X.2019.06.013     OR     http://www.zjujournals.com/eng/Y2019/V53/I6/1139


采用动网格技术的煤粉-玉米秸秆掺烧飞灰沉积数值模拟

为了研究煤粉和生物质掺烧形成飞灰的结渣特性，采用基于动网格技术的计算流体动力学（CFD）模型对煤粉-玉米秸秆掺烧积灰结渣实验（玉米秸秆掺比分别为0、5%和10%）进行数值模拟. 模拟过程中考虑灰渣导热系数和灰渣表面温度的变化，并将模拟结果和实验结果进行比较. 模拟结果表明：飞灰撞击质量流率随沉积进行而减小，这是因为沉积物引起的动网格变化影响探针附近流场；3种工况下飞灰在探针表面的最终沉积效率分别为75%、80%和87%，说明了玉米秸秆掺烧形成飞灰的易结渣倾向；灰渣实时形貌在动网格执行下得以实现. 在换热特性方面，灰渣表面温度和热流密度的模拟值和实验值较为接近；3种工况下0~100 min热流密度降低率分别为52.13%、46.96%和53.25%.


关键词： 灰沉积,  计算流体动力学（CFD）,  动网格技术,  生物质,  表面温度,  有效导热系数 
Fig.1 Sketch map of 300 kW pilot experimental rig
Fig.2 Sketch map of deposition sampling probe in furnace
灰成分（wt.%） 灰成分（wt.%） 工业分析（wt.%，ad） 元素分析（wt.%，daf）
项目 SH Corn 项目 SH Corn 项目 SH Corn 项目 SH Corn
Na2O 0.27 0.77 Cl 0.13 3.53 C 78.42 49.69 Mad 2.8 12.1
MgO 0.40 6.18 K2O 0.53 8.78 H 4.46 5.51 Vad 31.1 52.5
Al2O3 37.29 10.41 CaO 3.55 9.30 N 0.94 2.01 FCad 55.3 10.7
SiO2 50.63 52.76 TiO2 1.16 0.51 S 0.79 0.38 Aad 10.8 24.7
P2O5 0.32 1.66 MnO 0.03 0.08 O 15.39 42.41 HHV （MJ/kg） 27.4 12.4
SO3 0.90 2.16 Fe2O3 4.78 3.84 ? ? ? ? ? ?
Tab.1 Properties of the SH coal and corn straw
Fig.3 Time-dependent surface temperature of ash deposit with different ratios of corn straw in SH coal
Fig.4 Effective thermal conductivity of ash deposit vesus thickness with different ratios of corn straw in SH coal
Fig.5 Schematic diagram of computational domain used for numerical simulation
Fig.6 Meshing of computational domain used for numerical simulation
Fig.7 Mass of deposition on probe surface corresponding to different computational meshing numbers
Fig.8 Calculated results of liquid slag fraction with changing temperature with different ratios of corn straw in SH coal
Fig.9 Sketch map for displacement calculation of nodes in dynamic mesh
Fig.10 Schematic diagram of slagging numerical simulation
Fig.11 Mass flow of impact and deposition on surface of probe during deposition
Fig.12 Thickness of ash deposit versus time with different ratios of corn straw in SH coal
Fig.13 Ash deposit shape variation versus time
Fig.14 Surface temperature of ash deposit versus time with different ratios of corn straw in SH coal
Fig.15 Heat flux through probe versus time with different ratios of corn straw in SH coal
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