煤泥间歇微波干燥模拟及介电性质

doi:10.16085/j.issn.1000-6613.2022-1054

摘要/Abstract

摘要：

微波干燥是一种提高煤泥干燥效率的先进技术，其中间歇式在能耗和超温问题上具有更大的改进潜力。在微波干燥过程中，煤泥的介电性质会显著影响干燥性能，然而当前缺乏介电性质影响煤泥微波干燥的机理研究。本文首先建立了一种适用于间歇微波干燥的多相多孔介质模型，通过与实验数据对比，验证了模型的有效性。由于介电性质实际是温度和水分含量的函数，从机理上着重分析了温度、水分含量相关的介电性质（VP）对煤泥平均温度、水蒸气质量分数、气相压力及液态水饱和度的影响，通过与以往处理成常数的介电性质（CP）相对比，结果发现，CP平均温度明显低于VP，并且温升速率在干燥过程中没有显著变化，而VP的平均温度表现出先急剧升高后维持稳定的趋势。CP水蒸气质量分数和气相压力分布虽然与VP分布趋势相同，但是CP明显低于VP。VP能够模拟出间歇微波干燥期间的“泵送效应”，而CP不能有效显示此现象。因此在煤泥间歇微波干燥中VP比CP更加符合实际。

关键词: 煤泥, 间歇微波, 干燥, 多孔介质, 介电性质, 数值模拟

Abstract:

Microwave drying is an advanced technology to improve the drying efficiency of coal slime and intermittent drying technology has greater improvement potential in energy consumption and overtemperature. In microwave drying process, dielectric properties of coal slime can significantly affect the drying performance. However, there is a lack of research on the mechanism of influence of dielectric properties on microwave drying of coal slime. A multiphase porous media model was developed for intermittent microwave drying. Then the validity of the model was verified by comparing with experimental data in literature. Considering that the dielectric properties were function of temperature and moisture content, the influence of temperature and moisture content-related dielectric properties (VP) on the average temperature, vapor mass fraction, gas phase pressure and liquid water saturation of coal slime was analyzed in this paper by comparing with the conventional method (CP) which treated dielectric properties as constant. The results showed that average temperature of the CP was significantly lower than VP, and temperature rise rate did not change significantly during drying process, while average temperature of VP showed a trend of increasing sharply at first and then maintaining stability. Although the vapor mass fraction and gas pressure distribution trend of CP were the same as VP, CP was significantly lower than VP. VP could simulate the "pumping effect" during intermittent microwave drying, whereas CP could not effectively show the phenomenon. VP was more realistic than CP.

Key words: coal slime, intermittent microwave, drying, porous media, dielectric property, numerical simulation

中图分类号:

TQ536

王光宇, 孟境辉, 张锴. 煤泥间歇微波干燥模拟及介电性质[J]. 化工进展, 2023, 42(4): 1779-1786.

WANG Guangyu, MENG Jinghui, ZHANG Kai. Simulation of intermittent microwave drying of coal slime and dielectric properties[J]. Chemical Industry and Engineering Progress, 2023, 42(4): 1779-1786.

图/表 11

图1 煤泥微波干燥过程示意图

图2 间歇微波函数

图3 模型的边界条件

表1 输入参数表

参数	值或者表达式	参数	值或者表达式
液态水介电常数 $ε w'$	-0.283T+80.67^[18]	干空气介电常数 $ε a'$	1
固体基质介电常数 $ε s'$	1.88^[19]	液态水介电损失系数 $ε w ″$	0.05T+20^[18]
干空气介电损失系数 $ε a ″$	0	固体基质介电损失系数 $ε s ″$	0.1^[19]
液态水密度 $ρ w$	1000kg/m³	固体基质密度 $ρ s$	1250kg/m^3[19]
液态水定压比热容c_p_,w	4183J/(kg·K)^[20]	水蒸气定压比热容c_p_,v	2062J/(kg·K)^[20]
固体基质定压比热容c_p_,s	1250J/(kg·K)^[12]	液态水热导率k_th,w	0.644W/(m·K)^[20]
水蒸气热导率k_th,v	0.026W/(m·K)^[20]	干空气热导率k_th,a	0.026W/(m·K)^[20]
固体基质热导率k_th,s	0.46W/(m·K)^[19]	液态水黏度 $μ w$	$ρ w e x p (- 19.143 + 1540 / T)$ Pa·s^[12]
气相黏度 $μ g$	$0.017 × 10 - 3 T / 273 0.65$ Pa·s^[12]	液态水固有渗透率k_w	10^-15m^2[21]
气相固有渗透率k_g	$1 × 10 - 14$ m^2[21]	液态水相对渗透率k_r,w	(S_w)^3[22]
气相相对渗透率k_r,g	S_w<1/1.1时，取值1~1.1S_w； S_w>1/1.1时，取值0^[22]	液态水毛细扩散系数D_c	$10 - 8 e x p - 6.88 + 8 M w b$ m²/s^[13]
二元扩散系数D_va	$2.6 × 10 - 6$ m²/s^[19]	气相有效扩散系数D_eff,g	$D v a S g φ 4 / 3$ m²/s^[23]
平衡蒸气压p_v,eq	$p v, s a t T e x p (- 0.182 M d b - 0.696 + 0.232 e - 43.949 M d b M d b 0.0411 l n p v, s a t T)$ Pa^[24]	蒸发速率常数K_evap	1000s^-1[13]
环境中水蒸气分压力p_v,air	1420Pa	传质系数h_m	0.011m/s^[13]
传热系数h_T	10W/(m²·K)^[13]	周围空气温度T_air	300K
干基含水量M_db	$(c w + c v) / (1 - φ) ρ s$	湿基含水量M_wb	$M d b / (1 + M d b)$

表1 输入参数表

参数	值或者表达式	参数	值或者表达式
液态水介电常数 $ε w'$	-0.283T+80.67^[18]	干空气介电常数 $ε a'$	1
固体基质介电常数 $ε s'$	1.88^[19]	液态水介电损失系数 $ε w ″$	0.05T+20^[18]
干空气介电损失系数 $ε a ″$	0	固体基质介电损失系数 $ε s ″$	0.1^[19]
液态水密度 $ρ w$	1000kg/m³	固体基质密度 $ρ s$	1250kg/m^3[19]
液态水定压比热容c_p_,w	4183J/(kg·K)^[20]	水蒸气定压比热容c_p_,v	2062J/(kg·K)^[20]
固体基质定压比热容c_p_,s	1250J/(kg·K)^[12]	液态水热导率k_th,w	0.644W/(m·K)^[20]
水蒸气热导率k_th,v	0.026W/(m·K)^[20]	干空气热导率k_th,a	0.026W/(m·K)^[20]
固体基质热导率k_th,s	0.46W/(m·K)^[19]	液态水黏度 $μ w$	$ρ w e x p (- 19.143 + 1540 / T)$ Pa·s^[12]
气相黏度 $μ g$	$0.017 × 10 - 3 T / 273 0.65$ Pa·s^[12]	液态水固有渗透率k_w	10^-15m^2[21]
气相固有渗透率k_g	$1 × 10 - 14$ m^2[21]	液态水相对渗透率k_r,w	(S_w)^3[22]
气相相对渗透率k_r,g	S_w<1/1.1时，取值1~1.1S_w； S_w>1/1.1时，取值0^[22]	液态水毛细扩散系数D_c	$10 - 8 e x p - 6.88 + 8 M w b$ m²/s^[13]
二元扩散系数D_va	$2.6 × 10 - 6$ m²/s^[19]	气相有效扩散系数D_eff,g	$D v a S g φ 4 / 3$ m²/s^[23]
平衡蒸气压p_v,eq	$p v, s a t T e x p (- 0.182 M d b - 0.696 + 0.232 e - 43.949 M d b M d b 0.0411 l n p v, s a t T)$ Pa^[24]	蒸发速率常数K_evap	1000s^-1[13]
环境中水蒸气分压力p_v,air	1420Pa	传质系数h_m	0.011m/s^[13]
传热系数h_T	10W/(m²·K)^[13]	周围空气温度T_air	300K
干基含水量M_db	$(c w + c v) / (1 - φ) ρ s$	湿基含水量M_wb	$M d b / (1 + M d b)$

图4 干燥过程中平均干基含水量实验值与模拟值对比图

图5 煤泥样品整体平均温度随时间变化图

图6 煤泥样品平均介电性质随时间变化图

图7 500~600s内水蒸气质量分数沿中心轴线OA分布图

图8 500~600s内煤泥吸收的微波能和液态水蒸发吸热量变化图

图9 500~570s内气相压力沿中心轴线OA分布图

图10 500~600s内液态水饱和度分布图

参考文献 28

1	郭晋荣, 程鹏, 贾里, 等. 高硫煤泥燃烧过程中的汞排放特性[J]. 化工进展, 2021, 40(S2): 411-420.
	GUO Jinrong, CHENG Peng, JIA Li, et al. Combustion characteristics and mercury emission characteristics of high sulfur coal slime[J]. Chemical Industry and Engineering Progress, 2021, 40(S2): 411-420.
2	闫业成, 井传明, 宋占龙, 等. 热风和微波干燥对煤泥品质的影响[J]. 化工进展, 2019, 38(S1): 122-127.
	YAN Yechen, JING Chuanming, SONG Zhanlong, et al. Effect of hot air and microwave drying on the quality of coal slime [J]. Chemical Industry and Engineering Progress, 2019, 38(S1): 122-127.
3	杨景超, 许丽华, 张文娟. 微波技术在煤炭加工中的应用与进展[J]. 化工进展, 2011, 30(S1): 71-73.
	YANG Jingchao, XU Lihua, ZHANG Wenjuan. Application and progress of microwave technology in coal processing[J]. Chemical Industry and Engineering Progress, 2011, 30(S1): 71-73.
4	SONG Zhanlong, JING Chuanming, YAO Liansheng, et al. Microwave drying performance of single-particle coal slime and energy consumption analyses[J]. Fuel Processing Technology, 2016, 143: 69-78.
5	SONG Zhanlong, JING Chuanming, YAO Liansheng, et al. Coal slime hot air/microwave combined drying characteristics and energy analysis[J]. Fuel Processing Technology, 2017, 156: 491-499.
6	MARLAND S, MERCHANT A, ROWSON N. Dielectric properties of coal[J]. Fuel, 2001, 80(13): 1839-1849.
7	KUMAR Chandan, KARIM M A, JOARDDER Mohammad. Intermittent drying of food products: a critical review[J]. Journal of Food Engineering, 2014, 121: 48-57.
8	FU B A, CHEN M Q, LI Q H, et al. Non-equilibrium thermodynamics approach for the coupled heat and mass transfer in microwave drying of compressed lignite sphere[J]. Applied Thermal Engineering, 2018, 133(25): 237-247.
9	HONG Yidu, LIN Baiquan, LI He, et al. Three-dimensional simulation of microwave heating coal sample with varying parameters[J]. Applied Thermal Engineering, 2016, 93(25): 1145-1154.
10	SU Chang, ZHANG Yong, YANG Xinle, et al. Numerical simulation of the temperature field of coal subjected to microwave directional heating[J]. IEEE Access, 2020, 8: 45084-45095.
11	HUANG Jinxin, XU Guang, HU Guozhong, et al. A coupled electromagnetic irradiation, heat and mass transfer model for microwave heating and its numerical simulation on coal[J]. Fuel Processing Technology, 2018, 177: 237-245.
12	LI He, ZHENG Chunshan, LU Jiexin, et al. Drying kinetics of coal under microwave irradiation based on a coupled electromagnetic, heat transfer and multiphase porous media model[J]. Fuel, 2019, 256(15): 115961.
13	KUMAR C, JOARDDER M, FARRELL T, et al. Multiphase porous media model for intermittent microwave convective drying (IMCD) of food[J]. International Journal of Thermal Sciences, 2016, 104: 304-314.
14	HOU Lixia, ZHOU Xu, WANG Shaojin. Numerical analysis of heat and mass transfer in kiwifruit slices during combined radio frequency and vacuum drying[J]. International Journal of Heat and Mass Transfer, 2020, 154(12): 119704.
15	SIPAHIOGLU O, BARRINGER S A. Dielectric properties of vegetables and fruits as a function of temperature, ash, and moisture content[J]. Journal of Food Science, 2003, 68: 234-239.
16	ZHANG Kai, YOU Changfu. Experimental and numerical investigation of convective drying of single coarse lignite particles[J]. Energy & Fuels, 2010, 24(12): 6428-6436.
17	FU B A, CHEN M Q, SONG J J. Investigation on the microwave drying kinetics and pumping phenomenon of lignite spheres[J]. Applied Thermal Engineering, 2017, 124: 371-380.
18	ZHU Huacheng, GULATI Tushar, DATTA Ashim, et al. Microwave drying of spheres: coupled electromagnetics-multiphase transport modeling with experimentation. Part I: model development and experimental methodology[J]. Food and Bioproducts Processing, 2015, 96: 314-325.
19	LI He, SHI Shiliang, LIN Baiquan, et al. A fully coupled electromagnetic, heat transfer and multiphase porous media model for microwave heating of coal[J]. Fuel Processing Technology, 2019, 189(15): 49-61.
20	RAKESH Vineet, DATTA K, WALTON J H, et al. Microwave combination heating: coupled electromagnetics-multiphase porous media modeling and MRI experimentation[J]. AIChE J., 2012, 58: 1262-1278.
21	WARNING A, DATTA K, MITREA D, et al. Porous media based model for deep-fat vacuum frying potato chips[J]. Journal of Food Engineering, 2012, 110: 428-440.
22	TUSHAR G, DATTA A K. Coupled multiphase transport, large deformation and phase transition during rice puffing[J]. Chemical Engineering Science, 2016, 139(12): 75-98.
23	SU Tianyi, ZHANG Zhijun, HAN Jingxue, et al. Sensitivity analysis of intermittent microwave convective drying based on multiphase porous media models[J]. International Journal of Thermal Sciences, 2020, 153:106344.
24	RATTI C, CRAPISTE G H, ROTSTEIN E. A new water sorption equilibrium expression for solid foods based on thermodynamic considerations[J]. Journal of Food Science, 1989, 54(3): 738-742.
25	LI Longzhi, JIANG Xiaowei, BIAN Zhiguo, et al. Microwave drying performance of lignite with the assistance of biomass-derived char[J]. Drying Technology, 2019, 37(2): 173-185.
26	FU B A, CHEN M Q, HUANG Y W, et al. Combined effects of additives and power levels on microwave drying performance of lignite thin layer[J]. Drying Technology, 2016, 35(2): 227-239.
27	ZHU Jingyi, LI Xiaogang, YANG Zhaozhong, et al. Drying characteristics of oil shale under microwave heating based on a fully coupled three-dimensional electromagnetic-thermal-multiphase transport model[J]. Fuel, 2022, 308(15): 121942.
28	DUAN Zhenhua, JIANG Lina, WANG Julan, et al. Drying and quality characteristics of tilapia fish fillets dried with hot air-microwave heating[J]. Food and Bioproducts Processing, 2011, 89(4): 472-476.

[1]	王太, 苏硕, 李晟瑞, 马小龙, 刘春涛. 交流电场中贴壁气泡的动力学行为[J]. 化工进展, 2023, 42(S1): 133-141.
[2]	陈匡胤, 李蕊兰, 童杨, 沈建华. 质子交换膜燃料电池气体扩散层结构与设计研究进展[J]. 化工进展, 2023, 42(S1): 246-259.
[3]	郭强, 赵文凯, 肖永厚. 增强流体扰动强化变压吸附甲硫醚/氮气分离的数值模拟[J]. 化工进展, 2023, 42(S1): 64-72.
[4]	李宁, 李金科, 董金善. 乙烯裂解炉多孔介质燃烧器的研究与开发[J]. 化工进展, 2023, 42(S1): 73-83.
[5]	邵博识, 谭宏博. 锯齿波纹板对挥发性有机物低温脱除过程强化模拟分析[J]. 化工进展, 2023, 42(S1): 84-93.
[6]	刘炫麟, 王驿凯, 戴苏洲, 殷勇高. 热泵中氨基甲酸铵分解反应特性及反应器结构优化[J]. 化工进展, 2023, 42(9): 4522-4530.
[7]	徐茂淯, 陶帅, 齐聪, 梁林. 圆盘式环路热管的启动特性及温度波动[J]. 化工进展, 2023, 42(9): 4531-4537.
[8]	赵曦, 马浩然, 李平, 黄爱玲. 错位碰撞型微混合器混合性能的模拟分析与优化设计[J]. 化工进展, 2023, 42(9): 4559-4572.
[9]	汪健生, 张辉鹏, 刘雪玲, 傅煜郭, 朱剑啸. 多孔介质结构对储层内流动和换热特性的影响[J]. 化工进展, 2023, 42(8): 4212-4220.
[10]	叶振东, 刘涵, 吕静, 张亚宁, 刘洪芝. 基于钙镁二元盐的热化学储能反应器的性能优化[J]. 化工进展, 2023, 42(8): 4307-4314.
[11]	俞俊楠, 俞建峰, 程洋, 齐一搏, 化春键, 蒋毅. 基于深度学习的变宽度浓度梯度芯片性能预测[J]. 化工进展, 2023, 42(7): 3383-3393.
[12]	单雪影, 张濛, 张家傅, 李玲玉, 宋艳, 李锦春. 阻燃型环氧树脂的燃烧数值模拟[J]. 化工进展, 2023, 42(7): 3413-3419.
[13]	王硕, 张亚新, 朱博韬. 基于灰色预测模型的水煤浆输送管道冲蚀磨损寿命预测[J]. 化工进展, 2023, 42(7): 3431-3442.
[14]	周龙大, 赵立新, 徐保蕊, 张爽, 刘琳. 电场-旋流耦合强化多相介质分离研究进展[J]. 化工进展, 2023, 42(7): 3443-3456.
[15]	郑昕, 贾里, 王彦霖, 张靖超, 陈世虎, 乔晓磊, 樊保国. 污泥与煤泥混烧对重金属固留特性的影响[J]. 化工进展, 2023, 42(6): 3233-3241.