Heat and mass transfer and energy consumption for microwave drying of coal slime

doi:10.11949/0438-1157.20230122

Abstract

Abstract:

The basic characteristics of the coal slime drying process and its heat and mass transfer characteristics were investigated by microwave heating method, and the basic laws of dynamics and energy consumption changes in different stages were expounded. The results show that the process of microwave drying of coal slime may be divided into three stages, i.e., preheating stage, constant-rate drying stage and decreasing-rate drying stage. The free water within coal slim is removed mainly in the both preheating stage and constant-rate drying stage, whilst the bound water is removed in the decreasing-rate drying stage. The linear model and modified Page Ⅰ model can be used to describe the corresponding kinetic processes in the constant-rate and decreasing-rate stage, respectively. Furthermore, the apparent activation energy of the selected sample in the decreasing-rate stage is obtained as 3.23 W/g. The energy consumption in the constant-rate drying stage ranges from 2.94 kJ/g to 5.90 kJ/g, which is significantly lower than that in the preheating or decreasing-rate drying stage. The energy consumption is decreased gradually with the increase of microwave power ranging from 500 W to 800 W or initial mass from 150 g to 300 g.

Key words: coal slime, microwave, drying, transport processes, kinetics, energy consumption

摘要：

采用微波加热方法考察了煤泥干燥过程基本特征及其热量和质量传递特性，阐述了不同阶段动力学和能耗变化基本规律。结果表明煤泥微波干燥可以分为预热升温、恒速干燥和降速干燥三个阶段，其中自由水主要在预热升温和恒速阶段去除，而结合水则在降速阶段去除。恒速和降速干燥阶段的动力学特征可以采用线性模型和修正的Page模型(Ⅰ)分别描述，进而获得所选样品在降速阶段的表观活化能为3.23 W/g。样品在恒速干燥阶段脱水能耗(2.94~5.90 kJ/g)明显低于预热升温和降速干燥阶段，且脱水能耗随着微波功率(500~800 W)增大或初始质量(150~300 g)增加而逐渐降低。

关键词: 煤泥, 微波, 干燥, 传递过程, 动力学, 能耗

CLC Number:

TQ 536

Guangyu WANG, Kai ZHANG, Kaihua ZHANG, Dongke ZHANG. Heat and mass transfer and energy consumption for microwave drying of coal slime[J]. CIESC Journal, 2023, 74(6): 2382-2390.

王光宇, 张锴, 张凯华, 张东柯. 微波加热干燥煤泥热质传递及其能耗特性分析[J]. 化工学报, 2023, 74(6): 2382-2390.

Figures/Tables 12

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样品	工业分析/%(质量)					元素分析/%(质量)					热值Q_b.ad/(MJ/kg)
样品	M_ar	M_ad	A_ad	V_ad	FC_ad	C_ad	H_ad	N_ad	S_ad	O^*_ad	热值Q_b.ad/(MJ/kg)
煤泥	27.82	1.35	26.46	12.31	59.88	61.76	2.86	1.28	0.40	5.89	24.94

样品	工业分析/%(质量)					元素分析/%(质量)					热值Q_b.ad/(MJ/kg)
样品	M_ar	M_ad	A_ad	V_ad	FC_ad	C_ad	H_ad	N_ad	S_ad	O^*_ad	热值Q_b.ad/(MJ/kg)
煤泥	27.82	1.35	26.46	12.31	59.88	61.76	2.86	1.28	0.40	5.89	24.94

模型	功率/W	R²	χ²	RSS
Lewis模型 MR=exp(-kt)	500	0.670	0.014	0.154
	600	0.711	0.013	0.130
	700	0.638	0.016	0.115
	800	0.621	0.018	0.110
Page模型 MR=exp(-ktⁿ )	500	0.997	1.091×10^-4	0.001
	600	0.996	1.500×10^-4	0.001
	700	0.999	5.567×10^-5	3.340×10^-4
	800	0.999	2.423×10^-5	1.211×10^-4
修正Page模型(Ⅰ) MR=exp[-(kt) ⁿ ]	500	0.997	1.091×10^-4	0.001
	600	0.996	1.500×10^-4	0.001
	700	0.999	5.567×10^-5	3.340×10^-4
	800	0.999	2.423×10^-5	1.211×10^-4
修正Page模型(Ⅱ) MR=aexp(-ktⁿ )	500	0.997	1.046×10^-4	9.419×10^-4
	600	0.996	1.467×10^-4	0.001
	700	0.999	2.476×10^-5	1.236×10^-4
	800	0.999	1.375×10^-5	5.502×10^-5
线性模型 MR=at+b	500	0.999	4.985×10^-5	4.985×10^-4
	600	0.999	5.872×10^-5	5.285×10^-4
	700	0.999	6.192×10^-5	3.715×10^-4
	800	0.998	1.022×10^-4	5.108×10^-4

模型	功率/W	R²	χ²	RSS
Lewis模型 MR=exp(-kt)	500	0.670	0.014	0.154
	600	0.711	0.013	0.130
	700	0.638	0.016	0.115
	800	0.621	0.018	0.110
Page模型 MR=exp(-ktⁿ )	500	0.997	1.091×10^-4	0.001
	600	0.996	1.500×10^-4	0.001
	700	0.999	5.567×10^-5	3.340×10^-4
	800	0.999	2.423×10^-5	1.211×10^-4
修正Page模型(Ⅰ) MR=exp[-(kt) ⁿ ]	500	0.997	1.091×10^-4	0.001
	600	0.996	1.500×10^-4	0.001
	700	0.999	5.567×10^-5	3.340×10^-4
	800	0.999	2.423×10^-5	1.211×10^-4
修正Page模型(Ⅱ) MR=aexp(-ktⁿ )	500	0.997	1.046×10^-4	9.419×10^-4
	600	0.996	1.467×10^-4	0.001
	700	0.999	2.476×10^-5	1.236×10^-4
	800	0.999	1.375×10^-5	5.502×10^-5
线性模型 MR=at+b	500	0.999	4.985×10^-5	4.985×10^-4
	600	0.999	5.872×10^-5	5.285×10^-4
	700	0.999	6.192×10^-5	3.715×10^-4
	800	0.998	1.022×10^-4	5.108×10^-4

模型	功率/W	R²	χ²	RSS
Lewis模型 MR=exp(-kt)	500	0.643	0.002	0.024
	600	0.495	0.004	0.020
	700	0.557	0.004	0.022
	800	0.586	0.004	0.021
Page模型 MR=exp(-ktⁿ )	500	0.995	2.887×10^-5	2.887×10^-4
	600	0.990	7.870×10^-5	3.148×10^-4
	700	0.990	8.146×10^-5	4.073×10^-4
	800	0.998	1.192×10^-5	4.768×10^-5
修正Page模型(Ⅰ) MR=exp[-(kt) ⁿ ]	500	0.995	2.883×10^-5	2.883×10^-4
	600	0.990	7.574×10^-5	3.029×10^-4
	700	0.990	8.029×10^-5	4.014×10^-4
	800	0.998	1.189×10^-5	4.756×10^-5
修正Page模型(Ⅱ) MR=aexp(-ktⁿ )	500	0.995	3.566×10^-5	3.209×10^-4
	600	0.978	1.639×10^-4	4.918×10^-4
	700	0.988	9.559×10^-5	3.824×10^-4
	800	0.998	1.456×10^-5	4.369×10^-5
线性模型 MR=at+b	500	0.909	5.728×10^-4	0.006
	600	0.978	1.679×10^-4	6.717×10^-4
	700	0.964	3.613×10^-4	0.002
	800	0.953	5.970×10^-4	0.002