光热驱动褐煤固定床气化过程热质传递规律

doi:10.16085/j.issn.1000-6613.2024-0566

摘要/Abstract

摘要：

光热热源可解决中低价煤气化过程中元素利用率低等问题，但由于热源属性和传热方式改变，反应特性与传统煤气化过程不同，为消纳CO₂引入的混合气化剂会对反应器内的温度场产生影响。为研究上述问题，本文利用多场耦合软件Comsol Multiphysics，构建了光热热源的褐煤固定床气化反应器，研究了不同导热特性的气化介质水蒸气、二氧化碳、不同比例混合气化剂下反应器内温度分布和产物组成以及反应器内热质传递行为变化。结果表明，随着气化剂中CO₂添加比例由0增大至100%，由于CO₂加入带来了流体黏度、密度不断增大，使得流体间黏滞力增强，动量传递减少；气/固相间对流换热系数从26.3W/(m²·K)降至22.7W/(m²·K)。相较于水蒸气气化，CO₂的加入使得颗粒气化温度有所降低，煤气化反应速率下降，但CO₂浓度的增加又提高了半焦CO₂还原反应的速率，煤焦颗粒完全气化的综合时间没有明显改变。此外，光热储蓄热介质加热的方式使得反应器床层温度曲线整体呈“漏斗状”，导致炉内中心位置颗粒气化时间延长了70min，且在掺混CO₂后，传热效率的降低使得温升曲线出现明显的“滞后”效应。通过改变CO₂在气化剂中的添加比例发现，当CO₂添加比例增至40%（体积分数）时，气化炉表现出消纳外源CO₂的行为，其CO₂消纳量达0.013g/g；且随着气化温度的增加，CO₂气化反应速率升高， CO₂的消纳量增加，有效合成气产量增加，但H₂/CO下降。

关键词: 煤气化, 气化介质, 传热, 温度分布, 反应速率

Abstract:

The photothermal heat source can solve problems such as low elemental utilization in low and medium coal gasification processes, but the reaction characteristics are different from those of conventional coal gasification processes due to changes in the properties of the heat source and the heat transfer method, and the introduction of the mixing agent for CO₂ dissipation will have an impact on the temperature field in the reactor. In order to study the above problems, this paper constructed a lignite fixed-bed gasification reactor with a photothermal heat source using the multi-field coupling software Comsol Multiphysics, and investigated the influence laws of the temperature distribution and product composition as well as the changes of the heat and mass transfer behaviors in the reactor with different thermal conductivity characteristics of the gasification mediums steam, carbon dioxide and different ratios of the mixing gasification agents. As the proportion of CO₂ added to the gasification agent increased from 0 to 100%, the viscosity and density of the fluid continued to increase, resulting in an increase in the viscous force between the fluids and a decrease in the momentum transfer, and the convective heat transfer coefficient between the gas-solid phases decreased from 26.3W/(m²·K) to 22.7W/(m²·K). Compared with steam gasification, the addition of CO₂ reduced the particle gasification temperature and the reaction rate of coal gasification, but the increase of CO₂ concentration was conducive to increase the reaction rate of semi-coke CO₂ reduction. Under the combined effect, the complete gasification time of coal coke particles did not change significantly. In addition, the optical heat saving heat medium heating mode made the reactor bed temperature curve overall "funnel-shaped", which led to the extension of the particle gasification time in the center by 70min, and after the mixing of CO₂, the reduction of thermal conductivity made the temperature curve appeared obvious "lag effect". Finally, by adjusting the proportion of CO₂ added to the gasification medium, it was found that when the proportion of CO₂ added increased to 40%, the gasification medium exhibited the behavior of exogenous CO₂ absorption and its CO₂ absorption reached 0.013g/g. As the gasification temperature increased, the reaction rate of CO₂ gasification increased, which ultimately showed an increase in CO₂ consumption and the effective syngas yield, but a decrease in the H₂/CO ratio.

Key words: coal gasification, gasification medium, heat transfer, temperature distribution, reaction rate

中图分类号:

TQ546.2

袁梦丽, 宋云彩, 李文英, 冯杰. 光热驱动褐煤固定床气化过程热质传递规律[J]. 化工进展, 2025, 44(4): 2008-2019.

YUAN Mengli, SONG Yuncai, LI Wenying, FENG Jie. Heat and mass transfer law of photothermal-driven lignite fixed-bed gasification process[J]. Chemical Industry and Engineering Progress, 2025, 44(4): 2008-2019.

图/表 15

图1 光热驱动的固定床气化反应器模型T—储热腔室的温度；t—气化腔室的温度；Tw—靠近储热腔室的壁面温度；tw—靠近气化腔室的壁面温度

表1 化学反应及动力学参数[23-25]

反应	动力学表达式	动力学参数	ΔH/kJ·mol^-1
C+H₂O $→$ CO+H₂	$r C - H 2 O = k 1 K H 2 O P H 2 O 1 + K H 2 O P H 2 O + K H 2 P H 2$	$k 1 = (7.97 ± 0.9) × 10 - 9 s - 1$	131.3
		$K H 2 O = (8.07 ± 0.9) × 10 - 5 P a - 1$
		$K H 2 = (9.36 ± 0.9) P a - 1$
C+CO₂ $→$ 2CO	$r C - C O 2 = k 2 K C O 2 P C O 2 1 + K C O 2 P C O 2 + K C O P C O$	$k 2 = (5.53 ± 0.6) × 10 - 9 s - 1$	172.5
		$K C O 2 = (1.62 ± 0.2) × 10 - 5 P a - 1$
		$K C O = (1.0 ± 0.1) × 10 - 4 P a - 1$
C+2H₂ $→$ CH₄	$r C - H 2, F = k 3 c H 2$ $r C - H 2, r = k 3' c C H 4 0.5$	$k 3 = 1.368 × 10 - 3 m s T e x p - 8078 T - 7.087$	-74.8
C+2H₂ $→$ CH₄		$k 3' = 0.151 m s T 0.5 e x p - 13578 T - 0.372$	-74.8
CO+H₂O $⇌$ CO₂+H₂	$r 4 = k 4 c C O c H 2 O - c C O 2 c H 2 K e q$	$k 4 = 2.78 × 103 e x p - 1510 T$	-41.2
CO+H₂O $⇌$ CO₂+H₂	$r 4 = k 4 c C O c H 2 O - c C O 2 c H 2 K e q$	$K e q = 0.0265 e x p 3968 T$	-41.2
CH₄+H₂O $→$ CO+3H₂	$r 5 = k 5 c C H 4 c H 2 O$	$k 5 = 3.0 × 105 e x p - 15042 T$	206.1

表1 化学反应及动力学参数[23-25]

反应	动力学表达式	动力学参数	ΔH/kJ·mol^-1
C+H₂O $→$ CO+H₂	$r C - H 2 O = k 1 K H 2 O P H 2 O 1 + K H 2 O P H 2 O + K H 2 P H 2$	$k 1 = (7.97 ± 0.9) × 10 - 9 s - 1$	131.3
		$K H 2 O = (8.07 ± 0.9) × 10 - 5 P a - 1$
		$K H 2 = (9.36 ± 0.9) P a - 1$
C+CO₂ $→$ 2CO	$r C - C O 2 = k 2 K C O 2 P C O 2 1 + K C O 2 P C O 2 + K C O P C O$	$k 2 = (5.53 ± 0.6) × 10 - 9 s - 1$	172.5
		$K C O 2 = (1.62 ± 0.2) × 10 - 5 P a - 1$
		$K C O = (1.0 ± 0.1) × 10 - 4 P a - 1$
C+2H₂ $→$ CH₄	$r C - H 2, F = k 3 c H 2$ $r C - H 2, r = k 3' c C H 4 0.5$	$k 3 = 1.368 × 10 - 3 m s T e x p - 8078 T - 7.087$	-74.8
C+2H₂ $→$ CH₄		$k 3' = 0.151 m s T 0.5 e x p - 13578 T - 0.372$	-74.8
CO+H₂O $⇌$ CO₂+H₂	$r 4 = k 4 c C O c H 2 O - c C O 2 c H 2 K e q$	$k 4 = 2.78 × 103 e x p - 1510 T$	-41.2
CO+H₂O $⇌$ CO₂+H₂	$r 4 = k 4 c C O c H 2 O - c C O 2 c H 2 K e q$	$K e q = 0.0265 e x p 3968 T$	-41.2
CH₄+H₂O $→$ CO+3H₂	$r 5 = k 5 c C H 4 c H 2 O$	$k 5 = 3.0 × 105 e x p - 15042 T$	206.1

表2 气化炉初始条件

物理量	初始值
壁面温度/K	1173.15
压力/Pa	101325
气化剂入炉速度/m·s^-1	0.023
气化剂入炉温度/K	500
床层孔隙率	0.43
颗粒孔隙率	0.27
颗粒直径/m	10^-2
特征孔径/m	10^-7
颗粒密度/kg·m^-3	1100

表3 半焦样的工业分析与元素分析[34]

工业分析/%					元素分析/%
M_ad	A_d	V_daf	FC_daf		C	H	N	S	O
0.55	28.36	4.63	95.37		97.75	0.99	0.66	0.53	0.07

图2 不同时间段下H2O和CO2气化剂消耗量及颗粒碳消耗速率变化情况

图3 不同温度条件下合成气体积分数

图4 气化剂配比不同时传热参数变化情况

图5 80s时单独H2O气氛及单独CO2气氛下颗粒温度分布

图6 不同气化剂氛围下颗粒内反应热变化规律

图7 不同气化剂氛围下颗粒温度对比

图8 不同气化剂工况下颗粒表面气化反应速率及转化率对比

图9 料层径向位置温度分布及不同位置颗粒转化率对比

图10 煤焦颗粒料层径向位置反应速率分布

表4 不同CO2添加比例对气体组成的影响

参数	[CO₂/(CO₂+H₂O)]
参数	0	10%	20%	30%	40%	50%	60%	70%	80%
$V H 2$ /%	53.962	29.560	16.506	12.038	9.330	9.615	8.100	5.390	4.673
V_CO/%	38.115	23.064	14.218	11.204	9.356	10.132	9.060	6.499	5.941
H₂/CO	1.415	1.281	1.161	1.074	0.997	0.949	0.894	0.829	0.787
ξ/g·g^-1	—	—	—	—	0.013	0.057	0.228	0.380	0.507

表4 不同CO2添加比例对气体组成的影响

参数	[CO₂/(CO₂+H₂O)]
参数	0	10%	20%	30%	40%	50%	60%	70%	80%
$V H 2$ /%	53.962	29.560	16.506	12.038	9.330	9.615	8.100	5.390	4.673
V_CO/%	38.115	23.064	14.218	11.204	9.356	10.132	9.060	6.499	5.941
H₂/CO	1.415	1.281	1.161	1.074	0.997	0.949	0.894	0.829	0.787
ξ/g·g^-1	—	—	—	—	0.013	0.057	0.228	0.380	0.507

表5 温度对气体组成的影响

参数	温度
参数	1023K	1073K	1123K	1173K	1223K
$V H 2$ /%	5.511	7.117	7.665	9.615	10.451
V_CO/%	5.242	7.020	8.017	10.132	11.561
H₂/CO	1.051	1.013	0.956	0.949	0.904
ξ/g·g^-1	—	—	—	0.057	0.216

表5 温度对气体组成的影响

参数	温度
参数	1023K	1073K	1123K	1173K	1223K
$V H 2$ /%	5.511	7.117	7.665	9.615	10.451
V_CO/%	5.242	7.020	8.017	10.132	11.561
H₂/CO	1.051	1.013	0.956	0.949	0.904
ξ/g·g^-1	—	—	—	0.057	0.216

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