双流化床生物质气化的三维全循环数值模拟

doi:10.11949/0438-1157.20190192

摘要/Abstract

摘要：

基于多相质点网格方法（multi-phase particle-in-cell，MP-PIC）对工业尺度的双流化床生物质气化过程进行了三维全循环数值模拟。其中，在拉格朗日框架下求解颗粒团运动，采用大涡模拟法（large-eddy simulation, LES）求解气相湍流，同时考虑复杂的气固耦合以及生物质的热解、气化、均相/异相反应。首先，通过独立性检验确定了计算所需的最佳网格数与计算颗粒数，且模拟结果和实验结果对比良好。其次，揭示了流化床内生物质气化过程中的气固流动特性及气体组分分布规律，研究了床内温度、生物质粒径、曳力模型等因素对产物气体组分分布的影响。结果表明：温度升高，出口处的CO摩尔分数增加，而其余组分都减小；较小生物质粒径的气化效果要优于较大的生物质颗粒粒径；曳力模型对各产物气体组分的摩尔分数几乎无影响。

关键词: MP-PIC, 双流化床, 生物质气化, 数值模拟

Abstract:

A three-dimensional full-loop simulation of biomass gasification in an industry-scale dual fluidized bed is conducted based on the MP-PIC (multi-phase particle-in-cell) method. In this method, the parcel motion is descript under Lagrangian framework while the gas turbulence is solved by large-eddy simulation (LES), meanwhile, the complex gas-solid interaction, pyrolysis, gasification and homogeneous/heterogeneous reactions are considered simultaneously. Firstly, the independence of grids and particles per parcel (PPP) is conducted, and the numerical results agree well with the experimental data. Secondly, the gas-solid flow characteristics and syngas distributions in dual fluidized bed are revealed and the effects of bed temperature, biomass particle number and drag force correlation on syngas production are analyzed. The results show that the temperature increases, the CO mole fraction at the outlet increases, and the remaining components decrease; the gasification effect of the smaller biomass particle size is better than the larger biomass particle size. The drag model has a negligible effect on the syngas production.

Key words: MP-PIC, dual fluidized bed, biomass gasification, numerical simulation

中图分类号:

孔大力, 罗坤, 林俊杰, 王帅, 胡陈枢, 李德波, 樊建人. 双流化床生物质气化的三维全循环数值模拟[J]. 化工学报, 2019, 70(8): 3167-3176.

Dali KONG, Kun LUO, Junjie LIN, Shuai WANG, Chenshu HU, Debo LI, Jianren FAN. Three-dimensional full-loop simulation of biomass gasification in dual fluidized bed[J]. CIESC Journal, 2019, 70(8): 3167-3176.

图/表 13

表1 生物质工业分析及元素分析

Table 1 Proximate analysis and ultimate analysis of biomass

Proximate analysis/%(mass)				Ultimate analysis/%(mass)
Fixed carbon	Volatile	Ash	Moisture	C	H	O	N, S, Cl
20.2	72.53	2.09	5.18	51.3	5.29	40.9	0.71

表2 化学反应方程及反应速率

Table 2 Chemical reaction and reaction rates

方程	反应速率
$C + O 2 ? C O 2$	$r 2 = 4.34 × 107 θ s T p e x p (- 13590 / T p) [O 2]$
$C + H 2 O ? C O + H 2$	$r 3 f = 6.36 m c T p e x p (- 22645 / T p) [H 2 O]$
$C + H 2 O ? C O + H 2$	$r 3 r = 5.218 × 10 - 4 m c T p 2 e x p (- 6319 / T p - 17.29) [H 2] [C O]$
$C + C O 2 ? 2 C O$	$r 4 f = 6.36 m c T p e x p (- 22645 / T p) [C O 2]$
$C + C O 2 ? 2 C O$	$r 4 r = 5.218 × 10 - 4 m c T p 2 e x p (- 2363 / T p - 20.92) [C O] 2$
$C + 2 H 2 ? C H 4$	$r 5 f = 6.838 × 10 - 3 m c T p e x p (- 8078 / T p - 7.087) [H 2]$
$C + 2 H 2 ? C H 4$	$r 5 r = 0.755 m c T p 0.5 e x p (- 13578 / T p - 0.372) [C H 4] 0.5$
$C O + 0.5 O 2 ? C O 2$	$r 6 = 1.3 × 1011 e x p (- 15155 / T g) [C O] [O 2] 0.5$
$H 2 + 0.5 O 2 ? H 2 O$	$r 7 = 2.2 × 109 e x p (- 13110 / T g) [H 2] [O 2]$
$C H 4 + 2 O 2 ? C O 2 + 2 H 2 O$	$r 8 = 5.01 × 1011 e x p (- 24117 / T g) [C H 4] 0.7 [O 2] 0.8$
$C 2 H 4 + 3 O 2 ? 2 C O 2 + 2 H 2 O$	$r 9 = 1 × 1015 e x p (- 20808 / T g) [C 2 H 4] [O 2]$
$C 3 H 8 + 5 O 2 ? 3 C O 2 + 4 H 2 O$	$r 10 = 8.6 × 1011 e x p (- 15000 / T g) [C 3 H 8] 0.1 [O 2] 1.65$
$C O + H 2 O ? C O 2 + H 2$	$r 11 = 2.75 θ s e x p (- 10079 / T g) [C O] [H 2 O]$

表2 化学反应方程及反应速率

Table 2 Chemical reaction and reaction rates

方程	反应速率
$C + O 2 ? C O 2$	$r 2 = 4.34 × 107 θ s T p e x p (- 13590 / T p) [O 2]$
$C + H 2 O ? C O + H 2$	$r 3 f = 6.36 m c T p e x p (- 22645 / T p) [H 2 O]$
$C + H 2 O ? C O + H 2$	$r 3 r = 5.218 × 10 - 4 m c T p 2 e x p (- 6319 / T p - 17.29) [H 2] [C O]$
$C + C O 2 ? 2 C O$	$r 4 f = 6.36 m c T p e x p (- 22645 / T p) [C O 2]$
$C + C O 2 ? 2 C O$	$r 4 r = 5.218 × 10 - 4 m c T p 2 e x p (- 2363 / T p - 20.92) [C O] 2$
$C + 2 H 2 ? C H 4$	$r 5 f = 6.838 × 10 - 3 m c T p e x p (- 8078 / T p - 7.087) [H 2]$
$C + 2 H 2 ? C H 4$	$r 5 r = 0.755 m c T p 0.5 e x p (- 13578 / T p - 0.372) [C H 4] 0.5$
$C O + 0.5 O 2 ? C O 2$	$r 6 = 1.3 × 1011 e x p (- 15155 / T g) [C O] [O 2] 0.5$
$H 2 + 0.5 O 2 ? H 2 O$	$r 7 = 2.2 × 109 e x p (- 13110 / T g) [H 2] [O 2]$
$C H 4 + 2 O 2 ? C O 2 + 2 H 2 O$	$r 8 = 5.01 × 1011 e x p (- 24117 / T g) [C H 4] 0.7 [O 2] 0.8$
$C 2 H 4 + 3 O 2 ? 2 C O 2 + 2 H 2 O$	$r 9 = 1 × 1015 e x p (- 20808 / T g) [C 2 H 4] [O 2]$
$C 3 H 8 + 5 O 2 ? 3 C O 2 + 4 H 2 O$	$r 10 = 8.6 × 1011 e x p (- 15000 / T g) [C 3 H 8] 0.1 [O 2] 1.65$
$C O + H 2 O ? C O 2 + H 2$	$r 11 = 2.75 θ s e x p (- 10079 / T g) [C O] [H 2 O]$

图1 双流化床几何模型及网格

Fig.1 Geometry and grids of dual fluidized bed

表3 操作参数

Table 3 Operational parameters

参数	数值	参数	数值
进料量/(kg/h)	72.8	二次风量/(kg/h)	260
进料温度/K	293	二次风温度/K	632
气化室蒸汽质量流量/(kg/h)	85.6	三次风量/(kg/h)	362
气化室蒸汽温度/K	640	三次风温度/K	648
拨料蒸汽流量/(kg/h)	27.1	甲烷流量/(kg/h)	19.5
拨料蒸汽温度/K	640	甲烷温度/K	293
一次风量/(kg/h)	36	助燃空气流量/(kg/h)	561
一次风温度/K	602	助燃空气温度/K	293

图2 不同网格数和不同计算颗粒数下颗粒流量随时间的变化

Fig.2 Time-evolution solid flux under different grids number and particles number

表4 不同参数设置下平均颗粒流量

Table 4 Average solid flux under different parameters

算例	网格数	平均颗粒流量/(kg/s)	算例	计算颗粒数	平均颗粒流量/(kg/s)
Case 1	223125	6.43	Case 4	347705	6.30
Case 2	286875	6.50	Case 5	474369	6.38
Case 3	354375	6.85	Case 6	539796	7.09

图3 出口产物气体的摩尔分数

Fig.3 Molar fraction of export product gases

图4 出口气体摩尔分数的模拟结果和实验结果对比

Fig.4 Comparison of gaseous mole fraction at outlet between experiment and simulation

图5 双流化床内气固流型随时间的发展

Fig.5 Time evolution of gas-solid flow patterns in dual fluidized bed

图6 双流化床内气体组分的质量分数云图

Fig.6 Contour plots of syngas mass fraction in dual fluidized bed

图7 双流化床内气固温度分布云图

Fig.7 Distribution of gas and particle temperature in dual fluidized bed

图8 双流化床内压强分布

Fig.8 Pressure distribution in the dual fluidized bed

图9 不同工况对双流化床产物生成的影响

Fig.9 Effects of operating conditions on gaseous mole fraction in dual fluidized bed

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