Three-dimensional numerical simulation of biomass-coal mixed combustion in fluidized beds

doi:10.11949/0438-1157.20250586

Abstract

Abstract:

This work employs a multiphase particle grid method to couple sub-models for heat transfer, mass transfer, and chemical reactions, and conducts a full three-dimensional numerical simulation study on the mixed combustion process of biomass and coal in a fluidized bed. By comparing the simulation results with experimental data, the rationality of the developed model is verified. Subsequently, the gas-solid flow, gas-solid component distribution, and particle temperature distribution characteristics of the biomass and coal mixed combustion process in the fluidized bed were studied, and the effects of different inlet air mass flow rates (0.01, 0.012, 0.014 kg/s) and different fuel blending ratios (1∶4, 3∶7, 2∶3) on the temperature distribution of particle, particle heat transfer coefficient and gas product concentration were explored. The results show that due to differences in particle size and density, significant particle segregation occurred within the reactor, and a large gradient in particle temperature distribution was observed in the dense phase. Increasing the inlet air mass flow rate significantly reduces the bed material particle heat transfer coefficient and shortens the residence time of fuel particles in the high-temperature zone. When the inlet air mass flow rate increases from 0.01 kg/s to 0.014 kg/s, the mole concentration of O₂ at the outlet increases by 3.7%, while the concentrations of other gas components decrease. When the biomass blending ratio increases from 1∶4 to 2∶3, due to the high hydrogen-carbon ratio and high volatile content of the biomass, H₂O and CO₂ are promoted to be generated, resulting in a decrease of 2.1% in the mole concentration of O₂ at the outlet, an increase in the concentrations of other gas components, and an increase in the full bed layer temperature of the biomass particles, but the overall heat transfer coefficient is not significantly affected.

Key words: gas-solid two-phase flow, bubbling fluidized bed, biomass and coal combustion, multiphase particle-in-cell method, numerical simulation

摘要：

本文采用多相质点网格方法耦合传热、传质以及化学反应等子模型，对流化床内生物质与煤的混合燃烧过程开展了全三维数值模拟研究。通过模拟结果与实验数据进行对比，证明了所发展模型的合理性。研究了流化床内生物质与煤混合燃烧过程的气固流动、气固组分分布及颗粒温度分布等特性，并探讨了不同入口风质量流速（0.01、0.012、0.014 kg/s）和不同燃料掺混比（1∶4、3∶7、2∶3）对颗粒温度分布、传热系数以及气体产物浓度的影响。结果表明，由于颗粒尺寸/密度不同，反应器内存在明显的颗粒偏析现象，并且在密相区颗粒温度分布存在较大梯度。提高入口风质量流速显著降低了床料颗粒传热系数，缩短燃料颗粒在高温区的停留时间。入口风质量流速从0.01 kg/s增至0.014 kg/s时，出口O₂物质的量浓度升高3.7%，其余气体组分浓度降低。生物质掺混比从1∶4增至2∶3时，因生物质氢碳比高、挥发分含量高，促进H₂O和CO₂生成，出口O₂物质的量浓度降低2.1%，其余气体组分浓度上升，且生物质颗粒全床层温度升高，但对整体传热系数影响不显著。

关键词: 气固两相流, 鼓泡流化床, 生物质与煤掺混燃烧, 多相质点网格方法, 数值模拟

CLC Number:

TK 121

Panxi ZHANG, Dayong TIAN, Donghui CI, Shuai WANG, Kun LUO, Jianren FAN. Three-dimensional numerical simulation of biomass-coal mixed combustion in fluidized beds[J]. CIESC Journal, 2025, 76(11): 6027-6039.

张盼兮, 田大勇, 次东辉, 王帅, 罗坤, 樊建人. 流化床生物质与煤掺混燃烧的全三维数值模拟研究[J]. 化工学报, 2025, 76(11): 6027-6039.

Figures/Tables 15

Table 1 Proximate analysis and ultimate analysis of fuels

燃料类型	工业分析/%（质量，空气干燥基）									低位热值/（kJ/kg）
燃料类型	挥发分	固定碳	灰分	水分	碳	氢	氧	氮	硫	低位热值/（kJ/kg）
烟煤	33.23	45.50	9.27	12.00	63.51	3.90	7.47	0.98	2.87	26660
木屑	87.03	3.76	3.21	6.00	45.80	5.60	38.90	0.38	0.11	17086

Table 2 Chemical reaction equations and reaction rates

方程	反应速率
$C + H 2 O ⇌ C O + H 2$	$r 1 f = 1.272 m c T s e x p - 22645 / T s [H 2 O]$
$C + H 2 O ⇌ C O + H 2$	$r 1 r = 1.044 × 10 - 4 m c T s 2 e x p - 6319 / T s - 17.29 [H 2] [C O]$
$C + C O 2 ⇌ 2 C O$	$r 2 f = 1.272 m c T s e x p - 22645 / T s [C O 2]$
$C + C O 2 ⇌ 2 C O$	$r 2 r = 1.044 × 10 - 4 m c T s 2 e x p - 2363 / T s - 20.92 [C O] 2$
$C + 2 H 2 ⇌ C H 4$	$r 3 f = 1.368 × 10 - 3 m c T s e x p - 8078 / T s - 7.087 [H 2]$
$C + 2 H 2 ⇌ C H 4$	$r 3 r = 0.151 m c T s 0.5 e x p - 13578 / T s - 0.372 [C H 4] 0.5$
$C + O 2 → C O 2$	$r 4 = 4.34 × 107 θ s T s 0.5 e x p - 13590 / T s - 0.372 [O 2]$
$C O + H 2 O ⇌ C O 2 + H 2$	$r 5 f = 7.68 × 1010 θ s T s e x p - 36640 / T g [C O] 0.5 [H 2 O]$
$C O + H 2 O ⇌ C O 2 + H 2$	$r 5 r = 6.4 × 109 T s e x p - 39260 / T g [C O 2] [H 2] 0.5$
$C O + 0.5 O 2 → C O 2$	$r 6 = 5.62 × 1012 T s e x p - 16000 / T g [C O] [O 2]$
$C H 4 + 2 O 2 → C O 2 + 2 H 2 O$	$r 7 = 3.552 × 1011 T s - 1 e x p - 1570 / T g [C H 4] [O 2]$
$H 2 + 0.5 O 2 → H 2 O$	$r 8 = 1.63 × 1011 T s - 1.5 e x p - 34300 / T g [H 2] 0.5 [O 2]$
$C 2 H 4 + O 2 → 2 C O + 2 H 2$	$r 9 = 1 × 1012 T s - 1.5 e x p - 20818.3 / T g [C 2 H 4] [O 2]$
$C H 4 + H 2 O → C O + 3 H 2$	$r 10 = 3.0 × 105 e x p - 15042 / T g [C H 4] [H 2 O]$

Table 2 Chemical reaction equations and reaction rates

方程	反应速率
$C + H 2 O ⇌ C O + H 2$	$r 1 f = 1.272 m c T s e x p - 22645 / T s [H 2 O]$
$C + H 2 O ⇌ C O + H 2$	$r 1 r = 1.044 × 10 - 4 m c T s 2 e x p - 6319 / T s - 17.29 [H 2] [C O]$
$C + C O 2 ⇌ 2 C O$	$r 2 f = 1.272 m c T s e x p - 22645 / T s [C O 2]$
$C + C O 2 ⇌ 2 C O$	$r 2 r = 1.044 × 10 - 4 m c T s 2 e x p - 2363 / T s - 20.92 [C O] 2$
$C + 2 H 2 ⇌ C H 4$	$r 3 f = 1.368 × 10 - 3 m c T s e x p - 8078 / T s - 7.087 [H 2]$
$C + 2 H 2 ⇌ C H 4$	$r 3 r = 0.151 m c T s 0.5 e x p - 13578 / T s - 0.372 [C H 4] 0.5$
$C + O 2 → C O 2$	$r 4 = 4.34 × 107 θ s T s 0.5 e x p - 13590 / T s - 0.372 [O 2]$
$C O + H 2 O ⇌ C O 2 + H 2$	$r 5 f = 7.68 × 1010 θ s T s e x p - 36640 / T g [C O] 0.5 [H 2 O]$
$C O + H 2 O ⇌ C O 2 + H 2$	$r 5 r = 6.4 × 109 T s e x p - 39260 / T g [C O 2] [H 2] 0.5$
$C O + 0.5 O 2 → C O 2$	$r 6 = 5.62 × 1012 T s e x p - 16000 / T g [C O] [O 2]$
$C H 4 + 2 O 2 → C O 2 + 2 H 2 O$	$r 7 = 3.552 × 1011 T s - 1 e x p - 1570 / T g [C H 4] [O 2]$
$H 2 + 0.5 O 2 → H 2 O$	$r 8 = 1.63 × 1011 T s - 1.5 e x p - 34300 / T g [H 2] 0.5 [O 2]$
$C 2 H 4 + O 2 → 2 C O + 2 H 2$	$r 9 = 1 × 1012 T s - 1.5 e x p - 20818.3 / T g [C 2 H 4] [O 2]$
$C H 4 + H 2 O → C O + 3 H 2$	$r 10 = 3.0 × 105 e x p - 15042 / T g [C H 4] [H 2 O]$

Fig.1 Bubbling fluidized bed reactor: (a) geometry and dimensions; (b) computational mesh

Table 3 Operating parameters of bubbling fluidized bed co-combustion of biomass and coal

参数	数值	单位
进料量	0.0025	kg/s
进料温度	300	K
入口风温度	643	K
辅助风速	0.05	m/s
辅助风温度	300	K

Fig.2 Axial distributions of quantities in the bed under different grid resolutions: (a) pressure; (b) temperature

Fig.3 Gas species obtained at the reactor outlet: (a) time-evolution profiles of mass fraction of gas species; (b) time-averaged molar fraction of gas species in different statistical time periods

Fig.4 Comparison of gas species molar fraction between simulation results and experimental data: (a) coal combustion; (b) biomass combustion

Fig.5 Evolution of gas-solid flow patterns in the fluidized bed: (a) t = 0 s；(b) t = 0.4 s；(c) t = 1 s；(d) t = 2 s；(e) t = 5 s；(f) t = 30 s

Fig.6 Particle distribution in the bubbling fluidized bed: (a) snapshot of particle components; (b) axial distribution of biomass mass; (c) axial distribution of coal mass; (d) axial distribution of sand mass

Fig.7 Temperature distribution of particles in the bubbling fluidized bed: (a) instantaneous particle temperature distribution; (b) axial distribution of particle temperature

Fig.8 The influence of different operating conditions on the temperature distribution of particles: (a) biomass particles under different flow rates; (b) coal particles under different flow rates; (c) sand particles under different flow rates; (d) biomass particles under different biomass blending ratios; (e) coal particles under different biomass blending ratios; (f) sand particles under different biomass blending ratios

Fig.9 Axial HTC distribution of particle components under different operating conditions: (a) coal particles under different inlet flow rates; (b) biomass particles under different inlet flow rates; (c) sand particles under different inlet flow rates; (d) coal particles under different biomass blending ratios; (e) biomass particles under different biomass blending ratios; (f) sand particles under different biomass blending ratios

Fig.10 CO2 distribution in the reactor under different operating conditions: (a) inlet air mass flow rate of 0.01 kg/s, biomass and coal blending ratio of 1∶4; (b) inlet air mass flow rate of 0.012 kg/s, biomass and coal blending ratio of 1∶4; (c) inlet air mass flow rate of 0.014 kg/s, biomass and coal blending ratio of 1∶4; (d) inlet air mass flow rate of 0.01 kg/s, biomass and coal blending ratio of 3∶7; (e) inlet air mass flow rate of 0.01 kg/s, biomass and coal blending ratio of 2∶3

Fig.11 H2O distribution in the reactor under different operating conditions: (a) inlet air mass flow rate of 0.01 kg/s, biomass and coal blending ratio of 1∶4; (b) inlet air mass flow rate of 0.012 kg/s, biomass and coal blending ratio of 1∶4; (c) inlet air mass flow rate of 0.014 kg/s, biomass and coal blending ratio of 1∶4; (d) inlet air mass flow rate of 0.01 kg/s, biomass and coal blending ratio of 3∶7; (e) inlet air mass flow rate of 0.01 kg/s, biomass and coal blending ratio of 2∶3

Fig.12 The influence of different operating parameters on the gas products at the reactor outlet: (a) inlet air mass flow rate; (b) biomass blending ratio

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