Numerical analysis and research on coal pyrolysis characteristics in BGL gasification process
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摘要: 厘清煤颗粒热解的内部温度变化和挥发分析出规律，是优化炉体结构和操作参数、进一步提升BGL煤气化经济性的基础。本文通过剖析BGL煤气化热解过程构建了煤颗粒热解模型，并利用文献实验数据验证了模型合理性。模型求解采用解耦算法，其中传热模型采用追赶法，热解动力学模型采用4阶单步递推法，环境温度由移动床一维模型计算。模拟结果表明：BGL煤气化热解终温较高，颗粒内部径向温度变化大；粒径取10 mm，热解终温计算值1 372 K，煤颗粒表面和中心温差峰值计算值338 K；粒径取40 mm，相应计算值分别为1 412 K和381 K；煤颗粒挥发分析出过程与气固非催化缩核反应过程相似，印证了煤热解过程受传热过程控制；热解动力学的描述以FZ通用热解模型适应性更好；移动床一维模型预测BGL煤气化热解层高度时，热解蒸发模型优于FZ通用热解模型，预测值为0.616 5 m，与搅拌器运行情况相符。Abstract: Research on the patterns of the internal temperature change and volatile analysis on the law of coal particle pyrolysis are essential to optimizing the furnace structure and operating parameters, while further improves the economy of BGL coal gasification.Based on the analysis of BGL coal gasification pyrolysis process, this study established the coal particle pyrolysis model.The decoupling algorithm was sadopted in solving the model, in which the heat transfer model adopted the chasing method, the pyrolysis kinetic model adopted the fourth-order single-step push-up method, and the ambient temperature was calculated by the moving bed one-dimensional model.The rationality of the model was verified by experimental data in literature.The simulation results show that the final pyrolysis temperature of BGL coal gasification is higher, and the temperature gradient inside the particles changes greatly.The particle size is 10 mm, the calculated final pyrolysis temperature is 1 372 K, and the calculated peak temperature difference between the surface and center of coal particles is 338 K. Taking the particle size of 40 mm, the corresponding calculated values are 1 412 K and 381 K respectively; The process of coal particle volatilization is similar to that of gas-solid non-catalytic condensation reaction, which proves that the coal pyrolysis process is controlled by heat transfer process.Pyrolysis kinetics is described by FZ general pyrolysis model, which has better adaptability than distributed activation energy model.When the moving bed one-dimensional model predicts the height of BGL coal gasification pyrolysis layer, the pyrolysis evaporation model is superior to FZ general pyrolysis model.The predicted height of pyrolysis layer is 0.616 5 m, which is consistent with the operation of agitator.
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Key words:
- BGL coal gasification /
- coal particle /
- pyrolysis /
- numerical simulation
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图 1 DAEM和通用热解模型挥发分析出速率
Figure 1. Comparison of devolatilization rate between DAEM model and general pyrolysis
图 2 BGL煤气化热解段气固相温度变化
Figure 2. Temperature changes of gas-solid phase in the pyrolysis section of BGL coal gasification
图 3 煤颗粒挥发分析出量实验值与模拟值对比
Figure 3. Comparison between experimental and simulated values of coal particles devolatilization
图 4 煤颗粒挥发分析出速率实验值与模拟值对比
Figure 4. Comparison between experimental and simulated values of coal particles devolatilization
图 5 20 mm煤颗粒内部不同时刻径向温度分布
Figure 5. Radial temperature distribution in 20 mm coal particles at different times
图 6 不同粒径的煤颗粒表面和中心温度变化曲线
Figure 6. Surface and center temperature curves of coal particles with different sizes
图 7 不同粒径的煤颗粒表面和中心温差变化曲线
Figure 7. Curves of temperature difference between surface and center of coal particles with different sizes
图 8 20 mm煤颗粒不同时刻内部挥发分径向分布
Figure 8. Radial distribution of volatile matter in 20 mm coal particles at different times
图 9 不同粒径煤颗粒总挥发分析出速率变化
Figure 9. Changes of devolatilization rate of coal particles with different particle sizes
图 10 BGL煤气化热解层挥发分析轴向变化曲线
Figure 10. Axial changing curves of devolatilization in BGL coal gasification pyrolysis layer
表 1 原料煤工业分析和元素分析
Table 1. Proximate analysis and ultimate analysis of raw coal
工业分析(分析基)质量分数/% 元素分析(干燥无灰基)质量分数/% Mtad A V FC C H O N S 1.65 6.62 33.21 58.62 82.35 4.80 10.93 1.14 0.77 
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表 2 原料煤样热解试验与结果
Table 2. Pyrolysis test of coal samples and its results
序号 试验方法 单次煤样/g 粒度/mm 加热终温/℃ 操作压力/MPa 半焦/% 焦油/% 热解气/% a 铝甑热解试验 20 < 0.2 650 0.1 73.00 10.70 8.55 b 加压低温干馏试验 60 0.5~2.0 650 0.1 68.67 8.85 12.82 c 加压低温干馏试验 60 0.5~2.0 650 3.0 74.32 3.75 14.93 d 固定床热解试验 3 000 10~50 650 0.1 76.73 5.90 8.98
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表 3 3 kg固定床热解试验产物随温度变化
Table 3. Changes of pyrolysis products of 3 kg fixed bed under different temperature
温度/℃ 半焦/% 水/% 焦油/% 煤气/% 623 71.15 11.17 6.78 10.90 650 70.65 11.90 7.47 9.98 675 70.87 11.92 7.90 9.31 700 69.78 11.93 7.35 10.94 725 69.52 11.83 9.40 9.25 750 69.10 11.67 10.35 8.88 775 65.47 11.87 9.41 13.25 800 65.17 11.83 8.00 15.00
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表 4 BGL最终粗煤气和热解气组分摩尔流量
Table 4. Molar flow rate of each component of final crude gas and pyrolysis gas from BGL coal gasification
mol/s 项目 H2 CO CO2 CH4 H2O C2H4 H2S N2 合计 粗煤气 199.8 416.2 29.6 60.8 79.1 2.8 1.9 3.2 793.4 热解气 31.8 26.2 2.7 56.7 20.8 2.8 1.9 3.2 146.2
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表 5 煤颗粒热解物性参数模型
Table 5. Physical parameter model of coal particle pyrolysis
名称 模型 煤高位发热量 Qgr，daf=334.5Cdaf+1 275.4Hdaf-108.7Odaf+92St，daf-max[0，25.1(Ad-10)] 固定碳显焓 $\begin{aligned} & h_{\mathrm{fc}}=R \cdot\left[380 \cdot g_0\left(\frac{380}{T}\right)+3600 \cdot g_0\left(\frac{1800}{T}\right)\right] \\ & g_0=\frac{1}{\mathrm{e}^z-1} \\ & g_1=\mathrm{e}^z\left(\frac{z}{\mathrm{e}^z-1}\right)^2 \end{aligned}$ 挥发分比热 Cp，vol=0.9Cp，vol1+0.1Cp，vol2
基本挥发分Cp，vol1=728+3.391T
次级挥发分Cp，vol2=2 273+2.554T灰分比热 Cp，vol1=594+0.586T 焦油比热 Cp，tar=88.627+0.120 74T-0.127 35×10-4T2-0.366 88×10-7T-2 对流给热系数 $h=N u \frac{\lambda}{d_p}$
努赛尔数Nu=2.0+1.2Re0.5Pr0.33(Re为颗粒局域雷诺数，Pr为普朗特数)颗粒比热容 $C_p= \begin{cases}1 & 254, T_{\mathrm{s}}<623 \\ 1 & 254-1.75\left(T_{\mathrm{s}}-623\right), T_{\mathrm{s}} \geqslant 623\end{cases}$ 颗粒热导率 $\lambda_p=\left\{\begin{array}{l} 0.23, T_{\mathrm{s}}<673 \\ 0.23+2.24 \times 10^{-5}\left(1+0.0033 T_{\mathrm{s}}\right)^{1.8}, T_{\mathrm{s}} \geqslant 673 \end{array}\right.$
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