Experimental study on alkali lignin enhanced chemical looping gasification of pulverized coal char
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摘要: 中国煤炼焦工业副产物煤焦粉产量大、活性低，难以被直接回收利用，常规热化学利用方式反应条件苛刻、催化剂易失活且存在动力学限制。本研究通过造纸副产物碱木质素作为可弃型催化剂，构建碱木质素强化化学链气化的方式来处理煤焦粉，实现工业副产物协同资源化利用。热转化实验和动力学分析研究表明，碱木质素可强化煤焦粉化学链气化过程，促进煤焦粉热解峰向低温方向移动。当煤焦粉与碱木质素质量比为1∶3时，反应活化能比单独煤焦粉反应降低87.56%。固定床实验证实气化温度提高、碱木质素以及载氧体赋存量增加，可以有效提高燃料碳转化率及合成气产物择性，促进气化反应进行，但氧载体过量会导致合成气转化为终端产物，降低合成气选择性。在气化温度为950 ℃，煤焦粉与碱木质素质量比为1∶2， 氧载体与煤焦粉/碱木质素混合体系质量比为1∶1的最佳反应条件下，基于NiFe2O3的碱木质素/煤焦粉化学链气化合成气选择性高达82.85%。该研究为碱木质素与煤焦粉的资源化利用提供科学依据。Abstract: The pulverized coal char from the byproduct of China's coal coking industry has high yield and low activity, which is difficult to be directly recycled. The conventional thermochemical utilization method has harsh reaction conditions, catalyst deactivation and kinetic limitations. By using the alkali lignin from paper-making as a disposable catalyst, an alkali lignin enhanced chemical looping gasification method was constructed to treat coal coke powder, which can realize the collaborative resource utilization of industrial by-products. In this study, the reaction process of alkali lignin and coal char powder was studied by thermogravimetry and kinetic analysis. The thermal transformation experiment and kinetic analysis showed that alkali lignin could strengthen the chemical looping gasification process of pulverized coal char and promote the pyrolysis peak to move to low temperature. When the mass ratio of pulverized coal char to alkali lignin was 1∶3, the activation energy was 87.56% lower than that of coal coke powder alone, indicating that there was a synergistic effect between the two in the co pyrolysis process. The experiments in fixed bed reactor verified that the carbon conversion rate and the selectivity of syngas increased as the increasing of temperature and the content of alkali lignin and oxygen carrier, which effectively promoted the gasification reaction. However, excessive oxygen loading led to combustion reaction between syngas and lattice oxygen and reduce syngas selectivity. Under the optimal reaction conditions of 950 ℃, the mass ratio of coal char powder to alkali lignin is 1∶2, and the mass ratio of oxygen carrier to pulverized coal char/alkali lignin is 1∶1, the selectivity of syngas of alkali lignin/coal char powder in chemical looping gasification was 82.85%. This study provides a scientific basis for the resource utilization of alkali lignin and coal char powder.
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图 1 碱木质素强化煤焦粉化学链气化示意图
Figure 1 Schematic diagram of alkali lignin-enhanced coal char gasification chemical pathway
Note: MexOy: oxidized oxygen carrier; MexOy−1: reduced oxygen carrier; [O]: lattice oxygen.
图 2 碱木质素强化煤焦粉化学链气化实验装置示意图
Figure 2 Schematic diagram of experimental setup for alkali lignin-enhanced pulverized coal char gasification chemical pathway
图 3 不同升温速率下的TG/DTG曲线
Figure 3 TG/DTG curves under different heating rates
(a): Pulverized coal char and oxygen carrier; (b): Alkali lignin and oxygen carrier; (c): Pulverized coal char/Alkali lignin (1∶1) with oxygen carrier; (d): Pulverized coal char/alkai lignin (1∶3) with oxygen carrier.
图 4 不同升温速率下煤焦碱木质素混合体系的理论失重量与实际失重量对比图
Figure 4 presents a comparative analysis between the theoretical and experimental weight loss of a coal-coke-lignin composite system at various heating rate
(a): Pulverized coal char/alkali lignin (1∶1) with oxygen carrier; (b): Pulverized coal char/alkai lignin (1∶3) with oxygen carrier.
图 5 不同升温速率下的拟合直线
Figure 5 Fitted lines at different heating rates
(a): Pulverized coal char and oxygen carrier; (b): Pulverized coal char/Alkali lignin (1∶1) with oxygen carrier; (c): Pulverized coal char /Alkai lignin (1∶3) with oxygen carrier.
图 6 反应温度对煤焦粉与碱木质素（1∶2）化学链气化过程的影响
Figure 6 Effect of reaction temperature on the chemical pathway gasification process of C pulverized coal char and alkali lignin （1∶2）
图 7 碱木质素加入量对碱木质素与煤焦粉化学链气化过程的影响
Figure 7 Effect of alkali lignin addition on the chemical pathway gasification process of alkali lignin and pulverized coal char
图 8 氧载体加入量对碱木质素与煤焦粉化学链气化过程的影响
Figure 8 Effect of oxygen carrier loading on the chemical pathway gasification process of alkali lignin and pulverized coal char
图 9 NiFe2O4氧载体的XRD谱图
Figure 9 X-ray diffraction (XRD) pattern of NiFe2O4 oxygen carrie
图 10 氧载体与煤焦粉和氧载体与煤焦粉和碱木质素两者混合物反应后的SEM照片
Figure 10 The SEM images of the oxygen carrier, the mixture of oxygen carrier and coal char, and the mixture of oxygen carrier with coal char and alkaline lignin after reaction
(a): Pulverized coal char (b): Pulverized coal char: alkali lignin =1∶2 (c): Pulverized coal char: alkali lignin =1∶3.
表 1 碱木质素和云南褐煤的工业分析和元素分析
Table 1 Proximate and ultimate analysis of lignin alkaline and coal char
Sample Ultimate analysis wdry/% Proximate analysis wdry/% AAEMs/(mg·kg−1) C N H S O* V M A FC Na K Mg Ca Lignin alkaline 59.4 0.09 5.30 3.17 32.0 41.49 34.39 19.10 5.02 93110 14193 76 292 Pulverized coal char 69.77 0.61 3.91 1.06 12.97 40.30 10.22 11.68 37.8 − − − − O*: by difference. 
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表 2 常用固相动力学模型
Table 2 Common solid-state kinetic models
Symbol f (α) G (α) D1 $ {1/2\alpha} $ $ {{\alpha }}^{2} $ D2 ${\text{[}-\text{ln}\left(1-\alpha\right)\text{]} }^{-\text{1} }$ $ {\alpha + }\left(1-\alpha\right){\ln(1-\alpha)} $ D3 $ \left({3}/{2}\right){\text{[}{\left(1-\alpha\right)}^{-{1}/{3}}-{1]}}^{-{1}} $ $ 1-(2/3)\alpha -{(1-\alpha )}^{2/3} $ D4 $ \text{(}{3}/{2)}{\left(1-\alpha\right)}^{{2}/{3}}{\text{[1}-{\left(1-\alpha\right)}^{{2}/{3}}\text{]}}^{-{1}} $ $ {\text{[1}-{\left(1-\alpha\right)}^{{1}/{3}}\text{]}}^{{2}} $ A1 $ 1-{\alpha } $ $ -\mathrm{l}\mathrm{n}(1-{\alpha }) $ A2 $ \text{2}\left(1-\alpha\right){\text{[}-\text{ln}\left(1-\alpha\right)\text{]}}^{\text{1}/\text{2}} $ $ {\text{[}-\text{ln}\left(1-\alpha\right)\text{]}}^{{1}/{2}} $ A3 3/(1−α)[−ln(1−α)]2/3 $ {\text{[}-\text{ln}\left(1-\alpha\right)\text{]}}^{\text{1}/\text{3}} $ R1 $ 2{(1-{\alpha })}^{1/2} $ $ 1-{(1-{\alpha })}^{1/2} $ R2 $ 3{(1-{\alpha })}^{2/3} $ $ 1-{(1-{\alpha })}^{1/3} $ C $ {(1-{\alpha })}^{2} $ $ {(1-{\alpha })}^{-1}-1 $
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表 3 不同固相动力学模型下的Pearson相关系数和残差平方和
Table 3 Pearson correlation coefficients and sum of squares of residuals for different solid-state kinetic models
Symbol Pulverized coal char Pulverized coal char: alkali lignin=1∶1 Pulverized coal char: alkali lignin=1∶3 Pearson RSS Pearson RSS Pearson RSS D1 −0.95783 0.07751 −0.88223 0.07730 −0.90771 0.07487 D2 −0.98287 0.06168 −0.96501 0.06173 −0.97443 0.05194 D3 −0.99219 0.03960 −0.98555 0.04032 −0.99325 0.02115 D4 −0.99239 0.07720 −0.98712 0.08862 −0.99641 0.02670 A1 −0.9522 0.34100 −0.91697 0.40541 −0.93641 0.34202 A2 −0.94155 0.08440 −0.81679 0.09102 −0.87767 0.07790 A3 −0.92689 0.03717 −0.39472 0.03616 −0.67311 0.03140 R1 −0.99327 0.00832 −0.96960 0.00874 −0.99472 0.00211 R2 −0.99097 0.01910 −0.97629 0.01853 −0.99519 0.00465 C −0.85667 16.7274 −0.82857 22.3155 −0.84368 21.2446
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表 4 不同条件下热解过程的活化能
Table 4 Activation Energies of Pyrolysis Processes under Different Conditions
Sample Heating
rate/(K·min−1)Activation energy
E/(kJ·mol−1)Pulverized coal char 5 76.17875 10 84.09264 15 97.56443 20 125.00554 Pulverized coal char:Alkali lignin =1∶1 5 16.74055 10 24.11223 15 23.7565 20 24.28225 Pulverized coal char:Alkali lignin =1∶3 5 14.01977 10 15.12626 15 15.46651 20 15.55402
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表 5 氧载体与煤焦粉、煤焦粉/碱木质素混合体系反应后比表面积与粒径分布
Table 5 BET specific area and particle size distribution after the reaction of the oxygen carrier with pulverized coal char, pulverized coal char/alkali lignin mixture system
Oxygen carrier BET specific surface area/(m2·g−1) Particle size distribution/μm d10% d50% d90% NiFe2O4/C 2.38 5.8 108.9 904.8 NiFe2O4/CA 3.28 60.3 267.8 868.2
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