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摘要: 研究了生物质复合团块在高炉中的反应行为，该复合团块主要成分(质量分数)为：11.1% C、72.7% Fe3O4、11.25% FeO、0.77% Fe和4.67% 脉石。并对高炉环境下复合团块的反应行为进行了建模，通过高炉气氛下的等温动力学实验确定模型参数并进行了模型验证。进一步，结合模型模拟，模拟高炉环境的实验和团块微观结构分析，对模拟高炉条件下和实际高炉条件下团块的反应行为进行了分析。研究结果表明：模拟高炉条件下，在60 min (973 K) 到120 min (1273 K) 期间， 团块的微观结构发生明显变化，其微观结构由渣相网络结构向金属铁网络结构转变。在实际高炉中，复合团块的反应进程主要包括三个阶段：团块的高炉煤气还原（473~853 K）、团块的高炉煤气还原和部分自还原（853~953 K）以及团块的完全自还原（953~1150 K）。在团块自还原参与阶段，与烧结矿相比，团块内氧化铁还原速率更快；与焦炭相比，团块内生物质炭气化速率更高。同时，在此阶段，团块有提高高炉煤气利用率和降低高炉热储备区温度的作用。Abstract: Blast furnace (BF) ironmaking is considered to be the most popular technology to meet the increasing steel demand worldwide, but it is responsible for the most CO2 emissions in the blast furnace-basic oxygen furnace production process. The utilization of biomass/biochar in BF ironmaking is an effective countermeasure to reduce its CO2 emission, as biomass/biochar is a renewable carbon source and environment neutron. Charging the biochar composite briquette (BCB) is a convenient method to introduce biomass/biochar into BF. The present research investigates the reaction behavior of the BCB in the BF. The BCB for the BF was prepared using cold briquetting followed by low-temperature heat treatment. The BCB was composed of 11.1% carbon, 72.7% magnetite, 11.25% wustite, 0.77% metallic iron, and 4.67% gangue (all in mass fraction). The BCB reaction model in the BF was developed considering the step-wise gaseous reduction of iron-oxide particles, CO2 gasification of biochar particles, internal gas diffusion in the BCB, and mass transfer between the BCB and the environment. Isothermal BCB reaction tests were conducted for model validation. Using the model, the changes of the BCB iron-oxide reduction fraction and biochar conversion rate and the BCB microstructure evolution under simulated BF conditions were analyzed. The model was also applied to predict the change of the BCB iron-oxide reduction fraction, change of the BCB biochar conversion, change of the BCB CO generating rate, and change of the BCB CO2 generation rate along a solid flowing path near the mid-radius in an actual BF. Results showed that under simulated BF conditions, the BCB underwent fast self-reduction and structure changes (forming low-melting compounds and transforming from the slag matrix to the iron network) from 60 min (973 K) to 120 min (1273 K). In an actual BF, the BCB reaction route is mainly divided into three stages: (1) reduction by BF gas (473–853 K), (2) reduction by the BF gas and partial self-reduction (853–953 K), and (3) full self-reduction (953–1150 K). In the stages involving BCB self-reduction, the iron oxide in the BCB reduces faster than the sinter, and the biochar gasifies faster than the coke. Moreover, in these stages, the BCB has the functions of increasing the BF gas utilization efficiency and lowering the temperature level of the BF thermal reserve zone.
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Key words:
- biochar /
- composite briquette /
- blast furnace /
- reaction model /
- reaction behavior
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图 1 模拟高炉条件下气体成分和温度变化曲线
Figure 1. Simulated blast furnace (BF) gas composition and temperature profiles
图 4 团块样品的SEM图像.（a）烧结氧化铁基体; （b）生物质炭颗粒的微观形貌
Figure 4. SEM images of the BCB sample: (a) sintered iron-oxide texture; (b) microstructure of biochar particles
图 5 模拟高炉条件下部分反应后复合团块冷抗碎强度的变化
Figure 5. Change of the BCB cold crushing strength after partial reaction under simulated BF conditions
图 7 不同实验方案下实验和模型预测的质量损失曲线对比
Figure 7. Measured and model-predicted mass-loss curves under different scenarios
图 8 生物质炭复合团块样品的图像. (a) 原始图像; (b) 在方案Ⅰ下反应后图像;(c) 在方案Ⅱ下反应后图像; (d) 在方案Ⅲ下反应后图像
Figure 8. Images of the BCB sample: (a) original; (b) after reaction under scenario Ⅰ; (c) after reaction under scenario Ⅱ; (d) after reaction under Scenario Ⅲ
图 9 模拟高炉条件下生物质炭复合团块还原行为. (a)还原分数随时间的变化; (b)生物炭转化率随时间的变化
Figure 9. BCB reduction behavior under simulated BF conditions: (a) change in reduction fraction with time; (b) change in biochar conversion with time
图 10 不同时间下生物质炭复合团块的XRD谱. (a) 60 min; (b) 90 min; (c) 120 min
Figure 10. XRD patterns of BCB at different times: (a) 60 min; (b) 90 min; (c) 120 min
图 11 不同时间生物质炭复合团块的扫描电镜图像. (a) 60 min; (b) 90 min; (c) 120 min
Figure 11. SEM images of BCB at different times: (a) 60 min; (b) 90 min; (c) 120 min
图 12 （a）用于建模的固体流动路径的图示;（b）高炉变量沿路径的变化
Figure 12. (a) Illustration of solid flowing path for modeling; (b) change of BF variables along the path
图 13 实际高炉中的生物质炭复合团块反应行为.（a）沿路径的还原分数变化;（b）沿路径的生物炭转化率变化;（c）沿路径的CO和CO2生成速率变化;（d）在1150至1168 K温度下CO和CO2的生成速率变化
Figure 13. BCB reaction behavior in the BF: (a) change in reduction fraction along the path; (b) change in biochar conversion along the path; (c) changes in generation rates of CO and CO2 along the path; (d) changes in generation rates of CO and CO2 from 1150 to 1168 K
图 14 生物质炭复合团块和高炉煤气在生物质炭复合团块自还原区区域的CO还原势
Figure 14. CO potentials of the BCB and the BF gas in the zone with BCB self-reduction
表 1 制备用生物炭工业分析(质量分数)
Table 1. Proximate analysis of the prepared biochar fines
% Volatile Moisture Fixed carbon Ash 3.91 2.95 88.23 4.91 
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表 2 等温团块动力学实验方案
Table 2. Scenarios for isothermal biochar composite briquette ( BCB) kinetic tests
Scenario Temperature/K CO2 volume fraction/% CO volume fraction /% N2 volume fraction /% Ⅰ 1073 20 30 50 Ⅱ 1173 15 35 50 Ⅲ 1273 10 40 50
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表 3 模型中涉及的反应
Table 3. Reactions involved in the model
No. Reaction Reaction rate/(mol·m–3·s–1) Ref. 1 $ {\text{3 F}}{{\text{e}}_{\text{2}}}{{\text{O}}_{\text{3}}}\left( {\text{s}} \right) + {\text{CO}}\left( {\text{g}} \right) = 2{\text{ F}}{{\text{e}}_{\text{3}}}{{\text{O}}_{\text{4}}}\left( {\text{s}} \right) + {\text{C}}{{\text{O}}_{\text{2}}}({\text{g}}) $ ${R_i} = \dfrac{ {({P_{ {\text{CO} } } } - {P_{ {\text{C} }{ {\text{O} }_{\text{2} } } } }/{K_i})/(8.314T)} }{ {({K_i}/({k_i}(1 + {K_i}))} }{(1 - {f_i})^{2/3} }{a_ {\text{gs} } }$(i=1,2,3), ${K_1} = \exp ({\text{7} }{\text{.255 + 3720} }/T),$ ${k_1} = \exp ( - 1.445 - 6038/T),$ ${K_2} = \exp (5.289 - 4711/T),$ ${k_{\text{2}}} = \exp ( - {\text{2}}{\text{.515}} - {\text{4811}}/T),$ ${K_3} = \exp ( - 3.127 + 2879.63/T),$ ${k_3} = \exp (0.805 - 7385/T)$ [24,27] 2 $ {\text{F}}{{\text{e}}_{\text{3}}}{{\text{O}}_{\text{4}}}\left( {\text{s}} \right) + {\text{CO}}\left( {\text{g}} \right) = 3{\text{ FeO}}\left( {\text{s}} \right){\text{ + C}}{{\text{O}}_{\text{2}}}({\text{g}}) $ 3 $ {\text{FeO}}\left( {\text{s}} \right) + {\text{CO}}\left( {\text{g}} \right) = {\text{Fe}}\left( {\text{s}} \right){\text{ + C}}{{\text{O}}_{\text{2}}}({\text{g}}) $ 4 $ {\text{C}}\left( {\text{s}} \right) + {\text{C}}{{\text{O}}_{\text{2}}}\left( {\text{g}} \right) = 2{\text{ CO(g)}} $ $\begin{gathered} {R_4}{\text{ = } }{\rho _{ {\text{C,0} } } }{k_{\text{4} } }{\left( { {\text{1} } - {f_{\text{4} } } } \right)^{ {\text{2/3} } } }{\text{(} }{P_{ {\text{C} }{ {\text{O} }_{\text{2} } } } }{\text{/1} }{\text{.01} } \times {\text{1} }{ {\text{0} }^{\text{5} } }{\text{)/} }{M_{\text{C} } }_{\text{, } } \hfill \\ {k_4} = 1{\text{5} }00\exp ( - 13{\text{1} }00{\text{0} }/RT) \hfill \\ \end{gathered}$ [28]
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表 4 生物质炭复合团块的矿物组成 （质量分数）
Table 4. Mineralogical composition of BCB
% Carbon Magnetite Wustite Metallic iron Gangue 11.10 72.21 11.25 0.77 4.67
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表 5 不同的实验方案下团块的反应参数和实验测量值及模型预测值
Table 5. Measured and model-predicted parameters of the BCB reduced under different scenarios
Scenario BCB reduction fraction BCB biochar conversion Measurement Model prediction Measurement Model prediction I 0.14 0.16 0.10 0.20 II 0.44 0.49 0.33 0.53 III 0.85 0.90 0.86 0.94
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