Effect of oxidative torrefaction upgrade on physicochemical properties of rice straw
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摘要: 本研究通过模拟富氧燃烧烟气气氛探究了有氧烘焙过程中氧气和烘焙温度对稻秆理化特性的影响。结果表明,与氧气相比,温度对有氧烘焙的影响更加显著。在低温段(< 250 ℃),氧气对烘焙稻秆的质量和能量收率影响较小,但在高温段(> 250 ℃)作用明显。随着温度的上升(> 250 ℃),烘焙稻秆的质量和能量收率大幅下降。烘焙温度为250 ℃,氧气体积分数为6%是比较合适的有氧烘焙工况,此时烘焙稻秆的质量和能量收率能分别保持在70%和80%以上。提高温度主要增强了烘焙反应,氧化反应在氧气体积分数超过6%时作用明显。氯、钾的留存率随着温度和氧气的升高均表现出下降的趋势,但温度的影响更加显著。Abstract: Torrefaction atmosphere is one of the key problems in industrial application of torrefaction technology. In this paper, the effects of oxygen concentration and torrefaction temperature on the physicochemical properties of rice straw during oxidative torrefaction were investigated by simulating the atmosphere of oxy-fuel combustion flue gas. The results show that the effect of temperature on oxidative torrefaction is more significant compared with oxygen concentration. At low temperature (< 250 ℃), oxygen concentration has little effect on the mass and energy yield of torrefied rice straw, but it has obvious effect at high temperature (> 250 ℃). With the increase of temperature (> 250 ℃), the mass and energy yields of torrefied rice straw decrease significantly. When the temperature and oxygen concentration are 250 ℃ and 6%, respectively, it is a suitable oxidative torrefaction condition. Under this condition, the mass and energy yields of torrefied rice straw can be maintained above 70% and 80%, respectively. Increasing the temperature mainly enhances the torrefaction reaction, and the oxidation reaction has an obvious effect when the oxygen concentration exceeds 6%. The retention ratio of chlorine and potassium has an downward trend with the increase of temperature and oxygen concentration, and the effect of increasing temperature is more significant.
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Key words:
- biomass /
- oxidative torrefaction /
- oxygen concentration /
- chlorine /
- potassium
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表 1 稻秆的工业分析和元素分析(干燥基)
Table 1 Proximate and ultimate analyses of RRSa (dry basis)
Proximate analysis
w/%Ultimate analysis
w/%QHHV/
(kJ·kg−1)A V FCa C H N Ob 16217 9.86 76.27 13.87 40.31 5.44 0.94 43.45 a: raw rice straw, b: calculated by difference 表 2 烘焙稻秆的工业分析和元素分析
Table 2 Proximate and ultimate analyses of TRSa (dry basis)
100%CO2-0%O2-TRS 98%CO2-2%O2-TRS 200 ℃ 225 ℃ 250 ℃ 275 ℃ 300 ℃ 200 ℃ 225 ℃ 250 ℃ 275 ℃ 300 ℃ Proximate analysis w/% A 10.12 10.51 10.79 12.84 16.76 9.82 10.12 10.60 13.39 17.13 V 75.62 74.66 73.87 68.78 56.47 75.79 73.70 73.17 58.04 50.86 FC 14.26 14.83 15.34 18.38 26.77 14.39 16.18 16.23 28.57 32.01 Ultimate analysis w/% C 43.69 44.08 44.46 47.19 48.99 43.59 43.56 44.51 47.69 50.39 H 5.41 5.28 4.97 4.29 3.83 5.55 5.43 5.18 4.42 3.02 N 1.16 1.36 1.26 1.28 1.19 1.12 1.22 1.33 1.25 1.14 Ob 39.62 38.77 38.52 34.40 28.77 39.92 39.67 38.38 33.25 28.32 QHHV/(kJ·kg−1) 17412 17573 17679 18509 18963 17368 17371 17718 18694 19119 96%CO2-4%O2-TRS 94%CO2-6%O2-TRS 200 ℃ 225 ℃ 250 ℃ 275 ℃ 300 ℃ 200 ℃ 225 ℃ 250 ℃ 275 ℃ 300 ℃ Proximate analysis w/% A 9.98 10.78 11.03 14.14 19.13 10.12 10.52 12.17 14.20 19.46 V 77.41 75.32 70.26 55.94 42.11 74.44 72.44 69.23 54.09 41.86 FC 12.61 13.90 18.71 29.92 38.76 15.44 17.05 18.60 31.71 38.68 Ultimate analysis w/% C 42.67 43.23 45.67 47.91 51.36 42.90 43.86 45.46 49.19 49.47 H 5.65 5.45 5.04 4.20 3.16 5.59 5.42 5.27 4.00 3.04 N 1.03 1.09 1.38 1.25 1.35 1.39 1.29 1.53 1.36 1.39 Ob 40.68 39.45 36.88 32.50 24.99 40.02 38.92 35.57 31.24 26.64 QHHV/(kJ·kg−1) 17021 17237 18118 18720 19480 17154 17486 18085 19098 18902 92%CO2-8%O2-TRS 90%CO2-10%O2-TRS 200 ℃ 225 ℃ 250 ℃ 275 ℃ 300 ℃ 200 ℃ 225 ℃ 250 ℃ 275 ℃ 300 ℃ Proximate analysis w/% A 10.21 10.68 11.70 15.71 22.17 10.15 10.86 11.74 16.65 23.84 V 73.83 71.18 69.99 56.42 42.24 74.14 70.95 69.61 56.45 41.36 FC 15.96 18.14 18.30 27.87 35.58 15.71 18.19 18.64 26.89 34.80 Ultimate an alysis w/% C 43.36 44.74 45.09 48.01 50.01 43.01 44.97 45.58 48.15 50.54 H 5.69 5.42 5.29 4.20 2.72 5.66 5.45 5.30 4.11 2.73 N 1.19 1.25 1.39 1.14 1.38 1.24 1.11 1.15 1.36 1.22 Ob 39.56 37.90 36.54 30.94 23.71 39.94 37.61 36.23 29.73 21.67 QHHV/(kJ·kg−1) 17293 17801 17936 18737 18949 17172 17868 18082 18791 19068 a: torrefied rice straw, b: calculated by difference 表 3 烘焙稻秆的氯、钾含量
Table 3 Content of Cl and K in TRS under different conditions
RRS 6%O2-TRS 250°C-TRS 200 ℃ 225 ℃ 250 ℃ 275 ℃ 300 ℃ 0 2% 4% 6% 8% 10% Contents of chlorine and potassium w/% Cl 0.626 0.667 0.684 0.752 0.951 1.259 0.707 0.722 0.747 0.752 0.784 0.811 K 1.133 1.175 1.196 1.332 1.643 2.16 1.256 1.278 1.328 1.332 1.394 1.452 表 4 不同工况下烘焙稻秆的氯、钾留存率
Table 4 Retention ratio of Cl and K of TRS under different conditions
RRS 6%O2-TRS 250 ℃-TRS 200 ℃ 225 ℃ 250 ℃ 275 ℃ 300 ℃ 0 2% 4% 6% 8% 10% Cl/% 100 94.49 93.97 87.62 81.56 78.92 89.27 88.10 87.83 87.62 87.45 86.50 K/% 100 91.97 90.78 85.75 77.86 74.81 87.62 86.17 86.27 85.75 85.92 85.57 Cl/K 0.61 0.641 0.650 0.634 0.666 0.676 0.630 0.635 0.629 0.634 0.629 0.620 -
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