Effect of gas-pressurized torrefaction on the upgrading and pyrolysis characteristics of corn stalk
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摘要: 在不同温度及压力下对玉米秸秆进行了烘焙,通过元素分析、FT-IR、TGA以及固定床热解等方式分析了烘焙产物的理化特性与热解特性,研究了气体加压烘焙对生物质燃料特性及热转化行为的影响,结果表明,烘焙样品的脱氧效率及能量密度均随烘焙温度的升高而增加;在相同质量收率时,加压烘焙所需温度比常压烘焙低约40 ℃,且能量收率、碳收率、脱氧效率以及烘焙产物的能量密度分别为常压烘焙的1.125、1.142、1.539和1.131倍;加压烘焙样品比常压烘焙表现出更好的疏水性,且更易于脱水;当烘焙温度为250 ℃时,加压烘焙样品热解气相产物中CH4和H2含量分别为常压烘焙的2.135和1.439倍;加压烘焙样品热解液相产物中酚类相对含量增加,最高可达51.11%,而呋喃类和酸类物质含量则明显下降。相较于常压烘焙,加压烘焙在相同温度下对生物质具有更好的提质效果。Abstract: Corn straw was torrefied under at different temperatures and the torrefied products were characterized by proximate analysis, ultimate analysis, FT-IR, TGA and pyrolysis experiments; the effect of gas-pressurized torrefaction on the upgrading and pyrolysis characteristics of corn stalk was investigated. The results indicate that the deoxidation efficiency and energy density of torrefied products under both atmospheric pressure (AP) and gas pressured (GP) conditions increase with the increase of torrefaction temperature. The temperature required for GP torrefaction is almost 40 °C lower than that for AP torrefaction to obtain the same mass yield. The energy yield, carbon yield, deoxidation efficiency and the energy density of GP-torrefied corn straw are 1.125, 1.142, 1.539 and 1.131 times higher than those of AP-torrefied one, respectively. The GP-torrefied corn straw shows better hydrophobicity and is easier to dehydrate. In addition, the pyrolysis of GP-torrefied corn straw produces significantly higher fractions of CH4 and H2 in the gaseous product than the pyrolysis of AP-torrefied one; meanwhile, the relative content of phenols in the liquid products for the pyrolysis of GP-torrefied samples also increases up to 51.11%, whereas the contents of furans and acids decrease considerably. All these suggest that GP torrefaction performs better in biofuel upgrading than AP torrefaction under the same temperature.
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Key words:
- corn stalk /
- gas-pressurized torrefaction /
- upgrading /
- pyrolysis characteristics
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表 1 玉米秸秆灰分的XRF成分分析
Table 1 XRF analysis of corn stalk ash
Sample Content w/% SiO2 K2O CaO2 MgO P2O5 Al2O3 Fe2O3 Na2O Corn stalk 44.01 17.97 9.48 7.13 5.92 3.13 2.47 0.59 表 2 原生及烘焙玉米秸秆的基本性质
Table 2 Basic properties of raw and torrefied biomass samples
Sample Proximate analysis w/ %(dry base) Elemental analysis w/%(dry base) QHHV/(MJ·kg−1) V FC A C H O* N Raw 72.67 19.63 7.70 43.70 5.34 40.43 2.83 17.65 180-AP 72.42 19.84 7.74 44.73 5.21 40.23 2.09 17.91 210-AP 71.09 21.12 7.79 44.95 5.14 40.12 2.00 17.97 230-AP 68.06 22.63 9.31 45.25 5.18 38.22 2.04 18.09 250-AP 66.56 22.30 11.14 45.42 4.89 36.29 2.26 18.15 180-GP-5 65.40 26.0 8.60 50.12 4.97 34.36 1.95 19.82 210-GP-5 55.51 31.22 13.27 52.14 4.76 27.69 2.14 20.53 230-GP-5 53.82 31.58 14.60 55.00 4.79 23.49 2.12 21.67 250-GP-5 48.96 35.79 15.25 57.37 4.80 19.97 2.62 22.71 250-GP-1 48.49 36.38 15.13 57.02 4.80 20.36 2.69 22.58 250-GP-3 48.92 36.02 15.06 57.48 4.81 20.02 2.63 22.77 250-GP-7 48.53 35.88 15.59 58.20 4.79 18.79 2.63 23.06 O*:calculated by difference 表 3 不同温度5 MPa加压烘焙需要的初始压力与加压能耗
Table 3 Initial pressure and energy consumption for 5 MPa GP torrefaction at different temperatures
Torrefaction temperature/℃ Initial pressure/MPa Energy consumption/MJ 180 3.29 2.87 210 3.09 2.65 230 2.96 2.51 250 2.85 2.39 表 4 原生及烘焙样品的热解特性参数
Table 4 Pyrolysis parameters of the raw and torrefied corn stalk samples
Sample ti/℃ tp/℃ Rmax/(%·min−1) Rv/(%·min−1) wf/% Δt1/2/℃ Di/10−7 Raw 199.00 320.40 5.88 0.92 12.06 252.67 3.65 180-AP 231.00 325.96 5.52 0.93 19.75 250.00 2.93 210-AP 247.71 327.28 6.52 0.92 20.65 268.55 2.99 230-AP 260.99 326.69 6.74 0.90 22.68 286.56 2.76 250-AP 287.49 326.45 2.74 0.61 41.73 299.33 0.98 180-GP 235.64 316.11 4.38 0.93 20.04 272.83 2.15 210-GP 240.74 320.46 3.81 0.77 32.88 285.45 1.73 230-GP 237.19 319.87 2.56 0.69 40.05 283.15 1.19 250-GP 267.92 432.99 1.32 0.55 47.16 288.87 0.40 表 5 原生及烘焙样品的动力学参数
Table 5 Kinetic parameters for the pyrolysis of raw and torrefied corn straw samples.
Sample Temperature range/℃ E/(kJ·mol−1) A/min−1 R² Raw 220−350 37.99 1.14×104 0.9989 180-AP 220−350 55.43 5.09×105 0.9849 210-AP 220−350 70.97 1.32×107 0.9900 230-AP 220−350 81.47 9.89×107 0.9970 250-AP 220−350 68.44 1.15×107 0.9929 180-GP 220−350 49.07 7.61×104 0.9974 210-GP 220−350 49.73 7.79×104 0.9985 230-GP 220−350 41.17 9.38×103 0.9984 250-GP 220−450 34.11 8.05×102 0.9851 -
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