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2020年我国餐厨垃圾产量达到1.3×108 t[1]。厌氧发酵技术由于其无害化、资源化、减量化效果好,因此成为我国餐厨垃圾处理的主要技术手段[2]。餐厨垃圾厌氧发酵过程会产生大量的沼渣,沼渣营养成分不稳定且重金属含量高,如果处理不当会造成二次污染。目前,国内外对沼渣的综合利用途径主要是作为有机肥料施用于土壤[3],但由于经济和环境问题应用受到限制[4],因此,寻找更适当的沼渣处理技术尤为必要。
热解技术在处理沼渣过程中,能产生附加值较高的生物炭及热解油气,被认为是经济可行的沼渣无害化与资源化利用技术。AGRAFIOTI等[5]发现,沼渣中大分子物质主要转化为液体生物油。HUANG等[6]和JIN等[7]发现,热解气可以作为燃料,生物油可以升级为液体生物燃料或生物基化学品的原料,固体残渣也可以用作吸附剂。但是,由于沼渣含水率高、有机质含量低、灰分高的特性,在热解过程中存在能耗高、挥发分难析出、热解产物品质低的问题[8]。园林废弃物作为生物质,有机质含量高、灰分少、热值高,将园林废弃物与餐厨沼渣混合热解理论上可以解决上述问题,同时亦可以实现园林废弃物的无害化处理。
由于2种物料性质不尽相同,在混合热解过程中,园林废弃物与餐厨厌氧沼渣之间可能存在一定的相互作用,从而加速或抑制热解过程,但目前针对园林废弃物与餐厨厌氧沼渣混合热解的研究较少。本研究以园林废弃物和餐厨厌氧沼渣为原料,采用热重分析(TG)-微分热重(DTG)-差式扫描量热法(DSC)探究园林废弃物与沼渣单独热解及混合热解时的热解特性,并进行动力学分析,研究混合比例和升温速率对园林废弃物和沼渣混合热解的影响,以期通过加入园林废弃物改善餐厨厌氧沼渣热解特性。本研究拟为园林废弃物与餐厨厌氧沼渣混合热解处理提供参考。
园林废弃物与餐厨厌氧沼渣混合热解特性及动力学分析
Pyrolysis characteristics and kinetic analysis of co-pyrolysis of garden waste and kitchen anaerobic biogas residue
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摘要: 为了探究园林废弃物和餐厨厌氧沼渣的热解特性以及2者混合热解的交互作用。采用热重分析法对餐厨厌氧沼渣、园林废弃物及其不同比例的混合样品热解特性进行了分析,并研究了混合比例和升温速率对热解过程的影响。结果表明,园林废弃物与沼渣单独热解时,园林废弃物热解反应活性高且能耗低,热解终温为400 ℃左右;沼渣热解反应活性低且能耗高,热解终温为600 ℃左右。混合热解实验中,随着园林废弃物添加比例升高,样品热解残余率不断下降,综合热解指数不断增大,园林废弃物与沼渣混合热解适宜的添加比例为50%,热解终温为600 ℃左右。采用Coats-Redfern积分法对园林废弃物、沼渣及混合样品进行动力学分析,园林废弃物和餐厨厌氧沼渣反应活化能分别为12.08和1.79 kJ·mol−1,混合样品实际活化能均略高于理论值。这说明,2者混合热解过程中存在一定抑制作用,但对热解过程影响不大。本研究结果可为园林废弃物与餐厨厌氧沼渣混合热解处理提供参考。Abstract: To explore the pyrolysis characteristics of garden waste and kitchen anaerobic biogas residue and the interaction of their mixed pyrolysis. Thermogravimetric analysis was used to analyze the pyrolysis characteristics of kitchen anaerobic biogas residue, garden waste and the mixed samples in different proportions, and the effects of mixing proportion and heating rates on the pyrolysis process were studied. The results showed as follows, when the garden waste and biogas residue were pyrolyzed separately, the pyrolysis reaction activity of garden waste was high and the energy consumption was low, and the final pyrolysis temperature was about 400 ℃. While biogas slag had low pyrolysis activity and high energy consumption, and the final pyrolysis temperature was around 600 ℃. In the mixed pyrolysis experiment, with the increase of the addition proportion of garden waste, the sample pyrolysis residual rate decreased and the comprehensive pyrolysis index increased. The appropriate proportion ratio of garden waste and biogas residue was 50%, and the final pyrolysis temperature was about 600 ℃. Kinetic analysis of garden waste, biogas residue and mixed samples was performed by the Coats-Redfern integral method. The activation energies of garden waste and kitchen anaerobic biogas residue were 12.08 kJ·mol−1 and 1.79 kJ·mol−1, respectively. The actual activation energies of the mixed samples were slightly higher than the theoretical values, indicating that the two have a certain inhibitory effect in the mixed pyrolysis process, while the influence was not significant. The research results can provide a reference for the mixed pyrolysis treatment of garden waste and kitchen anaerobic biogas residue.
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Key words:
- garden waste /
- kitchen anaerobic biogas residue /
- pyrolysis /
- kinetics /
- thermogravimetric analysis
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表 1 样品工业分析及元素分析(干燥基)
Table 1. Industrial Analysis and elemental analysis of samples (dry basis)
样品 工业分析/% 元素分析/% 热值/(kcal·kg−1) 挥发分 灰分 固定碳 C H O N S GW 75.72 3.35 20.93 48.97 6.57 40.25 0.52 0.33 4 499 BR 50.52 45.45 4.02 22.28 3.75 25.11 2.67 0.75 1 829 表 2 样品热解特性参数及综合热解指数
Table 2. Pyrolysis characteristic parameters and comprehensive pyrolysis index of samples
样品 v/(℃·min−1) ti/℃ te/℃ (dw/dt)max/(%·℃−1) tmax/℃ (dw/dt)mean/(%·℃−1) η/% D/10−8 GW 10 272 410 −0.571 337 −0.089 25.03 12.52 G1B9 10 187 794 −0.314 725 −0.075 34.53 5.51 G3B7 10 248 764 −0.269 722 −0.077 32.66 2.95 G5B5 10 179 750 −0.369 337 −0.079 31.05 8.36 BR 10 188 783 −0.336 725 −0.072 38.15 5.42 表 3 不同升温速率下样品热解特性参数及综合热解指数
Table 3. Pyrolysis characteristic parameters and comprehensive pyrolysis index of samples at different heating rates
样品 v/(℃·min−1) ti/℃ te/℃ (dw/dt)max/(%·℃−1) tmax/℃ (dw/dt)mean/(%·℃−1) η/% D/10−8 10 248 764 −0.269 722 −0.077 32.66 2.95 G3B7 20 249 769 −0.259 743 −0.076 33.83 2.71 30 252 772 −0.260 339 −0.075 36.74 2.51 表 4 不同升温速率下样品热解动力学参数
Table 4. Pyrolysis kinetic parameters of samples at different heating rates
样品 v/(℃·min−1) 温度区间/℃ 方程 反应级数 R2 E/(kJ·mol−1) A/min−1 G3B7 10 200~400 Y=-794.013X-9.100 n=3 0.913 6.61 0.088 6 20 Y=-851.601X-9.069 n=3 0.961 7.11 0.196 1 30 Y=-862.726X-9.167 n=3 0.944 7.20 0.172 3 表 5 不同质量配比样品的热解动力学参数
Table 5. Pyrolysis kinetic parameters of samples with different mass ratios
样品 v/(℃·min−1) 方程 反应级数 R2 E/(kJ·mol−1) A/min−1 GW 10 Y=−1 453.05X−7.16 n=1 0.933 5 12.08 11.275 G1B9 10 Y=−323.27X−10.97 n=3 0.943 2 2.68 0.056 G3B7 10 Y=−794.01X−9.10 n=3 0.912 7 6.60 0.089 G5B5 10 Y=−1182.98X−7.72 n=3 0.909 1 9.83 5.231 BR 10 Y=−215.85X−11.26 n=3 0.953 8 1.79 0.028 G1B9* 10 Y=−321.01X−10.89 n=3 0.927 7 2.66 0.051 G3B7* 10 Y=−584.94X−10.06 n=3 0.919 5 4.86 0.026 G5B5* 10 Y=−896.19X−8.94 n=3 0.964 8 7.45 1.174 注:GiBi为实验样品动力学分析结果;GiBi*为理论计算值,通过单组份热重的实验值对混合组分的线性叠加计算得到。 -
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