Characteristics of NOx precursors and their formation mechanism during pyrolysis of herb residues
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摘要: 以凉茶药渣（HTW）和青霉素菌渣（PMW）为对象，结合热重（TGA）和X射线光电子能谱（XPS）表征，在水平管式反应器上对比研究了热解NOx前驱物的生成特征，考察了热力因素和燃料理化特性的影响。结果表明，蛋白质N为主要原料N结构，HTW占全部，PMW超过80%，决定了主导NOx前驱物为NH3；热力因素不改变此主导性，但会影响前驱物生成路径，改变组分比例及总产率，其强弱顺序为：高温快速>高温慢速>低温快速≈低温慢速；基于高温快速热解，大粒径和低含水率可分别降低总产率5%-11%和4%-6%；燃料组分影响NH3产率，低温或慢速下，N结构差别使PMW>HTW；高温快速下，灰分元素差异使PMW < HTW；半焦N结构及N分布表明，典型热解条件下总产率为20%-45%，与药渣种类无关，可为其清洁利用提供参考。Abstract: Based on two herb residues-herbal tea waste (HTW) and penicillin mycelial waste (PMW), characteristics of NOx precursors during their pyrolysis were investigated in a horizontal tubular reactor with the help of XPS and TGA technologies. Effects of thermal conditions and physicochemical properties of fuels were discussed and compared. The results demonstrate that protein-N is the main nitrogen form for both HTW and PMW, determining the dominance of NH3 among NOx precursors at any operational conditions. Thermal conditions would still change the ratio and total yield by intrinsically influencing their formation pathways. Subsequently, the effects could be sequenced as follows:high temperatures with rapid pyrolysis > high temperatures with slow pyrolysis > low temperatures with rapid pyrolysis ≈ low temperatures with slow pyrolysis. Moreover, at high temperatures with rapid pyrolysis, increase in particle size or decrease in moisture content would result in reduction of total yield by 5%-11% and 4%-6%, respectively. In addition, NH3 yield is produced at low temperatures or slow pyrolysis with sequence of PMW > HTW and vice versa, depending on components in the fuels. Consequently, analyses on nitrogen forms in char and nitrogen distribution indicate that total yield of 20%-45% is observed to be independent of fuel type under typical pyrolysis conditions, which may provide helpful guidance for the clean reutilization of herb residues.
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Key words:
- HTW /
- PMW /
- NOx precursors /
- pyrolysis /
- NH3 /
- total yield
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图 4 两种热解类型下NOx前驱物随热解温度的变化
Figure 4 Change of each NOx precursor vs. pyrolysis temperature under two pyrolysis types
(a): slow pyrolysis-15 ℃/min; (b): rapid pyrolysis
图 5 热解温度及类型对NOx前驱物生成的影响
Figure 5 Effects of pyrolysis temperature and type on the formation of NOx precursors
(a): ratio of HCN-N/NH3-N; (b): total yield of NOx precursors
图 6 快速热解下粒径对NOx前驱物生成的影响
Figure 6 Effect of particle size on the formation of NOx precursors under rapid pyrolysis
(a): ratio of HCN-N/NH3-N; (b): total yield of NOx precursors
图 7 快速热解下燃料含水率对NOx前驱物生成的影响
Figure 7 Effect of moisture content on the formation of NOx precursors under rapid pyrolysis
(a): ratio of HCN-N/NH3-N; (b): total yield of NOx precursors
图 8 快速热解各温度下半焦XPS (N 1s) 谱图
Figure 8 N 1s XPS spectra of Char-N at different temperature for rapid pyrolysis
(a), (b), (c), (d): 300, 500, 700, 800 ℃-HTW; (e), (f), (g), (h): 300, 500, 700, 800 ℃-PMW
图 9 快速热解N结构相对含量随温度的变化
Figure 9 Relative amount of each nitrogen functionality vs. the temperature under rapid pyrolysis
(a): HTW; (b): PMW
图 10 快速热解N分布随温度的变化
Figure 10 Nitrogen distribution vs. the temperature under rapid pyrolysis
(a): HTW; (b): PMW
表 1 药渣原料特性
Table 1 Properties of herb residues
Sample Proximate analysis wd/% Ultimate analysis wdsf/% V FC A C H S N Oa HTW 67.71 15.63 16.66 51.14 6.80 0.18 3.37 38.51 PMW 78.95 12.73 8.32 48.73 7.14 0.57 8.05 35.52 Ash analysis (expressed as w/% of metal oxides) SiO2 Al2O3 MgO Na2O Fe2O3 P2O5 CaO K2O TiO2 ZnO CuO SrO 21.98 7.92 7.66 0.40 4.82 4.56 20.78 7.64 0.44 0.09 0.03 0.08 0.39 0.14 3.62 2.85 0.50 30.82 22.64 19.15 0.01 0.09 0.02 0.03 a: by difference 
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表 2 实验因素及操作条件
Table 2 Operational conditions chosen for the experiments
Conditions Value range Pyrolysis temperature t/℃ 300, 500, 600, 700, 800, 900 Heating rate r/(℃·min-1) slow pyrolysis: 15; rapid pyrolysis: about 103 Particle size d/μm 0-300, 300-600, 600-900 Moisture content w/% 0, 5, 10, 15, 20
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