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厨余垃圾是指产生于居民小区经大类粗分后的有机垃圾。近年来,生活垃圾中厨余垃圾的比例逐渐增加,甚至高达70%~80%[1-2]。因厨余垃圾具有有机成分多、含水率高、易腐烂、热值低、有害成分少等特点[3],高湿的厨余垃圾给收集、运输以及末端的处理处置都带来一定的难度。另外,高含水率厨余垃圾还使得生活垃圾不同组分间相互粘连,机械分选效果差,也限制了通过分选实现垃圾处理过程优化的可能性[4]。生物干化是近几年来逐步兴起的一种生活垃圾预处理技术,与热干化不同,它无需消耗外界热能,而利用垃圾中可生物降解的有机物好氧分解释放的热量,使垃圾中水分汽化,通过强制通风对流,将汽化后的水蒸气带出,从而降低生活垃圾水分[5]。生物干化技术追求的目标是通过最小的有机质降解实现最大水分去除,快速去除有机物料中水分。经生物干化过程预处理后含水率较低的厨余垃圾仍保留了大部分的有机物,具有较高的热值,可以进行直接焚烧处理,或经过进一步加工后制备垃圾衍生燃料[6]。
由于厨余垃圾含水率高、C/N低、物料致密,通常在厨余垃圾堆肥或生物干化过程中通过添加辅料来调节理化性质。秸秆、木屑、稻壳、菌糠等不同的生物质辅料已被用于调节厨余垃圾好氧生物转化的含水率、C/N比和孔隙率[7-10]。这种添加辅料的联合生物干化方式既可以处理生物质废弃资源,同时也可将厨余垃圾高效地转化为垃圾衍生燃料(RDF)。目前, 生物干化技术主要用于干化脱水污泥[11-12]。GEA等[7]发现脱水污泥中添加20%的玉米棒作为辅料,可获得较高的水分去除率。CAI等[13]使用木屑作为辅料调节污泥的含水率进行生物干化。不同种类的辅料可以用来调节厨余垃圾生物干化的理化特性,同时也会改变物料的降解特性和组成,从而影响厨余垃圾燃烧热特性。
目前,大部分研究集中于利用生活垃圾中的塑料、纸质以及纤维等高热值的组分制备垃圾衍生燃料(RDF),这些组分的热解特性以及动力学参数已有报道[14-16]。LI等[17]研究了厌氧消化对污泥热解特性的影响,发现与原始污泥相比,经厌氧发酵后的沼渣的质量损失在180~550 ℃时较低,但在550~900 ℃时较高。ZHANG等[18]研究了混合生活垃圾生物干化过程的燃烧特性,发现生物干化过程可使混合垃圾的热值和表观活化能提高,这主要是由于有机质的降解使混合垃圾中的塑料占比增加,也意味着生物干化过程会使混合垃圾的燃烧更难。然而,生活垃圾的组成比较复杂,主要包括可降解和不可降解组分。目前,我国已经大力倡导生活垃圾源头分类,厨余垃圾需要被单独分离出来并进行单独的运输和处理处置。经生物干化后的厨余垃圾作为生物质能源的燃烧特性以及不同的辅料添加对厨余垃圾生物干化产品热特性的影响引起人们的广泛关注。
本研究以厨余垃圾为研究对象,研究了不同碳源的辅料添加对厨余垃圾生物干化产品燃烧热特性的影响,为厨余垃圾生物干化技术提供参考。
辅料添加对厨余垃圾生物干化产品燃烧热特性的影响
Effects of bulking agent amendments on the combustion properties of biological drying products of kitchen waste
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摘要: 为达到降低厨余垃圾含水率,使其可作为垃圾衍生燃料进行燃烧的目的,选择玉米秸秆和木本泥炭2种辅料与厨余垃圾进行联合生物干化,研究了辅料添加对厨余垃圾生物干化产品燃烧热特性的影响,以不添加任何辅料的厨余垃圾单独进行生物干化作为对照处理,生物干化周期为21 d。结果表明:单独进行厨余垃圾生物干化时挥发性固体(VS)降解率最高,添加木本泥炭处理时VS降解率最低;对照处理对VS降解损失主要的贡献组分为淀粉、纤维素和脂肪,然而,对于添加玉米秸秆和木本泥炭的处理,纤维素、半纤维素和淀粉是VS降解损失主要的贡献组分。随着生物干化反应的进行,物料的燃烧速率和燃烧率均降低,同时燃烬点推后,但燃点基本保持不变。其中,添加木本泥炭的处理燃点最高,燃烬点最低,燃烧率最高。各处理物料燃烧一级动力学方程拟合效果较好(R2 =0.86~0.97)。生物干化过程使厨余垃圾单独处理第2失重段反应变难,第3失重段反应变易。然而,对于添加辅料的处理,生物干化过程使第2失重段反应变易,第3失重段反应变更难。总体而言,生物干化过程使各处理的表观活化能(Em)降低了15.9%~29.4%,使得厨余垃圾的燃烧更加容易。以上研究结果可为厨余垃圾燃料化处理提供参考。Abstract: In order to reduce water and preserve energy of kitchen waste for subsequent utilization, e.g., as residue-derived fuels, two types of bulking agents: cornstalks (CS) and wood peat (WP) were selected to conduct a joint bio-drying of kitchen waste, and study the effect of bulking agent amendments on the combustion properties of biological drying products of kitchen waste. A control (CK) treatment was studied using only kitchen waste. The system used 60 L reactors and each test lasted 21 days. Results showed that the CK treatment had the higher VS degradation rate, while the WP treatment had the lower degradation rate. The main contributors to the organic material loss in the CK treatment were the degradation of amylums, cellulose, and lipids, while they were cellulose, hemicellulose and amylums in the CS and WP treatments. The combustion rate decreased and final burnout values delayed after bio-drying along the bio-drying reaction. Nevertheless, the ignition temperature remained steady, the organics degradation could not cause a significant change in ignition temperature. Of which the WP treatment had the highest ignition temperature, the lowest burnout temperature, and the highest mass loss rate. The first-order kinetic equation had a good fit (R2=0.83~0.98) for the combustion of each material. For the CK treatment, the bio-drying process made the second combustion stage harder and the third combustion stage easier. However, for the treatments amended with bulking agents, bio-drying made the second combustion stage easier and the third combustion stage harder. At the end of bio-drying, the apparent activation energy (Em) decreased by 15.9%~29.4% for all treatments, which led to easier combustion of kitchen waste. This study can provide the data support for the kitchen waste fuel treatment.
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Key words:
- kitchen waste /
- bio-drying /
- water content of kitchen waste /
- solid degradation rate /
- cornstalks /
- wood peat /
- combustion properties
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表 1 原料的基本性质
Table 1. Basic properties of the raw materials
处理组 物理化学特性 生物化学组成(以干基计)/% 工业分析(以干基计)/% 元素分析(以干基计)/% 含水率1)/% 容重1)/
(kg·m−3)C/N2) 挥发性固体 淀粉 脂肪 蛋白质 纤维素 半纤维素 木质素 水分 挥发分 固定碳 灰分 C H O N S 厨余垃圾 77.47 699 21.37 70.55 4.64 13.78 12.50 16.78 6.84 18.48 4.43 65.71 6.55 23.31 36.29 4.92 56.61 1.70 0.48 玉米秸秆 7.43 162 34.59 91.30 3.45 10.89 7.21 30.59 20.20 19.39 5.03 79.12 0.57 15.28 41.72 5.66 51.03 1.21 0.38 木本泥炭 13.19 814 80.34 94.70 0.27 14.40 3.55 0.00 0.00 72.36 4.60 75.65 0.45 19.3 52.14 4.97 41.86 0.65 0.38 注:1) 以湿基计;2) 以干基计。 表 2 生物干化过程生物化学组分含量
Table 2. Biochemical components before and after bio-drying
% 处理组 VS 淀粉 脂肪 蛋白质 纤维素 半纤维素 木质素 初始 结束 初始 结束 初始 结束 初始 结束 初始 结束 初始 结束 初始 结束 CK 70.55 51.62 10.64 1.44 13.78 10.74 12.50 10.37 16.78 11.11 6.84 3.40 11.48 14.84 CS 72.09 58.14 7.07 2.94 13.41 11.68 9.64 11.84 23.03 11.24 9.94 5.29 15.25 17.13 WP 74.04 62.85 7.01 2.64 11.37 11.48 10.72 10.39 17.29 10.67 5.30 2.13 32.68 35.00 表 3 生物干化过程各组分对总VS损失的贡献率
Table 3. Contribution of various biochemical components to total organic losses
% 处理组 淀粉 脂肪 蛋白质 纤维素 半纤维素 木质素 CK 27.45 17.44 14.60 25.30 12.62 2.58 CS 15.01 13.68 1.55 44.98 18.39 6.40 WP 21.80 6.45 7.86 37.12 15.96 10.80 注:贡献率基于表2数据计算得出;各组分贡献率=(各组分的初始百分含量×初始物料干重−各组分的结束百分含量×结束物料干重)/(初始VS量−结束VS量)。 表 4 初始原料及干化产品的燃烧失重特性
Table 4. Combustion weight-loss Characteristics of mixed samples at the beginning and end of the bio-drying process
处理组 阶段 第1失重段 第2失重段 温度/
℃最大燃烧
温度/℃最大燃烧速率/
(μg·min−1)损失率/% 温度/
℃最大燃烧
温度/℃最大燃烧速率/
(μg·min−1)损失率/% CK 初始 31~115 63.8 46.9 4.31 196~378 284.6 385.69 40.02 结束 29~113 61.6 42.06 3.28 194~360 279.6 331.55 29.55 CS 初始 33~108 64.9 32.17 2.56 183~379 282.03 525.15 40.77 结束 34~116 69.6 44.64 3.99 186~380 287.1 318.91 30.11 WP 初始 34~123 66.1 58.09 5.03 167~396 289.8 595.08 46.73 结束 34~144 77.3 44.42 5.25 176~402 301.3 231.5 31.82 处理组 阶段 第3失重段 第4失重段 温度/
℃最大燃烧
温度/℃最大燃烧速率/
(μg·min−1)损失率/% 温度/
℃最大燃烧温度/℃ 最大燃烧速率/
(μg·min−1)损失率/% CK 初始 378~490 438.5 1261.7 23.47 588~705 654.5 44.04 4.05 结束 393~530 456.4 502.58 17.68 577~709 653.5 48.58 3.86 CS 初始 393~532 442.5 485.75 18.92 578~701 647.3 31.80 3.19 结束 388~539 456 347.29 21.18 577~701 654.4 44.63 3.79 WP 初始 399~575 457.7 351.1 20.86 584~702 632.1 21.05 1.52 结束 406~577 465.7 270.61 23.76 581~711 658.3 33.95 3.60 表 5 初始原料及经生物干化后产品的燃烧特性
Table 5. Characteristic parameters of combustion of mixed samples at the beginning and end of the bio-drying process
处理组 阶段 Ti/℃ Th/℃ 燃烧率/% VM/% FC/% VM/FC 可燃性指数/
(10−3μg·(min·℃2)−1)综合燃烧特征指数/
(10−4μg2·(min2·℃3)−1)高位热值/
(kJ·kg−1)低位热值/
(kJ·kg−1)CK 初始 236.65 835.62 76.69 65.71 6.55 10.03 22.53 17.43 15 634 266 结束 248.01 845.83 60.91 50.15 7.28 6.89 8.17 5.95 12 740 1 331 CS 初始 252.36 829.32 69.20 61.70 3.20 13.04 8.25 6.16 17 496 1 479 结束 255.51 852.2 63.65 52.77 8.11 8.02 5.32 3.69 14 727 8 404 WP 初始 288.4 782.5 76.81 68.57 3.09 22.19 7.15 7.72 18 053 1 310 结束 284.8 796.5 67.19 56.97 5.37 10.61 3.34 2.43 16 808 6 327 表 6 初始原料以及经生物干化后产品的燃烧动力学参数
Table 6. Combustion kinetic parameters of the mixed samples at the beginning and end of the bio-drying process
处理组 阶段 第2失重段 第3失重段 Em/(kJ·mol−1) 温度/℃ E/(kJ·mol−1) A/min−1 R2 温度/℃ E/(kJ·mol−1) A/min−1 R2 CK 初始 196~378 31.19 35.06 0.954 378~490 31.42 22.85 0.864 19.86 结束 194~360 33.39 59.54 0.969 393~530 23.5 3.47 0.881 14.02 CS 初始 183~397 35.37 102.67 0.954 393~532 24.55 5.45 0.896 19.07 结束 186~380 27.41 12.27 0.945 388~539 25.68 5.45 0.888 13.69 WP 初始 167~396 26.04 10.16 0.931 399~575 20.99 2.75 0.86 16.55 结束 176~402 21.43 2.46 0.941 406~577 29.89 11.55 0.925 13.92 -
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