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煤、石油等燃料的燃烧产生的气体中富含SO2和NOx,它们不仅有毒,还是形成酸雨和光化学烟雾的主要原因[1]。物理、化学工艺净化SO2和NOx方法有湿法脱硫、选择性催化还原法等,虽然这些技术已经发展成熟且应用广泛,但存在运行费用高、容易产生二次污染等缺点[2-3]。随着20世纪80年代生物科学技术的迅猛发展,以环境友好、高效和低成本著称的环境生物技术成为了行业关注热点。有研究[4-5]表明,生物工艺在净化低质量浓度SO2和NOx废气时,可以表现出不错的去除能力,但传统的生物工艺存在长期运行时导致填料堵塞的问题,直到生物转鼓工艺(RDB)的出现,才得以较好地解决。CHEN等[6]的研究表明,RDB在厌氧条件下同步净化SO2和NO,可以达到较好的去除效果,但由于NO气液扩散效果差,需要额外添加络合剂Fe(II)(EDTA)。此外,WANG等[7]在生物滴滤塔同步净化SO2和NOx的研究中发现,将O2体积分数从4%提高到20%时,NOx的去除效果可以从49.28%提高至80.85%,这归功于O2对NO的氧化。此外,即使在好养环境下,填料内部由于外部微生物包裹易形成厌氧环境,也能为部分厌氧反应提供基础条件[7]。这为好氧条件下RDB同步脱硫脱硝提供了理论基础。其中,SO2最终的代谢产物为S,NOx则最终净化为N2,具体反应过程[8-12]如式(1)和式(2)所示。
然而,对RDB好氧同步脱硫脱硝的工艺条件和净化效果仍缺乏研究,因此,本实验探讨了好氧条件下RDB同步脱硫脱硝效果受SO2质量浓度、NOx质量浓度、营养液体积和EBRT变化的影响情况,并借助动力学模型分析和验证实验结果,以期为今后的研究提供参考。
好氧条件下生物转鼓同步脱硫脱硝性能及相应动力学模型的优化
Performance and kinetic model optimization of simultaneous desulfurization and denitrification for rotating drum biofilter under aerobic conditions
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摘要: 为探究高效同步脱硫脱硝的生物工艺,以生物转鼓反应器为实验对象,研究了好氧条件下SO2质量浓度、NOx质量浓度、营养液体积和气体停留时间(EBRT)的变化对生物转鼓同步脱硫脱硝效果的影响,并用动力学模型拟合值与实验数据进行了对比。实验结果表明:生物转鼓同步脱硫脱硝最适条件为SO2质量浓度1 200 mg·m−3,NOx质量浓度800 mg·m−3,营养液体积20.6 L,气体停留时间(EBRT) 75.36 s;SO2过程净化主要受液相传质控制,NOx传质过程由生物相和液相协同完成;修正求得了能较好描述好氧条件下生物转鼓脱硫脱硝效果的动力学模型,因存在生物相、液膜、污染物流动等变量与假设的差异,SO2和NOx模拟数据与实验数据分别有2.68%和3.18%的平均绝对误差;在最佳条件下,SO2和NOx的平均去除率分别为96.81%和92.98%,平均去除负荷分别为55.50 mg·(L·h)−1和35.53 mg·(L·h)−1,且出气质量浓度均低于100 mg·m−3。可见,生物转鼓是一种可行的高效同步脱硫脱硝生物工艺。Abstract: In order to explore a biological process that can efficiently and simultaneous desulfurization and denitrification, the rotating drum biofilter was taken as the experimental object, the effects of SO2 mass concentration, NOx mass concentration, nutrient solution volume and gas empty bed residence time in rotating drum biofilter on simultaneous desulfurization and denitrification under aerobic conditions were studied, and the fitted values of the kinetic model were compared with the experimental data. The results showed that the optimum conditions of simultaneous desulfurization and denitrification for rotating drum biofilter were SO2 mass concentration of 1 200 mg·m−3, NOx mass concentration of 800 mg·m−3, nutrient solution volume of 20.6 L and gas empty bed residence time of 75.36 s. The SO2 purification process was mainly controlled by liquid phase mass transfer, and the NOx mass transfer process was completed by the cooperation of biological phase and liquid phase. In addition, the kinetic model which can better describe the desulfurization and denitrification effect of rotating drum biofilter under aerobic condition was modified. Due to the differences of biological phase, liquid film, pollutant flow and other variables and assumptions, the average absolute errors of SO2 and NOx simulation data and experimental data were 2.68% and 3.18%, respectively. Under the optimum conditions, the average removal rates of SO2 and NOx were 96.81% and 92.98%, respectively, the average removal loads of SO2 was 55.50 mg·(L·h)−1 and NOx was 35.53 mg·(L·h)−1, respectively, and the outlet gas mass concentrations of SO2 and NOx were lower than 100 mg·m−3. It can be seen that the rotating drum biofilter is a feasible and efficient biological process for simultaneous desulfurization and denitrification.
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表 1 SO2和NOx的排放标准
Table 1. Effluent discharge standard of SO2 and NOx
标准 设备类型 SO2/
(mg·m–3)NOx/
(mg·m–3)石油化学工业污
染物排放标准
(GB 31571-2015)工艺加热炉 100 150 锅炉大气污染
物排放标准
(DB44/ 765-2019)燃煤锅炉(新建) 200 200 燃油锅炉(新建) 100 200 火电厂大气污染
物排放标准
(GB 13223-2011)燃煤锅炉(新建) 100 100 以油为燃料的锅炉或燃气轮机组(新建) 100 100 表 2 各模型SO2和NOx模拟数据与实验数据的比较
Table 2. Comparisons of SO2 and NOx removal efficiencies between model results and experiment data
污染物 工艺条件 各模型模拟数据与实验数据间的绝对误差/% 式(12) 式(13) 式(15) 最大 最小 平均 最大 最小 平均 最大 最小 平均 SO2 SO2浓度 53.62 9.34 33.79 8.54 0.42 3.89 NOx浓度 36.52 35.23 35.90 1.72 0.43 1.05 营养液体积 43.92 8.31 30.42 3.61 0.21 1.78 EBRT 56.61 2.06 32.18 11.60 0.60 4.01 NOx SO2浓度 16.80 22.53 19.62 11.00 5.27 8.19 4.00 0.55 2.18 NOx浓度 21.00 10.72 15.91 17.35 3.88 8.49 5.33 0.46 2.43 营养液体积 27.15 6.56 17.59 11.65 5.87 7.89 9.95 2.12 4.97 EBRT 31.00 0.91 16.68 15.17 1.58 6.30 6.67 1.29 3.16 -
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