-
挥发性有机物 (volatile organic compounds,VOCs) 是近地面O3的主要反应物之一。部分VOCs的化学性质活跃,进入大气后可能会导致光化学烟雾的产生[1-3],生成二次污染物,对大气质量环境和人类生产活动产生严重危害[4-5]。VOCs主要来源于汽车尾气排放、工业排放源、煤炭及生物燃料燃烧、柴汽油或天然气泄漏与挥发等[6-9]。常见VOCs控制技术主要有破坏性消除法和回收法[10-12]。破坏性消除法包括生物降解[13-15]、焚烧[16-17]、催化氧化[18-20] 和等离子体[21-22] 等;回收法包括吸附[23-25]、吸收[26-27] 和冷凝[28-30] 等。在回收方法中,吸附技术被认为是最有效的方法之一,主要是由于其灵活性、一次投资成本低、耗能低、净化效率高和资源可回收,故在工程中被广泛应用[31-33]。
吸附法包含了活性炭对废气中污染物的吸附过程,也包含了活性炭的脱附再生过程[34]。活性炭脱附是指通过能量或物质的引入,达到减弱活性炭与吸附物质之间作用力的目的,使得吸附组分分子获得一定的能量后脱离固体表面而解吸出来[35]。活性炭脱附VOCs方法有变温脱附法、变压脱附法和微波再生法等。变温脱附法具有再生时间短、效率高、无选择性等优点,故在实际工程中被广泛应用。常见的变温脱附法采用水蒸气脱附再生、热氮气脱附再生等方式[36]。
变温脱附工艺在实际工程的设计中,需要参考的评价因子较多。常见评价因子有吸附剂的脱附率及脱附气体浓缩比等。荀志萌等[37]在研究大风量低浓度VOCs气体二次吸附浓缩选取净化技术开发时,选取能源节约率和脱附浓缩比作为变温脱附VOCs的评价因子。李照海等[38]在研究活性炭和沸石分子筛处理非稳定排放VOCs气体的性能时,选取脱附浓缩比、脱附量和再生单位质量二甲苯所需能耗作为变温脱附VOCs的评价因子。大风量、低浓度的排放通过旋转浓缩后处理的运行费用低,需考虑浓缩比;中高浓度的排放一般不采用旋转浓缩,主要考虑脱附率和能耗比等因素[39]。
本研究以甲苯为VOCs类代表性的目标污染物,搭建实验装置以模拟活性炭吸附脱附处理VOCs工艺中的脱附阶段,通过常见评价因子探讨不同脱附工况下气体对各床层的脱附情况,进一步提高现有脱附工艺的能量利用效率,提高大风量、低浓度工况下的浓缩比,以及各工况下的脱附率,降低各工况下的能耗比,以期得到最佳脱附工艺条件,并降低活性炭吸附净化工艺的运行维护成本,促进资源回收,为变温脱附工程化应用的低碳化技术优化提供参考。
活性炭变温脱附高浓度VOCs的工艺参数优化与评价
Optimization and evaluation of process parameters of thermal desorption of high concentration VOCs using activated carbon at variable temperature
-
摘要: 以甲苯为VOCs类代表性的目标污染物,通过搭建实验装置模拟活性炭吸附脱附处理VOCs工艺,并在不同工艺条件下 (脱附温度、表观风速、高径比) ,选取常见评价因子 (甲苯脱附率、甲苯浓缩比、脱附能耗比) 以探讨不同脱附工况下气体对各床层的脱附情况进行研究。结果表明,甲苯脱附率随脱附温度和表观风速的增加而增加。甲苯浓缩比随脱附温度和高径比的增加,随表观风速的减小而增加,即表观风速是浓缩比的主要控制因素。在中温范围内,低风速、高径比的甲苯浓缩比小于高风速、高径比。在高温范围内,低风速、高径比的甲苯浓缩比仅在峰值段大于高风速、高径比。脱附温度越高,表观风速越小,高径比越大,相同脱附率下的甲苯浓缩比越大。脱附能耗比随脱附温度和表观风速的减小,高径比的增加而降低,即表观风速是能耗比的主要控制因素。高温低风速时的能耗比比中温高风速时的能耗比低。当脱附温度80 ℃、表观风速0.3 m·s−1时,脱附能耗比最低为1.170 6 kJ·g−1。本研究可为变温脱附工程化应用的低碳化工艺优化提供参考。Abstract: An experiment device was built to simulate the adsorption and desorption process of activated carbon to treat VOCs, by taking toluence as the reprentative target pollutant of VOCs. Common evaluation factors (toluene desorption rate, toluene concentration ratio, desorption energy consumption ratio) in the process were selected to study the gas desorption of each bed under different desorption conditions (desorption temperature, cross-section wind speed, height to diameter ratio). The results showed that the toluene desorption rate increased with the increase of desorption temperature and cross-section wind speed. The concentration ratio of toluene increased with the increase of desorption temperature and height to diameter ratio, and the decrease of cross-section wind speed, which was the main control factor of concentration ratio. In the range of middle temperature , the concentration ratio of toluene at low wind speed and height diameter ratio was smaller than that at high wind speed and height-diameter ratio. In the range of high temperature, the concentration ratio of toluene at low wind speed and high diameter ratio was higher than that at high wind speed and height-diameter ratio only at the peak stage. At the same desorption rate, greater toluene concentration ratio would be achieved under higher desorption temperature, lower cross-section wind speed, and higher height-diameter ratio. The desorption energy consumption ratio decreased with the decrease of desorption temperature and cross-section wind speed, and the increase of height-diameter ratio. The cross-section wind speed was the main control factor of energy consumption ratio. The desorption energy consumption ratio at high temperature and low wind speed was lower than that at medium temperature and high wind speed. When the desorption temperature was 80 ℃ and the apparent wind speed was 0.3 m·s−1, the lowest desorption energy consumption ratio was 1.170 6 kJ·g−1. This study can provide reference for low-carbon improvement in the engineering application of variable temperature desorption.
-
表 1 CTC 90活性炭对甲苯吸附等温曲线的Freundlich和Langmuir方程参数
Table 1. Freundlich and Langmuir equation parameters of the adsorption isotherm curve of CTC 90 activated carbon for toluene
温度/℃ Freundlich Langmuir k/ Pa−n n R2 qs/(g·g−1) b/(m³·g−1) R2 25 0.273 2 5.581 7 0.991 8 0.555 1 0.343 5 0.996 9 40 0.184 2 4.071 6 0.999 9 0.489 4 0.230 8 0.950 1 80 0.094 9 3.540 3 1.000 0 0.295 3 0.184 7 0.944 6 150 0.016 9 2.039 7 0.999 7 0.141 8 0.060 4 0.983 0 表 2 变温脱附各工况下高径比5、脱附率80%时的脱附时间和甲苯浓缩比
Table 2. Desorption time and toluene concentration ratio at the desorption rate of 80% and a height-diameter ratio of 5 under various conditions of variable thermal desorption
温度/ ℃ 表观风速/(m·s−1) 脱附时间/min 浓缩比 80 0.1 — — 0.2 84 2.016 7 0.3 84 1.299 2 120 0.1 62 5.644 0 0.2 43 3.990 9 0.3 36 3.267 8 150 0.1 41 8.651 0 0.2 30 5.718 9 0.3 28 4.253 1 -
[1] CARDELINO C A, CHAMEIDES W L. An observation-based model for analyzing ozone precursor relationships in the urban atmosphere[J]. Journal of the Air & Waste Management Association, 1995, 45(3): 161-180. [2] UTEMBE S R, WATSON L A, SHALLCROSS D E, et al. A common representative intermediates (CRI) mechanism for VOC degradation. part 3: development of a secondary organic aerosol module[J]. Atmospheric Environment, 2009, 43(12): 1982-1990. doi: 10.1016/j.atmosenv.2009.01.008 [3] 潘昕, 张巍, 黄银芝, 等. 典型涂料制造企业VOCs排放量核算与排放特征分析[J]. 环境工程学报, 2021, 15(3): 1049-1059. doi: 10.12030/j.cjee.202008022 [4] DU Z, MO J, ZHANG Y. Risk assessment of population inhalation exposure to volatile organic compounds and carbonyls in urban China[J]. Environment International, 2014, 73: 33-45. doi: 10.1016/j.envint.2014.06.014 [5] DU Z, MO J, ZHANG Y, et al. Benzene, toluene and xylenes in newly renovated homes and associated health risk in Guangzhou, China[J]. Building and Environment, 2014, 72: 75-81. doi: 10.1016/j.buildenv.2013.10.013 [6] TSAI W Y, CHAN L Y, BLAKE D R, et al. Vehicular fuel composition and atmospheric emissions in South China: Hong Kong, Macau, Guangzhou, and Zhuhai[J]. Atmospheric Chemistry and Physics Discussions, 2006, 6(3): 3687-3707. [7] MONOD A, SIVE B C, AVINO P, et al. Monoaromatic compounds in ambient air of various cities: a focus on correlations between the xylenes and ethylbenzene[J]. Atmospheric Environment, 2001, 35(1): 135-149. doi: 10.1016/S1352-2310(00)00274-0 [8] LESON G, WINER A M. Biofiltration: An innovative air pollution control technology for VOC emissions[J]. Journal of the Air & Waste Management Association, 1991, 41(8): 1045-1054. [9] DUMANOGLU Y, KARA M, ALTIOK H, et al. Spatial and seasonal variation and source apportionment of volatile organic compounds (VOCs) in a heavily industrialized region[J]. Atmospheric Environment, 2014, 98: 168-178. doi: 10.1016/j.atmosenv.2014.08.048 [10] KHAN F I, GHOSHAL A K. Removal of volatile organic compounds from polluted air[J]. Journal of Loss Prevention in the Process Industries, 2000, 13(6): 527-545. doi: 10.1016/S0950-4230(00)00007-3 [11] PARMAR G R, RAO N N. Emerging control technologies for volatile organic compounds[J]. Critical Reviews in Environmental Science and Technology, 2008, 39(1): 41-78. doi: 10.1080/10643380701413658 [12] 张丹庆, 卜龙利, 陈瑾, 等. 微波催化燃烧技术处理印刷包装行业VOCs[J]. 环境工程学报, 2022, 16(2): 524-534. doi: 10.12030/j.cjee.202012005 [13] ZHOU Q, ZHANG L, CHEN J, et al. Enhanced stable long-term operation of biotrickling filters treating VOCs by low-dose ozonation and its affecting mechanism on biofilm[J]. Chemosphere, 2016, 162: 139-147. doi: 10.1016/j.chemosphere.2016.07.072 [14] MOHAMED E F, AWAD G, ANDRIANTSIFERANA C, et al. Biofiltration technology for the removal of toluene from polluted air using Streptomyces griseus[J]. Environmental Technology, 2015, 131(9/10/11/12): 1197-1207. [15] GARCIA-PEREZ T, AIZPURU A, ARRIAGA S. By-passing acidification limitations during the biofiltration of high formaldehyde loads via the application of ozone pulses[J]. Journal of Hazardous Materials, 2013, 262: 732-740. doi: 10.1016/j.jhazmat.2013.09.053 [16] CHOI B S, YI J. Simulation and optimization on the regenerative thermal oxidation of volatile organic compounds[J]. Chemical Engineering Journal, 2000, 76(2): 103-114. doi: 10.1016/S1385-8947(99)00118-7 [17] ORDONEZ S, BELLO L, SASTRE H, et al. Kinetics of the deep oxidation of benzene, toluene, n-hexane and their binary mixtures over a platinum on γ-alumina catalyst[J]. Applied Catalysis B:Environmental, 2002, 38(2): 139-149. doi: 10.1016/S0926-3373(02)00036-X [18] JEON E C, KIM K J, Kim J C, et al. Novel hybrid technology for VOC control using an electron beam and catalyst[J]. Research on Chemical Intermediates, 2008, 34(8/9): 863-870. [19] LI J, LI B, SUI G, et al. Removal of volatile organic compounds from air using supported ionic liquid membrane containing ultraviolet-visible light-driven Nd-TiO2 nanoparticles[J]. Journal of Molecular Structure, 2021, 1231: 130023. doi: 10.1016/j.molstruc.2021.130023 [20] CHOUDHARY T V, BANERJEE S, CHOUDHARY V R. Catalysts for combustion of methane and lower alkanes[J]. Applied Catalysis A General, 2002, 234(1/2): 1-23. [21] FUTAMURA S, ZHANG A H, YAMAMOTO T. The dependence of nonthermal plasma behavior of VOCs on their chemical structures[J]. Journal of Electrostatics, 1997, 42(1/2): 51-62. [22] ZHOU A, LIU J L, ZHU B, et al. Plasma catalytic removal of VOCs using cycled storage-discharge (CSD) mode: An assessment methodology based on toluene for reaction kinetics and intermediates[J]. Chemical Engineering Journal, 2022, 433: 134338. doi: 10.1016/j.cej.2021.134338 [23] DAS D, GAUR V, VERMA N. Removal of volatile organic compound by activated carbon fiber[J]. Carbon, 2004, 42(14): 2949-2962. doi: 10.1016/j.carbon.2004.07.008 [24] LEE D G, KIM J H, LEE C H. Adsorption and thermal regeneration of acetone and toluene vapors in dealuminated Y-zeolite bed[J]. Separation and Purification Technology, 2011, 77(3): 312-324. doi: 10.1016/j.seppur.2010.12.022 [25] SERRANO D P, CALLEJA G, BOTAS J A, et al. Adsorption and hydrophobic properties of mesostructured MCM-41 and SBA-15 materials for volatile organic compound removal[J]. Industrial & Engineering Chemistry Research, 2004, 43(22): 7010-7018. [26] LIU L, TIAN S, NING P. Phase behavior of tweens/toluene/water microemulsion systems for the solubilization absorption of toluene[J]. Journal of Solution Chemistry, 2010, 39(4): 457-472. doi: 10.1007/s10953-010-9519-8 [27] LAWSON R B, ADAMS C D. Enhanced VOC absorption using the ozone/hydrogen peroxide advanced oxidation process[J]. Journal of the Air & Waste Management Association, 1999, 49(11): 1315-1323. [28] DAVIS R J, ZEISS R F. Cryogenic condensation: A cost-effective technology for controlling VOC emissions[J]. 2002, 21(2): 111-115. [29] GUPTA V K, VERMA N. Removal of volatile organic compounds by cryogenic condensation followed by adsorption[J]. Chemical Engineering Science, 2002, 57(14): 2679-2696. doi: 10.1016/S0009-2509(02)00158-6 [30] XU H, XU X, CHEN L, et al. A novel cryogenic condensation system based on heat-driven refrigerator without power input for volatile organic compounds recovery[J]. Energy Conversion and Management, 2021, 238: 114157. doi: 10.1016/j.enconman.2021.114157 [31] WANG S, LIANG Z, CHAO L, et al. Enhanced adsorption and desorption of VOCs vapor on novel micro-mesoporous polymeric adsorbents[J]. Journal of Colloid & Interface Science, 2014, 428(428): 185-190. [32] GHOSHAL A K, MANJARE S D. Selection of appropriate adsorption technique for recovery of VOCs: an analysis[J]. Journal of Loss Prevention in the Process Industries, 2002, 15(6): 413-421. doi: 10.1016/S0950-4230(02)00042-6 [33] 党小庆, 王琪, 曹利, 等. 吸附法净化工业VOCs的研究进展[J]. 环境工程学报, 2021, 15(11): 3479-3492. doi: 10.12030/j.cjee.202011052 [34] DAVINI P. Adsorption and desorption of SO2 on active carbon: The effect of surface basic groups[J]. Carbon, 1990, 28(4): 565-571. doi: 10.1016/0008-6223(90)90054-3 [35] 杨晓娜, 任晓玲, 严孝清, 等. 活性炭对VOCs的吸附研究进展[J]. 材料导报, 2021, 35(17): 17111-17124. doi: 10.11896/cldb.21010141 [36] BERCIC G, PINTAR A, LEVEC J. Desorption of phenol from activated carbon by hot water regeneration. Desorption Isotherms[J]. Industrial & Engineering Chemistry Research, 1996, 35(12): 4619-4625. [37] 荀志萌, 李照海, 何娇, 等. 大风量低浓度VOCs气体二次吸附浓缩净化技术开发[J]. 环境工程学报, 2016, 10(1): 283-288. doi: 10.12030/j.cjee.20160146 [38] 李照海, 羌宁, 刘涛, 等. 活性炭和沸石分子筛处理非稳定排放VOCs气体的性能比较[J]. 环境工程学报, 2017, 11(5): 2933-2939. doi: 10.12030/j.cjee.201611026 [39] 羌宁, 史天哲, 缪海超. 挥发性有机物污染控制方案的运行费用效能比较[J]. 环境科学, 2020, 41(2): 638-646. doi: 10.13227/j.hjkx.201907029 [40] 党小庆, 敬开锐, 马红周, 等. 吸附VOCs活性炭真空热再生及影响因素实验[J]. 环境工程, 2022, 40(8): 62-68. [41] 徐胜男, 羌宁, 裴冰. 活性炭处理甲苯气体吸附再生实验研究[J]. 环境污染与防治, 2008, 29(1): 57-59. doi: 10.3969/j.issn.1001-3865.2008.01.017 [42] 李慧, 陈哲, 钟缘, 等. 乙酸丁酯废气在活性炭上的吸附和脱附行为研究[J]. 离子交换与吸附, 2020, 36(1): 31-40. doi: 10.16026/j.cnki.iea.2020010031 [43] 刘义鑫. VOCs吸附箱结构及其吸附剂脱附效果优化研究[D]. 宁波: 宁波大学, 2019. [44] 陈君毅, 陈磊, 蒙昊蓝, 等. 基于神经网络的车辆交通协调性评价模型[J]. 同济大学学报(自然科学版), 2021, 49(1): 135-141. doi: 10.11908/j.issn.0253-374x.20243