层流环形通道热泳脱除可吸入颗粒物技术研究.pdf

烟 气 污 染 治 理 层流环形通道热泳脱除可吸入颗粒物技术研究 * 周 涛 杨瑞昌 赵 磊 清华大学, 北京 100084 摘要 依据热泳基本原理, 设计了一种新型层流方环形双壁冷却式通道。经过计算, 该类型通道比一般管通道有着较 高的脱除可吸入颗粒物的效率。同时, 在不同的气流进口温度下, 利用速度温度充分发展流与速度温度正在发展流的 有不同热泳沉积效率工况, 可以达到较高的沉积效率。通过结构设计, 可以达到较高的可吸入颗粒物脱除效率, 是值 得进一步探索的新路子。 关键词 双壁冷却 热泳 可吸入颗粒物 沉积效率 * 国家 973 重大课题子项目 2002CB211604 1 概述 可吸入颗粒物是当前大气污染的主要成分, 其脱 除技术的研究也是当前国际上热门和有难度的课题。 目前国际上研究还处于实验研究 [ 1,2] 阶段, 已有研 究 [ 1 4] 和我们的分析计算表明 单管层流情况下, 纯 热泳作用造成的沉积效率最高只达 30 左右, 对于 一般的速度温度充分发展流只有 0 20。显然, 单 纯由热泳作用造成的沉积效率是很低的。如果应用 于工程技术, 则显的效率不很合算。也正因为此, 除 了韩国利用热泳和惯性碰撞的综合作用实现的一个 新型碰撞机器 [ 5] 之外, 其他产品还鲜为人知。所以, 有效的成型技术并不多见。利用温度梯度产生的热 泳作用来脱除可吸入颗粒物也是处于理论基础研究 阶段, 国际上也极少有完善的成型产品。热泳效应由 于作用范围的限制, 要实现高效率的脱除效果就必须 设计出恰当的实现方式, 层流环形双壁冷却式方通道 的设计就成功地达到了这一目的。 2 基本原理 热泳原理就是利用主流温度与壁面温度产生的 温差而形成的温度梯度推动细微可吸入颗粒物向壁 面运动的机制。例如 灯罩变黑就是热泳原理造成的 结果。 21 热泳系数计算公式 要正确计算热泳沉积效率, 首先要计算正确的热 泳系数 Kth。Tobalt 公式 [ 6] 是近几年国际推荐选用的 公式 Kth 2CsC 1 3Cm Kn - 1 Ct Kn 1 2 - 1 2Ct Kn 1 式中 Cm 1. 146; Cs 1. 147; Ct 2. 20; 是热导比率, 为 pg 2 式中 p 粒子热导率 W mK ; g 气体热导率 W mK ; C 库宁汉滑移修正系数, 为 C 1. 0 Kn C1 C2exp- C3 Kn 3 式中 C1 1. 2; C2 0. 41; C3 0. 88; Kn 为努森数, 为 Kn 2 d 4 式中 d 微粒的直径, m; 空气分子自由程 m, 为 0. 499 8RT 5 式中 运动粘性系数 m 2 s; R 气体常数, 空气为 2867 J kgK ; T 是气体绝对温度 K。 22 热泳沉积率计算公式 在热泳力的作用下, 颗粒累积沉积效率 the cumulative efficiency 的定义是 从流体进口粒子沉积 为零开始, 流经一定距离后粒子沉积的百分数。层流 中, 累积沉积效率 表达式主要有 1979 年 Walker [7] 等提出的公式; 1994 年Stratmann [4] 等提出数值求解模 型; 2002年台湾新竹交通大学环境工程研究所的 Jyh - Shyan Lin 和 Chuen -Jinn Tsia 提出的公式 [ 3] ; 1985 年 Batch和 Shen [ 8] 提出的公式等等。这里选择 Walker 公 式和 Jyh -Shyan Lin 等公式进行分析研究。在此所指 33 环 境 工 程 2005年 2 月第23 卷第1 期 沉积效率均为颗粒累积沉积效率。 Walker 公式 1 PrKth Tw Te- Tw 6 Jyh -Shyan Lin 公式 对速度温度充分发展流 0. 783 0. 94 1, 0. 007 1 0. 19 7 对速度温度正在发展流 0. 549 0. 48 1, 0. 006 1 350 时, 速 度温度充分发展流的热泳沉积效率反而高于速度温 度正在发展流的热泳沉积效率。这说明, 在高温差 34 环 境 工 程 2005年 2 月第23 卷第1 期 图 3 进口温度与沉积效率关系图 1 Jyh -Shyan Lin公式对单管中速度温度充分发展流计算; 2 Jyh - Shyan Lin 公式对单管中速度温度正在发展流计算; 3 Jyh -Shyan Lin 公式对双壁冷却式通道中速度温度充分发展流计算; 4 Jyh -Shyan Lin 公式对双壁冷却式通道中速度温度正在发展流计算。 时, 热的效应超过流动的效应。 5 基本结论 1 层流双壁冷却式环形通道能够以较高的热泳 沉积效率脱除可吸入颗粒物。根据国际上热泳沉积 研究结论 实验一般要等于或大于理论公式的计算数 值, 可以考虑使用此类双壁冷却式通道技术进一步进 行成型产品开发, 但也还需要一些实验的确保验证。 2 随着气流温度的变化, 速度温度充分发展流 的热泳沉积效率与速度温度正在发展流的热泳沉积 效率的数值比较大小会发生变化, 是一个有趣的新鲜 现象, 目前还未见报道, 也需要实验的进一步验证。 在工程上, 可以利用这一特点在不同温度下, 改变流 动状态, 以获得较高的沉积效率, 从而实现最佳脱除 可吸入颗粒物。 3 依据热泳特点, 通过结构设计, 以达到较高的 脱除可吸入颗粒物效率, 是值得进一步探索的新路 子。如果再结合其它的技术, 产生综合的脱除效果, 就 可以发明出较多高效的脱除可吸入颗粒物的新技术。 4 层流双壁冷却式环形通道由于是双壁冷却, 在机理上会有很多不同于单通道流动沉积的新特点, 究竟是如何强化沉积作用的。还需要进一步进行理 论和实验研究。 参考文献 1 Francisco J. Romay, Sho S.Takagaki, David Y.H. Pui and Benjamin Y.H. Liu. Thermophoretic deposition of aerosol particles in turbulent pipe flow. Journal of Aerosol Science 1998. 29 8 943 959. 2 Jyh -ShyanLin, Chuen -Jinn Tsai and Da -Ren. Chen. Study on thermophoretic deposition of aerosol particles in laminar and turbulent tube flows. Journal of Aerosol Science.2004. 38 2 131 139. 3 Jyh -Shyan Lin, Chuen -Jinn Tsai.Thermophoretic deposition efficiency in a cylindrical tube taking into account developing flow at the entrance region. Journal of Aerosol Science, 2003. 34 569 583. 4 Stratmann, F. , Otto, E. , the same disposal made the disposal of the different wastewater more difficult; the equipments were seriously eroded.The different wastewater was physically and chemically disposed firstly, and then entered SBR reactor and further bio -chemically treated, a series of anticorrosive measures were taken during the equipments prefabrication and the problems were resolved very well in the er wastewater disposal line for the rebuilt wastewater disposal line. Keywords wastewater disposal system of automobile coating and optimization TREATMENT OF SLAUGHTERHOUSE WASTEWATER WITHPROCESS OF FLOATATIONAND SBRZhang Zhaohui et al 25 Abstract The process of floatation and SBR is usedto treat slaughterhouse wastewater. Whenthe influent CODCris inthe range of 1 200 1 850mg L, the effluent CODCris under 90 mg L, and allthe quality indications of the effluent could meet firs- t order of Wastewater Comprehensive Discharge standard GB8978 -1996. Furthermore part of the treated wastewater can be used again. Keywords slaughterhouse wastewater, SBR and air floatation PRIMARY EXPLORATION OF CONSTRUCTION OF MUNICIPAL WASTEWATER PLANT IN AREAS OF LOW -TEMPERATUREZhao Lijun et al 27 Abstract The characteristics of low -temperature municipal wastewater and the effect on wastewater treatment efficiency owing to the change of temperature were introduced, andthe problems that should be noticed in selecting wastewater treatment process in areas of low -temperature were pointed out too. Moreover, suggestions on the selection of designing parameters and the running management of project were brought forward. Keywords low -temperature, municipa- l wastewater, selection of process and design parameter TREATMENT OF ACIDICWASTE WATER FROM PRODUCTIONOF SEAMLESS STEEL TUBES Yang Weiguo 30 Abstract A complete waste water treatment process is supplied according to the fact that there is a lower pH value and a higher FeO or Fe2O3or Fe3O4in the waste water from hollow billet pickling process in a seamless steel tube mill. Practical running shows that this treatment process is outstanding and this technique is advanced, the treatment result is excellent, and that the processed water can be used for production again. This technique has obvious economic, environmental and social benefits. Keywords hollow billet, pickling waste water and treatment ENGINEERING EXAMPLE OF TREATING ARSENIC -BEARING WASTE WATER Chen Liaoyuan et al 31 Abstract A successful engineering case in which the arsenic -bearing wastewater is treated is introduced. The process, technical parameter and the special design of aerated system are also introduced.This design overcomes the defects in the er design. Keywords arsenic -bearing waste water, FeSO47H2O and aerated system TECHNICAL STUDY ON REMOVING INHALED PM2. 5 USING THERMOPHORESIS IN LAYER FLOW CYCLE CHANNELZhou Tao et al 33 Abstract A kind of new layer flow cycle channel withtwo cooledwallswas designed onbasic thermophoresis principle. This kind of channel has a higher cumulative efficiency for removing inhaled PM2. 5 than usual channel through calculation. In the meantime, the higher cumulative efficiency for removing inhaled PM2. 5 will be obtained by taking into account developing flow and developed flow of speed temperature at different inlet gas temperature conditions. It is a new way that isworth researching further. Keywords two cooled walls, thermophoresis, inhaled particle matter and cumulative efficiency EXPERIMENT AND APPLICATION OF FILTRATION PERANCE FOR NEW COMPOUND FILTER MEDIALi Hua et al 36 Abstract To decrease the pressure drop and increase filtration efficiency of the filter media in a bag filter, a new compound filter media namedHBT was introduced, and the experimental study on filtration perance was carried out. The results indicated that HBT filter media had the perance of high efficiency and low resistance in the same operating conditions,Therefore, it is more suitable for a coa- l fired boiler. Keywords compound filter media, filtration perance, application and coa- l fired boiler DEDUSTING ANDINVESTMENTBENEFITOF12 500 kVAFERROSILICONELECTRIC FURNACELiu Sheng 38 Abstract It was introduced that the dedusting technique, main equipment composition and the dedusting systems superiority of 12 500 kVA 3 ENVIRONMENTAL ENGINEERING Vol23, No1,Feb. , 2005