【作者】 李玉华；

【导师】 赵庆良；

【作者基本信息】 哈尔滨工业大学 ， 环境工程， 2007， 博士

【摘要】 甲醛是我国室内空气主要污染物之一,具有污染普遍、污染时间长等特点,长期接触会对人体健康造成危害。因此室内甲醛污染去除研究具有重要意义。光催化氧化法是近年来室内空气净化研究的热点。由于室内甲醛浓度水平很低,从气态到催化剂表面的传质阻力较大,致使其传质速率较低。此外,现有研究中普遍应用镀膜催化剂反应器,光能利用率低。因此,现有光催化反应器光催化氧化甲醛的转化率偏低。为更好的将光催化氧化法应用于室内空气净化的实践,需要寻找新的反应器形式,并研究设计高效的光催化氧化空气净化器。基于固定式填充床反应器是所有光催化反应器中转化率最高的特点,本研究选用固定式填充床反应器对甲醛进行光催化降解研究。通过改变反应条件,了解反应器入口甲醛浓度、反应气体温湿度、气体在反应器内停留时间及气体氧含量等因素对甲醛降解效果的影响。自主设计光催化空气净化器,对其净化效能进行考察,并对其应用进行模拟。此外,应用计算流体力学软件对光催化反应器及空气净化器内空气流速分布进行了模拟。通过比较,选取黑灯管为紫外光源,置于反应器中心位置,并以玻璃珠作光催化剂载体,填充于反应器内,构成本研究光催化反应器。通过计算模拟该光催化反应器内空气流速分布,发现其轴向流速均匀,但径向流速,从灯管处至反应器器壁处逐渐减少,直至接近零,易造成催化剂的浪费。在此基础上,对光催化反应器进行改进,设计新型填充式空气净化器。净化器选取侧面进风,单个装置侧壁开孔方式采取上宽下细形式。应用风速仪对单个净化装置进气流速测定结果表明,空气在整个侧面基本以0.05 m/s的速度均匀进入净化装置。空气净化器单个净化装置空气流速计算模拟结果显示,净化装置内空气流速分布均匀。因此催化剂可以得到充分利用。应用固定式填充床反应器对甲醛进行光催化降解,发现接近室内甲醛浓度水平时,甲醛光催化降解受反应温湿度影响很小,受浓度影响显著,并且甲醛浓度5~20 mg/m3时,甲醛光催化反应速率适宜用L-H模型描述;而0.6~1.2 mg/m3时,甲醛反应速率更适宜用Power-rate law模型表述,说明高浓度时对甲醛光催化反应适用的L-H模型,对于室内浓度水平并不一定适用。计算出L-H模型表观反应速率常数k为4.666~9.470 mg/g-hr,甲醛在光催化剂表面的吸附平衡常数K为0.0098~0.0128 mg-1;Power-rate law模型的常数k和n分别为0.317~0.452和1.082~1.370。L-H模型的表观反应速率常数k和Power-rate law模型的常数k均随温度的升高而降低,且两模型的常数k与温度的关系都基本符合阿仑尼乌斯公式。应用本研究自主设计空气净化器对室内甲醛进行净化研究,结果表明:甲醛初始浓度0.727~1.815 mg/m3时,甲醛净化效率为84.7%~92.0%,净化过程中没有新的气态有机污染物生成。基于净化试验结果得出空气净化器甲醛反应速率方程,建立有甲醛持续释放实验房间应用空气净化器室内甲醛浓度变化数学模型,经实验结果证实模拟结果基本可以反应室内甲醛浓度变化情况。通过人造板材使用量与室内甲醛浓度关系方程,应用数学模型对空气净化器在实际房间的应用进行模拟,结果表明:空气净化器的间歇应用可以保持室内甲醛浓度低于国家标准,空气净化器应用频率与室内人造板材等级及使用量密切相关。本研究基于应用固定式填充床光催化反应器对甲醛降解的理论研究,自主设计新型填充式空气净化器,并对其净化效果进行模拟,为室内空气甲醛净化提供了一种高效、实用的空气净化装置。同时,对其应用提供了指导,有助于人们更好的去除室内甲醛污染,为人们提供安全的生活环境。更多还原

【Abstract】 Formaldehyde is one of the major indoor pollutants, which has adverse effects on human health and could last a longer time in indoor environments. Consequently, it is worthwhile to develop an innovative measure for effectively removing indoor formaldehyde. Photocatalysis has been one of the most popular techniques for indoor air purification for the past two decades. However, due to low concentration of indoor formaldehyde, the mass transfer resistance between the air and the surface of photocatalyst is significant, which make the mass transfer rate of formaldehyde become relatively low. Besdieds, the film-coated photocatalytic reactors commonly applied in previous investigations can’t utilize the ultraviolet (UV) light sufficiently. These two reasons lead to lower formaldehyde conversion for the photocatalysis. In order to enhance the formaldehyde conversion, an innovative photocatalytic reactor has to be developed to achieve high performance of indoor air purifier.Packed-bed reactor was selected as the photocatalytic reactor for this study since it has the highest conversion among all the photocatalytic reactors. The packed-bed photocatalytic reactor was used to investigate the removal conversion and reaction rate of indoor formaldehyde. Moreover, the effects of operating parameters on the formaldehyde conversion were also investigated. The operating parameters investigated included influent formaldehyde concentration, reaction temperature, humidity, residence time, and oxygen content. An innovative air purifier was further designed to investigate its performance of indoor formaldehyde removal in a testing room. Furthermore, computational simulation was conducted for the velocity profile of the packed-bed photocatalytic reactor and the air purifier as well as the variation of formaldehyde concentration in then testing room.Black-light lamp was selected as the UV source for the photocatalytic reaction. The lamp was situated at the center of the reactor. Glass beads coated with TiO2 were filled inside the photocatalytic reactor as the photocatalysts. The simulated air velocity profile of the photocatalytic reactor showed that the velocity in the radial was not uniform. The velocity decreased from the center to the wall of the reactor, which could result in the insufficient utilization of the photocatalyst. Therefore, the photocatalytic reactor was modified and an innovative packed air purifier was designed. Air entered from the lateral surface of the air purifier. The width of the slots decreased from the top to the bottom of the lateral surfaces of the single purification device within the air purifier. The results measured with an anemoscope showed that the air uniformly entered the air purifier in a flow rate of 0.05 m/s. The simulation results of the air pattern in the single device showed that the air velocity was relatively uniform, which suggested that the photocatalyst can be utilized effectively.The decomposition of formaldehyde with packed-bed photocatalytic reactor was investigated for the formaldehyde concentration close to indoor level. The results showed that the decomposition of formaldehyde was apparently affected by influent formaldehyde concentration. Reaction temperature and humidity has limited effect on the decomposition of formaldehyde. The reaction rate for influent formaldehyde concentration of 5~20 mg/m3 can be accounted for by using the rate expression of L-H model. The reaction rate constant and adsorption equilibrium for the L-H model was 4.666~9.470 mg/g-hr and 0.0098~0.0128 mg-1 separately. However, Power-rate model was feasible for describing the photocatalytic oxidation for influent formaldehyde concentration of 0.6~1.2 mg/m3. The constant k and n for the Power-rate law was 0.317~0.452 and 1.082~1.370 separately. The constant k for the L-H model and the Power-rate law model decreased with the reaction temperature. The correlation between the constant k for these two models and the reaction temperature agrees with the Arrhenius equation.The experimental results of the innovative air purifier indicated that the formaldehyde removal efficiency was 84.7%~92.0% for initial concentration of 0.727~1.815 mg/m3. None new kind of organic pollutant was detected in the testing room during the operation of the air purifier. The formaldehyde reaction rate equation of the air purifier was developed. Based on mass balance, a mathematical model to simulate the variation of formaldehyde concentration in the testing room was constructed, in which there was continuous formaldehyde emission source and the air purifier was operated. The simulated results were proved by the experimental data. The relation expression of particle board amount and formaldehyde concentration in the room was used to approximately calculate the formaldehyde release rate. The variation of indoor formaldehyde concentration in actual room with using the air purifier was then simulated. The simulated results showed that the periodic operation of air purifier could keep the indoor formaldehyde concentration less than 0.1 mg/m3. The operation procedure of the air purifier was mainly determined by the release rate and amount of the release sources in the room.The decomposition of formaldehyde in the packed-bed photocatalytic reactor was investigated in this study. An innovative air purifier was designed based on the results obtained from the investigation of the packed-bed photocatalytic reactor. The application of the air purifier was further simulated to verify its performance on indoor formaldehyde removal. The outcome of this study provides the basic criteria for designing an innovative air purifier device. The operation procedure of the air purifier was also recommended in the study. Therefore, the results obtained from this study would be valuable for improving indoor air quality.更多还原