湿污泥在流化床中干燥特性

在鼓泡流化床干燥器内,床料采用0～1 mm的石英砂,以热空气作为干燥介质,对城市污水污泥的流态化干燥特性进行实验研究。通过控制送风温度、流化风量、加料量、污泥粒径等参数,研究在不同工况条件下床温以及干污泥含水率的变化情况。结果表明,随着送风温度的升高,床温升高,干污泥含水率下降,最终趋向于一个稳定值8%。床温随流化风量的增加先是减小而后升高,干污泥的含水率随流化风量的增加先是降低而后增大。当加料量从11 kg/h增加到13kg/h时,干污泥的含水率基本没有变化,当加料量超过13 kg/h时,干污泥的含水率从8.1%开始呈递增趋势。随污泥粒径的增大,床温升高,干污泥含水率也随之升高。     

泡沫化预处理对污泥干燥特性的影响

采用泡沫化预处理与污泥干燥相结合的方法提高脱水污泥的干燥效率。采用密度变化的间接测定法,研究了脱水污泥的起泡性能和泡沫稳定性。采用薄层干燥实验法探讨泡沫化污泥的干燥特性,并引入干燥曲线,深入分析泡沫化污泥快速干燥的机理。结果发现,脱水污泥中加入一定量Ca O后经搅拌可以形成泡沫化污泥,且泡沫的稳定性很强。当泡沫化污泥的质量和表面积相同时,在不同的干燥温度下,密度为0.70 g/cm3的泡沫化污泥均表现出最好的干燥性能。泡沫化处理后污泥与干燥空气的接触面积增大,泡沫化污泥中自由水含量增多以及干燥过程中泡沫化污泥内部形成的大量孔洞使得水分迁移和热量传递的阻力减小,这些是泡沫化污泥干燥速率得以加快的主要原因。     

酒精污泥干燥特性及数学模型

用红外干燥方法对酒精污泥进行干燥实验,研究了干燥温度和污泥厚度对水分蒸发速率、干燥速率及体积变化率的影响。实验表明,恒速干燥段的干燥速率仅与干燥温度有关;临界湿含量随污泥厚度增加而升高,随干燥温度的升高而下降;污泥体积在恒速干燥段收缩速度较快,在降速干燥段仍有微小的变化。对污泥干燥特性曲线进行分析,建立了恒速干燥段及降速干燥段的干燥模型,并将模型预测与实验结果进行了对比,误差较小。     

过量生石灰对污泥含水率和有机物含量的影响

为了研究生石灰(氧化钙,CaO)处理活性污泥对污泥含水率和有机物含量的影响,通过向南京某城市污水处理厂出厂污泥投加过量CaO进行脱水实验,测定投加CaO后污泥的含水率;烘干后的脱水污泥进行热重实验,研究CaO投加量对污泥中有机组分含量的影响.脱水实验表明:随着CaO与污泥质量比的增大,污泥含水率迅速减小,当质量比达到1.5时,污泥达到完全脱水;投加过量CaO的脱水污泥呈干燥的粉末状,粒度均匀,可作为水泥生产的辅料。热重实验表明:投加CaO后单位干泥失重百分比随CaO与污泥质量比增大而逐渐减小,向污泥中投加CaO有利于污泥中有机组分的释放和去除,实现污泥的稳定化。     

温度和相对湿度对污泥低温干燥速率的影响

对脱水污泥进行低温薄层干燥实验,研究了污泥厚度(3、5、7和9 mm)、温度(30、40和50℃)、空气相对湿度(20%、40%和60%)、污泥水分比等参数对脱水污泥干燥速率的影响。通过静态溶液法分析不同温度、湿度条件下污泥的平衡含水率,当相对湿度大于60%时,污泥平衡含水率的增长速率急剧增大。污泥低温干燥实验表明,升高温度、降低相对湿度均能够提高污泥的干燥速率,且较适温度、相对湿度分别为40℃和20%。采用SPSS软件对影响污泥干燥速率的因素进行偏相关性分析,结果表明,影响因素从大到小排列分别为污泥水分比、温度、相对湿度,且随着污泥厚度的增加,温度、相对湿度与干燥速率的Pearson相关系数的绝对值变大。     

流化床中煤与稻秆混烧污染物排放特性

在自主设计的流化床上开展煤与稻秆混烧的实验。通过对燃烧过程中烟气成分及飞灰含碳量的分析,研究了质量掺混比、燃烧温度、流化风速及二次风率对混烧的影响。实验结果表明,掺混稻秆有效改善了煤的燃烧特性,随着质量掺混比的增加,NO_x、SO_2及CO的排放浓度降低,飞灰含碳量降低。当掺混比由0%增加至30%、温度为850℃时,NO_x排放浓度由506.25 mg·m-3降低至404.33 mg·m~(-3),SO_2排放浓度由762.86 mg·m~(-3)降低至522.86 mg·m~(-3)。随着燃烧温度的增加,NO_x与SO_2排放浓度增加,而CO排放浓度和飞灰含碳量降低。随着流化速度的增加,NO_x与SO_2排放浓度增加,CO排放浓度和飞灰含碳量先降低后增加,并分别在流化速度0.234 m·s~(-1)和0.26 m·s~(-1)时达到最低。随着二次风率的增加,SO_2排放浓度与飞灰含碳量降低,NO_x排放浓度与CO排放浓度先减小后增加,均在20%二次风率时达到最低。     

污泥脱水和干燥新技术：微波加热工艺简评

引言各种生活废水处理和工业废水处理过程中经常产生大量难于处理的污泥,其固体物含量约为0.1～10％,经脱水后,污泥中固体物含量可增至30％。常见的工艺是将污泥进行加热或化学调理后用机械法脱水,所用机械设备有砂干燥床、真空过滤器、带式过滤器和离心机等。污泥脱水后再行加热干燥可使其固体物含量超过30％,常用的污泥干燥器有急骤干燥器、直接旋转干燥器、流化床干燥器、薄膜传导干燥器、多膛炉等。污泥干燥程度取决于干     

电渗透脱水对污泥热干燥特性的影响

以污水厂机械脱水后的污泥作为研究对象,提出了采用电渗透-热干燥结合进行深度脱水的方法。通过对原泥以及电渗透脱水至不同含水率(67%、71%和76%)的污泥在热干燥过程中含水率和干燥速率的测定,分析电渗透脱水对污泥热干燥特性的改善规律。结果表明,经电渗透脱水至含水率为67%和71%的污泥在热干燥过程中的传热传质速率及干燥速率有明显提高,且干燥温度越高,电渗透后污泥的干燥速率与原泥的干燥速率差距越大。相同电压梯度及相同温度下电渗透至67%后进行热干燥耗能最少。实际应用中应结合能耗分析选择合适的电渗透程度及干燥温度,以达到最优效果。     

微波功率、辐射时间及污泥量对污泥微波干燥效能的综合影响研究

通过正交实验探讨了微波功率、辐射时间及污泥量对污泥微波干燥效能的综合影响研究,实验结果表明:在微波功率为140～580 W,辐射时间为5～20 min,污泥量为200～350 g的实验条件下,微波功率、辐射时间及两者之间的交互作用对污泥微波干燥效能影响高度显著,污泥量影响不显著;并得出微波功率、辐射时间对污泥含水率综合影响的定量正交回归方程。     

城市污泥的低温热干燥

污泥是城市产生的重要废弃物之一,因较高的含水率而体积庞大,因此对其进行脱水和干燥是实现减量化的重要手段。低于100℃的低温热干燥方法因干燥温度较低,具有节能、减少臭气排放等优点,可有效利用工业余热、废热、太阳能,以及热效率很高的热泵干燥工艺。采用薄膜态污泥进行低温干燥,通过实验分析了在温度为50℃和70℃、表面风速为0.3~1.2 m·s-1条件下污泥质量与含水率的变化。结果表明,较低的干燥温度一定程度上延长了干燥时间,但采用薄膜形态可以缓解干燥速度减慢的问题,且可有效解决"硬壳"现象而实现等速干燥,对提高能源利用效率具有较大好处。给出了气流温度、流速、泥层厚度对干燥速度的影响,干燥消化污泥所需时间要快于同条件下的未消化污泥。还给出了2种低温干燥工艺流程,为工业应用提供借鉴。     

Relationship between pressure fluctuations and generation of organic pollutants with different particle size distributions in a fluidized bed incinerator

The hydrodynamic behaviors of fluidization perhaps significantly influence the uniformity of fluidization in fluidized bed incinerator. Good uniformity of fluidization expressed the air across uniformly through the bed and the particles being distributed well in the fluid stream. The aggregates, flocs and channels of particles do not happen during fluidization. The Good uniformity will maintain high heat and mass distribution to improve reaction efficiency. These parameters include the height of static bed, gas velocity, mixing and distribution of bed particle, which have rarely been studied in previous investigations. Consequently, this study examines how the hydrodynamic parameters affect the generation of organic pollutants (BTEXs and PAHs) during incineration. The statistical and power spectral analysis of the measured pressure fluctuation during incineration are used to elucidate the relationship between behaviors of fluidization and generation of pollutants during incineration. Experimental results show the organic concentration does not increase with uniformity of fluidization decreasing. The reason may be the explosion of the gas and the consequent thermal shock destroy the coalescent bubbles to form small bubbles again and enhance the efficiency of transfer of oxygen to increase combustion efficiency. Additionally, the mean amplitude and fluidized index of pressure fluctuation similarly vary with the concentration of organic pollutants. These two indices can be used to assess the efficiency of combustion. The four particle size distributions could be divided into two groups by statistical analysis. The Gaussian and narrow distributions belong to one group and the binary and flat the other. The organic concentration of the Gaussian and narrow distributions are lower than that of the other distributions. Consequently, the bed materials should maintain narrow or Gaussian distributions to maintain a good combustion efficiency during incineration.     

Heat transfer analysis of cylindrical anaerobic reactors with different sizes: a heat transfer model

The temperature is the essential factor that influences the efficiency of anaerobic reactors. During the operation of the anaerobic reactor, the fluctuations of ambient temperature can cause a change in the internal temperature of the reactor. Therefore, insulation and heating measures are often used to maintain anaerobic reactor’s internal temperature. In this paper, a simplified heat transfer model was developed to study heat transfer between cylindrical anaerobic reactors and their surroundings. Three cylindrical reactors of different sizes were studied, and the internal relations between ambient temperature, thickness of insulation, and temperature fluctuations of the reactors were obtained at different reactor sizes. The model was calibrated by a sensitivity analysis, and the calibrated model was well able to predict reactor temperature. The Nash-Sutcliffe model efficiency coefficient was used to assess the predictive power of heat transfer models. The Nash coefficients of the three reactors were 0.76, 0.60, and 0.45, respectively. The model can provide reference for the thermal insulation design of cylindrical anaerobic reactors.     

A critical review on different roughness geometries and their effect on heat transfer and friction factor

Solar air heater (SAH) is simple and the greatest effective approach to utilize and convert solar energy into thermal energy for heating utilizations. The employment of artificial roughness under side of the observer surface is the key technique for augmenting heat transfer with minimal friction factor penalty. Current paper summarized different kinds of artificial roughness used in SAH, which augments its performance. In this review article, 96 research papers are cited, which provide detailed information about the effect of different geometrical parameters on heat transfer and friction factor. This paper also brings the information about the optimum roughness parameters and heat transfer and friction factor correlation developed by different investigators in tabular form. Optimum roughness parameters and empirical correlations are used for comparative analysis of heat transfer, friction factor, and thermo-hydraulic performance parameter (THPP) of different roughness geometries. The best performing roughness geometry is reported on the basis of comparative analysis. Mathematical model is developed for predicting the thermal efficiency (η_th) of roughened SAH duct.

     

污水处理厂污泥干化焚烧处理可行性分析

以绍兴污水处理厂脱水污泥为研究对象,通过实验分析了污泥进行干化焚烧处理的可行性。对污泥泥质进行分析,采用桨叶式污泥干化机对污泥的热干化特性、干化过程污染排放特性进行研究,使用流化床污泥焚烧试验装置对污泥焚烧工况及焚烧过程中污染物的排放特征进行研究,结果表明,绍兴污水处理厂脱水污泥的泥质特征与大多数污水污泥类似,灰分较高、发热量较低,需干化后才可实现稳定燃烧;污泥在小型桨叶式污泥干化机内的干化速率最高达到0.6kg/(m2·min),并随污泥干化的进行而逐渐降低;干化过程产生的常规污染气体中氨气浓度最高,可达170 mg/Nm3;污泥干化冷凝水的COD高达820 mg/L,氨氮等指标也很高。污泥干化系统的设计需充分考虑污泥热干化过程中气体和液体污染物的排放,设置相应的处理设施。污泥干化至含水率30%时,可在不投加辅助燃料的情况下实现流化床焚烧炉内的焚烧处理,干化污泥焚烧时需关注烟气中常规污染气体和重金属的控制,焚烧灰渣浸出毒性未超过国标限值。     

Polymeric cracking of waste polyethylene terephthalate to chemicals and energy

Polyethylene terephthalate (PET) is a widely used thermoplastic. PET residues represent on average 7.6 wt% of the different polymer wastes in Europe. Pyrolysis of these wastes is attracting increasing interest, and PET is a potential candidate for this thermal process. The paper measures and discusses the kinetics of the pyrolysis reaction in terms of the reaction rate constants as determined by dynamic thermogravimetric analysis, with special emphasis on the required heating rate to obtain relevant results. The product yields and compositions are also determined. Gaseous products represent 16-18 wt%. The amounts of condensables and carbonaceous residue are a function of the operating mode, with slow pyrolysis producing up to 24 wt% of carbonaceous residue. Major condensable components are benzoic acid, monovinyl terephthalate, divinyl terephthalate, vinyl benzoate, and benzene. The present paper complements previous literature findings by (1) the study of the influence of the heating rate on the reaction kinetics in dynamic pyrolysis tests, (2) the isothermal investigation in a fluidized bed reactor to pyrolyze PET, and (3) the assessment of upgrading and recovery of the products. The paper concludes with a proposed reactor recommendation for PET pyrolysis, in either the bubbling or circulating fluidized bed operating mode.     

基于膨胀特性的厌氧流化床反应器的设计和运行控制

生物流化床的床层膨胀行为直接与生化反应区的水动力学和效率相关 ,床层膨胀特性是进行合理设计和运行的重要依据。目前流化床设计一般没有考虑生物膜的影响 ,但生物颗粒的流化行为有别于光滑载体 ,因此需要对曳力系数Cd 和膨胀特性方程中的ui 进行必要的修正。在综合分析基础上 ,探讨了优化两相流化床设计和运行的程序和方法     

A neural network-based approach for the prediction of urban SO2 concentrations in the Istanbul metropolitan area

A three-layer Artificial Neural Network (ANN) model was developed to forecast air pollution levels. The subsequent SO₂ concentration (24-hour averaged) being the output parameter of this study was estimated by seven input parameters such as preceding SO₂ concentrations (24-hour averaged), average daily temperature, sea-level pressure, relative humidity, cloudiness, average daily wind speed and daily dominant wind direction. After Backpropagation training combined with Principal Component Analysis (PCA), the proposed model predicted subsequent SO₂ values based on measured data. ANN testing outputs were proven to be satisfactory with correlation coefficients of about 0.770, 0.744 and 0.751 for the winter, summer and overall data, respectively.