入炉污泥含水率对污泥干化焚烧工艺影响研究

以上海某污水处理厂为例,通过理论计算和工程设计分析,研究了入炉污泥含水率(质量分数)对污泥干化焚烧工艺的影响.结果表明,随着干化程度的提高,对干燥机处理能力的要求提高,对干燥机型式的选择余地缩小,对焚烧炉、余热锅炉等设备的要求也将提高,对设备材质、系统安装、运行管理的要求也将相应提高.随着污泥干化程度的降低,进料量和烟气量增大,导致焚烧和烟气处理设备体积庞大.由于污泥泥质特性随时间变化大,在污泥热值整体偏低的地区,采用60%入炉污泥含水率存在一定的风险.污泥入炉含水率对污泥焚烧处理工程中的工艺选择及布置影响较大,工程设计中不应简单照搬国内外类似工程,而应根据当地污泥泥质特性、热值、辅助热源等实际情况,合理选择入炉污泥含水率.     

The characteristics of whole-tree fuel stocks from silvicultural cleanings and thinnings

The fuel properties of small-sized whole-tree fuel stocks were studied in roadside and in-stand storages. The significance of pile cover, season and storage site on moisture content and heating value of Scots pine (Pinus sylvestris) and pubescent birch (Betula pubescence) fuel stocks were observed.When the fuel stocks are placed in a well-ventilated location moisture content may be lowered below the 40% mark during one summer period. Covering the piles will give up to 6% units lower moisture content in comparison with non-covered piles. The most benefit is gained from covering during snow melting in spring and the least in midwinter when the snow is dry.Multi-tree harvested stemwood with no limbs seasoned equally well as the whole trees both in roadside and in-stand trials. This is because the processing of multi-tree bunches caused some debarking to take place. As a result, the transpiration drying capability of whole trees was equalized by the evaporation of moisture via the open wood surface. Both assortments reached moisture contents below 30% in in-stand conditions during one summer's seasoning.The effective heating values of neither birch nor pine showed significant changes. However, heating value deviated with the composition of the fuel stock. The presence or absence of crown material was a factor.The microbial counts of mesophilic fungi in whole-tree fuel stocks were only 1% of that found in logging residues. The counts of thermo-tolerant fungi were still much smaller. Leaving the Scots pine piles uncovered will increase the number of mesophilic fungal spores and bacteria.     

含易挥发组元炉渣的高温性能检测

冶金炉渣常含有易挥发组元,在加热过程中,这些组元的挥发使得炉渣成分发生变化,导致炉渣性能测定误差(或称为测不准),如炉渣的熔点、粘度等测定。基于对挥发机制和炉渣性能测定过程,探讨了现行冶金炉渣性能测定中易于造成误差的原因,提出了对现行测定方法中冶金炉渣成分进行修正进而与高温性能测定结果对应的方法。对含易挥发组元的炉渣,如高氟化物含量、高钾钠氧化物含量以及高铅锌氧化物含量的炉渣性能测定具有参考价值。     

加热法测量湿度探针取样过程的数值模拟与分析

建立了加热法测量湿度探针进口附近区域流场的数学模型,并通过对其进行数值模拟来分析由于非等动能取样及汽流方向偏离轴线所造成的测量误差,从而为加热法测湿探针的设计及其在工程中的运用提供依据。     

场地有机污染土壤原位热修复过程中热质传递机制研究

针对现有原位热修复技术能耗较高且在修复过程中热质传递机制不明的问题,研究了现场试验过程中的土壤温度场变化、修复效果和能耗,采用数值模拟方法对温湿度场的变化进行了验证。结果表明：加热井呈正六边形排布时,修复区域的受热较为均匀,各测温点在修复35 d后,温度均达到200.0℃以上,修复后场地满足第二类用地筛选值;在标准状态下,试验过程中天然气用量总计685 664.0 m³,每修复1.0 m³污染土壤约消耗62.8 m³天然气;加热井热量主要为修复场地侧壁供能,对于位置低于加热井的土壤作用较小,加热井轴向土壤体积含水率分布较为均匀,但加热井底部体积含水率较高,修复区域底部水分不利于修复场地温度的提升,数值模拟和试验数据的吻合度较高,平均相对误差MRE为20%,为场地有机污染土壤原位热修复技术应用提供技术支撑。     

锅炉飞灰采样装置结露堵灰的原因分析及其对策

锅炉飞灰采样装置常出现堵灰,影响飞灰含碳量测量装置的工作.为此,以自吸式飞灰等速采样装置为例,对结露堵灰问题进行了分析和计算,并提出了合理进行取样管线保温.压缩空气吹扫及吹扫空气预热等解决措施,取得了良好的运行结果.     

Thermal modelling of the high temperature treatment of wood based on Luikov's approach

A 3D, unsteady‐state mathematical model was used to simulate the behaviour of wood during high temperature treatment. The model is based on Luikov's approach and solves a set of coupled heat and mass transfer equations. Using the model, the temperature and moisture content profiles of wood were predicted as a function of time for different heating rates. Parallel to the modelling study, an experimental study was carried out using small birch samples. The samples were subjected to high temperature treatment in a thermogravimetric system under different operating conditions. The experimental results and the model predictions were found to be in good agreement. The results show that the distributions of temperature and moisture content are influenced appreciably by the heating rate and the initial moisture content. Copyright © 2005 John Wiley & Sons, Ltd.     

Effects of Moisture and Hydrogen Content on the Heating Value of Fuels

Abstract

In this work, effects of moisture and hydrogen contents on lower heating value (LHV) of fuels were investigated. The LHV at constant pressure measures the enthalpy change of combustion with and without water condensed, respectively. Moisture in biomass generally decreases its heating value. Moisture in biomass is stored in spaces within the dead cells and within the cell walls. Higher heating value (HHV) of a fuel decreases with increasing of its moisture content. The LHV of a fuel increases with increasing of its hydrogen content. The LHV of a fuel depends on its oxygen content and the LHV of a fuel decreases with increasing of its oxygen content. The LHV of a fuel increases with increasing the hydrogen content due to cause combustion water. Moisture in a fuel generally decreases its HHV. The LHV of a fuel increases with increasing the sulfur content due to cause SO_x gases absorbed by water.     

Effects of microwave pretreatment on the grinding characteristic of coal

The influence of microwave pretreatment on the heating response, moisture content, surface morphology, grindability, and liberation of coal were investigated. The results show that microwave irradiation has a weak effect on the chemical composition, but can reduce moisture content significantly. Intuitionistic evidence was discovered that microwave energy can induce micron cracks on the interface among different minerals. The results of grinding tests show that microwave pretreatment can remarkably promote the fine grinding of coal. Density analysis shows that the liberation degree of grinding products increases with the microwave pretreatment time due to the auxiliary grinding and selective heating effect of microwave radiation.     

Weather data for building energy cost-benefit analysis

This paper deals with European TRY weather data processing for climatic indexes generation, useful for HVAC energy and cost simplified evaluation. For nine Italian locations are presented: 99 and 2·5% dry bulb temperatures, 2·5% wet bulb temperatures, heating and cooling degree days, latent enthalpy days, unitary sensible and latent loads. TRY psychrometric data were processed according to a bin method that preserves the correlation between dry bulb temperature and moisture content, and then reduced by an averaging technique. An example is worked out in order to present an engineering shorthand for energy and cost evaluation of HVAC system. © 1998 John Wiley & Sons, Ltd.     

Drying of firewood - the effect of harvesting time, tree species and shelter of stacked wood

Firewood represents a renewable source of energy and is the main source of energy for about half the World’s population. When burning firewood in domestic stoves, combustion and thus energy efficiency is dependent on the moisture content of the wood. In Denmark, it is generally recommended that moisture content should be no more than 180 g kg⁻¹ total weight. This study aims to assess the effect of species, harvesting time and shelter on the drying of stacked firewood. After felling, the moisture content declined to a relative stable level for all species. The rate of drying depended on the felling time, tree species, and the presence of shelter. The lower asymptotic moisture content depended mainly on the presence of shelter and averaged 188 g kg⁻¹ total weight for frames left in the open and 154 g kg⁻¹ total weight for frames covered by a shelter. It is concluded that Norway spruce felled during the early summer may obtain an acceptable moisture content at the onset of the heating season. Deciduous trees should be felled during the winter or early spring and stored under shelter to be suitable for burning before the heating season. Shelter was found to be of great importance to maintain an acceptable moisture content of firewood in storage during winter.     

Changes in feedstock quality in willow chip piles created in winter from a commercial scale harvest

Storage and handling are important facets of biomass logistics because there are associated costs and biomass properties can change significantly as material proceeds through the supply chain. Thus, this aspect of biomass supply systems requires continued study. Shrub willow chips were harvested, and used to create six piles that each contained between 10 and 22 Mg (fresh biomass). Material was monitored for several months in temporary storage to assess changes in biomass quality (moisture, ash and energy content). Internal pile temperatures increased due to biological activity and conditions within a pile quickly differentiated based on location (shell, core, top, and side). Mean moisture content increased from 42 to 47% (mass fraction) between harvest and delivery of the chips, but ranged between 37 and over 60% over the next three months depending on pile location with the shell generally drier than the core. Mean ash content increased 1 to 2% points (mass fraction) between harvesting, reloading and delivery to the trial location, but became more variable during storage. Higher heating values (HHV) were stable between 18.6 and 19.0 MJ kg⁻¹ over the six months, but lower heating values (LHV) ranged between 8.6 and 11.7 MJ kg⁻¹ and mirrored changes in moisture content. There was minimal change in chip quality over two months, but quality became more variable over longer time periods. This period could be extended, and negative effects on chip quality could be mitigated, by improving storage methods, blending different types of chips, or employing pretreatments.     

A comparison of models and methods for simulating the microwave heating of moist foodstuffs

We study the problem of heating a one-dimensional approximation to a slab-sided moist foodstuff in a microwave oven, allowing for a phase change and drying. We initially investigate the accuracy of the Lambert law of exponential decay of the applied electric field into the foodstuff and derive an approximation for the field comprising the exponential decay term and an oscillatory component. We then show that the temperature of the foodstuff is given, to a good approximation, by only considering the heating effects of the exponentially decaying field. We then study the effects of drying. This process changes the dielectric properties of the material, which leads to changes in the field. However, these lead to smaller changes in the moisture content. A fast and accurate numerical method is derived which relies on smoothing the phase transition.     

含湿非饱和多孔介质的完全分形传热研究

为了探究在含湿情况下多孔介质有效导热率的变化,基于分形理论,考虑多孔介质在含湿时加热过程中相变的影响,结合加热过程中的热量守恒方程和傅里叶导热定律推导出计算有效导热率的新公式。将该模型相关数据代入进行计算,分析了孔隙率、含湿率、面积分形维数和迂曲分形维数对有效导热率的影响。研究发现,孔隙率与有效导热率呈负相关,含湿率与有效导热率呈正相关,分形维数与有效导热率呈负相关。该研究能够反映多孔介质内的传热进程,对于探究微孔结构物质的传热具有一定的指导意义。     

Experimental investigations of occupied volume effect on the microwave heating and drying kinetics of cement powder in a mono-mode cavity

This paper deals with the microwave heating and drying of cement powder in a mono-mode waveguide. The rapid volumetric heating and drying spare cement hardening and allow recuperation of the powder for reuse, as required from an industrial user. Based upon pilot scale extrapolation, the effect of occupied volume on microwave heating and drying kinetics constitutes the important aim of this experimental work. For different diameters, the parameters measured simultaneously in time are the temperature, the moisture and the mean absorbed power. The change in time of the dielectric properties according to the moisture is observed for different diameters of cylindrical glass support. The volumetric power density decreases while the diameter decreases resulting in rapidity of drying kinetics. This is in agreement with the heating rate before evaporation. The dielectric relaxation coefficient of the humidified powder presents a threshold value of the normalised moisture (45%), which corresponds to the decreasing of absorbed power.     

Influence of moisture content on measurement accuracy of porous media thermal conductivity

The thermal conductivity measurement accuracy of sand was experimentally studied with a hot disk thermal constant analyzer and water morphologies, distribution, and evolution at the pore scale were observed with a charge coupled device (CCD) combined with a microscope. It was found that thermal conductivities of samples with low moisture content (<25%) could not be accurately measured. For samples with low moisture content, the analysis showed that the water in the region adjacent to the analyzer sensor mainly existed as isolated liquid bridges between/among sand particles and would evaporate and diffuse to relatively far regions because of being heated by the sensor during measurement. Water evaporation and diffusion caused the sample constitution in the region adjacent to the sensor to vary throughout the whole measurement process, and accordingly induced low accuracy of the obtained thermal conductivities. Due to high water connectivity in pores, the rate of water evaporation and diffusion in porous media of high moisture content was relatively slow when compared with that of low moisture content. Meanwhile, water in the relatively far regions flowed back to the region adjacent to the sensor by capillary force. Therefore, samples consisting of the region adjacent to the sensor maintained the constant and thermal conductivities of porous media with relatively high moisture content and could be measured with high accuracy. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20272     

Correction of Non-Isokinetic Sampling of Wetness Measurement for Wet Steam Flow

IntroductionThe final stages of large steam turbines in fossilpower plant and all stages of turbines in nuclear powerp1ants operate in the wet steam region. It is important todevelop a simple direct method for measuring thewetness of flowing wet steam. The heating method hasmany advantages. First, compared with optical method,the measured wetness results of this method consist ofevery size of water droplets in wet steam flow. Second, itis not restricted to the measurement environment, it canb…     

A New Capacitance Probe for Measuring the Local Moisture Content in Wet Porous Media

INTRODUCTIONInthestudyofheatandmasstransferprocessesinwetporousmedia,theaccurateandquickmeasure-melltofmoisturecontentdistributioninwetporousmediaiscriticaltounderstandingheatandmasstransportmechanismsintheprocesses.ButthelackofPracticalmeasurementmethodformeasuringthemoisturefieldhinderedthestudyanddevelopmentofthefulldamefitalsoftheheatandmasstransferinwetporousmediatosomeextent[1].Althoughmanymethodsfordeterminingmoisturecontelltinwetporousmediahavebeendeveloped[','ltsuchasthegravimetr…     

Sampling procedure in a willow plantation for estimation of moisture content

Heating value and fuel quality of wood is closely connected to moisture content. In this work the variation of moisture content (MC) of short rotation coppice (SRC) willow shoots is described for five clones during one harvesting season. Subsequently an appropriate sampling procedure minimising labour costs and sampling uncertainty is proposed, where the MC of a single stem section with the length of 10–50 cm corresponds to the mean shoot moisture content (MSMC) with a bias of maximum 11 g kg⁻¹. This bias can be reduced by selecting the stem section according to the particular clone. The average difference in MSMC between the largest and smallest shoot in a stump was 31 g kg⁻¹. This variation is only marginally smaller than the variation found in MC between stumps. The MC of individual stem sections may vary as much as 190 g kg⁻¹ in one shoot. Variation in whole shoot moisture content was primarily influenced by the shoot diameter, but in addition significant effects of clone and shoot age were found.