【作者】 黄书峰；

【导师】 沈恒根；

【作者基本信息】 东华大学 ， 环境工程， 2011， 博士

【摘要】 我国能源结构以燃煤为主,燃煤锅炉及工业炉窑排放含尘烟气量大,随着环保要求的提高,高温含尘烟气处理需要采用高效的除尘净化设备,袋式除尘器以其高效的除尘性能成为钢铁、水泥、冶金、化工及垃圾焚烧等行业最主要的烟气净化设备。现有袋式除尘器在处理高温含尘烟气时滤袋易堵塞、烧穿。本文分析不仅是因为烟气温度过高或波动过大造成滤袋损坏,更主要是含尘烟气中的高温颗粒对滤袋造成的破坏。解决滤袋易损坏的问题,本文从整个除尘净化工艺角度出发,而不局限于袋式除尘器内气流组织优化和滤袋选用,提出配合袋式除尘器净化含尘烟气的预处理技术,以保护袋式除尘器稳定运行。含尘烟气预处理技术包括气固预分离及含尘烟气降温两个方面内容。现在工业应用中袋式除尘器常采用一级除尘,含尘烟气经风管均匀流直接输送进入袋式除尘器,多采用蛇形管等延长含尘烟气输送长度的方法通过风冷方法对烟气降温。本文提出通过改变管内输送含尘烟气的流场结构的方法把强化气固分离与传热相结合的理念。通过起旋器促使含尘烟气旋转运动,运动轨迹由轴向流变成螺旋流,延长含尘烟气的运动轨迹,有助于烟气的降温,烟气旋转运动引入较大的切向速度,加大对壁面的冲刷,减薄边界层厚度,强化了烟气通过管壁的传热,使烟气降温。同时旋流的离心力作用促使气固两相预分离去除粒径较大且温度较高的颗粒,保护滤袋,实现节能减排的目标。本文提出新型蜗向单进口及双进口圆管旋流起旋器,设计轴向旋流结构,并对起旋器的结构进行了初步优化。通过冷态圆管旋流试验,得出新型单进口及双进口蜗向起旋圆管旋流的流场及阻力特性,分析了三维流速分布的主要特点及对烟气预处理的强化特性,并分析了压力场分布特性。通过理论分析的方法,建立旋流流动流场分布模型及压力分布模型,采用数值模拟的方法,建立相应的物理模型,并采用雷诺应力模型(RSM), SIMPLEC耦合压力速度项,模拟新型蜗向起旋圆管旋流运动,模拟结果与试验及理论分析的变化规律较为吻合,表明数值模拟模型的有效性。在流场分析的基础上,本文理论分析了旋流流动中颗粒的运动特性,建立颗粒运动模型。采用边界层分离理论,确定了旋流气固分离的切割粒径,建立了气固分离的分级分离效率模型。通过数值模拟的方法,分析不同起旋方式的气固分离效率,模拟结果与理论分析基本一致。本文建立套管式换热试验模型,并通过光滑管的传热试验与经验数据的比较,验证了传热试验的有效性。在此基础上,研究了不同蜗向起旋圆管旋流的传热特性。根据试验结果得出Nu数拟合关系式,试验结果表明了双进口起旋方式比单进口起旋方式强化效果明显,增强25%左右。在对旋流传热试验的基础上,建立传热强化评价指标,并通过场协同理论探讨了旋流强化传热的机理及优化方法。在传热试验基础上,通过数值模拟的方法对不同起旋旋流强化的传热特性进行了分析。模拟结果与试验结果相比较基本一致。通过数值模拟,得出不同起旋圆管旋流的局部Nu数随轴向管长近似指数衰减,双进口起旋方式Nu数高于单进口起旋方式,设导流核后改变起始阶段旋流结构,局部Nu数增加。旋流越强,传热强化程度越高,且双进口起旋比单进口起旋的旋流衰减缓慢,设导流核后使初始切向速度较大,但相应衰减速度也较大,最终都趋向于充分发展湍流传热模式。本文分析了旋流中颗粒的受力运动,并采用分离变量法建立颗粒与气流的传热模型。一般高温烟气中尘粒的Bi≤0.1时,采用集总参数法简化颗粒降温模型,并初步分析颗粒降温与气流降温的动态平衡,引入时间常数σp,得出粒径越小的颗粒降温与气流降温达到动态平衡的时间越短,且与气流间的温差越小；反之粒径大的颗粒达到动态平衡时间越长,且与气流间的温差越大,这也为本文提出预处理烟气不仅需要降温而且要结合气固分离去除较大粒径颗粒提供理论依据。本文在试验研究、理论分析和数值模拟的基础上,针对马鞍山钢铁股份有限公司干熄焦炉用袋式除尘器运行存在的问题,根据本文提出的新的设计理念,应用新型蜗向起旋技术,对其进行配套改造,设计了烟气预处理系统,并对设计应用情况进行了归纳和总结以利于新技术的应用于推广。本文提出对烟气的预处理,可保护袋式除尘器稳定运行,保护滤袋。对新型蜗向起旋旋流强化气固分离与传热的特性进行了初步研究和分析,建立的分离效率模型还需通过试验分析进行进一步的验证,新技术与袋式除尘器的配合使用性能还需进一步试验验证。更多还原

【Abstract】 Huge amounts of smoke dust that boilers and industrial furnaces generated have been released into the atmosphere. The main energy in China still depends on coal providing. With increase of requirements for environment protection standards on emissions is enacting. Now dust emission must not exceed 30mg/m3 in some sectors. The bag type dust remover has high efficiency for dust remover which applies to power, coal burning boiler, metallurgy and chemical engineering. The bag dust remover becomes the important decontaminating equipment in china. However, the bag dust is not very thorough in domestic such as bag chocking up or bag burned through. Filter bag’s technology as the key technical of the bag type dust cleaning need to be further studied. It is pointed out that not only the high flue gas temperature or much volatility temperature fluctuant destroys the filter bag, but the particles of the high temperature is more importantly part of destroying the filter dust bag. The pretreatment of dusty gas is put forward.The pretreatment of dusty gas includes gas-solid separation and cooling. Now the dusty gas is conveyed straightly by duct and cooled by air extending transportation distance with snake-pipe. The change of straight flow to swirl flow is put forward. The tangential velocity of dusty gas is produced. The movement of dusty gas changes to spiral flow and the delivery distance of dusty gas increases. There is centrifugal force field for gas-solid separating. The movement has flushing function to wall surface to enhancing heat transfer in tangential direction.The new swirl generators of single helical inlet and double helical inlets are given. Swirl flow moves towards downstream. The devices mating bag filter are helpful to protect the bag and reduce the run cost。The operation mechanism and effect of the devices are carried out by using experimental, theoretical and simulated by using CFD method.Firstly, on the basis of reviewing the recent study in separation and heating transfer by swirl flow, new generating swirl devices by helices are presented which use the XCY-3.0’s inlet configuration. Swirl flow generating models include single inlet by 180 degree helix without guide-core (Model SO) and with guide-core (Model S1), double inlets compositing of 90 and 270 degree helix without guide-core (Model DO) and with guide-core (Model D1).Secondly, the characteristics of swirl flow and pressure field are studied by theoretical analysis. Mathematical models of velocity profile, pressure drop and separation for four models are developed. According to the Newton motion law, the traces of particles in axial swirl are analyzed. The unsteady heat transfer between particles and gas is discussed. A model of particle’s heat transfer was developed by using Lumped Para meter Method (LPM). It shows that the smaller particle will get to steady heating transfer between particles and gas more quickly and have smaller temperature difference. The heating enhancement of swirl flow is analyzed under the guidance of field coordination between velocity and heat flow fields.Thirdly, experiments of swirl flow by four kinds of swirl generators are carried on. It indicated the tangential velocity reaches a peak near the wall which divides the profile into central semi forced vortex and annular semi free vortex. Axial component differs from the developing or developed smooth pipe flow; flow is accelerated near the wall, despite being decelerated in the central region, and back flow appears in the core. Model S1 and D1 with guide-core can hold up more swirl intensity during axial initial sector, so better for gas-solid separation than SO and DO respectively. The flow resistance model with swirl generators is developed and the swirl flow intensity is described by swirl number S. The decaying swirl number decreases approximately in exponential with the axial distance. The experimental setup with a concentric tube heat exchanger has been demonstrated for studying the enhanced heat transfer performance of swirling flow. By comparing the smooth tube heating transfer test, it is proved that the experimental method is feasible. The relationship of Nusselt number, Reynolds number and swirl number is analyzed. The assessment index of enhancement efficiency and friction factor is used to evaluate heat transfer enhancement techniques. The results show that D1 model is better than other models for enhancing heat transfer.Fourth, numerical simulation is an effective approach of investigating swirl flow. The swirl flow field and temperature field were simulated by means of Reynolds Stress Model (RSM). The SIMPLEC algorithm is used to handle the pressure-velocity coupling. The flow fields of gas-solid separation are simulated with Discrete Phase Model (DPM). Comparing with the experimental results, it shows that the data determined by numerical simulation is reasonable. Results show that the enhancements in Nu number are higher in compare with smooth pipe flow based on generating swirl flow and increase with Re number.After all, based on the theoretical analysis, experimental research and numerical simulation, the pre-processing device working with bag type collector is devised to cooling and cleaning gas discharged by Mashan steel’s dry coke quenching (DCQ) furnaces. It has shell-tube construction, gas by swirl generator flows through the tube side, and cooled fluid flows through shell side with counter flow type cooling. It is provided clearly to avoiding to chocking up and burning through the filter bag. The design method and energy-economic analysis is provided.In general, the new type swirl structure with helices designs for gas-solid separating while simultaneously enhancing heat transfer. The pretreatment technology protects the filter bag and makes protection of bag filter and stable operation. The separation efficiency models are established by researching and analyzing on enhancing gas-solid separation and heating transfer by pipe swirl flow. It need go on with further study about the applications of pretreatment technology and the performances with the cooperation of bag filter.更多还原