【作者】 杨光；

【导师】 倪明江； 肖刚；

【作者基本信息】 浙江大学 ， 热能工程， 2017， 硕士

【摘要】 发展煤炭分级转化清洁发电技术、整体煤气化联合循环发电技术(IGCC)等煤炭清洁利用技术,是解决当前中国能源与环境问题的重要途径。高温下的气化气净化是这些先进技术的普遍要求与关键环节。高温静电除尘技术因为其除尘效率高、烟气处理量大、压损小等优势,是一种极具应用前景的高温气体净化技术。然而目前高温静电除尘技术的试验数据较为缺乏,理论欠完善,在试验与应用中也存在较多问题,例如反电晕放电、清灰方式等影响到除尘器长时间稳定运行的问题,高温静电除尘技术尚不能满足这些洁净煤技术的要求。论文开展了线管式静电除尘器在高温(350～700℃)下的积灰特性试验研究与颗粒捕集、沉积特性的模拟研究,以期为高温静电除尘器的长时间稳定运行提供理论指导。首先对350～700℃温度范围的线管式静电除尘器收尘极内壁的积灰层特性进行了试验研究。研究发现,存在四种典型积灰形式:灰带形、带灰肋的斜坡形、斜坡形和带厚底的斜坡形。积灰层厚度总体上随高度的增加而减小。当温度≤5000℃时,除尘器运行在较低端口电压下会出现灰带形积灰,随着端口电压增大,积灰带变宽而彼此重叠,形成带灰肋的斜坡形积灰;当温度≥500℃时,只要保证端口电压足够大,积灰层会呈较为光滑的斜坡形。当温度≥700℃时,大多数颗粒沉积在收尘极10cm以下的内壁上,形成带厚底的斜坡形积灰。积灰形式随运行工况的不同,能实现一定的转变关系。随着运行时间的增加,积灰层厚度增大,受积灰层与荷电颗粒间的静电斥力影响,积灰层厚度增长速率逐渐下降,积灰高度逐渐增加;反电晕放电通常发生在积灰层最厚处,其起始电压会随积灰层最大厚度增加而近似线性地减小。在500℃、17200V、650mg/Nm3工况下,随着最大积灰厚度从0.34mm增加到2.02mm,反电晕放电起始电压从19787V接近线性地下降到 17197V。为分析高温线管式静电器中的除尘过程与颗粒运动情况,建立了一个颗粒动力学与颗粒收集的三维理论模型,并利用商业CFD软件Fluent对模型进行模拟计算。计算结果表明:高温线管式静电除尘系统的除尘效率计算结果与实验结果符合较好;增大端口电压与增大气体停留时间是提高除尘效率的有效方法,7s以上的停留时间可以获得大于0.9的除尘效率;在620℃,17310 V的工况下,粒径大于6μm的颗粒收集效率接近100%,而亚微米颗粒(0.1-1μm)只有～40%;当气流中微小颗粒较多时,就要求更大的除尘器管长以获得更大的气体停留时间.而多级除尘器技术可用于增大微米和亚微米颗粒的捕集效率,同时也是一种处理量扩大化的布置方式。对于直径为1μm的颗粒,一段式、二段式、三段式ESP的除尘效率分别为0.44,0.69和0.82。颗粒进入除尘空间的初始位置对颗粒运动轨迹有很大影响,以粒径为10μm的颗粒为例,颗粒的初始位置靠近收尘极时,颗粒沉积高度更低,收尘所需时间越短。积灰层厚度随着高度增加而减小,且减少的速率较为稳定,大多数(>80%)的颗粒沉积在除尘器的下半部分。釆用较短的初级除尘器进行预除尘,二、三级除尘器进一步除尘,这种多级除尘布置方式可以增大清灰周期,减少清灰的工作量。更多还原

【Abstract】 Advanced clean coal technologies,such as the coal-staged conversion poly-generation system,integrated gasification combined cycle(IGCC)are important methods to solve the problem of energy and environment.High-temperature dust removal is a key issue for these technologies.Electrostatic precipitators(ESP)have a collection efficiency of greater than 0.99,wide operating ranges of flue gas volume and particle size,negligible pressure loss,reliability and ease of operation,high temperature ESP is a potential technology for high-temperature dust removal.However,reports on high temperature ESP are limited to date,and more investigations are needed.There are many problems in the test and application,such as back corona discharge and ash cake cleaning.Without solving these problems,high temperature ESP cannot meet the requirements of the advanced clean coal technologies.This present work studies the characteristics of ash layers and numerical simulation of particle collection and deposition in a high-temperature wire-cylinder electrostatic precipitator at temperatures from 350℃ to 700℃,to provide theoretical guidance for a long-term and stable application of high temperature ESP.Firstly,the characteristics of the ash layer on the internal surface of the anode pipe of a wire-cylinder ESP were studied at temperatures ranging from 350℃ to 700℃,including ash deposition forms,growth of ash layer and the effect of ash layer on back corona discharge.There are four typical ash deposition forms:the belt form,the slope with ribs form,the slope form and the slope with a thick bottom edge form.Ash layer thickness generally decreases with increasing height.When T ≤500℃,ash belts form under low port voltages,and with increasing port voltage,they will overlap each other to form ash ribs.When T≥ 500℃,particles are deposited in the smooth slope form if the port voltage is great enough.When T≥700℃,a thick bottom ash edge occurs.Ash deposition forms can vary under different operating conditions.As the operating time increases,the thickness growth rate at a given point decreases,and the ash layer height increases because of the repulsive electrical force between the ash layer and the particles.Back corona discharge always occurs on the thickest portion of the ash layer first.The back corona discharge onset voltage decreases nearly linearly with increasing ash layer thickness,from 19787 V to 17197 V as the maximum thickness of the ash layer increases from 0.34 to 2.02 mm when T =500℃,Up =17200 V and min = 650 mg/Nm3.To investigate the particle tracing and trapping process in a high-temperature wire-cylinder electrostatic precipitator,a 3D numerical model is developed to simulate the particle dynamic field and particle collection process.The commercial computational fluid dynamics software FLUENT is used to solve the numerical model,and the simulation results agree well with the experimental results.Increasing the port voltage(Up)and residence time is an effective means to improve collection efficiency.For example,a residence time of over 7 s can always result in a collection efficiency of over 0.9.The collection efficiency for particles larger than 6 μm is nearly 100%when the temperature is 620℃ and the port voltage is 17310 V.The collection efficiency for submicron particles is only about 40%.The height of the cylindrical precipitator should be large when many small particles are present.Multistage ESP technology should be adopted to achieve high collection efficiency for micron-and submicron-sized particles.A scale-up method is also proposed.The collection efficiency for 1 μm particles increases from 0.44 to 0.69 and then to 0.82 when the number of stages increases from one to two and then to three,respectively.The initial position of particles can much affect particle trajectory,e.g.particles of 10 μm diameter will deposit at a low height in a comparatively short time if they enter the ESP nearby the anode tube.Ash layer thickness decreases uniformly with increasing height,and most ash particles(>80%)are collected on the lower half of the ESP.Using a multistage ESP with a short pre-stage ESP is a probable means of prolonging the cleaning period and reducing the ash-cleaning workload.更多还原