炼化废液焚烧飞灰粒子沉积与分布特征研究

发布时间：2018-04-26 17:14

本文选题：炼化废液焚烧 + 余热锅炉　；参考：《大连理工大学》2015年硕士论文

【摘要】：石油化工、冶金、制药等行业排放的毒性大、生物降解能力弱的高含盐有机废液给生态环境带来的危害日趋严重。目前,国内外处理工业有机废液常用方法为热化学转化法,如焚烧法,此方法不仅可以使废液中有害物质彻底分解,而且可以回收焚烧过程产生的高温能量,达到节能环保的目的。但是,在回收余热过程中,余热锅炉换热元件往往会产生严重的积灰、结渣问题,给余热锅炉安全、稳定运行带来一系列不利影响,如积灰搭桥、热效率降低、高温腐蚀、换热元件磨损等。本文以某石化企业炼化废液焚烧余热锅炉为研究对象,对炉内飞灰粒子迁移、分布和沉积特征、余热锅炉换热及阻力特性进行数值模拟研究,主要研究内容及结论如下：(1)建立余热锅炉气-固两相流动及换热数学模型,利用热动力学平衡计算软件FactSage得到废液焚烧形成富碱(盐)型飞灰粒子的熔融曲线,并根据其物化特性,提出将临界速度黏附模型与熔融组分黏附模型相结合,即采用临界速度-熔融组分黏附模型对炉内飞灰粒子黏附情况进行评价。通过将数值计算结果与现场测试数据进行对比,验证了本文建立的气-固两相流动和换热数学模型的合理性,以及提出的飞灰粒子黏附模型的可靠性。大尺寸粒子沉积全部发生在换热管迎风侧-60°到600范围内,沉积层呈山峰状分布；微米级粒子在管子迎风侧沉积层同样呈山峰状分布,且主要集中在-500到50°区间内,在背风侧则均匀分布；亚微米级粒子均匀沉积于管子迎风侧和背风侧。(2)利用临界速度-熔融组分黏附模型对多种因素影响下锅炉内飞灰粒子迁移、分布及沉积特征进行研究。结果表明：粒子尺寸、管型、烟气流速、横向管间距对粒子沉积概率影响显著,而纵向管间距只对亚微米级粒子沉积概率影响明显；增大半椭圆管长短半轴比、横向管间距或减小烟气流速,均可以显著减小粒子沉积概率；随着纵向管间距的增大,亚微米级粒子沉积概率减小明显,而微米级和大尺寸粒子以及粒子总沉积概率则呈微弱增大趋势；粒子尺寸对沉积概率影响显著,粒子尺寸越大,沉积概率越大。(3)对余热锅炉内换热及阻力特性进行研究,并利用综合对流换热性能评价指标PEC反映换热与压力降变化产生的综合效果。结果表明：增大长短半轴比、烟气流速或减小横向管间距,均可以获得更好的综合对流换热性能,当S2/D取2时,PEC取得最大值。其中,烟气流速对PEC影响最为显著；入口烟气流速增大给炉内Nu数和压力降带来显著提高,而随着长短半轴比、横向及纵向管间距的增大,Nu热系数和压力降均随之降低。
[Abstract]:In petrochemical, metallurgical, pharmaceutical and other industries, organic waste liquid with high salinity and low biodegradability is harmful to the ecological environment. At present, the common methods of treating industrial organic waste liquid at home and abroad are thermochemical conversion method, such as incineration method. This method can not only completely decompose the harmful substances in the waste liquid, but also recover the high temperature energy produced by incineration process. Achieve the purpose of energy saving and environmental protection. However, in the process of recovering the waste heat, the heat transfer elements of the waste heat boiler often produce serious ash deposition, slagging problems, which bring a series of adverse effects to the safe and stable operation of the waste heat boiler, such as building bridges, reducing the thermal efficiency, and corroding at high temperature. Wear and tear of heat transfer elements, etc. In this paper, the characteristics of fly ash particle migration, distribution and deposition, heat transfer and resistance characteristics of waste heat boiler in a petrochemical enterprise are studied. The main research contents and conclusions are as follows: (1) the mathematical model of gas-solid two-phase flow and heat transfer in waste heat boiler is established. The melting curve of waste liquid incineration to form alkali (salt) type fly ash particles is obtained by using the thermal dynamic equilibrium calculation software FactSage. According to its physical and chemical characteristics, the critical velocity adhesion model and the melt component adhesion model are proposed to evaluate the adhesion of fly ash particles in the furnace by using the critical velocity-melting component adhesion model. By comparing the numerical results with the field test data, the rationality of the proposed mathematical model of gas-solid two-phase flow and heat transfer and the reliability of the proposed model are verified. The deposition of large size particles occurred in the range of -60 掳to 600 掳on the upwind side of the heat transfer tube, and the sediment layer was distributed in the form of a peak, while the micrometer particles distributed in the same way in the sediment layer of the tube side, and mainly concentrated in the range of -500 掳to 50 掳. On the leeward side, the submicron particles are uniformly deposited on the upwind and leeward sides of the tube. The critical velocity-melt component adhesion model is used to study the transport, distribution and deposition characteristics of fly ash particles in the boiler under the influence of many factors. The results show that particle size, tube type, flue gas flow rate and transverse tube spacing have significant effects on particle deposition probability, while longitudinal tube spacing has significant effect on submicron particle deposition probability, and increases the semi-elliptical tube length / half-axis ratio. The deposition probability of submicron particles decreased significantly with the increase of the longitudinal tube spacing or the decrease of flue gas velocity, and the deposition probability of submicron particles decreased significantly with the increase of the longitudinal tube spacing. However, the micrometer and large size particles and the total deposition probability of particles have a slight increasing trend, and the particle size has a significant effect on the deposition probability, and the larger the particle size, the greater the deposition probability.) the heat transfer and resistance characteristics in the waste heat boiler are studied. The comprehensive convection heat transfer performance evaluation index PEC is used to reflect the comprehensive effect of heat transfer and pressure drop. The results show that the better comprehensive convection heat transfer performance can be obtained by increasing the ratio of long and short axis, flue gas velocity or decreasing the transverse tube spacing, and the maximum value of PEC is obtained when S2 / D is 2. The influence of flue gas velocity on PEC is the most significant, and the increase of inlet flue gas velocity increases significantly the number of Nu and pressure drop in the furnace, while the thermal coefficient and pressure drop decrease with the increase of transverse and longitudinal tube spacing with the increase of the ratio of long and short axis.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X742

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