PDS脱硫体系物性及传质系数的研究

发布时间：2018-02-26 18:20

  本文关键词： 湿法脱硫 pH值 物性 传质系数　出处：《青岛科技大学》2017年硕士论文　论文类型：学位论文

【摘要】：在众多脱硫方法中,PDS法因具有碱耗低、硫容大、硫泡沫颗粒大、易分离、不堵塔等特点,已广泛应用于煤气行业、氮肥行业和焦化脱硫等其他相关行业,并取得了显著的脱硫效果。影响脱硫效果的因素有很多,其中最重要的是体系的pH值。PDS脱硫工艺以Na_2CO_3-NaHCO_3缓冲液为吸收剂来吸收H_2S和稳定体系的pH值,但由于存在副反应及吸收CO_2的现象,需要定期向脱硫液中补充Na_2CO_3,以维持体系pH值的稳定。在实际生产中,往往依靠经验进行调节,缺乏理论指导。本论文通过进行一系列的实验,系统地研究了脱硫液的性质及其对气液传质过程的影响,以期指导生产。PDS法脱硫的吸收液是Na_2CO_3和NaHCO_3组成的缓冲液,它能在一定程度上稳定溶液的pH值,为了研究缓冲液的组成对pH值的影响,本文配制了不同浓度的Na_2CO_3-NaHCO_3溶液,考查其pH值的变化规律,并研究了缓冲液的性质。然后固定溶液的pH值(8.5),考查Na_2CO_3和NaHCO_3的配比关系及对物性(密度、粘度和表面张力)的影响,为研究气液传质过程奠定了基础。脱硫过程中存在副反应,生成NaSCN、Na_2S_2O_3、Na_2SO_3和Na_2SO_4等副盐,打破了Na_2CO_3和NaHCO_3的平衡关系,脱硫液中的副盐对物性和NaHCO_3的溶解度产生一定影响。吸收液的pH值随着副盐含量的增加而降低,随着副盐含量的增加,吸收液的密度、粘度和表面张力都有增大的趋势,但增大的程度不一样,其中粘度变化最大。随着副盐含量的增加,NaHCO_3溶解度减小,温度对溶解度也有一定的影响,基本上呈现温度降低,溶解度下降的规律。为防止发生NaHCO_3析出现象,本文给出了实际运行中的密度操作区间及密度上限的计算公式,这一区间随副盐含量增加而减小。生产中应对脱硫液密度(或副盐含量)和NaHCO_3含量进行同时监测。通过在自制填料塔内模拟脱硫过程,并结合响应曲面设计方法发现:在实验范围内,Na_2CO_3浓度对总传质系数K_Ga的影响极为显著,这是因为Na_2CO_3浓度的变化改变了体系的pH值,从而改变了化学吸收的速率。体系中的副盐也会影响溶液的pH值,通过研究Na_2CO_3和副盐含量对K_Ga的影响发现总体积传质系数K_Ga的变化存在一个敏感区。将三组实验数据进行对比发现Na_2CO_3和副盐对K_Ga的影响主要是通过影响体系的pH值来实现的。采用双膜理论对湿法脱硫的吸收过程进行了描述,研究了气液传质过程中物质传递的机理,并提出了该过程的数学模型。本文采用Onda(恩田)等人的关联式,分别计算了气相传质系数kG和液相传质系数kL,结果表明,Na_2CO_3和副盐通过改变体系的物性改变了kL而对kG并不产生影响,而且从kL的的数值上看,k L的变化量并不大。同时还计算了相应的二级反应速率常数k2,结果显示,随着体系pH值的增大,k2的变化规律与K_Ga的大致相同,说明Na_2CO_3和副盐是通过改变体系的k2来改变总体积传质系数K_Ga的。
[Abstract]:Among the desulfurization method, PDS method has low alkali consumption, high sulfur content, sulfur foam particles, easy separation, no blocking tower and other characteristics, has been widely used in gas industry, fertilizer industry and Coking Desulfurization and other related industries, and has achieved remarkable desulfurization effect. There are many factors affecting the desulfurization effect among them, the most important is the pH value of the system of.PDS desulfurization process with Na_2CO_3-NaHCO_3 buffer as absorbent to absorb H_2S and stabilize the pH value of the system, but due to the presence of side reactions and CO_2 absorption phenomenon, need to be regularly to the desulfurization liquid Na_2CO_3, in order to maintain the pH value of the system stability. In the actual production, often rely on the experience of regulation, lack of theoretical guidance. This thesis through a series of experiments, systematically studied the properties of desulfurization liquid and its influence on the mass transfer process, in order to guide the production of.PDS desulfurization absorption liquid is Na_2CO_3 and NaHC O_3 buffer composition, it can stabilize the solution to a certain extent, the value of pH, in order to study the composition of the buffer effect on pH values, this paper prepared different concentrations of Na_2CO_3-NaHCO_3 solution, the variation of pH value, and study the properties of the buffer. Then fixed solution pH value (8.5 the effects of Na_2CO_3 and NaHCO_3), and ratio on physical properties (density, viscosity and surface tension) influence, laid the foundation for the research on the gas-liquid mass transfer process. The existence of side reaction, the desulfurization process to generate NaSCN, Na_2S_2O_3, Na_2SO_3 and Na_2SO_4 - salt, broke the balance between Na_2CO_3 and NaHCO_3, have a certain impact the solubility of by-product salt in desulfurizing liquid on physical properties and NaHCO_3. The pH value of absorption liquid decreased with increasing salt content on the side, with the increase of the content of secondary salt absorption liquid, density, viscosity and surface tension have a tendency to increase, but the increase of the 绋嬪害涓嶄竴鏍，

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