氧热法制备电石过程中复合原料颗粒的热质传递和反应性能研究

发布时间：2018-01-25 20:09

本文关键词： 电石合成氧热法煤钙复合颗粒热质传递数值模拟　出处：《北京化工大学》2015年硕士论文　论文类型：学位论文

【摘要】：电石,在工业上用于生产需求量极大的乙炔,对有效利用各种碳源有重要意义。氧热法合成电石工艺针对目前工业上电热法高消耗低产能的弊端进行改进,取得了较显著的进步。本文依托北京化工大学提出的氧热法电石工艺中的复合床反应器,提出使用煤和熟石灰粉末制成粒状复合颗粒的造粒工艺。考察了其在复合床反应器中的热质传递和化学反应行为,分别为氧热法工艺造粒及反应器设计的几何、操作参数提供参考。复合原料的组成之一为煤,该物质热质传递及反应行为较为复杂,直接影响到后续复合颗粒的燃烧及反应。故本文研究了煤热解过程适用性最广的分布活化能模型(DAEM),并对其进行了简化近似。通过改进后的高斯-埃尔米特求积公式对外层积分近似后,分别讨论了在典型的线性升温和非线性升温条件下对内层温度积分的近似。得到的DAEM的近似解,在一定的条件下能够耦合在CFD程序中,有较广的适用范围,大大减少了计算量,且相比于前人的近似方法,提高了精确度。其次考察了反应器密相段,复合颗粒原料与燃烧区生成的高温CO换热,有效吸收热量后热解的过程。研究了不同颗粒结构、组成及气速下复合颗粒热解过程中的热质传递行为,结果表明：(1)枕形、球形、蛋壳形三种结构的复合颗粒,在1280K下热解完成时的反应时间分别为115s、180s、350s。均相复合颗粒更有利于其热解过程。枕形结构颗粒热解性能最优。(2)Ca(OH)2分解是复合颗粒热解的控制步。煤中大量的水会明显延迟热解反应时间。(3)增大气速,对流换热效应增强,但其增大幅度随着气速的增大而逐渐减小。最后研究了复合颗粒热解后的固相产物在下落床段与高温氧气发生燃烧反应,为电石合成反应提供热量的过程。考察了辐射、颗粒结构、组分及操作温度的影响：(1)通过对比计及辐射模型和不计及辐射模型的计算结果,表明热辐射对燃烧过程传热有较大的影响,辐射传热不能忽略。(2)枕形、球形、蛋壳形颗粒在1400K下含碳量降至电石反应的需求时所需时间分别为155s、476s、1 10s,说明复合颗粒的结构对其燃烧过程有较大影响。反应结束时蛋壳形结构炭钙接触面温度未达到电石生成反应温度。枕形颗粒的燃烧性能也最优。(3)1400K的操作温度下,孔隙率是影响反应速率的主要因素。综合考虑,含水量少,孔隙率大的煤种有利于复合颗粒的热解及燃烧过程。(4)1600K和1400K时,燃烧反应为扩散控制。1200K下,反应初期为反应控制,20s以后,颗粒内部O：已消耗完全,为扩散控制。故推测转折温度在1200K左右。1200K的操作温度不能满足电石合成温度,1600K和1400K操作温度下,反应速率相差不大,故最优操作温度为1400K。
[Abstract]:For the production of calcium carbide, acetylene in great demand in the industry, is of great significance to the effective use of various carbon sources. Oxygen hydrothermal synthesis process for calcium carbide industry at present high consumption low capacity electric heating method was improved and achieved remarkable progress. Combined reactor thermal process based on oxygen acetylene Beijing University of Chemical Technology in the proposed granulation process using coal and lime powder made of granular composite particles was studied. The heat in the composite bed reactor transfer and chemical reaction, respectively. The geometric oxygen heating process granulation and reactor design, provide the reference operating parameters. One of the composite material composed of coal. The material of heat and mass transfer and reaction behavior is more complex, directly affects the combustion reaction and subsequent composite particles. Therefore, this paper studies the distribution of coal pyrolysis process is the most extensive activation energy model (DAE M), and the simplified approximation. The quadrature formula improved Gauss Hermite integral outer approximation, respectively discusses the approximation of the inner heating temperature integral under the condition of linear and nonlinear temperature typical. Approximate solution of the obtained DAEM can be coupled in the CFD program in a certain next, a wide range of application, greatly reducing the amount of calculation, and compared to the previous approximation method, to improve the accuracy. This is followed by the dense section of high temperature reactor, generating CO composite particles of raw materials and the combustion zone heat transfer process, effectively absorb heat after pyrolysis. Effects of different particle structure, heat the pyrolysis process of composite particle matter composition and gas velocity in the transfer behavior, results showed that: (1) pillow shaped, spherical, egg shaped composite particles of three kinds of structure, the reaction time in 1280K pyrolysis were 115s, 180s, 350s. composite Particle is more conducive to the pyrolysis process. The pyrolysis performance of the optimal structure of pincushion. (2) Ca (OH) 2 is the control step decomposition of composite particles in coal pyrolysis. The pyrolysis reaction time will be significantly delayed. A large amount of water (3) increase in gas velocity, heat transfer enhancement effect, but it increases with increasing gas speed decreases gradually. Finally the solid products of composite particles after pyrolysis combustion reaction occurs in the fall bed section and high temperature oxygen process provides the heat for the calcium carbide synthesis reaction was studied. The effects of radiation, particle structure, composition and operating temperature: (1) by comparing the calculation results of radiation model and. The model shows that the heat and radiation, radiation has a great influence on the heat transfer process of combustion, radiation heat transfer cannot be neglected. (2) pillow shaped, spherical, egg shaped particles in the time required for 1400K carbon to calcium carbide reaction needs respectively 155s, 476s, 10s 1, said The structure of the composite particles have great influence on the combustion process. At the end of the reaction shell shaped structure of carbon calcium contact surface temperature does not reach the reaction temperature. The combustion performance of calcium carbide is optimal pillow particles. (3) 1400K operating temperature, the porosity is the main factors influencing the reaction rate. Considering water content fewer, larger porosity of coal pyrolysis to composite particles and combustion process. (4) 1600K and 1400K, the combustion reaction is controlled by diffusion of.1200K, the initial reaction for reaction control, 20s, O, has been completely consumed inside the particles, as a diffusion control. It is speculated that the operating temperature of.1200K transition temperature in 1200K about not meet carbide synthesis temperature, 1600K and 1400K operating temperature, the reaction rate is small, so the optimal operating temperature of 1400K.

【学位授予单位】：北京化工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ161

【共引文献】