多组分复杂介质余热锅炉传热与动态特性研究

发布时间：2018-05-15 11:06

  本文选题：余热锅炉 + 受热面　； 参考：《山东大学》2017年博士论文

【摘要】：能源短缺是社会发展中的一个严重问题,能源回收利用已成为能源行业关注的焦点。余热锅炉是指利用工业废气、废料或废液中的余热加热给水,产生蒸汽的设备,是余热回收过程中最重要的部件。因此,相关余热锅炉运行的分析和优化已成为现阶段余热利用研究的重点。随着余热锅炉结构系统的复杂化及工况的多变性,相关动态特性对余热锅炉的安全、高效运行具有重要意义。同时,由于废气(液)中含有大量的固体颗粒杂质,是一种多组分的复杂介质。颗粒杂质会以不同的形态在换热管表面形成积灰及结渣。颗粒的沉积会导致余热回收效率降低、余热锅炉低负荷运行甚至被迫停机。因此,研究基于变工况、多组分的余热锅炉传热强化、传热动态响应特性及结构设计和优化具有重大意义。本文以U型直流余热锅炉为研究对象,运用理论分析、数值模拟和实验研究方法,分析了锅炉受热面传热、流动、飞灰颗粒沉积及动态特性,主要研究工作及取得的成果如下:1.理论分析颗粒在流体中运动和受力过程,求解了实际工况颗粒运动方程数值解,并分析颗粒运动过程中受到的不同作用力的影响程度。结合颗粒运动数值计算结果及颗粒碰撞、沉积和脱附临界速度参数,建立了一个新的适用于低温受热面的松散型颗粒沉积理论模型,能够较准确地预测受热面飞灰颗粒沉积位置、沉积数量及积灰形态。2.基于商业软件Fluent 15.0,通过自定义函数(UDFs),对U型直流余热锅炉整体进行了全尺寸数值模拟。研究得到各级受热面换热管束间的温度场和流场分布特征,分析了入口烟气温度和流量对锅炉性能的影响。对于单级受热面,包括传统顺排、叉排以及一种新型顺排错流结构,对比管排布置差异对受热面传热、流动和飞灰沉积的影响。针对多组分复杂介质烟气工况,利用低温受热面松散型颗粒沉积模型,研究了不同颗粒粒径和烟气流速对颗粒沉积的影响及沉积分布特征。数值模拟结果表明:在低温烟气工况下,颗粒粒径和烟气流速是飞灰颗粒沉积的主要影响因素。较高的烟气流速使小颗粒有较强的沉积倾向;较低的烟气流速会促进大颗粒的沉积。与传统顺排和叉排受热面相比,新型顺排错流受热面强化传热Nu提高9.8%～23.2%,飞灰沉积降低4.9%～5.6%,该受热面以增加压降及烟气流动阻力为代价,强化传热并有效减少飞灰沉积。3.设计并搭建了 U型直流余热锅炉综合实验平台,利用某水泥厂低温余热对锅炉的传热、流动、积灰特性进行分析,验证了数值模拟的合理性。以U型直流余热锅炉为研究对象,完成了不同烟气温度、烟气量、给水温度及给水量工况的余热实验,分析了不同工况参数对余热锅炉蒸汽温度及蒸汽量的影响。以系统(?)效率为目标,分析了余热锅炉各级受热面换热及(?)损失,并证明U型直流余热锅炉可有效回收低温余热。为进一步回收余热锅炉所产生高温给水中的余热,在理论分析的基础上,构建了变分流点与分流流量余热锅炉-闪蒸系统模型,通过选择不同给水量及给水分流温度,实现系统(?)效率优化。实验结果表明,烟气量32000 Nm3/h的典型工况下,利用余热锅炉-闪蒸系统,选择给水流量15.90 m3/h,分流水温度409.67 K,余热系统和余热锅炉本体最佳(?)效率分别为44.43%和54.61%,实现年收入861000RMB,并在1.1年后收回成本。4.基于热力学原理和质量、动量及能量平衡方程,提出了一个适用于直流余热锅炉不同受热面的动态仿真模型,该模型可模拟给水在换热管内相变过程,弥补实验无法观测的缺陷。模型利用Matlab/Simulink软件建立,同时基于实验工况,并利用遗传算法和粒子群算法对模型进行参数识别和优化。优化后余热锅炉动态模型与实验数据匹配度高,均方根误差范围2.97～4.43。两种优化方法适应度函数收敛值近似,粒子群算法收敛时间更短。模型可预测在启动和停机期间不同工况下的温度变化,在保证金属换热管使用寿命的前提下,获取最佳运行条件。仿真结果表明:余热锅炉停机时间约为启动时间2倍,在冷启动与停机过程中,水温变化呈现与烟气温度变化相同的趋势,但具有一定延迟。给水与烟气共同作用决定给水饱和状态临界点及时刻。
[Abstract]:Energy shortage is a serious problem in the development of society. Energy recovery and utilization has become the focus of attention in the energy industry. The waste heat boiler is the most important part in the process of waste heat recovery, which is the most important part of waste heat recovery process using the waste heat of industrial waste gas, waste or waste liquid, and it is the most important part in the process of waste heat recovery. Therefore, the analysis and optimization of the operation of related waste heat boiler With the complexity of the structure system of the waste heat boiler and the variability of the working condition, the relative dynamic characteristics are of great significance to the safety and efficient operation of the waste heat boiler. At the same time, because of the large amount of solid particle impurities in the waste gas (liquid), it is a complex medium of multi component. The deposition of different forms on the surface of the heat transfer tube forms the accumulation of ash and slag. The deposition of the particles will lead to the reduction of waste heat recovery efficiency, the low load operation of the waste heat boiler and even the shutdown. Therefore, it is of great significance to study the heat transfer enhancement of the waste heat boiler based on the variable conditions, the dynamic response characteristics of the heat transfer and the design and optimization of the structure of the heat transfer. This paper is based on the U type straight. Flow waste heat boiler is used as the research object. Using theoretical analysis, numerical simulation and experimental research methods, the heat transfer, flow, particle deposition and dynamic characteristics of the heated surface of the boiler are analyzed. The main research work and the achievements are as follows: 1. the motion and force process of particles in the fluid are analyzed theoretically and the numerical value of the particle motion equation in the actual working conditions is solved. The influence degree of different forces in the process of particle motion is analyzed. Combining the numerical results of particle motion, particle collision, deposition and desorption critical velocity parameters, a new theoretical model of loose particle deposition suitable for low temperature heating surface is established, which can predict the position of fly ash particles deposition in the heated surface accurately. .2. is based on the commercial software Fluent 15. Through the custom function (UDFs), the overall size numerical simulation of the U type DC waste heat boiler is carried out. The temperature field and flow field distribution characteristics between the heat transfer tubes at all levels are studied. The effects of the inlet flue gas temperature and flow on the performance of the boiler are analyzed. The thermal surface, including the traditional rows, the forks and a new type of dislocation flow structure, is used to compare the influence of the arrangement of the tube arrangement on the heat transfer, flow and fly ash deposition in the heated surface. The numerical simulation results show that the particle size and gas flow velocity are the main factors affecting the deposition of fly ash particles under the low temperature flue gas condition. The higher velocity of flue gas makes the small particles more inclined to deposit, and the lower gas flow velocity will promote the deposition of large particles. The heat transfer enhancement Nu increases 9.8% ~ 23.2% and the fly ash deposit decreases by 4.9% ~ 5.6%. The heating surface is at the cost of increasing pressure drop and flue gas flow resistance, intensification of heat transfer and effectively reducing the.3. design of fly ash deposition and building a comprehensive experimental platform for U type DC waste heat boiler. The rationality of the numerical simulation is verified by the analysis of the characteristics of the dynamic and accumulating ash. Taking the U type DC waste heat boiler as the research object, the waste heat experiment of different flue gas temperature, flue gas quantity, water supply temperature and water supply condition is completed. The influence of different working conditions on the steam temperature and steam quantity of the waste heat boiler is analyzed. The system (?) efficiency is the objective and the analysis of the effect of the system (?) The heat exchange and (?) loss of the heating surface at all levels of the waste heat boiler have been proved, and it is proved that the U type DC waste heat boiler can effectively recover the low temperature waste heat. In order to further recover the waste heat from the high temperature feed water produced by the waste heat boiler, based on the theoretical analysis, a model of the variable flow point and the flow flow waste heat boiler flash system is constructed, and the water supply is selected by the selection of different water supply. The system (?) efficiency is optimized. The experimental results show that, under the typical working condition of 32000 Nm3/h, the water flow rate is 15.90 m3/h, the water flow temperature is 409.67 K, and the best (?) efficiency of the waste heat system and the waste heat boiler is 44.43% and 54.61% respectively, and the annual income is 861000RMB and 1.1. After year, the recovery cost.4. is based on the thermodynamic principle and the mass, momentum and energy balance equations. A dynamic simulation model for different heating surfaces of DC waste heat boilers is proposed. This model can simulate the phase change process in the heat exchange tube and make up for the defects which can not be observed by the experiment. The model is based on the Matlab/Simulink software and is based on the model. The parameters of the model are identified and optimized by the genetic algorithm and particle swarm optimization. The dynamic model of the afterheat boiler is well matched with the experimental data, the average square root error range is 2.97 to 4.43., and the convergence of the fitness function is approximate, and the convergence time of the particle swarm optimization algorithm is shorter. The model can be predicted in the start and downtime. The temperature change under different working conditions and the optimum operating conditions are obtained on the premise of ensuring the service life of the metal heat exchange tube. The simulation results show that the shutdown time of the waste heat boiler is about 2 times the starting time. In the process of cold start and shutdown, the change of water temperature presents the same trend as the temperature change of the flue gas, but it has a certain delay. Gas interaction determines the critical point and time of water saturation.

【学位授予单位】：山东大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TK229.929
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本文编号：1892199