黑液燃烧过程建模及数值模拟

发布时间：2018-07-21 09:03

【摘要】：碱回收锅炉是应用于制浆企业的一种特殊设备,其燃料为制浆产生的黑液,通过燃烧能够在利用黑液中能源的同时还回收其中所含的碱盐。碱回收锅炉的设计和运行与传统的燃煤锅炉存在很大的差别,在当前精细化设计的要求下,传统的设计方法已经难以满足要求。国外应用数值模拟技术对碱回收锅炉进行模拟,可预知一定条件下锅炉燃烧状况,为优化设计和改善操作条件起到了很大的作用,而国内目前针对碱回收锅炉炉内燃烧数值模拟技术的研究很少。黑液的燃烧特性与煤存在很大的差别,Fluent中针对煤燃烧而提出的模型在应用于黑液燃烧模拟时会出现较大的误差,所以有必要给出针对于黑液颗粒燃烧的数学模型。本文提出了用于估算黑液颗粒内部具体成分的成分估算模型。根据黑液的燃烧过程不同阶段的特性,将黑液燃烧过程分成了干燥、热解、表面反应等阶段,通过检测颗粒内组分的含量来判断颗粒所处燃烧阶段,给出了针对黑液的颗粒燃烧模型。考虑到部分黑液颗粒粒径较大,且在炉膛气相空间中停留时间较短,还未来得及燃尽就落到了炉膛底部,提出了用于考虑颗粒落到炉膛底部继续燃烧的焦床模型。在确定颗粒燃烧过程计算流程的基础上,以流体动力学计算软件Fluent为平台,将黑液颗粒燃烧模型和焦床模型以UDF的形式嵌入了Fluent。之后在一个简单的二维网格中对该UDF程序的可用性与正确性进行检验,结果表明程序能够按要求运行且能够定性地模拟黑液颗粒的燃烧过程。针对一台处理量300tds/d的碱回收锅炉,在对锅炉炉内燃烧特征进行分析的前提下,提出了几何处理方案。根据一、二、三次风的布置以及锅炉的燃烧特性,提出了网格划分方案。利用自编的黑液燃烧UDF程序对该锅炉的燃烧情况进行了模拟,得到了炉内速度、温度、组分浓度的分布以及不同初始粒径的颗粒在气相空间中的运动轨迹,对锅炉内的燃烧、机械携带以及可能出现的腐蚀、结渣情况做出了定性的预测。
[Abstract]:Alkali recovery boiler is a kind of special equipment used in pulping enterprise. Its fuel is black liquor produced by pulping. By combustion, it can recover the alkali salt while utilizing the energy in black liquor at the same time. The design and operation of alkali recovery boiler is very different from that of traditional coal-fired boiler. Under the requirement of fine design, the traditional design method is difficult to meet the requirement. The application of numerical simulation technology to the simulation of alkali recovery boiler abroad can predict the combustion condition of the boiler under certain conditions, which plays a great role in optimizing design and improving the operating conditions. At present, there are few researches on the numerical simulation of combustion in alkali recovery boiler. There is a great difference between the combustion characteristics of black liquor and that of coal. The model proposed in fluent for coal combustion will have great errors when it is applied to the simulation of black liquor combustion, so it is necessary to give a mathematical model for black liquor particle combustion. In this paper, a component estimation model for estimating the specific components of black liquor particles is proposed. According to the characteristics of different stages of black liquor combustion, the combustion process of black liquor is divided into drying, pyrolysis, surface reaction and so on. A particle combustion model for black liquor is presented. Considering that the particle size of some black liquor is large and the residence time is short in the gas space of the furnace, it falls to the bottom of the furnace before burning out. A coke bed model is proposed to consider the continuous combustion of particles falling on the bottom of the furnace. On the basis of determining the calculation flow of particle combustion process, the black liquor particle combustion model and the coke bed model were embedded in the form of UDF on the platform of fluent. The usability and correctness of the UDF program are verified in a simple two-dimensional grid. The results show that the UDF program can run as required and can simulate the combustion process of black liquor particles qualitatively. Based on the analysis of combustion characteristics of a alkali recovery boiler with 300tds/d, a geometric treatment scheme is proposed. According to the layout of the first, second and third air and the combustion characteristics of the boiler, the scheme of grid division is put forward. The combustion of the boiler was simulated by using the UDF program of black liquor combustion, and the velocity, temperature, distribution of component concentration and the movement track of particles with different initial diameter in the gas phase space were obtained, and the combustion of the boiler was also obtained. Mechanical carrying and possible corrosion and slagging are predicted qualitatively.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TK229

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