Enhanced pulverized coal mass flow measurement

Two methods of coal flow measurement are described in this article for a pulverized coal injection (PCI) process into blast furnaces. The original coal flow design is based on vessel weight variation along the time, a moving average and an ordinary PID controller. Enhanced coal flow devices of mass solid correlation with an auto-calibration unit were specially designed and installed in the main conveying pipeline of three coal injection stations. Therefore, the PCI plant now takes advantage of each measurement and chooses the best for safety interlocks and control.     

Influence of strain on flame propagation in laminar flow

The influence of velocity gradients, in a laminar approach flow, on the local burning velocity was investigated, to supplement and verify recent theoretical work.Different velocity profiles were obtained at the exit from a circular burner, using pipes of different lengths between the exit and a settling chamber, and these profiles were measured using hot wire anemometry. The burning velocity and the velocity component parallel to the flame front were obtained by means of the “angle method” using direct photographs of the flame.The results, presented as burning velocity versus velocity gradient along the flame front, show that the local laminar burning velocity decreases as the rate of “stretching” of the flame is increased.     

On-line tracking of pulverized coal and biomass fuels through flame spectrum analysis

This paper presents a new approach to the on-line tracking of pulverized coal and biomass fuels through flame spectrum analysis.A flame detector containing four photodiodes is used to derive multiple signals covering a wide spectrum of the flame from visible,near-infrared and mid-infrared spectral bands as well as a part of far-infrared band.Different features are extracted in time and frequency domains to identify the dynamic ＂fingerprints＂ of the flame.Fuzzy logic inference techniques are employed to combine typical features together and infer the type of fuel being burnt.Four types of pulverized coal and five types of biomass are burnt on a laboratory-scale combustion test rig.Results obtained demonstrate that this approach is capable of tracking the type of fuel under steady combustion conditions.     

基于Fluent的煤粉燃烧器风管流场数值模拟与分析

利用Fluent软件对煤风管道内气-固两相流进行模拟仿真,通过观察固体颗粒运动轨迹,对管道内冲蚀磨损进行研究分析。利用RNG k-ε湍流模型和拉格朗日离散相模型对燃烧器煤风管道内煤粉颗粒-空气两相流场进行耦合数值模拟,对比分析了输煤管在不同角度α时的流场特性和颗粒运动轨迹,发现当α≤15°时,管道壁面冲蚀磨损率有所降低;管道中除了存在冲蚀磨损,同时还伴随有摩擦磨损。通过对计算结果的分析和讨论,发现燃烧器设计的不合理因素,对煤粉燃烧器结构改进和相关参数优化有一定指导意义。     

基于光照补偿和模糊增强的煤粉区分割方法

针对回转窑烧结带火焰图像中煤粉射流混合区域(“黑把子”或“煤粉区”)存在光照不均和粉尘影响的问题,提出一种基于自适应光照补偿和模糊增强的煤粉区分割方法.首先利用图像的局部均值对图像亮度进行垂直方向自适应光照补偿,然后采用水平投影隶属度均值作为渡越点对应的模糊阈值,对煤粉区进行水平方向自适应模糊增强,最后用快速模糊C均值聚类分割黑把子区.实验结果表明,所提出的方法可有效克服窑内火焰图像的光照不均和图像模糊问题,快速完整地分割模糊图像中的黑把子区域,具有较强的鲁棒性.     

Effect of devolatilization model on flame structure of pulverized coal combustion in a jet-burner system

Journal of Mechanical Science and Technology - A numerical simulation was performed with the two competing model in the devolatilization process for a pulverized coal combustion jet flame by means...     

锅炉煤粉气力输送状态在线监测系统研究

煤粉气力输送状态在线监测对磨煤机工作状态以及锅炉炉膛燃烧安全、均衡和稳定性的评估具有重要意义.在理论研究的基础上,研制了一种基于激光脉动法和互相关法测试原理的锅炉煤粉气力输送过程参数在线监测系统,以实现煤粉气力输送过程状态的在线监测.该系统通过煤粉流经系统探头测量区时的激光脉动信号,经过光电信号转换元件、信号滤波以及数据分析处理后得到煤粉浓度、细度以及速度特征参数,进而评估磨煤机和煤粉管道运行状态.现场安装和测试结果表明,该系统具有测量精度高、成本低以及安装简便等特点.     

火力发电厂煤粉流量测量技术研究

火力发电厂总燃料量的精确测量是进行锅炉燃烧控制优化的关键难点问题。本文系统地提出了火力发电厂煤粉流量的测量技术,并结合实际应用经验提出各种测量方法的技术要点以及制约点,同时结合工程实践提出了煤粉流量测量技术的发展展望,为进一步研究实践煤粉流量的测量技术奠定了基础。     

Large eddy simulation of two-phase reacting turbulent flow in a pilot-scale pulverized coal combustion furnace with flamelet model

Journal of Mechanical Science and Technology - A three-dimensional numerical simulation was performed to investigate the physics and combustion characteristics of a two-phase reacting turbulent...     

火电厂煤粉浓度软测量研究

软测量技术是基于推断控制理论的一门新兴工业技术。本文在介绍软测量技术的基本原理及其设计步骤的基础上,详细介绍了火电厂采用热平衡法、动压法建立煤粉浓度的软测量模型,通过模型校正和在装置上实现软测量,保证煤粉浓度的在线测量。     

锅炉送粉管道煤粉浓度的电容层析成像测量方法研究

锅炉燃烧过程中,准确测量各风管中的煤粉浓度并指导调节对锅炉的安全、经济运行非常重要.采用电容层析成像技术(ECT),对常温下锅炉煤粉气力输送的固体浓度进行了测试研究.为克服电容传感器敏感场的不均匀性对成像造成的影响,实验系统中装置了一个旋风分离装置,通过旋风分离作用将固体颗粒主要集中在壁面区域,传感器电极布置在分离器直管上.这种测试方法的优点在于不破坏原有系统的运行特性,属于非侵入式、在线的快速测试技术.通过搭建实验台及相应的在线测量系统,并对不同浓度工况进行测量及对比分析,实验结果证明了该测量方法的可行性及可靠性.     

锅炉分层燃烧装置使用中存在的问题及改造

链条锅炉分层燃烧技术是一项节能技术,但因所用燃煤特点未能充分发挥节能效果,通过技术改造针对燃煤特点采取有效措施,取得很好效果.     

高压煤粉混合及发电装置的设计

针对高炉煤粉喷吹过程中煤粉混合不均匀、压能浪费的问题,提出了一种新型工业设备——高压煤粉混合及发电装置。主要由直通闭式叶片轮、对称直通式空心轴转子组成。利用多叶道分流原理,使煤粉混合更均匀;由能量守恒定律,将高压煤粉压能转化为叶片轮的机械能并带动发电机转子转动,实现了煤粉发电的创新。用Solid Works对该装置进行了建模,用FLUENT对煤粉在叶道中的流场分析。结果表明,煤粉能较好的进入装置与空气混合,推动叶轮旋转发电。     

Thrust bearings in time-dependent laminar flow

An analysis of thrust bearing characteristics in a motion generated by an accelerating slider is presented. Numerical solutions to the governing differential equations are obtained for the case of constant but arbitrary acceleration and for the case of acceleration proportional to time. It is found that the space inertia effect increases the pressure and consequently the loadcarrying capacity. However, drag also increases. The results indicated three classes of solutions depending on the magnitude of a dimensionless number which is the ratio of the time required for the fluid particle to traverse the length of the bearing to the time required for the slider to reach its terminal velocity.     

Magnetic field effect on fluid flow characteristics in a pipe for laminar flow

The influence of a magnetic field on the skin friction factor of steady fully-developed laminar flow through a pipe was studied experimentally. A mathematical model was introduced and a finite difference scheme used to solve the governing equations in terms of vorticity-stream function. The model predictions agree favourably with experimental results. It is observed that the pressure drop varies in proportion to the square of the product of the magnetic field and the sine of the magnetic field angle. Also, the pressure drop is proportional to the flow rate. This situation is similar to what applies in the absence of a magnetic field. It is found that a transverse magnetic field changes the axial velocity profile from the parabolic to a relatively flat shape. At first, the radial velocity rises more rapidly and then gradually decreases along the pipe until falling to zero. A numerical correlation can be written for the considerable distance required for the new axial velocity profile to establish. Owing to the changes taking place in the axial velocity profile, it exhibits a higher skin friction factor. The new axial velocity profile asymptotically approaches its limit as the Hartmann number becomes large.     

Tables for boundary-layer thicknesses of similar compressible laminar flow

Similarity solution of the compressible, laminar boundary-layer equation depends on pressure gradient parameter β and wall to inviscid stagnation temperature ratiog _w . However, the derived quantities, such as various thicknesses, also depend on speed parameter S, thereby requiring three dimensional tables for the tabulated results. A new formulation is provided that enables all quantities of interest to be determined by the two-dimensional tables in which β andg _w are the input parameters. With such a set, accurate values can be found for the skin-friction coefficient, Stanton number, and the five most common viscous and thermal boundary-layer thicknesses for arbitrary values of the speed parameter. A comprehensive set of tables is provided in which β ranges from its separation value to 100 andg _w ranges 0 to 5. Quasi-linearization method is applied to the governing equations and generalized Newton-Raphson method is used to obtain successive initial condition. As a result computation time is reduced significantly.     

The characteristics of pulverized coal combustion in the two stage cyclone combustor

Numerical investigations on air staging and fuel staging were carried out with a newly designed coaxial cyclone combustor, which uses the method of two stage coal combustion composed of pre-combustor and main combustor. The pre-combustor with a high air/fuel ratio is designed to supply gas at high temperature to the main combustor. To avoid local high temperature region in this process, secondary air is injected in the downstream. Together with the burned gas supplied from the pre-combustor and the preheated air directly injected into main combustor, coals supplied through the main burner react rapidly at a low air/fuel ratio. Strong swirling motion of cyclone combustor keeps the wall temperature high, which makes slagging combustion possible. Alaska, US coal is used for calculations. Predictions were made for various coal flow rates in the main combustor for fuel staging and for the various flow rate of secondary air in the pre-combustor for air staging. In-scattering angles are also chosen as a variable to increase residence times of coal particles. Temperature fields and particle trajectories for various conditions are described. Predicted temperature variations at the wall of the combustor are compared with corresponding experimental data and show a similar trend. The in-scattering angle of 20° is recommended to increase the combustion efficiency in the main chamber.     

A solution of the thermohydrodynamic problem for laminar flow bearings

This paper introduces a semi-analytical method for solving the thermohydrodynamic problem in journal bearings. The momentum equation is reduced to three ordinary differential equations by separation of variables. Two of the resulting equations are integrated directly, while the third is interpreted and solved as an isoperimetric problem. The energy equation with its boundary conditions is solved by the Galerkin Kantarovich method.