大型电站锅炉煤粉输送系统均衡性分析及优化

大型电站锅炉煤粉输送系统 均衡性分析及优化 摘 要 电站锅炉煤粉输送系统中风粉的均衡分配影响着锅炉安全性和经济性运行，锅炉同层送粉管道风粉配平显得尤为重要。电站煤粉输送系统的设计以及均衡性调节一般依据《DL/T 5145-2002 火力发电厂制粉系统设计计算技术规定》，但在近些年的工程应用中，实际风粉量偏差过高，影响锅炉的正常使用。本文针对某600MW电站锅炉的直吹式送粉系统进行气固两相流模拟，得出基于数值计算的煤粉输送系统阻力配平方案，探索该方案可以取代通常繁琐的工程设计计算的可能性。 本文首先对电站锅炉煤粉输送系统中的气固两相流的流动特性和相应的数值模型进行了全面总结的基础上，采用FLUENT商用软件对稀相风粉两相流在水平、竖直、弯管等管道和三通管路元件中的流动进行求解，设计电厂锅炉单层并联四个煤粉输送管道分布，并通过加装节流元件对同层管道进行均衡性调节。然后在送粉管道入口加设格栅型煤粉分配器进行管道前风粉均衡分配，建立三维模型并通过数值计算对其进行分析及优化。最后对煤粉输送系统整体均衡性优化，形成较为系统和完善的煤粉输送系统管道设计方案。 数值模拟结果表明：对简单管道和管路元件内气固两相流的数值模拟来看，直管管道内的两相流动中，水平管道受重力影响较大，流动向管道下侧沉积；弯管和三通管内弯曲结构对流动产生较大影响，流动向管道外侧偏斜，需较长直管段才能恢复均匀流动；《DL/T 5145-2002》中的阻力计算不能应用于某一段管道或某个管路元件的阻力计算中，不利于煤粉输送系统的设计及后期改动；数值模拟较好的展现了管内气相和颗粒相的流动，为分析管道内两相流动规律提供指导。由于两相流动的内在复杂性，两相流模拟的准确性与单相流模拟的准确性相比，偏差较大；对于整个管道的模拟计算来说，引入偏差修正公式，对两相流的模拟结果进行修正，并通过对《DL/T 5145-2002》中算例的模拟，将偏差修正公式进行验证。为调节并联输粉管道前的均衡性，对格栅型煤粉分配器内部流动进行数值模拟，了解其流动特性；第一阶格栅对第二阶格栅的流动产生影响，且格栅的交错顺序会进一步破坏风粉分配的均衡性；二阶格栅型煤粉分配器内两相流动受结构的影响，向外侧发生偏斜，较内侧流量大，压力高；随着格栅数目的增多，分配器的流动阻力逐渐增大，当格栅数目增加到一定数量（7个）后，出口偏差不再减小。加装圆形节流孔板对并联输粉管道进行阻力调节，基本达到阻力调平的目的。通过对管道、管路元件和管路设备的数值模拟以及对模拟结果的修正，形成较为系统的煤粉输送系统管路设计方案，为实际生产应用提供指导。 关键词：煤粉输送系统 气固两相流 数值模拟 均衡性调节 ABSTRACT Unevenness distribution of air and pulverized coal is a major problem in the coal powder conveying system of utility boiler. It is most important to trim the air and pulverized coal in powder pipeline, which may pose utility boiler in the hearth. Design and adjustment on the coal powder conveying system of utility boiler generally based on DL/T 5145-2002 Technical Code for Design and Calculations of Coal Pulverizing System of Fossil-fired Power Plant. In recent years, we can find that excessive deviation of powder in the actual application has affected the normal use of the boiler. This article numerical simulates the gas-solid two-phase flow in the direct blowing pulverizing system of 600MW utility boiler. The resistance balancing scheme of coal powder conveying system is achieved based on numerical calculation, so as to explore the feasibility of replacing the tedious engineering calculations. First, comprehensively understand the flow characteristics of gas-solid two-phase flow and the corresponding numerical model for the coal powder conveying system of utility boiler. FLUENT was used to solve the flow of the dilute gas-solid two-phase flow in the horizontal pipe, vertical pipe, elbow pipe and three-way pipeline. The distribution of four coal pipelines in utility boiler is designed, and the equalization pipeline is adjusted by adding the throttle element. Then, the grille type pulverized coal dispenser is added to distribute the wind before the pipeline. Establishes 3D model to analyze and optimize it by numerical calculation. Finally, the systematic resistance balancing scheme of coal powder conveying system is achieved. The numerical simulation of the gas-solid two-phase flow in simple pipelines and the pipeline elements shows that, the two-phase flow in horizontal pipeline is easy affected by the gravity than vertical pipe, and the flow is deposited to the lower side of the pipeline. The bending structure of the elbow and the three-way pipe has a great influence on the flow. The flow is inclined to the outside of the pipe, and need a long straight pipe to restore the uniform flow. The calculation of the resistance in the design and calculation of the pulverizing system can not be applied to the calculation of the resistance of certain pipeline or pipeline element. The numerical simulation shows the flow of gas phase and particle phase nicely in the tube, which provides guidance for the analysis of the two-phase flow in the pipeline.Due to the inherent complexity of the two-phase flow, the accuracy of the two-phase flow simulation is greater than that the single-phase flow simulation. Thus, the deviation correction formula is introduced to correct the simulation results of the two-phase flow in whole pipeline, and the deviation correction formula is verified by the simulation of the example. In order to adjust the evenness before the parallel pipeline, the internal flow of the grill pulverized coal distributor is numerically simulated to understand its flow characteristics. The first order grills will have an effect on the flow of the second order grills, and the staggered order of the grills would further damage the equilibrium of the distribution. The two-phase flow in the second-order grill pulverized coal distribution is affected by the structure, inclining to the outside flow and the outside flow is larger than the inside flow. As the number of grids increases, the flow resistance of the dispenser increases gradually. The exit deviation is no longer reduced when the number of grids increases to a certain number. The installation of circular orifice to adjusts the resistance of the branch pipelines, basically reached the purpose of resistance evenness. By the above method to form a more systematic design scheme of the coal powder conveying system, which provides