Cold Model Experiments And Numerical Simulation Of The Second Air Injection Characteristic On A CFB Boiler

Because of many advantages as wide adaptability with fuels, ideal adjustability with load and well pollutant control, circulating fluidized bed (CFB) combustion technique become the best choice of clean coal combustion technique. But with the large-scale development of CFB boiler, many problems appear. The range of secondary air (SA) is one of the most important problems. The secondary air can't come to furnace center for low secondary air jet stiffness. It will influence the combustion in the furnace center.In a visual cold experimental apparatus, a series of cold experimental tests on the secondary air jet characteristics were completed with bed material of ash floater. The cold experimental tests mainly include:â‘ The cold fluidizing characteristic of the CFB boiler model;â‘¡The average solid particle concentration in the furnace cross section of secondary air nozzle;â‘¢The range of secondary air jet under different condition of solid particle concentration, secondary air velocity and diameter of secondary air nozzle.In order to measure the range of secondary air exactly, different temperature spout test method was used. The room air was used as primary air. In the same time, heated air was served as secondary air. The thermocouple temperature measuring net was fixed in the secondary air plane. The secondary air range was gotten through measuring the temperature in the furnace. A data acquisition and treatment system was used to complete the temperature measuring in temperature measuring net in the cross section of secondary air plane. Graphical treatment software was used to treat temperature data and realize the visible results.From the experiments and analysis, below results were gotten:â‘ The cold experimental tests indicate the critical fluidizing velocity was 0.17m/s when the bed material was floater. This result was basically equal to the critical fluidizing velocity calculated by experience formula (0.182m/s);â‘¡The solid particle distributed as core-annular in the secondary air plane, and the concentration of solid particle increased in direct ratio to the fluidized air;â‘¢The max range and diffusion of secondary air jet was in direct ratio to the momentum of secondary air jet when the concentration of solid particle remained steady, and in inverse ratio to the particle density when the momentum of secondary air jet remained steady.â‘£Through collecting data gained from experiments, a formula of max range was proposed.The cold numerical simulation to the characteristics of secondary air was completed based on the cold experimental texts. The results of the cold numerical simulation mainly included:â‘ The change trend of the range of secondary air decreased while the velocity of primary air increased in the same velocity of secondary air, different velocity of primary air and diameter of nozzle;â‘¡The velocity of secondary air decreased to zero in a certain distance;â‘¢The range of secondary air from numerical simulation basically equaled to the experiment result.