The Cold Experimental Study Of Mixing Characteristics Of Secondary Air Jet In Circulating Fluidized Bed Boiler

In recent years, due to the rapid development of economy, the demand of energy is excessively increasing and the energy problem has become an important restriction factor of economic development. Meanwhile, the extensive exploitation and utilization of resources strengthen the pressure of environment and ecosystem. The CFB combustion technique, with high adaptability of fule, high combustion efficiency and high combustion intensity, has become the optimal choice of clean combustion technology as well as an strong booster for the development of clean coal power generation technology,.However, the implementation of the Twelfth Five-Year Plan promotes the construction of ecological civilization and improve the requirements of environment protection. Hence, the CFB boiler must be large-scale, high parameterized and supercritical, which draw a higher demand of energy conservation and emission reduction, as well as the mixture of wind and coal. Secondary air jet is one of the most important combustion technologies needed to be solved and improved.In CFB boiler, the wind plate on a certain height will send a part of the fluidization air as secondary air into the chamber to guarantee the abundant supply of oxygen for combustion, maintain the bed temperature of dense-phase zone, strengthen the premixed combustion of furnace material and control the gas-solid flow field and the reaction process in the bed effectively.With the large-scale development of CFB boiler, the amount of secondary tuyere is restricted to improve the secondary air jet depth in the oven, which leads to the uneven diffusion or insufficient jet depth of secondary air.This paper aims to deal with the uneven diffusion or insufficient jet depth of secondary air. In a visual CFB boiler cold test bench, a series of cold experimental tests on the secondary air jet characteristics were completed with bed material of circulating ash of particle size less than 1 mm. The experiment includes four aspects:(1) An experimental study based on different fluidization wind and secondary wind velocity to research the effect of the primary air and secondary air on gas-solid mixture concentration.(2) An experimental study based on different fluidization wind velocity, secondary wind velocity and different secondary air nozzle shapes to research the range of secondary air.(3) An experimental study based on different fluidization wind velocity, secondary wind velocity and different secondary air nozzle shapes to research the diffusion of secondary air.(4) Referred to the test data, find out the relations among the range and diffusion of secondary air, the velocity of secondary air and fluidization wind, the cross area and shape of secondary air nozzle.Through isothermal jet method, which heats the secondary air rather than fluidization wind, this experiment reflects the range and diffusion of secondary air. By using the temperature measuring network, the data acquisition and processing system and the data image processing software, the change of temperature become visual to reflect the range and diffusion of secondary air. The result of the study shows:(1) Fluidization wind and secondary air’s effects on furnace concentration: as fluidization wind velocity increases, the material concentration dense-phase zone decreases while dilute phase zone increases; with the increase of secondary air velocity, the concentration of secondary tuyere declines.(2) Nozzle shape’s effect on the range and diffusion of secondary air: the range and diffusion of secondary air was mainly affected by the cross section area of nozzle. The range and diffusion of secondary air are enhanced with the increase of the nozzle cross section area; with a same cross-section area, the diffusion of circular nozzle is weaker than rectangular nozzle.(3) Fluidization wind velocity’s effect on the range and diffusion of secondary air: the range and diffusion of secondary air is weakened along with the augment of fluidization wind velocity.(4) The secondary wind velocity’s effect on the range and diffusion of secondary air: the range of secondary air increases while diffusion decreases with the augment of the secondary wind velocity.(5) According to experimental data, the relation between the range of secondary air and the cross section area of nozzle as well as between the fluidization velocity and the secondary wind velocity can be gained.