| Circulating fluidized bed(CFB)boilers have the advantages of wide adaptability of coal types,low pollution emissions,and large load adjustment range.It is one of the main clean coal combustion technologies in my country at this stage.In recent years,with the further improvement of boiler capacity parameters,the continuous increase of energy conservation and emission reduction requirements of all sectors of society and government departments,and the rapid increase in the proportion of new energy power generation,the peak shaving characteristics and operational reliability of large CFB boilers have been raised.Requirements.There is an urgent need to optimize and improve the air distribution system of large CFB boilers to improve the reliability of long-term low-load operation and rapid peak shaving.Therefore,the experimental method was used to study the gas-solid flow characteristics of 6 bellows nozzles with different structures and their perturbation characteristics to the surrounding bed material particles,and the numerical simulation was used to study the airflow characteristics near the nozzle.The results of the study are intended to provide specific industrial application data for the design and operation of large circulating fluidized beds.In terms of experimental research,this paper built a single nozzle gas-solid fluidization test bed and carried out the resistance characteristics,fluidization characteristics,gas-solid flow characteristics and large particle deposition characteristics of the bell-type air nozzle in the bed,etc.Cold and hot test research.The research results show that the size of the inner tube orifice of the nozzle is the main factor affecting the resistance of the nozzle,and the resistance coefficient of the nozzle A decreases first(from 50 to 32)as the wind speed increases(5.4-13.5m/s).Stable trend.In addition,the resistance method was used to measure the fluidization characteristics of the nozzle,and the disturbance range of each nozzle under different wind load was obtained.And through analysis,it is found that when the total area of the inner tube orifice and the cover outlets of the nozzle A(take the nozzle A as an example)is 1577.9mm~2 and 3890mm~2,the disturbance radius under the rated load is about170mm;when the amount of fluidized air is constant,with the increase of the total area of the inner tube orifice of the nozzle,the disturbance range of the nozzle is basically unchanged;as the total area of the cover outlets of the nozzle increases,the wind speed of the nozzle outlet decreases,the disturbance range of the nozzle becomes smaller,which means that the change of the cover outlets has a greater influence on the disturbance range than the change of the inner tube orifice.Based on the above research,the high-speed camera was used to visually measure the disturbance range of the bell-type nozzle A on the bed particles under cold(room temperature)and hot(100℃-300℃)conditions.In the cold state,the perturbation range of the wind cap is in the form of a "droplet" with a narrow upper and lower width.With the increase of the amount of fluidized wind,the perturbation range of the nozzle shows an increasing trend,which is consistent with the results obtained by resistance method.In the hot state,the disturbance radius of the disturbance range is close to 170 mm,which basically does not change with temperature.In addition,the analysis results show that there is the deposition of large particles near the bell-type air nozzle,but the height of the accumulation of large particles decreases with the increase of the amount of fluidized air or the temperature of the fluidized wind,which shows that the fluidization characteristics of the particles become better.Using Fluent software,the resistance distribution,fluidized wind velocity distribution and material concentration distribution in the bell-type air nozzle and the bed of the test bed were numerically analyzed.The research results obtained the distribution law of the resistance pressure drop inside the test rig and the nozzle;the distribution law of the fluidizing wind velocity near the bell-type air nozzle,the fluidizing wind flowed upward after a certain jet depth after being ejected from the cover outlets.The fluidized wind speed of the disturbance section under the rated load is calculated to be 0.62m/s.At the same time,it was found that the fluidized wind velocity pulsation value near the small hole outlet of the nozzle cover is large,and there is a fluidized dead zone at the top of the nozzle,which is an important reason for the wear of the top wall of the nozzle. |
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