| Reducing carbon emissions is an important measure to achieve sustainable development and carbon neutrality.In the future,wind power,solar power and other new energy power generation will obtain significant development opportunities,and its installed capacity will continue to increase.However,wind power and solar power have the characteristics of volatility,randomness and intermittence,which is unfavorable to the stable operation of power grid and power dispatching.In order to ensure the safe and stable operation of this kind of new energy power generation connected to the power grid and absorb its power generation to the greatest extent,the circulating fluidized bed boiler is required to undertake the task of depth and peak regulation of the power grid.In addition,the national energy administration has announced the relevant policies of thermal power participating in deep and peak regulation and flexible transformation.Therefore,it will become normal for circulating fluidized bed boilers to participate in deep peak shaving.When the CFB boiler participates in deep and peak regulation,the temperature of dense phase zone is too low.The practice shows that this problem affects the safe and stable combustion of the boiler,and even has the possibility of flameout.In view of this problem,it is found theoretically that the temperature of dense phase zone can be increased by reducing the amount of circulating ash.From this point of view,this paper studies the cyclone separator which can flexibly change the performance,so as to adjust the amount of circulating ash in the operation process,and puts forward two new types of pneumatic cyclone separators: conical cylinder air supply cyclone separator and non-vortex finder air curtain cyclone separator.The performance of two kinds of pneumatic cyclone separators was studied by cold state experiment and numerical simulation.Firstly,the cyclone separators of the cold test-bed were transformed into cone-shaped cyclone with air supply and non-central cyclone with air curtain,and the cold experiments were carried out to study the influence of air supply on separation performance under different transformation schemes.It is found that the two kinds of pneumatic cyclone separators can adjust the separation efficiency by controlling the gas flow in the cold state experiment,so as to realize the flexible control of the cyclone separator performance.After comparing the experimental results of the separation efficiency of the two kinds of pneumatic cyclone with the numerical simulation results,it is considered that the numerical simulation settings adopted in this paper are more reasonable,which can be used to study the performance of the separator and explain the performance changes.The gas-solid two-phase flow in the cone-shaped cyclone presents a spiral downward trajectory,which passes through the 0°,90° and 270° holes.Therefore,the effect of purging the three holes on reducing the separation efficiency of the cyclone is greater,and the separation efficiency of the 90° hole can be reduced by 0.83% at the gas supply speed of 10 m/s.The results show that the separation efficiency of the cyclone without vortex finder air curtain decreases after the vortex finder is removed,and the separation efficiency increases after the air curtain is formed.There is an optimal air curtain speed to make the separation efficiency reach the highest.In this paper,when the air curtain speed is 9 m/s,the separation efficiency reaches the maximum of 96.2%,which is 4.9% higher than that of the conventional cyclone with vortex finder.The reason why the air curtain can improve the separation efficiency of the separator is that the air supply can form a "W-shaped" air curtain,which can inhibit the short-circuit flow and the top ash ring.Finally,two retrofit schemes of pneumatic cyclone separator are applied to a 300 MWe CFB boiler cyclone separator.The performance of the cyclone separator is predicted by numerical simulation,and the influence of separation efficiency change of cone-shaped cyclone with air supply cyclone separator on dense phase zone bed temperature is analyzed by thermal calculation.Through simulation calculation,it is found that the effect of 0° and 90° hole gas supply on reducing separation efficiency is better,and the separation efficiency decreases with the increase of gas supply speed.The best effect is when the gas supply speed of 90° hole is 30m/s,and the separation efficiency decreases from 94.1% to 92.04% when there is no gas supply.In this paper,it is found that the separation efficiency is reduced by 90° based on the comprehensive efficiency and pressure drop.Using the separator to calculate the temperature change of dense phase region when the separation efficiency changes at 115 MWe load,the 90°hole gas supply scheme can increase the problem of dense phase region by 20 °C.In the air curtain type transformation without vortex finder,the separation efficiency is obviously reduced after removing the vortex finder,and the separation efficiency can be improved when the air supply forms the air curtain,and the separation efficiency increases with the increase of the air curtain speed,but it can’t reach the separation efficiency when the vortex finder exists.It is found that both the conical cyclone and the non central cyclone can flexibly change the separation efficiency after gas supply,but the pressure drop will increase after gas supply.Therefore,it can be considered that the flexible adjustment of the separation efficiency of the cyclone is at the cost of increasing energy consumption,Therefore,we should choose the aerodynamic form and speed carefully. |
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