Study On Triboelectrostatic Separation Unburned Carbon From Circulating Fluidized Bed Boiler Fly Ash

The utilization of fly ash removing unburned carbon is very significant forenergy conservation, emissions reduction and recycling economy.Thetriboelectrostatic separation has obviously technological advantages and very broadapplication prospects in fly ash removing unburned carbon field.This paper focused on the theoretical and experimental research work about thefly ash removing unburned carbon.The flow characteristics of gas and solid phase inthe friction device was analyzed.The flow field numerical simulation of gas-solidphases was achieved in the friction devices with different friction rod structure.Theparticles friction collision in the friction device was investigated in order to find theoptimal structure friction device model. The experiment system for particles collisionsin the friction devices was established.The temperature field distribution of the visualfriction devices was investigated by using non-contact measurement method—infrared thermal imaging technology.To point out a new method for evaluating theparticles friction and collision. The triboelectrification experimental system wasestablished.The experimental medium were single mineral and CFBB fly ash.Theelectrode section particles mass and yield distribution was analysed.The frictioncharged effect of all kinds of friction devices was compared. The LOI variety ofelectrode section was researched.To make a comparative study for removing unburnedcarbon effect in diferent friction devices according to average LOI, removingunburned carbon ratio and efficiency exponent.To probe into an optimal structure ofthe friction devices.These would provide the theoretical basis and technical supportfor the further practical application of fly ash removing unburned carbon withtriboelectrostatic separation.According to the numerical simulation results, the gas-solid flow fielddistribution is closely related with the distribution, spacing, section of frictionrods.The particles in friction devices have different characteristics in movement andcollision.The friction device with regular triangle distribution, spacing20mm, circularsection is an optimal structure.The airflow is accelerated in better station.Thehigh-speed air mass area is biggish and well-proportioned distribution.The particlesmovement path is longer and particles velocity changes concussively.The particlesnumber of velocity variation is the most because of collision.The particles movementis more decentralized and motion trajectory distribution is well-proportioned.The residence time in friction devices is longer.The friction and collision effect may aswell.The particles collision research shows that the temperature field distribution inthe friction devices is nonuniform.The temperature is under the great influence ofairflow, particles movement and collision. The temperature distribution is effected bythe distribution, spacing and section of friction rods.The temperature is higher for thefriction device with regular triangle distribution, spacing20mm and circularsection.The collision probability between particles and friction rods is bigger and thecollision effect is the best. This conclusion is consistent with flow field numericalsimulation.The temperature field distribution can indirectly reflect the frictioncollision properties of particles movement.For the friction charged characteristics, experiments with a single minerals andCFBB fly ash show that friction rods’s distribution, spacing and cross section have aneffect on charged particles mass and charged proportion except for air volume, voltageand particles size.The particles electriferous process is asymmetrical.The mass andyield distribution of electrode section is different each other.The mass and yield ofelectrode section decreases gradually along the particles moving direction.There is themost particles mass and the highest charge-mass ratio in the first interval of positiveand negative plates.The difference of particles mass and charged proportion in thefirst and second interval is obvious for friction devices.The friction rod that haveregular triangle distribution, spacing20mm, circular section have more chargedparticles and higher charged proportion, bigger particles mass and higher frictioncharged effect.Compared with the CFBB fly ash removing unburned carbon effect in differentfriction devices,the results show that the friction rods with regular triangle distribution,spacing20mm and circular section have the best integrative removing unburnedcarbon effect.The first interval and average LOI in the positive plate is maximal andthat of negative plate is minimal. The average removing unburned carbon ratio andefficiency is the best.The friction device can be used to CFBB fly ash removingunburned carbon process.