Experimental Study And Numerical Simulation Of Gas Solid Flow Characteristics In Separator's Inlet Ducts Of Imported 300MWe CFB Boiler

As a highly-efficient clean combustion technology, the Circulating Fluidized Bed (CFB) boiler, which effectively solves the problems of energy saving and environmental protection, has developed over 20 years, and it represents the great progress in combustion technology. The cyclone separator is the key equipment for warranting the certain particle circulation rate, good combustion and desulfurization efficiency of the circulating fluidized bed boiler, therefore the optimization of its performance is the key technology in the development of CFB boiler.To meet the demand of scale-up of the CFB boiler, a lot of improvements of cyclone separators have been made in the world these days. As for the improvements of cyclone separator's inlet duct, Alstom 300MW CFB boiler, which was imported by Sichuan BAIMA power station, used a unique duct that made a breakthrough compared with the previous designs of its inlet duct of cyclone. The new design adopts long inlet duct to help particles obtain enough high acceleration and pre-separation, which improves separation efficiency greatly and reduces carbon content of fly ash in flue gas.In order to digest and absorb the advanced foreign technology, the model inlet ducts used the modified long inlet duct and the traditional short inlet duct devised by Alstom Company as their prototypes. The model inlet ducts were reduced according to a certain ratio in geometry size and were installed on a circulating fluidized bed boiler's cold test rig. Cold tests were carried out on the cold test rig, and based on the cold tests, numerical simulation were carried out as well. The main tasks of the study are as follows:â‘ Cold tests on gas solid flow characteristics, including the pressure drop and the acceleration performance of particle phases in the two inlet ducts were carried out.â‘¡Measuring and computing the separation efficiency and the pressure drop of the cyclone connected with the two different inlet ducts.â‘¢Simulating the motion trajectories of particles in the two different inlet ducts, the flow fields and the separation efficiency of the cyclone connected with the two different inlet ducts, and the simulation results were compared with the results of cold tests.The results of the cold tests mainly include:â‘ Particles in the two kinds of inlet ducts were accelerated and the acceleration performance of particles in the long inlet duct was better than the one in the short inlet duct.â‘¡The separation efficiency of the cyclone connected with the long inlet duct was higher than that with the short inlet duct.â‘¢The pressure drop of the long inlet duct was higher under the same operating conditions; the pressure drop of the cyclone connected with the long inlet duct was higher under the same operating conditions.Based on the cold tests, the simulation results indicate:â‘ The stability of flow fields in the short inlet duct was better than that in the long inlet duct, and there were reflux in the long inlet duct; the stability and the symmetry of flow field in the cyclone connected with the long inlet duct was better than that with the short inlet duct.â‘¡Motion trajectories of particles obtained by numerical simulation in the two kinds of the cyclone's inlet ducts was almost the same as the ones photographed by a high-speed camera, which proved that the tracer particles selected were appropriate.â‘¢The separation efficiency of the cyclone connected with the long inlet duct was higher than that with the short inlet duct, which was the same as the results of cold tests; the separation efficiency of particles that injected from different positions of inlet duct's cross section was different; the difference of separation efficiency was caused by different injection positions of cyclone, and the difference was greater in the case of the cyclone connected with long inlet duct.