Numerical study on maldistribution of gas–solid flow in multiple-branching limestone-conveying pipelines of circulating fluidized bed
Shahong Zhu, Man Zhang, Juanli Zhang, Junfu Lyu, Hairui Yang*
As one of the most important auxiliary systems of a circulating fluidized bed boiler, the limestone pneumatic conveying system is of great significance to its operation. Maldistribution of powder in the different injecting ports seriously limits inner-furnace desulfurization performance owing to inefficient mixing of limestone powder and SO2. The gas–solid flow characteristics of an industrial-scale multiple-branching limestone-conveying pipeline system of a 200 MW circulating fluidized bed boiler were studied using a computational particle fluid dynamics method. The maldistribution intensity was studied under different operating conditions of air velocity and particle mass flow rate. Simulation results indicated that when the air velocity increased, the maldistribution was mitigated, but when the particle mass flow rate increased, the maldistribution strengthened. To solve this problem, two improved schemes were proposed: adding a deflector at different angles and changing the height of pipeline distributor. According to the simulation, the maldistribution could be efficiently mitigated using a distributor height in the range of 100–120 mm and a deflector angle of 10°–30°.
Circulating fluidized bed; Limestone; Pneumatic conveying; Multiple-branching pipeline; Maldistribution