Gas-solid Flow Characteristics Influenced By The Secondary Feeder And Its Optimum Placed Scheme To The CFB With Combined Combustion Technology

When the coal quality varied great, the CFB will not combust steadily. In order to solve the limitation of the common CFB which combusted the bad coal, the combined combustion will be added to it. For these years, the combined fluid dynamics of the gas-solid flow in the fluidized beds has been the subject of a great deal of academic research throughout the world. For more reliable and improved design and operation, it is necessary to study the hydrodynamics of two-phase flow in the beds.This paper uses the NG-35/3.82-M chain grate stroke as the subject, which adopted the technology of CFB combined combustion to retrofit and the basic parameters are confirmed. On this condition, the gas-solid flow model is constructed by using the two-phase flow model in the CFB adopted combined combustion to retrofit. The differential equations are converted into algebraic finite volume equations with the aid of discrete assumptions. Then, the simulation about influence of the secondary feeder to the flow characteristics in the CFB is carried out. And at last the optimal position of the secondary feeder is obtained.According to change the disposed positions, velocities of the secondary air and particles diameters, the flow characteristics are studied. Although the disposed positions are different, the core-annular structure still can be formed. The results shows that double disposed positions exceed unilaterally disposed positions. But at different velocities of secondary air and double disposed positions apart from horizontal patch board 2300mm whose positions are stagger, it can form annular flow which strengthen the mix of air and particles, and also can prolong the residue time of the particles in the CFB. In another, the bigger in the particles diameter, the more easily for those return to the dense phase zone. The simulation results of the particles velocities also show that when the double secondary air was used, the accelerated time will be extended, which will make the turbulence energy be strong and the reaction between the air phase and solid phase.In all, the results shows that in the circulating fluidized bed (CFB) reactor which adopted the technology of combined combustion to retrofit, when keep the velocity at 2m/s and the double disposed position at 2300mm and apart from centrosymmetric face about 700mm and also the double secondary air about 35m/s, the air vortex will form. This will strengthen the mixing between air and particle and make the residue time be extended. And also double secondary air makes the turbulence energy strong. In addition, higher particle-concentration will be formed above the dense phase zone,and make the particles combusted at high temperature. So this is the best way for optimum design. The study results in this paper have important reference and application value, and pave the way for the CFB combined combustion.