Numerical Simulation Of Three-dimensional Gas Flow Field In Boiler Tail Flue And Study On Flow-equalizing Equipment

Non-uniform distributions of gas velocity field and ash-particle concentration field due to turning and variable cross-section in power plant boiler tail flue then cause deposition and abrasion of flue and heat exchanger as well as uneven heat transfer of heat exchanger, which brings harm to the safety and economical operation of power plant. Therefore, the research on the flow characteristics in boiler tail flue and finding the flow-equalizing equipment is particularly important.A series of experiments and numerical simulations studies on the flow characteristics in curved pipe have been done in the domestic and overseas, but mainly focus on the small cross-section size pipes, which for the large cross-section size pipe such as the boiler tail bending flue are less. The analyses of sparse gas-solid two-phase flow mostly focus on velocity field characteristics, which for particle concentration distribution characteristics are less. And the researches on flow characteristics in irregular variable cross-section curved tail flue are relatively scattered. Furthermore, the studies of flow-equalizing equipments mainly concentrate upon fluid uniformity in inlet of the dust collector and SCR reactor, while the researches on fluid uniformity in curved tail flue with heat exchanges are less, and just considering the gas velocity field, uniformity optimization of ash particles concentration field fluid are often ignored.In this article, the model of horizontal-to-vertical curved tail flue was built by the method of CFD numerical simulation, and the characteristics of gas velocity field and ash particles concentration field were analyzed, and the influence laws of different inlet velocities, particle mass loadings, curvature ratios and cross-section aspect ratios on flow characteristics were discussed. The model of vertical-to-horizontal curved tail flue was built, and the ash particles concentration distribution characteristics of two kinds of curved tail flues were contrastively analyzed. According to real projects, the computational models of two common variable cross-section curved tail flues were built. The distribution characteristics of gas velocity field and ash particles concentration field were analyzed, then the positions of abrasion and deposition as well as uneven heat transfer of heat exchanger were discovered. By adjusting the structure of flue and installing guide plates, the gas velocity field and ash particles concentration field in variable curvature curved tail flue was optimized. The results of studies showed that different inlet boundary conditions and structure parameters had some influences on flow characteristics of gas in curved tail flue. Under the different inlet velocities, the dimensionless velocities of central intersection lines on cross sections of curved flue along the dimensionless radius were almost identical. With the increase of fly ash particles loadings, the uniformities of gas velocity and ash particles concentration distribution were worsened. The influence of curvature ratios on flow characteristic in bending section of flue was very obvious, but gradually weakened when arriving at downstream straight section. With the increase of cross-section aspect ratio, the nonuniformities of gas velocity and ash particles concentration distribution decreased at first and then increased, so cross-section aspect ratio was not the bigger, the better. Due to the different effects of gravity on the secondary flow, ash particles concentration distribution in vertical-to-horizontal curved flue turned to equalization more quickly. By comparing the situations of deposition and abrasion in two kinds of variable cross-section curved tail flues, it was better to use expanding after turning curved structure. By adjusting the structure of variable curvature curved tail flue and installing guide plates of joint utilization of straight plate and curved plate, the deposition in bending section of flue and uneven heat transfer of heat exchanger as well as abrasion of front pipes were effectively improved.