Numerical Simulation Of Black Liquo Rspray Characteristics And Cold Aerodynamic Field In Kraft Recovery Boiler

Black liquor spraying is an important parameter for proper combustion in a recovery boiler. Droplets will get property time to dry during exercise in the furnace and keep good combustion state by forming a certain shape of char bed at the bottom of the furnace, when the black liquor have fine atomization quality. However, droplets that are too fine get into the molten state so early that making char bed in a poor shape.In addition, those fine droplets are entrained with the flue gas. This carryover can deposit on the upper furnace tubes, potentially blew down to destroy the shape of char bed. Droplets that are too large do not have sufficient time to dry before reaching the char bed, causing bed instability and possibly plugging the air passage. Therefore, in view of the special properties of black liquor, it is necessary to study black liquor spraying in the recovery boiler by numerical simulation. Helping people optimize the structure design of recovery boiler and black liquor gun to reduce the production cost and improve the efficiency of boiler.This paper first studied pressure-swirl atomizer by volume of fluid(VOF) model. The assumptions of laminar flow was verified. The study shows that the viscosity and surface tension of black liquor are proportional to the droplets size, however, density of black liquor is on the contrary. Summarized five optimum collocation schemes of nozzle structure size after comparing the spray characteristics of atomizer by different initialization method, pressure of inlet and construct size. Then obtained their working pressure and spray characteristic parameters under boiler operating condition. In the recovery boiler, initial steady velocity of droplets is 3.5 m/s.Then, steady air flow field of recovery boiler was simulated by turbulence model. Found that primary air impinged in the four corners of furnace, causing energy loss and low turbulence. Both sides of the secondary air deflected to the side wall, which might accelerated slagging and corrosion. High-speed jet of tertiary air could break up the updraft in the center of the furnace effectively and reduce carryover. Nevertheless, air distribution of the recovery boiler was quite reasonable.Finally, an analogue simulation research on cold flow field of recovery boiler was conducted on the basis of calculation coupled with steady air flow field and black liquor spraying by cone injections of DPM for the five better nozzles above. During the research, droplet breakup, collision probability and collision outcomes of moving droplets were considered. In addition, analyzed pressure field, distribution of turbulent kinetic energy and particle size. Study showed that there was a risk of dust stratification and slag-bonding on the front wall and right wall surface. The atomization quality of black liquor sprayed by 16-11 nozzle was better than 8-8.5 nozzle in the furnace. Furthermore, the mainly atomization characteristic parameters which affected the effects of the black liquor drying and burning in furnace were cone angle of the spray nozzle and the range of initial droplet size. It had better effect on drying the drops and inhibition of carryover, when the minimum size of the black liquor droplet above 0.6 mm.