Numerical Simulation Of Structure And Operating Characteristics Of Municipal Sludge Spray Drying Tower

The output of urban sewage sludge in my country has been increasing year by year,the drying of sludge is one of the most important links in sludge treatment and disposal.Spray drying technology has an important position in the field of sludge drying.Its equipment is simple,fast drying and suitable for large-scale production.Therefore,improving spray drying efficiency is of great significance to reducing costs.Based on the spray drying technology,this paper analyzes the drying process of sludge in the spray drying tower.This thesis designs a parallel-flow spray drying tower with a treatment capacity of 50 kg/h for municipal sludge with a water content of 83%.According to related knowledge of fluid mechanics and numerical heat transfer,a mathematical model of sludge particle evaporation in hot air is established.Perform physical modeling of the direct-flow spray drying tower with the hot air inlet,and use Fluent software to perform numerical simulation calculations on the drying process of the sludge in the direct-flow spray drying tower.Change the spray cone angle,inlet air temperature,the initial average particle diameter,and other parameters,analyze the change law of the velocity,temperature,water vapor content,and cross-sectional evaporation rate in the tower.The results show that with the expansion of the spray cone angle,the higher the evaporation rate of the particles when the spray cone angle is 100°,the wall sticking phenomenon in the drying tower is more serious;The inlet air temperature is a key parameter that affects the evaporation rate.Increasing the inlet air temperature can speed up the evaporation rate,but it is limited by the nozzle flow rate and particle movement speed.When the inlet temperature is increased from453K to 473K,the effect of increasing the evaporation rate is not obvious;The finer the particles,the higher the evaporation rate,but at the same time,it will increase the cost.Under the best conditions selected,the overall evaporation efficiency of the once-through spray drying tower is 77.68%.This thesis also changed the hot air intake method,based on the designed size parameters,physical modeling of the swirling spray drying tower.The effects of different inlet angles on the velocity field and wall sticking phenomenon are emphatically discussed.At the same time,the effects of changing the inlet air temperature and the initial average particle diameter on the temperature and water vapor content and cross-sectional evaporation rate are also analyzed.The research results show that the air inlet angle has a great influence on the flow field in the drying tower.As the air inlet angle increases,the particle sticking to the wall becomes weaker.When the near air direction and tangential direction are 75°,the particle trajectory is chaotic;The higher the inlet air temperature,the greater the evaporation rate.When the inlet air temperature increases from 453K to 473K,the increase in the evaporation rate is not significant;as the initial diameter of the particles increases,the maximum evaporation rate of the cross-section decreases,80μm When the maximum evaporation rate of the cross-section is 3.858×10^-7kg/s,the value drops to 2.461×10^-7kg/s at 140μm.The smaller the particle diameter,the more serious the wall sticking phenomenon.Under the best conditions selected,the overall evaporation efficiency of the once-through spray drying tower is 78.22%.The cyclone spray drying tower can dry more adequately than the direct flow spray drying tower,but at the same time,the wall sticking phenomenon is more serious.