Numerical Study On Spray Evaporation Of Droplet In The Flue

At present,almost all power plants in China have adopted desulphurization technology,and most power plants use limestone-gypsum wet process of FGD technology,but this method will produce a certain amount of desulphurization wastewater.The traditional chemical treatment methods include neutralization,precipitation,flocculation,concentration and clarification are usually adopted for the wet process of FGD,but the chloridion in the water cannot be removed.Therefore,the treatment of desulphurization wastewater has become a hot spot of research.In recent years,from the perspective of environmental protection and energy comprehensive utilization of desulphurization wastewater at home and abroad,some scholars putforward a zero-discharge system of desulphurization wastewater by the spray evaporation technology which would use waste heat of flue gas.The advantage of this technology is that waste water can realize inexpensive zero-emission to meet the environmental protection requirements.In this paper,by analyzing the output and characteristic of desulphurization wastewater and stack size of domestic coal-fired power plants firstly,the spray evaporation of wastewater is simplified into a numerical simulation process,at the same time,the Eular-Lagrange discrete particle model will be used in this process.Finally,the characteristics and basic theory of the technology will also be researched.On this basis,the key influencing factors of droplet evaporation,evaporation characteristics and the influence of spray evaporation technology on flue were analyzed and studied in detail.In the first part of the paper,based on the properties of flue gas and droplet,the influencing factors of droplet group evaporation in flue were investigated.Firstly,the effects of flue gas temperature on evaporation mass and the absorbed energy of droplet group were studied.Secondly,the effect of droplet size on droplet group evaporation was studied.Finally,the effect of the initial droplet velocity on the evaporation characteristics of the droplet was analyzed.It was found that the flue gas temperature has the most important influence on the droplet evaporation,and then the initial particle size of droplet also has a great influence,while the velocity of flue gas and the initial velocity of droplet have little influence on the droplet evaporation.Based on the above research,the instantaneous diameter of droplet and the evaporation time in the process of droplet evaporation were further studied.Firstly,aiming at the flue gas environment in the spray evaporation technology,the heat and mass transfer characteristics of droplet in the flue gas and the evaporation process were analyzed theoretically,and a mathematical model was established.Then,the effects of droplet physical property,droplet size,initial velocity,flue gas velocity and temperature on droplet evaporation characteristics were analyzed.It was found that the initial diameter of the droplet had the greatest impact on the time required for completely evaporated in this paper.For every doubling of the initial diameter of the droplet,the time required for the droplet particles completely evaporated would increase four times than before.The second influence is flue gas temperature.Thirdly,the time required for pure water droplet completely evaporated was shorter than the calcium chloride droplet.Finally,the velocity of flue gas and the initial velocity of droplet have little effect on droplet evaporation.In the end,by the dimensionless treatment,the change trend of the unquantized diameter of the droplet over time was the same regardless of the working condition.In the droplet evaporation characteristics,only the droplet complete evaporation time is greatly affected by the working condition while the dimensionless diameter over time was consistent.In addition to the above researches,the effects of droplet group evaporation on the flue were studied.The effects of spray evaporation on flue gas characteristics and characteristics of dust in flue gas were also analyzed.Therefore,in the last of this paper,the evaporation and crash of droplet in curved flue was also studied.The study found that the bending of the flue had a stronger effect on the evaporation of the droplet group.After the droplet got through the bend of flue,the evaporation effect of the droplet group closed to the outer bend was obviously better than that droplets located in the central part of the flue.Besides,the crash of droplets in the curved pipe was affected by many factors.The flue gas velocity played a important role,and the spray angle of the nozzle and the initial velocity of the droplet had little effect.