Research On Method And System For Eliminating Wet Plume Using Liquid Desiccant

There is a large amount of water vapor in the flue gas after wet desulphurization.In the process of flue gas emission,when encountering the ambient air with lower temperature,the phenomenon of wet plume may be formed.It could cause great pollution to the environment and would contribute to the formation of the smog.Based on theoretical analysis,a new wet plume elimination system using liquid desiccant is proposed in this paper,including the flue gas condensation process and the flue gas liquid desiccant process.And the waste heat of the flue gas to be treated is recovered to drive the liquid desiccant circulation.It does not need to consume additional heat and could recover water from the flue gas.The steady-state mathematical model of the system is established to investigate the effects of various parameters on the system performance theoretically.Additionally,the new system is compared with the existing wet plume treatment technology.The main research contents and results are as follows:Firstly,working procedure of the wet plume elimination system using liquid desiccant is introduced and the system is analyzed from two aspects: water resource recovery and state change processes of the flue gas theoretically.The results show that under the premise of eliminating wet plume,the recovered water component of the system has a minimum value,and the temperature and humidity of the flue gas to be treated and the ambient air are the main factors affecting the minimum recovered water component.The liquid desiccant process of condensed flue gas is the cooling and dehumidification process or the heating and dehumidification process,and the accessible area of discharged flue gas state is further determined.Secondly,the plate falling film liquid desiccant dehumidification/regeneration experiment table is used to investigate the dehumidification and regeneration process of the calcium chloride aqueous solution.The effects of the mass flow rates of air and inlet liquid desiccant,temperature and concentration of inlet liquid desiccant on the mass transfer coefficient in the dehumidification and regeneration processes are mainly investigated,which could provide reference for setting the mass transfer coefficient in the mathematical model of the dehumidifier/regenerator.The experimental results show that the mass flow rates of air and liquid desiccant are the main factors affecting the mass transfer coefficient in the processes of dehumidification and regeneration.The increase of the mass flow rates of air and liquid desiccant could enhance the mass transfer coefficient significantly,while the temperature and concentration of liquid desiccant would affect less.Additionally,the error analysis of the experimental data under typical operating conditions is carried out.The relative error of the main parameter is within ±5%,which could indicate that the experimental data has certain reliability.Then,the steady-state mathematical model of the system is established and the calcium chloride aqueous solution is used as the liquid desiccant.The numerical simulation of system performance is carried out,which mainly explores the effects of different basic parameters(the mass flow rates of regeneration air,cooling water and liquid desiccant)and the temperature and humidity of the flue gas to be treated and the ambient air on the performance of eliminating wet plume.It could provide reference for system design and engineering application.The research shows that when the temperature and relative humidity of the flue gas to be treated increase,the ambient air temperature decreases and the ambient air relative humidity increases,the wet plume elimination performance of the system decreases gradually.The mass flow rates of regeneration air,cooling water and liquid desiccant would affect the performance of eliminating wet plume significantly.Therefore,under the premise of eliminating wet plume,various parameters should be set carefully for economic operation.Finally,the treatment technology using liquid desiccant is compared and analyzed with the flue gas condensation technology and the condensation and reheating technology in the existing wet plume treatment technology from four aspects,which are the system suitability,the recovered water component,the rising height of discharged flue gas and the economic costs.The comparison results show that the condensation and reheating technology and the treatment technology using liquid desiccant could eliminate wet plume effectively,but the condensation technology is suitable for application in the areas with higher temperature and lower relative humidity of ambient air.In most cities(except northeast and south China),the elimination of wet plume could be achieved by using the condensation technology to fully cool the flue gas naturally from April to October.Under the premise of eliminating wet plume effectively,the water recovered by the treatment technology using liquid desiccant is 93.22% and 72.82% more than the condensation technology and the condensation and reheating technology,respectively.The rates of change with discharged flue gas rising height of the treatment technology using liquid desiccant and the condensation technology are 95.30% and 54.56%,respectively.Compared with the condensation technology,the discharged flue gas of the treatment technology using liquid desiccant has higher temperature and better diffusivity.The condensation and reheating technology needs to consume thermal energy,while the treatment technology using liquid desiccant and the condensation technology do not require.The filler volume required and the power consumption in operation of the condensation and reheating technology and the treatment technology using liquid desiccant are equivalent,but far less than the condensation technology.