Experimental Study On Regeneration Of Calcium,Chloride Solution By Flash Evaporation

Wet FGD system is one of the important components of water consumption in power plant.In recent years,in order to meet the requirements of ultra-low emission,increasing the liquid-gas ratio or spray level in absorber become the main measures to meet the SO₂ emission standards.Before desulphurization,the flue gas's temperature is about 100?,after desulphurization with cooled and humidified by layer spray,a large amount of water vapor enters the flue gas.The moisture content of the flue gas reaches to 100g/kg?dry smoke?,while a great quantity of heat is discharged with the flue gas in the form of latent heat.With the deepening of the water-saving and consumption-reduce,the technology of flue gas dehumidification has attracted wide attention.Liquid desiccant-based dehydration with the higher dehumidification performance is one of the mainstream flue gas dehumidification processes.The LDDS?liquid desiccant dehumidification system?is mainly composed of two modules,absorber and regenerator.However finding a way to regeneration with high efficiency has become a key problem restricting the development of the liquid desiccant dehumidification.The regeneration of the liquid desiccant is mainly divided into constant pressure regeneration and low pressure regeneration.Flash evaporation,as the low pressure regeneration,is the phenomenon that the solution evaporates rapidly because of overheating when the pressure of the solution is suddenly drops below the saturation pressure.It has great application potential in the field of solution regeneration because of the advantages of fast evaporation rate,low energy consumption,strong cooling capacity and so on.More importantly,in view of the characteristics of small available area and large amount of solution regeneration in the coal-fired power plant,this paper selects the flash evaporation of low-pressure solution regeneration as the research object,studding the influence of various factors on the flash evaporation of liquid desiccant.Firstly,the characteristics of CaCl₂ droplet flash evaporation process are studied by numerical simulation.The energy and mass control equations of droplet flash evaporation process are established,the heat and the mass change process of droplet in flash evaporation is investigated by Simulink,and the effects of the temperature,mass concentration,droplet diameter and flash pressure on regeneration performance are studied.The calculation results show that the regeneration process of CaCl₂ solution based on flash evaporation is feasible.The solution can be restored to the state before absorption.The evaporation rate of flash can be effectively increased by raising the temperature,reducing the mass concentration and flash pressure,and the lower the initial concentration of solution and the lower the pressure,the lower the final temperature of the droplet,which is beneficial to improve the absorption efficiency of the solution in absorber.The simulation results provide a reference for the further experimental research.Secondly,an adiabatictest rig for spray flash evaporation regeneration of CaCl₂ solution is built.The effects of physical properties of CaCl₂ solution and flash pressure on regeneration characteristics are studied.The dimensionless Jakob,superheat ?T and dimensionless pressure P*are introduced to the test results.The result show that the spray flash evaporation method of CaCl₂ solution can meet the demand of high efficiency regeneration of liquid desiccant;the influence of various factors in the test results is consistent with the trend of simulated results;the solution temperature and the flash pressure influence the evaporation rate by affecting the superheat,the concentration and the temperature of solution influence the evaporation rate by affecting the solution vapor pressure.All the measure that can increase the superheat and the vapor pressure can both promote the evaporation rate;the decrease of flash pressure can increase the evaporation rate,but the lower steam temperature is not conducive to the recovery of condensation.The evaporation pressure of 10kPa can meet the material balance of the LDDS,and the temperature of steam and solution at the outlet about 50 ? is also more suitable.The experimental correlation of flash evaporation rate obtained by dimensionless analysis is ?=e7.823 Ja-1 254P*1.079L1.524?T0.455,the results above provide a reference for further Pilot-Scale research and application.