Research On High Temperature And High Pressure Flash Evaporation Flow Field And Heat And Mass Transfer Characteristics

How to efficiently and cost-effectively achieve zero discharge of desulfurization wastewater from coal-fired power stations is one of the important issues facing the thermal power industry.It is an important part of the zero-emission process route that the flash evaporation technology is used to achieve wastewater concentration.The atomized nozzle is used to atomize the superheated waste liquid into fine droplets,and then sprayed into a low-pressure environment to expand and evaporate.While improving the efficiency of water extraction,it can also effectively avoid the occurrence of scaling,thereby achieving the purpose of efficient utilization and low-cost operation.In this paper,the flash evaporation process of single superheated droplets and superheated sprays under normal pressure in high temperature and high pressure is studied.According to the working principle of the flash tank,an empirical formula was used to design a high temperature and high pressure expansion flash tank with a capacity of 0.3t/h for wastewater treatment.The Gambit software is used to establish a three-dimensional model and mesh it.The DPM(discrete phase)model and the heat-mass exchange model under the superheated liquid droplet decompression environment established in this paper are used for FLUENT15.0 for the internal continuous and discrete phases.The flow field is numerically simulated and analyzed.The results show that the flashing process of the superheated droplets not far from the nozzle is completed.The VOF(fluid volume function)model in the multiphase flow model was used to simulate the flashing process of a single superheated droplet and the nucleation of bubbles in the droplet.The results show that the superheated droplet gradually moves from the inside to the outside in a low-pressure environment.The broken form evaporates.This paper also studies the effects of feed water pressure,temperature,mass flow rate,and nozzle atomization angle on the flash evaporation characteristics of high temperature and high pressure sprays.The results show that:feed water temperature is the main factor affecting the flash vaporization rate of superheated spray;To some extent,shorten the time for flash to reach equilibrium,but it has no effect on the final water extraction efficiency.Increasing the spraying angle of the nozzle has a very small gain effect on the high temperature and high pressure spray flash water extraction efficiency;it is limited by the constant In the flash space,the simulation results show that the vaporization rate of the superheated spray flash increases first and then decreases with the increase of the feedwater mass flow.