Study On Recovery Of Steam From Flue Gas By Hollow Fiber Membrane Method

The power plant membrane whitening technology is a new type of membrane flue gas steam recovery technology with great application prospects in recent years.It has the characteristics of high efficiency,simplicity and convenience,energy saving and environmental protection,and can capture and recover the steam in the flue gas with high quality.At the same time,it can effectively alleviate the problem of saturated water vapor in high-humidity flue gas condensing and corroding the chimney.In this paper,laboratory experiments and on-site pilot tests of hollow fiber membranes for recovering water vapor in flue gas were carried out,and the performance of hollow fiber membranes for recovering water vapor was investigated.Based on the research conclusions,A scheme for recovery of steam from flue gas by hollow fiber membrane of 600 MW unit was designed.First of all,in the laboratory pure water vapor recovery experiment,based on PVDF and PTFE membrane,circulating water cooling method and vacuum condensate cooling method were used respectively,the operating conditions such as the intake air temperature and the form of components such as component form on the performance of water vapor recovery performance.The results show that under the circulating water cooling mode,increasing the intake air temperature,intake air flow rate,adopting the gas-liquid countercurrent method and the woven module form,appropriately increasing the module filling fraction and membrane porosity,and using more hydrophilic PVDF membranes can all effectively improve the water recovery and water recovery rate of steam,but the change of circulating water flow has little effect,and the increase of intake air temperature and the use of low-porosity membrane can greatly improve the quality of recovered water;while in vacuum condensate cooling mode,The use of a more hydrophobic PTFE membrane is conducive to increasing the amount of recovered water,and changing the filling fraction has little effect on the quality of the recovered water.In addition to this,the changes of other conditions are the same as those of the circulating water-cooling method,and the increase in vacuum is conducive to improving the quality of recovered water.Through the laboratory simulated flue gas experiment,under the water circulation cooling mode,the amount of water recovered in the simulated flue gas is slightly worse than the pure water vapor experiment.However,under the vacuum condensate cooling mode,the amount of water recovered and the water recovery rate of the simulated flue gas experiment are much lower than the pure water vapor experiment,and the recovered water quality does not change much.On-the-spot pilot tests were carried out on the basis of laboratory experimental research.Under the actual conditions on site,a circulating water-cooling method test was carried out based on PVDF membrane modules.The effects of different placement forms of components,flue gas flow into the component on the flue gas water vapor recovery performance were studied,and the changes of flue gas composition during the operation of the component were investigated.The results show that the component placement method is changed reasonably,the maximum amount of recovered water reaches25 kg·m^-2·h^-1,the maximum temperature difference between inlet and outlet water and smoke temperature are 12.9℃and 1.9℃,respectively;The flow rate increases and the temperature difference between the inlet and outlet flue slightly decreases.When the flow rate of the flue gas reaches 8000 m³·h^-1 or more,the temperature difference between the recovered water and the inlet and outlet water is the largest,but the steam recovery efficiency begins to decline.Before and after the test,the conductivity and p H of the circulating water are basically unchanged.The conductivity is much lower than the conductivity of the natural condensate of the flue.The p H is always neutral at about 7.5,and the p H of the natural condensate of the flue is 3.4.Indicating that the recovered water quality is good during the operation of the membrane module.After the pilot test,the performance of the polluted membrane was tested,and the influence of the membrane pollution degree and the water vapor recovery performance was analyzed.The results show that both hollow fiber membranes have good anti-smoke pollution performance,and the polluted PVDF membrane can still maintain a good amount of recovered water under the water circulation cooling mode,but the recovered water quality is worse than the original membrane,and the polluted PTFE The volume of water recovered by the membrane under vacuum condensate cooling is lower than that of the original membrane,and the quality of recovered water is basically unchanged..Finally,based on the results of the pilot test,designed a scheme for recovering flue gas and steam from a 600 MW coal-fired power plant.According to the design operating conditions,when the flue gas moisture recovery rate is greater than 60%,the amount of recovered water can reach 102.5 t·h^-1.The membrane area is about 4100 m².The research results will provide an important reference for the construction of energy-saving water-saving systems of new energy-saving power plants.