Design And Optimization Of A Novel Compound Demister

The demisters,widely employed in a variety of industrial processes,are faced with increasingly rigorous demands of their performance.Desired demisters are supposed to maintain high separation efficiencies under a wide range of operating conditions.In the meantime,accessible pressure drops of demisters are required for the economy of operation.However,according to the literature review,the most widely adopted demisters,i.e.wave-plate demisters and wire mesh demisters,are still suffering from weakness of low separation efficiency under some conditions.For instance,the wave-plate demisters could hardly achieve high separation efficiency for fine mist or at low gas velocities.Also,the wire mesh demisters are found to be vulnerable to droplet re-entrainment.In order to overcome the above disadvantages,a novel compound demister that combines an upstream tube bank and downstream wave plates was proposed in this work for industrial application.Its performance was evaluated by experimental and numerical methods.Compared with the individual tube-bank and wave-plate demisters,the compound demister is found to have the highest separation efficiency?>95%?with much less fluctuation for a wide range of gas velocities.At low gas velocities??4 m/s?or for removing small droplets?<20?m?,the separation efficiency of the compound demister is much higher than that of the wave-plate demister mainly because of the large separation capability of the tube bank.At high gas velocities?>4 m/s?,the compound demister shows higher resistance to droplet re-entrainment that occurs at inlet gas velocity of approximately 7 m/s compared with the tube-bank demister.This is due to the compensation from the wave plates in the compound demister that separate secondary droplets generated by tubes.The compound demister possesses higher dry pressure drops than either the tube-bank or wave-plate demister,but is acceptable for industrial application.All these advantages make the compound demister a promising candidate for droplet removal in the desulfurization system.For further improvement of its performance to separate small droplets at low gas velocities,related work was also conducted to optimize the configurative parameters of the tube-bank part in the compound demister.CFD simulation was carried out to investigate the effects of design parameters?i.e.,tube diameter,ratios of tube pitch and row spacing to tube diameter,and the number of rows?on the performance of the tube-bank part.Based on the simulation results,the optimization work was then conducted by using response surface methodology.It is found that the separation efficiency and friction factor of the tube-bank part are both highly impacted by the tube pitch/diameter ratio?K₁?.Meanwhile,the effects of other parameters on the performance also vary largely according to different levels of K₁.Under different operating conditions,correlations of the separation efficiency and friction factor were obtained with good fitness as function of the investigated design factors,from which corresponding optimal designs were derived.The attained data will be of great significance to the design of compound demisters for practical application in the desulfurization systems with various requirements.