| Under the background of ‘ultra-low emission' control for coal-fired flue gas in China,the traditional wet flue gas desulfurization(WFGD)technology faces great challenges including high operating cost to reach ‘ultra-low emission',poor adaptability for load variation,flue gas with high humidity after desulfurization,et al.To deal with these challenges,the current research carried out experimental studies,numerical simulation,and theoretical analysis,to systematically investigate the gas-liquid flow and mass transfer process in the spraying tower of WFGD system.Firstly,a self-designed deflectors was installed in spraying tower to organize the flow field,alleviate the ‘bias flow' phenomenon and improve gas-liquid contact condition.On a pilot-scale experimental setup,the flow filed in spraying zone was compared and analyzed for different t ypes of spraying tower.The flow uniformity of flue gas was improved by installing porous tray or deflectors.The system resistance could be reduced by adding deflectors under some operation conditions.Based on Euler-Lagrange model and two-film theory,a calculation method was proposed and verified for predicting the gas-liquid multiphase flow and reaction process in spraying tower.According to the calculation results,the influences of deflectors on the desulfurization performance of WFGD system in a 660 MW coal-fired power plant were studied.Secondly,a gas-liquid flow pattern controlling(FPC)device was proposed to control the flow filed in spraying tower and enhance gas-liquid mass transfer.Comparing with the open spraying tower,the mass transfer process was significantly improved after adding the FPC unit.Comparing with open spraying unit,the desulfurization efficiency increased from 52.3% to 76.8% at the cost of 360 Pa increase in the pressure drop under a typical operation condition.A relationship between the desulfurization efficiency and operation conditions including superficial flue gas velocity,liquid-gas ratio,aperture ratio,and hole number was established according to experimental results.The synergetic removal of particulate matters in the spraying tower was also studied.It was found that the gas-liquid flow condition in FPC unit was much more efficient for the particles capture due to the improved impaction and diffusion collection when comparing to the open spraying unit.Pilot-scale experimental results showed that the spraying tower with FPC device could enhance the synergetic particles collection efficiency while with a lower resistance loss than the spraying tower installed with traditional porous tray.The gas-liquid flow patterns for open spraying unit and FPC unit were characterized by high-speed camera and image-processing technology.Generally,a falling film flow was observed on the wall in open spraying unit,while an obvious bubble flow or churn flow was developed in the FPC unit.At last,a novel dehumidification method was proposed by combining the current WFGD system and liquid-desiccant-based dehumidification system.The FPC device was also used for enhancing the dehumidification process.The dehumidification efficiency and pressure drop were 41.3% and 314 Pa,respectively,under typical operating conditions.By analyzing the effects of structure and operation parameters in the dehumidification process,the relationship between mass transfer coefficient and superficial flue gas velocity,liquid-gas ratio,and dehumidification temperature was established.Based on theoretical analysis,the mass and heat transfer process in this work was compared to the ‘condensation heat exchange & flue gas reheat' method.It can be found that the proposed method in this work could achieve relatively higher dehumidification efficiency with lower gas-liquid ratio.In addition,the temperature of flue gas at outlet of spraying tower would not decrease in dehumidification process. |
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