| The venturi scrubber-cum-circulation washing tower purification technology was developed to remove dust from crude gas in the coal gasification process.In this research background,the systematic study on hydraulic characteristics and fly ash washing performance of the key equipment circulation washing tower was carried out with experimental research and computational fluid dynamics numerical simulation.In the hydraulic research stage,the effect of superficial gas velocity,clear liquid height above the draft tube and liquid flow rate on hydraulic performances of circulation washing tower was investigated with air and water for experimental system.The results indicate that the overall gas holdup,riser gas holdup,downcomer gas holdup,local gas holdup in the downcomer and liquid circulation velocity increase with increasing superficial gas velocity.Increasing the clear liquid height above the draft tube helps to improve the circulation speed,whereas gas holdup is not obviously affected by changed clear liquid height above the draft tube or liquid flow rate.Based on momentum balance,a mathematical model of downcomer liquid circulation velocity was derived.Considering the impact of local resistance to flow at the top corner of the draft tube,the model was corrected and predicted well with the experimental results.The maximum error was ±4.52%,with an average error of 2.15%.Combined with CFD simulation,the gas holdup was analyzed comparatively,revealing the reason of deviation.In the experimental stage of dust removal,particle size distribution and morphology of the fly ash material were obtained with Mastersizer2000 laser particle size analyzer and scanning electron microscope.The mean particle size is about14.94?m,with 0~30?m particles accounting for 66.67% of total mass.Particles size above 5?m substantially have irregular shape.There are both spherical particles and irregularly shaped particles among fly ash of 5?m or less.Size of spherical particles are generally 1?m or less,and exist in the form of aggregates.The influence of operation variables,namely gas and liquid flow rate in ‘one scrubber cum one tower' dust removal process on washing efficiency was studied.The experiment results indicate that circulation water tower has a good advantage in terms of dusty droplets and gas two-phase separation so that the combined process obtains thecollection efficiency of up to 99.99% for particles above 1?m.In addition,collection efficiency for different particle size under various operation conditions was obtained.It was found that ‘one scrubber cum one tower' dust removal process can achieve good removal efficiency for particles between 1 and 20 ?m,especially for particles between 1and 5 ?m,solving the problem of microparticles removal. |
PDF Full Text Request