Transfer Characteristics And Application Research Of Integrated Cross-flow Rotating Packed Bed

With the development of economic globalization,shipping transport plays an important role in traditional trade.The emission of NO_x from ship increased,leading to the more serious pollution of port cities and marine environment.The international maritime organization make the stricter standards of NO_x emission.An efficient method for NO_x removal is urgently required.The wet denitrification method could reduce the emission of NO_x and has potential to remove SO₂ and NO_x simultaneously.Due to the limitation of working space and energy supplement on ship,how to efficiently preoxidate of NO_x and absorb oxidized NO_x are two pivotal problems for using wet denitrification on ship.Higee technology,was conducted in a rotating packed bed（RPB）,has the advantages in device size and mass transfer.It could be employed to intensify the process of NO_x removal.To achieve the coupling of oxidation and absorption,an integrated cross-flow rotating packed bed（CFRPB）was developed.Macroscopically,the rotor structure is optimized,and the gas-liquid contact changed from countercurrent to cross flow;combined with spraying tower for liquid-phase oxidation.Microscopically,the surface of packing is modified to enhance the liquid dispersion.In this work,the flow behavior and the performance of NO_x removal were investigated.High-speed photography,CFD simulation,and Doppler optical probe were employed to explore the flow behavior in CFRPB.A new wet denitration process,suitable for the CFRPB,was proposed.The NO_xremoval performance of CFRPB was carried out.Based on the investigation of flow behavior,packing surface is modified to further intensify the NO_x removal process.Main conclusions are as follows:1.The CFD-VOF simulation coupled four contact angle models was employed to investigate the process of liquid droplet impacting on the single fiber with different wettabilities.Effect of contact angle model on simulation results was investigated and Modified-Kistler model was developed.Modified-Kistler model could predict more precise in the contact angle range of 45°-155°.The results of force analysis indicated that the flow pattern were one-drop and two-film dripping when coalescence and dispersion action dominated the impaction process respectively;the flow pattern was one-film dripping when coalescence and dispersion action compromise in competition.The gas-liquid contact area increased and energy utilization efficiency increased with the increase of surface hydrophobicity.2.The liquid flow behaviors of jet impacting on the rotating single-layer wire mesh with different surface wettabilities were studied by high speed photography and CFD simulation.The liquid dispersed in circumferential and axial directions were captured by high speed photography.The flow patterns of linear-ligament,curved-ligament,and droplet were observed after liquid passed the wire mesh.Circumferential and axial dispersion angles increased with the increase of surface hydrophobicity.The CFD simulation results indicated that the obstacle effect of wire mesh on liquid increased with the surface hydrophobicity when jet passing through the wire mesh;the adhesion effect of wire mesh on liquid decreased with the surface hydrophobicity when jet passed through the wire mesh.The difference in obstacle and adhesion effect resulted in different flow pattern.Liquid specific surface was used to assess the dispersion performance.Results indicated that the liquid dispersion performance of wire mesh increased with the increase of surface hydrophobicity.3.A new method was developed to evaluate the dispersion characteristics of liquid jet impacting on the multilayer wire mesh with different surface wettabilities via using a Doppler optical probe.The Sauter mean diameter of droplets increased with the increase of surface hydrophobicity,initial liquid velocity,and mesh number when packing arrangement is 3 layers.R-R distribution was a reasonable droplet size distribution.The distribution is narrower when surface hydrophobicity,initial liquid velocity,and mesh number increased.The droplet velocity increased with the increase of initial liquid velocity and mesh number.Based on dimensionless analysis,correlation of the Sauter mean diameter of droplets,distribution exponent,characteristic droplet diameter,and the droplet velocity were proposed.4.The oxidation efficiency of oxidation section was intensified via optimizing the gas and liquid distribution.The gas distribution in oxidation section was optimized by adding a gas phase disturbance（GPDI）.According to simulation results,the structure of GPDI was selected.Introducing multilayer hydrophobic wire mesh to enhance liquid dispersion in oxidation section.Na Cl O₂ solution was employed as oxidant.After the optimization of fluid distribution,the oxidation ratio increased to 1.7 times.The oxidation ratio increased with the decrease of the initial p H of oxidation solution,the ratio of gas-liquid（oxidant）volumetric flow rate,and the inlet NO_x concentration,and the increase of Na Cl O₂ concentration.The oxidation ratio could reach up to92%.5.Na₂SO₃ solution was used as absorbent.The denitrification performance of CFRPB was studied.The removal efficiency（η）and the volumetric mass-transfer coefficient（K_Ga）increased with the increase of OR,the Na₂SO₃concentration,initial p H of Na₂SO₃ solution,and rotational speed,and the decrease of the ratio of gas-liquid（absorbent）volumetric flow rate and the inlet NOx concentration.Under optimal conditions,ηand K_Ga could reach up to 84%and 264.06 kmol/m³·h.According to the studies of flow behavior,the packing was optimized.ηand K_Ga were further improved,and could reach up to 91%and 351.63 kmol/m³·h.Compared with scrubbers in literatures,CFRPB has higher value of K_Ga.It indicated that the CFRPB has potential for wet denitrification method on ship.