Contrast Studies Of Cyclone Separators With High Solid Loadings At Inlets

Coal gasification is one of the key technologies of Clean Coal Technology (CCT) such as IGCC and poly-generation. The Pulverized Coal Pressurized Dense Transport Bed Gasifier can deal with coal of high ash and high ash melting point in China. Transport Bed Gasifier is operated at high solid flux, which makes the cyclone separator work at high inlet solid loadings and meet the requirements of high efficiency, low pressure drop and geometry simplicity. It is required to improve and select the structures of cyclone separators based on the traditional'barrel-cone' cyclone separator.In this thesis, the gas-solid flow and separation performance of four different kinds of cyclone were investigated at high solid loadings by means of cold-model experiment, theoretical analysis and numerical simulation. The main work is shown as follows:(1) Three different kinds of cyclone separators were designed on the basis of traditional barrel-cone cyclone separator. Orthogonal tests of efficiency and pressure drop were conducted in above-mentioned four kinds of cyclone separators at different inlet air velocities (16～28 m/s), different inlet solid concentrations (0-55 kg/m3) and different particles (sand andγ-Al2O3). The change curves of efficiencies and pressure drops with inlet air velocities and solid concentrations were obtained. According to the technology requirements of the high solid loading gas-solid separation, two new indicators'solid handing ability'and'structure complexity' were introduced to evaluate above-mentioned four cyclone separators by Grey Correlation Method. The results showed that the association degree of'Low and inclined inlet cone-barrel' cyclone separator was maximum in the four kinds and could be used as the primary cyclone of Transport Bed Gasifier. On the other hand, the traditional'barrel-cone' cyclone separator was selected as the secondary cyclone of Transport Bed Gasifier.(2) The pure gas flow field and tracer particle movement in the two selected cyclone separators were numerical simulated. The static pressure, dynamic pressure and velocity distribution in this two cyclone separators were obtained. The results showed'double vortex'structure and'single vortex'structure in the barrel and cone of the'Low and inclined inlet cone-barrel'respectively. Low efficiency at low solid loadings (less than 20 kg/m3) of 'Low and inclined inlet cone-barrel' cyclone separator was also analyzed by means of'turn numbers'simulation and'swirl number' calculation.(3) Based on the simulation results, Wang's (2006) 'Turn Number Model'was improved and combined with the Rosin' s (1932)'Residence Time Model'. By this method, the pressure drops of particle-free flow and separation efficiencies at low solid loadings (less than 0.2 kg/m3) were calculated for the two selected cyclone separators. The results showed good agreement with experimental data in literatures and this work for'Low and inclined inlet cone-barrel'cyclone separator and showed good agreement with experimental data in this work for'barrel-cone'cyclone separator.(4) Based on Theory of Similarity, the proximate modeling was conducted for the'Low and inclined inlet cone-barrel'cyclone separator. A group of similarity criterion numbers were obtained and used to fit the experimental pressure drop data. According to the conceptions of 'Agglomeration Separation', 'Agglomeration-Centrifugation Separation'and'Centrifugation Separation', correlations for separation efficiencies were developed. The fitted expressions were in good degree of correlation (correlation coefficients were close to 1).(5) The EMMS drag force model combined with Two Fluid Model was used to simulated the gas-solid flow in the full-loop of Transport Bed Gasifier at very high solid flux (Gs=508 and 907 kg/m2s). Details of gas-solid flow in each unit of the Transport Gasifier were obtained. The flow parameters of gas and solid phases and 'Secondary flow'structure in'Low and inclined inlet cone-barrel' cyclone were also numerically investigated. The results showed: Reduction of' Turn Number' and increment of downward axial velocity were important factors of high efficiency for this new type of cyclone separator at high solid loadings; the downward movement of particles had a significant influence on axial and radial velocities of gas phase; the increment of'short corrent'flow rates with the increment of inlet solid concentrations was one of the most important reasons of the increment of efficiencies increment with the increment of inlet solid loadings.