An attrition index test method for microspherical materials in gas-liquid-solid three-phase fluidization
Objective The three-phase fluidized bed is extensively employed in chemical industry due to its low mass transfer resistance,uniform temperature distribution,and maximized contact between catalysts and reactants.The attrition resistance of catalysts is a crucial parameter due to the severe collisions between catalyst particles and the inner walls of reactors,as well as among the particles themselves.However,existing attrition resistance tests are typically conducted in gas-solid two-phase environments,and the catalysts are also applied in the similar system.Therefore,designing a new method which simulates a three-phase fluid-ized bed is both academically and practically significant.Methods In this paper,deionized water was introduced as the liquid phase to transform the traditional gas-solid two-phase attri-tion test into a gas-liquid-solid three-phase test.Attrition tests were conducted on pristine samples and samples that were pre-screened to remove fines under 20 pm or 45 μm to determine the influence of sample pre-screening on test results.An orthogo-nal test was designed to evaluate the contributions of gas flow volume(6 to 8 L/min),sample mass(20.0 to 30.0 g),and water volume(100 to 140 mL)to the attrition index.The combination of levels that resulted in the highest attrition index from the orthogonal test was proposed as the optimal test condition for the new method,and its repeatability was evaluated.Attrition tests with durations ranging from 0.5 to 2.5 h were conducted to study the time-profile characteristics of microspherical materials in gas-liquid-solid three-phase fluidization.Results and Discussion In traditional tests,fines collected in the filtering flask often contain intact microparticles,which are mistakenly calculated as attrited fines,leading to systematical bias.Additionally,fines with diameter below 20 μm in the sample can interfere with attrition test results for the same reason and should therefore be pre-screened.With these improve-ments,the fines collected in the novel method were solely those generated during the attrition test.The orthogonal test showed the relative significance of different factors in the following order:gas flow volume＞sample mass＞water volume,with the first factor positively correlated with the result and the last two negatively.The highest attrition index was observed when using 20.0 g of the sample,100 mL of water,and a gas flow volume of 8.0 L/min.To evaluate the repeatability of the new attrition test method,three batches of samples were tested,with five parallel experiments for each sample.The relative standard deviation ranged from 3.48％to 4.46％,indicating good reliability.Attrition test results over time corresponded well with the Gwyn model,indicating that the attrition mechanism in the three-phase fluidized bed was similar to that in the gas-solid two-phase system.Conclusion A novel method for evaluating attrition resistance of microspherical materials used in three-phase fluidized beds was established.To more precisely reflect attrition resistance in real three-phase reactors,fines with diameter below 20 pm should be removed.The orthogonal test showed that gas flow volume had the most significant influence on attrition.The repeatability of the test was confirmed,with a relative standard deviation of less than 5％,indicating good reliability.The new method can be used to determine the attrition resistance of different materials used in three-phase reactors,which has important practical applications.
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