Sampling and mixing - LTH

1 11L U N D U N I V E R S I T YSampling and mixing2L U N D U N I V E R S I T YMixtures Type of mixtures Positive mixtures- spontaneously homogenously - solutions Negative mixtures-Spontaneously separate-emulsions Neutral mixtures- neutral -powders Neutral mixtures Homogeneity depends on handling and process conditions Type of neutral mixtures Random mix Perfect mix Ordered mix23L U N D U N I V E R S I T YSampling of powders Why do we take samples? How many samples? Where and with what technique? How much?4L U N D U N I V E R S I T YWhy do we take samples? To detect variation validate processes Product quality variations To describe the sample - gross sample generalprov To control processes35L U N D U N I V E R S I T YHow many samples?

2 Depends on what information you want Remember the statistics Accuracy Precision Variance6L U N D U N I V E R S I T YVariance Example 400g A with a weight of 0,05g 400g B with a weight of 0,1g Sample weight 50 g What is the Variance Effect of sample size onVariance4,3%102,7%251,88%501,3%100 Sample47L U N D U N I V E R S I T YVariance as a tool to estimates number ofsamples How representative is asample Normal distribution 95% conf. Interval t=1,96 t-distribution 95% conf. Interval t=2,14for n=15-1 Number of samples Depends on wantedprecision and standarddeviations of samples true value=xm tsn n=tstE 28L U N D U N I V E R S I T YWhere and with what technique?

3 Discuss the following situations A lorry comes in with grains to a mill Validation of a tray dryer Process Sampling from a mill stream Sampling from an oral dispersion in a bottle59L U N D U N I V E R S I T YGolden rules of Sampling A powder should be sampled when in motion The whole stream of powder should be taken formany short increments of time in preference topart of the stream being taken for the whole time10L U N D U N I V E R S I T YHow much? Best rule adjust to the situation (scale of scrutiny) Product characteristic Demand on accuracy However To few particles will give to much variation Low amount of one component increase theneed of large samples for detection611L U N D U N I V E R S I T YEffect of scale of scrutinyTrue value 1/1000 Sample numberN=1000 N=10 000N= 100 0001171082010913281054115116501384611093 716113average /10000,857142860,985714291,01428571s0,69 0065560,323669440,1214985812L U N D U N I V E R S I T YMixing Purpose.

4 To obtain as homogenous bulk aspossible Common problems Mix in a small amount of one substance in alarge bulk Segregation and over mixing mixing that effects the size of the particles713L U N D U N I V E R S I T YQuality of a mix A mix is evaluated from standard mean and standarddeviation (of appropriate kind) Problem Segregated materials are not following a normaldistribution Is dependent on sample size Variance might give a better picture mixing index also an alternative M= randommix sample14L U N D U N I V E R S I T YMixing mechanisms Convection Due to circulating flow of powder duringmixing Shear mixing The momentum exchange between thepowder particles having different velocities Diffusion The random motion of powder particles815L U N D U N I V E R S I T YThe mixing curveFrom Powder technology handbook16L U N D U N I V E R S I T YMixing Standard equipment High share mixers

5 Tumbling mixers Y-cone Rotating cube Double cone Fluidized bed Agitator mixers Things to consider Homogeneity Risk for overmixing Leading to demixing Influence properties ofparticles High share rates Influence particle sizefor week powders Scaling up Not always linear917L U N D U N I V E R S I T YMixer types Segregating Rotating drum V-blender Double cone blender Cubic blenders Non segregating Ribbon blender Nauta blender L diger Fluidizing blender(Forberg) Characterized by Froudesnumber Fr<1 Thrust mixers -Ribonblender,Nauta mixer Free fall mixers -V-blender Fr 1 Fluidized beds Fr>1 Centrifugal mixers Intensive mixers18L U N D U N I V E R S I T YHow do they look1019L U N D U N I V E R S I T YFrom Powdertechnology handbookDouble cone blenderNauta blenderribbon blenderHigh speed blenderV-type blenderRotating diskHorizontal cylinderfluidized bedMotionlessVibration andmechanical agitation20L U N D U N I V E R S I T YWhat to consider when designing a mixingprocess What's needed forhomogenous mixer mixing time Batch size Degree of filling Energy need Temperature Mild or shearing mixing

6 Deagglomeration Segregation Handling of powder Cleaning Worker protection Explosion risks Prize Material Etc etc etc1121L U N D U N I V E R S I T YSegregation mechanisms Percolation-slip through the holes Trajectory Effect - size or density segregation due to airdrag during filing or feeding Rolling Effect -Due to friction and gravity Stumbling Effect , Push-Away Effect Elutriation effects- dusting segregation-dust layer formedon top of particle bed Densification22L U N D U N I V E R S I T YSegregation Can occur During mixing Storage Transport Can be counteracted by Narrow particle size Ordered mixtures Irregular and coehisivepowder Granulation Ordered mixtures Reduce vibrations