Figure 6. 6. Design and selection of flow promotion devices 6.1 Flow additives (glidants and lubricants) 6.2 Size enlargement (agglomeration) 6.3 Flow promotion devices
Figure 6.1 Prof. Dr.-Ing. habil. J. Tomas chair for Mechanical Process Engineering Measures and Flow Promotion Devices to avoid Bridging and Chanelling Flow promotion devices objectives Increasing Avoid Avoid flow channel- bridging channel ling Improve Flow additives (anti-caking X X X flowability of powder agents, glidants, lubricants ) Size enlargement (agglomeration, X X X pelletizing, tabletting) Wall liners Slippery paints, wall coatings X X - and coatings Rigid plates X X - Flexible walls (X) (X) X Rigid inserts Cone, roof, beams, grid, bin X X - Pneumatic flow promotion devices Oscillating devices Rotating devices Continous aeration (pneumatic X X X bottom or bin) Bin cushion, aeration tube, box, - (X) X whistle Rapid aeration in batch (nozzles, - X X lance, cannon) Gas shocks waves by explosions - X X External vibrator, rapper, knocker - (X) X Internal vibrating grid or cone (X) (X) X Soil penetration rocket - - X Oscillating bins X X X Flexible arm agitator - (X) X Beam, arm, plough, plate agitator (X) - X paddle shaft (X) - X Feeders Arm agitators in convergent or X X X with flow promotion divergent hoppers Rotary plough feeder (bunker discharge X X X function wagon) Transverse driven screw feeder X X X (X) partially effective
6.1 Flow additives (glidants and lubricants) Figure 6.2 Effect of flow additive on heap formation of a technical herbicide Herbicide with.3% Aerosil Herbicide with.9% Aerosil Consolidation functions σ c = f(σ 1 ) and time consolidation function of herbicide 3,3 Ma.-% ff c = 1 Einaxiale Druckfestigkeit σ c [kpa] 25 2 15 1 5,3 Ma.-% (24h),9 Ma.-%,9 Ma.-% (24h) ff c = 2 ff c = 4 ff c = 1 5 1 15 2 25 3 Verfestigungsspannung σ 1 [kpa] Estimation of optimal guest particle size and their content: Adhesion force Guest particle size at F H,min Load of guest particle at F H,min ff c = σ 1 /σ c flow function acc. to Jenike C F 24 dfh = d(d ) µ 2 d + = H,sls h g H 2 g g n g m = 2 m h g d ( ) 2 d g + 2 a a d h = a 2 a 2 / 3 a a 2 d h d d g,min 3 π ρ = 2 ρ s,g s,h h
Figure 6.3 6.2 Agglomeration - Size Enlargement Operation principles of agglomeration processes: a) tumble agglomeration (growth or agitation agglomeration) pelletizing A feed material (for agglomeration), Q heat flow b) press agglomeration (compaction) in partially open or closed die continuous sheets (ribbon) solid forms (tablets, briquettes) c) sintering (thermal process)
Tumble Agglomeration (Pelletizing) Figure 6.4 1. Balling drum and balling pan a) balling drum b) balling pan A P W feed material green pellets water
Press Agglomeration Operation principles of press agglomeration : Figure 6.5 a) a) in a closed die b) in a open die c) by roller pressure b) c) A feed B agglomerate F P compaction or press force F R wall friction force in the die channel h punch stroke length l filling level (not compacted) s thickness of compacted material k compaction (k=l/s) β 1 half of nip angle 1 punch 2 pressing die
Figure 6.6 Microprocesses and deformation mechanism at powder press agglomeration (compaction) h p h(t) p h(t) a) Feed of loose packing b) Elastic-plastic contact deformation c) Pore filling by fine particles p p p h(t) h(t) h(t) d) Plastic deformation of particles to create large contact areas e) Breakage of f) Plastic deformation edges, particle of entire tablet breakage, pore filling Compaction function of cohesive powder Tablet, briquette or ribbon strength σ T compact strength lg(σ T in MPa) σ T = f(p) uniaxial compressive strength σ c For hopper design σ c = a 1 σ 1 + σ c, consolidation stress σ 1 1-3 compaction pressure lg(p in MPa)
6.3 Flow promotion devices Lining of Bins Material data of ultrahigh-molecular weight polyethylen Figure 6.7 no bulging bolts or edges! rounded edge profiles promote mass flow fastening
Rigid Hopper Inserts Figure 6.8 a) before b) Plate insert Θ G, con flow zone dead zone Θ G Θ G b Θ Θ G hopper angle limit of the flow zone b b min Θ c) Cone insert d) Bin insert ("Binsert") Θ G Θ G, wedge 2 Θ G, con b min, wedge Θ G, con b min, con b min, con b min, wedge
Figure 6.9 Pneumatic Flow Promotion Devices a) Fluidisation of whole bin b) Aeration bottom porous bottom poröser Boden c) Aeration box d) Bin wall cushion at rest Ruhestellung Ruhestellung e) Porous aeration tube f) Aeration whistle at rest g) Movable air lance h) Air cannon
Figure 6.1 Air Pressure Shock Device (Air Cannon) filling shock wave outflow rapid releasing valve Arrangement of air cannons: channelling piping (ratholing) bridging in hopperr in shaft
Vibrating discharge aids Figure 6.11 a) Unbalanced motor at hopper wall (dashed lines: wall oscillations at highfrequency excitation f > 1 Hz) b) Silo with flexible connected vibrating hopper and conical deflector (Δx < 4 mm, f < 25 Hz) Additional options for convex deflector and/or oscillating inserts (rods, cages, screens, flexible grids): c) Matcon-Bules as valve with lowered cone (left) and with lifted and vibrating cone by pneumatic excitation as discharge aid (right) Kollmann, Th.: Schwingungsinduziertes Fließen feinstkörniger, kohäsiver Pulver, Diss. Otto-von-Guericke- Universität Magdeburg 22
Figure 6.12 Arrangement of Discharge Aids at Time Consolidations 1. Minimum discharge width versus storage time at rest outlet width b min b min (t max ) b min (t 1 ) b min, b2 _ t b min (t) = b min, + b [1 - exp(- )] t 63 hopper height y b min (t max ) b min (t 1 ) b min, b 2 no bridging for t < t max no bridging for t < t 1 no bridging for t = bridging t 1 t max storage time t 2. Outlet design b min (t max ) a) no discharge aid necessary b min (t max ) b min (t 1 ) b) discharge aid necessary for t > t 1 b min (t max ) b min (t max ) b min (t 1 ) c) discharge aid necessary for t > b min (t 1 ) d) discharge aid necessary for t > b min, b min, b 2 e) discharge aid always necessary see Schulze, D., Austragorgane und Austraghilfen, Chem.-Ing.-Techn. 65 (1993) 48-57