Thermomechanical Cooking and Expansion. Part 2

Thermomechanical Cooking and Expansion Part 2

SUMMARY Basic description of a twin screw extruder Introduction to the extrusion process: Preconditioning Thermomechanical Cooking and Expansion Part 1 : extrusion variables and effects on the process/product Part 2: Screw profile design Part 3: Die-level expansion/texturization 2

CASE OF EXPANDED SNACKS 3

EXTRUSION OPERATING VARIABLES AND EFFECT ON THE PRODUCT DIRECT EXTRUSION OPERATING VARIABLES Water, feed rate, rpm, temperature INDIRECT EXTRUSION OPERATING VARIABLES Die temperature, product temperature, die pressure, SME, residence time EFFECT ON THE PRODUCT characteristics of melt expansion 4

EXPERIMENT WITH CORN BASE CONTROL: Recipe Feed rate 100% corn grits 100 kg/h Moisture 18% Product Temperature 176 C Screw speed 350 rpm LEI 2.5 Effect on texture, expansion SEI/LEI, Bulk density SEI 17.8 Bulk density 49 g/l 5

EXPERIMENT WITH CORN BASE screw speed effect (rpm) Screw speed: 350 rpm 400 rpm 450 rpm 500 rpm SEI 17.8 18.1 17.6 18 LEI 2.5 2.85 2.95 3.59 Bulk density g/l 49 45 41 38 6

EXPERIMENT WITH CORN BASE screw speed effect (rpm) LEI ISOTROPIC EXPANSION LEI=SEI 1/2 ANISOTROPIC EXPANSION RPM SEI 7

EXPERIMENT WITH CORN BASE Screw speed effect (rpm) DENSITY (g/l) 45 40 35 30 25 350 400 450 500 550 SCREW SPEED (rpm) 8

EXPERIMENT WITH CORN BASE effect of moisture content Moisture content: 18% 21% 23.7% 26.3% IBM = F x Mf + W F + W In Barrel moisture F feeder flow Mf moisture flour W water flow SEI 17.8 12.1 7.6 5.9 LEI 2.5 2.4 2.0 1.82 Bulk density g/l 49 88 160 234 9

EXPERIMENT WITH CORN BASE Effect of moisture content LEI ISOTROPIC EXPANSION LEI=SEI 1/2 ANISOTROPIC EXPANSION MOISTURE CONTENT SEI 10

EXPERIMENT WITH CORN BASE Effect of moisture content DENSITY (g/l) 300 250 200 150 100 50 18% 20% 22% 24% 26% MOISTURE CONTENT (%) 11

EXPERIMENT WITH CORN BASE Effect of feed rate Feed rate: 100 kg/h 110 kg/h 130 kg/h 150 kg/h SEI 17.1 17.2 17.6 17.8 LEI 2.5 2.65 3.25 3.34 Bulk density g/l 62 55 54 49 12

LEI EXPERIMENT WITH CORN BASE Effect of feed rate ISOTROPIC EXPANSION LEI=SEI 1/2 ANISOTROPIC EXPANSION FEED RATE SEI 13

EXPERIMENT WITH CORN BASE effect of feed rate DENSITY g/l 60 58 56 54 52 50 100 kg/h 110 kg/h 120 kg/h 130 kg/h 140 kg/h Feed rate 14

EXPERIMENT WITH CORN BASE Effect of temperature profile Product temperature. (Front plate): 176 C 180 C 183 C 188 C SEI 17.8 17.1 18.1 17.6 LEI 2.5 3.04 3.00 3.12 Bulk density g/l 49 49 45 42 15

LEI EXPERIMENT WITH CORN BASE Effect of temperature profile ISOTROPIC EXPANSION LEI=SEI 1/2 ANISOTROPIC EXPANSION PRODUCT TEMPERATURE IN FRONT PLATE SEI 16

EXPERIMENT WITH CORN BASE Effect of product temperature DENSITY g/l 50 48 46 44 42 40 176C 179C 182C 185C 188C PRODUCT TEMPERATURE AT THE FRONT PLATE 17

RELATIONSHIP BETWEEN PARAMETERS-PROCESS-PRODUCT case of snacks and cereals Corn-based snack - SME < 150 Wh/kg Variables increase Pressure Temperature Residence time Moisture Content --- --- -- - SEI LEI - Bulk density Temperature - +++ = + - + Screw speed - + -- - + Material flow +++ - --- Reverse screw element length - + ++ ++ ++ - Decrease effect + Increase effect = Neutral effect 18

RESPONSE VARIABLES AND THERMOMECHANICAL COOKING Specific Mechanical Energy (SME) in Wh/kg: AC motor DC motor SME = Power Qt SME = V Amps rpm(r) Rpm max Qt = Motor efficiency (0.9) V = induced voltage Rpm (r) = screw speed Qt = Total input from the extruder Specific Thermal Energy (STE): Die temperature Back pressure STE = P thermal Qt 19

INTERNAL STRUCTURE OF EXTRUDED PRODUCTS SME increase (screw speed) The higher the SME, the finer the cell structure SME = 152 Wh/kg SME = 145 Wh/kg SME = 132 Wh/kg SME = 125 Wh/kg 3 20

INTERNAL STRUCTURE OF EXTRUDED PRODUCTS constant SME = 125 Wh/kg (throughput/screw speed) At a constant SME, the internal structure of the extrudate is homogeneous from low throughput/screw speed conditions to high throughput/screw speed conditions 500 kg/h 600 rpm 700 kg/h 800 rpm 800 kg/h 950 rpm 900 kg/h 1050 rpm 21

THERMOMECHANICAL COOKING OF STARCH H2O : 16-30% - SME > 100-110 Wh/kg - T 110 C Water molecules COOKED MIXTURE ENERGY INPUT 22

LEI EXPANSION CHART OF THERMOMECHANICAL COOKING corn grits base 4.0 3.5 3.0 2.5 Moisture decrease Isotropic expansion VEI 4 VEI 8 VEI 12 VEI 16 VEI 20 Process 1 - Industrial unit Process 2 - Industrial unit Process 3 - Lab unit 2.0 1.5 SME increase 1.0 0.5 0.0 0 5 10 SEI 15 20 23

DENSITY (g/l) Relation SME / PRODUCT characteristic Case of snacks 65 60 55 50 45 40 35 30 125 130 135 140 145 150 155 SME (Wh/kg) 24

CASE OF PET FOOD & FISH FEED 25

STRUCTURAL FORMATION OF EXTRUDED PRODUCTS THERMOMECHANICAL COOKING MELT EXPANSION EXPANDED PRODUCT. Q DIE EXPANSION PHASE SHRINKAGE PHASE t, µ a, t, residence time µ a, viscosity shear µ a, T melt, P melt SME ~ U. I ~ t. µ a. 2 T mass ~ SME and Q P mass ~ µ a and m 26

LEI EXPANSION CHART PET FOOD VERSUS SNACKS 4,0 EXPERIMENTAL DATA 3,5 Isotropic expansion LEI SEI 0.5 3,0 2,5 2,0 Control DX SNACKS 1,5 1,0 0,5 0,0 DRY PET FOODS 0 2 4 6 8 10 12 14 16 18 SEI VEI=20 VEI=16 VEI=12 VEI=8 VEI=4 27

LEI THERMOMECHANICAL COOKING EXPANSION TABLE case of expanded pet food/fish feed ISOTROPIC EXPANSION LEI=SEI 1/2 ANISOTROPIC EXPANSION SEI IMPORTANCE OF STEAM lowers the viscosity and elasticity of the melt Favours longitudinal expansion LEI and radial expansion SEI SME ~ U. I ~ t. µ a. 2 AREA OF VALUES OF PET FOOD AND FISH FEED PELLETS 28

INFLUENCE OF SCREW SPEED Pet food SME,Wh/kg 80 70 60 When the SPEED, => SME 50 40 30 20 400 450 500 550 600 650 700 750 800 850 SCREW SPEED, rpm 29

DENSITY, g/l INFLUENCE OF SCREW SPEED Pet food 500 480 When the SPEED, => DENSITY 460 440 420 400 380 360 340 320 300 400 450 500 550 600 650 700 750 800 850 SCREW SPEED, rpm 30

SME, Wh/kg INFLUENCE OF MOISTURE CONTENT Fish feed 39 37 35 EVOLUM 53 Flow 600 kg/h Screw: 750 rpm Vapour: 3 % Water/vapour liquid: 33 31 29 27 25 16 18 20 22 24 26 28 MOISTURE CONTENT in the extruder, %. SME ~ t. µ a. 2 When the moisture, µ a => SME 31

DENSITY, g/l INFLUENCE OF MOISTURE CONTENT Fish feed 690 670 650 EVOLUM 53 flow: 600 kg/h screw: 750 rpm vapour: 3 % 630 610 590 570 550 14 16 18 20 22 24 26 28 MOISTURE, % When the moisture, pellet density 32

DENSITY, g/l EFFECT OF THE FAT Fish feed 500 495 EVOLUM 53: Flow: 400 kg/h Constant moisture and vapour 490 485 480 2 3 4 5 6 7 8 9 10 FAT CONTENT, % When the FAT, DENSITY low 33