Cryogenic grinding with liquid nitrogen, Alpine
Pin Mill CW with Screwcooler
Why nitrogen cooling?At normal temperatures tough and elastic materials cannot be ground to a fine grained powder, even when the grinding media are run at high speed. With "cool" grinding, however, the use of liquid nitrogen render the material brittle prior to the cool grinding stage, with the effect that plastics and rubber granulates, etc. can now be grounded to a fine, easily-flowing powder.
Typical materals are:
-Polyamide-fusion adhesive-PVC-Polyester-caoutchouc-rubber, etc.
Dependent on the product and the fineness, the specific nitrogen consumption ranges between approc. 0,7 and 2,5 kg N2/kg powder. In the majority of cases, employment of the 250 CW and 400 Cw models is sufficient to cover the customary demands.
Contraplex cool grinding advantages:
- extremely high grinding finenesses
- favourable N2 consumption due to low milling air volume
Existing maschines can be converted to operate as "cool" grinding mills.
Cryogen grinding of foodstuffsWheras cryogenic grinding is employed predominantly for spices, the Alpine cryogenic grinding systems are also used in practise for other materials with an extremely low melting point, such as fatty mixtures, baking agents, and pure coffee, etc.
The advantages are:
- Optimal retention of aroma and strength. In contrast to normal grinding,
where between approx. 15 and 43 % essential oils are lost, the loss with
cryogenic grinding is minimal (approx. 3-10%).
- Approx. 2 or 3 times more grinding capacity.
- No danger of overheating etc.
System constructionThe schematic shows the basic construction of a cryogenic grinding system.
1 = Feed screw, alternatively: vibratory channel or rotary valve
2 = Screw cooler with whirling motion and liquid nitrogen feed (LN2)
3 = Contraplex Stud Mill (Pin Mill)
4 = Automatic filter in quick-change design; advantageous if the product is
changed frequently
T = Temperature sensor
Turquoise = Insulated system components
Consumption kg LN2/kg production(non-binding standard values)
| Specific Grinding Capacity | Temperature at mill outlet | ||
| -10 degrees Celcius | 0 degrees Celcius | + 10 degrees Celcius | |
| 0,02 kWh/kg | 0,25 | 0,20 | 0,15 |
| 0,05 kWh/kg | 0,50 | 0,45 | 0,40 |
| 0,10 kWh/kg | 1,00 | 0,90 | 0,85 |
| 0,15 kWh/kg | 1,45 | 1,40 | 1,35 |