OPTIMISING DRYER PERFORMANCE WITH STICKY LINE INDICATION SYSTEMS (SLI SYSTEM)
Milk powders with a high lactose content such as Non-Fat Dry Milk (NDM), Skim Milk Powder (SMP) and lower protein Whey Protein Concentrates (WPC 34) are inherently “sticky” under certain conditions and sticky powders lead to plugged up dryers, cyclones and bag houses.
Most crystalline solids such as lactose can exist in two distinct states – glassy and rubbery. The glassy state is rigid, brittle and non-sticky. The Rubbery state is pliable and sticky. Changing the temperature and humidity surrounding the powder particles containing lactose will change the state of the lactose from one to the other – a phenomena called the “glass transition”.
Drying conditions with lower humidity favours the non-sticky glassy (safe) state whereas higher humidity favours the sticky rubbery (unsafe) state. Unfortunately, operating the dryer under low humidity conditions also leads to reduced capacity.
Installation of a SLI System allows for optimising the dryer’s operating conditions – balancing the stickiness vs. capacity while avoiding plugging – by continuously monitoring the factors impacting the humidity within the dryer:
- Ambient air temperature and humidity
- Combustion moisture
- Inlet air flow and temperature
- Feed composition, solids and temperature
- Secondary drying air flow and temperature
This real time information is processed via complex algorithms within the dryer’s PLC, to arrive at a calculated 'Operating Point', which is then compared to current product’s sticky line (border between safe and un-safe conditions) and displayed graphically on the HMI screen. Trained operators use the display to guide the Operating Point close (for maximum capacity) to the Sticky Line while staying on the safe side of the sticky line.
Instances where SLI Systems are especially valuable:
- Switching production between products with varying Lactose content (such as NDM vs SMP)
- Seasonal weather changes – Winter with cold, dry air vs summer with Hot, humid air
- Daily weather changes – colder, drier mornings vs warmer, humid afternoons.