Controlling the cooling crystallization of lactose
Controlling the crystallization process of lactose is still done in old-fashioned ways in many dairy plants. The most typical solution is based on using prescribed temperature curves, or just constant rate of cooling. These approaches however are very sensitive to any changes in the parameters of the whey or temporary malfunctions in the cooling system. Supersaturation-based control of the lactose cooling crystallization process offers a modern, adaptive solution that guaranties high quality product at the end of every batch.
In 2020 we developed our first system capable of controlling the cooling crystallization process of lactose based on supersaturation. We delivered the system to a customer in Eastern Europe. The system consists of 3 instruments:
1. A Vaisala K-Patents process refractometer.
2. A special version of SeedMaster-3, modified to operate with lactose.
3. Zutora’s LACTOCOOL control system.
Transmitter of the refractometer, SeedMaster and LACTOCOOL installed
The process refractometer is installed in the crystallizer. It measures concentration and temperature of the mother liquor. There is no need for any other measurement device to be installed.
The SeedMaster provides an online supersaturation signal based on the concentration and temperature measured by the refractometer. Calculating the supersaturation of the whey is challenging, as we need to consider the mutarotation and temperature-dependent equilibrium of α- and β-lactose in the solution. As α-lactose is less soluble than β-lactose, the α form will crystallize in the typical crystallizers. Then, as ratio of dissolved α-lactose reduces and the dynamic equilibrium is disturbed, β-lactose will start turning into the αform.
Examining the traditional control
After installing the new system, we did not start controlling the process with it, we only used it to monitor the crystallization.
Starting purity of the whey in the lactose crystallization process is typically around 74 %. Our customer uses a solution with higher purity around 90 %, thanks to a purification process performed before crystallization.
Starting temperature is around 58 – 60 °C, concentration is 51-52 %. They cool this solution with a relatively high speed for 15 hours, a bit slower for another 7 hours and very slowly for the final 26 hours. Final temperature is slightly above 10 °C.
During these 48 hours, concentration is reduced from the original 51-52 % to approximately 29 %.
With the SeedMaster we were able to monitor supersaturation, crystal content, crystal size and other key parameters of the crystallization process. The most interesting phenomenon that we noticed was that crystal growth rate reduced significantly towards the end of the batch. Even though supersaturation was high, and that is the “driving force” of crystallization, crystal content and crystal size remained practically constant at temperatures under 20 °C. Based on the recorded data, 97 % of crystal growth happened during the first 36 hours of the batch and only 3 % happened during the last 12 hours. This is due to the very low temperatures.
Advanced control of lactose crystallization
Zutora’s advanced control solution for lactose cooling crystallization works as described below:
1. The refractometer measures the temperature and concentration of lactose dissolved in the mother liquor.
2. Using the measured concentration and temperature, the SeedMaster calculates supersaturation.
3. LACTOCOOL takes the temperature and supersaturation signals from SeedMaster and controls the temperature of the solution to keep supersaturation in the optimal range.
Note: LACTOCOOL control functions are now included in SeedMaster-4, it is not a separate instrument anymore.
Supersaturation-based control of lactose cooling crystallization
Improved product quality
After fine-tuning the system, our customer recorded the parameters of the product crystals for months. We managed to significantly improve crystal quality, yield and energy efficiency.
Yield
Yield of the crystallization process was in the 45-50 % range with the old control. Using the supersaturation-based control, we managed to increase it to more than 60 %.
Crystal size
Target crystal size is 200-250 microns in our customer’s process. With the old control they could not reach this in many cases, typical crystal size was around 150 microns. With the new control, we achieved 230 microns average crystal size.
Fines
Our customer had a large number of fines in the product with the old control. This is severe product quality issue, but we managed to get rid of it with the new control system.
Energy consumption
We managed to increase the yield of the process using less energy than before, as final temperatures of the process are higher, therefore less energy is required for cooling.
Product crystals made with the old control
Wide crystal size distribution, lots of fines.
Product crystals made with the new control
Uniform crystals, without fines or conglomerates.
Conclusion
We managed to significantly improve the process of lactose cooling crystallization at our customer’s facility. Using all the experience gained in this project, we designed our new SeedMaster-4 to have it all-in-one: it has the features of the SeedMaster and the LACTOCOOL. It is a turnkey solution for the control of lactose cooling crystallization. For further details, feel free to contact us.