Abstract
Conventional spray dryers are very energy-demanding and occupy a significant amount of floor space. Also, their energy efficiency is quite low. To overcome these issues, a new spray dryer should be developed and optimized. Besides this, conventional dryers always have a vortex separator to segregate the solid phase.
This thesis presents details of a novel spray drying technology. Currently, the application is limited to milk drying. However, this technique could be extended to other products suitable for spray drying.
In the conventional configuration of milk drying devices, the drying medium and the milk droplets enter the drying chamber from the same direction. This co-current drying technique is practiced along with a relatively low drying medium temperature to prevent the milk particles from overheating. In the spray drying technology, as presented in this work, the milk droplets and the drying medium enter the drying chamber in the counter-current configuration, which increases the slip velocity and thus enhances heat transfer. This also improves the throughput of the dryer; this is known as process intensification.
In this case, the drying air temperature is relatively high. To prevent the milk from burning at this high temperature, it is ensured that the residence time of milk droplets in the drying zone is in order of a few milliseconds. After that, the dried product is immediately evacuated to the cold zones. Multiple tangential inlets create a vortex flow to extract the dried milk powder. This dryer configuration is called Radial Multizone Dryer (RMD).
To optimize the design of the Radial Multizone Dryer and to achieve optimum quality of the product particles, CFD tools are used. The quality of the products depends upon the final temperature of the product, hence the heat transfer within the reactor has to be optimized that the droplets gain heat just enough for evaporation, and do not overheat. Multi-phase calculations are performed to capture the flow field of the drying medium, the trajectories, and the evaporation of the milk droplets. Simulation results show that the capacity of a pilot-scale model is 108[kg/hr]. Based on the studied conditions, the dryer’s performance is optimized when the Sauter mean diameter of the spray droplets is between 40 to 60 μm. This leads to the drying and evaporation of most of the products.
This thesis presents details of a novel spray drying technology. Currently, the application is limited to milk drying. However, this technique could be extended to other products suitable for spray drying.
In the conventional configuration of milk drying devices, the drying medium and the milk droplets enter the drying chamber from the same direction. This co-current drying technique is practiced along with a relatively low drying medium temperature to prevent the milk particles from overheating. In the spray drying technology, as presented in this work, the milk droplets and the drying medium enter the drying chamber in the counter-current configuration, which increases the slip velocity and thus enhances heat transfer. This also improves the throughput of the dryer; this is known as process intensification.
In this case, the drying air temperature is relatively high. To prevent the milk from burning at this high temperature, it is ensured that the residence time of milk droplets in the drying zone is in order of a few milliseconds. After that, the dried product is immediately evacuated to the cold zones. Multiple tangential inlets create a vortex flow to extract the dried milk powder. This dryer configuration is called Radial Multizone Dryer (RMD).
To optimize the design of the Radial Multizone Dryer and to achieve optimum quality of the product particles, CFD tools are used. The quality of the products depends upon the final temperature of the product, hence the heat transfer within the reactor has to be optimized that the droplets gain heat just enough for evaporation, and do not overheat. Multi-phase calculations are performed to capture the flow field of the drying medium, the trajectories, and the evaporation of the milk droplets. Simulation results show that the capacity of a pilot-scale model is 108[kg/hr]. Based on the studied conditions, the dryer’s performance is optimized when the Sauter mean diameter of the spray droplets is between 40 to 60 μm. This leads to the drying and evaporation of most of the products.
| Original language | English |
|---|---|
| Awarding Institution |
|
| Supervisors/Advisors |
|
| Award date | 31 Oct 2023 |
| Place of Publication | Enschede |
| Publisher | |
| Publication status | Published - 31 Oct 2023 |