Question:
The temperature of air in a ‘Fluid-bed dryer' in spray drying plant is about:
The temperature of air in a ‘Fluid-bed dryer' in spray drying plant is about:
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In multi-stage spray dryers, the inlet air to the spray chamber is around 180-200$^\circ$C, while the secondary fluid-bed dryer uses air at a lower range of 100-120$^\circ$C for safe moisture extraction.
Updated On: Aug 7, 2026
- 60-65 $^\circ$C
- 100-120 $^\circ$C
- 170-175 $^\circ$C
- 195-200 $^\circ$C
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Verified By Collegedunia
The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
In a modern two-stage or multi-stage spray drying plant, the primary drying takes place in the main spray chamber, and the secondary drying is carried out in an integrated or external fluidized bed dryer (fluid-bed dryer).
The fluid-bed dryer is designed to remove the remaining bound moisture from the milk powder particles gently, bringing the final moisture content down to less than 4% while protecting heat-sensitive components.
Step 2: Detailed Explanation:
The partially dried milk powder leaves the main spray drying chamber at a relatively high moisture content of around 8% to 10% and enters the fluid-bed dryer.
In this secondary drying stage, hot air is passed upward through a perforated plate to fluidize the powder particles, ensuring excellent heat and mass transfer.
The temperature of the drying air supplied to this fluid-bed dryer is typically maintained in the range of 100$^\circ$C to 120$^\circ$C.
This temperature range is sufficient to evaporate the residual moisture without causing thermal damage or scorched particles, as the evaporative cooling effect keeps the actual product temperature much lower.
Air temperatures below 100$^\circ$C (like 60-65$^\circ$C) would be too low for efficient secondary moisture removal, while temperatures above 170$^\circ$C would cause severe browning, protein denaturation, and solubility loss in the milk powder.
Step 3: Final Answer
The correct option is (B).
In a modern two-stage or multi-stage spray drying plant, the primary drying takes place in the main spray chamber, and the secondary drying is carried out in an integrated or external fluidized bed dryer (fluid-bed dryer).
The fluid-bed dryer is designed to remove the remaining bound moisture from the milk powder particles gently, bringing the final moisture content down to less than 4% while protecting heat-sensitive components.
Step 2: Detailed Explanation:
The partially dried milk powder leaves the main spray drying chamber at a relatively high moisture content of around 8% to 10% and enters the fluid-bed dryer.
In this secondary drying stage, hot air is passed upward through a perforated plate to fluidize the powder particles, ensuring excellent heat and mass transfer.
The temperature of the drying air supplied to this fluid-bed dryer is typically maintained in the range of 100$^\circ$C to 120$^\circ$C.
This temperature range is sufficient to evaporate the residual moisture without causing thermal damage or scorched particles, as the evaporative cooling effect keeps the actual product temperature much lower.
Air temperatures below 100$^\circ$C (like 60-65$^\circ$C) would be too low for efficient secondary moisture removal, while temperatures above 170$^\circ$C would cause severe browning, protein denaturation, and solubility loss in the milk powder.
Step 3: Final Answer
The correct option is (B).
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