how does air to air heat exchanger work in Spray drying heat recovery

In spray drying heat recovery, an échangeur de chaleur air-air is used to recover waste heat from the hot, moist exhaust air leaving the drying chamber and transfer it to the incoming fresh (but cooler) air. This reduces the energy demand of the drying process significantly.

How It Works:

1. Exhaust Air Collection:

   • After spray drying, hot exhaust air (often 80–120°C) contains both heat and water vapor.

   • This air is pulled out of the chamber and sent to the heat exchanger.

2. Heat Exchange Process:

   • The hot exhaust air flows through one side of the heat exchanger (often made of corrosion-resistant materials due to possible stickiness or mild acidity).

   • At the same time, cool ambient air flows through the other side, in a separate channel (counter-flow or cross-flow setup).

   • Heat is transferred through the exchanger walls from the hot side to the cool side, without mixing the air streams.

3. Preheating Incoming Air:

   • The incoming fresh air gets preheated before entering the spray dryer’s main heater (gas burner or steam coil).

   • This lowers the fuel or energy required to reach the desired drying temperature (typically 150–250°C at the inlet).

4. Exhaust Air Post-Treatment (optional):

   • After heat extraction, the cooler exhaust air can be filtered or treated for dust and moisture before being released or further used.

Benefits:

• Energy Savings: Cuts down fuel or steam consumption by 10–30% depending on setup.

• Lower Operating Costs: Less energy input reduces utility expenses.

• Environmental Impact: Reduces CO₂ emissions by improving energy efficiency.

• Temperature Stability: Helps maintain consistent drying performance.