I. Why Food Drying Is Suitable for Recovery
Drying of fruits, vegetables, nuts, meat products, tea, etc. often directly vents 60~140°C humid-hot air. This kind of waste heat has three advantages: moderate temperature, stable flow, year-round continuous operation, the most "worry-free" condition for heat exchangers. Take a line with daily treatment and exhaust air of 12000 m³/h as an example; at 120°C exhaust, the carried sensible heat is considerable.
II. Typical Recovery Path
- Exhaust → plate air-to-air heat exchanger → make-up air: Returns the heat of the about-to-be-vented hot air to the fresh make-up air entering the drying room, saving the new energy needed to heat the make-up air;
- Exhaust → air-to-water heat exchanger → hot water: Preheating of plant domestic hot water and washing water;
- Dehumidify high-humidity exhaust first: Contains large amounts of water vapor; if necessary, recover heat first then condense to remove water, avoiding condenser fouling and corrosion.
III. A Simplified Verification
| Parameter | Value |
|---|---|
| Exhaust air volume | 12000 m³/h |
| Exhaust temperature | 120°C → reduced to 70°C |
| Make-up air temperature | 20°C → raised to 65°C |
| Air mass flow | ≈ 3.2 kg/s |
| Recovered heat | ≈ 3.2 × 1.0 × (65−20) ≈ 144 kW |
Estimated at 8000 hours/year and electricity price 0.7 RMB/kWh, annual electricity saving ≈ 144×8000×0.7 ≈ 806,000 RMB; equipment investment usually pays back in 1~2 years.
IV. Notes
- Anti-condensation: Exhaust contains moisture; low-temperature-side walls may fall below the dew point; select material (e.g., stainless steel/aluminum) and consider drainage;
- Hygiene requirements: Food grade requires washable, food-contact materials, periodic CIP;
- Wind resistance matching: The added heat exchanger pressure drop must be included in the original fan margin; replace with a larger fan if necessary.
Food drying waste heat recovery is often not "whether it can," but "whether the two checkpoints of hygiene and condensation are passed."