AIRLESS DRYING VS CONVENTIONAL HOT AIR DRYING

The UK Department of Environment’s Energy Efficiency Best Practice Programme sponsored industrial trials to compare airless and conventional hot air drying of various products¹. Airless Drying gave the following benefits over hot air drying:

• Reduced drying times in all cases of between 30% and 90%. The higher heat capacity of steam, as compared to air, reduces the mass flow rate of steam required to dry the product and that its higher heat transfer coefficient, compared to air, means faster during times.
• Higher throughput, smaller plant, significant capital and operating cost savings.
• Improved product quality including sterilisation, conditioning, oxidation prevention.
• Energy consumption between 50% & 90% lower.
• Demineralised water, virtual elimination of noxious emissions, reduced anti-pollution costs.
• Not needing a large hot air exhaust stack is another significant positive for some clients.

Other benefits Airless drying technology offers over other drying technologies:

• The system operates in an essentially air free environment. The near absence of oxygen will help mitigate the risk of fire and explosion hazards².
• The absence of oxygen allows for a higher temperature to be used without concerns for product denaturing through overheating.
• The technology uses significantly less energy than conventional indirect drying due to the fact that flow-through air is not required, which wastes a lot of heat energy.
• Options are available for cost-effective reuse of the energy in the steam vented from the dryer

Therefore, the basic business case is:

• Higher IRR (payback of investment) than conventional hot air drying.
• Significantly reduced pollution than conventional drying.

In summary, compared to conventional hot air drying, airless drying has demonstrated significant cost and environmental benefits in multiple commercial applications. Airless drying’s much lower energy consumption offers faster payback of the capital invested.

¹1998 UK Department of Environment’s Energy Efficiency Best Practice Programme.
²Mujumdar A., (1991) ‘Drying technologies of the future’ Drying Technology, 9(2), 325-347.