Table of Contents
- Grain drying towers (grain driers) blow heated air through a bed of corn, rice or wheat to carry away moisture. The exhaust leaving the tower is hot and humid, so a large share of the burner's fuel simply leaves as waste heat in that damp airstream. Cutting that loss is the main energy-saving opportunity in grain drying.
- A rotary (wheel) heat exchanger is mounted in the air path so the hot, humid exhaust rotates past the incoming fresh or combustion air. As the wheel turns, its matrix picks up heat from the exhaust and releases it to the incoming stream, pre-heating the air before the burner or before it enters the tower. Because the wheel is a continuous rotating mass, it delivers steady, high sensible effectiveness (often 70-85%) in a compact footprint - well suited to the high airflows of a drying tower.
- For drying you want the process air to stay dry, so the goal is to recover heat, not to push moisture back into the incoming air. A plain (sensible) rotary wheel or a plate core is therefore the usual choice; an enthalpy wheel that also transfers water vapour is generally avoided here because re-wetting the incoming air would work against drying. Some closed-loop designs instead use a desiccant wheel on a separate regeneration stream, but the dominant, simplest win is sensible pre-heat of combustion or make-up air.
- Fuel saving - pre-heating combustion air with exhaust heat typically cuts burner fuel use by 15-30% depending on inlet and exhaust temperatures. Capacity - the same burner delivers more effective drying because less energy is wasted, raising tower throughput in peak harvest windows. Emissions - lower fuel burn means less CO2 and fewer particulates per tonne of grain dried.
- At the very high airflows of a grain tower, a rotary wheel recovers more heat per unit of space than a flat plate stack and handles the temperature swing continuously. Plates remain attractive where the exhaust is dusty and must be cleaned often. Either way, the recovered heat is the same waste-heat-recovery principle described throughout this Encyclopedia - only the application is agriculture.
Grain drying towers (grain driers) blow heated air through a bed of corn, rice or wheat to carry away moisture. The exhaust leaving the tower is hot and humid, so a large share of the burner's fuel simply leaves as waste heat in that damp airstream. Cutting that loss is the main energy-saving opportunity in grain drying.
A rotary (wheel) heat exchanger is mounted in the air path so the hot, humid exhaust rotates past the incoming fresh or combustion air. As the wheel turns, its matrix picks up heat from the exhaust and releases it to the incoming stream, pre-heating the air before the burner or before it enters the tower. Because the wheel is a continuous rotating mass, it delivers steady, high sensible effectiveness (often 70-85%) in a compact footprint - well suited to the high airflows of a drying tower.
For drying you want the process air to stay dry, so the goal is to recover heat, not to push moisture back into the incoming air. A plain (sensible) rotary wheel or a plate core is therefore the usual choice; an enthalpy wheel that also transfers water vapour is generally avoided here because re-wetting the incoming air would work against drying. Some closed-loop designs instead use a desiccant wheel on a separate regeneration stream, but the dominant, simplest win is sensible pre-heat of combustion or make-up air.
- Fuel saving - pre-heating combustion air with exhaust heat typically cuts burner fuel use by 15-30% depending on inlet and exhaust temperatures.
- Capacity - the same burner delivers more effective drying because less energy is wasted, raising tower throughput in peak harvest windows.
- Emissions - lower fuel burn means less CO2 and fewer particulates per tonne of grain dried.
At the very high airflows of a grain tower, a rotary wheel recovers more heat per unit of space than a flat plate stack and handles the temperature swing continuously. Plates remain attractive where the exhaust is dusty and must be cleaned often. Either way, the recovered heat is the same waste-heat-recovery principle described throughout this Encyclopedia - only the application is agriculture.