Dryer Throughput & Fuel Cost per Tonne

Use the wet-basis shrink formula: water removed per wet tonne = (Mᵢ − M_f) ÷ (100 − M_f). For 20% to 14% that is (20 − 14) ÷ (100 − 14) = 6 ÷ 86 = 0.0698, so about 70 kg of water per tonne, or roughly 7 tonnes of water from a 100-tonne batch. The dry grain that remains is 100 × (100 − 20) ÷ (100 − 14) = 93 tonnes — a 7% weight shrink.

The heat to evaporate the water is mass of water × 2,400 kJ/kg latent heat. Divide by your dryer efficiency to get the gross fuel energy, then divide by each fuel's delivered energy (heating value × burner efficiency) to get the fuel quantity per tonne, and multiply by the fuel price. The tool does this for LPG, diesel, natural gas, firewood and electricity at once.

Dryer efficiency here is the useful evaporation energy divided by the fuel energy put into the chamber — it folds in heat lost to warming the air and grain, exhaust and the surroundings. High-temperature continuous dryers commonly land around 45–60%; low-temperature or poorly maintained dryers can be lower. The specific energy of drying that implies is shown so you can sanity-check it against the 3,300–6,000 kJ per kg of water typical range.

It depends on local prices, but the tool ranks all five live. Firewood and natural gas are often cheapest per delivered MJ; electric resistance heat is usually the most expensive because you pay for premium energy to make low-grade heat. The bar chart sorts the fuels by cost per tonne so the cheapest option is obvious at your prices.

Throughput = (rated burner heat × dryer efficiency × 3,600) ÷ the useful heat each wet tonne needs. A 2 MW burner at 50% efficiency delivers 1 MJ of useful evaporation per second, or 3,600 MJ per hour; dividing by the ~167 MJ a 20→14% wet tonne needs gives about 21 t/h. It is a heat-limited guide figure — real capacity also depends on airflow, bed depth and grain type.

The water you evaporate was part of the sale weight, so removing it shrinks the tonnage. Drying 100 t from 20% to 14% leaves 93 t — a 7% shrink. That shrink is real lost weight you are also paying fuel to remove, which is why over-drying below the contract moisture costs you twice: extra fuel and extra shrink.

The tool uses 2,400 kJ per kg of water. Pure water's latent heat of vaporisation is 2,257 kJ/kg at 100 °C, but in a grain dryer the air is warmer than the grain and some energy goes into desorbing tightly-bound moisture, so 2,400 kJ/kg is the standard effective value used in grain-drying energy work.

Yes, proportionally. Each point of moisture removed adds roughly the same slab of water and therefore fuel. Going from 14% to 13% on a 20% incoming crop adds about 12 kg more water per tonne — so trimming the target to the lowest safe storage moisture, and no lower, is one of the cheapest savings on the whole job.

This tool prices fuel-fired and electric drying. Sun or ambient-air drying uses free or near-free energy but is slow, weather-dependent and capacity-limited. Use the throughput and cost figures here to decide whether mechanical drying pays for the speed and reliability it buys you over natural drying.

Enter your dryer's rated heat input in megawatts (MW). Many continuous farm dryers are in the 1–5 MW range; the nameplate or manual lists it in MW, kW (÷1,000 to MW), or BTU/h (1 MW ≈ 3.41 million BTU/h). The rating only affects throughput and drying time, not the cost per tonne, which is set by physics and fuel price.

The fuel cost per tonne depends on moisture removed, dryer efficiency and fuel price — not on the burner size. A bigger burner dries faster (higher t/h, fewer hours) but burns proportionally more fuel, so the cost per tonne is the same. Size changes your throughput and drying time; efficiency and fuel price change your cost.