Dryer Throughput & Fuel Cost per Tonne
Costs out LPG
Drying 100 t of corn from 20% to 14% removes about 7 t of water and needs roughly 167 MJ of evaporation heat per wet tonne — this tool turns that into tonnes-per-hour throughput and fuel cost per tonne for LPG, diesel, natural gas, firewood and electricity.
Dryer job
Runs entirely in your browser — nothing is uploaded. Latent heat 2,400 kJ/kg water; fuel heating values from EIA / ASABE drying data.
Next: budget about 7.9/t in lpg (propane) (790 for the 100 t batch) and plan 4.2 h of dryer time at 23.7 t/h. Switching to Firewood / biomass would cut the fuel cost to 2.3/t.
Drying heat = water removed × 2,400 kJ/kg latent heat, divided by your dryer efficiency. Specific energy here is ≈ 4,361 kJ/kg water (typical high-temp dryers run 3,300–6,000). Throughput is the rated burner heat the dryer can usefully deliver divided by the heat each wet tonne needs — a guide figure; real capacity also depends on airflow and bed depth.
Grain drying — key facts
- Water removed / t
- (Mᵢ − M_f) ÷ (100 − M_f)
- 20% → 14% corn
- ≈ 70 kg water/t · 7% shrink
- Latent heat
- 2,400 kJ/kg water
- Heat / t (20→14%)
- ≈ 167 MJ useful
- Specific energy
- 3,300–6,000 kJ/kg water
- Dryer efficiency
- ≈ 45–60% high-temp
- LPG / diesel HHV
- 46.1 MJ/kg · 38.6 MJ/L
- Source
- ASABE / EIA heating values
Drying fuel energy contents & burner efficiency
Each fuel's higher heating value per sales unit, the typical burner efficiency that converts it to drying-air heat, and the delivered energy per unit (heating value × burner efficiency) that the cost calculation actually uses.
| Fuel | Sold by | Heating value (MJ/unit) | Burner eff. | Delivered (MJ/unit) | Typical price |
|---|---|---|---|---|---|
| LPG (propane) | kg | 46.1 | 92% | 42.4 | 1.10/kg |
| Diesel | L | 38.6 | 85% | 32.8 | 1.30/L |
| Natural gas | m³ | 38.7 | 92% | 35.6 | 0.50/m³ |
| Firewood / biomass | kg | 16.0 | 65% | 10.4 | 0.08/kg |
| Electric (resistance) | kWh | 3.6 | 99% | 3.6 | 0.15/kWh |
Heating values from US EIA and standard engineering heating-value tables; burner efficiencies and the 2,400 kJ/kg drying latent heat from ASABE / extension grain-drying energy data. Default prices are illustrative — enter your local price in the calculator.
Throughput and fuel cost are two different questions
The energy to dry a tonne of grain is set by physics: the water you remove times the latent heat of vaporisation, divided by how efficiently your dryer turns fuel into evaporation. That number, in megajoules per tonne, is the same no matter how big your burner is — which means your fuel cost per tonne depends only on moisture removed, dryer efficiency and fuel price. A bigger burner does not make drying cheaper per tonne; it makes it faster.
Throughput is the other question. A dryer can only deliver so much useful heat per hour, so the tonnes per hour it sustains is the rated burner heat times efficiency, divided by the heat each wet tonne needs. Removing more moisture both raises the cost per tonne and lowers the throughput, because each tonne needs more heat. This tool answers both at once and ranks the five common fuels by cost per tonne, so you can see the cheapest option at today's prices. Pair it with the Grain Drying Cost, Crop Drying Time and Safe Storage Moisture tools for the full harvest-drying plan.
Cost per tonne, any fuel
LPG, diesel, gas, firewood and electric side by side.
Real throughput
Tonnes per hour and drying time from your burner rating.
See the shrink
The weight you lose evaporating water, in tonnes.
Find the cheapest fuel
The bar chart sorts fuels by cost at your prices.
Frequently Asked Questions
How much water do I remove drying grain from 20% to 14%?+
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.
How is the fuel cost per tonne calculated?+
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.
What is dryer efficiency and what value should I use?+
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.
Which fuel is cheapest for drying grain?+
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.
How do I find the dryer throughput in tonnes per hour?+
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.
Why does drying cause weight shrink?+
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.
What is the latent heat figure used?+
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.
Does removing one extra point of moisture cost much?+
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.
Can I compare this to drying outdoors or in the sun?+
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.
What burner heat input should I enter?+
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.
Is the cost per tonne the same for any dryer size?+
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.