Steam is re-packaged fuel. Whatever your plant pays for husk, coal or gas, the steam main is where that money travels — so the first economic skill in the boiler house is converting any fuel quote, in any unit, into one honest number: rupees per thousand kilocalories of useful heat. Master that and every fuel argument in every purchase meeting becomes short.
GCV: the size of the packet
Gross calorific value is the heat in a kilogram of fuel, measured generously — it includes the latent heat of the water vapour formed in combustion, which a real boiler mostly cannot recover (that distinction is GCV vs NCV; the glossary and lesson B4 hold the details — just never compare a GCV price against an NCV efficiency). Typical working values for the Indian basket:
| Fuel | GCV, typical | Indicative price* | ₹/1000 kcal useful† | Steam, ₹/t† |
|---|---|---|---|---|
| Rice husk | ~3,200 kcal/kg | ₹2,500/t | ≈ 1.0 | ≈ 600 |
| Wood chips (20% moisture) | ~2,800 kcal/kg | ₹3,500/t | ≈ 1.7 | ≈ 960 |
| Biomass briquette | ~3,800 kcal/kg | ₹5,500/t | ≈ 1.9 | ≈ 1,100 |
| Indian coal (G11) | ~4,300 kcal/kg | ₹6,500/t | ≈ 2.0 | ≈ 1,160 |
| Imported coal | ~5,800 kcal/kg | ₹9,000/t | ≈ 2.1 | ≈ 1,190 |
| Furnace oil | ~10,200 kcal/kg | ₹48/kg | ≈ 5.5 | ≈ 3,180 |
| Natural gas (PNG) | ~8,500 kcal/SCM | ₹55/SCM | ≈ 7.6 | ≈ 4,370 |
| LPG | ~11,900 kcal/kg | ₹95/kg | ≈ 9.4 | ≈ 5,390 |
*Indicative market levels, written August 2026 — fuel prices move constantly and regionally; recompute with your delivered price before deciding anything. †At 75% boiler efficiency for solid fuels, 85% for oil and gas; steam column for the practice plant's 574 kcal/kg net investment.
The method behind the table
Three steps, one line each:
1. Useful heat per kg of fuel = GCV × boiler efficiency. Husk:
3,200 × 0.75 = 2,400 kcal useful.
2. ₹ per 1000 kcal = price per kg ÷ useful heat × 1000. Husk:
₹2.5 ÷ 2,400 × 1000 ≈ ₹1.04.
3. Steam cost (fuel-only) = ₹/1000 kcal × net heat per tonne of steam.
The practice plant invests 574 kcal into each kilogram (664 at the crown valve minus the
90 °C feedwater already on board), so: 1.04 × 574 ≈ ₹600/tonne — the
number lesson F1 built its cost stack on.
Equivalently: fuel per tonne of steam = 574,000 ÷ 2,400 ≈ 240 kg of husk. At 6 TPH across a 20-hour day, that is 29 tonnes of husk — count the lorries and you have audited your own boiler with arithmetic (lesson B4's opening move).
The traps in fuel arithmetic
Moisture is theft. Wet fuel spends its own heat boiling off its own water: wood at 40% moisture can carry barely two-thirds the useful heat of the same wood at 20%. Buy solid fuel with a stated, tested moisture and GCV — a bomb-calorimeter test costs a few thousand rupees against lorry-loads of doubt. Efficiency belongs in the price. A fuel burned at 85% in a clean gas boiler competes better than its raw ₹/kcal suggests against husk burned at 70% in a tired furnace — always compare useful heat. "Free" fuel isn't. A rice mill burning its own husk forgoes the ₹2,500/t the market would pay — the steam still costs ₹600/t in opportunity, and projects that save steam still pay back. Price captive fuel at market, or every efficiency project on your desk dies of imaginary free heat.
Run your own fuel through the method:
- Get GCV and moisture into every solid-fuel purchase order, with testing rights. Pay for kilocalories, not kilograms.
- Track ₹/1000 kcal monthly on one chart for every fuel you could burn. Conversion decisions read straight off it.
- Compare fuels at their own realistic boiler efficiencies — not the brochure's.
- Captive fuel: book it at market price in every costing. Finance may argue; physics will not.
- ₹/1000 kcal useful = price ÷ (GCV × efficiency) × 1000 — the only fair way to compare fuels.
- Steam fuel-cost = ₹/1000 kcal × net kcal per tonne (574 kcal/kg at the practice plant → ₹600/t on husk).
- Moisture steals GCV; buy solid fuel on tested kcal, not weight alone.
- The Indian ladder spans roughly ninefold, husk to LPG. That spread funds most steam-side projects.
- State GCV or NCV every time — mixing them moves answers by ~10%.
Rice husk was a disposal problem before it was a fuel — mills paid to cart it away, and its 20% ash (mostly silica) clinkers grates that were designed for coal. The furnaces that finally tamed it in the 1980s–90s turned Indian rice belts into steam country: today husk fires boilers, its ash sells to steel and refractory makers as rice-husk-ash silica, and the "waste" commands ₹2,500 a tonne. Fuel is not a substance; it is a price and a furnace that can burn it.