Rice husk is a good boiler fuel when it is dry, clean and burned in equipment designed for it. Its heat value, ash and moisture vary from lot to lot, so buy it on tested properties rather than appearance: ask for moisture, ash and calorific value from a laboratory, check every load for sand, dust and rice, compare offers on cost per unit of heat, and plan for its bulk and its ash before the first truck arrives.
Key takeaways
- Husk is roughly a fifth of paddy by weight and very bulky, so freight is a large share of its delivered cost.
- Published tests put its calorific value at about 12 to 16 MJ/kg and its ash at about 12 to 22%. That spread is why testing matters.
- Moisture and contamination lower the useful heat and raise the ash. Check every load.
- Compare offers on cost per gigajoule of heat, not cost per tonne.
In this guide
What makes husk a fuel
Husk is the outer shell removed from paddy at de-husking. A techno-market survey by TIFAC, under the Government of India’s Department of Science and Technology, put husk at about 20% of paddy by weight, with a calorific value of about 3,500 kcal/kg (roughly 14.7 MJ/kg), a bulk density of about 110 kg/m³ and an ash content of about 16.5%, high in silica. Laboratory studies elsewhere report figures on both sides of these: one 2023 study measured a gross calorific value of 16.05 MJ/kg with 12.1% ash, while another found ash between 14% and 22% across samples.
| Property | What it tells you | Published figures |
|---|---|---|
| Moisture | Water that must be driven off before the husk gives useful heat | Varies with storage and weather; test each lot |
| Ash | Mineral matter, mostly silica, left to collect and dispose of | About 12 to 22% |
| Calorific value | Heat released on burning, stated as gross (GCV) or net (NCV) | About 12 to 16 MJ/kg |
| Bulk density | Weight per cubic metre, which decides what fits in a vehicle or bunker | About 110 kg/m³, loose |
| Contamination | Sand, dust, broken rice, bran fines, stones | Close to nil; agree a limit |
Check the boiler before the husk
Husk burns well in furnaces and boilers designed or adapted for it, and poorly in those that are not. Its high ash and silica content means the boiler must remove ash continuously and cope with abrasion and fouling, and its light, bulky form needs a feeding system that delivers it evenly. Ask your boiler supplier whether the unit is rated for rice husk, at what moisture, and what ash handling it needs.
Rice mills are among the largest users of husk as fuel. The TIFAC survey noted that mills producing parboiled rice use much of their own husk for steam and drying; the steaming stage is described in how parboiled rice is processed.
Check every load for moisture and contamination
- Moisture: wet husk gives less useful heat and feeds unevenly. Store it under cover, and test loads that look or feel damp.
- Sand and dust: they raise ash and wear and add nothing to heat. Look at the vehicle floor after unloading.
- Rice and bran in the husk: a sign of poor separation. They are worth more as food or feed than as fuel.
- Stones, metal and plastic: a hazard for feeders and grates.
- Heat and smell in the load: damp husk in a large heap can heat up. Spread out any load that is warm or smells sour.
Compare offers on cost per unit of heat
Hypothetical figures, to show the method. Use your own test results and prices.
| Item | Lot A | Lot B |
|---|---|---|
| Price delivered, per tonne | ₹3,200 | ₹2,900 |
| Tested calorific value, as received | 14.0 MJ/kg | 12.5 MJ/kg |
| Heat per tonne | 14.0 GJ | 12.5 GJ |
| Cost per GJ | ₹229 | ₹232 |
| Ash | 16% | 20% |
| Ash to remove per tonne burned | 160 kg | 200 kg |
Lot B is cheaper per tonne but dearer per unit of heat, and it leaves a quarter more ash to handle. Compare calorific values on the same basis for every lot. If you pay for husk as delivered, use the as-received figure rather than a dry-basis one.
Freight, storage and ash
At a bulk density of about 110 kg/m³, 30 m³ of loose husk weighs only about 3.3 tonnes, so freight per tonne is high and delivery distance matters. Agree whether the price is per tonne by weighbridge or per load, and how moisture is treated when loads are weighed wet.
Store husk under cover, on a dry floor and away from sources of ignition. It is combustible, and dry husk dust burns readily; follow the fire-safety arrangements for your site. Plan for the ash as well: it has to be collected, stored and disposed of or sold according to local rules.
A buying checklist
RICE HUSK FUEL ENQUIRY Boiler type and rating for husk (from your boiler supplier): Quantity (MT per month) and delivery frequency: Delivery point and unloading arrangement: Price basis (per tonne by weighbridge, or per load): Moisture (maximum %, how it is tested): Ash (maximum %, laboratory method): Calorific value (GCV or NCV, as received, laboratory method): Contamination limits (sand, dust, rice and bran fines, stones): Sampling (where and when samples are drawn, counter-samples kept): Covered storage at your site (tonnes):
SONIK sells rice husk in bulk from Ghentugachhi. Husk is the largest by-product stream from a paddy lot; our milling recovery guide shows how it fits with bran and finished rice, and buying rice bran covers the other main by-product. Send your quantity in MT, delivery point, frequency and the properties you test through the bulk enquiry form.
Sources
- TIFAC, Department of Science and Technology. Techno-market survey on technologies for use of rice husk as source of energy in rural area.
- Fire 6(6), 230 (2023). Study of the thermochemical properties of rice straw and rice husk: gross calorific value 16.05 MJ/kg and ash 12.11% for the husk tested.
- NTNU master’s thesis. Technical and economic analysis of a power plant based on rice husk: ash 14 to 22%, bulk density about 120 kg/m³.
