Two fuel quotes land on a plant manager's desk for the same boiler house. One is priced at ₹2.50 per kg, the other at ₹48 per cubic metre. Neither number says which fuel makes cheaper steam. A kilogram of rice husk, a kilogram of coal and a cubic metre of gas hold different amounts of heat, and each is burned in a boiler that converts that heat to steam at a different efficiency.
The useful comparison is the cost of useful steam, in rupees per kg or per tonne at your steam conditions. Fuel-only cost is the first filter. Labour, ash disposal, emission control, storage and capital cost then decide whether the cheapest fuel on paper is the cheapest on site.
This guide shows the calculation step by step, works through a 5 TPH example with every assumption stated, and explains what moves the result: price, moisture, efficiency, load, compliance and supply. All prices, heating values and efficiencies below are illustrative assumptions, not dated market quotations. Replace them with your own supplier quotes before drawing conclusions.
The cheapest boiler fuel is the one that gives the lowest cost per kg of steam at your site, not the lowest price per kg, litre or cubic metre. Calculate it from steam energy demand, the fuel's heating value, boiler efficiency and landed price, then add handling, ash, emissions and maintenance costs before comparing.
Fuel price per unit is not steam cost. A 5 TPH boiler running 500 hours a month produces 2,500 tonnes of steam, so every ₹1 per kg of steam equals ₹25 lakh a month. Under the illustrative prices used here, rice husk gave the lowest fuel-only steam cost, followed by coal, PNG, LPG and diesel. Each ranking can flip when landed price, moisture or efficiency changes. Fuel-only cost also leaves out labour, ash disposal, emission control, storage and capital cost, which often decide the real winner. Treat every figure as an assumption to replace with your own quotations.
The real cost of boiler fuel is the cost of the steam it produces. That depends on five things working together:
Keep three cost layers separate. Fuel-only cost is what this article calculates. Variable operating cost adds auxiliary electricity, water treatment, ash disposal, labour and routine maintenance. Total cost of ownership adds capital items such as fuel handling, civil work, emission-control equipment and installation, minus residual value. Mixing them into one unexplained number is the most common reason fuel comparisons mislead. Our industrial boiler price guide explains how quotation scope changes the capital side.
Cost per kg of steam equals the fuel needed to make one kg of steam multiplied by the landed fuel price. Fuel needed depends on the heat steam must absorb, the fuel's heating value and the boiler's efficiency.
1. Steam energy requirement (kJ/kg) = steam enthalpy − feedwater enthalpy
2. Fuel per kg of steam = steam energy requirement ÷ (fuel heating value × boiler efficiency)
3. Fuel-only cost per kg of steam = fuel per kg of steam × landed fuel price
Use efficiency as a decimal (0.80, not 80). Cost per tonne of steam = cost per kg × 1,000. 1 kcal = 4.1868 kJ.
Take coal with an assumed GCV of 5,000 kcal/kg (20,934 kJ/kg), 80% efficiency and a landed price of ₹14/kg.
Combustion efficiency and boiler efficiency also differ. Combustion efficiency describes how completely fuel burns and how much heat leaves with the flue gas. Boiler efficiency is useful heat in steam divided by fuel energy input. Our guide on how to improve boiler efficiency covers how plants keep that figure from drifting.
Coal suits plants with dependable supply, space for storage and ash handling, and a compliance plan for emissions. Its quality varies widely by source and grade, so the invoice price alone says little.
Biomass can deliver a low fuel-only steam cost near a reliable agro-waste source. Moisture, seasonal supply, low bulk density and ash make the result strongly site-specific. Our biomass boiler guide covers working principle and fuel types in more depth.
Low bulk density limits truck payload, so delivered cost per unit of heat rises with distance. There is no fixed distance cutoff. The break-even depends on price, density, route, moisture and storage, and the sensitivity table below shows one way to test it. Biomass also needs a covered yard, a feeding system engineered for the specific fuel and ash handling that matches the fuel's ash content.
PNG and LPG are not interchangeable. PNG depends on pipeline access and a supplier tariff, while LPG is delivered by road, stored on site and priced by mass. Both burn cleanly, need no ash handling and suit automated control.
Our industrial gas boiler guide covers gas boiler types, pricing factors and running cost in more detail.
Diesel and LDO are mostly used as backup or standby fuels, though some plants without other options run them as primary fuel. They are different products. Specifications, density, price and permitted applications differ, so calculate each with its own data.
The table applies the formula above under identical steam conditions. Prices are illustrative, not dated quotations.
| Fuel | Price Basis / Date | Heating-Value Basis | Efficiency Assumption | Fuel-Only Steam Cost | Operational Considerations |
|---|---|---|---|---|---|
| Coal | ₹14/kg landed, illustrative | GCV 5,000 kcal/kg (20,934 kJ/kg) | 80% (GCV basis) | ₹2.04/kg steam | Yard, ash, emission control, grade variation |
| Rice husk, near source | ₹2.50/kg landed, illustrative | GCV 3,300 kcal/kg (13,816 kJ/kg), as received | 75% (GCV basis) | ₹0.59/kg steam | High ash, bulky, seasonal supply, covered storage |
| Rice husk, transported | ₹5.00/kg landed, illustrative | GCV 3,300 kcal/kg, as received | 75% (GCV basis) | ₹1.18/kg steam | Freight sensitivity, supply contract needed |
| PNG | ₹48/SCM, illustrative, tariff varies | GCV 8,500 kcal/SCM (35,588 kJ/SCM) | 86% (GCV basis) | ₹3.83/kg steam | Pipeline access, no storage or ash |
| LPG | ₹100/kg, illustrative | GCV 11,900 kcal/kg (49,823 kJ/kg) | 86% (GCV basis) | ₹5.71/kg steam | On-site storage, vaporisation, safety provisions |
| Diesel | ₹92/litre, illustrative (₹109.5/kg at 0.84 kg/L) | GCV 10,800 kcal/kg (45,217 kJ/kg) | 85% (GCV basis) | ₹6.97/kg steam | Price volatility, tanks, backup role |
| LDO | Not calculated | Use the supplier's specification and density | Per burner and boiler data | Calculate with its own inputs | Not equivalent to diesel; confirm permitted use |
All rows use 5,000 kg/h of 10 bar(g) saturated steam, 80°C feedwater, 500 operating hours and 2,500,000 kg of steam a month at continuous rated output. If your average load is lower, scale the monthly figure by the load factor and show it as a separate scenario.
| Fuel | Fuel Consumption / Hour | Fuel Cost / Hour | Cost / kg Steam | Cost / Tonne Steam | Monthly Fuel Cost |
|---|---|---|---|---|---|
| Coal at ₹14/kg | 730 kg | ₹10,220 | ₹2.04 | ₹2,044 | ₹51.1 lakh |
| Rice husk at ₹2.50/kg | 1,180 kg | ₹2,949 | ₹0.59 | ₹590 | ₹14.7 lakh |
| Rice husk at ₹5.00/kg | 1,180 kg | ₹5,899 | ₹1.18 | ₹1,180 | ₹29.5 lakh |
| PNG at ₹48/SCM | 399 SCM | ₹19,173 | ₹3.83 | ₹3,835 | ₹95.9 lakh |
| LPG at ₹100/kg | 285 kg | ₹28,532 | ₹5.71 | ₹5,706 | ₹142.7 lakh |
| Diesel at ₹92/litre | 379 litres (318 kg) | ₹34,836 | ₹6.97 | ₹6,967 | ₹174.2 lakh |
Reconciliation check: cost per hour ÷ 5,000 kg gives cost per kg of steam. Cost per kg × 1,000 gives cost per tonne. Cost per hour × 500 hours, or 2,500,000 kg × cost per kg, gives the monthly figure. For coal, ₹10,220 ÷ 5,000 = ₹2.04 per kg, and 2,500,000 × ₹2.044 ≈ ₹51.1 lakh. Figures are rounded and cover fuel only.
In this example the husk-fired boiler burns about 590 tonnes of fuel a month, against about 365 tonnes of coal. That is the storage, feeding and ash-handling load hidden behind a lower price per kg.
Because cost per kg of steam is price multiplied by a fixed fuel requirement, a change in any input moves the result in proportion. The table changes one input at a time from the base cases above.
| Scenario | Change From Base Case | Cost / kg Steam | Monthly Fuel Cost |
|---|---|---|---|
| Coal | Price ₹12/kg (base ₹14) | ₹1.75 | ₹43.8 lakh |
| Coal | Price ₹16/kg | ₹2.34 | ₹58.4 lakh |
| Rice husk | GCV 3,000 kcal/kg, 75% efficiency, ₹2.50/kg | ₹0.65 | ₹16.2 lakh |
| Rice husk | Wet fuel: GCV 2,700 kcal/kg, 70% efficiency, ₹2.50/kg | ₹0.77 | ₹19.3 lakh |
| Rice husk | Delivered price ₹8/kg, base GCV and efficiency | ₹1.89 | ₹47.2 lakh |
| PNG | Price ₹40/SCM (base ₹48) | ₹3.20 | ₹79.9 lakh |
| PNG | Price ₹55/SCM | ₹4.39 | ₹109.8 lakh |
| PNG | Efficiency 82% at ₹48/SCM (base 86%) | ₹4.02 | ₹100.5 lakh |
| PNG | Efficiency 90% at ₹48/SCM | ₹3.66 | ₹91.6 lakh |
Three lessons follow from the numbers. First, moisture matters: falling from 3,300 to 2,700 kcal/kg while efficiency drops from 75% to 70% raises husk steam cost by about 31%. Second, distance matters: under these assumptions husk delivered above about ₹8.7/kg costs more per kg of steam than coal at ₹14/kg, and above about ₹16/kg it costs more than PNG at ₹48/SCM, before counting handling, labour or ash. Third, a few points of efficiency are worth several lakh rupees a month at this scale.
Emission control adds cost that fuel prices do not show. Keep capital and recurring items apart, and do not assume one device handles every pollutant.
Bag filters and ESPs capture particulate matter. They do not remove gaseous NOx or SOx by themselves. NOx is mainly managed through burner and combustion design and, where required, add-on controls. SOx depends on fuel sulphur and may need scrubbing.
Applicable limits come from your consent conditions, notifications from the Central Pollution Control Board and your State Pollution Control Board, and any local fuel restrictions. Confirm them with the authority for your site before choosing a fuel.
No industry has a single best fuel. The table lists options commonly evaluated and the factor that usually decides between them.
| Industry | Fuels Commonly Evaluated | Deciding Factors |
|---|---|---|
| Textile | PNG, biomass, coal | Gas access, local biomass, urban emission rules |
| Food processing | PNG, LPG, biomass | Steam quality, hygiene, batch load pattern (see our food processing boiler guide) |
| Pharmaceutical | PNG, LPG, diesel standby | Cleanliness, reliability, redundancy |
| Chemical | PNG, coal, biomass | Pressure, continuity, compliance burden |
| Paper | Biomass, coal | Large continuous demand, own residues |
| Agro-processing | Husk, bagasse, shells | On-site residue supply, seasonality |
Sometimes, but the answer depends on what kind of change you mean. Three situations are often confused:
A boiler built well for one fuel is not automatically well built for another. Ask each shortlisted manufacturer for reference installations on your fuel at a similar capacity and pressure. Ask what efficiency is guaranteed, on which heating-value basis, with which fuel analysis, steam conditions, feedwater temperature and load. Ask how it will be tested at handover, and what emission performance and spare support are offered. Our boiler manufacturer selection checklist gives a structured way to compare quotations, and our roundup of boiler manufacturers in India is a starting point for shortlisting.
Par Boiler is an Ahmedabad-based industrial boiler manufacturer. Its steam boiler range includes solid-fuel-fired and oil and gas-fired configurations, so the same team can compare options against your actual site rather than a single fuel. To get a comparison on equal terms, send these details with your enquiry:
Comparing fuel options for a new boiler or a fuel change? Contact Par Boiler to review your steam requirement and landed fuel quotations on the same basis.
No fuel is cheapest everywhere. The lowest-cost fuel is the one with the lowest cost per kg of steam at your site, after landed price, heating value and boiler efficiency are applied. In this article's illustrative example rice husk ranked lowest on fuel-only cost, but that result changes with price, moisture, distance and efficiency.
Divide the steam energy requirement by the fuel's heating value multiplied by boiler efficiency, then multiply by landed fuel price. Steam energy requirement is steam enthalpy minus feedwater enthalpy. Use consistent units, a decimal efficiency, and the same GCV or NCV basis for both heating value and efficiency.
Not automatically. Biomass often has a lower fuel-only steam cost near reliable supply, but moisture, low bulk density, transport, seasonal availability and ash handling can erase the gap. In this article's example, husk delivered above roughly ₹8.7/kg would cost more per kg of steam than coal at ₹14/kg.
PNG arrives by pipeline, is metered by volume and needs no on-site storage, but depends on pipeline access and supplier terms. LPG is delivered by road, stored on site, priced by mass and needs storage, vaporisation and safety provisions. Their prices and infrastructure differ, so compare them separately.
It depends on fuel, efficiency and steam conditions. Under this article's assumptions (10 bar(g) saturated steam, 80°C feedwater), a 5 TPH boiler would use about 730 kg/h coal, 1,180 kg/h rice husk, 399 SCM/h PNG, 285 kg/h LPG or 379 L/h diesel. Treat these as illustrations, not guarantees.
Multiply monthly steam production by fuel-only cost per kg of steam. For 5,000 kg/h, 20 hours a day and 25 days a month, production is 2,500,000 kg (2,500 tonnes). A cost of ₹2.04 per kg of steam therefore gives about ₹51.1 lakh a month. Use actual average load if it is below rated output.
Moisture lowers the as-received heating value and absorbs heat during evaporation, so more fuel is needed per kg of steam. It can also reduce efficiency and combustion stability. In the sensitivity table, a fall from 3,300 to 2,700 kcal/kg with 70% efficiency raised fuel-only cost from ₹0.59 to ₹0.77 per kg of steam.
GCV (gross calorific value, or HHV) includes the latent heat recoverable if water vapour in the flue gas condenses. NCV (net calorific value, or LHV) excludes it. Efficiency figures change with the basis, so heating value and efficiency must use the same one.
Combustion efficiency describes how completely fuel burns and how much heat leaves with the flue gas. Boiler (thermal) efficiency is useful heat in steam divided by fuel energy input, so it also reflects radiation, blowdown and other losses. On the same basis it is normally lower than combustion efficiency.
It can be, but it is usually the most expensive option for sustained operation, and its price follows crude oil. It suits backup duty, low operating hours or sites without other fuels. In this article's example it gave the highest fuel-only steam cost, so test the economics before committing.
Yes, usually. Biomass combustion produces particulate matter and can produce NOx, so controls such as cyclones, bag filters or ESPs may be needed depending on fuel, boiler and site conditions. Applicable requirements are set through consent conditions and notifications, so confirm them with your State Pollution Control Board.
Sometimes, but it is an engineering project, not a burner swap. Furnace volume, heat-transfer surfaces, draught, fuel handling, controls, emissions and statutory approvals may all change. Request a feasibility study and performance guarantee from the boiler manufacturer before assuming conversion is possible or economical.
It should state the delivered price basis, unit, taxes, delivery point and validity date, plus fuel specification: heating-value basis, moisture, ash and size or composition. For gas, include the reference volume and pressure; for biomass, as-received moisture and delivery schedule. Without these, prices cannot be compared reliably.
Share your steam requirement, site fuel quotations and operating hours, and Par Boiler can help you compare options on the same steam conditions.
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