Oil and Gas Boiler Fuels: Furnace Oil, LDO, HSD, LPG and PNG
Oil and gas are the easy fuels to burn: no ash to handle, quick to start and stop, simple to control. What separates them is cost, availability and handling. Furnace oil must be heated before it can be pumped and burned; gas needs nothing but a pipe and careful safety.
You'll learn
- Know the common liquid and gaseous boiler fuels in India
- Compare their heat values and units
- Understand why furnace oil is preheated
- Know the safety and emission points of each
Before this: GCV vs NCV
The fuels
| Fuel | Indicative GCV | Character |
|---|---|---|
| Furnace oil (FO) | 9,800 kcal/kg | Heavy, viscous residual oil; must be heated to pump and atomize |
| Light diesel oil (LDO) | 10,100 kcal/kg | Lighter blend; pumps cold, used in smaller boilers |
| High-speed diesel (HSD) | about LDO’s | Transport fuel; clean but expensive for boilers |
| LPG | high, per kg | Stored as liquid under pressure; vaporized for burning |
| Natural gas (PNG) | 9,000 kcal/SCM | Piped; cleanest to burn; no storage on site |
Typical figures marked low confidence in the tool. Supplier certificates and gas distributors give actual values.
Notice the units. Liquid fuels are bought and measured by kilogram or liter; piped gas by standard cubic meter (SCM). Comparing them means converting each to price per unit of heat.
Handling each fuel
- Furnace oil is too viscous to pump or atomize cold. Storage tanks are heated (often with steam coils) and a line heater raises it to the temperature the burner needs for fine atomization. Too cold and it atomizes poorly and smokes; too hot and it can carbonize in the heater.
- LDO and HSD pump cold and need only filtering. They suit small boilers and standby firing.
- LPG is stored under pressure as a liquid and vaporized; large installations use vaporizers. It is heavier than air, so a leak pools at ground level and in pits.
- Natural gas arrives by pipeline through a pressure-regulating station. It is lighter than air and disperses upward, but a leak in an enclosed space is still explosive.
All of them need the same discipline at the burner: proven air flow before ignition, a purge of the furnace before every light-up, a flame detector that shuts the fuel off if the flame fails. The burners and flame safety lesson covers that in detail.
Sulfur, dew point and choosing a fuel
Furnace oil carries significant sulfur. Burnt, it forms SO₂ and a little SO₃, which raises the flue gas acid dew point. That sets a minimum stack temperature and a minimum economizer feedwater temperature, so an oil-fired boiler cannot recover as much flue gas heat as a gas-fired one. Natural gas is essentially sulfur-free, which is why gas boilers can carry deeper heat recovery, including condensing economizers.
Oil and gas have high hydrogen content, so their GCV and NCV differ more than coal’s in percentage terms: natural gas’s NCV is about a tenth below its GCV. Burner and boiler efficiency claims for gas are therefore especially sensitive to which basis is quoted.
Key takeaways
- FO must be heated to pump and atomize; LDO and HSD pump cold; LPG is stored under pressure; PNG arrives by pipe.
- Compare fuels by price per unit of heat, converting kg, liters and SCM.
- Sulfur in oil raises the acid dew point and limits heat recovery; gas is nearly sulfur-free.
- LPG is heavier than air and pools; natural gas rises. Both demand purge and flame safety.