How much furnace oil does an air preheater save on a galvanizing or annealing furnace?

Close to one litre in twenty, 4.8%, in BEE's Howrah report: 5,647 litres a year out of 118,080, by cooling flue gas from 490 C to 380 C and heating combustion air with it. That is about 17 t CO2. Cost Rs 2.49 lakh, payback 1.47 years (2010), but the report gives the unit only a 3 year life.

What BEE measured

• Furnaces in the cluster dump flue gas at 490 to 600 C; the audited furnace at about 470 to 490 C, with 4.5% oxygen.
• A typical unit burns 118,080 litres of furnace oil a year at Rs 30 a litre.
• The air preheater takes flue gas in at 490 C and lets it out at 380 C, a 110 C drop.
• Installation needs about 4 days of downtime to change the flue line.

How the 4.78% was worked out

The report uses a rule of thumb: each 23 C taken out of the flue gas improves efficiency by 1%. 110 / 23 = 4.78%, applied to the oil bill. It is an estimate, not a measured trial. Your saving depends on how much air the preheater actually warms and how airtight it stays.

The 3 year life changes the sums

• Cost: Rs 1.80 lakh for the unit, Rs 0.40 lakh to install, Rs 0.29 lakh taxes and freight.
• Saving: about Rs 1.69 lakh a year at 2010 oil prices.
• Over the 3 year life the report assumes: about Rs 5.1 lakh saved for Rs 2.49 lakh spent.
• Ask the supplier why the life is 3 years and what a replacement costs.

Keep it working

• Check for leaks between the flue side and the air side; leaking flue gas into the burner air cancels the saving.
• Log flue temperature after the preheater weekly. If it creeps up, the surfaces are fouling.
• Keep oil litres and tonnes galvanized in the same monthly log, so oil per tonne can be compared.

One furnace, one year

• Oil before: 118,080 L x 2.97 = 350.7 t CO2
• Oil saved: 118,080 x 4.78% = 5,647 L
• CO2 saved: 5,647 x 2.97 = 16.8 t a year
• Report says 18 t; the difference is the oil factor used

Furnace oil at our factor of 2.97 kg CO2 per litre, an estimate.

What Senseible does here

Senseible reads furnace oil invoices into monthly records with CO2 at 2.97 kg per litre, so a 5% drop in oil per month is visible once the preheater is in. The green loan check shows what a lender will want to see.

• Green loan readiness check
• Galvanizing energy per tonne benchmark
• Howrah galvanizers and CBAM
• Coal galvanizing furnace to biomass gasifier

Sources: BEE, Detailed project report: air pre-heater for galvanizing and annealing furnaces, Howrah cluster (2010, SAMEEEKSHA)

Last reviewed 2026-10-31. Equipment figures are from a BEE SME programme project report; costs and paybacks are at that report's prices. Recheck with today's fuel and power prices and a current quote.