How much furnace oil does an air preheater with a drying bed save in hot-dip galvanizing?

About 19,083 litres a year in BEE's Howrah report: zinc furnace flue gas heats the drying bed, saving 14,994 litres, and an air preheater saves 4,089 more. That is about 57 t CO2, not the report's 65 t. Cost Rs 5.32 lakh, saving Rs 5.72 lakh, payback 11 months, against a stated life of 3 years.

Two fires where one would do

A Howrah galvanizing unit runs a main furnace under the zinc kettle at about 465 C and a second burner under the drying bed, where pickled and fluxed jobs dry before dipping. In the audited unit the kettle burner takes 41 litres of furnace oil an hour and the drying bed burner up to 27. Meanwhile the kettle's flue gas leaves at 464 to 574 C. The job only needs to reach 80 to 150 C on the bed.

What gets built

• A flue gas channel under the 6.2 m x 1.5 m drying bed, taking 200 to 250 kg of hot gas an hour and dropping it to 300 to 350 C. The bed's own burner is no longer needed.
• An air preheater warming 657 kg an hour of combustion air from 30 C to 120 C, as the flue cools 110 C.
• Five days of downtime to reroute the flue line.

The numbers, checked

• Unit: about 1,712 to 1,969 t a year galvanized, 105,000 litres of furnace oil a year.
• Drying bed: 17.6% of the oil bill, from six readings at a unit already running one, 14,994 litres.
• Air preheater: 4.8% from the 110 C flue drop, 4,089 litres.
• Both percentages are taken on a Rs 25.56 lakh oil bill, about 85,200 litres at Rs 30, not on the full 105,000.
• Money: 19,083 litres x Rs 30 = Rs 5.72 lakh. Cost: units Rs 3.80 lakh, installation Rs 0.90 lakh, taxes and freight Rs 0.62 lakh = Rs 5.32 lakh. Payback 5.32 / 5.72 = 0.93 years.

Before you order

1. Ask why the life is only 3 years and what a rebuild costs. Over 3 years you save about Rs 17 lakh for Rs 5.32 lakh at the report's prices.
2. Seal the air side from the flue side. A leak lets flue gas into the burner air and ruins combustion.
3. Log oil per tonne galvanized for a month before and after.

One galvanizing unit, one year

• Oil saved: 14,994 + 4,089 = 19,083 litres
• CO2: 19,083 x 2.97 = 56.7 t
• The report's 65 t counts 21,873 kg of oil, more than 19,083 litres weighs
• Per tonne galvanized at 1,712 t: about 33 kg CO2 less

Furnace oil at 2.97 kg CO2 per litre. Galvanized wire, bolts and tower parts can be CBAM goods, so an EU buyer may ask for this figure.

What Senseible does here

Senseible reads furnace oil invoices into monthly records with CO2, so oil per tonne before and after the drying bed change is on file. The green loan check lists what a lender asks for on a furnace retrofit.

• Green loan readiness check
• Air preheater on a galvanizing furnace
• Galvanizing flux solution on flue heat
• Howrah galvanizing and wire units

Sources: BEE, Detailed project report: air preheater and drying bed for galvanizing and annealing furnaces, Howrah cluster (SAMEEEKSHA)

Last reviewed 2026-11-01. Report figures are from a BEE SME programme project report; costs and paybacks are at the report year's prices. Check today's furnace oil price and a current quote.