# Can furnace waste heat warm the flux solution in a galvanizing line, and what does it save?

Canonical: https://senseible.earth/answers/galvanizing-flux-solution-heating-waste-heat

Yes. In BEE's Howrah report, zinc furnace flue gas at 490 C keeps the flux vat at 90 to 100 C, so its diesel burner stops: 19,200 litres of diesel a year. With an air preheater saving 5,647 litres of furnace oil, CO2 falls about 68 t. Cost Rs 2.94 lakh, saving Rs 8.80 lakh, payback 4 months.

## The unit in the report

- About 2,399 t galvanized a year; 120,480 litres of furnace oil for the zinc kettle and 19,200 litres of diesel for the flux vat.
- Kettle burner: 41 litres of oil an hour, zinc at about 465 C, flue gas out at about 490 C.
- Flux vat: 250 litres held at 90 to 100 C by a diesel burner using 7 litres an hour.

## How the heat gets there

1. The flue duct is rerouted through a channel under the flux vat. The gas gives up about 230 C, 490 down to 260 C, and the diesel burner is switched off.
2. What is left passes through an air preheater that warms combustion air from 30 C to 120 C, worth about 4.7% of the kettle's oil.
3. Five days of downtime to change the flue line.

## A bonus: no drying bed

A job lifted out of boiling flux is hot enough to dry on its own heat, so units using a boiling flux vat do not need a fired drying bed before the kettle. If you dry on a bed today, see the drying bed option instead; the two use the same flue heat.

## Money and the catch

- Diesel saved: 19,200 litres x Rs 37 = Rs 7.10 lakh. Oil saved: 5,647 litres x Rs 30 = Rs 1.69 lakh. Total Rs 8.80 lakh.
- Cost: vat channel and preheater Rs 2.25 lakh, installation Rs 0.40 lakh, taxes and freight Rs 0.29 lakh = Rs 2.94 lakh. Payback 2.94 / 8.80 = 0.33 years.
- The report gives the equipment a 3 year life. Ask what a rebuild costs.
- Log diesel and oil per tonne galvanized for a month before and after, so the saving is on paper for a lender or buyer.

## One galvanizing unit, one year

- Diesel: 19,200 litres x 2.645 = 50.8 t CO2
- Furnace oil: 5,647 litres x 2.97 = 16.8 t CO2
- Total: about 67.6 t; the report says 70.6 t
- Per tonne galvanized at 2,399 t: about 28 kg CO2 less

Diesel at 2.645 and furnace oil at 2.97 kg CO2 per litre.

## What Senseible does here

Senseible reads diesel slips and furnace oil invoices into monthly records with CO2, so the diesel line dropping out after the change shows on record. Before you ask a bank to fund the vat channel, run the green loan check.

- [Green loan readiness check](https://senseible.earth/green-loan-check)
- [Galvanizing drying bed on flue heat](https://senseible.earth/answers/galvanizing-air-preheater-drying-bed-oil-saving)
- [Air preheater on a galvanizing furnace](https://senseible.earth/answers/galvanizing-furnace-air-preheater-oil-saving)
- [Zinc bath temperature control](https://senseible.earth/answers/zinc-bath-temperature-control-oil-saving)

Sources: [BEE, Detailed project report: air preheater and flux solution heating for galvanizing and annealing furnaces, Howrah cluster (SAMEEEKSHA)](https://sameeeksha.org/pdf/Howrah_galvinising/DPR_on_Air-Pre_Heater_and_Flux_Solution_Heating_for_Galvanizing_and_Annealing_Furnaces.pdf)

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 diesel and furnace oil prices and a current quote.