# What does a heat pipe air preheater save on a galvanizing furnace?

Canonical: https://senseible.earth/answers/galvanizing-heat-pipe-air-preheater-oil-saving

The Bureau of Energy Efficiency (BEE) report for Howrah: 4,935 litres of furnace oil a year by passing flue gas heat to combustion air through heat pipes. Cost Rs 3.73 lakh, saving Rs 1.68 lakh, payback 2.22 years, life 7 years. Its hourly sum implies about 7% more oil than the 4,590 kg it states.

## How a heat pipe preheater works

A bank of finned, gravity-assisted heat pipes sits between the flue and the air duct. Hot flue gas heats one end of each pipe and the supply air cools the other, in counterflow, with a partition keeping the two streams apart. It has no moving parts and uses no power of its own. It is a box of 1 m x 1 m x 1.5 m, installed apart from the furnace. The report allows four days of downtime to change the flue line.

## What BEE measured

- A furnace burning 42 litres of oil an hour, with flue gas at about 300 C and 833 kg of combustion air an hour.
- The specification table has air going from 30 C to 140 C and flue gas leaving at 190 C. The annexure sum uses 120 C and 200 C. The report says the burners in use cannot take air hotter than 120 C.
- Operation: 12 hours a day, 240 days a year, so 2,880 hours.

## A slip worth checking

The annexure gives 1.71 kg of oil saved an hour. Over 2,880 hours that is about 4,925 kg, against the 4,590 kg the report states, so the yearly figure is about 7% low. The report's litres are its kilograms divided by 0.93, which is correct: 4,590 / 0.93 = 4,935. Its 16 tonnes (t) of CO2 is 4,935 x 3.24 / 1,000, which treats litres as if they were kilograms of oil; the 3.24 is a factor per tonne.

## Before you buy

- The 120 C burner limit caps the gain. The report says better burners could allow more recovery from the 190 C flue gas.
- Measure your own flue temperature and oil use. The sum scales with both.
- Compare with an ordinary air preheater, which is a different design with its own report and numbers.

## The sum, and the unit check

- Heat to the air: 833 x 0.24 x 90 = about 17,993 kcal an hour. Oil: 17,993 / 10,500 = 1.71 kg an hour
- Per year: 1.71 x 2,880 = about 4,925 kg, against 4,590 kg in the report. In litres at 0.93: about 5,300, against 4,935
- Report: 4,935 litres x Rs 34 = Rs 1,67,790. Payback 3.73 / 1.68 = 2.22 years
- If 5,300 litres: Rs 1.80 lakh and a payback of 2.07 years
- CO2 at 2.97 kg a litre: 4,935 x 2.97 = 14.7 t; 5,300 x 2.97 = 15.7 t. The report's 16 t is 4,935 x 3.24 / 1,000

Furnace oil at 2.97 kg CO2 a litre, an estimate from Intergovernmental Panel on Climate Change (IPCC) carbon content. Other figures from the report, at its 2010 prices.

## What Senseible does here

Senseible reads furnace oil invoices into monthly litres and carbon dioxide equivalent (CO2e) at 2.97 kg a litre, each linked to its bill, so a drop after the preheater shows against the months before. The green loan check shows what a lender asks for.

- [Green loan readiness check](https://senseible.earth/green-loan-check)
- [An ordinary air preheater on a galvanizing furnace](https://senseible.earth/answers/galvanizing-furnace-air-preheater-oil-saving)
- [Oxygen sensor on a galvanizing furnace](https://senseible.earth/answers/galvanizing-furnace-oxygen-sensor-blower-vfd-saving)
- [Galvanizing plant energy per tonne](https://senseible.earth/answers/galvanizing-plant-energy-per-tonne-benchmark)

Sources: [BEE, Detailed project report: air preheater using heat pipe heat exchangers, Howrah galvanizing and wire drawing cluster (2010, SAMEEEKSHA)](https://sameeeksha.org/pdf/Howrah_galvinising/DPR_on_Air_Pre-heater_Heat_Pipe_Heat_Exchangers_for_Galvanizing_and_Annealing_Furnaces.pdf), [IPCC 2006 Guidelines, Volume 2 Energy, Tables 1.2 and 2.3](https://www.ipcc-nggip.iges.or.jp/public/2006gl/vol2.html)

Last reviewed 2026-11-04. Report figures are from a BEE SME programme project report; costs and paybacks are at the report year's prices. Check today's prices and a current quote before you rely on the payback.