# How much coal does an online flue gas analyser save on a textile boiler?

Canonical: https://senseible.earth/answers/coal-boiler-online-flue-gas-analyser-saving

BEE's Surat report books 1% of fuel, 70 t a year on a boiler burning 7,200 t of coal and lignite, worth Rs 1.98 lakh. Cost Rs 2.36 lakh, payback 1.19 years. The audited boilers ran 169 to 567% excess air, so the real saving depends on whether someone trims the air when the reading is high.

## What BEE found in the stack

- Unit 1: 7,200 t of fuel a year, 14.7% oxygen in flue gas, 234% excess air.
- Unit 2: 6,048 t a year, 17.85% oxygen, 567% excess air.
- Unit 3: 1,800 t a year, 13.19% oxygen, 169% excess air.
- None had an oxygen meter, and most operators held no boiler certificate.

## Read the oxygen yourself

Excess air % = oxygen % / (21 minus oxygen %) x 100. At 14.7% oxygen that is 14.7 / 6.3 = 233%: more than three times the air the coal needs, all heated and thrown up the chimney. The report uses the rule that every 15 points less excess air lifts boiler efficiency about 1%.

## What the analyser costs and saves

- A zirconia probe in the chimney and a panel display reading oxygen every few seconds. Rs 2.31 lakh with taxes and supply, plus Rs 0.05 lakh for cabling and fitting: Rs 2.36 lakh.
- No boiler shutdown to fit it.
- Saving booked: 1% of 7,200 t, rounded to 70 t, at Rs 2,830 a tonne = Rs 1.98 lakh a year. Payback 2.36 / 1.98 = 1.19 years.
- The report calls 1% conservative. With 234% excess air, the room is far larger, but only if the ID and FD dampers are actually adjusted to the reading.

## Make the reading count

1. Agree a target oxygen band for your boiler and fuel with the boiler maker.
2. Seal air leaks at doors, ash pits and duct joints first; leaks show up as high oxygen too.
3. Log fuel per tonne of steam, or per lakh metres processed, each month before and after.

## 70 t of fuel saved, CO2 by fuel (estimate)

- If imported coal: 70 x 2.44 = 171 t CO2
- If Indian coal: 70 x 1.76 = 123 t CO2
- If lignite, IPCC default: 70 x 11.9 GJ x 101 kg = about 84 t CO2
- The report's 51 t is below each of these

The report names the saved fuel as lignite in one place and coal in another. Lignite at the IPCC 2006 default net calorific value and carbon factor; check your lignite's own analysis.

## What Senseible does here

Senseible reads coal invoices into monthly records with CO2 on its Indian or imported coal factor. It has no lignite factor, so for lignite apply the IPCC based figure above to the tonnes on your invoices. The green loan check shows whether a small loan for the analyser is worth asking for.

- [Green loan readiness check](https://senseible.earth/green-loan-check)
- [Boiler excess air and fuel saving](https://senseible.earth/answers/boiler-excess-air-fuel-saving)
- [Surat process houses: buyer carbon data](https://senseible.earth/answers/surat-textile-processing-units-buyer-carbon-data)
- [Jet dyeing machine efficient pump](https://senseible.earth/answers/jet-dyeing-machine-efficient-pump-saving)

Sources: [BEE, Detailed project report: online flue gas analyser, Surat textile cluster (SAMEEEKSHA)](https://sameeeksha.org/pdf/dpr/surat_system.pdf), [IPCC 2006 Guidelines, Volume 2 Energy, Tables 1.2 and 1.4](https://www.ipcc-nggip.iges.or.jp/public/2006gl/vol2.html)

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 coal or lignite price and a current quote.