# How much pet coke does automatic excess air control save on a Pali dyeing house boiler?

Canonical: https://senseible.earth/answers/boiler-excess-air-control-petcoke-saving

About 98 t of residual pet coke a year per boiler, by BEE's 2010 project report for Pali's process houses, roughly 311 t CO2 at the IPCC default. Auditors found flue gas at 15 to 17% oxygen, which is 250 to 425% excess air, where about 65% is enough for pet coke.

## What the auditors found in Pali

- Boilers of 1 to 4 t an hour, most built for pulverised lignite or lump coal.
- When lignite from Gujarat stopped, units moved to residual pet coke and converted the boilers to bubbling fluidised beds with a lime bed for its sulphur. The report says the conversions were done without engineering the combustion, and efficiency fell.
- Flue gas oxygen of 15 to 17% at most boilers. Of the boilers audited, only one had automatic excess air control.
- A typical power process unit burns 100 to 300 t of pet coke a month.

## What 16% oxygen means

Excess air is O2 x 100 / (21 minus O2). At 15% oxygen that is 250%; at 17%, 425%. The boiler is heating three and a half to five and a quarter times the air the coke needs and blowing it up the chimney. The report puts the right level for pet coke globules at about 65% excess air, which is roughly 8.3% oxygen.

## What gets fitted

- A zirconia oxygen probe in the flue close to the boiler, ahead of any damper or leak.
- A PLC controller with display, and a VFD on the forced draft fan so the air follows the reading.
- About a week of boiler downtime, six weeks from order to running.
- BEE costed it at Rs 3.0 lakh, including Rs 45,000 for the VFD, against Rs 7.35 lakh a year of coke at 2010 prices: payback about five months.
- The report counts more than 30 boilers in Pali that could take it, about 3,827 t of pet coke a year between them.

## Size it against your own coke

98 t a year is about 3 to 8% of what a unit burning 100 to 300 t a month uses, so the saving can hide inside a busy month. Compare coke per tonne of steam, or per thousand metres processed, for the same months before and after. Take the oxygen reading before any economiser: air leaking into the ducts raises oxygen downstream and makes a tuned boiler look worse.

## Two lines beside the coke CO2

- Nitrous oxide: fluidised bed combustion makes far more than a stoker grate, and it counts in Scope 1.
- If the bed is topped up with limestone rather than burnt lime, each tonne releases about 0.44 t CO2 as it breaks down. Count the limestone bought.

## One Pali boiler, one year

- Coke saved: 98.06 t x 3.17 t CO2 = about 311 t CO2. The report says 243 t, worked out with an older calculator
- For a unit burning 200 t a month: 98.06 / 2,400 = 4.1% of its coke
- Air through the boiler: from 4.2 times the theoretical amount at 16% oxygen to 1.65 times at 65% excess air
- Pali's 30-plus boilers: 3,827 t x 3.17 = about 12,130 t CO2 a year

## What Senseible does here

Senseible turns pet coke invoices and stock changes into monthly tonnes and CO2, so the drop after an O2 trim shows on the same record a lender looks at.

- [Check your green loan readiness](https://senseible.earth/green-loan-check)
- [Boiler excess air: the full calculation](https://senseible.earth/answers/boiler-excess-air-fuel-saving)
- [Pet coke emission factor](https://senseible.earth/answers/petcoke-emission-factor-india)
- [Fluidised bed boilers and N2O](https://senseible.earth/answers/afbc-coal-boiler-n2o-emissions)

Sources: [BEE, Detailed project report: excess air control in boiler, Pali textile cluster (2010)](https://sameeeksha.org/pdf/dpr/PAL_TXT5.pdf), [IPCC 2006 Guidelines, Volume 2: Energy](https://www.ipcc-nggip.iges.or.jp/public/2006gl/vol2.html)

Last reviewed 2026-11-03.