# How much gas does using tunnel kiln exhaust to pre-dry material save?

Canonical: https://senseible.earth/answers/tunnel-kiln-exhaust-dryer-preheat-gas-saving

About 7.5% of the kiln's gas in BEE's Morbi report for a 1,000 piece a day sanitaryware tunnel kiln: 43,382 scm a year, about 89 t CO2. The 120 C air now blown out of the cooling zone heats loaded cars in an insulated chamber before they enter. Cost Rs 6.64 lakh, payback about a year.

## Where the heat goes now

A sanitaryware tunnel kiln fires to about 1,200 C and loses heat two ways: flue gas from the preheating zone and hot air from the rapid cooling zone. The report's kiln burns about 1,800 scm of gas a day, 578,431 scm a year over 321 days, and blows 2,826 m3 an hour of cooling air out at about 120 C. Kiln efficiency in the cluster audits was 19 to 26%.

## What gets built

1. An insulated chamber, built like a dryer, where loaded kiln cars wait before entering the kiln.
2. Ducting from the cooling zone exhaust to that chamber, with a small axial fan if the draught is weak.
3. Thermometers on the duct and in the chamber to show the heat is arriving.
4. Four to five days of downtime to make the duct connection.

## How the saving is worked out

- Heat given to the ware: 2,826 m3 x 0.91 kg per m3 x 0.24 kcal per kg C x about 80 C of cooling = 49,375 kcal an hour.
- Gas equivalent: 49,375 / 8,800 kcal per scm = 5.61 scm an hour, about 135 scm a day.
- Over the year: 43,382 scm, 7.5% of the kiln's gas, worth Rs 6.50 lakh at Rs 15 a scm.
- Cost: Rs 5.00 lakh material, Rs 0.75 lakh erection, Rs 0.89 lakh interest and other costs, Rs 6.64 lakh in total. Payback 6.64 / 6.50 = 1.02 years.

## Watch for

- Space beside the kiln entry for a chamber that holds cars, which many sheds do not have.
- If your cooling air already goes to the mould or ware dryers, this heat is spoken for. Count it once.
- Log gas per piece fired for a month before and after, at the same pull rate.

## One kiln, one year

- Gas saved: 43,382 scm x 2.05 kg = 88.9 t CO2
- Kiln gas after: 578,431 minus 43,382 = 535,049 scm
- All 43 Morbi sanitaryware units: about 3,820 t CO2 a year
- The report's 89 t matches today's natural gas factor

Natural gas at 2.05 kg CO2 per scm. Money at the report's Rs 15 a scm.

## What Senseible does here

Senseible reads gas bills and electricity bills into monthly records with CO2, so the kiln's gas before and after the chamber is on record against each bill. For a kiln retrofit loan, the green loan check lists what to bring.

- [Green loan readiness check](https://senseible.earth/green-loan-check)
- [Tunnel kiln low thermal mass cars](https://senseible.earth/answers/tunnel-kiln-low-thermal-mass-car-gas-saving)
- [Roller kiln waste heat recovery](https://senseible.earth/answers/roller-kiln-waste-heat-recovery-saving)
- [Kiln exhaust heat to a dryer](https://senseible.earth/answers/kiln-exhaust-heat-to-dryer-fuel-saving)

Sources: [BEE, Detailed project report: dryer on tunnel kiln for preheating of material, Morbi ceramic cluster (SAMEEEKSHA)](https://sameeeksha.org/pdf/dpr/MRV_CRM4.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 gas price and a current quote.