# Why do Morbi tile kilns not reuse their exhaust heat to warm the burner air when sanitary ware kilns can?

Canonical: https://senseible.earth/answers/morbi-tile-kiln-exhaust-sulphur-blocks-heat-recovery

The Morbi manual says tile kiln exhaust carries sulphur from raw material additives, which corrodes heat recovery equipment, and that units who tried it saw it fail. Sanitary ware raw materials are sulphur free, so its tunnel kiln exhaust can warm burner air. For tiles it suggests high grade stainless steel, replaced every 4 to 5 years.

## What a recuperator does, in plain words

Hot exhaust gas leaves a kiln and carries heat up the chimney. A recuperator is a metal heat swapper. The hot exhaust passes along one side of its metal walls and the cold air for the burners passes along the other. The burners then get warm air and burn less fuel for the same firing.

## Why tile kilns hold back

- The manual says tile kiln exhaust, at 150 to 250 degrees Celsius (°C), is not used because of sulphur in it. The manual says the sulphur comes from additives in the raw materials.
- Sulphur in hot, damp exhaust corrodes ordinary metal. The manual says many units tried to use the heat and their trials failed from corrosion.
- Natural gas has no sulphur, as the roller kiln project report notes. So moving from coal to gas does not take the sulphur out of a tile kiln's exhaust.
- The project report adds that unit owners fear corrosion, and that recuperator suppliers in Morbi have little interest in these projects.

## What the manual suggests

- Make the recuperator from high grade stainless steel, bought from an experienced supplier.
- It will cost more, but the equipment survives for 4 to 5 years.
- Because the recuperator pays back faster than its life, the manual says it still makes economic sense.
- Its table prices this for a single tile unit at rupees (Rs) 2,50,000 to Rs 24,00,000 (2.5 to 24 lakh, a lakh being 100,000) with a saving of Rs 2,00,000 to Rs 40,00,000 a year and payback of 5 to 30 months, at 2010 prices. The manual's text says payback within 1 year; its table says 5 to 30 months.

## Why sanitary ware is different

The manual says sanitary ware raw materials and additives are sulphur free, so the exhaust of a sanitary ware tunnel kiln can be used to preheat burner air without the corrosion problem. A tunnel kiln there bakes a load for about 14 to 18 hours. Its table prices the recuperator at Rs 89,000 to Rs 5,30,000, saving Rs 50,000 to Rs 4,50,000 a year, payback 7 to 14 months.

## What to ask before you order

1. What alloy is the recuperator, and has the supplier fitted one on a tile kiln before?
2. How long is it guaranteed, and what does a replacement cost? The roller kiln report's own supplier terms give a 12 month guarantee and exclude corrosion, so ask for corrosion cover in writing.
3. Where will the exhaust temperature after the recuperator be logged, and who checks it each week? A rising reading can mean the surface is fouling.
4. Add the replacement to the payback sum, as in the example.

## Payback with a short life, using one report's numbers

- One roller kiln report: cost Rs 8.46 lakh, saving Rs 10.44 lakh a year, payback 0.80 years as printed
- Manual's life for a stainless unit: 4 to 5 years
- Spread the cost over 5 years: 8.46 / 5 = Rs 1.69 lakh a year, so the net saving is 10.44 less 1.69 = Rs 8.75 lakh a year
- Over 4 years: 8.46 / 4 = Rs 2.12 lakh a year, net Rs 8.32 lakh a year

The cost and saving are from one kiln's report at 2010 prices. Use a current quote and your own gas price.

## What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, so a unit's own gas, oil and power lines are on file to set beside the report's figures. It does not measure a kiln or replace an audit.

- [Roller kiln waste heat recovery](https://senseible.earth/answers/roller-kiln-waste-heat-recovery-saving)
- [Morbi reports ranked by payback](https://senseible.earth/answers/morbi-bee-ceramic-reports-ranked-by-payback)
- [Kiln exhaust heat to the dryer](https://senseible.earth/answers/tile-kiln-exhaust-heat-to-dryer-gas-saving)
- [Green loan readiness check](https://senseible.earth/green-loan-check)

Sources: [BEE, Manual on Energy Conservation Measures in Ceramic Industry, Morbi cluster (SAMEEEKSHA)](https://sameeeksha.org/pdf/clusterprofile/Morbi_Ceramic_Cluster.pdf), [BEE, Detailed project report: waste heat recovery in roller kiln, Morbi (SAMEEEKSHA)](https://sameeeksha.org/pdf/dpr/MRV_CRM13.pdf)

Last reviewed 2026-11-07. Sulphur statements, lives and ranges are from the April 2010 Bureau of Energy Efficiency (BEE) Morbi manual (sections 3.3.1, 3.4.1 and 4.1.3) and the roller kiln project report. Prices are 2010 prices.