# How much coal does a 10 TPD tunnel kiln save over downdraft firing for refractories?

Canonical: https://senseible.earth/answers/refractory-tunnel-kiln-10-tpd-coal-saving

It roughly halves coal per tonne fired. BEE's Godavari report puts downdraft kilns at 1.5 t of coal per tonne of refractories and a 10 TPD tunnel kiln at 0.78, saving 646 t of coal and about 1,137 t CO2 a year. Cost Rs 91 lakh, payback 3.30 years at 2011 prices.

## Why downdraft kilns burn so much

A downdraft kiln heats its walls and the whole setting from cold every 8 to 10 days, then lets the heat go in cooling. The report measured 10 to 15% efficiency. A tunnel kiln fires continuously: ware is preheated by outgoing gas and cools inside the kiln, and the report assumes 35% efficiency.

## The report's figures

- Downdraft: 45 t of 4,200 kcal/kg coal to fire 30 t of refractories, 1.5 t of coal per tonne.
- Tunnel kiln: 1,150 kcal of heat per kg of product at 35% efficiency, 7.82 t of coal a day for 10 t, about 23.47 t for the same 30 t.
- Saving 21.53 t a batch, 646 t a year over 30 batches, and Rs 27.57 lakh a year after Rs 1.50 lakh of extra power.
- 48 hours cool to cool; 24 hours from ambient to 1,200 C, 6 hours soaking at 1,000 C, 18 hours cooling.
- Project cost Rs 91 lakh with civil and erection work included.

## When a tunnel kiln makes sense

- It only earns its saving running full: 10 t a day, every day, about 300 t a month of similar shapes.
- 35% efficiency is a design figure. Ask the supplier to guarantee kcal per kg fired.
- Log coal and output for several months on the old kilns first, so the before figure is yours.

## Per tonne fired and per year

- Downdraft: 1.50 t coal x 1.76 = 2.64 t CO2 per tonne of refractories
- Tunnel kiln: 0.78 t coal x 1.76 = 1.37 t CO2 per tonne
- Year: 646 t coal saved x 1.76 = 1,137 t CO2
- The report's 1,162 t used 1.8 t CO2 per tonne of coal

Coal at our Indian coal factor, an estimate. The tunnel kiln's extra fan power is costed in the report but not given in kWh, so it is left out.

## What Senseible does here

Senseible reads coal and electricity invoices into monthly CO2 records linked to each bill. Add tonnes fired and you have coal and CO2 per tonne, the before and after a lender wants for a kiln loan.

- [Green loan readiness check](https://senseible.earth/green-loan-check)
- [Tunnel kiln or shuttle kiln](https://senseible.earth/answers/tunnel-kiln-vs-shuttle-kiln-emissions)
- [Kiln waste heat recovery](https://senseible.earth/answers/downdraft-kiln-waste-heat-recovery-coal-saving)
- [Refractory kiln on a biomass gasifier](https://senseible.earth/answers/refractory-kiln-coal-to-biomass-gasifier-co2)

Sources: [BEE, Detailed project report: tunnel kiln 10 TPD, East and West Godavari refractories cluster (2011, SAMEEEKSHA)](https://sameeeksha.org/pdf/dpr/East_and_West_Godavari_refractories_cluster/07_Tunnel_kiln_10_TPD.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 2026-10-31. Report figures are from a BEE SME programme project report; costs and paybacks are at the report year's prices. Check today's fuel and power prices before you rely on the payback.