Which Bureau of Energy Efficiency tunnel kiln report pays back fastest for a refractory unit: 10, 20 or 50 tonnes a day?
In three Bureau of Energy Efficiency (BEE) Godavari reports, a tunnel kiln costs rupees (Rs) 91, 150 and 260.50 lakh and pays back in 3.30, 2.52 and 2.87 years. The tunnel kiln burns the same coal per tonne fired in all three. Payback differs because the price per tonne fired in a year differs.
The three reports side by side
- 10 tonnes a day: Rs 91 lakh. It replaces a downdraft kiln firing 30 tonnes a batch, 30 batches a year. Saves 646 tonnes of coal, Rs 27.57 lakh a year, payback 3.30 years. Report carbon dioxide (CO2): 1,162 tonnes.
- 20 tonnes a day: Rs 150 lakh. Replaces a kiln firing 90 tonnes a batch, 20 batches a year. Saves 1,392 tonnes of coal, Rs 59.63 lakh a year, payback 2.52 years. Report CO2: 2,505 tonnes.
- 50 tonnes a day: Rs 260.50 lakh. Replaces a kiln firing 180 tonnes a batch, 15 batches a year. Saves 2,088 tonnes of coal, Rs 90.65 lakh a year, payback 2.87 years. Report CO2: 3,757 tonnes.
- All three use coal at 4,200 kilocalories (kcal) a kilogram and Rs 4,500 a tonne, a tunnel kiln heat need of 1,150 kcal a kilogram of product at 35% efficiency, and a 20 year kiln life.
Why the paybacks differ
The tunnel kiln burns 0.78 tonnes of coal for every tonne fired in all three (23.47 for 30 tonnes, 70.41 for 90, 140.82 for 180). The downdraft baseline is 1.50 tonnes per tonne in the 10 tonne report and 1.56 in the other two (140 for 90, 280 for 180), so the saving is 0.72 tonnes of coal per tonne fired in the first and 0.77 in the others.
What really moves payback is price against yearly output. Tonnes fired in a year are 900, 1,800 and 2,700. Rs 91 lakh over 900 is about Rs 10,100 per yearly tonne, Rs 150 lakh over 1,800 is about Rs 8,300, and Rs 260.50 lakh over 2,700 is about Rs 9,650. The 20 tonne quote is simply the cheapest per tonne, which is why it pays back first. It says little about which size suits you.
Where the reports do not add up
The text says downdraft kilns run at 10 to 15% efficiency, and each report lists one typical unit: 10.2%, 13.75% and 15%. But the annexure sums imply more. In the 10 tonne report 45 tonnes of coal at 4,200 kcal a kilogram gives 6,300 kcal for each kilogram fired, and the report's own 1,150 kcal need over 6,300 is 18.3%. For 140 tonnes over 90 and 280 over 180 it is 17.6%. The saving uses coal tonnes, not the efficiency figure, so it stands or falls on the coal per batch you actually weigh. The 10 tonne report's text also gives the downdraft batch as 35 tonnes, while its annexure uses 30.
What the saving leaves out
- It counts only today's batches. The reports add that production becomes daily instead of by batch, but give no extra output figure.
- Fan and blower power is costed, Rs 1.50, 3.00 and 3.30 lakh a year, but never given in kilowatt hours.
- Each report says no unit in the cluster has a tunnel kiln, so these are design figures, not results from a running plant.
- The 50 tonne report says a separate structure built inside the plant avoids lost production; replacing the downdraft kiln in place would mean 6 months of downtime.
The 20 tonne report, one batch and one year
- Coal saved a batch: 140 minus 70.41 = 69.59 tonnes
- Value: 69.59 x Rs 4,500 = Rs 3.13 lakh, less Rs 0.15 lakh of fan power = Rs 2.98 lakh
- Year: 20 batches x Rs 2.98 lakh = Rs 59.6 lakh (report: Rs 59.63 lakh)
- Payback: Rs 150 lakh / Rs 59.63 lakh = 2.52 years
- Cost per yearly tonne fired: Rs 150 lakh / 1,800 = about Rs 8,300
All report figures except the cost per yearly tonne, which divides the report's cost by its batches x tonnes a batch.
What Senseible does here
Senseible reads fuel invoices and electricity bills into monthly records, so a year of fuel and power use before a new kiln is already on file to compare against. The green loan check shows what a lender asks for.
- Green loan readiness check
- Tunnel kiln of 10 tonnes a day: coal saved
- Coal gasifier on a 100 tonne downdraft kiln
- Heat recovery on a downdraft kiln
Sources: BEE, Detailed project report: tunnel kiln 10 tonnes a day, Godavari refractories cluster (SAMEEEKSHA), BEE, Detailed project report: tunnel kiln 20 tonnes a day, Godavari refractories cluster (SAMEEEKSHA), BEE, Detailed project report: tunnel kiln 50 tonnes a day, Godavari refractories cluster (SAMEEEKSHA)
Last reviewed 2026-11-04. Report figures are from BEE's Small and Medium Enterprises (SME) programme project reports; costs, tariffs and paybacks are at the report year's prices. Check today's prices and a current quote before you rely on the payback.