Why does the payback of an efficient oil-fired brass pit furnace fall from 0.92 to 0.57 years across the Bureau of Energy Efficiency Jamnagar 150, 300 and 400 kg reports?

All three Bureau of Energy Efficiency (BEE) Jamnagar reports save the same 35 litres of oil per tonne of brass, 130 down to 95. Payback falls from 0.92 to 0.65 to 0.57 years because the reports assume 300, 600 and 800 tonnes a year while furnace prices rise less than output.

The three reports side by side

• 150 kilograms (kg) an hour: 300 tonnes a year, 10,500 litres saved, a 1 horsepower (HP) blower adding 1,492 kilowatt hours (kWh). Saving rupees (Rs) 2.87 lakh, cost Rs 2.64 lakh (Rs 2.40 lakh furnace plus Rs 0.24 lakh erection), payback 0.92 years.
• 300 kg an hour: 600 tonnes, 21,000 litres, a 2 HP blower adding 2,984 kWh. Saving Rs 5.73 lakh, cost Rs 3.74 lakh (Rs 3.40 lakh plus Rs 0.34 lakh), payback 0.65 years, net present value (NPV) Rs 17.21 lakh, internal rate of return (IRR) 116.68%.
• 400 kg an hour: 800 tonnes, 28,000 litres, 2,984 kWh. Saving Rs 7.69 lakh, cost Rs 4.35 lakh (Rs 3.95 lakh plus Rs 0.395 lakh), payback 0.57 years, NPV Rs 23.60 lakh, IRR 133.31%.
• Each is seven days of downtime and about 15 weeks to install.

Where the same 35 litres comes from

• Old furnace: 19.50 litres an hour on 150 kg heated to 900 degrees Celsius, 130 litres a tonne, efficiency 6.5%.
• New furnace: 14.25 litres an hour on 150 kg heated to 1,000 degrees, 95 litres a tonne, efficiency 10%.
• The 300 and 400 kg reports reuse this 150 kg measurement. Their tonnes are the rated kg an hour times 2,000 hours (my reading of the printed sums), so no larger furnace was measured at its own size.
• The new furnace is also credited with a hotter melt, 1,000 against 900 degrees. At the old 900 degrees, 14.25 litres an hour would give about 8.9%, not 10% (my arithmetic: 11,745 / 131,670).

Why payback shortens as the furnace grows

Savings scale with the tonnes assumed: 35 litres x Rs 28 = Rs 980 a tonne, less blower power. The price does not scale: it goes from Rs 2.64 lakh to Rs 3.74 lakh to Rs 4.35 lakh while the tonnes go from 300 to 600 to 800. The bigger furnace wins on paper because it is assumed to run full every hour. A unit that melts 300 tonnes a year in a 400 kg furnace earns the 150 kg saving at the 400 kg price.

Which oil, and the carbon dioxide (CO2)

• The reports call the fuel furnace oil at Rs 28 a litre, density 0.88, but each specification sheet lists diesel or light diesel oil. Check your own bill before you pick a factor.
• Printed CO2 cuts: 31, 62 and 83 tonnes a year, about 2.95 kg a litre. The blower is not subtracted.
• At the 2.645 kg a litre we use for diesel, and the blower at 0.675 kg a kWh, the cuts would be about 27, 54 and 72 tonnes. We have no sourced factor for furnace oil, so this is a diesel reading.

The 300 kg furnace, report sums

• Oil saved: (130 minus 95) x 600 tonnes = 21,000 litres
• Money: 21,000 x Rs 28 = Rs 5.88 lakh, less 2,984 kWh x Rs 5 = Rs 0.15 lakh, gives Rs 5.73 lakh
• Payback: Rs 3.74 lakh / Rs 5.73 lakh = 0.65 years
• CO2 on the diesel factor: 21,000 x 2.645 = 55.5 tonnes, less 2,984 x 0.675 = 2.0 tonnes, about 53 tonnes

Prices are the reports' own at 2010. The CO2 line is an estimate using our diesel factor.

What Senseible does here

Senseible reads oil invoices and electricity bills into monthly records, so litres per tonne of brass before and after a furnace change are on file. It does not size furnaces or confirm which oil the burner takes.

• Green loan readiness check
• Brass: efficient 150 kg oil pit furnace
• Oil crucible or induction for brass
• Jamnagar brass cluster energy and carbon

Sources: BEE, Detailed project report: energy efficient oil fired pit furnace, 150 kg, Jamnagar brass cluster (2010, SAMEEEKSHA), BEE, Detailed project report: energy efficient oil fired pit furnace, 300 kg, Jamnagar brass cluster (2010, SAMEEEKSHA), BEE, Detailed project report: energy efficient oil fired pit furnace, 400 kg, Jamnagar brass cluster (2010, SAMEEEKSHA), Central Electricity Authority (CEA), CO2 Baseline Database, version 22.0

Last reviewed 2026-11-06. Report figures are from BEE's Small and Medium Enterprises (SME) programme project reports; costs, oil prices and paybacks are at 2010 prices. Redo the payback with today's oil price and a current quote.