Which melting furnace swap in the Bureau of Energy Efficiency Jamnagar manual pays back fastest on 200 tonnes of brass a year?
In the Bureau of Energy Efficiency (BEE) Jamnagar manual, on 200 tonnes a year, a gas pit furnace in place of coal saves rupees (Rs) 3.40 lakh for Rs 2.50 lakh (0.74 years), a gas rotary furnace Rs 4.20 lakh for Rs 12 lakh (2.9 years), and a better oil furnace Rs 1.88 lakh for Rs 4 lakh.
The three swaps as the manual prints them
- Coal pit to gas fired pit: coal 195 kilograms a tonne at 11% efficiency (1.08 million kilocalories a tonne) becomes 72 cubic metres of gas (Nm3) at 17% (0.69). Fuel cost per kilogram of brass Rs 3.50 falls to Rs 1.80, saving Rs 1,700 a tonne and Rs 3.40 lakh a year. Cost Rs 2.50 lakh, payback 0.74 years.
- Coal pit to gas fired rotary: 58 cubic metres a tonne at 21% (0.57 million kilocalories). Fuel cost Rs 1.40 a kilogram, saving Rs 2,100 a tonne, Rs 4.20 lakh. Cost Rs 12 lakh, payback 2.9 years. The manual adds a melting loss of 4 to 5% in the coal pit furnace that a rotary furnace is said to reduce.
- Oil pit to efficient oil pit: 130 litres a tonne at 10.20% becomes 95 litres at 13.96%. Fuel cost Rs 3.60 falls to Rs 2.66 a kilogram, saving Rs 940 a tonne, Rs 1.88 lakh. Cost Rs 4.00 lakh, payback printed as 2.20 years.
What the Rs a kilogram column means, and checks
- The column says Rs per kilogram but is Rs per kilogram of brass melted (my reading): 195 kilograms of coal x Rs 18 = Rs 3,510 a tonne, so Rs 3.51 a kilogram, printed Rs 3.50.
- Gas: 72 x Rs 24 = Rs 1,728 a tonne, which is Rs 1.73 a kilogram and does not round to the printed Rs 1.80. The printed saving of Rs 1,700 a tonne follows the printed 1.80 (3,510 minus 1,800); 3,510 minus 1,728 would be 1,782. Rotary: 58 x 24 = Rs 1,392, printed Rs 1.40. Oil: 95 x Rs 28 = Rs 2,660, printed Rs 2.66.
- Oil payback: Rs 4.00 lakh / Rs 1.88 lakh = 2.13 years, not 2.20.
- Heat check: efficiency times heat in the fuel is about 0.12 million kilocalories a tonne in every row (11% x 1.08, 17% x 0.69, 21% x 0.57, 10.20% x 1.21, 13.96% x 0.88). The manual keeps the useful heat fixed.
- Coal is Rs 17 a kilogram at 6,500 kilocalories in Table 2.1 but Rs 18 in the savings tables, and 195 kilograms at 1.08 million kilocalories implies about 5,540 kilocalories a kilogram.
Why the gas pit furnace looks cheap here
The same BEE series has detailed project reports. Its 200 kilogram an hour gas pit furnace uses about 104 cubic metres a tonne and costs Rs 12.65 lakh, payback 3.61 years. Its 250 kilogram gas rotary furnace uses 56.25 cubic metres a tonne and costs Rs 8.80 lakh, payback 1.27 years. So the manual's Rs 2.50 lakh for the pit furnace is about a fifth of the detailed report's cost.
Most of the 72 versus 104 cubic metres gap is a checkable difference in gas heat value, not unit type. The manual prices gas at 9,500 kilocalories a cubic metre in Table 2.1 (72 x 9,500 = 0.68 million kilocalories, the 0.69 it prints), while the detailed report assumed 6,880 (104 x 6,880 = 0.72). The rotary goes the other way, Rs 12 lakh against Rs 8.80 lakh. After the heat value, my reading is that the manual's table is a typical-unit estimate and the detailed reports are the better guide to price. Get a quote before you use either payback.
A summary table that does not tie
Table 5.1 lists the rotary swap as saving 114 million kilocalories (mkCal) a year. The body gives 1.08 less 0.57 = 0.51 a tonne, so 102 on 200 tonnes. 114 is 0.57 x 200, the rotary furnace's own fuel use, which looks like the wrong column (my reading). The gas pit row prints 76.4 where the body gives 0.39 x 200 = 78. The cluster potentials of 45,458 and 15,960 mkCal are those printed figures times 595 and 140 units.
Coal and oil carbon per tonne of brass (estimate)
- Coal pit: 195 kilograms x 1.76 kilograms of carbon dioxide (CO2) = 343 kilograms (476 on imported coal at 2.44)
- Oil pit today: 130 litres x 2.97 = 386 kilograms. Efficient oil pit: 95 litres x 2.97 = 282 kilograms
- Oil swap on 200 tonnes: 386 minus 282 is 104 kilograms, x 200 = about 20.8 tonnes of CO2 a year
- Gas side: the manual's fuel is listed as gas at Rs 24 per Nm3, and its Table 2.1 calls it Liquid Petroleum Gas. Use the factor your supplier gives for the fuel on your bill.
Indian coal 1.76 and imported coal 2.44 kilograms of CO2 a kilogram, from India's Second Biennial Update Report; furnace oil about 0.95 kilograms a litre at the Intergovernmental Panel on Climate Change (IPCC) default. All estimates; blower power is not in the manual's tables.
What Senseible does here
Self-serve, Senseible reads fuel invoices and electricity bills into monthly records; furnace efficiency is custom, on request. Coal, oil or gas bought each month is on file, and the brass you cast comes from your own records.
- Your carbon number for buyers and banks
- Coal pit to 200 kilogram gas pit furnace
- Coal pit to 250 kilogram gas rotary furnace
- Efficient 150 kilogram oil fired pit furnace
Sources: BEE, Manual on energy conservation measures in brass cluster Jamnagar (Winrock International India), IPCC 2006 Guidelines, Volume 2 Energy, BEE, Detailed project report: energy efficient gas fired pit furnace, 200 kg an hour, Jamnagar brass cluster (2010, SAMEEEKSHA), BEE, Detailed project report: energy efficient gas fired rotoberatory furnace, 250 kg, Jamnagar brass cluster (2010, SAMEEEKSHA), India, Second Biennial Update Report to the UNFCCC, Table 2.3 (Indian coal 1.76; list of reports)
Last reviewed 2026-11-06. Figures are from BEE's Jamnagar cluster manual, which prints no year on the pages used. Prices are that report's. The two detailed project reports are listed in the sources and linked above.