# How do the Bureau of Energy Efficiency Jamnagar gas rotary furnace reports for 250, 500 and 750 kg a batch differ?

Canonical: https://senseible.earth/answers/jamnagar-gas-rotary-furnace-250-500-750-kg-compared

The three Bureau of Energy Efficiency (BEE) Jamnagar reports use 56.25 normal cubic metres (Nm3) of gas in place of 192.16 kilograms of coal per tonne of brass. What differs is the batch: 250, 500 and 750 kilograms (kg) give 333, 667 and 1,000 tonnes a year, and payback of 1.27, 1.32 and 0.99 years.

## The three reports side by side

- 250 kg a batch: 333 tonnes a year, 64 tonnes of coal replaced by 18,750 Nm3 of gas, a 1 horsepower (HP) blower adding 1,492 kilowatt hours (kWh). Saving rupees (Rs) 6.95 lakh, cost Rs 8.80 lakh, payback 1.27 years.
- 500 kg a batch: 667 tonnes, 128 tonnes of coal, 37,500 Nm3, 1,492 kWh. Saving Rs 13.99 lakh, cost Rs 18.43 lakh (Rs 16.75 lakh furnace plus Rs 1.68 lakh erection), payback 1.32 years, net present value (NPV) Rs 33.53 lakh, internal rate of return (IRR) 57.02%.
- 750 kg a batch: 1,000 tonnes, 192 tonnes of coal, 56,250 Nm3, a 2 HP blower adding 2,984 kWh. Saving Rs 20.94 lakh, cost Rs 20.63 lakh (Rs 18.75 lakh plus Rs 1.88 lakh), payback 0.99 years, NPV Rs 57.25 lakh, IRR 79.18%.

## What every report shares

- Coal 192.16 kg a tonne, from one audit melt of 255 kg on 49 kg of coal.
- Gas 45 kg a tonne, which at 0.8 kg a cubic metre is 56.25 Nm3, and a vendor efficiency of 31%. That is 46% less gas than the 103.74 Nm3 a tonne in the pit furnace reports.
- Coal at Rs 18 a kg and gas at Rs 24 a Nm3: Rs 3,459 against Rs 1,350 a tonne, a saving of Rs 2,109.
- A 1.5 hour batch, 2,000 operating hours, seven days of downtime.

## Why 750 kg pays back fastest

The tonnes come from the batch: 250 kg every 1.5 hours is about 167 kg an hour, and over 2,000 hours that is 333 tonnes. At 500 kg it is 667 and at 750 kg, 1,000 (my reading of the printed sums). Each tonne saves the same Rs 2,109, so saving per furnace grows with batch size faster than price does: 750 kg costs Rs 2.20 lakh more than 500 kg but is assumed to melt 333 tonnes more. The 750 kg report's cash-flow sheet labels its capacity 750 kg an hour, while its title and its 1,000 tonnes say 750 kg a batch.

## Carbon dioxide (CO2): the printed cuts are too high

- Printed net cuts are 128, 256 and 384 tonnes a year. They count the coal at about 2.6 tonnes of CO2 a tonne (166, 332 and 499 tonnes) and the gas at about 2.03 kg a Nm3 (38, 76 and 114 tonnes). The blower is left out.
- At the 1.76 kg of CO2 a kg we use for Indian coal, and the blower at 0.675 kg a kWh, the cuts are about 74, 148 and 222 tonnes, or about 222 kg per tonne of brass in each case.
- On imported coal at 2.44 kg a kg the 750 kg cut would be about 352 tonnes (my arithmetic: 192 x 2.44 = 468, less 114 and 2).

## 750 kg a batch, one year

- Tonnes: 750 kg / 1.5 hours x 2,000 hours = 1,000 tonnes
- Money: 1,000 x Rs 2,109 = Rs 21.09 lakh, less 2,984 kWh x Rs 5 = Rs 0.15 lakh, gives Rs 20.94 lakh. Payback Rs 20.63 lakh / Rs 20.94 lakh = 0.99 years
- CO2: coal 192 x 1.76 = 338 tonnes, less gas 114 tonnes, less blower 2,984 x 0.675 = 2 tonnes, net about 222 tonnes

Prices are the reports' own at 2010. Coal factor is our estimate; the gas figure is the report's own.

## What Senseible does here

Senseible reads coal invoices, gas bills and electricity bills into monthly records, so coal or gas per tonne of brass before and after a furnace change is on file. It does not size furnaces or confirm a vendor's efficiency figure.

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Sources: [BEE, Detailed project report: energy efficient gas fired rotoberatory furnace, 250 kg, Jamnagar brass cluster (2010, SAMEEEKSHA)](https://sameeeksha.org/pdf/Jamnagar_brass_cluster/DPR_Energy_Efficient_Gas_Fired_Rotoberatory_Furnace_250%20kg.pdf), [BEE, Detailed project report: energy efficient gas fired rotoberatory furnace, 500 kg a batch, Jamnagar brass cluster (2010, SAMEEEKSHA)](https://sameeeksha.org/pdf/Jamnagar_brass_cluster/DPR_on_Energy_Efficient_Gas_Fired_Rotoberatory_Furnace_500_kg.pdf), [BEE, Detailed project report: energy efficient gas fired rotoberatory furnace, 750 kg a batch, Jamnagar brass cluster (2010, SAMEEEKSHA)](https://sameeeksha.org/pdf/Jamnagar_brass_cluster/DPR_on_Energy_Efficient_Gas_Fired_Rotoberatory_Furnace_750_kg.pdf), [Central Electricity Authority (CEA), CO2 Baseline Database, version 22.0](https://cea.nic.in/cdm-co2-baseline-view?mappingId=234&lang=en)

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