Why do the two Bureau of Energy Efficiency (BEE) Solapur economiser reports, one titled boiler and one thermic fluid heater, save 38 and 30 tonnes of wood?

BEE's Solapur economiser reports cost rupees (Rs) 1.56 lakh and Rs 1.29 lakh, saving 38 and 30 tonnes of wood a year. The 38 tonne report prints Rs 1.14 lakh at Rs 3,000 a tonne, its text says Rs 0.75 lakh, and its annexure also lists Rs 2,500.

The two reports side by side

• Thermic fluid heater report: flue gas leaves at 360 degrees Celsius (C) and an economiser rated 2,500 litres a day takes it down to about 120 C. Wood saved 30 tonnes a year of the unit's 144, which the report prints as 20% of total wood consumption (30 / 144 = 20.8%). At Rs 2,500 a tonne, Rs 0.75 lakh. Cost Rs 1.29 lakh. Payback 1.7 years, internal rate of return (IRR) 33.75%, net present value (NPV) Rs 0.78 lakh over 3 years.
• "Boiler" report: wood saved 38 tonnes, which is 8% of the unit's 480 tonnes (38 / 480 = 7.9%). Printed benefit Rs 1.14 lakh, cost Rs 1.56 lakh in the table (Rs 1.50 lakh equipment, 0.02 erection, 0.04 interest) and Rs 1.55 lakh in the text. Payback 1.37 years in the summary, 1.36 in the text.
• Both heat process water to 55 to 60 C, 8 hours a day, 240 days, with wood at 3,200 kilocalories a kilogram and 2 days to fit, which can be done on a weekly holiday.

The boiler report does not agree with itself

• Rs 1.14 lakh is 38 tonnes at Rs 3,000 a tonne, the price in its Table 3.1. Its Annexure 3 lists wood at Rs 2,500 for the existing line and 3,000 for the proposed one, and the heater report uses Rs 2,500. At Rs 2,500, 38 tonnes is Rs 0.95 lakh and payback is 1.56 / 0.95 = 1.64 years. Its text in section 3.2 says Rs 0.75 lakh, the heater report's figure.
• The flue gas temperature is 270 C in the summary, 230 to 270 C in the text, and 360 C in the annexure, which is the heater report's figure.
• Its title says boiler. Its baseline table is a boiler of 2 tonnes an hour making 1,800 kilograms of steam a day, but its summary and text speak of the flue gas of a thermic fluid heater making hot water.
• Its summary leaves net present value, internal rate of return, return on investment and debt service cover blank. Its text prints IRR 49.24% and NPV Rs 1.35 lakh, and its annexure 46.18% and Rs 1.26 lakh.

What to take from the pair

Both agree on the idea: put a shell and tube heat exchanger in the flue, and use the hot water in the dye bath or as boiler feed. One report saves 20% of a heater's wood, the other 8% of a boiler's. Our reading: the gap probably comes from the baselines, a heater with 360 C flue gas against a boiler with 230 to 270 C, though the boiler report's own annexure also uses 360 C. Test either against your own flue temperature and the litres of hot water you really use a day.

The carbon dioxide (CO2) lines

The boiler report prints 53 tonnes of CO2 for 38 tonnes of wood, which is 1.4 tonnes a tonne. The report counts this as a cut in non renewable wood and ties it to carbon credit benefit under the Clean Development Mechanism, so the 53 tonnes rests on that premise. Our reading: wood is biogenic, so this is not a Scope 1 cut; the linked heater page works the same point. With the Intergovernmental Panel on Climate Change (IPCC) default of 112 kilograms (kg) of CO2 per gigajoule and the report's 3,200 kilocalories a kilogram, 38 tonnes of wood carries about 57 tonnes of biogenic CO2. Report the wood tonnes beside your carbon figure, with that CO2 on its own line.

Before you buy

• Measure flue temperature with a probe at full firing. The saving needs a hot stack.
• Count the hot water you can use. An economiser that makes water nobody needs saves no wood.
• Price wood at today's rate and rerun the payback.

The boiler report's money, rebuilt

• Printed: 38 tonnes x Rs 3,000 = Rs 1.14 lakh; payback 1.56 / 1.14 = 1.37 years
• At Rs 2,500, the annexure's existing-line price: 38 x Rs 2,500 = Rs 0.95 lakh; payback 1.56 / 0.95 = 1.64 years
• Heat in the 38 tonnes: 38,000 x 3,200 x 4.1868 = 509 gigajoules
• Biogenic CO2 at 112 kg per gigajoule: 509 x 112 = 57.0 tonnes

Printed lines are the reports' own at the reports' prices. The CO2 line is our arithmetic with the IPCC 2006 wood default, an estimate, biogenic and kept apart from Scope 1.

What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, so wood purchased by month is on file to test a baseline against. It has no wood factor, so keep wood tonnes beside the figure.

• Economiser on a thermic fluid heater
• Solapur wood boiler reports compared
• Towel and bed sheet unit: wood and power per kg
• Green loan readiness check

Sources: BEE, Detailed project report: waste heat recovery through economizer (boiler), Solapur textile cluster (SAMEEEKSHA), BEE, Detailed project report: waste heat recovery through economizer, Solapur textile cluster (SAMEEEKSHA), IPCC 2006 Guidelines, Volume 2, Energy (default emission factors and net calorific values)

Last reviewed 2026-11-05. Report figures are from BEE's Small and Medium Enterprises (SME) programme project reports, with wood at Rs 2,500 to Rs 3,000 a tonne. Check today's wood price, your flue temperature and a current quote before you rely on the payback.