How much wood does an economiser on a thermic fluid heater save?

Thirty tonnes of wood a year in BEE's Solapur report, about a fifth of a dyeing unit's 144 t, by cooling heater flue gas from 360 C to 120 C to make process hot water. Cost Rs 1.29 lakh, payback 1.7 years at Rs 2,500 a tonne (2010). Size it to your hot water use first.

The heater in the report

• Thermic fluid heater of 3 lakh kcal an hour, fired on wood of about 3,200 kcal a kg, 8 hours a day, 240 days a year.
• Efficiency 35 to 45%. Flue gas leaves at 330 to 360 C and carries 33 to 38% of the heat.
• The unit burns 144 t of wood a year for 288 t of product.
• Proposed: a shell and tube economiser in the flue, rated 2,500 litres a day, heating process water to 55 to 60 C, with flue gas leaving at about 120 C.

Check the 30 tonnes against your water

Heating 2,500 litres a day from 27 C to 55 C takes about 70,000 kcal. At the heater's 35 to 45% efficiency that replaces about 49 to 63 kg of wood a day, roughly 12 to 15 t a year. The report's 30 t needs about 5,000 to 6,400 litres of hot water a day from the economiser. If you use only 2,500 litres, expect the smaller saving and a payback nearer 4 years.

Cost and fitting

• Rs 1.25 lakh for the economiser, insulation, piping and tank; Rs 1.29 lakh in all.
• About 2 days to fit; it can be done on a weekly holiday.
• Saving in the report: 30 t x Rs 2,500 = Rs 0.75 lakh a year.

What it does to your carbon figures

• Fossil CO2: no change; the saving is wood
• Wood saved: 30 t x 3,200 kcal/kg x 4.1868 = about 402 GJ
• Biogenic CO2 avoided: 402 GJ x 112 kg = about 45 t
• The report's 42 t used 1.4 t CO2 a tonne of wood
• Wood per kg of product: 0.50 kg falls to about 0.40 kg

Wood CO2 uses the IPCC 2006 default of 112 kg CO2 a GJ with the report's calorific value. It is biogenic and reported separately, outside Scopes 1 to 3.

What Senseible does here

Senseible reads your electricity bills into records with CO2. It has no factor for wood, so keep wood tonnes from purchase bills as a separate biogenic line; the green loan check shows what a lender asks for on heat recovery.

• Green loan readiness check
• Solapur textiles: wood fuel and carbon
• Thermic fluid heater emissions
• Efficient wood hot water generator

Sources: BEE, Detailed project report: waste heat recovery through economizer, 2,500 LPD, Solapur textile cluster (2010, SAMEEEKSHA), IPCC 2006 Guidelines, Volume 2 Energy, Tables 1.2 and 2.3, GHG Protocol Corporate Standard (biogenic CO2 reported separately)

Last reviewed 2026-10-31. Report figures are from a BEE SME programme project report; costs and paybacks are at 2010 prices. Check today's wood price and your own hot water use.