Why do the Bureau of Energy Efficiency (BEE) Surat reports for 1.5 and 2.5 kilolitre drain heat recovery print different paybacks and carbon dioxide (CO2) per tonne of coal?

BEE's Surat reports put a heat exchanger on the 90 degrees Celsius (C) drain of jet machines for rupees (Rs) 3.11 lakh and Rs 7.02 lakh, saving 89 and 178.1 tonnes of coal a year. Payback is printed as 1.08 and 1.04 years. The 2.5 kilolitre report prints 320 tonnes of CO2; its own 45% carbon content gives about 294.

The two reports side by side

• 1.5 kilolitre (kL) report: a typical unit with 8 jet machines drains 31,000 litres a day at 90 C. 80% is counted as recoverable, 24,800 litres, cooled to 50 C: 992,000 kilocalories (kcal) a day. 2.5 kL report: 15 jet machines, 62,000 litres a day, 49,600 recoverable: 1,984,000 kcal a day.
• Both use a 65% boiler, coal at 6,000 kcal a kilogram (kg), 350 days and Rs 3,800 a tonne. Coal saved: 1,984,000 / (0.65 x 6,000) x 350 = 178.05 tonnes, printed 178.1; half that is 89. Money: Rs 3.38 lakh and Rs 6.77 lakh.
• Cost: Rs 3.00 lakh equipment plus Rs 0.11 lakh to erect is Rs 3.11 lakh; Rs 6.75 lakh plus Rs 0.27 lakh is Rs 7.02 lakh. Per tonne of yearly coal saved that is Rs 3,494 against Rs 3,942.
• Printed indicators, 1.5 kL against 2.5 kL: internal rate of return (IRR) 84.28% and 75.04%, net present value (NPV) Rs 9.42 and 18.18 lakh, 10 days of downtime each in the summaries, though both annexure notes say downtime is considered for one week only. The 2.5 kL report's title rates it per hour while its sizing is the 62,000 litres drained a day.

What CO2 should be

The 2.5 kL report says "Carbon content 45%". 178.1 x 0.45 x 44 / 12 = 293.9 tonnes, not 320. On imported coal at 2.44 kg CO2 a kg, 178.1 tonnes is 434.6, and 89 tonnes is 217.2. Both reports call the saving equivalent imported coal, so 2.44 applies; if you burn lignite or Indian coal, use that fuel's own factor. The coal is burnt in your own boiler, so the cut shows up in Scope 1.

Two ways the paybacks are printed

Payback is cost divided by yearly saving. The 2.5 kL report prints 1.04 years: 7.02 / 6.77 = 1.037. The 1.5 kL report prints 1.08, which looks like saving divided by cost: 3.38 / 3.11 = 1.087, which would print as 1.09, so the printed figure also looks truncated. Cost divided by saving gives 3.11 / 3.38 = 0.92 years, about 11 months. The linked page on dyeing effluent heat recovery makes this point in full.

Summary and body differ

• Each summary text gives a fuel saving about 9% above its own body and table: 97 tonnes against 89, and 194 against 178.1. The tables and money use the lower figures, so use those.
• The CO2 lines are 64 tonnes for the 1.5 kL report and 320 for the 2.5 kL, which is 0.72 and 1.80 tonnes for each tonne of coal. The same coal and the same method gave two very different ratios.

Before you buy

• Measure your own drain: litres a day and temperature at the machine outlet. Both reports assume 90 C.
• The saving only happens if the warm water is used, in the next dye bath, for washing or as boiler feed.
• Dye liquor fouls tubes; plan cleaning and expect the real recovery to be below 100% of the heat.

The 2.5 kL report, rebuilt

• Heat: 49,600 litres x (90 down to 50) = 1,984,000 kcal a day
• Coal: 1,984,000 / (0.65 x 6,000) = 508.7 kg a day x 350 = 178.05 tonnes
• Money: 178.1 x Rs 3,800 = Rs 6.77 lakh
• Payback: Rs 7.02 lakh / Rs 6.77 lakh = 1.04 years
• CO2 on imported coal: 178.1 x 2.44 = 434.6 tonnes (estimate), against 320 printed

Figures are the reports' own at the reports' prices. The 2.44 kg CO2 a kg for imported coal is Senseible's standard factor, applied here as an estimate.

What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, so the coal bought each month is on file to test the report's baseline against. It does not measure drain temperature or litres; those come from your own log.

• Heat recovery from hot drained dyeing water
• Surat 3 and 4 tonne boiler reports compared
• Surat processing house fuel per metre
• Green loan readiness check

Sources: BEE, Detailed project report: waste heat recovery system (1.5 kl/hour), Surat textile cluster (SAMEEEKSHA), BEE, Detailed project report: waste heat recovery system (2.5 kl/hour), Surat textile cluster (SAMEEEKSHA)

Last reviewed 2026-11-05. Report figures are from BEE's Small and Medium Enterprises (SME) programme project reports, with coal at Rs 3,800 a tonne. Check today's coal price, your drain temperature and a current quote before you rely on the payback.