How much boiler fuel does heat recovery from hot drained dyeing water save?

About 254 kg of imported coal a day in BEE's Surat report: a heat exchanger cools 24,800 litres of 90 C jet machine drain to 50 C and heats fresh water with it, saving 89 t a year, about 217 t CO2. Cost Rs 3.11 lakh, saving Rs 3.38 lakh, so payback is 0.92 years, not the report's 1.08.

The heat going down the drain

In the audited unit, eight jet machines of 50 to 200 kg run 24 hours a day and drain about 31,000 litres of dye liquor a day to the CETP at 90 C, for about 50,000 metres of fabric. Two other units drained 32 and 36 kL a day. BEE found none of the 75 units it studied recovering this heat.

What gets installed

• A shell and tube heat exchanger: drain liquor through the tubes, fresh water in the shell.
• Collection and hot water tanks, a small circulation pump and pipes to the jets or the boiler feed tank.
• Fabricated locally, Rs 3.00 lakh, plus Rs 0.11 lakh to erect: Rs 3.11 lakh.
• Space for the tanks and pipe runs is the usual obstacle.

The saving, step by step

1. Count 80% of the drain as recoverable: 24,800 litres a day.
2. Heat: 24,800 x 40 C (90 down to 50) = 992,000 kcal a day.
3. Coal: 992,000 / (65% boiler efficiency x 6,000 kcal a kg) = 254 kg a day, x 350 days = 89 t.
4. Money: 89 t x Rs 3,800 = Rs 3.38 lakh a year. Payback 3.11 / 3.38 = 0.92 years, about 11 months. The report's 1.08 is the two numbers divided the wrong way round.

Where the estimate is generous

• It assumes every kcal taken from the drain reaches the fresh water. A real exchanger passes only part of it, and dye liquor fouls the tubes, so plan cleaning.
• The saving is real only if the warm water is used: in the next dye bath, for washing or as boiler feed.
• Log coal per day and drain temperature for a month before and after.

One unit, one year (estimate)

• Imported coal saved: 89 t x 2.44 = 217 t CO2
• At 70% exchanger effectiveness: 62 t coal, about 152 t CO2
• The report's 64 t equals only 0.72 t of CO2 per tonne of coal, well below the imported coal factor

Imported coal at 2.44 kg CO2 per kg. The 70% case is an example of a typical exchanger, not a figure from the report.

What Senseible does here

Senseible reads coal invoices into monthly records with CO2 on its imported coal factor, so the tonnes before and after the exchanger sit next to each other with the bill behind each. If the bank wants proof of savings, the green loan check lists it.

• Green loan readiness check
• Dyehouse hot effluent heat recovery
• Jet dyeing machine efficient pump
• Surat process houses: buyer carbon data

Sources: BEE, Detailed project report: waste heat recovery (1.5 kL an hour), Surat textile cluster (SAMEEEKSHA)

Last reviewed 2026-11-01. Report figures are from a BEE SME programme project report; costs and paybacks are at the report year's prices. Check today's coal price and a fabricator's quote.