How much fuel can a dye house save by recovering heat from hot drain water?
Heat recovered = flow x 4.186 kJ per kg per degree C x (drain temperature minus fresh water temperature) x exchanger effectiveness. With 200 kL a day of 70 degree C drain heating 28 degree C fresh water at 60% effectiveness, that is about 21 GJ a day, or about 30 GJ of boiler fuel.
What sets the saving
- Hot drain you can capture: keep hot dyeing and soaping drains apart from cold rinses. Mixed drains are cooler and give back less.
- The temperature gap between the drain and incoming water.
- Exchanger effectiveness: plate exchangers recover more but foul with lint; shell and tube or self-cleaning designs suit dirty drains. Effectiveness falls as fouling builds.
- Timing: drains come in bursts. A hot drain tank and a warm water tank let you use the heat when the next bath fills.
From recovered heat to fuel and CO2
Fuel saved = heat recovered / boiler efficiency, provided that fresh water would otherwise have been heated with steam to at least the preheated temperature. CO2 avoided = fuel energy x the fuel's IPCC 2006 factor per GJ. BEE Guide Book 2, in its waste heat recovery chapter, uses the same heat balance.
What cuts the real saving
- Pump power for the drain and fresh water circuits: subtract kWh x 0.710 kg CO2.
- Lint and fibre filters need daily cleaning; a fouled exchanger loses effectiveness.
- Preheated water used where cold water would do saves nothing.
- Low production days and holidays.
A side benefit at the ETP
Cooler effluent suits the biological stage of an ETP, which works poorly when wastewater is too hot. Treat this as a side benefit, not part of the fuel saving.
Worked example: 200 kL a day of hot drain
- Hot drain 200 kL a day at 70 degrees C; fresh water 28 degrees C at an equal flow; effectiveness 60%
- Heat recovered: 0.60 x 2,00,000 kg x 4.186 x (70 minus 28) = 21,097,440 kJ, about 21.10 GJ a day; fresh water leaves at about 28 + 0.6 x 42 = 53 degrees C
- Boiler at 70% efficiency: 21.10 / 0.70 = 30.14 GJ of fuel a day
- Coal at 94.6 kg CO2 per GJ: 30.14 x 94.6 = 2,851 kg CO2 a day
- Pumps: 15 kW x 20 h = 300 kWh x 0.710 = 213 kg CO2 a day, so net 2,638 kg a day
- 300 working days: about 9,042 GJ of fuel and 791 t CO2 net
Flows, effectiveness, boiler efficiency and pump power are illustrative. Use measured drain flows and temperatures. The fuel line stays in GJ because the per-kg coal factor of 2.42 assumes coal of about 25.6 MJ per kg; weaker coal emits less per kg.
What Senseible does here
Senseible reads boiler fuel invoices and electricity bills, so the fuel saved and the extra pump power both show in the monthly Scope 1 and 2 records. Drain flows and temperatures come from your own measurements.
- Emissions saved by waste heat recovery
- ETP electricity per kL of effluent
- Low liquor ratio dyeing savings
- Textile industry
Sources: BEE Guide Book 2, Energy Efficiency in Thermal Utilities, Chapter 8 Waste Heat Recovery, 2006 IPCC Guidelines, Volume 2 (Energy), Chapter 2, Table 2.2
Last reviewed 2026-10-18.