# How much fuel can a dye house save by recovering heat from hot drain water?

Canonical: https://senseible.earth/answers/dyehouse-hot-effluent-heat-recovery-saving

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](https://senseible.earth/answers/emissions-saved-by-waste-heat-recovery)
- [ETP electricity per kL of effluent](https://senseible.earth/answers/etp-electricity-per-kl-effluent)
- [Low liquor ratio dyeing savings](https://senseible.earth/answers/low-liquor-ratio-dyeing-steam-co2-saving)
- [Textile industry](https://senseible.earth/industries/textile)

Sources: [BEE Guide Book 2, Energy Efficiency in Thermal Utilities, Chapter 8 Waste Heat Recovery](https://beeindia.gov.in), [2006 IPCC Guidelines, Volume 2 (Energy), Chapter 2, Table 2.2](https://www.ipcc-nggip.iges.or.jp/public/2006gl/vol2.html)

Last reviewed 2026-10-18.