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What hot condensate down the drain costs a Bangladesh dye house
In many dye houses the condensate runs to the drain at 90°C. We costed bringing more of it back to the boiler.
US$61,000
of gas a year goes down the drain as hot condensate
- 28,800 m³of treated, hot water back in the boiler each year
- 478 tof CO₂ avoided each year
The problem
Walk behind the dyeing machines in a lot of factories in Gazipur and Narayanganj and you'll find a pipe running hot water into the drain. That is condensate. A few minutes earlier it was boiler water that had already been treated and heated once.
Once it's gone, the boiler house replaces it with fresh water at about 30°C, treats it again and heats it all the way up again. The factory pays for that heat twice. The hot water then lands in the effluent treatment plant, which has to cool it and handle the extra volume.
We took a 10-tonne-per-hour boiler serving a dyeing and finishing unit, running 7,200 hours a year and returning 20% of its condensate. A recovery system raises that to 60%.
The working
Each line follows from the one before it. The inputs and their sources are listed further down, so you can redo it with your own numbers.
Where the boiler's water goes, t a year
Today
Returned to the boiler 14,400To the drain 57,600
With recovery
Returned to the boiler 43,200To the drain 28,800
Extra condensate returned
steam output × hours × (return after − return today)
= 10 t/h × 7,200 h × (60% − 20%)
= 28,800 t a year
Heat that comes back with it
water × specific heat × (condensate − make-up temperature)
= 28,800 t × 4.19 kJ/kg·K × (90°C − 30°C)
= 7,240 GJ a year
Gas the boiler no longer burns
heat ÷ boiler efficiency ÷ calorific value
= 7,240 GJ ÷ 85% ÷ 0.034 GJ/m³
= 250,530 m³ a year
Money
gas saved × tariff ÷ exchange rate
= 250,530 m³ × BDT 30 ÷ 123.55
= US$60,833 a year
Carbon
gas saved × calorific value × CO₂ factor
= 250,530 m³ × 0.034 GJ/m³ × 56.1 kg CO₂/GJ
= 478 t CO₂ a year
The fix
Condensate recovery is mostly plumbing: return lines from the machines to a receiver tank near the boiler house, and a pump that lifts the water back to the feed tank. Some streams can pick up dye or chemicals, so they get a conductivity check and a valve that sends a bad batch to drain on its own.
Factories on the higher tariff for new gas connections, BDT 40 per cubic metre, save a third more. The water that stops going to the drain also takes load off the ETP.
What would change the answer
Not every stream can come back. Long pipe runs, the risk of contamination and machines that discharge at low pressure all limit the return.
A site survey maps each source of condensate and decides which ones are worth the pipe. That survey is where your own figure comes from.
Inputs and sources
- Boiler steam output10 t/hAssumption for a typical site, dyeing and finishing unit
- Operating hours7,200 h a yearAssumption for a typical site
- Condensate returned today20%Assumption for a typical site
- Condensate returned after recovery60%Assumption for a typical site
- Condensate temperature90 °CAssumption for a typical site
- Make-up water temperature30 °CAssumption for a typical site
- Specific heat of water4.19 kJ/kg·KPhysical constant
- Boiler efficiency85%Assumption for a typical site
- Natural gas net calorific value0.034 GJ/m³Typical Bangladesh pipeline gas
- Industrial boiler gas, existing connection30 BDT/m³BERC order, April 2025; new connections BDT 40
- BDT per USD123.55 BDT/USDBangladesh Bank reference rates, 18 Oct 2026
- Natural gas CO₂ factor56.1 kg CO₂/GJIPCC 2006 default
Services behind this example
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