Scouring and bleaching heated by its own drain
How a processing house pre-treating 2 tonnes of cotton a day can heat scouring, bleaching and wash water to 60–90 °C with heat pumps on washer drain water, against a briquette-fired boiler.
▶Video: Heat pumps for textile and leather processing
V03 · 2–2.5 minDyeing, pre-treatment and tanning, with heat recovered from hot drain water
Video coming soon01Problem statement
- Large hot-water volumes. Pre-treatment uses more hot water per kilogram of fabric than any other wet process, mostly at 70 to 90 °C.
- Live steam dilutes and wastes. Many machines are heated by direct steam injection, which adds water, loses condensate and gives uneven bath temperatures.
- Hot wash water to drain. Rinse and wash water leaves at 50 to 70 °C, so a large part of the heat input goes straight to effluent.
- Losses between fuel and process. Burning briquettes in a boiler or heater and distributing the heat loses a quarter or more of the fuel's energy before it reaches the process.
- Compliance, safety and handling. Fired equipment brings boiler inspections, fuel storage and unloading, flue emissions and an attendant on every shift.
02Use case
The reference unit scours, bleaches and washes about 2 tonnes of cotton fabric and yarn a day in batch machines and washers. It works three shifts and drains hot wash liquors continuously.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Combined scour and bleach | 90 °C | 2,000 kg × 1:5 liquor = 10,000 L, 30 → 90 °C | 697 |
| Hot wash after bleaching | 70 °C | 10,000 L/day, 30 → 70 °C | 464 |
| Neutralisation and warm rinse | 60 °C | 10,000 L/day, 30 → 60 °C | 348 |
| Storage and pipework standing losses | – | about 5% | 75 |
| Total useful heat | 1,585 | ||
Averaged over 20 running hours, the heat pumps need about 79 kW.
03P&ID
Tags: HP heat pump, TK tank, SG steam generator, P pump, PHE plate heat exchanger, TCV temperature control valve, TIC temperature indicating controller (panel), TT temperature transmitter, MT moisture transmitter, PT pressure transmitter, LT level transmitter, FS flow switch, NC normally closed. Process fluids are heated through their own exchanger, coil or jacket.
04Solution
System description
- 3 × SE-WWUHT-27 (81 kW total) (SE-WWUHT water-source, R245fa) delivering 95 °C, covering the day's 1,585 kWh in about 19.6 running hours.
- A 2,500 L insulated storage tank decouples the heat pumps from the process peaks.
- Heat source: hot washer drain water at about 50 °C. Drain water leaves the recovery exchanger cooler, which helps the ETP.
- The briquette-fired steam boiler stays connected behind a normally closed valve as standby.
- Washer drain water is screened and passed through a recovery exchanger, which supplies the heat pump source loop at about 50 °C.
- Machines are converted from live steam to indirect heating from the hot-water loop, keeping liquor volumes and chemical strength stable.
- Hot and warm rinse tanks are filled from the heat pump tank, so rinsing starts at the right temperature.
Selected equipment
| Model | SE-WWUHT-27 × 3 |
|---|---|
| Heating capacity | 27 kW each, 81 kW total |
| COP | 2.93 estimated for a 50 °C source (the data sheet is rated on a 60/55 °C source) |
| Rating | water or steam to 120 °C, R245fa |
| Supply temperature | 95 °C |
| Storage | 2,500 L insulated tank |
Capacity is sized from the heat demand above. COP is an estimate until Sunniva engineering confirms the design.
Control philosophy
TT-101 holds the tank between 88 and 95 °C, with the heat pumps enabled only while the drain sump has water. TIC-201 to TIC-203 control each user by its own valve. When drain heat or tank temperature is short, the existing steam supply is the standby.
05Energy saving and ROI
Change any input to match a customer's site. Defaults are typical Indian prices for October 2026. The installed cost is a placeholder; replace it with the actual quotation.
| Existing | Heat pump | |
|---|---|---|
| Daily consumption | – | – |
| Annual energy cost | – | – |
| Cost per tonne of fabric | – | – |
| CO₂ per year | – | – |
06Benefits
Stable bath chemistry
Indirect heating stops steam condensate diluting the peroxide and caustic baths.
Wash heat recycled
Heat in the drain water preheats the next batch instead of warming the effluent.
Even bath temperature
Hot-water heating avoids hot spots near steam spargers that can weaken fabric.
Lower energy cost
Each kWh of electricity delivers about 2.9 kWh of heat at the required temperature, against well under one kWh of useful heat per kWh of fuel burnt.
No flame on site
No burner, flue or fuel tank for this duty, and no fuel deliveries to schedule.
Built-in redundancy
Several machines share the load. If one is serviced, the others and the storage carry most of the day, with the existing heater in reserve.
07Engineering pointers
Site data to collect
- Fabric and yarn pre-treated per day
- Liquor ratios and process temperatures
- Drain flow and temperature from washers
- Present heating method (live or indirect steam)
- Fuel use per day
- Present fuel or electricity use and monthly bill
- Sanctioned electrical load and spare capacity
- Space for the heat pumps and storage, with service access
Design notes
- Peroxide and alkali. Bleach liquors contain hydrogen peroxide and caustic. Use stainless steel 316 on wetted parts and avoid copper alloys on the drain side.
- Scale. Hard water scales hot surfaces at 90 °C. Use softened water in the hot-water loop and fill tanks.
- Lint. Cotton lint blocks plate exchangers. Fit a rotary screen ahead of the drain recovery exchanger.
- Source stream. The source must give up roughly two-thirds of the heat delivered. Confirm its flow and temperature over a full production day, and filter it before the evaporator.
- Water quality. Scale forms quickly above 60 °C. Use softened make-up and keep the heat pump loop closed, with process fluids on the far side of an exchanger or coil.
- Performance figure. The COP on this page is an engineering estimate, not a data sheet value. Sunniva engineering will confirm it for the actual source and supply temperatures.
Service and warranty
Sunniva has supplied 5,000+ heat pumps since 2012, with nine service technicians across India, including remote sites such as Leh. All components carry a one-year warranty.
Talk to us
Scouring and bleaching heated by its own drain
How a processing house pre-treating 2 tonnes of cotton a day can heat scouring, bleaching and wash water to 60–90 °C with heat pumps on washer drain water, against a briquette-fired boiler.
▶Video: Heat pumps for textile and leather processing
V03 · 2–2.5 minDyeing, pre-treatment and tanning, with heat recovered from hot drain water
Video coming soon01Problem statement
- Large hot-water volumes. Pre-treatment uses more hot water per kilogram of fabric than any other wet process, mostly at 70 to 90 °C.
- Live steam dilutes and wastes. Many machines are heated by direct steam injection, which adds water, loses condensate and gives uneven bath temperatures.
- Hot wash water to drain. Rinse and wash water leaves at 50 to 70 °C, so a large part of the heat input goes straight to effluent.
- Losses between fuel and process. Burning briquettes in a boiler or heater and distributing the heat loses a quarter or more of the fuel's energy before it reaches the process.
- Compliance, safety and handling. Fired equipment brings boiler inspections, fuel storage and unloading, flue emissions and an attendant on every shift.
02Use case
The reference unit scours, bleaches and washes about 2 tonnes of cotton fabric and yarn a day in batch machines and washers. It works three shifts and drains hot wash liquors continuously.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Combined scour and bleach | 90 °C | 2,000 kg × 1:5 liquor = 10,000 L, 30 → 90 °C | 697 |
| Hot wash after bleaching | 70 °C | 10,000 L/day, 30 → 70 °C | 464 |
| Neutralisation and warm rinse | 60 °C | 10,000 L/day, 30 → 60 °C | 348 |
| Storage and pipework standing losses | – | about 5% | 75 |
| Total useful heat | 1,585 | ||
Averaged over 20 running hours, the heat pumps need about 79 kW.
03P&ID
Tags: HP heat pump, TK tank, SG steam generator, P pump, PHE plate heat exchanger, TCV temperature control valve, TIC temperature indicating controller (panel), TT temperature transmitter, MT moisture transmitter, PT pressure transmitter, LT level transmitter, FS flow switch, NC normally closed. Process fluids are heated through their own exchanger, coil or jacket.
04Solution
System description
- 3 × SE-WWUHT-27 (81 kW total) (SE-WWUHT water-source, R245fa) delivering 95 °C, covering the day's 1,585 kWh in about 19.6 running hours.
- A 2,500 L insulated storage tank decouples the heat pumps from the process peaks.
- Heat source: hot washer drain water at about 50 °C. Drain water leaves the recovery exchanger cooler, which helps the ETP.
- The briquette-fired steam boiler stays connected behind a normally closed valve as standby.
- Washer drain water is screened and passed through a recovery exchanger, which supplies the heat pump source loop at about 50 °C.
- Machines are converted from live steam to indirect heating from the hot-water loop, keeping liquor volumes and chemical strength stable.
- Hot and warm rinse tanks are filled from the heat pump tank, so rinsing starts at the right temperature.
Selected equipment
| Model | SE-WWUHT-27 × 3 |
|---|---|
| Heating capacity | 27 kW each, 81 kW total |
| COP | 2.93 estimated for a 50 °C source (the data sheet is rated on a 60/55 °C source) |
| Rating | water or steam to 120 °C, R245fa |
| Supply temperature | 95 °C |
| Storage | 2,500 L insulated tank |
Capacity is sized from the heat demand above. COP is an estimate until Sunniva engineering confirms the design.
Control philosophy
TT-101 holds the tank between 88 and 95 °C, with the heat pumps enabled only while the drain sump has water. TIC-201 to TIC-203 control each user by its own valve. When drain heat or tank temperature is short, the existing steam supply is the standby.
05Energy saving and ROI
Change any input to match a customer's site. Defaults are typical Indian prices for October 2026. The installed cost is a placeholder; replace it with the actual quotation.
| Existing | Heat pump | |
|---|---|---|
| Daily consumption | – | – |
| Annual energy cost | – | – |
| Cost per tonne of fabric | – | – |
| CO₂ per year | – | – |
06Benefits
Stable bath chemistry
Indirect heating stops steam condensate diluting the peroxide and caustic baths.
Wash heat recycled
Heat in the drain water preheats the next batch instead of warming the effluent.
Even bath temperature
Hot-water heating avoids hot spots near steam spargers that can weaken fabric.
Lower energy cost
Each kWh of electricity delivers about 2.9 kWh of heat at the required temperature, against well under one kWh of useful heat per kWh of fuel burnt.
No flame on site
No burner, flue or fuel tank for this duty, and no fuel deliveries to schedule.
Built-in redundancy
Several machines share the load. If one is serviced, the others and the storage carry most of the day, with the existing heater in reserve.
07Engineering pointers
Site data to collect
- Fabric and yarn pre-treated per day
- Liquor ratios and process temperatures
- Drain flow and temperature from washers
- Present heating method (live or indirect steam)
- Fuel use per day
- Present fuel or electricity use and monthly bill
- Sanctioned electrical load and spare capacity
- Space for the heat pumps and storage, with service access
Design notes
- Peroxide and alkali. Bleach liquors contain hydrogen peroxide and caustic. Use stainless steel 316 on wetted parts and avoid copper alloys on the drain side.
- Scale. Hard water scales hot surfaces at 90 °C. Use softened water in the hot-water loop and fill tanks.
- Lint. Cotton lint blocks plate exchangers. Fit a rotary screen ahead of the drain recovery exchanger.
- Source stream. The source must give up roughly two-thirds of the heat delivered. Confirm its flow and temperature over a full production day, and filter it before the evaporator.
- Water quality. Scale forms quickly above 60 °C. Use softened make-up and keep the heat pump loop closed, with process fluids on the far side of an exchanger or coil.
- Performance figure. The COP on this page is an engineering estimate, not a data sheet value. Sunniva engineering will confirm it for the actual source and supply temperatures.
Service and warranty
Sunniva has supplied 5,000+ heat pumps since 2012, with nine service technicians across India, including remote sites such as Leh. All components carry a one-year warranty.