Dye baths heated from the dye-house drain
How a 3-tonne-a-day knit dye-house can heat its 60–95 °C dye and soaping baths with heat pumps that recover heat from hot 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
- Heat poured down the drain. Spent dye baths and soaping liquors leave the machines at 50 to 90 °C and go straight to the effluent plant, taking most of their heat with them.
- Slow heating with steam. Machine heat exchangers fed by a distant boiler give slow and uneven heating gradients, which affects shade repeatability.
- Hot effluent hurts the ETP. Warm effluent above 40 °C upsets biological treatment and may need cooling before the aeration tank.
- 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 dye-house processes 3 tonnes of cotton and polyester knit fabric a day in soft-flow machines. It runs three shifts and dumps hot dye, soaping and rinse liquors to the effluent plant.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Reactive dye baths | 60 °C | 2,000 kg fabric × 1:6 liquor = 12,000 L, 30 → 60 °C | 418 |
| Soaping and wash-off | 90 °C | 12,000 L/day, 30 → 90 °C | 836 |
| Disperse dye baths (carrier) | 95 °C | 1,000 kg fabric × 1:6 liquor = 6,000 L, 30 → 95 °C | 453 |
| Storage and pipework standing losses | – | about 5% | 85 |
| Total useful heat | 1,792 | ||
Averaged over 20 running hours, the heat pumps need about 90 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
- 4 × SE-WWUHT-27 (108 kW total) (SE-WWUHT water-source, R245fa) delivering 105 °C, covering the day's 1,792 kWh in about 16.6 running hours.
- A 3,500 L insulated storage tank decouples the heat pumps from the process peaks.
- Heat source: hot dye-house drain water at about 50 °C. Cooling the drain water before the ETP protects the biological treatment stage.
- The briquette-fired steam boiler stays connected behind a normally closed valve as standby.
- Hot drain water is collected in a lined sump, screened for lint and passed through a cleanable heat exchanger that feeds the heat pump evaporator.
- The heat pumps charge a hot-water tank at 100–105 °C. Machines fill with hot water and heat through their own exchangers from the secondary loop.
- Filling machines with hot water from TK-202 removes most of the heat-up time from each cycle.
Selected equipment
| Model | SE-WWUHT-27 × 4 |
|---|---|
| Heating capacity | 27 kW each, 108 kW total |
| COP | 2.6 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 | 105 °C |
| Storage | 3,500 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 starts the heat pumps below 98 °C and stops them at 105 °C, as long as the drain sump level is above minimum. TIC-201 on each machine follows its dyeing curve by modulating the hot-water valve. If the tank falls below 85 °C or drain water runs short, the PLC alarms and the existing steam supply takes over.
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
Heat recovered twice
Heat from spent baths goes back into the next fill instead of to the ETP.
Better shade repeatability
Hot-water heating follows the programmed gradient more closely than throttled steam.
Cooler effluent
Drain water leaves the recovery exchanger at about 25 to 30 °C, which suits biological treatment.
Lower energy cost
Each kWh of electricity delivers about 2.6 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 dyed per day by type
- Liquor ratio and dyeing programmes
- Drain volumes and temperatures per cycle
- Boiler fuel use per day
- Space for a drain sump near the machines
- 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
- Lint and fouling. Drain water carries fibre and dye. Use a self-cleaning screen and a wide-gap or removable-plate exchanger on the drain side, never the heat pump evaporator directly.
- Drain timing. Hot drops are intermittent. A drain sump of at least one hour's flow evens out the heat supply to the heat pumps.
- Alkali and salt. Reactive dye liquors are alkaline and salty. Specify stainless steel 316 or titanium plates on the drain side.
- 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
Dye baths heated from the dye-house drain
How a 3-tonne-a-day knit dye-house can heat its 60–95 °C dye and soaping baths with heat pumps that recover heat from hot 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
- Heat poured down the drain. Spent dye baths and soaping liquors leave the machines at 50 to 90 °C and go straight to the effluent plant, taking most of their heat with them.
- Slow heating with steam. Machine heat exchangers fed by a distant boiler give slow and uneven heating gradients, which affects shade repeatability.
- Hot effluent hurts the ETP. Warm effluent above 40 °C upsets biological treatment and may need cooling before the aeration tank.
- 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 dye-house processes 3 tonnes of cotton and polyester knit fabric a day in soft-flow machines. It runs three shifts and dumps hot dye, soaping and rinse liquors to the effluent plant.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Reactive dye baths | 60 °C | 2,000 kg fabric × 1:6 liquor = 12,000 L, 30 → 60 °C | 418 |
| Soaping and wash-off | 90 °C | 12,000 L/day, 30 → 90 °C | 836 |
| Disperse dye baths (carrier) | 95 °C | 1,000 kg fabric × 1:6 liquor = 6,000 L, 30 → 95 °C | 453 |
| Storage and pipework standing losses | – | about 5% | 85 |
| Total useful heat | 1,792 | ||
Averaged over 20 running hours, the heat pumps need about 90 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
- 4 × SE-WWUHT-27 (108 kW total) (SE-WWUHT water-source, R245fa) delivering 105 °C, covering the day's 1,792 kWh in about 16.6 running hours.
- A 3,500 L insulated storage tank decouples the heat pumps from the process peaks.
- Heat source: hot dye-house drain water at about 50 °C. Cooling the drain water before the ETP protects the biological treatment stage.
- The briquette-fired steam boiler stays connected behind a normally closed valve as standby.
- Hot drain water is collected in a lined sump, screened for lint and passed through a cleanable heat exchanger that feeds the heat pump evaporator.
- The heat pumps charge a hot-water tank at 100–105 °C. Machines fill with hot water and heat through their own exchangers from the secondary loop.
- Filling machines with hot water from TK-202 removes most of the heat-up time from each cycle.
Selected equipment
| Model | SE-WWUHT-27 × 4 |
|---|---|
| Heating capacity | 27 kW each, 108 kW total |
| COP | 2.6 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 | 105 °C |
| Storage | 3,500 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 starts the heat pumps below 98 °C and stops them at 105 °C, as long as the drain sump level is above minimum. TIC-201 on each machine follows its dyeing curve by modulating the hot-water valve. If the tank falls below 85 °C or drain water runs short, the PLC alarms and the existing steam supply takes over.
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
Heat recovered twice
Heat from spent baths goes back into the next fill instead of to the ETP.
Better shade repeatability
Hot-water heating follows the programmed gradient more closely than throttled steam.
Cooler effluent
Drain water leaves the recovery exchanger at about 25 to 30 °C, which suits biological treatment.
Lower energy cost
Each kWh of electricity delivers about 2.6 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 dyed per day by type
- Liquor ratio and dyeing programmes
- Drain volumes and temperatures per cycle
- Boiler fuel use per day
- Space for a drain sump near the machines
- 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
- Lint and fouling. Drain water carries fibre and dye. Use a self-cleaning screen and a wide-gap or removable-plate exchanger on the drain side, never the heat pump evaporator directly.
- Drain timing. Hot drops are intermittent. A drain sump of at least one hour's flow evens out the heat supply to the heat pumps.
- Alkali and salt. Reactive dye liquors are alkaline and salty. Specify stainless steel 316 or titanium plates on the drain side.
- 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.