Spray dryer inlet air preheated by heat pumps
How a 100 kg-per-hour spray dryer can preheat its inlet air to about 110 °C with heat pump hot water, cutting the furnace-oil burned in the main air heater.
▶Video: Hot air from heat pump hot water
V05 · 2–2.5 minAir coils for spray dryers, stenters, kilns, paint booths and ovens
Video coming soon01Problem statement
- All the air heat comes from fuel. Every kilogram of drying air is heated from ambient to the full inlet temperature with steam or oil.
- The first stage is low grade. Heating air from 30 to 110 °C is the largest part of the duty, and hot water is enough for it.
- Dryer runs long hours. Spray dryers run continuously between cleans, so the air heater is a large steady fuel user.
- Losses between fuel and process. Burning furnace oil 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 plant runs a spray dryer making about 100 kg of powder an hour from evaporated concentrate. It works two shifts on skim milk powder, with campaigns of egg powder and soluble coffee. Inlet air is drawn from ambient and heated by a steam coil followed by the main heater.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Inlet air preheating | Air 30 → 110 °C | 5,000 kg/h air × 1.006 kJ/kg·K × 80 K = 112 kW × 16 h | 1,788 |
| Concentrate preheating before atomiser | 50 → 70 °C | 200 kg/h × 16 h = 3,200 L at 48% solids | 64 |
| Storage and pipework standing losses | – | about 5% | 93 |
| Total useful heat | 1,945 | ||
Averaged over 16 running hours, the heat pumps need about 122 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
- A SE-UHT air-source cascade, R245fa machine of about 125 kW, air-source cascade to 120 °C, sized per project.
- A 4,000 L insulated storage tank decouples the heat pumps from the process peaks.
- The furnace-oil fired steam boiler and air heater stays connected behind a normally closed valve as standby.
- A hot-water coil is added upstream of the existing air heater. It lifts the inlet air to about 110 °C.
- The existing heater then provides only the last part of the lift to the final inlet temperature.
- The concentrate heater runs from the same hot-water loop, replacing a small steam user.
Selected equipment
| Machine | SE-UHT air-source cascade, R245fa |
|---|---|
| Capacity | about 125 kW, built to duty |
| Concept | air-source cascade to 120 °C, sized per project |
| COP used | 1.6 (estimate) |
| Supply temperature | 120 °C |
| Storage | 4,000 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 at the tank top starts the heat pumps below 112 °C and stops them at 120 °C. TIC-201 holds air leaving the pre-heater coil at 110 °C. The existing heater controller keeps the final inlet temperature as before and simply fires less. If the tank falls below 105 °C, the pre-heater valve closes and the main heater takes the full load.
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 powder | – | – |
| CO₂ per year | – | – |
06Benefits
Main heater fires less
The existing air heater only supplies the top part of the lift.
No change to drying conditions
Final inlet and outlet temperatures stay the same, so powder quality is unaffected.
Retrofit friendly
The coil fits in the existing inlet duct ahead of the current heater.
Lower energy cost
Each kWh of electricity delivers about 1.6 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.
Solar-ready
Running hours can be placed in daylight so rooftop solar supplies much of the electricity, which also cuts CO₂ further.
07Engineering pointers
Site data to collect
- Powder output and evaporation rate
- Inlet air flow, inlet and outlet temperatures
- Existing air heater type and fuel
- Running hours and CIP schedule
- Space in the inlet duct for a coil
- Present fuel or electricity use and monthly bill
- Sanctioned electrical load and spare capacity
- Space for the heat pumps and storage, with service access
- Winter minimum ambient at site
Design notes
- Pressurised hot water. At 115–120 °C the loop must be held above about 2.5 bar(g). Use a sealed system with expansion vessel and relief valve.
- Air-side pressure drop. The extra coil adds pressure drop. Check the supply fan has margin, and fit filters ahead of the coil.
- Exhaust heat. Exhaust air at 75–85 °C is a further heat source. It can be studied once the pre-heater is running.
- Ambient correction. Ratings are at 20 °C air. Ask Sunniva for the correction at your site's winter design temperature.
- 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
Spray dryer inlet air preheated by heat pumps
How a 100 kg-per-hour spray dryer can preheat its inlet air to about 110 °C with heat pump hot water, cutting the furnace-oil burned in the main air heater.
▶Video: Hot air from heat pump hot water
V05 · 2–2.5 minAir coils for spray dryers, stenters, kilns, paint booths and ovens
Video coming soon01Problem statement
- All the air heat comes from fuel. Every kilogram of drying air is heated from ambient to the full inlet temperature with steam or oil.
- The first stage is low grade. Heating air from 30 to 110 °C is the largest part of the duty, and hot water is enough for it.
- Dryer runs long hours. Spray dryers run continuously between cleans, so the air heater is a large steady fuel user.
- Losses between fuel and process. Burning furnace oil 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 plant runs a spray dryer making about 100 kg of powder an hour from evaporated concentrate. It works two shifts on skim milk powder, with campaigns of egg powder and soluble coffee. Inlet air is drawn from ambient and heated by a steam coil followed by the main heater.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Inlet air preheating | Air 30 → 110 °C | 5,000 kg/h air × 1.006 kJ/kg·K × 80 K = 112 kW × 16 h | 1,788 |
| Concentrate preheating before atomiser | 50 → 70 °C | 200 kg/h × 16 h = 3,200 L at 48% solids | 64 |
| Storage and pipework standing losses | – | about 5% | 93 |
| Total useful heat | 1,945 | ||
Averaged over 16 running hours, the heat pumps need about 122 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
- A SE-UHT air-source cascade, R245fa machine of about 125 kW, air-source cascade to 120 °C, sized per project.
- A 4,000 L insulated storage tank decouples the heat pumps from the process peaks.
- The furnace-oil fired steam boiler and air heater stays connected behind a normally closed valve as standby.
- A hot-water coil is added upstream of the existing air heater. It lifts the inlet air to about 110 °C.
- The existing heater then provides only the last part of the lift to the final inlet temperature.
- The concentrate heater runs from the same hot-water loop, replacing a small steam user.
Selected equipment
| Machine | SE-UHT air-source cascade, R245fa |
|---|---|
| Capacity | about 125 kW, built to duty |
| Concept | air-source cascade to 120 °C, sized per project |
| COP used | 1.6 (estimate) |
| Supply temperature | 120 °C |
| Storage | 4,000 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 at the tank top starts the heat pumps below 112 °C and stops them at 120 °C. TIC-201 holds air leaving the pre-heater coil at 110 °C. The existing heater controller keeps the final inlet temperature as before and simply fires less. If the tank falls below 105 °C, the pre-heater valve closes and the main heater takes the full load.
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 powder | – | – |
| CO₂ per year | – | – |
06Benefits
Main heater fires less
The existing air heater only supplies the top part of the lift.
No change to drying conditions
Final inlet and outlet temperatures stay the same, so powder quality is unaffected.
Retrofit friendly
The coil fits in the existing inlet duct ahead of the current heater.
Lower energy cost
Each kWh of electricity delivers about 1.6 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.
Solar-ready
Running hours can be placed in daylight so rooftop solar supplies much of the electricity, which also cuts CO₂ further.
07Engineering pointers
Site data to collect
- Powder output and evaporation rate
- Inlet air flow, inlet and outlet temperatures
- Existing air heater type and fuel
- Running hours and CIP schedule
- Space in the inlet duct for a coil
- Present fuel or electricity use and monthly bill
- Sanctioned electrical load and spare capacity
- Space for the heat pumps and storage, with service access
- Winter minimum ambient at site
Design notes
- Pressurised hot water. At 115–120 °C the loop must be held above about 2.5 bar(g). Use a sealed system with expansion vessel and relief valve.
- Air-side pressure drop. The extra coil adds pressure drop. Check the supply fan has margin, and fit filters ahead of the coil.
- Exhaust heat. Exhaust air at 75–85 °C is a further heat source. It can be studied once the pre-heater is running.
- Ambient correction. Ratings are at 20 °C air. Ask Sunniva for the correction at your site's winter design temperature.
- 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.