What is Spray Cooling?

Spray cooling (alternatively spray congealing) is defined as a process by which a melt is formed into particles of spherical shape by spraying the melt into a cooling chamber through which ambient or cooled, low temperature air is passing. Rotary (wheel) atomisers and nozzles are used to spray the melt. Spray cooling finds application in the chemical, food, and pharmaceutical industries. It is a most convenient method of transforming melted feed stocks into free-flowing particulates of controlled particle size.

Reference Products

Spray Cooler is used for following products:

• Fats
• Glycerides (GMS/DMG)
• Hydrates
• Inorganic/organic melts
• Quaternary ammonium compounds
• Stearic acid/stearates , and
• Waxes

The selection of a spray cooling plant design depends upon the particle size specified as well as the need for post-cooling/crystallisation for the cooled product. Fine particle products with mean particle size 50-150 micron; co-current conical based cooling chamber with high-speed rotary atomisation. Coarse particle products with mean particle size 150-300 micron; conical based cooling chamber with fountain nozzle.

Importance of Melt Properties

Products that form melts have a solidification curve. When a spray of melt droplets contacts a cool air environment, the melt cools to a solidification temperature. Congealing then takes place at a constant temperature during release of the product's heat of solidification. When no longer in a fluid state, the droplets further cool to give stable solid particulate forms.

Utilising closed cycle spray cooling enables optimisation of cooling energy require-ments and product quality

Plant operation in warm and humid climates will normally require the ambient air supply to the spray cooler to be dehumidified and cooled. To reduce the extra energy consumption involved, it is common practice to recycle the process air, thereby minimising the load on the dehumidification/cooling unit.

The recycle system is designed to permit a bleed of air from the system, enabling an intake of ambient air in cases, where there is a degree of evaporation associated with the spray cooling. The multi-way damper incorporated in the recycle system also allows the plant to run in open cycle without the dehumidification/cooling unit in operation during the colder and dryer seasons of the year. This reduces operational costs.

The main components of a Spray Cooler are:
Cooling chamber; Conveying duct; Cyclone separator; Centrifugal fans; Heat exchanger; Feed tank - jacketed; Feed pump; Feed line and spraying nozzle, and; Instruments - pressure switch, SRV, temperature controller, VFD.

Working Principle of the Spray Cooler

• Hot melt is sprayed in the cooling chamber that consists cool air
• Heat transfer takes place between hot particle and cool air, forming fine powder
• Proper cooing and particle hardening of particle takes place in conveying duct
• In cyclone separator air and powder gets separated and powder is discharged through rotary valve
• Air containing less amount of fine particles comes to centrifugal fan, and
• The air gets chilled in heat exchanger and again supplied to the chamber.

Salient Features of the Supreet Spray Cooler

• Single point collection of powder. This ensures less handling of finish product
• No mitre bends in the ducting avoids material deposition in the system
• Pressure from 10 kg/cm2 to 200 kg/cm2 can be achieved
• Thick slurries can be handled and sprayed by giving high pressure
• Very low maintenance is required (periodical cleaning of heat exchanger tubes)
• All valves are jacketed only- avoids external heating of valve body during start up, and
• Total plant is automatic and no man interference is required. Only one man for the powder collection is required.

(Contact: Mr Anil R Deshpande (Director-Technical), Supreet Engineers Pvt Ltd, Pune. Tel: 020-66307824. Mobile: 092256-28902. Fax: 91-20-27122451. Email: supreet.anil@gmail.com)