High-Speed Centrifugal Spray Dryer

Overview

The high-speed centrifugal spray dryer turns a pumpable liquid — solution, suspension, emulsion or paste — straight into dry powder in one pass. A disc spinning at up to 25,000 rpm throws the feed into a mist, hot air meets the droplets in the chamber, and the water is gone in seconds. There is no filtering, no drying oven and no milling stage in between.

Models run from a 5 kg/h laboratory unit to production lines evaporating 2,000 kg of water per hour.

What it dries

The feed has to be pumpable. Beyond that the range is wide:

• Food — milk and whey powder, coffee, egg, soy and pea protein, flavourings, maltodextrin
• Pharmaceutical and biological — herbal extracts, antibiotics, vitamins, enzymes, probiotics
• Chemical — dyes, pigments, resins, catalysts, detergents, water treatment chemicals
• Ceramic and mineral — alumina, zirconia, ferrite and other slurries granulated for pressing
• Battery and nano materials — cathode precursors, nano oxides

If your material arrives as a wet filter cake or a stiff paste that cannot be pumped, it belongs in a spin flash dryer instead. Free-flowing granules that only need surface moisture removed belong in a fluid bed dryer.

Choosing the atomiser

This is the decision that shapes the whole machine, because the atomiser sets particle size and decides which feeds you can run:

For low-melting, high-sugar botanicals that soften and stick to the chamber wall, the herbal extract spray dryer adds the wall-cooling and scraping arrangements that problem needs.

Selecting a model

Size the dryer on the water it has to evaporate per hour, not on how much powder you want out. A feed at 20% solids carries four times the water of one at 50%, and it is the water that sets the machine.

Work out that duty, then read the Water Evaporation row of the specification table on this page. Inlet air runs 140–350°C and outlet 80–90°C across the range; the disc turns between 8,000 and 25,000 rpm depending on size, and disc diameter goes from 50 to 340 mm.

Check the height as well as the footprint. The 150 kg/h model stands 7 m tall, and chamber height is usually what decides whether a machine fits an existing building.

What keeps powder off the wall

Wall-sticking is the failure that ruins a spray-drying project, and two parts of the machine decide it:

• The air distributor shapes how hot air enters the chamber. Done properly it feeds air at even velocity, avoids local hot spots and steers the flow so sticky material meets less wall. Done badly, no amount of temperature tuning will save the run.
• The chamber design. A three-section body, with an air broom or vibration device where the material demands it, keeps the wall clear on feeds that would otherwise build up.

Cyclone and bag filter recover at least 95% of the powder and keep the exhaust within emission limits.

A limitation to plan for

Spray dryers are thermally inefficient. Typical thermal efficiency is 30–50% — you are heating a large volume of air to evaporate a comparatively small mass of water, and most of the energy leaves with the exhaust. On a large continuous line the running cost is a real number, and heat recovery on the exhaust is worth costing at the design stage rather than retrofitting later.

They are also tall, and the capital cost is significant relative to a fluid bed or flash dryer of the same evaporation duty. What you buy for that is a one-step route from liquid to finished powder, with particle size under control — which is often worth more than the energy bill.

Features

• Liquid to finished powder in one pass — no filtering, drying or milling in between
• Drying takes seconds, so heat-sensitive products keep their activity
• Particle size, bulk density and residual moisture set by atomiser speed and air temperature
• Electric, steam, oil or gas heating; electric control holds ±1°C
• At least 95% powder recovery through cyclone and bag filter
• PLC and touchscreen with inlet/outlet temperature and feed-pump control, trending and fault diagnosis
• Contact parts in 304 or 316L stainless steel; GMP arrangements available

Request a configuration

We build these to the material, so a model number alone is not enough to quote. Send:

• The material, and whether it is a solution, suspension, emulsion or paste
• Solids content of the feed, and the residual moisture you need in the powder
• Throughput — as litres of feed per hour, or kilograms of finished powder
• Particle size and bulk density requirements, if any
• Heat source available on site — electricity, steam, thermal oil, gas
• Any compliance requirement: GMP, CIP, ATEX, solvent recovery, closed-cycle nitrogen

Background reading: how spray drying works, types of spray dryer and spray dryer components.