Hot-air drying is important in pretty much all the modern industries you can think of. It’s used to dry fruits and vegetables, preserve grains and spices, and make everything from powdered milk and instant coffee to fertilizers, fabrics, and medicines. Evaporating all that moisture with hot air takes a lot of energy. Most of that energy still comes from burning natural gas, and there are a few serious issues with that.
Not only does it produce a lot of carbon emissions, but it also wastes a lot of the heat as it simply escapes into the atmosphere – just like when we use a hair dryer. Now, imagine using a giant hair dryer on an industrial scale: the heat loss multiplies by thousands of times, which means huge amounts of wasted energy and money.
That’s why the researchers at the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB have been looking for a more efficient alternative, and they may have found one. Their idea is pretty straightforward: use electricity-generated superheated steam, keep it inside the enclosed system, and reuse it instead of letting it escape.
Superheated steam is essentially dry steam that has been heated beyond its vaporization point: in simple words, we heat water until it boils and becomes steam, and then we heat that steam even more.
When hot steam evaporates moisture from wet materials, it creates excess steam containing that moisture. Instead of just releasing it into the atmosphere, the new technology cools the steam down until it condenses back into water. At the same time, the system also recovers heat at around 90-100 °C (194-212 °F), which can then be reused in other industrial processes.
The researchers also figured out how to put that excess steam back to work in the dryer itself. To achieve that and make the new method even more efficient, they added a special heat pump. It compresses the excess steam, which increases its temperature, so the heat can be recovered and reused for drying. Think of it as recycling the same heat in a closed container instead of constantly heating more new air and letting part of it escape.
There’s also an integrated smart control system that helps decide when the dryer should run, which would be especially beneficial for manufacturers that rely on green energy. Since the amount of electricity produced by wind and solar power changes throughout the day, the system can activate the dryer only when renewable electricity is plentiful and cheaper, helping cut operating costs.
Superheated steam technology can be used in different types of dryers, including belt, drum, and spray dryers. The ultimate goal is to reduce the energy needed for drying by a factor of two to four compared with traditional methods. The final results will also depend on the drying method and temperature level.
Laboratory testing was carried out on mineral raw materials, construction materials, and food and showed that, combined with heat pumps and smart controls, the new technology could reduce energy consumption by up to 80%, which is a very impressive result.
The pilot system for superheated-steam spray drying has already been put into operation, which means the technology is getting one step closer to real-world use.
Source: Fraunhofer
