Abstract:
In many industries such as food, chemicals, building materials and pharmaceuticals, drying is an indispensable process link. From the dehydration of fruits and vegetables, the preservation of grains and spices, to the production of milk powder, instant coffee, fertilizers, textiles and pharmaceuticals, drying is indispensable. However, the currently widely used hot air drying method has high energy consumption, and the energy required still mainly comes from natural gas combustion, which not only brings considerable carbon emissions, but also causes a large amount of waste heat to be directly lost.
Fraunhofer Institute for Interface Engineering and Biotechnology, Germany Researchers at IGB are exploring alternatives: using electricity to generate superheated steam, drying it in a closed system and recovering and recycling the heat to improve the energy efficiency and sustainability of industrial drying processes.
The so-called superheated steam refers to dry steam that is heated to a temperature exceeding its vaporization temperature after water boils and vaporizes. The system proposed by the research team uses high-temperature superheated steam to remove moisture from wet materials, subsequently producing excess steam containing moisture. Instead of venting this part of the steam directly into the air in the traditional process, the new system will first cool it and condense it into water, while recovering the heat energy at a temperature of about 90 to 100 degrees Celsius for use in other industrial processes.
To further improve efficiency, the researchers also added a special heat pump to the drying device. Heat pumps compress excess steam and increase its temperature so that the heat can be recovered and used for subsequent drying. Compared with the traditional model of continuously heating fresh air and then letting part of the heat escape, this solution is equivalent to repeatedly "reusing" the same heat energy in a closed system.
The system also integrates intelligent control functions to determine the best operating time of the drying equipment. For manufacturing companies that rely on renewable energy sources such as wind power and photovoltaics, this means that equipment can choose to operate during periods when green power supply is sufficient and electricity prices are lower, thereby further reducing operating costs.
Superheated steam technology can be adapted to a variety of drying equipment, including belt dryers, drum dryers and spray dryers. The research team's goal is to reduce drying energy consumption to one-half to one-quarter compared to traditional technology. The actual effect will be affected by factors such as drying method and temperature level.
Researchers have conducted laboratory tests on mineral raw materials, building materials and food. The results show that this new drying technology can reduce energy consumption by up to 80% if combined with a heat pump and intelligent control system. Currently, a spray drying pilot system using superheated steam has been put into operation, indicating that the technology is taking a step closer to practical industrial applications.
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