Drying with superheated steam at atmospheric pressure

Challenges

Drying is an essential process step in various branches of industry for the production, treatment and processing of solid materials. Conventional drying processes with hot air or flue gas often involve a long retention time and require considerable space. In many cases, drying represents the largest part of the energy consumption in the whole process chain.

 

Solution

Fraunhofer IGB offers a process for industrial users in which products are dried with superheated steam at atmospheric pressure. Several plants on laboratory and pilot-plant scales are available for studying and developing potential customer products.

Efficient drying process using superheated steam

© Fraunhofer IGB

Food dried in a superheated steam drying plant.

Using superheated steam as drying medium can provide significant advantages in terms of retention time, energy consumption and further aspects such as product quality. An advantages of this drying process is that valuable volatile compounds can be recovered selectively from the condensate to be recycled or further processed.

 

Applications

Fraunhofer IGB has already tested superheated steam drying (SHSD) in several projects with industrial partners for a wide variety of applications. The method was successful for drying organic fertilizers, mineral raw materials, construction materials and both food and feed stuffs in a gentle manner and was proved energy-efficient.

Systematic tests have proven that steam drying is also suitable for the hygienization of foodstuffs. For reference data, please see below (Projects).

Advantages of superheated steam drying

The use of superheated steam drying (SHSD) at atmospheric pressure has many advantages over conventional methods with hot air.

The oxygen content in the process atmosphere is low, thus preventing oxidation processes affecting the product and thereby contributing towards maintaining product quality. Degradation of valuable constituents, such as vitamins, is also prevented.

The thermodynamic properties of the drying medium (water vapor) allow more intensive heat and mass transfer during the drying process. This means that shorter residence times are achieved than with conventional drying methods, resulting in less damage to the products through thermal degradation during the drying process. The product quality is thereby enhanced. However, the high drying gradient can cause undesirable changes to the structure of the material. This risk can be addressed by volumetric preheating of the product with microwaves.

Furthermore, food products contain components in their material matrix that become volatile at significantly lower temperatures than the drying temperature of approx. 120–150°C. These compounds must be removed using exhaust air treatment in conventional drying plants. Thanks to the partially open reactor concept in SHSD, these compounds are collected together with the excess vapor and can be separated selectively and recovered as recyclable material. This means that these highly valuable compounds are not lost, but can make a significant contribution towards covering the costs of the drying process step.

The semi-open plant concept allows all conveyor techniques to be used, thus permitting the most suitable technique to be used for the food product.

The plants can be designed compact and energy-efficient due to the more rapid drying process.

Furthermore, the absence of atmospheric oxygen reduces the risk of explosion, resulting in a significantly simpler construction and operation.

Beispiele für getrocknete Güter

Examples of dried products.

Range of services

We accompany you from the first preliminary investigations through the realization of the developed plant concepts to the commissioning of a plant:

  • Scientific characterization and specification, research on tasks related to drying and heat transfer
  • Development of specific drying process concepts according to the individual needs of customers
  • Layout and specification of process by an interdisciplinary team with expertise in process engineering, design, chemistry, microbiology and electric engineering
  • Laboratory plants for test trials
  • Product-related analysis of the drying process with a wide range of analytic equipment and competences
  • Design specification of process unit and components, e.g. by integrated combination of 3D CAD design and numerical modeling of fluids, heat transfer etc., with latest software releases
  • Assisting and monitoring clients from first test trials up to commissioning of a plant
We will be happy to make you an individual offer.

Recovery and valorization of condensate

Range of services and equipment

This page gives you a quick overview of our R&D services and the technical infrastructure.

Torrefaction with superheated steam

We have further developed the technology for energy-efficient torrefaction of biomass residues.

Reference projects

HiPerDry – A novel microwave-enhanced superheated steam process for high performance drying of hygroscopic polymers

Project duration: October 2013 – September 2016

Aim of HiPerDry was the development of a new drying technology for hygroscopic plastics. The new approach combining microwave heating with superheated steam convective drying will not only lead to significant savings in energy costs, but also allow time efficient drying of thermo-sensitive bioplastics.

more info

MCure – Development and demonstration of accelerated low energy curing in the repair and refurbishment of concrete structures

Project duration: January 2013 – September 2015

In this project, a new energy-efficient system will be developed to improve and accelerate hardening of the repaired concrete patches during renovation – and thus save costs.

more info

DryCheck – Electrical impedance-based system to monitor drying process in sausages

Project duration: September 2011 – August 2014

The DryCheck project will provide SMEs with a practical multisensory-based tool to facilitate monitoring and controlling the quality of dry fermented sausages during drying with a user-friendly albeit advanced technology at an affordable price.

more info