Radio wave technology platform for environmental process engineering

Radio wave heating   photo: André Künzelmann / UFZ In many environmentally relevant technical processes material heating is a crucial step. Technologies like off gas cleaning, drying and decontamination of brickwork as well as thermally enhanced soil vapour extraction or thermally initiated reactive immobilisation require heating steps. The application of radio waves (RW) provides due to its special for almost all non-conductive materials a unique heating possibility.

Beside a rapid dielectric heating in the temperature range from -20°C to 400°C a homogeneous heating of volumes in the cubic meter range is a major advantage of RW heating. Due to direct heat production within the volume neither heat carrier gases nor heating surfaces are needed leading to a more flexible process engineering. In addition, the possibility of selective heating governed by several parameters like electrode design, gas pressure, main diameter of the heated particles or dielectric material properties is a further unique aspect of this heating technique.

With the experience of more then 15 years the Department of Environmental Engineering uses RW technology (with a frequency of 13.56 MHz) as a tool to develop new technical concepts and processes in different areas of environmental engineering. The focus is on an applied research to find technical solutions for problems in heating and energy-transfer processes in industry and society. Thereby, development does not stop at the lab scale. The main goal consists in up-scaling of new technologies to the pilot plant and, finally, to a technical scale in cooperation with companies.

The thermally enhanced soil vapour extraction for in situ soil remediation, as the starting point of research on RW heating at the UFZ, has been successfully implemented by two companies being active in the field of soil remediation. Today, RW heating in the Department of Environmental Engineering has a focus in the following fields:

Mode of action of dielectric heating                     

mode of action of dielectric heating   scheme: Markus Kraus  / UFZ

Dielectric heating using radio waves is a direct heating technique. This means, electric energy is transferred by an electromagnetic wave into the volume of a material. There the energy will be converted into heat due to relaxation processes on a microscopic scale.

These relaxation processes are caused by interactions of charged particles with high frequency electrical fields. In non-conductive materials these particles are often represented by dipole molecules exhibiting a negative and a positive charge. In general, dipoles align in the direction of the applied field. This effect is called polarization. In an oscillating field dipoles will permanently realign. For low frequencies dipole realignment is nearly loss-free, with other words, no heat will be produced within the material. By raising the frequency of the external field the inner friction increases due to dipole-molecule and dipole-dipole interactions as well as the inertia of the dipoles itself resulting in internal heat production. As consequence, the temperature of the material increases.