Generating green energy is currently an absolute priority to respect the environment and strive towards a sustainable society. Thermosolar systems, of which compound parabolic concentrator (CPC) systems are the most developed, are amongst the technologies that have proven their added value in this area. Substances can also be released within this context that could be an issue if emitted into the atmosphere. Desotec solutions are an appropriate remedy for this challenge.

The radiation of the sun is concentrated in long, straight tubes through cylindrical parabolic solar collectors in compound parabolic concentrator (CPC) systems. These tubes are essential for heating the heat transfer fluid (HTF), a synthetic organic fluid that is crucial for heat transfer.

This fluid is a mixture of biphenyl and diphenyl ether. It can quickly reach temperatures of up to 400°C without it leading to evaporation and/or an increase of volume, which would be the case with standard water. A negative consequence of this high temperature is the formation of VOCs (volatile organic compounds) such as benzene, toluene, ethylbenzene, xylene (BTEX), naphthalene, diphenyl ether and biphenyl. Those responsible for the thermosolar systems must prevent these substances from entering the atmosphere. This is prevented to the greatest extent possible through an expansion vessel and different separation processes, but a contaminated gas flow will always remain.

A Spanish company that runs five such CPC plants of 50 MW each was searching for a suitable solution for this and contacted Desotec at their own initiative. After a thorough analysis based on a few extensive measuring campaigns, the decision was taken to use two AIRCON 3000 filters in series set-up. They were filled with activated carbon that adsorbs all contaminated components and cleans the airflow. Upon filter saturation, a quick replacement takes place and enables the filtration process to continue without interruption and continuously. The filter will be used as soon as the client is ready. The company is currently still busy with the engineering for the alignment of the facilities with the filters.

The variable conditions represent a challenge in this project. The operational regimes of the systems cannot be easily predicted because they depend on the season and solar radiation. An average rate of 800 m³/h and a VOC concentration of approximately 400 mg/m³ are being expected.

An additional asset for the client is the solution that Desotec can offer if the HTF emissions end up in rainwater. A MOBICON 2000 filter ensures the correct wastewater treatment in that scenario.

At DESOTEC’s facilities, all used carbon is analysed so the right measures can be taken for handling and removing the saturated carbon out of the mobile filters. All molecules that were adsorbed on the activated carbon at the customers’ site, are desorbed inside DESOTEC’s reactivation furnaces. These contaminants are then fully destroyed, in accordance with National and European legislation, by an incineration and neutralisation setup. The entire installation and it's emissions are under continuous on-line monitoring, which guarantees that only harmless water vapour is seen exiting the chimney.