AirWater

As part of the “AirWater” cooperation project, a system is being developed that enables quasi-continuous (i.e. during the entire sunshine period), solar-sorptive water extraction from the atmosphere using only solar energy. The main application will be in arid regions where alternative methods reach their economic and physical limits or where a reliable supply of electrical energy from the grid cannot be guaranteed.

According to the UN World Water Report 2020, around 2.2 billion people have no access to clean water. This means that around one sixth of the world's population is affected by severe water shortages. Water scarcity is particularly severe in remote regions with arid and semi-humid climates. The water content of the air in the entire atmosphere is 13,000 km³. Although only the layers of air close to the earth can be used, this offers great potential for obtaining drinking water, as this source is accessible everywhere.

In order to condense water vapor from the atmosphere, it is necessary to bring the temperature of the air below the dew point. Concepts that have been researched to date include night-time radiation cooling against the night sky and cooling air during the day using an electrically powered compression chiller. The latter is already being offered commercially by several mainly (South) American companies (including Rayaqua, ATC and Tsunami). In arid regions, however, the water content of the air is often so low that these processes are either associated with high equipment and energy costs or are not feasible due to a low dew point. For this reason, the IGTE is working on sorptive water extraction. Previous concepts for this are predominantly dependent on naturally occurring changes in ambient conditions, e.g. due to day and night, and can therefore only be operated intermittently. Systems that enable quasi-continuous water extraction have so far been limited to low water yields and laboratory conditions.

Together with the project partners HydroTec GmbH and Richter & Stegner Steuerungstechnik GmbH, a demonstrator plant is being developed and operated as part of the project, which enables an increase in the water content of the process air through adsorption and subsequent desorption of the water. In this way, the dew point temperature is raised above the ambient temperature. In contrast to other sorption-based water recovery concepts, the air circulates in a closed desorption circuit so that all the desorbed water is available for condensation and is not released unused into the environment (see Fig. 1). The water is condensed by cooling the process air with ambient air in several heat exchangers. No additional electrical cooling is required to dissipate the condensation enthalpy.

The quasi-continuous operation of the system is achieved by locally decoupling heat generation and desorption as well as the parallel operation of two sorption beds. In order to reduce the pressure loss, a reactor concept with radially flowing packed beds of zeolite spheres was developed. While adsorption takes place in one sorption bed, desorption takes place in the other. Several flaps can be used to control which process takes place in which sorption bed. In this way, adsorption and desorption can take place simultaneously and several times a day. The size of the system was designed to produce 24.5 liters per day in ten hours of sunshine. This corresponds to supplying around seven people with the minimum amount of 3.5 liters of drinking water per day. In order to be as independent as possible from electrical infrastructure, the system is to be operated exclusively with solar energy.

The process is designed to obtain as much water as possible in a single cycle (adsorption, desorption and condensation). The goal is to provide water harvesting independent of an electricity connection in continuous operation (24h per day), in very arid areas.

01/2021 – 12/2024

HydroTec Gesellschaft für ökologischeVerfahrenstechnik GmbH
Roland‐Dorschner‐Straße 5
95100 Selb

Richter & Stegner Steuerungstechnik GmbH
Grün 34
95195 Röslau