CO2: Food for Chlorella sorokiniana marrakechensis
Geesthacht’s polymer research membranes used for the Algae House
Gas bubbles flow throughout the bioenergy façade filled with algae and liquid, which usually appears green. But the Algae House isn’t just an eye catcher from the outside: the technology inside is also extraordinary. Using membranes from the HZG’s Institute of Polymer Research, carbon dioxide is separated from the flue gas of the in-house gas heating system - and is used to feed the algae.
The Algae House in Hamburg-Wilhelmsburg is an absolute eye-catcher. Photo: HZG/ Christian Schmid
Thorsten Wolff again checks whether the module has been correctly connected. Then it all begins: the first real working application for the new membrane module in the Algae House. The process engineer from the Geesthacht Polymer Research unit has already been involved in the project for six years. The system works very robustly, but something needs to be changed every now and then in order to attain the most from it. For example, experiments are conducted with different types of algae. Most recently, the operator wanted to cultivate rapidly growing algae from North Africa: Chlorella sorokiniana marrakechensis.
Engineer Thorsten Wolff installed the new membrane module (centre of image) in the boiler room of the Algae House, which is operated by Dr Martin Kerner. Photo: HZG/ Christian Schmid
The new membrane, like its predecessor, consists of several polymer layers. The actual separation layer is made up of the “PolyActive” block copolymer. Using the membranes produced in Geesthacht, a large portion of the carbon dioxide (CO2) can be separated from the conventional gas heating’s flue gas. Wolff explains, “The flue gas consists of ten per cent carbon dioxide with a residual oxygen content of five per cent, while the rest is nitrogen and water vapour. The membranes allow CO2 and water vapour to pass through particularly well, but they are not one hundred per cent selective. We therefore cannot separate CO2 exclusively. We have, however, managed to concentrate a large portion of the CO2 so that we can obtain a gas mixture that consists of 40 per cent CO2. This mixture is introduced into the algae liquid, and the rest is emitted outside, via the chimney.”
Thorsten Wolff has been working at the HZG in Geesthacht since he completed his master’s thesis in 2003. Photo: HZG/ Christian Schmid
Through photosynthesis - that is, with the help of sunlight - the algae utilize CO2 and water and convert them into biomass and oxygen. “The new North African algae grow especially quickly and therefore require a great deal of carbon. This is why we have now increased the membrane surface by half and adapted the module. A total of 104 membrane envelopes are installed within it. This is how a great deal more CO2 can now be separated than before,” explains Thorsten Wolff. The membrane surface measures approximately twelve square metres.
At the Institute of Polymer Research, the scientists map the entire process chain, which is a unique feature in this field. This includes computer simulations, which have taken many years to develop, and numerous experiments. “We are constantly comparing the measurement values from our tests with the digital models. If the data matches, we know that we’re on the right path and that the module is working flawlessly.“
Dr Martin Kerner completed his “Habilitation” in environmental science at the GKSS (now HZG) in 1996. Today Kerner is managing director of the biotechnology firm SSC Strategic Science Consult, which operates the Algae House in Hamburg. Photo: HZG/ Christian Schmid
The membranes are produced at the in-house membrane production hall and are installed in self-designed pressure vessels, so called membrane modules. “The combination of process simulation, experiments and pilot studies using HZG’s pilot plants as well as the subsequent integration into operational systems makes the work here so exciting,” says Thorsten Wolff.
The algae serve as a valuable raw material in diverse industries, such as food, cosmetics and the pharmaceutical sector. Thirty to fifty per cent of all algae biomass is harvested daily. This was also a reason for the new algae: more rapid and increased growth leads to more biomass, which then can be utilised. During the operational period between March and October, the fully automatic system runs up to ten hours a day in several cycles. Ten cubic metres of flue gas are filtered per hour, resulting in one cubic meter of CO2-rich gas as "algae feed”.
The module developed at the Institute of Polymer Research measures 30 centimetres in diameter and 50 centimetres in height; inside it houses 104 membrane pockets layered on top of one another. Photo: HZG/ Gesa Seidel
There is an additional bonus for the climate: the bioenergy façade works like a solar thermal facility, generating heat, which has been used since 2016 to fully supply the building with warm water and heating. The Algae House’s sustainable technology is now marketed internationally. “The Algae House is a unique and very beautiful project. I’m really happy that we can contribute in part with our membranes,” says Thorsten Wolff. “In addition, it always feels good to see how research can make its way into very concrete applications.”
Author: Gesa Seidel (HZG)
Published in in2science #10 (December 2020)