Power-to-Protein: efficient input of hydrogen (phase 3)

During phase 1 of the project (2015/2016), a desk study focused on the technical and economic aspects of the concept. In phase 2 (completed in early 2019) the concept was upscaled in the form of a pilot, with a volume of 500 litres, and tested at two locations. The results of this research have been published.

In general terms, it is possible to successfully grow a productive HOB microbiome. During the practical research, it became apparent that the addition of hydrogen to the fermentation broth is the most important sticking point for the success of the Power-to-Protein concept.

Technology

Hydrogen is the energy carrier in the Power-to-Protein concept. A good economic business case requires the optimal use of this hydrogen. But a complication arises in this regard, because the reactor system must also be fed with oxygen and carbon dioxide.

Challenge

By means of a literature study, knowledge sharing with experts and modelling, this research has led to a greater understanding of the mass transfer of hydrogen and other gases in bioreactors, so that proteins can be produced from ammonium, which comes from wastewater.

Basic insights contribute to a better design of a bioreactor with an optimal input of fermentation broth, hydrogen and other gases. This will make possible the upscaling of the Power-to-Protein concept in a follow-up phase.

Solution

The literature study showed that bubble column reactors and slurry bubble column reactors are suitable reactor types or configurations to achieve high performances regarding the mass transfer of gas to liquid, as well as a better gas retention. This conclusion was confirmed by experts consulted during a knowledge sharing meeting. Furthermore, the literature and the expert consultations provided the bases for the key design and operational parameters for the development of a CFD model, which simulated the performance of the bubble column reactor under varying design and operational conditions. From the model study it was concluded that the key parameters for improving the performance are the size of the bubbles, the pressure and the reactor’s height-width (aspect) ratio. These study findings supported the methodology followed by Avecom, which provided extra backing to the use of the bubble column reactor currently being operated on a pilot scale. Recommendations were also made regarding the parameter values that could be considered for the design of a larger-scale reactor. In addition, concrete recommendations were made about the monitoring of the operational parameters by means of sensors. With the availability of complementary data, the current CFD model could be further calibrated and validated to increase the accuracy of the predictions.