Techno-economic Evaluation of the Effects of Decarbonisation and Waste Heat Utilisation on Green Hydrogen Produced from Microalgae Steam Gasification

A comprehensive techno-economic evaluation of the application of steam gasification to different microalgae for hydrogen production was performed. The production of hydrogen-rich syngas from three microalgal feedstocks (namely S. Acuminatus; S. Almeriensis and a co-culture of the two microalgae) was firstly considered and then separated to produce hydrogen. The flue gases were decarbonised using Calcium Looping Combustion (CaLC) process. Since decarbonisation comes with a significant energy penalty, waste heat utilization (WHU) was applied to the CaLC for combined heat and power generation. S. Acuminatus produced the highest amount of syngas and correspondingly the greatest amount of hydrogen (157.3 kg hr⁻¹). The yields of the produced decarbonised hydrogen of the three microalgae ranged from 13.4 to 16.5%, higher than published values ranging from 8.0 to 12.0%. Since S. Acuminatus showed the most favourable technical performance, an economic analysis was performed, resulting in levelised costs of hydrogen (LCOH) ranging from 2.46 to 3.87 $/kg. Optimising the operation conditions of CaLC process resulted in an overall decarbonisation of 97% with final carbon emission intensities less than 0.5 kg CO₂/kg H₂, less than reported intensities for green hydrogen production. Implementing CaLC process resulted in energy penalties ranging from 10.36 to 11.24%. Nevertheless, applying WHU resulted in overall surplus in energy generation and overall plant efficiency. Finally, CO₂ abatement costs were estimated and found to be comparable to published values. Overall, this research proves that steam gasification of microalgae combined with CaLC technology is a feasible option for green hydrogen production.