Abstract

Hydrogen will be a very important energy carrier in the near future. Nowadays, well over 95% of hydrogen is “grey”, i.e. obtained from fossil fuels with accompanying high CO₂ emissions. The objective should be to produce hydrogen in a sustainable way, without emitting additional CO₂ into the atmosphere. For a vast amount of required hydrogen, the technology openness is very important in order to produce “green” hydrogen as fast as possible in large quantities at low cost. Consequently, biomass has to be considered as a very important source of such hydrogen.

A very effective process for hydrogen generation based on allotherm steam reforming using energy from biomass is developed and tested in a pilot facility. Excess chemical energy from the process is used to generate steam and superheat it up to 1,200°C or even higher. Steam is the gasification and oxidation agent, energy carrier for the process and supplier of hydrogen molecules, as it reacts with biochar at the bottom of the reactor. Produced synthesis gas has up to 60% of H₂, as it comes not only from biomass but mainly from steam. The handling of tars is much easier than in other systems, due to presence of excess steam. Heavier tar fraction is separated in a cyclone and introduced back in the hottest zone of the reactor. The synthesis gas with light tar fractions is introduced into a high-temperature cracker, where tars and methane are cracked in presence of steam in lower hydrocarbons and H₂. The removal of other impurities is done in a cryocooler, active-coal and ZnO-filter. It has been proved that combination of high temperature steam with updraft reactor, tar cyclone, and new developed components like thermal cracker and cryocooler is the most effective combination for getting clean gas.

By scaling up the pilot facility, a demonstration facility has been designed. As in the pilot facility, the input biomass is waste material or low-quality wood chips, which cannot be used in other technologies (no tank-plate competition). The advantages are: a) achieved energy efficiency up to 70%, b) electricity consumption lower than 5 kWh/kg H₂, c) production costs considerably lower when compared to the electrolysis based processes for renewable electricity, d) CO₂-emission are under 1 kgCO₂/kgH₂ and e) several useful by-products like biogenic CO₂ or benzenes are obtained.