The larger pellets employed in existing conventional fixed-bed FT systems face challenges both in terms of heat and mass transfer. The lower pressure drop offered by CANS allows it to operate using a smaller catalyst pellet, delivering the following improvements:
- A small pellet has a shorter pathway to the catalyst active surface, which minimises the partial pressure gradient of the reactants within the pellet
- This delivers a higher reaction rate with lower by-products make
- Active site blockage is also reduced, increasing their accessibility for reactants.
For the highly exothermic FT reaction, heat
removal is vital for catalyst protection and maintaining selectivity.
The parameters crucial to achieving this heat removal are particle size and structure.
A smaller pellet has:
- Shorter heat transfer route
- Lower centre temperature
- Better heat transfer to bulk gas.