Passive intensification of straight-tube sulfuric acid decomposers via inert SiC packing for thermochemical hydrogen production

Abstract

Sulfuric acid (H 2 SO 4 ) decomposition, the most energy-intensive step in the sulfur–iodine cycle, is limited by flow maldistribution in straight-tube decomposers. We propose a passive intensification strategy that an inert SiC packing-bed is placed upstream of the catalyst to homogenize the inlet flow without altering the catalyst or reactor shell. A two-dimensional axisymmetric multiphysics model coupling flow, heat transfer, phase change, species transport, and reaction kinetics was developed and validated with a CuFe 2 O 4 catalyst. The optimal configuration including packing length of 30 mm, porosity of 0.30, and particle diameter of 0.425 mm flattened radial velocity and concentration profiles, reduced the area-weighted concentration coefficient of variation by up to 95.5% and expanding the effective reaction zone. At equal axial occupation, it achieved 5.90% higher conversion than an all-catalyst bed. Experiments showed H 2 SO 4 conversion increased from 80.2% to 83.8% with SiC packing, and a 100 h test maintained an average conversion of 80.9%. By lowering the unreacted acid recycle load, this simple, cost-effective strategy offers a practical retrofit route for industrial decomposers.