Investigation and modeling of CPC based tubular photocatalytic reactor for scaled-up hydrogen production

The tubular reactor combined with compound parabolic collector (CPC) has been proposed to be a potential choice for large-scale photocatalytic hydrogen production. However, comprehensive study and modeling of hydrodynamic and resultant radiation absorption properties for such reactors is rare, which should be of valuable guidance for the scaled-up of the technology. In this study, catalyst-liquid two phase flow within the reactor was studied via CFD. Under the studied condition, inlet velocity above 0.06 m s−1 and particle size below 10 μm is recommended for keeping well suspended particulate slurry. For the investigation of the radiation absorption, the radiation distribution onto the external reactor surface was firstly simulated using ray tracing algorithm considering CPC's geometry. The radiation was then introduced into the inner part of the tubular reactor considering the photocatalyst distribution. Using a modified differential approximation method, 2D radiation distribution within the tubular reactor was obtained. Interestingly, it was found that specific catalyst concentration gradient resulted from sluggish flow velocity or large particle size is beneficial for radiation absorption enhancement within the reactor. Under the desired CPC configuration, the dependence of system energy output on the catalyst loading and flow rate has been evaluated. As long as the particle can be well suspended, lower flow rate is always favored. Our modeling theoretically predicts that catalyst loading of higher than 1 g L−1, even up to 16 g L−1 will not lead to significant increase of power density, which is in well agreement with the widely accepted experimental findings.