Intensification of co-current gas–liquid reactors using structured catalytic packings: A multiscale approach

Cross-flow structured packings for tubular fixed bed reactors operated with co-current gas–liquid flow perform significantly better in terms of overall heat transfer than a randomly packed bed (glass beads), knitted wire packing, and Al-foam structure at a range of gas and liquid flow rates. This is mainly the result of radial directed convective transport of heat, realized by the channel structure of the cross-flow packings. A pseudo-homogeneous 2D (two-dimensional) plug flow model is found inadequate to quantify variations in overall heat transfer for experiments with different packing orientations and different gap sizes between the packing structure and the cooling wall, because it does not take directed convective transport of heat into account. Numerical simulations are performed to investigate in detail the fluid flow inside the packing. The geometry is defined as sheets separating layers of diagonal channels. For simplicity we assume no fluid exchange between different layers and we approximate the flow in the individual layers as 2D. The simulated velocity distribution inside the packing is highly inhomogeneous, showing regions of almost zero flow. These inhomogeneities in the flow are shown to depend on geometrical parameters, such as the packing width-to-height ratio and can have strong impact on reactor efficiency.