Abstract: The constant development of industry results in an intensive search for increasingly efficient and less energy-intensive solutions. This also applies to chemical processes, where new active catalysts and carriers are desirable, ensuring reduced energy consumption while simultaneously increasing process efficiency. It is estimated that the majority of chemical reactions carried out on an industrial scale are catalytic processes. Catalytic processes are typically carried out using catalysts in a packed bed. However, this type of packing has numerous drawbacks. Due to its stochastic nature, it can cause uneven fluid flow, vortex formation, reverse flow, and other phenomena, which can in turn lead to the formation of so-called hot spots and local deactivation of the active layer. These factors adversely affect the conversion and selectivity of the process. An additional challenge is the need for processes that require strictly defined temperature conditions to be properly conducted. To overcome the problem of uneven temperature distribution within the bed and insufficient heat transfer, many different solutions have been proposed. One of these is the use of metal supports, which have significantly better heat transfer properties than traditionally used ceramic supports. However, despite the high potential of metal supports with a catalytic layer applied to their surface, these supports are not without their drawbacks. First and foremost, the amount of catalyst (available active sites) is significantly smaller compared to a traditional bulk bed.
A solution that combines the advantages of metal packing (high heat transfer coefficients) with ceramic packing is a "packed structure" type of packing, in which a bed of fine catalyst grains is placed within the voids of the metal structure. Such metal structures can be, for example, monoliths, solid foams, or POCS-type packings. These solutions have been experimentally tested in exothermic and endothermic processes ensuring higher efficiency and more uniform temperature distributions within the bed compared to a conventional packed bed. Problems with this type of packing, in turn, include the packing density of the metal structure with catalyst grains and flow resistance. However, a solution to this problem could be the use of a POCS structure with a properly defined geometry adapted to the process requirements (grain size) and manufactured using 3D printing. This type of filling ("filled POCS") is characterized by more favorable flow properties compared to a packed bed. It's also worth noting that one of the fundamental requirements for packings with intense radial heat transfer is ensuring adequate contact between the metal structure and the reactor wall. This is a parameter that determines the temperature profiles in the reactor bed. Even a small amount of contact between these two surfaces (on the order of 10–20%) ensures sufficient heat exchange between the foam and the reactor wall; further increases in contact area yield only minor improvements in this parameter.
This article reviews new types of packing for reactors with intensive radial heat transfer, highlighting the significant potential of so-called "packed packing." Furthermore, the advantages and disadvantages of various types of ceramic-metal packing are identified. Additionally, an algorithm for determining the radial heat transfer coefficient, implementable in Matlab, is proposed. The advantages and disadvantages of the experimental methodology were indicated, recommending the water bath method (ice water) as suitable for laboratory-scale research.
