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ePaper created 2013-09-24, 11:56:35 | version 1.25.20
Adsorbents for heat storage and material separation The principle of adsorption is used in many technical applica- tions, for instance to dehumidify air or gases or to separate mixtures of materials. A further application is sorptive thermal storage, which can be used to increase energy efficiency in in- dustrial processes and thermal technology applications. Due to ease of handling and manufacture, pelleted adsorbents (e.g. zeolites, activated carbon, silica gel etc.) in spherical or cylindrical forms are generally used. However, these often have restricted mechanical stability and extremely limited ther- mal conductivity. This is a disadvantage for the performance of many applications and thermal storage in particular. Improved sorption pellets – increased stability and thermal conductivity Within a project funded by the Fraunhofer-Gesellschaft, the Fraunhofer Institutes IGB, IKTS and IWU are developing metal- coated pellets that, when used as packing provide distinctly increased thermal conductivity, while retaining the same ad- sorption capacity and are mechanically stable. When used in heat storage devices or heat pumps, increased heat conduc- tion enables significantly increased power density through faster loading and unloading. This should make the tempera- ture regulation of the sorption bed in chemical reaction tech- nology simpler and more effective. An additional goal is to minimize abrasion losses in the transport of materials and fill- ing of the reactor due to increased mechanical stability. This leads to longer lifetimes in sorbent packing and enables new reactors (flow reactor) and mobile applications. In order to achieve the best possible adsorption characteristics the pellets should have a high internal porosity. The manufacturing meth- od should be suitable for the production of large quantities. Manufacturing process and material tests The project involves the manufacture of cylindrical pellets coated with copper, aluminum or other metals, in which sorb- ent granules are filled into thin-walled metal tubes. The ini- tial step was the design of a suitable manufacturing process, which consists of the four partial steps of granulation, filling the metal tubes, flow-rolling and separation of the pellets. It is a particular challenge here to carry out the thickening of the material so that the sorbent remains in the metal casing but still retains sufficient porosity to maintain the adsorption char- acteristics. Model experiments were carried out at the Fraun- hofer IKTS using NaY zeolite and various binders. The output pellets are pressed into cylindrical pellets and their strength and specific surface are determined. Based on these previous experiments, the Fraunhofer IWU de- signed and constructed a test facility for the manufacture of 5–10 kg of adsorption pellets. The facility will shortly make larger quantities of coated pellets available, in order to test these in the model thermal storage unit at the Fraunhofer IGB. Examination of the adsorption characteristics In parallel, reference measurements were carried out using uncoated pellets at the Fraunhofer IGB. Two qualities of zeo- lite spheres (diameter 1.6–2.5 mm and 2.5–5 mm), as well as uncoated cylinders (5.25x10 mm) with an alternative bind- er, which is also used in the coated pellets, were tested with 120 HIPEL – METAL-COATED SORPTION PELLETS FOR THERMAL STORAGE AND ADSORPTION APPLICATIONS Dipl.-Ing. Mike Blicker ENERGY 1 2 3