Optimization of the Flow Schemes in Radiant Recuperators

Abstract

In glass production and metallurgical processes, radiant recuperators are used to preheat combustion air by heat exchange with high temperature flue gases. For these recuperators, the most popular is concurrent flow arrangement, which compared to other solutions has the lowest interface temperature and the longest lifetime. Compared with concurrent, radiant countercurrent recuperators have only one drawback: the interface temperature is higher at the flue gas entrance. Their comparative advantages are: lower average interface temperature, higher efficiency and smaller pressure drop. Compared with pure concurrent and countercurrent radiant recuperators, designs with double air annulus are slightly more efficient and have a bit smaller interface temperatures, whereas cost and pressure drop are their disadvantages. In the paper, all these four flow configurations are combined by the division of airflow and by the use of different airflow schemes. The improved design is a combination of a countercurrent and a concurrent radiant recupreators. Depending on the geometry, there is an optimal airflow division in the combined recuperator. For the analysis, a cell modeling method validated on a 15 m high, concurrent radiant recuperator used in a glass fiber production process is used. Different solutions are analyzed comparing their effectiveness, energy and exergy efficiencies, and interface temperatures.