Radiant recuperator modelling and design

Abstract

Recuperators are frequently used in glass production and metallurgical processes to preheat combustion air by heat exchange with high temperature flue gases. Mass and energy balances of a 15 m high, concurrent radiant recuperator used in a glass fiber production process are given. The balances are used: for validation of a cell modeling method that predicts the performance of different recuperator designs, and for finding a simple solution to improve the existing recuperator. Three possible solutions are analyzed: to use the existing recuperator as a countercurrent one, to add an extra cylinder over the existing construction, and to make a system that consists of a central pipe and two concentric annular ducts. In the latter, two air streams flow in opposite directions, whereas air in the inner annular passage flows concurrently or countercurrently to flue gases. Compared with the concurrent recuperator, the countercurrent has only one drawback: the interface temperature is higher at the bottom. The advantages are: lower interface temperature at the top where the material is under maximal load, higher efficiency, and smaller pressure drop. Both concurrent and countercurrent double pipe-in-pipe systems are only slightly more efficient than pure concurrent and countercurrent recuperators, respectively. Their advantages are smaller interface temperatures whereas the disadvantages are their costs and pressure drops. To implement these solutions, the average velocities should be: for flue gas around 5 m/s, for air in the first passage less than 2 m/s, and for air in the second passage more than 25 m/s.

Experimental and CFD analysis of wire coil turbulators in biomass boilers

“…Basic temperature-dependent thermodynamic properties are taken from [32,33]. The model is validated in [25] except for the convective heat transfer rate from the outer pipe wall to the water. This term has the smallest heat transfer resistance in the overall heat transfer coefficient, and, like all other submodels, comes from a reliable and confirmed source [31].…”

Intensity of the Heat Transfer in Radiation Recuperators

“…The constructive arrangement and the function of the recuperators are described in detail in a number of other [5,6,7,8,9] and our [2,3,4,10,11,12] publications. In many of them a special attention is paid to the heattechnical dimensioning of the most widespread types of such apparatuses.…”

“…However, the intervals that occur most often [6,8] are also adopted in this work and given in Table 1. The basic indicators of the recuperator are also systematized, representing an input at the conducted heat-technical calculations.…”

“…The basic indicators of the recuperator are also systematized, representing an input at the conducted heat-technical calculations. In consequence of the striving for achievement of recuperators efficient in energy and technical-economical relationship, as a lower border of the air velocity at normal conditions the level 20 m/s is preferred, which is available in the most of the cited publications [1,6,8,14].…”