Experimental and Numerical Investigations on Heat Transfer of Bare Tubes in a Bubbling Fluidized Bed with Respect to Better Heat Integration in Temperature Swing Adsorption Systems

Abstract

In this paper experimental and numerical investigations on heat transfer within a bubbling fluidized bed will be presented with respect to better heat integration in continuous temperature swing adsorption (TSA) processes for biogas upgrading. In the literature, mainly heat transfer measurements with glass or sand particles are carried out, thus special reference measurements with adsorbent material in a fluidized bed are missing. Therefore firstly, a series of experiments were carried out in the fluidized bed test facility to obtain heat transfer coefficients between tube surface and bed which were then compared to calculated heat transfer coefficients to determine whether suitable models were available. Horizontal bare tubes with different arrangements (i.e., single tubes and especially tube bundles) are immersed in fluidized amine layered particles with a mean diameter of 650 µm which are used in the adsorption industry as adsorbent. The test facility enables a cross-current flow of the solids and gas phase as it prevails in a multi-stage fluidized bed reactor for TSA-applications. The heat transfer measurements with different arrangements and adsorbent material show very similar values in the range of 200 W/m2K. The mathematical model for single tubes multiplied by a tube diameter factor shows approximate agreement with the experimental results. However, the mathematical models for tube bundles were not able to predict the measured heat transfer coefficients with the required accuracy. Secondly, a computer fluid dynamics (CFD) program was used to perform a numerical investigation of the test facility using the Euler–Euler method in order to describe the required two-phase characteristic of a fluidized bed. The results of the numerical simulation were compared and validated with the experimental results. Bubbling fluidized bed flow regimes could be reproduced well but the heat transfer coefficients between tube and bed were clearly underestimated. However, a numerical study for a bubbling fluidized bed with external circulation, as used in novel continuous TSA systems, could be carried out and thus a tool for better heat integration measures was developed.