TITLE: Solvent-Refined-Coal (SRC) Process: Axial Dispersion in Tall Bubble Columns - Tracer Tests.

AUTHOR: K. Parimi;   M. D. Pitchford.

INST.  AUTHOR: Pittsburg and Midway Coal Mining Co., Englewood, CO.

SPONSOR: Department of Energy, Washington, DC.

LANGUAGE: English

PUB.  TYPE: Technical Report

PUB.  COUNTRY: United States

SOURCE: Department of Energy [DE],  Jan 82,  52p.

ABSTRACT:

The degree of backmixing is an important consideration in the design and scale-up of SRC-II reactors. Several qualitative tests were conducted on the 25 ft plexiglass bubble column in order to visually observe the axial dispersion or backmixing characteristics of a column of this size. A concentrated solution of Methyl-Orange was injected, and the dispersion of the dye throughout the column was observed and photographed. These observations indicated that the backmixing level was not as extensive as existing correlations would predict. Since backmixing plays an important role in the design and scale-up of SRC II reactors, it was decided to follow up with additional quantitative tests for further elucidation of this aspect of bubble column performance. The required test apparatus was assembled and tracer tests using an electrolytic tracer in the form of a10 N NaOH solution were conducted. The results confirmed the visual observations; that the degree of backmixing was less than existing literature correlations predicted. Part of the reason for the discrepancy may be due to the large extrapolation involved, but more importantly, there is the question of adequacy of the model to describe the complex mixing patterns present in the column. Implicit in using any of the existing correlations to predict backmixing is the assumption that a simple dispersion model can adequately describe the complex mixing patterns observed. This is not a valid assumption when the column operates well beyond the quiescent bubble flow regime. There is, therefore, a real need to identify models which would represent more closely the fluid dynamic behavior of large columns and which can be used confidently for design and scale-up. (ERA citation 07:041999)

REPORT  NUMBER: DOE/ET/10104-40

CONTRACT  NUMBER: AC05-76ET10104