Study of Two-Phase Flow in a Direct Coal Liquefaction Preheater

摘要

Experimental data collected from an apparatus designed to simulate a direct coal liquefaction preheater are compared to theoretical analyses describing two-phase flow of a gas and liquid in vertical upflow and downflow. Several flow experiments were performed with nitrogen and four different liquids, including a coal-derived liquid at both atmospheric and elevated pressure. The analytical methods selected for study are the Lockhart and Martinelli, Hughmark and Pressburg, and the multistream annular flow models. Of particular significance, the multistream annular flow model was developed primarily for use in water/steam systems characteristic of the nuclear industry and has not previously been applied to direct coal liquefaction preheaters. The uniqueness of this approach is the inclusion of separate continuity and momentum equations for the liquid and gas phases, creating a more physically realistic model for flow regimes with high gas rate. Results from this study indicate that the best correlation for accurately predicting pressure gradient in vertical two-phase flow is largely dependent upon the flow direction, the flow regime, and the specific fluids flowing in the pipe. The Lockhart and Martinelli, and Hughmark and Pressburg correlations have good agreement when compared to experimental data in the bubble and slug flow regimes, while the multiphase annular flow model was more effective in the froth and annular flow regimes. 14 refs., 8 figs., 6 tabs. (ERA citation 10:033117)