This project focuses on the fluid dynamics of vertical gas-solid risers. Its principal objective is to produce data for evaluating theories elaborated by Professors Sundaresan and Jackson at Princeton. Thus in this report, we review Cornell activities in the area of gas-solid suspension flows.
At Cornell, we possess a unique facility with the ability to recycle - rather than discard - fluidization gases of adjustable composition to a vertical riser of 20cm diameter and 7m height. This allows us to simulate the fluid dynamics of industrial units (atmospheric and pressurized coal-burning circulating fluid beds, catalytic crackers) in a cold, atmospheric riser by matching the dimensionless parameters that govern the flow. The facility is equipped with capacitance, optical fiber and pressure instrumentation that records solid concentration profiles in the vertical and radial directions.
In the first year of the award, we have established that, under typical industrial conditions, dense gas-solid flows are nearly independent of gas density in the fully-developed region of the riser. This observation of a viscous flow regime suggests that particle clusters dominate the exchange of momentum between the two phases. It further suggests that extrapolations of flow behavior from atmospheric to pressurized conditions should be more straightforward than previously envisaged.
To inform closure of theories elaborated at Princeton, we have also carried out simultaneous measurements of pressure fluctuations and local wall volume fraction. Here we have shown that, because gas pressure reflects fluctuations originating throughout the vessel, they are not closely correlated with local solid volume fractions.
In addition, we have begun a study of cyclone performance under conditions of high gas density and solid loading, which have not yet received much attention despite their importance for a new generation of high efficiency coal gasifiers and other dense gas-solid processes operating at high pressures.
In 1996, we have also made progress in the area of instrumentation, which is often of interest to industry. In particular, we have designed an uncooled capacitance instrument capable of recording instantaneous solid volume fraction near the wall of an industrial vessel operating up to 950°C and 15 bar. In addition, we have completed a technology review of instrumentation for dense gas-solid suspensions to be presented at an upcoming IFPRI meeting.