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By observation, the team also consistently found an upflow velocity which maintained a good fluidized bed in the vertical column. A failure to maintain the suspension, as discussed in the second initial hypothesis above, is not believed to be a major cause of failure. However, there are difficulties associated with finding the appropriate flow rates for the two reactors. From observation and alkalinity tests of the effluent, the team knows that there is often significant solid lime leaving the reactor when it is fully loaded, which indicates that the upflow velocity is to too high to keep the smallest particles in the suspension. At the same time, depending on how the dry lime is broken up prior to the experiment, there are also often particles which are large enough to settle through the jet at the entrance to form a bed at the bottom of the column. The best upflow velocity depends on the particle size distribution, which is thought to be variable over the course of an experiment. It is likely that we have not found the ideal upflow velocity to keep the best mix of the solid lime particles in suspension. An additional practical limitation of this investigation is that the suspension takes a very long time to respond to changes in flow rate (which is linked directly to upflow velocity) due to the very slow settling velocity of most of the particles, which makes trial and error very tedious.
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