...
The 2.5 cm tube settler had a better performance, as seen in Figure 1, staying above a pH of 12 for 14.6 hours and after approximately five more hours, it increased again to above 12 for 2 hours. The fluctuations in the graph near the 30 hour point are due to washing the pH probe and switching pH probes between both reactors to determine if there was a problem with the readings. Readings above 12.6 are observed again, thus it is strongly probable that there is a problem with the pH probes or with the data acquisition system. It is difficult to accurately measure pH when the solution is flowing.
After analyzing the results the team now considers that by increasing up-flow velocity the amount of lime in the reactor can decrease and the performance will get worse. Therefore, the team is now considering the effects of lime particle size. Because the slurry and mixing method is not exact and reproducible, it is possible that all the experiments have been done with different particle size distributions. Big particles remain trapped in the middle part of the elbow and it is difficult to clean the reactors after each experiment. For future experiments a blender or a coffee grinder will be required in order to ensure a homogeneous distribution of particles size. In addition, the team asked for new pH probes and signal conditioning boxes.
Figure 1
The purpose of this experiment was to keep the same conditions as Experiment 4 but to double the upflow velocity in the 5 cm tube settler apparatus.