Experiment 6: Blending the Lime Slurry

Overview

The purpose of this experiment was to test the effect of blending the lime into a lime slurry before feeding it to the apparatus. It was suggested that by blending the lime, smaller lime particles could be achieved and possibly more surface area available for lime to dissolve and interact with the water. 100 grams of lime was chosen in order to easily compare it to previous experiments in which 100 grams was added, both as dry powder and as a lime slurry that was manually blended.

Procedure

Two 100 gram samples of lime slurry were prepared by blending them in the blender on the "liquefy" setting.  Unfortunately, the lime slurries were not prepared in the same manner with the same amount of water - this is an issue that the team corrected in Experiment 8. The slurries were then fed into each apparatus via the vertical column. The water used was tap water and A1 had a flow rate of 30 mL/min and A2 had a flow rate of 40 mL/min. The overall method followed is outlined in the materials and methods page.

Results and Discussion

The experiment lasted approximately 12.5 hours for A2 and 16.5 hours for A1. Both failed and then leveled off. Neither apparatus reached the saturation point for lime (pH = 12.6), with A1 reaching 12.3 and A2 reaching 11.6 as the peak pHs. However, it is important to note that this experiment was conducted before new pH probes were purchased and implemented.
Visually, it was noted that while the lime remained primarily in the vertical column of A2, it traveled up into the tube settler of A1 sometimes filling up to 80% of it.  In A1, the solids particle time was increased while the capture velocity was decreased, allowing some of the particles to leave out the top in the effluent. For both apparatuses, it was discovered that a significant amount of lime was getting caught in the elbows---despite blending the slurry and keeping a low upflow velocity. From observing the experiment after failure, the team also noted that there may be preferential flow paths through the settled lime slurry in the tube settler and this may result in the relatively quick failure (despite having such a large amount of lime).
After this experiment, the team hypothesized that pulsing in a lime slurry could allow the experiments to reach the target ANC levels.

                                                                                                                                  Figure 1 - Experiment 6
                                               This experiment was conducted to test the effect of blending the lime slurry to observe how smaller particles act in the two apparatuses.