h1. *ANC CONTROL*
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h2. *Experiment 1: Minimum amount of lime input in two reactors*
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h4. Introduction
In the first experiment of Spring 2010 team, the goal was to evaluate the lime feeder's performance with respect to its effluent pH with a minimum lime input based on theoretical calculations. This is the mass of lime which would dissolve in 12 hours given the flow rate and the calcium hydroxide solubility constant (equation 1.1). As can be seen in equation 1.2, the theoretical lime requirement is simply based on what could dissolve in twelve hours, and didn't take into account other factors which limit how much of the available lime will actually dissolve.
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h4. Procedure
The team basically used the same procedure described in the materials and methods section, although the lime is now fed through a vertical tube.
So that the experiment could be compared with the last experiment carried out by the Fall 2009 team (Experiment 3, Trial 4), the Spring 2010 team used the same flow rate, which was 40mL/min in both reactors, and a lime mass of 8gm based on the solubility calculations (figure 1.1). One important change was that the lime in this experiment was fed dry, not mixed with water as a slurry. This may affect the particle size distribution, which is discussed in the hypotheses section. The following was used to determine the amount of mass necessary for a 12-hour run with a given flow rate. K ~sp~ is the lime solubility constant, MW is the molecular weight of lime, Q is the volumetric flow rate, and \[OH ^\-^ \] in the second equation is the concentration of hydroxide in a saturated lime solution (pH \~12.6).
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$$[C{a^{ + 2}}] \times {[O{H^ - }]^2} = {K_{sp}}$$
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$$Lime(Q) = \left( {{{{K_{sp}}} \over {{{[O{H^ - }]}^2}}}} \right)(MW)(Q)(12hr)$$
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h4. Results and ConclusionDiscussion
From the experimental data shown in figure 1.2 we can see that the small reactor (A1) failed to reach saturation and the large reactor (A2) produced saturated effluent only very briefly. In Comparedcontrast to the Trialexperiments 4run fromin Fall 2009, the lime in whichthis theexperiment previouswas teamadded usedas finedry hydrated limepowder instead of mixed powderedwith formwater in this run, the comparison parameter--lime input, could be a very important factor and further discussion is shown in (kinetic hypothesis). The experiment also showed that the A2 reactor could create a much better suspension than A1, which means its new geometry reaches our expectation, but the 40mL/min flow rate is far from the ideal velocity to get the best suspension. By kept changing the up-flow and observing the suspension in A2 reactor, the team assumed the optimum flow rate was 120mL/min, which around this level best suspension could be acquired in A2 reactorform of a slurry. This likely has an effect on particle size, as the large particles are never broken up if the lime is never stirred with water. A discussion of particle size can be found in the hypotheses section. The results of this run also suggest that the new large reactor performs better than the small one. For this particle size and this amount of lime, the team observed that the flow rate of 40mL/min is too low to get the best suspension; the large reactor, in particular, could have handled a much higher flow rate.
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