ANC CONTROL
Design 2010
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Introduction
The Spring 2010 ANC Control team inherited the original apparatus used by the Fall 2009 team. The original design of the apparatus was giraffe-like in shape, with two 1" pipes connected at a 45 degree angle. See , as depicted in Figure 1.
Figure 1
Spring 2010 Design
In order to address the Hypothesis and also to increase the ease with which the lime is fed, our team redesigned the apparatus. We added initial failure hypotheses and provide an easy way to feed lime, the team chose to redesign the apparatus. By adding a vertical column to the top half of the apparatus to allow for lime to simply be poured in. As the lime traveled down the vertical column, the particles would settle in the lower part of the apparatus and/or flow into the diagonal piece, but then settle out before leaving in the effluentreactor which is open to the atmosphere at the top, we can now simply pour lime in while the apparatus is running. Because the water in the upper vertical column is still, lime settles down and joins the fluidized bed in the lower segment.
The vertical column addressed the issue of feeding the lime but in order to address the other hypotheses, we decided to build two apparatuses: one with all 1" tubes, one with 1" vertical columns and 2" diagonal tubingimprove the reactor's performance and address some hypotheses, the team built an additional apparatus with an upper slanted segment of 2" diameter instead of 1". By doubling the diameter of the tubing, we divided the flow rate through the diagonal portion by the design reduces the upflow velocity in that segment by a factor of four. This allowed allows for a lower capture velocity, which attempts to address addresses the issue of lime being lost out with the effluent and allows higher flow rates. See Figures 2 and 3 depict the two apparatuses constructed by the Spring 2010 ANC Control Team.
Figure 2
Figure 3
The redesigned apparatus took the original apparatus and added a vertical 1" column by which lime is to be fed.
Figure 3
A second apparatus was built with an almost identical design, only 2" columns for the upper half of the apparatus were implemented.
Siphon Problem
In designing the new apparatuses, we the team made the vertical column taller than the diagonal column to ensure that water would flow out the diagonal column. We determined that the head loss through the fixtures at the end of the diagonal column would be negligible. However, when we began running experiments we discovered a problemthe former, which is open to the atmosphere, would not overflow when water was pumped through. However, the team discovered a problem when it began running experiments. At the end of our the effluent tube, we had there is a candy-cane shaped piece shown in Figure 4 that the water flowed through - this was in order to have the water pass over the pH probe properly (see Figure 4). However, because this resulted in a dip of the height of the water, and the water filled up the tube, the atmospheric pressure at the top of the water in the tube forced the water in the vertical column to drop to its same height (see Figure 5).
Figure 4
Figure 5
We flows through which backs up the flow enough that the pH probe can be immersed. This creates a free surface open to the atmosphere at the elevation of the sink. Basically, the only other free surface in the system exposed to atmospheric pressure is the water in the vertical feeding tube, which should be at a much higher elevation. This creates a siphon which drains the reactor to the elevation of the pH probe, as shown in Figure 5.
Figure 4
Figure 5
The team attempted to correct this problem by sealing the top of the vertical column with a cap. This would result in a vacuum in the area about the water level and would allow It was hoped that this would create a vacuum above the water in the column to remain vertical column and hold that surface at a constant height (see elevation, depicted in Figure 6). However, we were not able to fully seal the cap and having an open vertical column to pour lime directly into was part of the design's attractiveness.
Figure 6
We decided to alter the design instead by opening the very the cap would not seal well enough to solve the problem, and the solution meant that the reactor would be drained each time the cap was removed for lime feeding.
Figure 6
Instead, the team altered the design by opening the top of the diagonal column to atmospheric pressure. Doing so allowed for open channel flow in the tube and allowed the height of the water in the vertical column to remain constant, matching the height of the water level in the diagonal column. (See Figure 7)
Figure 7
Future design improvements
• Tubes: ½ " vertical 1" vertical 1" diameter
• Pumping the lime up to the top of the vertical column
• Determining how the apparatus could be incorporated into a real Agua Clara plant
Things that we would like to work on in the future would be changing the lower half of the apparatus. Throughout our experiments, we have determined that the lower vertical column is needed to keep the larger lime particles in suspension. Our experiments have shown that the smaller, finer lime particles travel up into the 2" diagonal column and are either suspended there, settle onto the lower diagonal, or travel up the upper diagonal and escape in the effluent. We would like to keep more of the lime mass suspended in the lower vertical column. One idea for achieving this would be to switch from a 1" column to a 2" column in the vertical section. (See Figure 8)
Figure 8
Another design change we are considering is the possibility of pumping the lime slurry up to the vertical column. This would make it more "user-friendly" as two of our members are not tall enough to feed the lime and thus, cannot run an experiment independently. Concerns associated with this method would be configuring Process Controller to run multiple pumps, differing flow rates for water verses lime slurry, when to pump which, and more. The pumping method also raises the issue that lime has to travel through so much tubing to reach the apparatus, providing it with a lot of surface area to settle on or coat. This will make it difficult to know exactly how much lime is actually making it into the apparatus.
, shown in Figure 7.
Figure 7 One final design challenge that we need to tackle in the coming weeks is thinking about how our design could be implemented into an Agua Clara plant. Due to the height of the apparatus, it may be necessary to have the bottom rest below the floor where the operator would be walking. If the apparatus started at the lower level of the sedimentation tank (or floc tank) and then rose above ground to expose the vertical and diagonal columns, it might be at an appropriate height for the operator to feed the lime manually (without a ladder).