ANC CONTROL
FALL 2009 Research
INTRODUCTION
The former ANC group experimented on different designs for a lime feeder, including a column model, a conical vessel, a funnel-column and an inverted traffic cone model. These results can be found on pages 10 through 17 of ANC control with lime.docx and in Table 1 below. The descriptions and diagrams pertaining to the experimental set-ups are explained in pages 4 through 8 of the above report.
The column
The Column model succeeded in keeping the lime suspended for a few hours but the water began to flow in a preferential path after the lime settled on the bottom. For the conical column, the mixing at the bottom of the vessel proved to be insufficient in keeping all the lime in a suspended state. On the other hand, the funnel-column apparatus worked well for 20 hours but only because it was unclogged periodically, which would not possible in a real-time set up.
As a result, the inverted cone model that supplied saturated limewater at a pH between 11 and 12 for about 18 hours without having to be unclogged and without the above difficulties was selected as the best alternative among them.
The most effective design was the inverted cone because it . However, the main problem with it is was that inverted cones are extremely difficult and expensive to construct, install and maintain. So the task of the ANC team is was to search for a simpler solution for the lime feeder design. Since the upflow velocities were also highly variable (as seen in Table 1), another goal was to find the optimal upflow velocity for the limefeeder.
Wiki Markup |
---|
{float:left}*Table 1. Results of 2006 Experiments. M_init is the initial mass of lime; Q is the flow rate; T_obs is the time the effluent had a pH of 12; T is the theoretical duration; Vb is the upflow velocity; and Vbottom is the velocity at the bottom of the vessel.{float} |
Reactor | M_init (g) | Q (L/min) | Res.Time | T_obs (hr) | T(hr) | Vb | Vbottom |
---|---|---|---|---|---|---|---|
HalfCone | 400 | 0.6 | 12.48 | 9 | 12.56 |
| 84.9 |
Funnel | 200 | 0.1 | 46.10 | 20 | 37.67 | 0.71 | 12.4 |
Funnel | 200 | 0.1 | 46.10 | 25 | 37.67 | 0.71 | 12.4 |
Funnel | 100 | 0.1 | 46.10 | 7.75 | 18.84 |
| 12.4 |
Cone | 300 | 0.4 | 31.95 | 6 | 10.69 | 1.5 | 19.6 |
Cone | 300 | 1 | 12.78 | 1.25 | 4.28 |
| 49.0 |
Cone | 500 | 0.88 | 14.52 | 4.75 | 8.10 | 2.35 | 43.1 |
Cone | 1800 | 0.55 | 23.24 | 18 | 46.65 |
| 26.9 |
Cone | 1000 | 0.52/0.84 | 22.02 | 11 |
|
|
|
Cone | 1000 | 0.67 | 20.00 | 12 |
| 1.65 | 32.8 |
ALKALINITY IN HONDURAN WATER
The table below shows the actual measures measurements of pH and alkalinity in AguaClara treatment plants in Honduras. To have high accuracy in the lime feeder designmore accurately research ANC, the conditions of Honduran raw water were simulated in the laboratory will be simulated. The results in the table demonstrate a decrease of pH during the treatment process which . It is strongly visible on Cuatro Comunidades and Tamara plants.
Table 1: Water Quality in Honduras
Source: Honduras water reports, 2009
Therefore, one goal was to increase the alkalinity of the water, creating a buffer system against acidity.
Wiki Markup |
---|
{float:left}*Table 2: Water Quality in Honduras
Source: Honduras water reports, 2009{float} |
OJOJONA | RAW WATER | TREATED WATER |
---|---|---|
pH (UN) | 6.51 - 6.8 | 6.26 - 6.56 |
Alkalinity (mg/L CaCO3) | 34.7 - 36.3 | 17.3 - 19.4 |
MARCALA | RAW WATER | TREATED WATER |
pH (UN) | 6.44 - 7.28 | 6.07 - 6.45 |
Alkalinity (mg/L CaCO3) | 15.3 | Before chlorination 8.7 |
CUATRO COMUNIDADES | RAW WATER | TREATED WATER |
pH (UN) | 6.34 - 7.00 | 6.80 - 6.85 |
Alkalinity (mg/L CaCO3) | 7.65 | Before chlorination 4.59 |
TAMARA | RAW WATER | TREATED WATER |
pH (UN) | La Chorrera: 6.44 | 6.56 - 6.66 |
Alkalinity (mg/L CaCO3 | La Chorrera: 7.14 | 4.08 |
PROPERTIES OF LIME
The pH of calcium Hydroxide or hydroxide(lime) solution decreases with an increase in pHtemperature. (see figure 1 Figure 3 below) The temperature at the Honduran plants is generally in the range of 19-21 degrees C but during summers it can go up increase to about 27 degree degrees C. This temperature change differential can change the pH of lime limewater and thereby affect the working of the lime feeder and needs to be taken into consideration while designing the lime feeder.
Table 2:
Figure 3. Changes in pH of lime with respect to Temperature changes
Wiki Markup |
---|
{float}{float} |
PROCEDURES AND RESULTS
One of the first tasks was to calculate the dosage of lime required by the lime feeder and the measure the relationship between the changes in pH and ANC with changing flow rates in the lime feeder. The analysis of lime feeder flow requirements was made with the help of MathCAD software.
...
Experiment 3: Addition of sloping glass column above the lime feeder and Tube-length Calculations
FUTURE TASKS
...
...