ANC CONTROL
TRIAL 1. TAP WATER
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INTRODUCTION
The first trial on the sloped-column lime feeder used consisted of using tap water. (Fragment sentence) To keep the upflow velocity to be the same as for the vertical column lime feeder (previous lime feeder), the flow rate for the new feeder was calculated to be 120mL/min. The flow rate for this experiment 120mL/min which was calculated based on an upflow velocity of 4.42mm/s, as found in experiments 1 and 2. The amount of lime taken for the new feeder this experiment was 80 grams, which was calculated in volumetric proportion with the old feeder. (What do you mean old feeder and new feeder? What changed? I thought the diameter was the same. Why will the upflow velocity or amount of lime you add change?)
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experiment 2.
The objectives for this trial were:
• To check if the sloped column lime feeder model works.
• Determine if there are any preliminary technical difficulties within the model and/or process and make improvements for them for future experiments.
• Find the maximum time for which the pH at the effluent remains at 12.
PROCEDURE
The experiment consisted of the injection of tap water with a flow rate of 120mL/min (Again, include upflow velocities, not flow ratei.e. an up flow velocity of 4.421mm/s ) regulated with a peristaltic pump being operated by the process controller software. At the effluent end (top of the sloped column)a pH probe was connected to collect periodic (every 5 seconds) data of the effluent pH. (Where is your process control file? How did you regulate flow rate in process control? You should have a separate materials and methods section)
OBJECTIVES
• To check if the sloped column lime feeder model works.
• Determine if there are any preliminary technical difficulties within the model and/or process and make improvements for them for future experiments.
• Find the maximum time for which the pH at the effluent remains at 12The Process Controller files can be found in the Materials and Methods section.
RESULTS
The apparatus worked well with the established upflow velocity. The movement of particles was clearly visible and in accordance with the hypothesized movements (similar to the particle movements in the tube settler spacing apparatus). (You never told us the hypothesized movements. What about it worked well, be specific if you are going to include observations), i.e. a fluidized bed up to the middle portion of the lime feeder and a relatively clear effluent towards the top end of the (sloping) column which acted like a tube settler. At the top of the sloped column, the water looked clear of and free from visible particles but according to the pH sensor measurements, it was saturated with base (i.e. pH 12), which was in accordance with the main objectives. A great amount of lime remained captured in the middle of the apparatus, although it was held in suspension. This signifies that the upflow velocity was high enough to give good suspension but the sloped column took care that the extra lime did not fall out with the effluent water but remained inside the columnthat would have been flushed out had it not been there. This was a desirable behavior because the more lime was still in the apparatus, giving donating hydroxides to the solution the protons needed by water.
However, the pH remained stable at 12 just for 20 minutes. It was necessary to calibrate the pH probe again, to clean the apparatus and to review the calculations in order to determine the reason for the abnormal pH behavior. Other reasons for this behavior included the fact that since the lime was poured into the narrow column in a powder-form, it resulted in the clogging and pressurizing of the column. (Why only 20 minutes? Give more explanation behind observations you make)Subsequent flushing (using higher flow rates to force the lime to unclog) caused loss of lime. More importantly, during this period of time, data was not recorded since the lime feeder had to be overturned manually to get the solidified, stuck-up lime to dissolve.
Figure 1. pH vs time
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As the lime was poured into the apparatus in powder form with very little water inside, this resulted in the solidifying of the lime sludge and caused initial pressurizing within the column. It also took up time to clear out the clogging clog especially since the apparatus was extremely long and difficult to deal withunusually shaped. To overcome this difficulty it was decided that henceforth for all future experiments, lime will first be made into a slurry form and poured into the apparatus.
Secondly, since the experiment lasted for only 20 min, it was necessary to run at least one more trial using tap water using a different (larger) amount of lime.
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