ANC CONTROL
TRIAL 1. TAP WATER
OVERVIEW
The first trial on the sloped-column lime feeder, was developed using tap water. The flow rate for this experiment (120mL/min) was calculated based on the upflow velocity found for experiments 1 and 2. The amount of lime for this experiment was 80 grams, which was calculated in volumetric proportion with the experiment 2.
INTRODUCTION
The experiment consisted of the injection of tap water with a flow rate of 120mL/min (Again, include upflow velocities, not flow rate) 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 12.
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)
At the top of the sloped column, the water looked clear of 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 column. This was a desirable behavior because the lime was still in the apparatus, giving donating hydroxides to 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. (Why only 20 minutes? Give more explanation behind observations you make)
Figure 1. pH vs time
CONCLUSIONS
The design seemed to work as expected and the movement of the particles was desirable. However there were some difficulties faced in the running of this trial.
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 especially since the apparatus was extremely long and difficult to deal with. 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.
Hence the next step was to run a second trial using tap water, the same upflow velocity but a larger amount of lime.