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ANC CONTROL


EXPERIMENT 2: Testing the lime feeder performance using a pH probe


INTRODUCTION

The new apparatus was equipped with a pH probe whose values could be logged into the computer via Process Controller. In addition, Process Controller was utilized to automate the experiment. With those additions, the team measured the pH of the effluent, looking for the optimal flow rate that could maintain a pH of 12 for 24 hours.

IMPROVEMENT

The design of the water outlet was changed in order to ensure an adequate pH measure This included putting the pH probe in a vertical tube and making a curved outlet for the effluent. With these changes, the apparatus could get a more stable pH measure.

DESCRIPTION

The mass of lime added was 17.89gm. With this amount of lime, the flow rate chosen was 40mL/min, because the lime remained suspended and it was assumed the apparatus would run for a longer time. The initial pH reading was 12 and stayed that way for 2 hours. It gradually decreased to 8.85 by the 24th hour.

Because pH was decreasing at a constant rate during the trial, the flow rate was increase to 60 mL/min. When the change was made, the probe registered an increase to a pH of 9.4.

After the change in flow rate was made, Process Controller showed the same behaviour decreasing constantly. When a pH of 8.5 was reached, the experiment was terminated, despite the fact that there was still a suspended bed of lime.

IDENTIFIED PROBLEMS

  1. The arrangement of the pH probe was not stable so the pH data was not accurate.
  2. The simple column design was not adequate in giving any range in terms of flow rates that could fulfill the objectives of maintaining a good suspension and maintaining a stable pH for 24 hours on the effluent.
  3. The vertical column was not enough to store the required amount of lime to run the experiment for 24 hours.

RESULTS

  1. With a flow rate of 40mL/min, the pH dropped from 12 to 11 after about 3.5 hours.
  2. After increasing the flow rate to 60mL/min and keeping the other parameters constant, no significant changes were noted.
    Figure 1 shows the pH measures during the experiment.The results of the experiment are on an attached excel file. Excel Spreadsheet
    Figure 1. Time vs pH

    Figure - 2 Apparatus used for experiment 2, using a pH probe
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