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ANC CONTROL



TRIAL 3. DISTILLED WATER, CHANGED BRAND OF LIME



OVERVIEW

This trial was carried out using distilled water to determine how long the experiment would last without the influence of carbonates (present in tap water). In addition, another parameter that was inadvertently changed was the brand of lime, since the previous supply of lime was depleted. The new lime brand had 70% calcium hydroxide compared to the older lime containing 96% Calcium Hydroxide. Thus during this trial, not only was the effect of water quality was evaluated but also the effect of lime quality. For this trial the pH remained stable at 12 for just 3.5 hours.

INTRODUCTION

For this trial tap water was replaced by distilled water. In addition, the lime was changed, looking for a better quality of the compound. The apparatus was kept the same as for the previous two trials.

Although the change in the brand of lime was not pre-decided for this particular trial, it would allow us to evaluate if the performance of the lime feeder changes on using a different lime brand. This change is important to study taking into account the fact that the operators would have to deal with a different brand(s) in the local Honduran markets.

OBJECTIVES

• Confirm if the carbonates or other quality characteristics of tap water, have any influence on the lime feeder performance.
• Evaluate the apparatus performance with a different brand of lime.
• Look for improvements for future experiments.

RESULTS

For the above trial, the pH remained at 12 for about 3.5 hours but the performance of the apparatus changed drastically. The new lime was much more soluble in water and generally was composed of finer particles. The new lime did not accumulate in clusters at the bottom of the apparatus. This gave an almost perfect and uniform suspension of lime throughout the apparatus leaving no scope of observing the particle movements.

This presented a new challenge of verifying whether the hypothesized plate settler theory was true for different brands (having different particle size distributions and different composition)of lime or if the unexpected results of the experiment was due to some impurities present in the distilled water supply system. (A much higher performance for the lime feeder had been expected - much greater than 4 hours but less than 14 hours;4 hrs being the duration obtained using tap water and 14 hrs being the theoretical run length with the given amount of lime and given water flow rate.)

Figure 1. pH vs Time (h)





CONCLUSIONS

The information obtained from this trial was not enough to probe the influence of the two considered variables. Since 2 variables got changed simultaneously, different conclusions can be extracted:

One, that the distilled water made little impact on the working of the lime feeder or the distilled water supply system had a presence of impurities.

Second, the decrease in efficiency of the system was due to the fact that a different lime quality was used and did not match the hypothesis on which the design was based.

Further experiments were needed to probe or reject the distilled water hypothesis. It is necessary to check the performance of the experiment with the first lime brand and distilled water, and with the second lime brand and tap water. Those results will provide comparable parameters. Hence the next trial involved usage of the older lime brand (96% Calcium Hydroxide) with distilled water.

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