While circulating heated sulfuric acid through a feed water heater of a flash evaporator for the purposes of scale removal, what would be the indication of successful removal of the scale?
• Reaction of acid with scale (calcium carbonate) and production of carbon dioxide gas • Relationship between pH, color change, and acid strength as the acid is consumed • What happens to gas evolution when there is no more scale left to react
• Think about what scale (usually calcium carbonate) does when it reacts with a strong acid like sulfuric acid. What visible sign tells you the reaction is still going on? • As the acid dissolves scale, is the acid getting stronger, weaker, or staying the same? How would that affect its pH and indicator color? • When all of the carbonate scale has been dissolved, what should happen to the production of carbon dioxide gas?
• Is the continued venting of carbon dioxide gas a sign that there is still scale left, or that it is all gone? • Does a pH of 2.0 (red) represent fresh, strong acid or partially neutralized, weaker acid? • Does a higher pH and color shift toward orange suggest that the acid has been consumed by reacting with scale?
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