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Target by using acid Whether acid is in use, the target of the acid treatment is to keep pH at the level of 8,3 to 8,5 In large systems, where the economics can be a significant factor, acid feed has to be selected not according to pH but according to Ryznar Index criteria. Under those circumstances, we select the Ryznar Index area, where we can guarantee effective corrosion and scale inhibition using our chemicals, and we try to lead the water tendencies to this range by using the acid. An example of this procedure is presented at the following graphs. NEVER USE AN ACID ALONE FOR SCALE INHIBITION. You have to use it always in combination with chemicals. The use of the acid reacting with alkalinity will control only the pH, not the scaling/corrosive tendencies. Tendencies are also related to the Calcium Hardness and the water temperature. AND THERE IS NOT A UNIQUE TEMPERATURE ALL OVER THE SYSTEM. NOT EVEN AT A SINGLE HEAT EXCHANGER the temperature is uniform. The water temperature varies from as low as 15-25 deg C at the cooled water, till as high as 125 deg C at the surface of critical, high load heat exchangers. Never consider the returning water bulk temperature (p.e. 35-41 deg C) as the main water temperature as to calculate the tendencies. Heat exchangers surface temperatures are much more different, and deposition and corrosion is taking place at those temperatures.
First we calculate the pH and the tendencies which will be evolved into the system, without the use of acid, as a function of the Cycles of Concentration fluctuation. Being outside the acceptable limits, we decide to use H2SO4 for pH control. Using specific software, we calculate the evolved tendencies, within the operational Cycles of concentration limits, as a function of the quantity of acid feed. Selecting the required limits of the acid, we calculate the pH range in which the pH control has to be adjusted. |
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