Why is it necessary to maintain the pH value of the water vapor system between 9 and 10 in SHELL gasifiers?
Thread Content
Why is it necessary to keep the pH value of the water vapor system between 9 and 10 in SHELL gasifiers? When the pH value cannot be maintained within this range, trisodium phosphate is added. What is the purpose of adding this substance?
The pH level is maintained between 9 and 10 to keep the boiler water alkaline and prevent corrosion of the system’s pipes. Sodium triphosphate is added to prevent calcium and magnesium ions in the water from forming scale, which then can be removed as loose sludge through the drain valve.
For more detailed information, it is recommended to consult literature on boiler water quality control; the principles are basically the same.
After adding trisodium phosphate, hydrolysis produces hydroxide ions, resulting in alkalinity. The calcium and magnesium ions in the boiler water react with phosphate and hydroxide ions to form a loose type of scale, which is then discharged from the drum (gas-liquid separator) through the waste discharge pipeline. Generally, to control the pH value, a mixed formulation is used, with two of sodium monophosphate, disodium phosphate, and trisodium phosphate being combined; in special cases, caustic soda can be added directly.