Which element’s deposition is tightly controlled in OTSG feedwater to prevent deposits?

Which element’s deposition is tightly controlled in OTSG feedwater to prevent deposits?

• A. Silica
• B. Copper
• C. Iron
• D. Sodium

Answer: (A)

In an OTSG, keeping the feedwater free of mineral deposits on the hot surfaces is critical, and silica is the element whose deposition is tightly controlled. Silica readily precipitates and forms hard scale at the high temperatures inside a once-through steam generator. Once silica deposits form, they insulate the tubes, reduce heat transfer, raise operating temperatures locally, and are very difficult to remove. Because of this, feedwater chemistry targets keeping silica at very low levels (often in the parts-per-billion range) through pretreatment and continuous purification. Iron and copper are mainly managed as corrosion products; their deposition is addressed by controlling corrosion processes and filtration, but they don’t cause the same hard-scale deposition challenges as silica. Sodium affects conductivity and corrosion behavior, but it’s not the primary cause of troublesome deposits in the OTSG like silica is.

In an OTSG, keeping the feedwater free of mineral deposits on the hot surfaces is critical, and silica is the element whose deposition is tightly controlled. Silica readily precipitates and forms hard scale at the high temperatures inside a once-through steam generator. Once silica deposits form, they insulate the tubes, reduce heat transfer, raise operating temperatures locally, and are very difficult to remove. Because of this, feedwater chemistry targets keeping silica at very low levels (often in the parts-per-billion range) through pretreatment and continuous purification.

Iron and copper are mainly managed as corrosion products; their deposition is addressed by controlling corrosion processes and filtration, but they don’t cause the same hard-scale deposition challenges as silica. Sodium affects conductivity and corrosion behavior, but it’s not the primary cause of troublesome deposits in the OTSG like silica is.