For feedwater used in high-pressure boilers and steam turbines, which impurity is generally considered the most damaging due to carryover and deposition risks?

Introduction / Context:
High-pressure boilers and turbines demand ultrapure water to prevent corrosion, scaling, and deposition. Among common impurities, silica poses unique challenges because it can volatilize with steam and deposit on turbine blades, severely degrading efficiency.

Given Data / Assumptions:

• High-pressure service where steam purity requirements are stringent.
• Boiler drum and turbine susceptible to carryover effects.
• Comparison among typical impurities.

Concept / Approach:
Silica forms hard, glassy deposits that are very difficult to remove. At high pressures, silica’s volatility increases, enabling it to travel with steam and foul superheaters and turbine stages. While dissolved oxygen is corrosive, modern deaeration/scavenging can reduce O2 to near zero; silica control requires deep demineralization and close monitoring.

Step-by-Step Solution:
Identify deposition risk: silica deposits reduce heat transfer and turbine efficiency.Consider removal methods: strong-base anion exchange, mixed-bed polishers, or reverse osmosis plus polishing.Conclude that silica is the most detrimental impurity for high-pressure steam systems.

Verification / Alternative check:
Industry water-chemistry guidelines set silica limits that become extremely low as pressure rises, reflecting its outsized damage potential in turbines.

Why Other Options Are Wrong:
Turbidity: largely removed by clarification/filtration and does not carry over as silica does.
Phenol: an organic contaminant of concern for emissions/odor, not primary for turbine scaling.
Dissolved oxygen: critical for corrosion but manageable with deaeration and scavengers.

Common Pitfalls:
Assuming oxygen is always the worst impurity; at high pressures, silica is the key limiting constituent for steam purity.

Final Answer:
Silica