Abnormal Operating Conditions in Oxygen Control Valves

Analysis and Countermeasures for Abnormal Operating Conditions in Oxygen Control Valves

High-Pressure Oxygen Valves in Blast Furnaces: Flow Surges at Small Openings and Reverse Fluctuations in Opening-Flow Characteristics

In the oxygen-enriched injection systems of blast furnaces, the precise control of oxygen flow valves is critical to furnace stability and energy safety. This article addresses two typical user-reported issues, excessive flow at small valve openings (2–5%) and a counterintuitive flow decrease at 20–30% openings. By examining working conditions such as a high pressure drop (from 16 MPa to 3 MPa), a DN150 valve body with a DN125 trim, and high-inlet/low-outlet flow direction, we analyze the failure mechanisms and propose targeted solutions from the perspectives of fluid dynamics, valve characteristics, and process compatibility.

Oxygen Control Valve

Excessive Flow at Small Openings: Miscontrol Caused by "Cv Overload"
1. Cv Mismatch: Design Selection Deviations
Understanding Cv
The Cv (flow coefficient) represents a valve's flow capacity at full opening. It's governed by the formula:

Cv = Q / (ΔP / ρ)

where Q is the flow rate, ΔP is pressure differential, and ρ is fluid density.

In this case, oxygen density varies significantly with pressure (about 180 kg/m³ at 16 MPa vs. 35 kg/m³ at 3 MPa).

If Cv is sized based on inlet conditions, actual flow capacity becomes severely oversized:

Design scenario:

At 16 MPa inlet and 3000 m³/h flow, Cv ≈ 150

Actual scenario:

At 3 MPa outlet, gas expansion per Boyle's Law increases flow to 8500 m³/h.

The required flow at 5% opening is 850 m³/h, but the existing valve delivers over 3000 m³/h at that opening.

Nonlinearity at Small Openings
Valve flow characteristics (equal percentage or linear) often enter dead zones or overshoot regions below 10% opening.