Troubleshooting of Copes Vulcan bypass valve

Principles and Troubleshooting of Algorithmic Temperature Control (ATC)

Traditional temperature control relies on plug-in thermocouples, but there are unevaporated water droplets adhering to the thermocouple sleeve at the outlet of the bypass system (especially the LP bypass), resulting in significantly low temperature measurement. After the controller is fully turned on to reduce the temperature, the temperature actually drops and oscillations occur. The Algorithmic Temperature Control of Copes Vulcan directly determines the required cooling water volume through feedforward calculation, fundamentally solving this problem.

6.1 Working principle of ATC

The system collects the following input signals:

Steam temperature T1 and pressure P1 in front of the valve → enthalpy value h1 obtained by checking the table

Steam flow Q1 (calculated from throttle orifice or valve position flow curve)

Valve pressure P2 (condenser pressure) → Determine outlet saturation enthalpy value h2

Cooling water temperature (set as a constant, with minimal impact from changes)

Calculation formula:

Q w=Q one×h one−h two h two−hw 

Q w=Q one× h two−h w h one−h two

After the PLC calculates the required cooling water flow rate Qw, it directly controls the cooling water regulating valve to the corresponding opening (based on the valve characteristic curve). This process does not rely on outlet temperature feedback, so it is not affected by water droplet adhesion. In actual operation, a slow PI loop is used to fine tune residual errors.

6.2 Common on-site issues

Problem cause handling

The actual outlet temperature is much higher than the calculated cooling water temperature. Assuming a large deviation (such as a 10 ° C increase in summer water temperature), hw is used as a variable input and connected to a water temperature transmitter

The opening of the cooling water valve is always 100%, but the temperature is still high. The pressure of the cooling water is insufficient or the nozzle is blocked. Check the outlet pressure of the water supply pump and clean the nozzle

The flow Q1 signal is inaccurate, and the range setting of the orifice plate differential pressure transmitter is incorrect; Re calibrate the differential pressure transmitter if the valve position feedback does not match the Cv curve; Download the correct Cv table to PLC

After stabilizing the control, there is a sudden jump in the steam inlet pressure P1 and a significant fluctuation. Check if there is a condensate column or blockage in the main steam pressure transmitter in front of the bypass valve

6.3 Special Applications: No Calculation Cycle Delay (Case Inspiration)

In the bypass system of the back pressure machine, Copes Vulcan applies the "2-second look back" logic: the PLC samples the steam parameters every 2 seconds and continuously stores the latest values. When the trip signal arrives, the system calculates the valve position using the last valid parameter before the trip to ensure undisturbed switching. If it is found on site that the pressure overshoot is too large after switching, the "look back" window duration should be checked to ensure it matches the system inertia (generally recommended 1-3 seconds).

Case Analysis of Back Pressure Turbine Bypass System (96TW20706)

This case is an HP back pressure machine driven by a synthesis gas/CO ₂ compressor, downstream of which is a catalyst unit, with extremely high requirements for steam pressure and temperature stability. The bypass system needs to achieve "disturbance free" switching when the turbine trips, directly supplying steam to downstream processes.

System configuration:

A 6 × 12 "Class 2500 HP DSCV bypass valve (forged steel F22)

A 2 "Class 2500 cooling water regulating valve (WC9)

Centralized HPU electro-hydraulic actuator, fault open

Key points of control logic:

During normal operation, the PLC continuously monitors the flow rate, pressure, and temperature at the inlet and outlet of the steam turbine, and pre calculates the target opening of the bypass valve and desuperheating water valve when the turbine trips.

The calculated value is locked in the PLC output register and not output.

When the DCS sends a digital signal for tripping, the switch switches and the valve moves directly to the locked position within milliseconds.

Maintain this position for about 10 seconds (adjustable), then switch to the regular PID slow adjustment mode.

Typical on-site fault: If the valve fails to accurately stay in the predetermined position when the machine trips, it is usually due to the locking register being erroneously updated in the previous sampling cycle. Check logic: Ensure that the 'maintain output' function is only updated when there is no trip signal and the operating conditions are stable.

This case ultimately achieved a pressure fluctuation of less than 1 bar, proving the effectiveness of the feedforward+preset position strategy.

Integrated steam regulation system for combined heat and power (CHP)

Modern CHP factories often require steam supply at multiple pressure levels, and Copes Vulcan can provide a complete set of equipment from the main bypass valve to the end temperature and pressure reduction station. Common integration issues on site include: