Fluid handling – Line condition change responsive valves – Pilot or servo controlled
Reexamination Certificate
1998-10-27
2001-04-17
Jordan, Charles T. (Department: 3641)
Fluid handling
Line condition change responsive valves
Pilot or servo controlled
C137S486000, C137S487500, C376S245000, C376S210000, C376S211000, C376S246000, C376S247000, C376S313000
Reexamination Certificate
active
06216728
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a valve control apparatus for generating an anticipatory output response for controlling a fluid flow in a fluid flow line and, more particularly, a valve control apparatus with a tunable anticipatory output response.
When changing a nuclear power plant configuration from a variable letdown/fixed charging chemical volume control system to a variable charging/fixed letdown control scheme, the letdown back-pressure controller is not able to control letdown back-pressure without employing the fluid flow line's relief system when a letdown orifice-type valve is opened under normal operating conditions. As the associated letdown orifice does not develop a pressure drop instantaneously, a transient pressure pulse passes through the letdown heat exchanger and associated piping to the letdown back-pressure valve because the response time associated with the instrumentation typically provided for a conventional proportional, integral, and derivative (PID) controller (approximately 300 ms plus valve response time at analog based, and 500 ms plus valve response time if microprocessor based) cannot change the output signal to the valve fast enough to overcome valve stiction and thereby control the transient pressure pulse without lifting the fluid flow line's relief.
SUMMARY OF THE INVENTION
A valve control apparatus including a letdown back-pressure controller including an anticipatory output response feature solves the transient pressure pulse problem by providing an anticipatory output response whenever opening of any one of the letdown orifice valves is initiated. More specifically, initiating a response in the letdown back-pressure controller lowers system pressure before and/or concurrent with the development of the transient pressure pulse to limit the peak system pressure during the transient condition to less than the system relief pressure. Further, specific hardware and software configurations interface with the letdown back-pressure controller address variations in system designs, including changes over time. Specifically, the anticipatory output response is tunable by a technician with a personal computer.
The valve control apparatus for generating an anticipatory output response for controlling a fluid flow in a fluid flow line in a variable charging/fixed letdown chemical volume control system for a nuclear power plant that includes a back-pressure valve provided inside the fluid flow line, multiple orifice valves fluidly connected to said back-pressure valve, a sensor disposed before the valve in the fluid flow line for providing an input signal in response to properties of the fluid flow at the multiple orifice valve, and a letdown back-pressure controller receiving the input signal and providing a tunable output signal for selectively opening and closing the back-pressure valve to vary pressure in the flow line. The tunable anticipatory output signal is generated by the letdown back-pressure controller in response to any of the external digital input signals. Once the transient pressure pulse passes, the letdown back-pressure controller reverts to a PID controller generating a typical output signal. Preferably, the letdown back-pressure controller includes a computer, whereby the anticipatory output signal can be tuned by an operator. The anticipatory output signal is tunable with respect to output magnitude and a decay time constant. The letdown back-pressure controller also includes an auto closure feature and a process alarm feature.
A method for controlling fluid flow through a valve in a fluid flow line with an anticipatory output response includes measuring fluid flow properties in the fluid flow line in advance of the back-pressure valve, providing an input signal responsive to the properties of the fluid flow to a letdown back-pressure controller, processing the input signal by the letdown back-pressure controller, generating a tunable output signal from the letdown back-pressure controller for selectively opening and closing the valve to vary flow in the flow line responsive to the input signal and tuning the PID output of the letdown back-pressure controller.
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International Preliminary Examination Report of Dec. 10, 1999.
CE Nuclear Power LLC
Crenshaw, Jr. Henry T.
Jordan Charles T.
Kananen Ronald P.
Rader Fishman & Grauer
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