Data processing: generic control systems or specific application – Specific application – apparatus or process – Mechanical control system
Reexamination Certificate
1999-02-12
2001-11-13
Gordon, Paul P. (Department: 2121)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Mechanical control system
C701S100000
Reexamination Certificate
active
06317655
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to a method and apparatus for antisurge control of a turbocompressor by experimentally defining a surge reference that approximates a surge limit. More specifically, it relates to a method that accurately estimates both the shape and the location of the surge limit. The technique is employed during compressor testing (either without generating surge or with a minimum number of surges), and it uses the resultant test data to configure an antisurge controller.
BACKGROUND ART
To provide and sustain efficient, economical control of a turbocompressor, it is necessary to know both the location and the shape of its surge limit line, as plotted on a performance map. The exactness of this surgelimit information determines how safely a compressor can operate, and it also helps to determine the size of the compressor's operational envelope. Therefore, the more accurately the surge-limit characteristics are estimated, the larger is the region (operational envelope) in which a compressor can function with a closed antisurge valve. However, during normal operation, compressor-system performance characteristics often change significantly due to inherent influences, such as mechanical degradation of its flow-through parts and defects in its seal system that, in turn, cause the location and shape of the surge limit line, as well as the performance limits, to vary.
Establishing the largest possible operational envelope (with the antisurge valve closed) requires compressor testing to identify the actual characteristics of a surge limit, and then using this information to configuring an antisurge controller. A sufficient number of test points must be found to accurately describe the complete interface between stable and unstable operation. Consequently, if a compressor operates within the broad ranges of rotational speed or guide vane position or both of them, the unit must be repeatedly tested using different values of these process variables; as a result, each test leads the compressor into surge which can be detrimental because of strong dynamic loading.
DISCLOSURE OF THE INVENTION
A purpose of this invention is to improve upon the prior art by eliminating (or decreasing to a minimum) occurrences of surge and the resulting detrimental dynamic loading when testing a turbocompressor for the purpose of defining both the shape and the location of its surge limit. This curtailment of surge and its adverse effects is achieved while accurately estimating surge points by using characteristic curves corresponding to constant parameters (equivalent speed, guide vane angle, or other parameters if they exist). The tested characteristic curve is curve fitted using tested data points with calculated performance-map coordinates. The maximum of the curve then determines the surge point.
The curve fit, called the first function, is defined and checked for accuracy at each incremental step toward surge and is developed in the following manner:
A compressor's operating point is moved toward surge by increasing the resistance of its compression system while maintaining parameters (such as, equivalent speed and guide vane angle) constant.
During compressor testing, process variables are measured from which, generally, unmeasurable variables and parameters are usually calculated.
Values of the calculated process variables and the calculated parameters (used as performance-map coordinates and parameters required to estimate where the compressor will surge) are stored in an estimating module.
Accumulated data are fitted by a curve (the first function) that is updated after every incremental move toward surge.
A maximum for the calculated function is found by computing a zero of the function's first derivative.
A surge reference is then defined, based upon (1) the location of the first function's maximum or (2) a predetermined relationship between its coordinates and the first function's maximum.
After repeating the test using different operating parameters, multiple maxima are known. The surge reference is defined by curves (called second functions) fitting these maxima.
To prevent compressor surge, a surge control line should be defined on a performance map (at a preset distance from the surge reference line) and used by an antisurge controller to modulate an antisurge valve. To help confirm that the surge control line's location is accurately chosen, it should be reached (during testing) by the compressor's operating point without encountering surge.
Should the shape and location of a surge limit line depend on guide vane position or other process parameters, testing is carried out for the full range of these parameter values.
Implementing this invention provides a nearly surge-free method for defining a surge reference because the probability of surge under these conditions is minimized. If there is a sudden surge, testing is stopped and the point at which surge occurs is recorded.
REFERENCES:
patent: 5508943 (1996-04-01), Batson et al.
patent: 5752378 (1998-05-01), Mirsky et al.
patent: 5879133 (1999-03-01), Mirsky et al.
patent: 5908462 (1999-06-01), Batson
patent: 5951240 (1999-09-01), Mirsky et al.
patent: 5967742 (1999-10-01), Mirsky et al.
Khots Boris S.
Lakov German D.
Shcharansky Leonid
Cabrera Zoila
Compressor Controls Corporation
Gordon Paul P.
Henderson & Sturm LLP
LandOfFree
Method and apparatus for estimating a surge limit line for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for estimating a surge limit line for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for estimating a surge limit line for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2573784