Compressor Controls Corporation

Leonid Shcharansky

Boris S Khots

German D Lakov

Compensating for the complex changing shape and location of a turbocompressor's surge limit line can be difficult and imprecise when using antisurge controllers that do not incorporate sufficient capability. Based upon various operating conditions, surge limit line changes can be attributed to a number of process variables. These effects are particularly relevant to multistage centrifgal and axial turbocompressors operating with variable rotational speed and equipped with adjustable inlet or diffuser guide vanes, or both. This invention relates to an innovative method of antisurge control in which the function of those process variables (comprising the turbocompressor operating condition parameters) is used to calculate distances to the surge reference line. The function is formed as a superposition of the functions of lesser numbers of variables. For instance, these functions are formed as polynomials where the power of each polynomial function is determined by real characteristics of correlation between the shape and location of the surge limit line and the variables to which this polynomial function is being formed.

Method and apparatus for antisurge control of turbocompressors having complex and changing surge limit lines

The exactness of surge-limit information facilitates the determination of how safely a turbocompressor can operate as well as determining the size of the operational envelope in which a compressor can function with a closed antisurge valve. Furthermore, in order to accurately describe the complete interface between stable and unstable operation, a sufficient number of test points must be found. Consequently, if a turbocompressor 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 process variables; as a result, each test leads the turbocompressor into surge which can be detrimental because of strong dynamic loading. For that reason, this invention describes a technique employed during turbocompressor testing (either without generating surge or with a minimum number of surges) for defining both the shape and the location of a turbocompressor's surge limit. The procedure is performed by (1) testing a turbocompressor, (2) measuring appropriate values associated with the turbocompressor's operation and then storing the accumulated data, (3) curve fitting the data, (4) estimating the surge point based on curve fit, and (5) repeating step 3 for multiple rotational speed and guide vane positioning. These data are accumulated in the form of calculated performance-map coordinates. The surge reference is defined by the maxima of the curve fits at multiple constant equivalent speed and guide vane position values.

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Clive, IA, United States of America

Leonid Shcharansky