Method and apparatus for estimating a surge limit line for configuring an antisurge controller

Abstract

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.