Boiler Response to Partial Load Rejections Resulting from System Upsets

The need for further discussions on the subject of boiler response to partial load rejections was prompted by a system islanding and high frequency incident experienced in the Missouri-Illinois area on February 13, 1978. While low frequency incidents occur periodically, the high frequency incident was unusual and required a partial load runback. Test data that demonstrate the capability of once-through boilers to accept runbacks are presented. Similar experience and data for drum boilers are limited. The requirement for instant runback of fuel and its results on the shrink of drum level contribute to the difficulties encountered when drum boilers are run back quickly. Potential directions for resolving difficulties are presented. To achieve not only immediate response to frequency disturbances, but also second minute (>30 seconds) stability, greater effort must be placed on achieving a balance between steam generator thermal input and the generated load.