Variable Pressure Peaking Boiler, Operation, Testing, and Control

During the last few years many utilities have been purchasing fossil fueled power plants designed to be used for initial or future cycling service. As more large nuclear units are placed in service with their low incremental operating cost, it is anticipated that many fossil units will be operated to meet daily cycling load demands while still retaining the ability to efficiently supply a large amount of the system base load, if it is required. This paper discusses the operation and control of a gas and oil fired variable pressure drum boiler specified and designed for peaking operation at a major U. S. utility company. Operating results obtained during normal unit shutdowns, startups for morning peak load, and rapid, variable, and constant pressure load changes are presented. Also discussed are the major control system features employed for variable pressure operation as well as operation of the superheater by-pass system. The advantages of variable pressure operation are pointed out and explained along with supporting operational data.