Variable pressure operation: effects and correlation of computer modeling to testing results with and without automatic controls

Power plants designed for baseload service increasingly are being required to operate in a cycling mode due to overcapacity problems. Improved cycle capability due to conversion to variable pressure operation (VPO) results in performance benefits and drawbacks. To evaluate these changes, computer simulation calculations and field testing were carried out for Niagara Mohawk Power Corporation's Huntley Steam Station Units 67 and 68 and Dunkirk Steam Station Units 3 and 4 combined Tandum Compound-double flow turbines and ABB Combustion Engineering separated furnace, controlled circulation tangentially fired 200 MW (coal-fired) boilers. Furthermore, limited computer studies were done with gas and oil fuels to simulate conditions on Albany Station's CE boilers (converted from coal to gas/oil). Runs were also made on the combined turbine and T-fired, CE 100 MW (coal-fired) to evaluate general conclusions. Technical background, effects of VPO on the boiler, turbine and balance of plant and correlation of computer modeling to testing results at constant and sliding pressure with and without automatic controls are discussed.