Competition in the electric power generation market demands that power plants operate efficiently and generate the maximum amount of power for which they were designed consistently and safely. In addition, the significant increase in the price of natural gas has caused a renewed interest in coal-fired power plants, both existing and new-build. Existing coal-fired plants are being retrofitted with emissions control equipment to meet stricter standards. This equipment consumes significant amounts of auxiliary power, which plant owners might like to regain by increasing the retrofitted units’ maximum output.
Central station power plants have been designed with a significant amount of margin. Boosting a generating unit’s output by taking advantage of this design margin can provide plant owners with an available source of new power with attractive returns. Improvements in equipment efficiency and control system performance allow electric generating units to take advantage of the existing design margins.
In taking advantage of equipment design margins, it almost always is the case that one or more design limits will prevent full utilization. Usually, the best performance results are identified in finding improvements in the major energy conversion equipment such as boilers and steam turbines. With new computer-based analytical methods, steam generator and steam turbine manufacturers can identify significant power increase potentials. An evaluation of the power plant auxiliary systems is necessary to assess the full effect major system uprates have on plant operation. Balance-of-plant equipment may limit the potential improvement of major power uprates.
This article discusses the need to thoroughly examine the balance-of-plant equipment and systems as part of any power uprate study. Examples will be given from recent studies to
show how much additional generated power can be obtained if the balance-of-plant equipment and systems are considered as part of the boiler and turbine uprate.
Power plant owners investigate restoring or increasing plant capacity for many reasons including:
• Recovery from degradation—In many cases older coal-fired power plants, which were scheduled for retirement, are now planned to run well into the future.
• Recovery from emissions control retrofits—The addition of control equipment to reduce plant emissions have significantly increased the auxiliary power consumption of fossil-fueled power plants.
• Design margin availability—Central station power plants have been designed with a significant amount of margin. The ability to increase a generating unit’s output by taking advantage of this margin provides an available source of new power with a minimum of capital cost.
• Competition—In those regions where coal-fired power plants are competitive because of high-priced natural gas generated power or higher-priced imported power, investment in capacity upgrades is attractive.
•Technology improvements—New-generation steam turbine inner cylinders and rotors equipped with high-efficiency nozzles and blades can generate more power using the same amount of steam flowing through the original turbine frame.
At a minimum, power plant owners want to restore the original net power output of these plants, with a preference to increase the net power output if it is economical to do so. Over the last 20 years, boiler and turbine manufacturers have improved their equipment’s performance and efficiency so that major uprates of existing equipment are possible.
To add steam capacity, boiler manufacturers can add heat transfer surface utilizing improved designs and materials, if
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