The efficiency of coal-based power plants, as measured by their Heat Rate, is notably affected by three key factors: the main steam temperature, main steam pressure, and reheater steam temperature. By adjusting these variables, it is possible to increase the potential energy harnessed by the turbine, leading to higher power generation.
Some studies performed for the Electric Power Research institute EPRI reveal the profound impact of these improvements. A modest increase of 10% in main steam pressure and temperature translate to a 2-3% reduction in Heat Rate. Similarly, increasing just 10% the reheater steam temperature can result in a 1-2% reduction. The financial implications are considerable, with potential savings exceeding hundreds of thousand dollars accompanied by reduced emissions.
However, there are also some restrictions for increasing these parameters, such as follows:
- Raising pressure and temperature demands the use of more costly materials for the boiler and steam turbine.
- Increased pressure and temperature magnify the likelihood of dangerous occurrences, including boiler explosions, tube failures, and turbine blade failure.
- Higher reheater steam temperature amplifies the stress on steam turbine components, elevating the risk of untimely component failures and subsequent escalated maintenance and repair expenditures.
- Higher the reheater steam temperature, the greater the risk of turbine blade erosion and corrosion.
Determining the optimal main steam and reheat steam conditions for coal-fired power plants is a multifaceted task, contingent on diverse elements such as coal quality, power plant classification, boiler efficiency, turbine performance, and operational circumstances. Adhering to manufacturers’ recommendations and maintaining proximity to design conditions emerges as a wise strategy for attaining optimal power plant efficiency.
Further, for evidence of stress and thermal fatigue on boiler waterwalls, visual inspection and boiler pipe thickness monitoring are necessary during planned outages. The turbine blades should also be inspected boroscopically to detect erosion or corrosion caused by high temperatures. Combining these recommendations with routine performance testing is a high effective way to reduce Heat Rate.
Finally, for operators and managers to maximize the performance of their daily operations and maintenance projects, it is important that Heat Rate information is accessible, as well as awareness of controllable losses.