Peak rating is definitely the actual evaporation which could be suffered by steam boiler for a specific time of, such as, two or four hour in a day, to fulfill a greater need for power plant, industries or process. The following below some attentions related to peak rating:
- Operating steam boiler continually on peak rating is better prevented simply because the lifetime of steam boiler is influenced as a result of continual increased temperatures in superheater, reheater and furnace areas, leading to erosion, fouling and slagging troubles in addition to a greater loss.
- Nevertheless, when length of time of peak rating is increased, the steam boiler needs to be resized surely having the productivity optimized at normal continuous rating or maximum continuous rating and its components measured to match the peak rating. Usually within power plant the peak responsibility is additionally to fulfill the condition of VWO (valve wide open of turbine), which can be commonly 5–10% of the maximum continuous rating flow of turbine. This can be maximum flow if most of control valves in chest of steam turbine inlet tend to be totally open. This situation can provide extra power by using a new steam turbine and also could protect against probable power loss in the next years because of aging reasons.
- Commonly the peak work will not exceed or meet 110% maximum continuous rating (MCR) and four hours in one day, and also the peak rating is generally achieved by generating utilization of design and examination block borders of steam boiler without needing to oversize its components.
- Peak work is usually attained at lowered efficiency, when the exit temperature output of gas from steam boiler will be far more compared to that at maximum continuous rating condition (when the flow of fuel is increased), resulting in greater losses in stack.
The principle of peak rating doesn't implement to Heat Recovery Steam generator (HRSG). Gas turbine generator rating is provided at its ideal conditions and Gas turbine generator is not possibly run at higher temperature as compared to design loads with regard to the concern of serious shortening of hot component's lifetime.