Dry And Wet Mode in Supercritical Boiler

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Wet and Dry Mode operation of supercritical boiler
Wet Mode
Operation of the boiler in which we get a mixture of water and the steam at the exit of boiler(vertical tubes) .In this condition the steam separates from water in separators because the boiler tubes from bottom ring header of boiler to separator filled with water thats why we call it wet mode
In wet mode operation we use Boiler Recirculation Pump /BCP to pick water from the separator and put it back at the economiser inlet so a flow can be maintained in the boiler . This circulating water helps to avoid tube damage which occurs due to localised heating of eco tubes and boiler tubes.

Dry Mode
As the name suggests in dry mode there is no moisture or water present in the separator and the exit of the boiler .
This type of operation is taken into service when we reach a certain load where the main steam flow is more than 40% subsequently we have sufficient flow of feed water at the inlet of the economiser to prevent damage of tubes due to thermal stress (tube leakage) . Now we don't need any recirculating water so we have to stop the BCWP .
The Dry Mode also called as Once through Mode because there is no recirculation happens in boiler
For Dry mode operation the separator outlet temperature should be greater than saturation temperature and we have to maintain dT greater than 17 deg centigrade . So we can ensure the dryness of steam .