The steam is generated by boiling the water in the water tubes which run between the water drums and the steam drum. Wet steam exits from the steam drum and is piped to the superheater.
11. Steam Superheater
This is an enclosed nest of pipes located in the hottest section of the exhaust gasses, usually to the underside of the steam drum. From here the superheated high pressure steam is piped to the superheater header and into the turbine hall, where it enters the HP stage of the steam turbine.
There are numerous sootblower units located around the water tubes economiser and air heater tubes.
These are basically a long perforated pipe which rotates spraying steam or compressed air onto the boiler tubes removing the coating of soot deposited by the combustion gasses.
They are controlled to operate periodically maintaining the boiler water tube, economiser, and heat exchanger heat transfer efficiency.
13. Safety Valves
In order to protect the boiler from overpressure there are two safety valves fitted to the steam drum outlet piping and one safety valve fitted to the superheater outlet header.
The superheater safety valve is always set to lift before the two steam drum valves in order to prevent the superheater from collapsing due to lack of steam flow. (If the drum valves lifted first this would starve the superheater of steam.)