Attemperation is the primary technique used for controlling the degree of superheat in a boiler or a Heat Recovery Steam generator (HRSG). This is achieved through a controlled injection of water into the superheated steam. Attemperators are typically installed between superheater stages in order to regulate the output temperature of the boiler/HRSG, as well as protect any secondary superheater pipes from damage owing to excessive heat. The temperature controller for this attemperator (called inter-stage) bases its temperature regulation on input from a temperature transmitter placed on the boiler/HRSG output. A secondary attemperator (called final stage) is often placed after the inter stage temperature transmitter in order to prevent thermal damages to the steam turbine during start-up. The final stage attemperator ensures that the steam temperature upstream the turbine does not rise too fast.
The DAM-B is a high performing ring style attemperator with a welded flow profiling liner for superior evaporation and performance. It complies with all existing standards and is always pressure tested on both the steam side as well as the water side.
The DAM-B attemperator is installed in the steam pipe with a number of water atomising nozzles attached. The size of the nozzles, their number and insertion length may differ depending on steam desuperheating needs and steam pipe diameter.
- The DAM-B is able to handle severe thermal cycling.
- The nozzles receive water from a common spray water pipe encircling the steam pipe, supplying water evenly across the nozzles.
- Spray water flow is controlled via an external spray water valve connected to the DAM-B water connection piece. This valve is regulated via a temperature control system that uses the downstream steam temperature to determine the amount of spray water needed. The placement of the temperature transmitter and the installation of the steam pipe are of critical importance for achieving accurate steam temperature regulation. For more information see IMI CCI document II500.12: System Design Considerations – DAM-B’.
- A flow profiling liner is welded to the inside of the DAM-B body to improve system turndown and to protect the steam pipe against thermal shock and erosion in the downstream pipe.