The process of cooling superheated steam by direct injection of water is called desuperheating. This is typically done to meet the conditions required for downstream process(es) when the available steam happens to be at higher temperature and there is also a source for injecting spraywater into it. It is required in many industrial processes where the steam temperature, and/ or quality, is critical for reliable and efficient operation of the system. Such systems are common in power stations, refineries, pulp & paper industry and desalination plants, where a boiler producing superheated steam already exists.
There are four basic steps :
1) Injection of the correct amount of spraywater.
2) Spray atomization (primary and secondary)
3) Spray penetration and pre-evaporation mixing
4) Evaporation and mixing
Injection of the correct amount of spraywater flow is the first and most fundamental requirement to correct operation of any desuperheating system. This requires careful, and correct, selection of the spraywater flow control element. This control element, which may be an external control valve, must be capable of providing good control over the entire range of spraywater flow required. Multi-stage pressure drop is necessary in cases of high pressure drop for long-term reliability.