Desuperheaters / Attemperators
Desuperheater is a device which is sprays the high pressure water in the steam line thereby reducing the steam temperature to a point at or nearly at saturation temperature. An attemperator controls steam temperature while a desuperheater removes whatever superheat there is in steam.
Attemperators are generally found in and/or associated with boiler steam, in zones where too high of a temperature affects something down stream of that point. An attemeperator might be used between superheater zones in a multi-zone superheater boiler or in a re-heater zone to control reheater outlet temperature.
Desuperheaters are generally found in steam lines away from the boiler or boiler outlet piping where there is a downstream use for saturated steam.
Desuperheated steam is generally controlled to 5-10 Deg C. above saturation temperature (depending on the sophistication of the device) because if the temperature is controlled at saturation when it goes below the saturation line into the moisture region, the temperature controller cannot detect this.
The amount of water to be sprayed / injected is decided based on the degree of superheat. The temperature sensor installed at the downstream of desuperheater senses the steam temperature & gives signal to Spray water control valve. This signal decides the opening /closing action of control valve. More the degree of superheat, more will be the CV opening & more water will be sprayed through desuperheater. This process continues in loop. The selection of desuperheater depends upon the required water quantity & the steam line size. In case of more amount of water is required then we may have to select multiple nozzles.