In power plants and heavy process industries, steam is often generated in superheated states (very high temperature and pressure) to maximize turbine efficiency. However, for process heating applications, saturated steam is much more desirable due to its high latent heat and ease of temperature control. A Pressure Reducing & De-Superheating Station (PRDS) performs the dual role of reducing both steam pressure and steam temperature simultaneously.
De-superheating is the process of reducing the temperature of superheated steam. This is achieved by injecting a finely atomized spray of cooling water (feedwater) directly into the superheated steam flow. The heat from the steam evaporates the water droplets, which lowers the overall steam temperature closer to its saturation point.
Traditionally, pressure reduction and temperature reduction were handled by separate valves. Today, modern plants use Combined PRDS Valves, which integrate the steam pressure throttling and cooling water spray nozzle into a single valve body. This design offers several advantages:
When designing a PRDS, precise control loops are vital. High-rangeability control valves, fast-responding temperature transmitters, and proper piping layout (with a straight run downstream of the water injection point) are required to avoid water droplet impingement and piping erosion.
