Whereas superheated steam offers an excellent source of energy for mechanical power generation, in most cases, steam at greatly reduced temperatures, near saturation, proves a more desirable commodity especially for most heat-transfer applications. Precise temperature control is required to enhance heating efficiency; eliminate unintentional superheat in throttling processes; or to protect the downstream product or apparatus from heat related damage. One technique used to reduce temperature is the installation of a desuperheater. Therefore, a desuperheater is a system that injects a controlled predetermined amount of water into a steam flow to lower the temperature of the steam. The schematic diagram illustrates the controls of a steam desuperheater:
To accomplish its function efficiently, the desuperheater must be designed and selected correctly for the application. A desuperheater integrates with a wide variety of complex thermal and flow dynamic variables to achieve efficiency. As illustrated in the schematic diagram above, the control of the water quantity, and thus the steam temperature, employs a temperature control loop. This loop includes a downstream temperature sensing device, a controller to interpret the measured temperature relative to the desired set point, and the transmission of a proportional signal to water controlling valve/actuator assembly to modulate/control the required quantity of water.
The key factor for the efficient desuperheater operation is to choose the correct design for the respective application. Desuperheaters are available in different shapes and sizes and employ different energy transfer and mechanical techniques to accomplish the desired performance within the limits of the system environment.
Some of the physical parameters that influence the performance of a desuperheater system include:
- Installation orientation.
- Spray water temperature.
- Spray water quantity.
- Pipeline size.
- Steam velocity.
- Equipment vs. system turndown.
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- The Instrumentation for Furnace Control
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