The superheated steam is generated at the Boiler and is distributed to various locations in the plant through a steam piping network.
In the process industry, there are several auxiliaries at different locations that require different steam parameters (Steam pressure & temperature).
According to their application in the Process Industry requirement, the Superheated Steam Temperature and Pressure are reduced in PRDS.
PRDS is known as the Pressure Reducing and Desuperheating System.
The PRDS usually has two types
As the name implies, the Pressure Reducing and Desuperheating Station (PRDS) is a unit that conditions steam from a Main System (Boiler) to an Auxiliary Steam source of supply by reducing steam Pressure and Temperature using a Pressure Control Valve and a Temperature Control valve.
After Pressure Reduction is done, the steam is then allowed to pass through the Desuperheating station to lower the temperature of the steam to the required value.
PRDS is a combination of Mechanical and Instrumentation components.
In General, the Control Valve is Known as the Final Control Element. And it is the heart of the Instrumentation Loop.
A safety Valve is the most Essential Component in High-pressure Operation.
In a Pressure Reducing and Desuperheating control system, there exist two loops,
Components of Pressure Loop Control System:
This system includes a
The Pressure Control Valve (PCV) in the Pressure loop control system reduces the pressure of the superheated steam by opening the Valve.
The Pressure Value to be reduced is given as a set point to the controller. The Pressure Transmitter senses the outlet Steam Pressure and sends the proportional signal to the PID controller as a Measured value.
The PID controller then compares the Process Variable (Measured Value) received from the Pressure Transmitter with the given SetPoint (SP) and generates an error signal which is then given to the Positioner of the Pressure Control Valve (PCV).
The Control Valve opens and relieves excess Pressure until the Pressure reaches the desired value. When the Steam Pressure reaches the Desired Set Point the control valve gets closed and prevents the further release of Pressure after normal conditions have been restored,
i.e. Process Variable (PV) must be equal to SetPoint (SP).
PV=SP
The Steam Inlet Isolation Valve and Outlet Isolation Valve of the Pressure Control Valve (PCV) are controlled with two remotely operated motorized valves for isolating the Pressure Control Valve during maintenance.
Components of Temperature Loop Control system:
This System includes a
The Attemperation water is sprayed at high velocity through Spray nozzles in an adequate quantity. To reduce the temperature of superheated steam to the required temperature.
The Temperature element (TE) senses the outlet Steam Temperature and gives a proportional current signal to the PID controller via the Temperature transmitter (TT).
The PID controller then compares the Process Variable (Measured Value) received from the Temperature transmitter (TT) with a given SetPoint (SP), generates an error signal, and is then given to the Positioner of the Temperature Control Valve (TCV)
This valve opens accordingly and sprays atomized water through the spray nozzle until the steam temperature reaches the set value, and re-closes to prevent the further spray of water after normal conditions have been restored,
i.e. Process Variable (PV) must be equal to SetPoint (SP).
PV=SP
DeSuperheater has two types:
Usually, all power plant uses Split type and Integrated-type PRDS
The steam required for the process (Sugar Industries, Distilleries) is called exhaust steam which is at low temperature and pressure.
Note: Inlet Steam is the Main steam and outlet Steam is Exhaust Steam
A Safety Valve is used at the outlet of the system to ensure that the pressure does not exceed the preset limit. When the pressure exceeds the preset limit the safety valve opens and relieves the excess pressure to the atmosphere, when the pressure reaches its preset limit the Valve gets closed.
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