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What is a moisture separator reheater?
Moisture separator reheaters are used in thermal power stations and are common in the nuclear power generation industry. A Moisture Separator Reheater (MSR) has two main purposes:
- It separates moisture from the steam that is discharged from a high-pressure steam turbine.
- It reheats the high-pressure discharge steam, increasing its thermal energy (heat) before it is discharged to a low-pressure steam turbine, or turbines.
Separating the moisture and reheating the steam leads to an overall increase in power plant efficiency.
Good to know - steam with a very low moisture content is referred to as 'dry steam' or 'clean steam'. Steam with a high moisture content is referred to as 'wet steam'.
Moisture Separator Reheater Parts
Moisture Separator Reheater (MSR) Parts
Condensate Drain
Moisture (condensate) that has been separated from the steam, is drained from the system via the condensate drain(s); condensate is fed back to the boiler feedwater system.
Cycle Steam Inlet
Steam from the intermediate or high-pressure turbine(s), is discharged to the MSR through this connection.
Cycle Steam Discharge
After moisture has been removed from the cycle steam, and the cycle steam has been reheated, it is discharged through this connection; the steam is then fed to the low pressure turbine(s).
Low Pressure Tube Bundle
Low-pressure, low temperature, steam, is used to initially heat the cycle steam. Low pressure steam passes through the u-tube shell and tube heat exchanger on the tube side. The cycle steam passes over the outside of the tubes and is thus the shell-side fluid. As both flowing mediums are in close proximity with each other, heat is transferred between them. The temperature of the cycle steam increases as it passes over the heat exchanger tubes, whilst the temperature of the low pressure steam decreases as it passes through the tubes.
High Pressure Tube Bundle
High-pressure, high temperature, steam, is used to further heat the cycle steam. High pressure steam passes through the u-tube shell and tube heat exchanger on the tube side. The cycle steam passes over the outside of the tubes and is thus the shell-side fluid. As both flowing mediums are in close proximity with each other, heat is transferred between them. The temperature of the cycle steam increases as it passes over the heat exchanger tubes, whilst the temperature of the high-pressure steam decreases as it passes through the tubes.
Steam Distribution Pipe
Cycle steam enters the MSR and is then fed to two steam distribution pipes (one on each side of the MSR). Each steam distribution pipe has slots perforating the lower side of the pipe wall. Each of the slots becomes progressively smaller as the steam passes from the inlet to the end of the distribution pipe. The slots become incrementally smaller in order to maintain a constant steam velocity from all discharges (the gradual reduction in pressure as the steam exits the distribution pipe would cause a gradual reduction in discharge velocity as the steam travels further from the inlet end, but reducing the size of the slots compensates for this).
Chevron Moisture Separator
The shape of the chevrons creates a torturous flow path for the steam. Steam is a gas, and flows easily through the chevrons, despite being forced to change direction multiple times. Moisture (water) entrained in the steam is a liquid, which is denser than steam, and consequently is not able to change direction as easily as steam. As moisture flows through the chevrons, it impinges upon the chevron plates and drips down to the base of the MSR due to gravity. The water accumulated at the base of the MSR is referred to as condensate.
Low Pressure Inlet
Low pressure steam enters through this connection.
Low Pressure Discharge
Low pressure steam is discharged through this connection.
High Pressure Inlet
High pressure steam enters through this connection.
High Pressure Discharge
High pressure steam is discharged through this connection.