How do steam letdown stations work?
To reduce the temperature of the steam, a device is utilised that adds water to the superheated steam. To vaporise the water a large amount of energy is required to overcome the latent heat. The high temperature steam provides this. The result is an increased flow of steam at a reduced temperature.
What happens when steam pressure is reduced?
Condensate from lower pressure steam loses less energy from flash than condensate from high-pressure steam. The result is that at lower pressure, the boiler must supply less energy to the condensate to raise it from the feedwater condition to the saturation point.
What does a steam letdown control valve do in a steam header?
Summary of pressure reducing valves A valve that senses and controls the downstream pressure is often referred to as a ‘let-down’ valve or ‘pressure reducing valve’ (PRV). Such valves can be used to maintain constant steam pressure onto a control valve, a steam flowmeter, or directly onto a process.
How does steam pressure reducing valve work?
Steam reducing pressure valves are valves that precise control the downstream pressure of steam and automatically adjust the amount of valve opening to allow the pressure to remain unchanged even when the flow rate fluctuates by pistons, springs or diaphragms.
Where are the letdown valves in a steam plant?
Many industrial facilities produce steam at a pressure higher than that demanded by process requirements. Steam passes through pressure-reducing valves (PRVs, also known as letdown valves) at various locations in the steam distribution system to let down or reduce its pressure.
What is the function of a let down valve?
When the turbine is off line, or is not passing enough flow to satisfy the requirements of the lower pressure header, some of the steam is “let down” as opposed to the operation of a “pressure reducing valve”, whose function from day one is to reduce pressure from one level to another one.
Why does a steam turbine have a let down valve?
In addition to what has already been said, the use of the term “let down valve” often conotes that it is acting in lieu of some other device that normally reduces the steam from one pressure to a lower one, such as a steam turbine operating at a given inlet pressure and exhausting or extracting to a lower pressure.
What kind of valve is used to control steam pressure?
A valve that senses and controls the downstream pressure is often referred to as a ‘let-down’ valve or ‘pressure reducing valve’ (PRV). Such valves can be used to maintain constant steam pressure onto a control valve, a steam flowmeter, or directly onto a process. Pressure reducing valves are selected on capacity and type of application.
