Relation Between Steam Turbine Inlet pressure and Steam Generator Outlet Pressure
- Thread starter rokan_123
- Start date
>Is there any relationship between steam pressure at the
>outlet of Boiler & steam pressure before steam turbine
>control valve & or stop valve?
The answer is yes; as boiler outlet pressure increases, so should steam turbine "inlet pressure." And, as boiler outlet pressure decreases, so should turbine inlet pressure. (I'm defining turbine inlet pressure as the steam pressure immediately upstream of the stop/control valve(s).)
By the same token, if turbine inlet pressure increases then boiler outlet pressure should increase, and if turbine inlet pressure decreases then boiler outlet pressure should decrease.
Normally, the outlet of the boiler is piped to the inlet of the steam turbine. There may be some losses due to the length of the piping and the number of turns, but the design causes the relationships above to be pretty normal. There are the odd arrangments where sometimes there is a pressure regulating valve between the boiler outlet and the turbine inlet, but that's rare.
When the boiler is firing at a steady rate and the steam turbine control valves are at a steady position and then the operator (or some other signal) causes the steam turbine control valve(s) to open generally one of the first things to happen is that the pressure at the steam turbine inlet will begin to drop as flow increases. The boiler control usually has to play "catch up" and fire harder (increase fuel flow to the boiler burners) to maintain steam pressure. And the opposite happens when things are steady and something causes the steam turbine control valve(s) to close--the boiler outlet pressure (and the pressure at the turbine inlet) will increase and the boiler control will have to reduce fuel flow to the burner, and there's usually a slight lag.
The above is true for a typical fired boiler. Cogeneration units which use gas turbine exhaust heat to produce steam are usually operated and operate slightly differently. On a steam turbine in a cogeneration plant, once the steam turbine control valve(s) reach a certain position/flow-rate they are usually then moved to the VWO position (Valve(s) Wide Open). And, then as the gas turbine load changes and the exhaust heat/flow changes, the steam pressure will just be what it is and the steam turbine will convert the energy in the steam to electricity (amperes, to be more correct).
So, the answer really depends on the type of boiler and the arrangement of the sensors on the steam turbine piping and the type of power plant. Again, there will likely be a very small pressure drop in the piping between the boiler outlet and the turbine "inlet" (as defined above), and a small drop across the valves, also (depending on their opening)--that's why turbine inlet pressure is usually measured immediately upstream of the valve(s).
Hope this helps!
>outlet of Boiler & steam pressure before steam turbine
>control valve & or stop valve?
The answer is yes; as boiler outlet pressure increases, so should steam turbine "inlet pressure." And, as boiler outlet pressure decreases, so should turbine inlet pressure. (I'm defining turbine inlet pressure as the steam pressure immediately upstream of the stop/control valve(s).)
By the same token, if turbine inlet pressure increases then boiler outlet pressure should increase, and if turbine inlet pressure decreases then boiler outlet pressure should decrease.
Normally, the outlet of the boiler is piped to the inlet of the steam turbine. There may be some losses due to the length of the piping and the number of turns, but the design causes the relationships above to be pretty normal. There are the odd arrangments where sometimes there is a pressure regulating valve between the boiler outlet and the turbine inlet, but that's rare.
When the boiler is firing at a steady rate and the steam turbine control valves are at a steady position and then the operator (or some other signal) causes the steam turbine control valve(s) to open generally one of the first things to happen is that the pressure at the steam turbine inlet will begin to drop as flow increases. The boiler control usually has to play "catch up" and fire harder (increase fuel flow to the boiler burners) to maintain steam pressure. And the opposite happens when things are steady and something causes the steam turbine control valve(s) to close--the boiler outlet pressure (and the pressure at the turbine inlet) will increase and the boiler control will have to reduce fuel flow to the burner, and there's usually a slight lag.
The above is true for a typical fired boiler. Cogeneration units which use gas turbine exhaust heat to produce steam are usually operated and operate slightly differently. On a steam turbine in a cogeneration plant, once the steam turbine control valve(s) reach a certain position/flow-rate they are usually then moved to the VWO position (Valve(s) Wide Open). And, then as the gas turbine load changes and the exhaust heat/flow changes, the steam pressure will just be what it is and the steam turbine will convert the energy in the steam to electricity (amperes, to be more correct).
So, the answer really depends on the type of boiler and the arrangement of the sensors on the steam turbine piping and the type of power plant. Again, there will likely be a very small pressure drop in the piping between the boiler outlet and the turbine "inlet" (as defined above), and a small drop across the valves, also (depending on their opening)--that's why turbine inlet pressure is usually measured immediately upstream of the valve(s).
Hope this helps!
