Steam Turbine Flow Factor

T

Thread Starter

Tomas Eduardo

What does Steam Turbine Flow Factor at HP First Stage refer to? It may not matter, but I am looking at a standard GE Steam Turbine used in a 7FA 2 on 1 combined cycle configuration.
 
The term meaning depends on what the writer is saying.

Most tg's have steam bypass valving to deal with changes in load. So the term may refer to the percentage of incoming steam used to generate power, or to the turbine efficiency.

It is a term with double meanings, so you have to track it down.
 
Tomas,

Stage flow factors are a useful diagnostic parameter for determining turbine flow passing capabilities. They are commonly calculated at the turbine throttle, 1st stage and Hot Reheat inlet to the IP turbine. The flow factor is related to the steam flow area, FF = W / Sqrt(P/v)
Where:
W = Steam Mass Flow
P = Steam Pressure
v = Specific Volume of Steam
When calculated at the throttle conditions, FF will move as a function of valve positions (changing area). For combined cycle, which typically operate at VWO with sliding pressure, Flow Factor should remain constant. The same goes for the 1st Stage Flow Factor as this is also a constant area.

The calculation essentially reduces down to units of area. Think of it as the required area needed for the steam flow to pass at the given conditions. If we have a constant area, and we increase the steam flow through that area, the pressure will increase (reducing its specific volume) to be able to pass through that constant area. Thus, a reduction in flow factor may indicate a reduced flow area (steam path deposits) while an increase may indicate more flow area (steam path erosion).

Flow factor can also be helpful in identifying Cycle Isolation issues (leakage through drain and bypass lines). Flow is usually measured at the HRSG, not the turbine inlet, under the assumption that the full flow reaches the steam turbine. If leakage is occurring through drain/bypass lines between the HRSG and the steam turbine, the actual flow reaching the turbine will be less than the measured steam flow. Since the FF calculation is using flow at the HRSG, but pressure at the turbine (which will be lower due to lower actual steam flow to the turbine) the result will be an increase in Flow Factor.

Hope this helps Tomas Eduardo.... if that's your real name....
 
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