Solved Problem 6.1 - A Supercritical Steam
Power Plant for Athens, Ohio
Consider the supercritical steam power plant
with reheat for Athens, Ohio, which we evaluated in Solved
Problem 4.1. The system diagram is repeated here for convenience:
In this exercise we wish to evaluate the high
pressure (HP) and low pressure (LP) turbines of this system (circled
in red), both of which are assumed to be adiabatic.
- 1) Plot the two turbine processes (Stations
(1)-(2) and (3)-(4)) on the enthalpy-entropy h-s "Mollier" diagram. Plot also the equivalent isentropic turbine processes
on the diagram, and indicate the actual turbine specific work
as well as the isentropic turbine specific work for both turbines
on the h-s diagram.
- 2) Using steam
tables, determine the turbine adiabatic efficiency
T of both
turbines.
- 3) Discuss your results as well as the feasibility
of the turbine set and the feedwater pump.
Justify all values
used and derive all equations used starting from the basic
energy equation for a flow system, the basic definition of turbine
adiabatic efficiency T.
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Solution Approach:
- 1) Plot the two turbine processes (Stations
(1)-(2) and (3)-(4)) on the enthalpy-entropy h-s "Mollier"
diagram below. Plot also the equivalent isentropic turbine processes
on the diagram, and indicate the actual turbine specific work
as well as the isentropic turbine specific work for both turbines
on the h-s diagram. [refer
h-s diagram below]
- 2) Using steam
tables, determine the turbine adiabatic efficiency T of both
turbines. [enthalpy and
entropy data derived from steam tables shown in red on schematic
diagram below. State (2s) required linear interpolation of the
superheat
table values and
both states (4a) and (4s) required the saturation
properties (pressure) table and use of the quality relation X indicated below.
These values were then indicated on the above h-s diagram
plot in order to validate their feasibility.]
- 3) Discuss your results as well as the feasibility
of the turbine set and the feedwater pump. [Both adiabatic efficiencies seem to be feasible and
do not violate the second law. We need to question why the LP
turbine efficiency (90%) is so much higher than the HP turbine
efficiency (77%) - it may be due to the ability of higher relative
accuracy in the manufacture of a much larger turbine however
this large difference is suspect and needs more investigation.]
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Engineering Thermodynamics by Israel Urieli is licensed under a
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