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A power plant is using a regenerative Rankine cycle as shown in Figure Q 4 , operating at a boiler pressure of 4 MPa and
A power plant is using a regenerative Rankine cycle as shown in Figure Q
operating at a boiler pressure of MPa and a maximum temperature of
The mass flow rate of water into the boiler is The inlet into both pump
and pump is a saturated liquid. Superheated steam for regeneration is bled
from the turbine at kPa, and mixed with the water leaving pump in an open
feedwater heater OFWH The power plant uses water from a nearby river as
cooling liquid for the condenser. The river water can be assumed to have a
constant temperature of
iii Determine the dryness fraction at the outlet of the turbine.
iv Calculate the mass flow rate of steam removed from the turbine at point
entering the OFWH in
v Calculate the net power output and the thermodynamic efficiency of the
power plant.
You discover a leak in the regeneration system, which loses of the steam
that was bled from the turbine. The leak is in the pipework before the feedwater
heater as indicated in figure Q Fixing the leak is not immediately possible, so
you make some adjustments to the cycle to keep it operating:
First, you add water at the inlet of pump to make up for the steam lost at the
leak. The water added can be assumed to be saturated liquid.
Second, you adjust the power of pump such that the fluid entering pump is
a saturated liquid.
vi To what power do you adjust pump for this scenario?
Give your answer in kW
The leak is getting worse, and to be able to repair the leak you close the pipework
between the turbine and the feedwater heater. In this new scenario, no more
steam is bled from the turbine, and no more steam enters the feedwater heater.
vii Without doing any calculations, explain how this influences the efficiency
and the net power output of the cycle.
i Draw a Ts diagram of the cycle.
ii Choose a suitable condenser pressure for the cycle, explaining your
choice. Use your chosen value for all following questions.
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