Problem 4.3 - A Geothermal
Hybrid Steam Power Plant
A small community of about 500 households have
discovered an underground geothermal brine source that can be
used to boil water at 100°C and would like to use this to
generate power. The following diagram shows the initial design
of a low pressure geothermal plant in which the water is boiled
by the geothermal source to 100°C and subsequently superheated
to 200°C by a wood-fired superheater. Notice that the high
pressure of the system is at 100kPa allowing a convenient de-aerator
to be placed at the pump outlet.
- 1) Neatly sketch the complete cycle on the
pressure-enthalpy P-h diagram below, indicating clearly
all 5 stations on the diagram.
- 2) Using steam tables, and assuming that
the turbine is adiabatic, determine the power output of the turbine
- 3) Assuming that the feedwater pump is adiabatic,
and that the compressed liquid experiences no change in temperature
while passing through the pump, determine the power required
to drive the pump [0.23kW].
- 4) Using steam tables, determine the heat
transferred to the boiler [6271kW] as well as the heat transferred to the superheater
- 5) Determine the overall thermal efficiency ηth of this power plant [11%]. (Thermal efficiency is
defined as the net work done by the system (turbine and feedwater
pump) divided by the total heat supplied externally).
- 6) Discuss the proposed system with respect
to its environmental impact and feasibility. Is this a well designed
system? What do you consider to be the major advantages and disadvantages
of this system? Your discussion should include a comparison of
the external fuel used and the turbine power.
Justify all values
used and derive all equations used starting from the basic
energy equation for a flow system.
Engineering Thermodynamics by Israel Urieli is licensed under a
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