Problem 4.4 - Solar Pond Hybrid Steam Power
Plant
We wish to evaluate the proposed Solar-Pond
Steam Power Plant shown in the following diagram. A solar
pond is a large body of water having a varying salinity
gradient (halocline) which traps the sun's energy such that the
storage layer at the bottom of the pond can reach temperatures
of greater than 100°C. The diagram following shows the initial
design of a low pressure solar-pond steam power plant, using the
storage layer as the boiler heat source, and the upper layer as
the heat sink. Notice the wood-fired superheater in which the
steam at the outlet of the boiler is heated from 100°C to
250°C.
- 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
[976kW].
- 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 [6210kW] as well as the heat transferred to the superheater
[747kW].
- 5) Determine the overall thermal efficiency ηth
of this power plant [14%]. (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, as well as the
practical aspects of maintaining a system with a low pressure
of 10kPa.
Justify all values
used and derive all equations used starting from the basic
energy equation for a flow system.
