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.

• a) Neatly sketch the complete cycle on the pressure-enthalpy P-h diagram below, indicating clearly all 5 stations on the diagram. Once this is done then use the Steam Tables to determine the following:

• b) Assuming that the turbine is adiabatic, determine the power output of the turbine [ 976kW ].

• c) 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 ].

• d) Using steam tables, determine the heat transferred to the boiler [ 6210kW ] as well as the heat transferred to the superheater [ 747kW ].

• e) Determine the overall thermal efficiency η _th 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).

• f) 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 absorption of oxygen and other gasses in the water.

Justify all values used and derive all equations used starting from the basic energy equation for a flow system.