Question

A solar-thermal plant is used to produce power. A molten salt transfers heat to a non-ideal Rankine cycle to produce electricity from a turbine. The molten salt has an average temperature of 800 oC when transferring heat to the boiler in the Rankine cycle. The condenser for the power cycle exchanges heats with water in a river that is at 20 oC. The steam flow rate through the cycle is 10 kg/s. The inlet of the boiler is at 9 MPa absolute and steam leaves the boiler at 9 MPa absolute and 600 oC. The exit of the turbine operates is at 20 kPa absolute and has a quality of 95%. The exit of the condenser is at 20 kPa absolute and is a saturated liquid.

Draw a diagram of the Rankine cycle. Include all the unit operations (pieces of equipment). Show the direction of flow and where heat and work enters and leaves the cycle. Number the streams in the cycle. State proper assumptions.

1. What is the power consumption for the pump (in MW), the power produced by the turbine (in MW), the thermal efficiency of the cycle?

2. What is the maximum thermal efficiency that a heat engine can have operating between the temperatures of the heat source molten salt and heat sink river? Why should the efficiency calculated would be less than this maximum? List at least four places in the cycle that contribute to the real plant having a lower thermal efficiency than the maximum.

Answer 1