Answer the following question : 1-a) Determine the pressure ratio across the compressor of an ideal Brayton cycle for the

maximum net work output per unit mass flow if the state at the compressor inlet and the temperature at the turbine inlet are fixed. Use a cold air standard analysis and ignore kinetic and potential energy effects.

b) A regenerative and reheat gas turbine unit consists of a two stage compressor with

inter cooling with 85% efficiency and a two stages turbine with re-heating to maximum temperature. The output power of H.P.T. is used to drive the H.P.C. The L.P.T. and the L.P.C. are on the same shaft with the electrical generator. The maximum and minimum temperatures in the cycle are 727 оC and 13 оC respectively. The pressure ratio for each stage compressor is 4. The efficiency of the regenerator is 75 %, and the isentropic efficiency for all compressor and turbine stages is 86%.

Determine the following: 1- the pressure of the gases entering low pressure turbine 2- the net specific power 3- the cycle efficiency , and 4- the work ratio

2-a) Discuss the main requirements of power plants supplying base and beak loads? b) In a regenerative steam power plant has two feed water heaters. Steam enters the

first stage turbine at 100 bar and 540 C , and expands to 20 bar where some of steam extracted to a closed feed water heater. The reminder of the flow expands through the second stage turbine to 7 bar, where apportion of the flow is extracted to another closed feed water heater, and the rest expands through the third stage turbine to the condenser pressure of 0.06 bar. The condensate leaves each closed feed water heater as saturated liquid at the respective extraction pressure. The feed water streams leave each closed heater at temperature equal to the saturated temperature at the respective extraction pressure. The condensate from the first closed feed water heater is passes through trap into the second closed feed water heater is pumped to the steam generator pressure. If each turbine stage has an isentropic efficiency of 85% and pumps operate isentropically. Draw the cycle scheme and then determine:

1- the thermal efficiency of the cycle. 2- the mass flow rate of steam entering the first stage turbine if the net power

output is 200 Mw. Mechanical and generator efficiencies are 94% and 95% respectively.

3-a) In a simple open cycle gas turbine power plant operates with a pressure ratio 5 and

the ratio of maximum to minimum temperature of the cycle is 3. If the isentropic efficiency of the turbine is 87%, find the minimum isentropic efficiency of compressor for which the unit will produce power.

Benha University Time: 3 Hrs Benha High Institute of Technology Department: Electric (Power) 11/6/ 2011 – Fall semester Course name: Power Station Technology. Exam (regular) Year: Fifth

b) Consider a simple ideal Rankine cycle with fixed turbine inlet. What is the effect of lowering the condenser pressure on the.

Pump work input: i) increases ii) decreases iii) remains the same Turbine work output: i) increases ii) decreases iii) remains the same Heat added: i) increases ii) decreases iii) remains the same Heat rejected: i) increases ii) decreases iii) remains the same Cycle efficiency: i) increases ii) decreases iii) remains the same Moisture content i) increases ii) decreases iii) remains the same at exit the turbine 4-a) Explain the following terms:

1- Load factor 2- Diversity factor

3-Capacity factor 4- Plant use factor b) A central power station has annual factors as follows: Load factor = 60% Capacity factor = 40% Use factor = 45% Power station has a maximum demand of 15000 kW. Determine the following: . 1- annual energy production. 2- reserve capacity over and above peak load, and 3- hours per year not in service.

Good luck Examiner: Dr. Samia Naser El-deen Abedo

Model Answer