ME-471 Power and Desalination Plants

Final Exam 1st Semester 1429-1430 Time Allowed : 3 hours

Always State Your Assumptions

The Plant The plant is composed of four(4) gas turbine units, a steam power plant and a multi- stage flashing desalination plant (MSF). With an output power equals 144 MW. Hot gases from the gas turbine are fed to the heat recovery boiler (HRB) which has no supplementary firing. Exhaust gases leave the HRB at 550oC. Steam leaves the steam turbine to heat the brine in the brine heater of MSF plant.

Steam Power Plant The plant capacity is 24 MW. Steam enters the steam turbine at 350oC and 5 Mpa. Two feed water heaters (F/H) are used. The HP F/H, which is a closed type with drain pumped forward, receives 0.05 of steam flow rate. The LP F/H is of open type, receives 0.10 of steam flow rate. Both F/H are optimally placed. Expansion through the turbine is assumed to be isentropic.

Gas Turbines Air enters the compressor at 1atm and 30oC. The maximum temperature is 1100oC. The pressure ratio is 8. Polytropic efficiency for both turbine and the compressor is 0.9. o [Cp=1.005 Kj / kg K for air and 1.15 for hot gases. Gas index, k=1.4 for air and 1.333 for hot gases.]

MSF Plan The brine heater of the desalination plant receives steam at 84.93 Kpa where it condenses to saturated liquid water.

Load Curve Load curve of the power plant is presented on a graph where 1x1 cm2 represents 5000 KWhr. The total area under the curve is 311.04 cm2. The maximum load during 30 min is 140,000 KW.

Questions

A. Plot the schematic of the plant and the corresponding T-s diagram. B. What would you call this plant. C. Calculate: 1. Work input of the pump (s). 2. Percent of power loss due to use of HP F/H. 3. Starting from saturating liquid leaving BH, write down energy balance to determine the enthalpy of feed water entering HRB. 4. Overall thermal efficiency of the plant. 5. Percent of heat gain by steam in the superheat section of HRB. 6. Load factor of the power plant.