الجامعة المستنصرية – كلية الھندسة قســــم الھندســــــــة الميكـــــانيكيـــة محطــــــــــــات طاقــــــــــــــــــــــــــة
CHAPTER (6) Gas Turbines & Combined Cycles
أ.م.د .مشعل عبد االمير 10‐Feb‐15
Chapter 6 Gas Turbine & Combined Cycles The Ideal Brayton Cycle, Example (1), The Actual Simple Gas Turbine Cycle, Example (2), Splitting the Turbine, Example (3), Modification to the basic cycle: Intercooling, Reheat, Heat-Recovery Exchanger, Example (4), Combined Cycles with Heat-Recovery Boilers, Example (5), Tutorial Sheet 6.
Power Plant Engineering
TUTORIAL SHEET ‐ 6
Gas Turbine & Combined Cycles
الجامعة المستنصرية – كلية الھندسة
قسم الميكانيك – محطات طـــــــاقة
Assume the following: For compression process: ‐
1.005
1.15
For combustion and expansion processes: ‐
,
. .
,
1.4 1.333
‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ 1‐ A gas turbine unit has an overall pressure ratio of (5/1) and a maximum cycle temperature of (550 Co). The turbine drives the compressor and an electric generator. The mechanical efficiency of the drive is (97%). The ambient temperature is (20 Co) and the isentropic efficiencies of the compressor and turbine are (80 and 83%) respectively. Calculate the power output in kilowatt for airflow of (15 kg/s). Also, calculate the thermal efficiency and the work ratio. Neglect changes in kinetic energy and the pressure losses in the combustion chamber. 2‐ In a marine gas turbine unit, a High‐pressure turbine stage drives the compressor, and a low‐pressure turbine stage drives the propeller through suitable gearing. The overall pressure ratio is (4/1), and the maximum temperature is (650 Co). The isentropic efficiencies of the compressor, HP and LP turbines are (80, 83 and 85%) respectively, and the mechanical efficiency of both shafts is (98%). Calculate the pressure between turbine stages when the air intake condition are (1.01 bar and 25 Co). Also, calculate the thermal efficiency and the shaft power when the mass flow is (60 kg/s). Neglect changes in kinetic energy and the pressure losses in the combustion chamber. 3‐ A combined power plant consisting of a simple open cycle gas turbine unit, using air as the working fluid (neglect fuel mass flow rate), and a steam turbine is to be designed such that the heat rejected at the gas turbine unit is to be utilized to produce steam at the generator for the steam turbine. The exhaust air leaving the generator is at (200 Co). Draw a simple sketch for the plant and the (T‐s) diagram and calculate the mass flow rate of steam per (kg/s) of airflow, the total power output per (kg/s) of airflow and the overall thermal efficiency of the plant. Assume ideal cycles. Neglect the feed pump work of Rankine cycle. The data of each cycle are as follows:‐ Gas Turbine Cycle Steam Turbine Cycle Pressure Minimum 1 0.07 (bar) Maximum 5 30 Minimum 20 Temperature o (C ) Maximum 830 300 119
