Marine Steam and Gas Turbine Systems: Key Parameters and Configurations
Marine Steam Turbine Fundamentals
1. Typical Parameters of a Marine Steam Turbine
- Power output
- Steam pressure and temperature
- Rotational speed
- Condenser vacuum
2. Main Propulsion Steam Turbine System Configuration
The flow path is: Boiler → Turbine → Condenser → Feed Pumps → Boiler.
3. Multistage Steam Turbine Necessity
Multistage operation is required because gradual steam expansion increases efficiency and reduces energy losses.
4. Ship’s Astern Steam Turbine Configuration
An astern turbine is typically integrated in the Low Pressure (LP) casing, operating only during reverse motion.
5. Vacuum Condenser Operation
The main propulsion steam turbine operates on a vacuum condenser because a vacuum increases the expansion ratio, improving efficiency and power.
6. Methods of Regulating Steam Turbine Power
Power is regulated by controlling steam admission valves and steam mass flow.
7. Ways to Increase Steam Turbine Cycle Efficiency
Efficiency is increased through: superheating, reheating, regenerative feed heating, and achieving a higher vacuum.
8. Methods of Increasing Steam Turbine Power
Power is increased by raising the steam pressure, temperature, or mass flow rate.
9. Gas Removal from Installations
Gases are removed by steam ejectors or vacuum pumps to maintain the necessary condenser vacuum.
10. Main Disadvantages of Marine Steam Turbines
- Large size
- Slow start-up time
- Low efficiency at part load
Gas Turbine Technology
11. Why Gas Turbines Use Open Cycles
Open cycles are preferred because they are simpler, lighter, and allow continuous air intake.
12. Methods to Increase Gas Turbine Efficiency
Efficiency is improved via: heat recovery, intercooling, reheating, and a higher compression ratio.
13. Necessity of Reduction Gear
A reduction gear is essential because turbines rotate at very high speeds while propellers require low rotational speeds.
14. Twin-Shaft Turbine with Intercooling Configuration
The sequence is: LP compressor → Intercooler → HP compressor → Combustion Chamber → Turbine.
15. Protection Against Gas Turbine Surging
Surging is prevented by using bleed valves and airflow control to maintain stable compressor operation.
16. Thermodynamic Cycle of a Gas Turbine
The cycle used is the Brayton cycle, which consists of compression, combustion, and expansion.
17. Compressor vs. Turbine Stages
Gas turbines use many compressor stages and few turbine stages because compressors require smaller pressure increases per stage, whereas turbines extract more energy per stage.
18. Functions of the Combustion Chamber
The chamber’s functions are to: mix fuel and air, ensure stable combustion, and generate hot gases.
19. Gas Turbine Starting Procedure
A starter motor accelerates the compressor until the necessary ignition speed is reached.
20. Disadvantages of Steam Injection
Steam injection increases system complexity, corrosion risk, and water consumption.
Advanced Turbine Concepts
1. Limits of Super-Supercritical Steam Turbines
These turbines are limited by extreme temperatures and pressures, which necessitate advanced materials and increase cost.
2. Purpose of Steam Interstage Superheating
Interstage superheating is used to reduce moisture content and improve turbine efficiency.
3. Rationale for Multi-Casing LP and VLP Turbines
These casings are used to handle large steam flow rates and reduce aerodynamic losses.
4. Advantages of ~800 MW Gas Turbines
These turbines offer high unit power and high thermal efficiency.
5. Advantages of Two- and Three-Shaft Gas Turbines
These configurations provide better control, flexibility, and improved part-load efficiency.
6. Use of Cogeneration Steam Turbines
Cogeneration turbines are employed to efficiently use waste heat for combined power and heat production.