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Technical questions with answers on gas turbines

By NTS.


  1. What is a gas turbine?

A gas turbine is an engine that converts the energy from a flow of gas into mechanical energy.

  1. How does a gas turbine work?

Gas turbines work on the Brayton cycle, which involves compressing air, mixing it with fuel, and igniting the mixture to create a high-temperature, high-pressure gas. This gas expands through a turbine, which generates mechanical energy that can be used to power a variety of machines and equipment.

  1. What are the different types of gas turbines?

There are three main types of gas turbines: aeroderivative, industrial, and heavy-duty. Aeroderivative gas turbines are used in aviation and small-scale power generation. Industrial gas turbines are used in power generation and other industrial applications. Heavy-duty gas turbines are typically used in large power plants.

  1. What are the main components of a gas turbine?

The main components of a gas turbine include the compressor, combustion chamber, turbine, and exhaust system. Other auxiliary components may include control systems, lubrication and cooling systems, fuel and air delivery systems, and instrumentation and monitoring systems.

In the compressor section, air is drawn in and compressed up to 40 times ambient pressure and directed to the combustor section, where fuel is introduced, ignited, and burned.

  1. What are the 5 major parts of the gas turbine engine?

Any gas turbine engine consists of:

An air inlet.

Compressor section.

Combustion section.

Turbine section.

Exhaust section.

Accessory section.

  1. What is the gas composition in gas turbine?

Today the main gas turbine fuel is natural gas with methane as the dominating component and smaller fractions of heavier hydrocarbons. Future gas turbine fuels will likely include hydrogen gas and biogas with large fractions of carbon dioxide.

  1. What is the difference between a gas turbine and a steam turbine?

A gas turbine generates mechanical energy by burning fuel to create a high-temperature, high-pressure gas that expands through a turbine. In contrast, a steam turbine uses steam generated from boiling water to create mechanical energy.

  1. What are the advantages of using a gas turbine?

Gas turbines offer several advantages over other types of power generation, including high efficiency, low emissions, fast start-up and shutdown, and the ability to operate on a variety of fuels. They are also relatively compact and require less maintenance than other types of engines.

  1. What is the role of the compressor in a gas turbine?

The compressor is responsible for compressing air before it enters the combustor. This increases the pressure and temperature of the air, which allows for more efficient combustion.

  1. What is the function of rotor blades in the compressor?

Rotor blades in the compressor are responsible for compressing air and providing the force needed to move the air through each stage.

  1. How is the air compressed in a gas turbine engine?

The air is compressed by a series of rotating blades in the compressor section. As the air passes through each stage of the compressor, it becomes more compressed and its temperature increases.

  1. What is the role of the combustor in a gas turbine?

The combustor mixes fuel with compressed air and ignites the mixture to create a high-temperature, high-pressure gas that is used to drive the turbine.

  1. What is the function of Crossfire tubes?

Crossfire tubes are used to enable flames from one combustion chamber to propagate to other chambers in a gas turbine for better combustion stability and efficiency.

  1. What is the role of the turbine in a gas turbine?

The turbine extracts energy from the high-pressure gas created by the combustor, which is used to power the generator.

  1. What is the role of the generator in a gas turbine?

The generator converts the mechanical energy from the turbine into electrical energy that can be used to power equipment.

  1. How is the performance of a gas turbine measured?

The performance of a gas turbine is typically measured by its thermal efficiency, which is the ratio of the energy output to the energy input. Other performance measures include power output, exhaust gas temperature, and emissions.

  1. What is the difference between an open cycle and a closed cycle gas turbine?

An open cycle gas turbine uses atmospheric air as the working fluid, which is compressed and heated in the combustion chamber, and then exhausted to the atmosphere. In contrast, a closed cycle gas turbine uses a fluid such as helium or carbon dioxide as the working fluid, which is circulated through the compressor, combustion chamber, and turbine, and then cooled and compressed again.

  1. What is the role of the inlet guide vanes in a gas turbine?

The inlet guide vanes control the amount of air entering the compressor, which affects the pressure and temperature of the compressed air.

  1. What is the purpose of the diffuser in a compressor?

The diffuser is responsible for slowing down the high-speed, low-pressure air exiting the compressor and converting it into high-pressure, low-velocity air that can be used for combustion.

  1. What is the function of the combustion chamber in a gas turbine?

The combustion chamber mixes fuel with compressed air and ignites the mixture to create a high-temperature, high-pressure gas that expands through the turbine.

  1. What are the most common fuels used in gas turbines?

The most common fuels used in gas turbines are natural gas, diesel, and aviation fuels.

  1. What is the purpose of the exhaust system in a gas turbine?

The exhaust system directs the high-temperature, high-pressure gases exiting the turbine to a heat recovery system or to the atmosphere.

  1. What is the function of exhaust diffuser in gas turbine?

Gas-turbine exhaust diffusers play an important role in turbine power output by increasing the pressure ratio across the last stage of the turbine by making the turbine exit static pressure subambient.

  1. What is the role of the bearing system in a gas turbine?

The bearing system supports and rotates the turbine and compressor shafts and helps to reduce friction and wear.

  1. What is the importance of blade cooling in gas turbine design?

Blade cooling is important to prevent high temperatures from damaging the turbine blades, which can lead to failure and reduced performance.

  1. What is the function of the control system in a gas turbine?

The control system is responsible for monitoring and regulating various parameters of the gas turbine, such as temperature, pressure, fuel flow, and speed, to ensure safe and efficient operation. It may also include advanced features such as remote monitoring, predictive maintenance, and fault diagnosis.

  1. How is the speed of a gas turbine controlled?

The speed of a gas turbine is typically controlled by adjusting the fuel flow to the combustion chamber. As more fuel is burned, the temperature and pressure of the gas produced by the combustion process increase, which in turn drives the turbine faster.

  1. What is the maximum efficiency that can be achieved by a gas turbine?

The maximum efficiency of a gas turbine is typically around 60-65%, depending on the design and operating conditions.

  1. What is the purpose of the compressor bleed air system in a gas turbine?

The compressor bleed air system provides compressed air to other parts of the engine, such as the combustion chamber or turbine cooling system.

  1. What is the function of the intercooler in a gas turbine?

The intercooler reduces the temperature of the compressed air between stages of the compressor, which improves efficiency and reduces the risk of compressor stall.

  1. Where does compress air will be used?

Compressed air in a gas turbine is used for various purposes, including turbine cooling, bearing sealing, pulsation control, and purging.

  1. What is a dual-fuel gas turbine?

A dual-fuel gas turbine is a type of gas turbine that can operate on two different types of fuel, typically natural gas, and diesel oil. This allows for greater flexibility in fuel choice and can help to reduce fuel costs.

  1. What is the function of the inlet guide vanes in a gas turbine?

The inlet guide vanes regulate the flow of air into the compressor section of the gas turbine. By adjusting the angle of the vanes, the amount of air entering the compressor can be controlled, which affects the power output and efficiency of the turbine.

  1. What is the difference between a heavy-duty and an aeroderivative gas turbine?

A heavy-duty gas turbine is designed for continuous operation in power generation or industrial applications, while an aeroderivative gas turbine is designed for high-speed, lightweight, and efficient operation in aviation or marine applications.

  1. What is the function of the turbine shroud in a gas turbine?

The turbine shroud helps to prevent the hot gases from bypassing the turbine blades, which can reduce efficiency and cause damage to the turbine.

  1. What is the purpose of the annular combustor in a gas turbine?

The annular combustor is a type of combustion chamber that provides efficient mixing of fuel and air and helps to reduce emissions.

  1. What is the difference between a single-shaft and a multi-shaft gas turbine?

A single-shaft gas turbine has a single shaft connected to both the compressor and the turbine, so the two components spin at the same speed. A multi-shaft gas turbine has separate shafts for the compressor and the turbine, allowing them to operate at different speeds and providing greater flexibility and efficiency in certain applications.

  1. What is the function of the exhaust heat recovery system in a gas turbine?

The exhaust heat recovery system recovers the waste heat from the exhaust gases and converts it into useful energy, such as steam for power generation or heating.

  1. What is the function of turbine legs?

Turbine legs are used to support the weight of the gas turbine and maintain proper alignment with the generator and other components.

  1. Why is turbine leg cooling required?

Turbine leg cooling is required to minimize thermal expansion of the support legs and maintain proper alignment between the turbine and generator.

  1. What are some common maintenance issues with gas turbines?

Common maintenance issues with gas turbines include compressor fouling, turbine blade erosion, combustion chamber damage, and bearing wear. Regular maintenance and inspections can help to prevent these issues and ensure optimal performance.

  1. What is the function of the axial flow turbine in a gas turbine?

The axial flow turbine extracts energy from the high-temperature, high-pressure gas leaving the combustion chamber and converts it into rotational energy to drive the compressor and generator.

  1. Explain the stages of the gas turbine.

The stages of a gas turbine typically consist of a row of fixed nozzles followed by a row of rotating turbine buckets, with each stage providing an increase in kinetic energy and pressure drop as the air moves through the turbine.

  1. What is a combined cycle gas turbine (CCGT) plant?

A combined cycle gas turbine (CCGT) plant is a power generation facility that uses a gas turbine and a steam turbine together to achieve high efficiency. The waste heat from the gas turbine is used to generate steam, which drives a steam turbine to produce additional electricity.

  1. What is the purpose of the nozzle guide vanes in a gas turbine?

The nozzle guide vanes direct the high-velocity gas leaving the turbine to the exhaust system, which helps to maximize the energy extraction from the gas.

  1. What is the function of turning vanes?

Turning vanes are used to turn the flow of gases from axial to radial direction for better efficiency and performance.

  1. What is a simple cycle gas turbine?

A simple cycle gas turbine is a gas turbine that operates independently to generate electricity without any additional energy recovery systems.

  1. What is the function of the combustor liner in a gas turbine?

The combustor liner is a component of the combustion chamber that is designed to withstand high temperatures and protect the surrounding structure from heat damage. It typically contains fuel injectors, flame stabilizers, and cooling holes.

  1. What is the role of the turbine blade airfoil shape in a gas turbine?

The turbine blade airfoil shape is designed to maximize energy extraction from the high-temperature, high-pressure gas leaving the combustion chamber, and to minimize losses due to friction and turbulence.

  1. What is the importance of turbine blade cooling in gas turbine design?

Turbine blade cooling is critical to prevent blade damage due to high temperatures, and to maintain the efficiency and performance of the gas turbine.

  1. What is the function of the afterburner in a gas turbine?

The afterburner is a combustion chamber located downstream of the turbine that allows for additional fuel combustion and energy extraction, which can improve the performance of military aircraft engines.

  1. What is the purpose of the inlet filtration system in a gas turbine?

The inlet filtration system removes contaminants and particulate matter from the air entering the compressor, which helps to improve performance and reduce wear on the compressor.

  1. What is the function of the turbine blade tip clearance control system in a gas turbine?

The turbine blade tip clearance control system adjusts the clearance between the turbine blade tips and the turbine casing to optimize performance and prevent blade damage due to rubbing.

  1. What is the function of the variable stator vanes in a gas turbine?

The stator vanes (also called nozzles) form convergent ducts that convert the gaseous heat and pressure energy into higher velocity gas flow (Pi). In addition to accelerating the gas, the vanes "turn" the flow to direct it into the rotor blades at the optimum angle.

  1. What is the difference between a simple cycle gas turbine and a combined cycle gas turbine?

A simple cycle gas turbine operates independently to generate electricity without any additional energy recovery systems, while a combined cycle gas turbine uses waste heat from the gas turbine to generate steam, which drives a steam turbine to produce additional electricity.

  1. What is the role of the bleed valve system in a gas turbine?

The bleed valve system allows for the controlled release of compressed air from the compressor to prevent compressor stall and improve performance.

  1. Why is air bleeding required through bleed valves?

Air bleeding through bleed valves is required for various purposes, including compressor surge protection, cooling and purging, and control of gas turbine power output.

  1. What is the function of the flame holder in a gas turbine combustor?

The flame holder helps to stabilize the combustion process by creating a region of recirculation and turbulence, which promotes efficient fuel-air mixing.

  1. What is the purpose of the turbine rotor in a gas turbine?

The turbine rotor is the rotating component that extracts energy from the high-temperature, high-pressure gas leaving the combustion chamber, and converts it into rotational energy to drive the compressor and generator.

  1. What is the difference between a can-type and an annular-type combustion chamber in a gas turbine?

A can-type combustion chamber has individual combustion chambers located around the turbine, while an annular-type combustion chamber has a single combustion chamber surrounding the turbine.

  1. What is the function of the transition duct in a gas turbine?

The transition duct connects the combustor to the turbine and helps to direct the hot gases into the turbine while maintaining high efficiency and minimizing losses.

  1. What is the importance of air cooling in gas turbine design?

Air cooling is important to prevent thermal damage to the turbine components due to high temperatures, and to improve efficiency and performance.

  1. What is the function of the power turbine in a gas turbine?

The power turbine is the component that converts the rotational energy from the gas turbine into mechanical energy to drive the generator and produce electricity.

58.   What is the function of the turbine nozzle in a gas turbine?

The turbine nozzle is responsible for directing the high-velocity gases from the combustion chamber onto the turbine blades, converting the kinetic energy of the gases into rotational energy to drive the turbine.

59.   How are gas turbines cooled?

Gas turbines are cooled using a variety of methods, including air cooling, water cooling, and a combination of the two. Air is used to cool the turbine blades and vanes, while water is used to cool the combustion chamber and other high-temperature components.

  1. How is the turbine rotor cooled in a gas turbine?

The turbine rotor is cooled by circulating air or cooling fluid through internal channels in the rotor blades and disks.

  1. How is the fuel-air mixture ignited in a gas turbine?

The fuel-air mixture is ignited by a spark plug or a pilot flame, which ignites the mixture in the combustion chamber.

  1. What is the function of the generator in a gas turbine power plant?

The generator converts the mechanical energy from the turbine into electrical energy, which can then be transmitted to the power grid.

  1. What material are some gas turbine components coated with?

Turbine blades are often coated with a thermal barrier coating (TBC) made of ceramic materials such as zirconia. The function of the TBCS is to provide thermal insulation from the hot gas that flows through the turbine blades. TBCS consist of two layer coating system which comprise of an oxidation and corrosion resistant layer called the bond coat and an insulating ceramic top layer called the top coat.

Compressor blades are sometimes coated with a layer of anti-corrosive material, such as titanium aluminide (TiAl), to protect against oxidation and corrosion at high temperatures.

Combustor liners and transition pieces may be coated with a thermal barrier coating to protect against high temperatures and improve efficiency.

Some components may also be coated with special materials to reduce friction and wear, such as diamond-like carbon (DLC) coatings or ceramic coatings.

  1. What materials are used in the gas turbine engine combustor?

The materials of interest are the nickel- and cobalt-base superalloys for turbine and burner sections of the engine, and titanium alloys and composites for compressor and fan sections of the engine.

  1. Which material is best for gas turbine?

For most turbine blades are made of Nickel super-alloys. They have good creep resistance at up to 80% of their melting point, making them the material of choice for turbine blades.

  1. What are the common materials used for gas turbine fabrication?

Common materials used in gas turbine fabrication include nickel-based alloys, titanium alloys, and ceramic matrix composites.

 

  1. Why are nickel-based alloys used in gas turbine fabrication?

Nickel-based alloys are known for their high-temperature strength, corrosion resistance, and thermal fatigue resistance, making them well-suited for the high-temperature, high-pressure environments found in gas turbines.

  1. What are some common nickel-based alloys used in gas turbine fabrication?

Common nickel-based alloys used in gas turbine fabrication include Inconel 718, Inconel 625, and Hastelloy X.

  1. Why are titanium alloys used in gas turbine fabrication?

Titanium alloys are known for their high strength-to-weight ratio, good corrosion resistance, and ability to withstand high temperatures, making them a popular choice for gas turbine components such as compressor blades.

  1. What are some common titanium alloys used in gas turbine fabrication?

Common titanium alloys used in gas turbine fabrication include Ti-6Al-4V, Ti-6Al-2Sn-4Zr-2Mo, and Ti-6246.

  1. What are ceramic matrix composites (CMCs) and why are they used in gas turbine fabrication?

CMCs are composite materials consisting of a ceramic matrix reinforced with ceramic fibers. They are known for their ability to withstand high temperatures and thermal shock, making them well-suited for use in gas turbine components such as combustors and turbine blades.

  1. What are some common CMCs used in gas turbine fabrication?

Common CMCs used in gas turbine fabrication include silicon carbide (SiC) and carbon fiber reinforced SiC (C/SiC).

  1. What are some challenges associated with using CMCs in gas turbine fabrication?

CMCs are relatively new materials and are still being developed and optimized for use in gas turbine applications. Challenges include cost, manufacturing complexity, and potential for brittleness under certain conditions.






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