- 1 What is a Gas Turbine?
- 2 Gas Turbine Working Principle:
- 3 Gas Turbine Cycle
- 4 Types of Gas Turbine Engine
- 5 Gas Turbine Efficiency
- 6 Gas Turbine Engine Components
- 7 Advantages and Disadvantages of Gas Turbines
- 8 Applications of the Gas Turbine
- 9 FAQ Section
A gas turbine is the most common and famous type of turbine. Gas turbines and gas engines are most widely used all over the world for different purposes. Nowadays, these turbines are the highest extensively used power generation technologies. These types of turbines are mainly used to produce cheap electricity by using gas as a working fluid. In the previous articles, we discussed steam turbines, wind turbines and water turbines. Therefore, in this article, we will mainly examine different aspects of the gas turbine.
What is a Gas Turbine?
A gas turbine is a type of I.C engine that transforms the kinetic energy of the gas into rotational energy (mechanical energy). This mechanical energy further runs a gas generator which converts this mechanical energy into electricity.
It is known as a “gas turbine” because it uses gas as a working fluid. In essence, this turbine can be supposed as an energy converter that can convert the stored energy in the gas into rotational power. This rotational power runs a generator that generates electricity. After electricity generation, this electricity delivers to different businesses and households via cables.
In 1791, the first gas turbine engine was invented by John Barber. His design was included most of the parts found in the latest gas turbines. It was planned to drive horseless cars.
Latest gas turbines work at an extensively higher temperature compared to steam turbines. The maximum efficiency of the gas turbine is up to 60%.
Gas Turbine Working Principle:
A gas turbine work on the base of the Brayton cycle. During this cycle, the air-fuel mixture is pressurized, burned, passed through a gas turbine, and discharged.
In the working cycle of a gas turbine, air uses as a working medium. A gas turbine works in the following the stages:
- Suction Process
- Compression Process
- Combustion Process
- Turbine Section
- Electricity Generation
1) Suction Process
First of all, the turbine sucks air into the compression chamber from the atmosphere into the turbine and sends this air to the compressor.
2) Compression Process
As the air enters the compressor, it compresses the air and converts the air kinetic energy into pressure energy. After this, it converts the air into high-pressure air.
3) Combustion Process
After the compression process, the compressed air enters the combustion chamber. In the combustion chamber, an injector injects fuel into the chamber, which mixes with the air. After mixing, the combustion chamber ignites the air-fuel mixture. Due to the ignition process, the air-fuel mixture converts into high pressure and high-temperature gases.
4) Turbine Section
As the combusted gas enters into the turbine section, some energy of this gas transforms into mechanical energy, and some energy is exhausted. As the combustion gas expands through the turbine, it rotates the turbine blades. The rotating blades have a dual function: they run the compressor to draw in more air for operation and also drive a gas generator connected with the turbine.
5) Electricity Generation Process
A generator is connected with the shaft of the turbine. The generator receives mechanical energy from the turbine and converts this energy into electrical power.
Useless energy escapes from the exhaust gases. The exhaust gas can be used for external tasks, like to generate thrust directly in a turbojet engine or to rotate a second independent turbine (referred to as a power turbine) that can be connected to an electric generator, propeller, or fan.
Gas Turbine Cycle
A working cycle of the gas turbine is explained below with the help of the P-V diagram:
Compression (A to B): –
As the ambient air enters into the compressor, the compressor compresses it and increases its pressure. After compression, the air enters in the combustion chamber (at point B in the above diagram).
Combustion (B to C): –
When compressed air comes into the combustion chamber (line B to C), an injector injects fuel which mixes with the air. An ignitor ignites to this air-fuel mixture and increases its pressure and temperature.
Expansion (C to D): –
After passing through the combustion process, the air enters into the turbine section (line C to D represents this process), where it expands. As the air expands, it rotates the turbine blades, which further rotate the turbine shaft and compressor. Some power of this expanded air uses to drive the compressor, while the remaining power is used to drive the coupled generator. The generator transforms this power into electricity.
Types of Gas Turbine Engine
There are multiple types of gas turbines. The most common types of the gas turbine are given below:
- Turboprop Scale
- jet engine
- Aeroderivative gas turbine
1) Turboprop Gas Engine
The first type of gas engine is the turboprop engine. A turboprop engine has a propelling nozzle, turbine, combustor, compressor, an intake and a reduction gearbox.
This gas engine uses a reduction gearbox to power the propeller of an airplane. The turboprop engine is used in small aircraft like the Embraer’s EMB312 Tucano military trainer and General Aviation Cessna 208 caravan. Turboprop engine also uses in large size airplanes like the Airbus A400M transport. Also, it uses in medium commuter aircraft like the Bombardier Dash 8.
The exhaust gases run the power turbine, which couples via a shaft that further runs the reduction gear. Turboprop engines require a reduction gearbox because the best propeller performance achieves at speeds much lower than the engine’s operational speed.
These gas turbines have extreme efficiency at 250-400 mph and altitudes of 18,000-30,000 feet. The lowest fuel consumption for turboprop turbines is typically available in the altitude range of 25,000feet to the tropopause. This turbine uses approximately 80% to 85% of the produced power to run the propeller. In contrast, the remaining available energy uses as a thrust to remove the exhaust gases.
Advantages and disadvantages of Turboprop Engine: –
|These engines have small sizes.||They have a low cruising speed.|
|These have lightweight.||The propeller of this engine loses efficiency at a higher altitude.|
|Turboprop engines are most efficient for a short distance.||These are not best for the long journey.|
|These engines burn less fuel per hour than jet engines.||Turboprop engines produce high noise than jet engines.|
2) Turbojet Engine
The second type of gas turbine is a jet engine. It is an optimized gas turbine. It generates power with the help of the exhaust gas or ducted fan linked to the turbine. The engines that generate power from direct pulses of the exhaust gases is referred to as turbojet engines.
A turbojet gas engine uses in aircraft. These engines were first designed in Great Britain and Germany before World War II and were the simplest engines than other jet engines. A turbojet engine has the disadvantage that it has high noise and consumes a high amount. These engines have a limited range and durability. These are currently mainly used in military aviation.
A turbojet engine has the following four parts:
- Combustion chamber
The compressor part sucks the air, compresses it and transfer the compressed air into the combustion chamber at high speed. The combustion chamber has a fuel injector and an igniter for igniting the air-fuel mixture. The expanded gas runs the turbine. This turbine is connected to the compressor and engine via a shaft and keeps the engine running.
Advantages and disadvantages of Turbojet Engine: –
|These engines have a simple design.||They consume a high amount of fuel.|
|These can run at high speed.||They produce a high nose.|
|Turbojet engines have small sizes.||These have poor performance at low speed.|
|These have low weight.||These gas engines can’t use for long-distance traveling.|
3) Turbofan Engine
The jet engine that generates power by using a ducted fan is commonly referred to as a turbofan engine. The word “turbofan” is a combination of “turbine” and “fan“: the word turbine represents a gas turbine that gets mechanical power by the combustion chamber, and the fan represents the ducted fan, which gets mechanical power from the turbine to drive air rearwards.
This engine uses a ducted fan and exhaust to deliver pulsation. Turbofan engines are also most widely used in aircraft.
The evolution of turbofans is a combination of some of the best features of turboprop and turbojet engines. These gas engines are developed to generate extra thrust by redirecting the secondary airflow around the combustion chamber.
Turbofan gas engine has low noise and consumes low fuel compared to other jet engines. It has two or more shafts inside the engine.
Advantages and disadvantages of Turbofan: –
|This turbine consumes less fuel than other jet engines.||These have a large size than turbojet engines.|
|It has low noise.||Turbofan engines can’t control sudden fluctuation in load.|
|It is best suitable for long-distance traveling.||It needs a ducted fan to generate power.|
4) Scale jet engine
Scale jet engine is the fifth type. These engines are also called micro-jets. With this in mind, the pioneer of the latest microjet, Kurt Schrekling, developed the world’s first microturbines (FD3/67). These engines can generate 22N of force. Also, it can be made by most professionals with experience in mechanical engineering using essential technical tools.
5) Turboshaft engine
A gas turbine engine that is optimized to generate shaft power instead of jet propulsion is called a turboshaft engine. The working principle of a turboshaft engine is very similar to a turbojet engine, but with additional turbo, expansion to remove heat energy from the exhaust gases and transform it into output power of the shaft. In 1949, the French Turbomeca company built the first turboshaft gas turbine engine.
The main shaft of the engine equips with a compressor and its turbine, and both coupled with the combustion is called a gas generator. A separately rotating power turbine uses to power the helicopter rotors. You can add design flexibility by rotating the power turbine and gas generator at their respective speeds.
The main difference between a turboshaft engine and a turbojet engine is that in a turboshaft engine, the maximum part of the energy generated by the expanding gas is utilized to power the turbine instead of generating thrust.
These gas engines are best suitable for applications that need light weight, small size, high reliability, and continuous high performance. Most helicopters have a turboshaft engine. A turboshaft gas turbine engine also uses as an auxiliary engine for large aircraft. These engines also use in natural gas liquefaction stations.
Advantages and disadvantages of Turboshaft Engine: –
|These engines have high reliability.||They produce high noise.|
|Turbofan engines have continuous high performance.||These gas engines have high manufacturing costs.|
|These have small sizes.||They need high power for the initial startup.|
6) Aero-Derivative gas turbine
First of all, these are often constructed on gas turbine engines in existing aircraft. The industrial gas turbine is more extensive than the aero-derivative turbine.
Secondly, these are used for electricity production. Because these turbines shut down faster than industrial engines and can respond rapidly to changing loads, they are also used in the maritime industry for weight reduction.
A microturbine is a gas turbine that generates relatively both electricity and heat on a small scale. This gas turbine engine is developed from turbochargers with piston engines, small jet engines, or aircraft APUs. Their size corresponds to a 25-500 kW refrigerator.
The efficiency of microturbines is around 15% without a heat exchanger. And 20% to 30% with a heat exchanger. With combined heat and power, the combined thermoelectric efficiency can reach 85%
Compared to other small-scale power generation technologies, microturbines have many benefits: low energy cost, low emission, light weight, high efficiency, compact design, low number of moveable parts, and the ability to use waste fuel. Waste heat recovery can also utilize in these turbines to attain efficiencies of over 80%.
Microturbines are expected to occupy a significant portion of the distributed generation market due to their low maintenance and operating costs, low capital cost, small size, and automatic electronic control. Furthermore, these gas turbines offer an efficient and clean solution for direct-drive markets, e.g., compressors and air conditioners.
Gas Turbine Efficiency
The operating temperature (ignition temperature) of the gas turbine influences its efficiency. If the temperature is higher, the turbine efficiency will also be higher. However, the inlet temperature of the turbine is fixed with the help of thermal conditions that the turbine blades can withstand.
In maximum cases, turbine inlet gas temperatures range from 1200°C-1400°C. Still, some designers raise the inlet temperature to 1600°C by developing blades coverings and cooling systems that prevent metallurgical parts from thermal harm.
Due to the power needed to run the compressor, the energy conversion efficiency of a single cycle gas turbine power plant is approximately 30%, and even the most efficient design has efficiency up to 40%.
A lot of heat remains in the exhaust gas, which has a temperature up to 600°C as it exits the turbine. The gas turbine powerplant may achieve efficiency between 55% to 60% by recovering waste heat in a combined cycle configuration to create more valuable work.
|Gas turbine type||Power output (MW el)||Efficiency, Combined cycle (%), LHV||Efficiency, Simple cycle (%), LHV|
|Large scale heavy duty||200-500||54-60||37-40|
|Small scale heavy duty||70-200||53-55||35-37|
Gas Turbine Engine Components
The gas turbine has the following major parts:
1) Compressor: –
The compressor includes in the components essential gas turbines. Firstly, the compressor sucks air into the turbine. After this, it pressurizes the air and increases the pressure of this air according to the turbine requirements. Finally, the compressor sends air into the combustion chamber at a rate of hundreds of miles/hour.
2) Shaft: –
The rotating shaft allows the compressor to continuously suck air and pressurize more air for regulating continuous combustion. It has multiple turbine blades. The shaft rotates with the rotation of the turbine blades. The excess power of the shaft uses to run the generator to generate electrical power.
3) Combustion Chamber: –
It consists of a series of injectors that insert a steady fuel stream into the combustion system and mix it with the combustion chamber’s air. The mixture burns at a temperature above 2,000 degrees Fahrenheit. The combustion chamber also includes in the essential gas turbine components. It creates a high-pressure and high-pressure gas flow that enters the turbine and partially expands.
4) Turbine Section: –
It consists of a complex set of fixed and rotating vanes. As the hot flue gas expands through the turbine, then the rotating vanes turn. The rotary vanes have two functions. Firstly, it causes the compressor to draw more compressed air into the combustion zone. And secondly, it rotates the generator to generate electrical energy.
The gearbox of the turbine provides torque to the driven equipment.
This part emits low emissions from the turbine section.
Advantages and Disadvantages of Gas Turbines
Advantages and disadvantages of the gas turbine are given below:
Advantages of Gas Turbines
- These turbines are easy to transport and quick to start.
- Global support and services.
- Low costs and low consumption of lubricants.
- Different fuels can be used.
- Due to excess air, it burns the air completely, and flames on the cold surface do not “quench,” which leads to very low toxic CO and HC emissions.
- It has high availability.
- Great reliability.
- It′s operation cost is low.
- Use other clean, renewable fuels.
- The gas turbines have a High power density.
- It emits low toxic gases.
- It has low construction expenses.
- Comprehensive performance module block.
Disadvantages of Gas Turbines
- Requires high maintenance cost.
- Lower power: weight ratio.
- The use of exotic materials can add to the cost of the core engine.
- The efficiency of gas turbines is lower than that of a reciprocating engine when idling.
- Longer starting time than a reciprocating engine.
- Characteristic complaints can be challenging to control.
Applications of the Gas Turbine
- These turbines use to drive aircraft.
- It is using in trains.
- These turbines are used to drive ships.
- The gas turbine engine also use to drive electrical generators.
- These are used to pwer pumps.
- This turbine uses in different applications of gas compressors.
Who invented the gas turbine?
In 1791, the first gas turbine engine was invented by John Barber.
Gas turbine works on which cycle?
A gas turbine works on the base of the Brayton (or Joule) Cycle.
What are gas turbines used for?
The gas turbines use to drive:
- Industrial machinery
- Gas compressors
What fuel does a gas turbine use?
A gas turbine uses fuels such as vaporized fuel oil gas, low-Btu coal gas, process gas, and natural gas. But the world’s 90% of gas turbines use liquefied natural gas or natural gas as operating fuels.
Why gas turbine is called a gas turbine?
This turbine is known as a gas turbine because gas uses as working in this turbine.
Which type of compressor is used in a gas turbine plant?
A multistage axial flow compressor uses in a particle gas turbine plant.
How long does a gas turbine take to start?
A combustion engine gas turbine can start up in less than 5 minutes to reach full load, while combined cycle gas turbines can take 30 minutes or more to start.
The cost of gas turbines is very low as compared to other types of turbines. Due to that these turbines are most widely used all over the world. These turbines have high power density. These turbines are too useful in our industries. And it has low operation cost and good reliability.
I hope that you will be clear about all concepts related to this topic. If you have any questions, then you can tell me without any hesitation.