What is a Gas Turbine : Working & Its Applications

A turbine is a rotating mechanical device that uses the kinetic energy (KE) of some liquid like water, air, combustion gases, or steam & changes this into the rotating motion of the device itself. There are different types of turbines available like a water turbine, gas turbine, wind turbine, and steam turbine. Among them, this article discusses an overview of a gas turbine and its working.

The first gas turbine was invented in 1791 by John Barber. So most of the parts from his design were included in the latest turbines. As compared to steam turbines, these turbines work at a higher temperature. The gas turbine’s maximum efficiency is up to 60%. This turbine uses the air as a working medium and the fuels used in this turbine are process gas, low-Btu coal gas, natural gas & vaporized fuel oil gas. But 90% of these turbines around the world use natural gas or liquefied natural gas as operating fuels.

What is a Gas Turbine/Gas Turbine Definition?

A combustion engine within a power plant that is used to change the natural gas or fuels of liquid to mechanical energy is known as a gas turbine. This converted energy is used to drive an electric generator that generates the electrical energy that is used from power lines to businesses & homes.

First, this turbine heats a mixture of fuel & air at high temperatures to generate electricity to cause the turbine blade to rotate.

This rotating turbine drives an electric generator to convert the energy into electricity. At present in modern gas turbines, the formation of pressurized gas can be done by using fuel-burning like kerosene, natural gas, jet fuel, or propane. The heat generated by the fuel can expand air to flow throughout the turbine to provide useful energy.

Gas Turbine Construction

The gas turbine components mainly include a compressor, shaft, combustion chamber, gearbox & Exhaust. The working of this turbine includes different processes like suction, compression, combustion, turbine & electricity generation.  The gas turbine parts & their functions are explained below.

Suction

In the suction process, the turbine sucks the air from the atmosphere to the compression chamber then the air is transmitted to the compressor.

Compression

In the compression process, once the air comes into the compressor, then it reduces the air & changes the energy from kinetic to pressure. After this, the energy changes the air into high-pressure air.

Combustion

After the process of compression, the compressed air moves into the combustion chamber. This chamber includes an injector that injects fuel into the combustion chamber and mixes the fuel with the air. Once the mixing is done, the chamber ignites the mixture of air & fuel. This mixture changes into high-temperature & high-pressure gases because of the ignition process.

Turbine

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.

Electricity Generation

A generator is connected through the shaft of the turbine, so the generator gets mechanical energy from the turbine & changes into electrical power.

Hope now it is clear on different process involved in electricity generation in gas turbine. Lets get into the operating principle of gas Turbine.

Gas Turbine Working & Operation Principle

The gas turbine working principle mainly depends on the Brayton cycle or Joule cycle.

The Brayton cycle states that it is a thermodynamic cycle that explains a particular heat engine operation that has gas or air as its working fluid. Sometimes, it is also called the Joule cycle. Throughout this Brayton cycle, the mixture of air-fuel is burned, pressurized & supplied through a turbine & discharged.

Once the air enters into the inlet of the turbine, the compressor in the turbine increases the pressure of air before it goes into the combustion chamber. After that, this compressed air is mixed with fuel & ignited to create an expanding gas. At last, this hot gas drives the turbine & produces electrical energy.

Types of Gas Turbine

There are different types of gas turbine which include the following.

• Turbojet Gas Turbine.
• Turboprop Gas Turbine.
• Turbofan Gas Turbine.
• Turboshaft Gas Turbine.

Turbojet Gas Turbine

Turbojet is the first gas turbine although they look completely different as compared to reciprocal engines their operating principle is the same as intake, compression, power & exhaust.  In this type of turbine, air moves at a high speed toward the inlet of fuel & ignitor of the chamber. Once the air expands then the turbine induces accelerated exhaust gases.

The advantages of turbojet turbine are being small size, less weight, simple design and runs at high speed. The disadvantages of turbojet turbine are; they generate high noise, their performance is low at high performance, consumes a high amount of fuel and they cannot be used for traveling long distances.

Turboprop Gas Turbine

This type of turbine includes a turbine, propelling nozzle, an intake, combustor, a reduction gearbox & compressor. This turbine is mainly used in small, medium commuter, and big aircraft. Turboprop turbines need a reduction gearbox because the finest propeller performance can be achieved at much less speeds than the operational speed of the turbine.

The efficiency of turboprop ranges from 250 to 400 mph & altitudes range from 18,000 to 30,000 feet. The less fuel consumption available for this turbine will be in the altitude range which ranges from 25,000feet to the tropopause. So this type of turbine approximately uses the generated power from 80% to 85% to drive the propeller. The remaining accessible energy utilizes as a force to eliminate the exhaust gases.

The advantages of turboprop include; these turbines are available with less weight, are small in size, are most efficient for a short distance, and burn less fuel for every hour as compared to jet engines. The disadvantages of turboprop include; they have less speed, generate high noise, are at a high altitude, lose efficiency, and are not suitable for a long journey.

Turbofan Gas Turbine

When the jet engine generates power through a ducted fan then it is known as a turbofan turbine. It is the combination of a fan and a turbine. In a turbofan turbine, the turbine gets mechanical power from the combustion chamber whereas the fan gets the power from the turbine.

Turbofan turbine can be simply connected to the front side of the turbojet turbine through a duct fan. After that, the fan creates an additional push to cool the turbine & also reduce the noise output. These turbines are used in aircraft.

The advantages of turbofan include; consume less fuel, less noise, and is suitable for long-distance traveling whereas the disadvantages are; available in large size, cannot control unexpected variation within the load, and using a ducted fan to generate power.

Turboshaft Gas Turbine

When the gas turbine is optimized to produce shaft power rather than jet propulsion is known as a turboshaft engine. The turboshaft engine working principle is extremely similar as compared to a turbojet type. The main dissimilarity between a turboshaft & a turbojet is that in a turboshaft, the highest energy part generated through the expanding gas is used to power the turbine rather than generating thrust.

These turbines are used where small size, less weight, continuous high performance & high reliability is required. Most of the helicopters, large aircraft & liquefaction stations of natural gas use turboshaft

The advantages of turboshaft include; reliability is high, available in small sizes, and continuous high performance whereas the disadvantages are; generate high noise, they use high power for starting and manufacturing cost is high.

Difference b/w Gas Turbine vs Steam Turbine

Generally in power plants, two common elements are used to create electricity like gas & steam turbines. The difference between gas turbine and steam turbine include the following.

Advantages

The advantages of gas turbines include the following.

• Quick to start.
• Easily transport.
• Less cost.
• Lubricants consumption is low.
• It uses different fuels.
• High reliability.
• It has high accessibility.
• Less operation cost.
• Its power density is high.
• It generates less toxic gases.

Disadvantages

The disadvantages of gas turbines include the following.

• Maintenance cost is high.
• The power-weight ratio is less.
• It takes more time to start at the beginning.
• The core engine cost is high due to the use of exotic materials used.
• An exterior unit is necessary to spin the compressor to turn ON the turbine.
• More power is required to drive the compressor thus it gives low output.
• The overall efficiency of this turbine is less as exhaust gases include most of the heat.

Applications

The applications of gas turbines include the following.

• These turbines are applicable where maximum speed and power are required.
• These are used within jet population unit of aircraft.
• Used as population unit in ships.
• Used in the supercharging system of automobiles.
• In locomotives.
• These turbines are used in trains & also to drive aircraft & ships.
• These are used to drive generators & to power pumps.

Thus, this is all about an overview of a gas turbine that is used to drive pumps, trains, ships, tanks, industrial machinery, and gas compressors. Here is a question for you, what is the efficiency of a gas turbine?