For power generation, multiple environmentally-conscious industries depend on gas turbines for high-level electric power generation. Statistically, the gas turbine industry market value is expected to cross $20 billion in 2021. Notably, the operation of gas turbines mostly occurs in an open-cycle setup.
Here, the air in the atmosphere enters the turbine engine and is compressed with an axial-flow or centrifugal compressor. Later, the air enters the combustion chamber where fuel is added. Here, the compression process is not isentropic in nature but adiabatic; enthalpy losses in internal friction are visible. Typically, this occurs when the compression efficiency is at 85% approximately.
In this article, you will learn more details about how the gas turbine components operate in the open-cycle turbine engine.
What is an open-cycle gas turbine?
Open cycle gas turbine is a type of combustion turbine power plant. Here, liquid fuel is necessary for the generator rotation and that produces the electrical power. Typically, the heat that comes out of the engine during the power generation process is around 550°C.
Generally, each of the turbine components and generators takes up around 75m x 25m of surface area. Also, they are present in an enclosed space to ensure low noise emission.
How does an open-cycle gas turbine engine work?
Overall, power plants that run on natural gases utilize gas turbine components in the facility. The three main sections of an open-cycle gas turbine engine include:
This component takes in the air from the atmosphere inside the engine. Then, it pressurizes it and channels the air into the combustion chambers. The speed at this step reaches approximately 100 miles per hour.
2. Combustion system
The next phase of the turbine performance includes the combustion system. Typically, there is a ring of fuel injectors in this system. These are useful for channeling a steady fuel stream into the combustion chambers. Thereafter, the fuel combines with the air molecules present inside the chamber.
To note, the combustion process creates a huge level of temperature when the fuel burns. Overall, the temperature inside the chamber can rise up to over 2000°F. As a result, a gas stream that has high temperature and pressure is produced which moves into the turbine section and expands.
The gas turbine essentially includes a big range of rotating as well as stationary aerofoil-section blades. When the high-temperature combustion gas spreads through the gas turbine, it reaches the rotating blades. Thereafter, the force of the gas spins the blades which accomplish two main functions.
Indeed, the centrifugal force of the blades allows the compressor to pull in more pressurized gas inside of the combustion system. Also, the rotating blades power the generator which produces electricity.
Types of gas turbine
Gas turbines based on land are available in two versions, namely:
- Heavy frame engines- These are engines that are broader in size and have (below 20) low-pressure ratios. To note, the term ‘pressure ratio’ implies the ratio of the discharge pressure from compressors and the air pressure from inlets. These engines produce large quantities of power emissions and supply high power output overall.
- Aeroderivative engines- These engines work at high compression ratios (over 30) and have a compact structure. Parts that require smaller power outputs can utilize these engines, like in jet engines.
Features of open-cycle gas turbines
Statistically, the gas turbine market is expected to have a CAGR of 8% in the forecast period of 2020-2026. A major contributor to this rise is the features power plant owners can expect from these turbines. They include:
- Back work ratio- The back work ratio of the open-cycle gas turbine engine is high, approximately around 50%. In comparison, steam power plants have a lesser back work ratio.
- Cycle type- Power plant owners can utilize the gas turbines mainly for combined energy generation cycles.
- Time to start– Steam-propulsion systems take around four hours to completely start the turbine. Comparatively, gas turbines have a faster start-up time, averaging at 2 minutes.
- Reliable- The open-cycle gas turbine engine has a resilient build and can provide long-term service. Thus, it is a reliable system for industries to use for power generation.
- Uses– The gas turbine engines that run in an open-cycle manner have a high thermal-based efficiency of 44%. Not only is it a useful system for generating electricity, but it also lowers aircraft propulsion.
Is the high-temperature output of gas turbines useful?
Typically, the temperature at which the fuel turns into electricity via open-cycle gas turbines is very high. This does contribute to a highly efficient power supply and for consumers, it is an economical solution.
Yet, while the combustion gases can reach over 2000°F, it is important to note that some of the critical metals in these turbines cannot withstand such temperature hikes. At the most, such critical metals can handle 1500-1700°F. Here, the air that enters through the compressors can work as a cooling agent for the turbine components. Still, that affects the overall thermal efficiency.
All in all, open-cycle gas turbines are effective systems for a high amount of electric output. The engine works with natural gases which combine with heated fuel to create pressurized air. That powers the generator and electricity output is possible. Overall, these have simple structure and functionality, and powers multiple industrial and aviation components.