Initial ignition occurs from one or more spark plugs depending on combustor design. The thermodynamic process used in gas turbines is the Brayton cycle. Two significant performance parameters are the pressure ratio and the firing temperature.
The fuel-to-power efficiency of the engine is optimized by increasing the difference or ratio between the compressor discharge pressure and inlet air pressure. This compression ratio is dependent on the design. Gas turbines for power generation can be either industrial heavy frame or aeroderivative designs. Industrial gas turbines are designed for stationary applications and have lower pressure ratios — typically up to Aeroderivative gas turbines are lighter weight compact engines adapted from aircraft jet engine design which operate at higher compression ratios — up to They offer higher fuel efficiency and lower emissions, but are smaller and have higher initial capital costs.
Aeroderivative gas turbines are more sensitive to the compressor inlet temperature. The temperature at which the turbine operates firing temperature also impacts efficiency, with higher temperatures leading to higher efficiency.
However, turbine inlet temperature is limited by the thermal conditions that can be tolerated by the turbine blade metal alloy. Because of the power required to drive the compressor, energy conversion efficiency for a simple cycle gas turbine power plant is typically about 30 percent, with even the most efficient designs around 40 percent.
By recovering that waste heat to produce more useful work in a combined cycle configuration, gas turbine power plant efficiency can reach 55 to 60 percent.
However, there are operational limitations associated with operating gas turbines in combined cycle mode, including longer startup time, purge requirements to prevent fires or explosions, and ramp rate to full load. Aeroderivative engines tend to be very compact and are useful where smaller power outputs are needed. As large frame turbines have higher power outputs, they can produce larger amounts of emissions, and must be designed to achieve low emissions of pollutants, such as NOx.
One key to a turbine's fuel-to-power efficiency is the temperature at which it operates. Higher temperatures generally mean higher efficiencies, which in turn, can lead to more economical operation.
Gas flowing through a typical power plant turbine can be as hot as degrees F, but some of the critical metals in the turbine can withstand temperatures only as hot as to degrees F.
Therefore, air from the compressor might be used for cooling key turbine components, reducing ultimate thermal efficiency. One of the major achievements of the Department of Energy's advanced turbine program was to break through previous limitations on turbine temperatures, using a combination of innovative cooling technologies and advanced materials. When the fire is established and stabilized in the combustion chamber, the ignition system will be put out of service.
The most critical process in normal turbine operation is to manage the combustion and produce a proper amount of high-pressure exhaust gas. This exhaust gas is applied to the turbine blades and after rotating the turbine shaft, conducted to the exhaust stack. The air is prone to contaminations or having some unwanted particles which can harm the system and degrade the overall performance.
The screening and filtration are basic requirements for incoming air. Also, proper instrumentation is mounted on the Air Duct to monitor the draft pressure and temperature. In harsh environments, the air might need to be preheated or conditioned.
Also, differential pressure monitoring of air filters will warn the turbine operator of filter clogging. The discharge pressure and temperature of the air compressor are monitored to manage the combustion quality at the combustion chamber.
The manufacturers need to know the details of fuel gas and only based on its characteristics they can guarantee the performance of their Gas turbines.
Also, the pressure and temperature of fuel gas are monitored during normal operation of a Gas turbine. There are different technologies in properly mixing the air and gas and making efficient combustion from manufacturer to manufacturer. Combustion chambers are of some tubular heat resistant structures and fuel is usually injected into it from the circumference and at different cross-sectional locations. The temperatures at different locations of the combustion chamber are thoroughly monitored by means of proper sensors like thermocouples.
Also, the technologies used in the design and construction of the combustion chamber are of the topmost ones. At this stage, the high RPM of Gas Turbine rotor should be tightly monitored and based on the load driven by the turbine, the surge of turbine gets the topmost importance for turbine performance and turbine protection. Vibrations axial and radial and speeds, both at the air compressor and Gas turbine should be continuously taken into consideration. This was the simplest way to address major parts of Gas Turbines and as one of the most sophisticated man-made machines, a Gas Turbine deserves more elaboration.
Also, there are different technologies which some manufacturers use as their proprietary technology and were not considered in this article. Thank you so much for reading, watching and adding your voice to this automation conversation.
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