Gas turbines are used to power aircrafts, trains, ships, electrical generators, pumps, gas compressors, and tanks. Since their initial use for generating electricity in 1939, gas turbines have been an integral part of global transportation and energy. It makes sense that the market continues to grow. In 2020, the gas turbine market size was USD 13.41 billion, and it is projected to grow from USD 13.80 billion in 2021 to USD 17.29 billion in 2028, exhibiting a compound annual growth rate (CAGR) of 3.3%. ASME PTC 22-2023: Gas Turbines specifies the rules and directions that ensure the safe thermal performance of gas turbines.
The ASME PTC 22-2023 Standard for Gas Turbines
ASME PTC 22-2023 provides rules for conducting and reporting thermal performance test results of gas turbines. These gas turbines are specifically open-cycle gas turbine power plants and gas turbine engines, whether aero-derivative or industrial frame. In other words, gas turbines supplied with gaseous or liquid fuels (or solid fuels converted to liquid or gas prior to entry into the gas turbine) are in the scope of this standard.
ASME PTC 22-2023 determines the thermal performance of the gas turbine when operating at test conditions, and correcting these test results to specified reference conditions laid out in the Code. When planning the test, an uncertainty analysis should demonstrate that the proposed instrumentation and measurement techniques meet the requirements of the Code. The Code provides explicit procedures for the determination of the following performance results:
- Corrected power
- Corrected heat rate (efficiency)
- Corrected exhaust flow
- Corrected exhaust energy
- Corrected exhaust temperature
Performance tests may satisfy different goals, including absolute performance and comparative performance. Moreover, the goal of the Code is to provide results with the highest level of accuracy that is consistent with the best engineering knowledge and practice in the gas turbine industry.
How Do Gas Turbines Work?
A gas turbine system, according to ASME PTC 22-2023, is machine that converts thermal energy into mechanical work. Further, gas turbines are a type of internal combustion (gas) engine in which burning an air-fuel mixture produces hot gases that spin a turbine to produce power. It is the production of hot gas during fuel combustion, not the fuel itself that gives gas turbines its name. Gas turbines involve three main sections:
- The compressor: draws air into the engine, pressurizes it, and feeds it to the combustion chamber at speeds of hundreds of miles per hour. For gas turbines driving compressors, the determination of output shaft power is generally required. Reference should be made to ASME PTC 19.7 for guidance in these measurements.
- The combustion system: usually made up of a ring of fuel injectors that inject a steady stream of fuel into combustion chambers where it mixes with the air. The mixture is burned at temperatures of more than 2000 degrees F. The combustion produces a high temperature, high pressure gas stream that enters and expands through the turbine section.
- The turbine: an intricate array of alternate stationary and rotating aerofoil-section blades. As hot combustion gas expands through the turbine, it spins the rotating blades. The rotating blades perform a dual function, driving the compressor to draw more pressurized air into the combustion section and spin a generator to produce electricity.
Specially, ASME PTC 22-2023 specifies that a gas turbine consists of one or several rotating compressors, one or more thermal devices that heat the working fluid, one or several turbines, a control system, and essential auxiliary equipment. Any heat exchangers—excluding exhaust heat recovery exchangers—in the main working fluid circuit are considered to be part of the gas turbine. The gas turbine system includes the gas turbine and all essential equipment necessary for the production of power in a useful form (e.g., electrical, mechanical, or thermal).
How Eco-Friendly and Efficient Are Gas Turbines for Producing Electricity?
Gas turbine power plants are environmentally-friendly because they run on natural gas. Yes, natural gas is a fossil fuel and contributor to air pollution, but natural gas is also far more environmentally friendly than electricity. Its chemical structure is quite different to coal, meaning its emissions are much lower. Since gas turbines run on natural gas unlike internal combustion engines, they produce less exhaust gas pollution. In fact, gas turbines use the excess air for combustion purposes. In addition` to natural gas, gas turbine power plants make use of digester gas: synthetically produced gases like diesel fuels and landfill gas.
A simple cycle gas turbine can achieve energy conversion efficiencies ranging between 20 and 35%. With the higher temperatures achieved in the Department of Energy’s Advanced Turbine Program, future hydrogen and syngas fired gas turbine combined cycle plants are likely to achieve efficiencies of 60 percent or more. When waste heat is captured from these systems for heating or industrial purposes, the overall energy cycle efficiency could approach 80%.
ASME PTC 22-2023: Gas Turbines is available on the ANSI Webstore.