Gas Turbine Units and Their Impact on the Environment – Part 1

Part 2

The earliest device for extracting rotary mechanical energy from a flowing gas stream was the windmill. It was followed by the smokejack, first sketched by Leonardo da Vinci and subsequently described in detail by John Wilkins, an English clergyman, in 1648. This device consisted of a number of horizontal sails that were mounted on a vertical shaft and driven by the hot air rising from a chimney. With the aid of a simple gearing system, the smokejack was used to turn a roasting spit. Various impulse and reaction air-turbine drives were developed during the 19th century, making use of air compressed externally by a reciprocating compressor to drive rotary drills, saws, and other devices. While many such units are still in use, they bear little resemblance to the modern gas turbine engine, which includes a compressor, combustion chamber, and turbine to make up a self-contained prime mover. The first patent approximating such a system was issued to John Barber of England in 1791, though no working model was ever built [1].

The first successful gas turbine, built in Paris between 1903 and 1906, consisted of a three-cylinder, multistage reciprocating compressor, a combustion chamber, and an impulse turbine. It operated by supplying air from the compressor, which was then burned in the combustion chamber with liquid fuel. The resulting gases were cooled somewhat by the injection of water and then fed to an impulse turbine. This system, with a thermal efficiency of about 3 percent, demonstrated for the first time the feasibility of a practical gas turbine engine [1]. More detailed information about the history of the development of gas turbine units can be found in [2].

Figure 1: The Armengaud-Lemale Early Experimental Gas Turbine. St Denis, Paris,1906.

Continuous engineering development has significantly increased the electrical efficiency, advancing from 18% in the first commercially operational gas turbine, the 1939 Neuchatel gas turbine, to current maximum levels of approximately 40% for simple cycle operation (Figure 2, a). Gas turbines find application in various fields, including powering aircraft, trains, ships, generating electricity in power plants, powering pumps, gas compressors, tanks, marine propulsion, locomotive propulsion, and automotive propulsion.

Improvements to the simple cycle and additions of steam turbine bottoming cycles offer the capability of further increases in efficiency. Today, a combined gas turbine and steam turbine cycle is capable of achieving an efficiency of almost 60% (Figure 2, b) [3]. Figure 3 shows a timeline of the development of power generation technology.

A combined cycle power plant is a type of power generation facility that utilizes a combination of two thermodynamic cycles to generate electricity efficiently. It incorporates a gas turbine cycle, known as the Brayton cycle, and a steam turbine cycle, known as the Rankine cycle, in a coordinated manner. Combined-cycle units are one type of a wider group of combined units. Internal connections between the gas and steam cycles, which can be variable in structure, are important for effective operation. Combined steam-gas power units can have separate or mixed circuits of the working fluid – water, steam, and gas. In units with a waste boiler, most of the power is produced in the gas circuit. Fuel consumption in installations of this type mainly falls on the gas circuit, in which the air excess factor is usually 1.3-2.5, so a significant part of the turbine’s work is spent compressing the excess air [11].

Gas Turbine Cycles
Figure 2: Examples of Simple Gas Turbine and Combined Cycles
Figure 3: Gas and Steam Turbine Efficiency Evolution, McDonald (1994) [4]
The Integrated Gasification Fuel Cell (IGFC) cycle is a power cycle based on the gasification of solid fuel and solid oxide fuel cells (SOFCs). It is analogous to an integrated gasification combined cycle power plant but replaces the gas turbine power generation unit with a fuel cell (high-temperature type such as SOFC) power generation unit [12]. By leveraging the intrinsically high energy efficiency of SOFCs and process integration, exceptionally high power plant efficiencies become possible. Furthermore, in the IGFC cycle, SOFCs can be operated to isolate a carbon dioxide-rich anodic exhaust stream, enabling efficient carbon capture to address the greenhouse gas emissions concerns of coal-based power generation [1]. The integration of a fuel cell and a gas turbine is a natural evolution in the quest for improved generation efficiency with clean emissions. Integration is achieved by using the gas turbine compressor as the air mover for the fuel cell and using the high-temperature exhaust of the fuel cell to replace the gas turbine combustor [13].

Another way to increase efficiency is to raise the temperature of the gas turbine cycle (the temperature at the turbine inlet) (Figure 4). In this case, an increase in temperature necessitates the cooling of turbine elements, especially in the first stages. The most promising developments are primarily implemented in aviation gas turbine units and are subsequently used in installations for power engineering. Over the years of development, the aircraft engine has turned into a unique product, which has practically no analogs in terms of stress level and thermal state. Each new generation of the aircraft engine is characterized by an increase in the degree of pressure increase and an increase in the temperature of the working fluid at the turbine inlet (Figure 5). For stationary power gas turbine units and gas turbine units of other types, it is also relevant today to increase the initial gas temperature in the operating cycle and the thermodynamically associated degree of air compression in the compressor. However, an increase in the initial temperature, in addition to problems associated with the strength of turbine elements, leads to environmental problems. Thus, one of the problems solved when creating modern gas turbine units is the reduction of emissions of harmful substances – nitrogen oxides (NOx), carbon oxides (COx), and unburned hydrocarbons (CxHy or UHC). For example, when natural gas is burned at relatively high temperatures, the NOx content determines the toxicity of the exhaust by 90-95% [5].

Figure 4: Efficiency Changes in Gas Turbine Units Between 1955 and 2005, Depending on Initial Gas Temperatures [6].
Thus, one of the primary challenges in gas turbine design is the reduction of harmful emissions in the exhaust gases of power and transport installations. The optimization of operating modes, proper monitoring, and maintenance of gas turbine units during operation, along with the preparation of fuels and rational regulation of fuel supply systems, significantly influence their environmental characteristics [9].

Evolution of turbine inlet temperature and metal operating temperature over the years
Figure 5: Evolution of Turbine Inlet Temperature and Metal Operating Temperature (Figure Reproduced by Data from Rolls Royce Jet Engines) [7].
Join us in part two of this blog where we explore various strategies to reduce emissions such as:

  1. Injection of water or steam into the combustion chamber of a gas turbine unit to boost power and reduce NOx content.
  2. Creation of low-emission multi-zone combustion chambers with variable geometry, pneumatic nozzles, and special flame stabilization.
  3. The use of catalytic combustion chambers or coherent afterburning systems.
  4. Use of environmentally friendly fuel – hydrogen as the main and additional fuel.

 

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Part 2

References:

  1. https://www.britannica.com/technology/gas-turbine-engine/Development-of-gas-turbine
  2. https://blog.softinway.com/the-evolution-of-gas-turbines-from-the-first-designs-to-the-latest-environmentally-friendly-development-trends-part-1/
  3. Analysis of Gas Turbine Systems for Sustainable Energy Conversion. – Marie Anheden, – Royal Institute of Technology Stockholm, Sweden 2000 TRITA-KET R112 ISSN 1104-3466 ISRN KTH/KET/R–112–SE.
  4. York, M. Hughes, J. Berry, T. Russell, Advanced IGCC/hydrogen gas turbine development, Final Technical Report, DE-FC26-05NT42643 (2015) submitted to US Department of Energy
  5. Reduction of nitrogen oxides in gas turbine exhaust gases, Postnikov A.M. – Publishing house of the Samara Scientific Center of the RAS. – 2002 – 286 pages.
  6. http://energetika.in.ua/ru/books/book-3/part-1/section-3/3-9
  7. https://www.cambridge.org/core/journals/aeronautical-journal/article/abs/performance-analysis-of-an-aero-engine-with-interstage-turbine-burner/FB31C38A3C51C5EE83FEAF4E3112FFE1
  8. Manushin E.A. Gas turbines: problems and prospects M.: Energoatomizdat, 1986. – 168 p.
  9. https://dspace.library.khai.edu/xmlui/bitstream/handle/123456789/1623/Gerasim.pdf?sequence=1
  10. https://myengineeringworld.net/2013/06/gas-turbine-combustor-concepts-low-emissions.html
  11. https://ela.kpi.ua/bitstream/123456789/39487/1/2020-7.pdf
  12. https://en.wikipedia.org/wiki/Integrated_gasification_fuel_cell_cycle
  13. https://vibrationacoustics.asmedigitalcollection.asme.org/GT/proceedings/GT1999/78590/V002T02A067/248338
  14. https://link.springer.com/article/10.3103/S1068799811020103
  15. https://www.mdpi.com/1996-1073/13/19/5230
  16. https://www.researchgate.net/publication/346054984_Review_of_Gas_Turbine_Combustion_Chamber_Designs_to_Reduce_Emissions
  17. https://www.hindawi.com/journals/ijce/2022/9123639/
  18. https://www.sciencedirect.com/topics/engineering/steam-injection
  19. https://en.wikipedia.org/wiki/Catalytic_combustion
  20. https://technology.matthey.com/article/23/4/134-141/
  21. https://www.ge.com/content/dam/gepower-new/global/en_US/downloads/gas-new-site/future-of-energy/hydrogen-overview.pdf
  22. https://www.turbomachinerymag.com/view/the-future-of-hydrogen-as-a-gas-turbine-fuel
  23. https://blog.softinway.com/the-evolution-of-gas-turbines-from-the-first-designs-to-the-latest-environmentally-friendly-development-trends-part-2/

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