Gas Turbine Units and Their Impact on the Environment – Part 2

Part 1

As discussed in Part 1 of this blog, Part Two will delve into various development strategies aimed at reducing emissions and enhancing gas turbine performance. Several approaches are currently being explored or employed to mitigate exhaust gas toxicity, as outlined below:

  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.

 

As previously mentioned, the toxicity and composition of exhaust gases from a gas turbine plant depend on the type of fuel used. For instance, a critical factor in understanding the mechanism of NOx generation in fuels is the content of chemically bound nitrogen [N]. However, NOx and CO emissions exhibit opposite dependencies on most parameters in the combustion zone (temperature, residence time, volume of the combustion zone, air flow, etc.), prompting the search for a compromise solution to minimize them.

As an illustration, Figure 5a depicts the dependencies of mass emissions of NOx and CO, and the excess air factor when using burner devices with diffusion mixture formation in afterburning chambers [9]. At α = 1.7…2.0, NOx and CO emissions are minimal. Figure 5b illustrates the dependence of NOx and CO emissions on temperature.

Figure 6 - Effect of Air Excess Factor and Temperature on NOx and CO Emissions
Figure 6 – Effect of Air Excess Factor and Temperature on NOx and CO Emissions [9,10]
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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. Read More

Nozzle Cascades for Turbines: Types and Design Features

The gas turbine is a rotary heat engine with double conversion of energy. In guide vanes (nozzles), the potential energy of steam is converted into kinetic energy, which is then converted into mechanical work by rotating the turbine shaft (rotor). The turbine rotor drives the rotor of the consumer machine, like in alternators, compressors, pumps, etc. [1]

Scheme of Turbine Flow Path
Figure 1 Scheme of turbine flow path [Huzel D.K., Huang D.H. Modern engineering for design of liquid-propellant rocket engines.- American institute of aeronautics and astronautics – 1992. ]
To increase the efficiency of turbine installations one must increase the thermal efficiency of the cycle, as well as the efficiency of individual elements of the installation’s thermal scheme. A familiar method of increasing the efficiency of the thermal cycle is by increasing the temperature of the working fluid in front of the turbine. However, this not only requires using high-temperature materials, but also requires cooling the blade apparatus. As a result, installation costs increase, and the efficiency of the turbine stages decreases [2]. Read More

The Evolution of Gas Turbines From the First Designs to the Latest Environmentally Friendly Development Trends: Part 2

Part 1

Gas Turbine Development Trends: Hydrogen Energy

Recent world trends related to the development of clean energy have led to an increased focus on the use of hydrogen as a cleaner fuel for gas turbines and with it, the need to develop gas turbine plants that can operate both on a mixture of hydrogen with natural gas and on pure hydrogen. The use of hydrogen as a fuel can significantly reduce COx emissions, but burning hydrogen with air increases the amount of nitrogen oxides NOx, therefore leading gas turbine manufacturers have made great efforts over the past decades to develop low NOx combustion technologies that can provide a high proportion of hydrogen content in the fuel, up to 100%.

Heavy Duty Gas Turbine, GT 26
Figure 7 Heavy Duty Gas Turbine, GT 26

In a modern gas turbine in a premixed combustor, operating conditions close to the lean-burn flammability limit are chosen to reduce oxides of nitrogen (NOx), where the lean-burn flammability limit is determined by whether or not a flame is ejected. The flame is blown off under the condition that the speed of the combustible mixture entering the combustion chamber is greater than the speed of the flame. The flame speed is highly dependent on the composition of the fuel, and in the case of hydrogen, the turbulent flame speed is known to be at least 10 times higher than that of a methane flame under gas turbine combustion chamber conditions due to its high diffusion and chemical reaction rate. In the case of gas turbine combustion chambers for power generation using natural gas, lean-burn combustion technology is mainly applied to reduce NOx (since NOx is exponentially dependent on the temperature in the combustion region), while gas turbines using fuel containing hydrogen (syngas ), are prone to flashback (flame speed is much higher than the speed of the incoming fuel mixture so that the flame moves back towards the entrance to the combustion chamber and nozzles). Previously, in such cases, combustion chambers without premixing were used to avoid the risk of damage and destruction of the nozzles and the entire system. In this case, a technique is applied that involves the injection of a large amount of steam or nitrogen to minimize the increase in NOx, but this, in turn, leads to a decrease in the temperature at the turbine inlet. Thus, for the latest hydrogen-fuelled gas turbines, leading manufacturers around the world have begun to develop special combustion technologies with pre-mixing or with special micro-mixers. Read More

The Evolution of Gas Turbines From the First Designs to the Latest Environmentally Friendly Development Trends: Part 1

Part 2

Gas turbines have a rich history and play a key role in many of the modern-day technology we rely on. Welcome to part 1 of this blog where we’ll look at the history and evolution of gas turbines and don’t forget to join us for part 2 (next week) which will take a deeper look into hydrogen energy and where these machines are headed. 

The First Industrial Gas Turbines

Gas turbines are unique in many respects. First, they are among the most ancient turbomachines in their idea (approximately the 15th century) and at the same time, quite young in terms of practical implementation (the turn of the 19th–20th centuries).

Prototypes of gas turbines, which included the so-called smoke machines, began surfacing as early as the 17th century. However, the starting point in the development of gas turbines can be considered to have taken place in 1791 when Englishman John Barber filed an application for a heat engine patent.[1].  The turbine was equipped with a chain-driven reciprocating compressor and had a combustor and turbine. Barber proposed the use of charcoal, gas, or other suitable fuels to produce inflammable gas. The gas from the producer went into a common receiver and then into the combustion chamber where it mixed with compressor air and was ignited. The resulting hot gasses were allowed to impose on a turbine wheel.  To prevent overheating of the turbine parts, provisions to cool the gas by means of water injection were incorporated. There is no record of this engine being built but, in any event, it is unlikely that it would have self-sustained because of the large power requirements of the reciprocating compressor.  A patent drawing of Barber’s device is shown in Figure 1 [2].

Figure 1 John Barber’s Gas Turbine. English Patent 1791 [2]
In 1872, Franz Stolze designed an engine with an axial compressor, an axial turbine on the same shaft, a heat exchanger, a gas producer, and a combustion chamber. The gas turbine unit (Figure 2) was created and designed to produce 200 hp at a speed of 2000 rpm. However, the tests were not successful and instead only produced 20 hp. [1] Read More

Hydrogen Energy: History, Applications, and Future Developments

A Brief History Of The Discovery Of Hydrogen 

The release of combustible gas during the interaction of metals and acids was observed as early as the 16th century. That is, during the formation of chemistry as a science. The famous English scientist Henry Cavendish had studied the substance since 1766, and gave it the name “combustible air”. When burned, this gas produced water. Unfortunately, the scientist’s adherence to the theory of phlogiston (the theory that suggested the existence of a fire-type element in materials) prevented him from coming to the correct conclusions.

Henry Cavendish (1731 – 1810)
Henry Cavendish (1731 – 1810) Source: https://www.butterflyfields.com/henry-cavendish-contributions-in-science/

In 1783 the French chemist and naturalist A. Lavoisier, together with the engineer J. Meunier, and with the help of special gas meters carried out the synthesis of water, and then its analysis by means of decomposition of water vapor with hot iron. Thus, scientists were able to come to the correct conclusions, and dismantle the phlogiston theory. They found that “combustible air” is not only a part of water but can also be obtained from it. In 1787, Lavoisier put forward the assumption that the gas under study is a simple substance and, accordingly, belongs to the number of primary chemical elements. He named it hydrogene (from the Greek words hydor – water + gennao – I give birth), that is, “giving birth to water”.

Antoine-Laurent
Antoine-Laurent
de Lavoisier (1743 – 1794). Source: https://educalingo.com/en/dic-en/lavoisier

A Little About The Properties Of Hydrogen 

In a free state and under normal conditions, hydrogen is a gas, and is colorless, odorless and tasteless. Hydrogen has almost 14.5 times mass less than air. It usually exists in combination with other elements, such as oxygen in water, carbon in methane, and organic compounds. Because hydrogen is chemically extremely active, it is rarely present as an unbound element. Read More