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Moliere, M. Gas Turbines to the Hydrogen Energy Move. Encyclopedia. Available online: (accessed on 23 April 2024).
Moliere M. Gas Turbines to the Hydrogen Energy Move. Encyclopedia. Available at: Accessed April 23, 2024.
Moliere, Michel. "Gas Turbines to the Hydrogen Energy Move" Encyclopedia, (accessed April 23, 2024).
Moliere, M. (2024, March 14). Gas Turbines to the Hydrogen Energy Move. In Encyclopedia.
Moliere, Michel. "Gas Turbines to the Hydrogen Energy Move." Encyclopedia. Web. 14 March, 2024.
Gas Turbines to the Hydrogen Energy Move

Land-based gas turbines (GTs) are continuous-flow engines that run with permanent flames once started and at stationary pressure, temperature, and flows at stabilized load. Combustors operate without any moving parts and their substantial air excess enables complete combustion. These features provide significant space for designing efficient and versatile combustion systems. In particular, as heavy-duty gas turbines have moderate compression ratios and ample stall margins, they can burn not only high- and medium-BTU fuels but also low-BTU ones. Hydrogen is an energy carrier and not a primary energy as there are very scarce natural sources thereof; the rare reservoirs of hydrogen originate from chemical reactions inside the earth crust and are sometimes referred to as “natural H2”or “white H2”.

gas turbine fuel flexibility alternative fuels hydrogen

1. Introduction

The current decade will see disruptive changes in the energy scene as a dramatic abatement of GHG emissions, especially those of CO2, has become a global, inescapable necessity [1]. However, as pointed out by the IEA [2], the thermal power segment will survive, initially, in order to deliver the massive power additions that will be required by the upcoming electrification of the economies, particularly, that of the transportation sector. Then, the thermal sector will continue to play a critical role since electrical grids will need dispatchable units and “spinning reserves” to support the grids and offset the intermittency of renewables. Currently, among thermal power facilities, land-based gas turbines are serious candidates to support the energy transition as they meet all the requisites, including efficiency, reliability, controlled emissions, and peak shaving capability, with fast start and ramp-up ability [3]. The irreplaceable role played by gas turbines in the reliability of power grids and their potential contribution to a decarbonized economy in conjunction with the advent of hydrogen as an energy vector has been discussed elsewhere [4][5].
In addition, gas turbines have the additional advantage of being highly fuel flexible, a key asset in addressing the volatile and uncertain fuel market of the future. Indeed, they have managed to build a wide fuel portfolio, starting from natural gas and light distillate—which are their historical fuels—and now encompassing a large variety of alternative gases and liquids.

2. The “Hydrogen Rainbow”

The main supply of hydrogen is currently from fossil fuels via two main routes which are (i) the steam reforming of natural gas that yields “grey” or “blue” H2, depending on whether the resultant CO2 is captured or not; and (ii) the gasification of coal which leads to “black” (or “brown”) H2. These processes are very energy intensive. However, an increasing number of projects are conducted or planned to produce H2 by the electrolytic splitting of water into H2 and O2, using either solar power (“yellow” H2), wind/hydro power (“green” H2), or nuclear power generated during off-peak hours (“pink” or “purple” H2). There are in fact numerous approaches under investigation to produce hydrogen, resulting in the so-called “H2 rainbow” (Figure 1) [6].
Figure 1. The “H2 rainbow”: the various types and production routes of dihydrogen.
The development of hydrogen as an energy vector must deal not only with its production, but also with the delicate development of all the infrastructures that are required for its storage and transportation, as well as its conversion into power or its adaptation to cars. This vast theme, along with the associated feasibility and safety aspects, fall by far beyond the scope of the present paper. This set of topics generates an exponential number of publications. Extensive information is available from different sources, namely, from the EU commission [7], the USDOE [8], or the UK government [9].
The advent of hydrogen of the green, yellow, or pink type as a universal substitute for fossil fuels would procure a dramatic solution to some critical environmental problems. Indeed, it would provide not only the sought route towards carbon-neutral economies but also a radical solution to endemic urban pollutions by suppressing all emissions of VOCs, CO, SOx, O3, PAH, and soot particles.
However, the development of the “hydrogen economy” must overcome several technology challenges since, apart from high R&D investment needs, hydrogen has critical physical and chemical properties which impact the safety of its entire application chain, i.e., its production, storage, transportation, and end usages. With regard to the performance and the safety of combustion, hydrogen features a set of challenging properties, which are as follows: a wide flammability range; a high diffusivity with metallurgical impacts on materials; and a very-high flame speed and low ignition energy. In this respect, Table 1 shows a comparison between hydrogen and methane [10][11].
Table 1. Compared combustion properties of hydrogen and methane.

3. The Possible Role of Gas Turbines

Gas turbines can burn both pure and blended hydrogen and, as discussed above, they boast high energy effectiveness in combined cycles as well as fast installation. Therefore, these machines are placed in the front of the energy scene, as they are in position to boost the deployment of hydrogen energy in the power generation sector. Figure 2 shows a possible energy system involving gas turbines: green, yellow, or pink hydrogen is produced in electrolysis “power-to-gas” units fed by wind, PV, and nuclear plants; it is partly used as an automotive fuel and partly mixed with NG (and possibly with some carbon-neutral biogas streams) in gas networks which, in turn, feed “gas-to-power” GTCC nodes (or large Fuel Cell units) [12].
Figure 2. Projection of a possible integration of gas and power systems.
Energy wise, H2 is also a very singular fuel since; on one hand, it has a weak volume LHV (10.7 MJ/Nm3) that would place it in the category of LCV gases; however, on the other hand, it boasts the highest mass LHV (120 MJ/kg) of all fuels [13].
Moreover, NOx emissions pose a serious challenge due to the addition of two effects:
Hydrogen flames are very hot (Figure 3a) [14]. Indeed, one molecule of H2 generates three times less molecules of combustion products than does CH4; therefore, its stoichiometric combustion temperature (at the flame front) is much higher (2120 °C versus 1950 °C, in E-class GT conditions) since its combustion heat is transferred to one molecule instead of three. This is why hydrogen generates much higher NOx in diffusion flames than methane;
Conventional Dry Low NOx systems based on the current fuel/air premix devices are defeated due to the very fast flame speed (Figure 3b) [15] that results in very short flames (Figure 3a) but causes very difficult flashback issues.
Figure 3. (a): Flame front temperatures and (b) laminar flame speeds of H2-CH4 mixtures.
Therefore, the combustion of hydrogen in GTs requires innovative approaches to design appropriate DLN systems likely to avoid flashbacks and secure proper flame holding.
It should be noted that the combustion of ammonia (NH3) as a potential substitute of dihydrogen is not feasible as it would generate huge amounts of organic NOx. Consequently, an intense activity has been deployed for several years to develop “hydrogen-capable” low-NOx combustors. To prevent flashbacks, current designs focus on multiple small H2/air jets passing at high velocity through small injection orifices and become intimately mixed with corresponding air jets. Such devices, based on “micromix” injectors, are very promising; they enable the fine control of the spatial distribution of the fuel richness, down to the sub-millimetric scale, and minimize the risks of both core-flow and boundary-layer flashbacks. Figure 4 shows such a device that has been successfully lab tested [16][17]. Other similar designs exist [18][19].
Figure 4. Sketch of a GT micromix burner: a pair of H2/air orifices is circled [16] (with permission and minor changes).
Another important specificity of hydrogen resides in the fact that due the intrinsically high thermal conductivity of gaseous H2O at high temperature, there are intense convective heat exchanges between the H2O-rich combustion gases and the hot parts of the expansion turbine; this tends to increase metal skin temperatures and requires the reinforcing of the cooling of the hot parts to avoid premature creep and thermal fatigue effects.
Finally, hydrogen can cause the embrittlement of some metallic alloys, depending on pressure and temperature, so compatibility testing is required [20].

4. Exploiting the Experience Gained with H2-rich fuels

From a historical perspective, the ability of gas turbines to handle industrially H2-rich gases and eventually pure hydrogen is demonstrated by the wide experience that has been gained over the years in tens of refining and petrochemical plants burning by-process gases worldwide.
For instance, Spanish, UK, Korean, and Chinese refiners/petrochemists have managed major revamping programs of their utilities in the 1990s and 2000s, replacing aging refinery boilers with CHP units driven by 40 MW-class and sometimes 100 MW-class gas turbines that can burn up to 70% H2 rich gases [21][22][23].
However, the “hydrogen fleet leader” is a 40 MWe gas turbine installed at the Daesan Petrochemical Plant in Korea (Figure 5) [24]. In the 1970s, this site hosted a first petrochemical unit (marked as #1 Pet-Chem Unit in that figure) equipped with a naphtha cracker along with a 25 MWe gas turbine (#1 GT), which began to burn a C3-rich “petrochemical net gas” (PNG) coming from that cracker. Thereafter, the petrochemical company (Samsung General Chemicals at that time) installed an aromatization reactor that generated a net gas highly rich in H2 (H2-rich PNG) and was associated with a 40 MWe gas turbine (#2 GT) that drove an additional power unit (marked as #2 Pet-Chem Unit). Since 1997, this second GT has been reliably running for hundreds of thousands of hours on that H2-rich PNG with hydrogen contents up to 90–95%. Although this machine operates with conventional diffusion flames and is equipped with DeNOx steam injection, this experience has amply demonstrated, with a hindsight of six years at present, the feasibility of operating a GT with nearly 100% hydrogen from both safety and reliability standpoints.
Figure 5. Sketch of the Daesan plant with the addition of the H2-rich PNG.
This plant also illustrates the multifaceted fuel flex and the high integration potential of heavy-duty gas turbines since (i) the two GTs use a C4-LPG as startup fuel; and (ii) the first one burns a C3-rich gas stream produced by the naphtha cracker and its flue gas serves as hot fluid to heat the same cracking reactor.


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