The hydrogen gas turbine, successfully fired with a 30% fuel mix, is a major step towards a carbon-free society
April 26, 2018
- Expectations for hydrogen energy and technologies
- Successful 30% hydrogen combustion represents a major step toward a hydrogen society
- 100% hydrogen power generation—achieving a complete hydrogen-fired gas turbine
1. Expectations for hydrogen energy and technologies
Coping with the conflict between robust energy demand and global decarbonization
As energy choices steadily increase, thermal power still remains a key energy source. “With regard to thermal power using fossil fuels, efforts have continuously been made toward reducing emissions by enhancing efficiency through technological innovation,” said Tanimura. “CO2 emissions per unit with gas turbine combined cycle (GTCC) plants, which combine gas and steam turbines, are less than half those generated by coal-fired thermal power. But it doesn’t change the fact that CO2 is still emitted in the generation of gas-fired thermal power; we cannot close our eyes to this fact. As an engineer, I’m particularly sensitive to global issues and expectations toward resolving them. And we must develop technology to cope with the conflicting issues of strong demands for energy and for CO2 reduction.”
A clear roadmap to the achievement of a hydrogen society
As this technology enables the use of existing facilities, large-scale modification of power generation facilities becomes unnecessary. This makes it possible to lower costs and other hurdles, promoting a smooth transition to a hydrogen society.
But can hydrogen be infused into the fuel mix of existing facilities so easily? Aspects such as fusion, combustion, and the quality and behavior of hydrogen must be different from those of LNG. What is this hydrogen-mixed combustion technology developed by Mitsubishi Power? Where was the technological breakthrough? And what is the next move? We will now take a detailed look at the many challenges that Tanimura had to overcome.
2. Successful 30% hydrogen combustion represents a major step toward a hydrogen society
Easy-to-burn hydrogen and the battle with “flashback”
“In the case of a 20% hydrogen fuel mix, the existing gas turbine can be used,” said Satoshi Tanimura of Mitsubishi Power. “However, making it usable with 30% hydrogen poses quite a challenge for the gas turbine engineer. It is necessary to understand the combustion characteristics and control the air mixing and behavior.” Even with superior materials, the technology must control those aspects, the facilities be made durable, and high quality consistently maintained. It is the job of an engineer to resolve these issues.
Obstacles standing in the way of a 30% hydrogen mix are flashback, combustion pressure fluctuation, and NOx. The unique characteristics of hydrogen and the mixing of hydrogen with air are the cause of flashbacks. Flashback is a phenomenon where the flames inside the combustor travel up the incoming fuel and leave the chamber. As hydrogen burns rapidly, flashback commonly occurs.
Furthermore, the mixing method complicates the mitigation of flashback. This technology employs premixing combustion. The fuel and air are mixed prior to entering the combustor. While this enables low-NOx combustion, flashback occurs more commonly when fuel containing hydrogen is used. By securing sufficient distance, sufficient mixing can be accomplished while also achieving low NOx, but this ends up increasing the risk of flashback. To resolve this, improvements were made to the swirler nozzle. The low velocity area in the center of the nozzle was successfully reduced, significantly enhancing flashback resistance.
Burning of fuel anywhere but inside the combustor absolutely must be avoided. If flashback cannot be prevented, a hydrogen gas turbine cannot be successfully developed.
Innovative technology to control combustion pressure fluctuation that can destroy a combustor
While suppressing these phenomena and satisfying the necessary conditions, Tanimura and his team must also extend the service life of the facility by enhancing maintenance capabilities and the performance of the facility overall. Moreover, they must constantly search for the best materials, the optimum form, and the ideal combination—from the optimization of the shape and material of the fuel delivery nozzle and the combustor shape and material to the quality of the thermal insulation ceramic coating and adjustment of particle size. The repetition of this trial-and-error process brings them ever closer to the development of a CO2-free power generation system and ultimately to the realization of a carbon-free society.
Of utmost importance to power plant operators—users of the gas turbine—are safety, stable supply, and cost. In providing a steady supply of electricity, naturally a stable supply of fuel is a requirement, along with the mitigation of outages, longer intervals between periodic inspections, and low operation costs. “The gas turbine has to withstand three years of continuous operation under rigorous conditions including a fast rotation speed of 3,600 revolutions per minute at over 8,000 hours per year,” said Tanimura. “The flexibility to continue generating power with only LNG should the supply of hydrogen stop temporarily is undoubtedly another great benefit to the user.”
A hydrogen gas turbine that can adjust flexibly to fluctuations in fuel supply and price, and highly resistant to thinning, wear, and oscillation results from the synergy of numerous technologies, which is demonstrated in its performance.
3. 100% hydrogen power generation—achieving a complete hydrogen-fired gas turbine
The dream of a CO2-free society—100% hydrogen thermal power generation
As Mitsubishi Power has successfully achieved mixed-combustion power generation at 30% hydrogen, Satoshi Tanimura’s next objective is CO2-free power generation, or 100% hydrogen power generation technology. However, with a high concentration of hydrogen, the risk of flashback rises, as does the concentration of NOx. A combustor for hydrogen-fired power generation demands technology that enables efficient mixing of hydrogen and air, and stable combustion.
“There are important conditions concerning the mixing of hydrogen and air as well,” said Tanimura. “It is difficult to mix hydrogen and air in a large space, and using a rotational current and mixing them well requires a rather large space. This is what pushes the risk of flashback upward. In order to mix hydrogen and air in a short period of time, it has to be done in as confined a space as possible. The problem is that in this case the fuel nozzle jets and flame are in closer proximity, making flashback increasingly likely. We thought about how to deal with this, and it occurred to us that we needed to disperse the flame and reduce the fuel spray particle size. The key technology to this method is the fuel delivery nozzle. We upgraded the design, which normally features eight nozzles, and created the distributed lean burning, or multi-cluster combustor, which incorporates many nozzles. We reduced the size of the nozzle opening and injected air, and then sprayed hydrogen and mixed them. As this method does not employ a rotational current, mixing is possible on a smaller scale, and low-NOx combustion can be accomplished.”
Hydrogen is an excellent fuel, but difficult to handle. Changing thinking in mixing methods by upgrading the nozzle. That’s the kind of challenges engineers are wrestling with in the battlefield of development.
Creating a hydrogen fuel supply chain as a bridge to the future
As engineers developing gas turbines, Tanimura and his colleagues have a clear understanding of the need for a comprehensive hydrogen usage plan. “In Japan, as we don’t have a developed pipeline, naturally the transport of hydrogen constitutes a major issue,” Tanimura said. “As of now, there are schemes for extracting hydrogen from renewable energy, petroleum, and natural gas. If renewable energy, regarded as unstable, is converted into hydrogen, the storage and transport of energy becomes possible, which is a huge benefit. Today, liquid hydrogen, methyl cyclohexane (MCH), and ammonia (NH3) are regarded as the most promising hydrogen transport vehicles, and if demand increases further, we should see economies of scale emerge in transport as well,” said Tanimura.
Gas turbine engineers factor in everything from production to costs. “We need a vision for hydrogen use, encompassing everything from creation of infrastructure to the various methods of use,” Tanimura said. “For instance, a fuel mix of 20% hydrogen can be used without any technological improvements, and if we use a gas turbine with an output capacity of 500MW, and a turbine efficiency rating of 60, it requires 1.4 tons of hydrogen per hour. This equals the volume of hydrogen used by around 100,000 to 130,000 fuel-cell vehicles. If we are going to proceed in earnest with hydrogen use, it’s imperative that we quickly move to upgrade the hydrogen infrastructure, through measures such as proactively increasing the number of turbines using hydrogen. This is another reason hydrogen gas turbines will drive the forthcoming hydrogen society,” he said.
Human beings discovered fire and began using it purposefully about 500,000 years ago. And now we are about to obtain CO2-free combustion technology that will turn into energy that supports society.
Tanimura and his colleagues remain dedicated to achieving 100% hydrogen combustion technology by 2025.