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April 26, 2018The hydrogen gas turbine, successfully fired with a 30% fuel mix, is a major step towards a carbon-free society

1. Expectations for hydrogen energy and technologies

Coping with the conflict between robust energy demand and global decarbonization

“Energy is the cornerstone of industry,” said Satoshi Tanimura—Chief Engineer and Senior Manager of MHPS’ Gas Turbine Technology Administrative Division—a leader in the development of hydrogen-fueled gas turbines that feature CO2-free combustion technology. “If demand exists, supply will be provided by electric power companies, and power-generating facilities are necessary to provide this supply. At the same time, there is increasing public scrutiny toward power-generation that produces CO2 emissions. They want electricity, but they don’t want the attendant CO2 emission. It’s the mission of engineers to pursue thermal power generation that emits zero CO2.”

In Japan, the country’s primary energy is mainly converted into electricity, accounting for 43% of all energy. Thermal power accounts for 85% of the electricity supply volume with the fuel type break-down being as follows: LNG at 44%; oil and petroleum at 9%; and coal at 32% (as of 2015).

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

Satoshi Tanimura’s focus is on thermal power generation that does not emit CO2. “Our area of involvement is the development of hydrogen gas turbines,” he said.

Japan’s Basic Hydrogen Strategy includes the target of commercialization of hydrogen power generation by 2030. However, is it possible to commercialize hydrogen power generation in a little over ten years? Even if technology is successfully developed, how many power plant operators can afford to renew their facilities?

“Even if hydrogen power-generating facilities are installed at power plants already scheduled for renewal, it’s not realistic to expect substantial power generation volume to be secured in only ten years,” said Tanimura. “That’s where MHPS comes in—we conceived a hydrogen power generation system that utilizes existing gas turbine facilities.”

Tanimura and his colleagues at MHPS succeeded in developing a large-scale hydrogen gas turbine combustor that uses a mix of LNG—the fuel used in gas-fired thermal power—and 30% hydrogen. It burns hydrogen while allowing suppression of NOx emissions to the level of gas-fired thermal power. The technology is compatible with an output equivalent to 700MW (with temperature at turbine inlet at 1600℃), and it offers a reduction of about 10% in CO2 emissions compared with GTCC.

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 MHPS? 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”

Hydrogen—atomic element number 1—is the first element students learn about, and the lightest of all elements. Hydrogen is clean—when it burns, it produces only water. Conversely, it is a substance that is difficult to handle. It burns violently, so the idea of hydrogen is often accompanied by the fear of explosions. It is highly combustible, only needs energy equivalent to static electricity to ignite, and has a broad combustion range. These are difficulties that come with such a combustible element. Thus there are many challenges that engineers must overcome in order to realize a hydrogen fuel mix of 30%.

“In the case of a 20% hydrogen fuel mix, the existing gas turbine can be used,” said Satoshi Tanimura of MHPS. “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

Combustion oscillation presents yet another obstacle. Temperatures inside the combustor reach 1,600℃, and it is known that imposing an extremely high thermal load on the combustor cylinder results in the generation of a very loud noise due to the cylinder’s specified eigenvalue. This is the phenomenon known as combustion pressure fluctuation.

Put the oscillation from the loud sound together with the oscillation of the flames from combustion and they amplify, producing immense power. Also, given the particularly short interval when combusting hydrogen, the flame and the oscillation are more likely to match, increasing the likelihood of combustion pressure fluctuation.

So how loud is the sound?

“It’s actually beyond loud. And once oscillation occurs, it will destroy the combustor in an instant,” said Tanimura. “In order to avoid this, not only do we adjust the fuel burning location and method of burning; we have incorporated a number of innovations such as a sound absorption device.”

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

The values below are emissions per unit indicating CO2 emission volume when generating 1kWh of electricity.

Standard coal-fired power generation:
863g-CO2 /kWh

Ultra-supercritical (USC) coal-fired power generation:
820g-CO2 /kWh

GTCC power generation:
340g-CO2 /kWh

Hydrogen 30% mixed-combustion gas turbine:
305g-CO2 /kWh

As MHPS 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

A gas turbine alone is not enough to achieve 100% hydrogen-fired combustion technology. Stable sources of hydrogen must be secured. Considering a supply source and way to transport the hydrogen to a pipeline-less Japan; developing technology to extract hydrogen from the source material, as well as technology to collect and retain the CO2 emitted during the process. Such hydrogen infrastructure must mature along with the development of hydrogen combustion technology.

“Simply increasing gas turbine efficiency does not necessarily lead to enhanced efficiency overall,” said Tanimura, when taking a comprehensive perspective of the practical use of hydrogen. “In Japan, we simply assume we’ll have hydrogen transported from abroad and use it in fuel-cell vehicles and industry. Meanwhile, there is a blueprint overseas from the hydrogen supply phase through to use, including the CCS scheme for processing CO2 emitted during manufacturing. In Europe, with the advantage of their existing natural gas pipeline being well-developed, they are proceeding with hydrogen use while taking a holistic view through to supply, considering it part of the overall infrastructure,” he said.

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 2023.

Satoshi Tanimura

Chief Engineer, Senior Manager
Large Frame Gas Turbine Engineering Department

Mitsubishi Hitachi Power Systems, Ltd.

An expert in gas turbine combustor development, from basic design to combustion adjustment, his focus at MHPS. Joined Mitsubishi Heavy Industries in 1986 and was assigned to the Gas Turbine Engineering Department, where he pursued the development of large-scale gas turbine combustors and also served as an engineer. Worked on the development of a 1300℃-class gas turbine combustor, and spearheaded efforts to develop low-NOx technology for the 1500℃- and 1600℃-class models.