Accelerated effort towards a Hydrogen Society
On October 23, 2018, the world's first international conference on the use of hydrogen, Hydrogen Energy Ministerial Meeting, was held in Tokyo. Joining the ministers were over 300 members from the auto and energy industries, the governments, and research. As MHPS is currently driving the practical application of large-size hydrogen gas turbine, its executive vice president and CTO, Chief Technology Officer, Akimasa Muyama, gave a talk titled, "Upstream & Global Supply-chain for Global Hydrogen Utilization ."
There are increasing number of examples of hydrogen application coming out of Europe. In January 2017, the Hydrogen Council, a global initiative to position hydrogen as the new energy, was set up, which started with 13 world-leading companies in energy, transport, and manufacturing. As of September 2018, 53 companies have joined the initiative. With Mitsubishi Heavy Industries being a supporting member of the Council, MHPS is also participating in the initiative as part of the Mitsubishi Heavy Industries Group.
Why much expectation is riding on hydrogen energy?
Why is there much focus on hydrogen energy? First of all, it's an energy that greatly contributes to the issue of global warming as it produces no COs upon use. Secondly, it offers greater energy security. Japan is heavily reliant on import for the fossil fuel we use. On the other hand, we can expect to reduce the sourcing and supply risks as hydrogen can be obtained from a wide variety of sources, along with greater storage and transport potential.
So how is hydrogen produced? There are mainly three ways to produce hydrogen:
First, we have the hydrogen produced from fossil fuels. These are byproducts from the existing chemical factories as well as from reformulating or gasifying oil, natural gas, and coal.
The second method is to combine the hydrogen derived from fossil fuel with CCUS (Carbon Capture, Utilization, and Storage). This is the method considered for hydrogen production in the project MHPS is currently engaged in where a feasibility study is underway to convert the thermal power generation facility in the Netherlands which burns natural gas into a 100% hydrogen — fired power generation plant
The third method is to produce hydrogen from electrolyzing water. If we use renewable energy for the electricity necessary for the electrolysis, no COi is emitted even in the production phase.
Muyama (MHPS) of MHPS shared his projection where, "Given the future trend in hydrogen, I suspect hydrogen from fossil fuel using CCUS will be the common method in the mid-term. The cost reduction and technical advances in the long term will make hydrogen from renewable energy the norm."
Shifting to hydrogen in power generation
Since the adoption of the Paris Agreement, the global effort to decarbonize or to realize a low carbon society is gathering pace and there is a growing expectation for electrical power generation to reduce their CO, emission.
"What is the situation for power generation in Japan today? Although we see a fast growing production of renewable energy from sun and wind, as of 2016, 83.6% of all energy is produced from thermal generation using fossil fuel (LNG, oil, coat etc.)
The plan is to continuously develop technology to improve the efficiency in thermal generation as well as expand the use of renewable energy. In addition, there is much expectation for the potential of hydrogen as the fuel for power generation as it can dramatically reduce CO2 emission.
Muyama (MHPS) of MHPS says. "In the move to reduce CO2 emission in thermal energy generation in Japan, we would probably first deploy the method where we combine burning natural gas and hydrogen together and eventually shift to 100% hydrogen. By using the latest technology in thermal power generation, we must first stabilize the supply by converting fuel to hydrogen, which will evidently allow for CO-free power generation."
There are various application and possibilities in hydrogen, but one issue remains which is the cost. In the roadmap for "Basic Hydrogen Strategy," the Japanese government has set a target of reducing the cost by a 1/3 by 2030 to 3$/kg (current station price: 10$/kg) when the international hydrogen supply chain is set up.
Muyama (MHPS) of MHPS continued to say that When you run a 400MW-class gas turbine combined-cycle power generation for a year, the hydrogen consumed will equal 2 million FCVs. The power generation will directly had to massive hydrogen consumption, which will contribute to the cost reduction." The use of hydrogen in power generation will reduce the cost of hydrogen production, which will potentially drive application in other areas.
Muyama (MHPS) of MHPS continued to say that When you run a 400MW-class gas turbine combined-cycle power generation for a year, the hydrogen consumed will equal 2 million FCVs. The power generation will directly had to massive hydrogen consumption, which will contribute to the cost reduction." The use of hydrogen in power generation will reduce the cost of hydrogen production, which will potentially drive application in other areas.
Hydrogen as the Energy Carrier
The potential of hydrogen extends beyond being the secondary energy in power generation to be an "energy carrier which allows energy to be stored and transported.
As the volume of power generated must be in par with the volume consumed, there may be excess energy produced from renewable generation given the unpredictability of nature. Being able to store hydrogen (gas) converted from such excess energy (power) will contribute to reducing the cost of hydrogen production itself. This process is called P2G (Power to Gas).
If this method is deployed, it is possible to "transport' energy, which is the hydrogen produced from the excess in the renewable power generation in locations where we have enough sunlight, wind, etc. (for example, in remote islands with no power grid or desolate area where energy consumption is limited with potential for excess energy). Being able to convert power generated from low-cost renewable power and other unutilized energy (lignite, by-product hydrogen, etc.) into hydrogen may also be an advantage for import into Japan. There are multiple options in hydrogen carrier which includes liquid hydrogen, MCH (methykydohexane), ammonia amongst others, and various research is underway across a range of fields.
The Future for Hydrogen
In June 2019, Japan hosted the G20, where the role and the importance of hydrogen were discussed in the "Ministerial Meeting on Energy Transitions and Global Environment for Sustainable Growth" held in Karuizawa.
Also, the Tokyo Olympic/Paralympic Games in 2020 will be a stage to showcase the potential of hydrogen energy in our daily lives. To realize a hydrogen based society, the Tokyo Metropolitan Government has announced a target for the adoption of FCV, FC bus, hydrogen station as wel as introduction of fuel eels in homes.
Globally, MHPS is taking part in a feasibility study in the Netherlands, where a 440MW large-scale natural-gas-fired gas turbine combined-cycle (GTCC) power plant is being converted into a 100% hydrogen-fired power generation plant by 2025. This will reduce the current CO, production (1.3 million tons/year) to almost zero.
When we look at the history of global energy policies, we can see a different source is chosen every few decades, which is reflective of our value during that time period. Energy changes with the times, and society evolves with it.
There is no doubt that the roadmap to realizing a hydrogen society will pick up pace as nations, businesses, and researchers continue
Expectations for hydrogen energy and technologies
Coping with the conflict between robust energy demand and global decarbonization
"Energy is the corner stone of industry," said Satoshi Tanimura Chief Engineer and General Manager, Gas Turbine Technology & Products Integration Division, MHPS—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 dose 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-fred thermal power. The technology is compatible with an output equivalent to 700MW (with temperature at turbine inlet at 1600°C), 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 hurt, 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 introduce the many challenges that Tanimura had to overcome.
Successful 30% hydrogen combustion represents a major step toward a hydrogen society
Easy-to-burn hydrogen and the struggle for safety
Hydrogen—atomic element number 1—is the first element students learn about, and the lightest of all elements. Hydrogen is dean—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 ratifies 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 &stance, sufficient mixing can be accomplished while also achieving low NOx, but this ends up increasing the risk of flashback, To resole this, improvements were made to the swifter 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°C, 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?
Its actuate 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, natural/ 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 fluctuation in fuel supply and price, and highly resistant to thinning, wear, and oscillation remits from the synergy of numerous technologies, witch is demonstrated in its performance.
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 CO, 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 successfuly 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 then 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 materiel, 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 necessary lead to enhanced efficiency overall" said Tanimura, when taking a comprehensive perspective of the practical use of hydrogen. in Japan, we simply assume well 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 CO, emitted during manufacturing. In Europe, with the advantage of their existing natural gas pipeline being well-developed, they are proceeding with hydrogen use wile taking a holistic new through to supply, considering it part of the overall infrastructure," he said.
As engineers developing gas turbines, Tanimura and his eclogues have a clear understanding of the need for a comprehensive hydrogen wage plan. "In Japan, as we don't have a developed pipeline, natural 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, & 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 volatile of hydrogen used by around 100,000 to 130,000 fuel-cell vehicles. If we are going to proceed in earnest with hydrogen use, its 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.
Technical Review
As a key corporation n the fields of thermal power generation and environmental technology, MHPS is developing high efficiency power generation technologies. This includes the field of gas turbine power generation technologies where MHPS has made possible hydrogen-mixed combustion and is in the process of taking the technology to its next phase. Energy market needs are diversifying and MHPS is working to meet such decentralized needs. We will now introduce our large-scale hydrogen gas turbines, which have potential for mass consumption, and fuel cells that are able to efficiently employ a diverse array of fuel types inducing hydrogen as dispersion type power sources through the Mitsubishi Heavy Industries technical review.
Hydrogen Gas Turbine
- Operating Results of J-series Gas Turbine and Development of SAC
MHPS' development of high efficiency gas turbines that contribute to reducing environmental impact and waver generation costs. - Development of Hydrogen and Natural Gas Co-firing Gas Turbine
Hydrogen-mixed combustion technology in high efficiency gas turbines.
Achievement of 10% reduction in CO, emissions compared to prior gas fired power generation. - Hydrogen-fired Gas Turbine Targeting Realization of CO2-free Society
Hydrogen single fuel firing technology in high efficiency gas turbines.
We lead the field in creating an international hydrogen supply chain to achive a CO2-free Hydrogen Society.
Fuel Cells
- Development of Next Generation Large-Scale SOFC toward Realization of a Hydrogen Society
Our fuel cell power generation technology meets today's decentralized energy source needs.
We contribute to the realization of a "safe and sustainable energy environment based society". - Efforts toward introduction of SOFC-MGT Hybrid System to the Market.
Development with the goal to achieve a Low Carbon Society.
The 250kW class have been empirically demonstrated. We have begin testing the 1MW class.
Operating Results of J-series Gas Turbine and Development of JAC
Mitsubishi Hitachi Power Systems, Ltd. (MHPS) has continued to contribute to the preservation of the global environment and the stable supply of energy through constant gas turbine development based on our abundant operating results, research and verification of state of the an technology. In recent years, using development results from the "1700°C Class Ultrahigh-Temperature Gas Turbine Component Technology Development" national project that we have participated in since 2004, MHPS has successfully developed the highly-efficient M501J, which achieved the world's first turbine inlet temperature of 1600°C and started verifying operations using the verification facility in the MHPS Takasago Works in 2011. Thereafter, the M501J has been delivered all over the world, and has accumulated operating results. In addition, to further improve the efficiency of the gas turbine combined cycle power generation (GTCC) and enhance the operability, we replaced the steam-cooled system for the cooling of the combustor and developed a new enhanced air-cooled system. This paper presents the development and operational situation of the state-of-the-art, high-efficiency gas turbine of MHPS and the development of the next-generation 1650°C class JAC (J Air Cooled) gas turbine using an enhanced air-cooled system as the core technology based on the technology adopted for the M501J.
1. Introduction
For higher GTCC efficiency, a higher temperature of the gas turbine has played an important role, and MHPS developed the M701D, a 1150°C class, large-capacity gas turbine, in the 1980s This was followed by the M501F, which had a turbine inlet temperature of 1350°C, and the M501G, which employs a steam-cooled combustor and has a turbine inlet temperature of 1500°C (Figure 1). Through these developments, we have demonstrated high plant thermal efficiency and reliability, as well as low emission. From 2004, we participated in the national project "1700°C class Ultrahigh-Temperature Gas Turbine Component Technology Development" to take on research and development of the latest technology necessary for higher temperature/efficiency and used the results of the development to develop the M501J, which achieved the world's first turbine inlet temperature of 1600°C. Verification operation of the M50IJ GTCC started in 2011 at the demonstrator (T-point) in the MHPS Takasago Works and operating results have steadily accumulated.
The J-series gas turbine adopts the steam-cooled system for cooling the combustor, but if as air-cooled system can be used while maintaining the high turbine inlet temperature, further improvement in the efficiency and operability of GTCC can be expected. Therefore, MHPS worked on the development of next-generation GTCC that realizes air cooling of high-temperature gas turbines, and devised the enhanced air-cooled system that is a core technology thereof. In the spring of 2015 we completed the verification test of the entire system at the gas turbine combined cycle power plant verification facility in the MHPS Takasago Works and since then we have been performing long-term operation. This paper presents the development and operational situation of MHPS's state-of-the-art high-efficiency gas turbine and the development of the next-generation 1650°C class JAC (J Air Cooled) gas turbine using the enhanced air-cooled system as its core technology.
Figure 1 History of development of large gas turbine models
2. Development and results of M501J gas turbine
The M501J was able to achieve a turbine inlet temperature of 1600°C based on the component technologies already demonstrated by the abundantly-proven F-series gas turbine and G-/H-series gas turbines, with turbine inlet temperature classes of 1400°C and 1500°C, respectively, and the application of the development of the most advanced 1700°C class technology resulting from a national project. Due to the increase of the turbine inlet temperature and the adoption of the latest component technology, the GTCC power generation end thermal efficiency has greatly increased in comparison with existing equipment. CO2 emissions can be reduced by about 60% when a conventional coal-fired thermal power plant is replaced with a natural gas-fired 3-series gas turbine combined cycle power plant. Figure 2 shows the technical features of ths M501J.
Figure 2 Technological characteristics of M501J gas turbine
The development of the M50IJ gas turbine was carried out by conducting verification tests of each element at the basic design stage, reflecting the results in the detailed design, and finally verifying the actual operation of the entire gas turbine in the verification power generation facility. Figure 3 shows the appearance of the gas turbine combined cycle power plant demonstrator (T-point) in the MIIPS Takasago Works. We carried out 2,300 special measurements on the first model of the M50IJ and verified that the performance, mechanical characteristics, and combustion characteristics satisfied the target values, before the shipping of the commercial product. We have received orders for 45 J-series gas turbines from domestic and overseas customers, and are shipping them as they become available. Up to now, 23 units have been put into commercial operation, and the total operational time of more than 400,000 hours has been reached. (Figure 4)
Figure 3 Gas turbine combined cycle power generation plant demonstrator (T-point) in the MHPS Takosogo Works
Figure 4 Operating results of M501J gas turbine (including 50 Hz units)
3. Core technology of next-generation gas turbine
The J-series gas turbine adopts the steam-cooled system for cooling the combustor, but if an air-cooled system can be used while maintaining the high turbine inlet temperature, further improvement in the efficiency and operability of GTCC can be expected. Therefore. MHPS worked on the development of next-generation GTCC that realizes air cooling of high-temperature gas turbines, and devised the enhanced air-cooled system that is a core technology thereof. Fly adopting this enhanced air-cooled system, air cooling of gas turbines even with a turbine inlet temperature of 1650°C can be realized, achieving high combined power generation efficiency and improving the operability of the entire plant. In the spring of 2015, we completed the actual equipment verification test of the entire system at T-point. This section presents an overview of the air-cooled system.
3.1 Overview of enhanced air-cooled system
In the enhanced air-cooled system, air extracted from the compressor outlet (combustor casing) is cooled by the enhanced cooling air cooler, pressurized by the enhanced cooling air compressor, used for cooling the combustor, and then returned to the casing. Figure 5 shows a schematic diagram of the enhanced air-cooled system.
The characteristics of the enhanced air-cooled system are described below.
- The efficiency of the system can be improved by recovering the waste heat of the enhanced cooling air cooler on the bottoming cycle side.
- Cooling performance equal to or higher than that of existing steam-cooled system can be achieved by optimizing the combustor cooling structure.
- The startup time of the entire GTCC can be shortened in comparison with the steam-cooled system.
It is important for the efficiency improvement of next-generation GTCC with an enhanced air-cooled system to develop a combustor that can perform efficient cooling with a small amount of cooling air, reduce the waste heat from the enhanced cooling air cooler, improve the recovery efficiency, and reduce the power of the enhanced cooling air compressor.
Figure 5 Schematic diagram of enhanced air-cooled system
3.2 Enhanced air-cooled combustor
The cooling structure of the enhanced air-cooled combustor adopts an MT-FIN structure utilizing convective heat transfer similar to the steam-cooled system adopted by the J-series gas turbines. The upstream side of the combustor is cooled by air in the combustor chamber and the downstream side is cooled by enhanced cooling air through the enhanced cooling air compressor.
The amount of cooling air passing through the enhanced cooling air compressor is minimized by limiting the cooling range using the enhanced cooling air only on the downstream side.
Furthermore, the cooling direction on the downstream side is designed to perform cooling efficiently while securing the coaling rapacity at the outlet by supplying the cooling air from the combustion liner outlet where the heat load is high. On the upstream side, an acoustic liner is installed to suppress combustion dynamics and the structure is designed so that the air that convectively cooled the combustion liner through the MT-FIN is purged through the acoustic liner holes. Figure 6 shows a schematic of the cooling structure of the combustion liner. Prior to the verification of the entire enhanced air-cooled system to be described later, it was confirmed by the high-pressure combustion test facility that there was no problem in cooling performance and combustibility of this enhanced air-cooled combustor.
Figure 6 Cooling structure of combustion liner of enhanced air-cooled combustor
3.3 Enhanced air-cooled system actual equipment verification
Figure 7 shows the overall view of the facility and the system overview of the enhanced air-cooled system verification executed at T-point. In the enhanced air-cooled system, the waste heat of the enhanced cooling air cooler is recovered in the bottoming cycle, but a radiator type cooler was added as an enhanced cooling air cooler because the verification at i-point used the existing bottoming system.
Figure 7 Enhanced air-cooled system verification equipment and system of T-point
In the spring of 2015, we verified the operability of the enhanced air-cooled system, that is, the responsiveness to transient changes such as start/stop, load change, and load rejection, using this demonstrator (T-point), and confirmed that there was no problem. The enhanced cooling air compressor operating point behavior during the gas turbine trip test was also tested and it was confirmed that the enhanced cooling air compressor could be stopped safely without entering the surging state at a trip from the 100% load of the gas turbine.
In addition, the metal temperature of the enhanced air-cooled combustor was measured and the cooling performance of the actual equipment was verified. Figure 8 shows the behavior of the combustor metal temperature when the amount of cooling air was changed. Although the metal temperature rose as the amount of cooling air decreased, it was lower than the design tolerance even if the amount was smaller than the initial planned amount of cooling air, and there was no problem in the cooling performance. In addition, the combustion dynamics characteristics and exhaust gas emissions were not problematic and it was confirmed that stable operation is possible.
Figure 8 Metal temperature of enhanced air-cooled combustor
Based on this enhanced air-cooled system, we also verified the system that enables clearance control during load operation. This system includes two supply systems: one supply method that supplies cooling air to the combustor directly by bypassing the turbine blade ring and the other method that supplies cooling air to the combustor after ventilating the turbine blade ring to maximize the performance by reducing the turbine clearance during load operation, and these two systems can be switched using the switching valve (three-way valve) even during load operation. The former makes it possible to cope with a large load changing operation by opening the clearance (Flexible Mode). On the other hand, the latter makes it possible to reduce the clearance during load operation and maximize the performance (Performance Mode). Figure 9 shows the clearance behavior when the three-way valve is switched during load operation. Using this system, it is expected that the operability can be improved more than before while maximizing the performance.
Figure 9 Turbine clearance control using enhanced air-cooled system
4. Development of 1650 °C class next-generation JAC gas turbine
In the spring of 2015 we verified that there was no problem with the operation of the enhanced air-cooled system, conducting actual equipment verification at T-point. Even now, the enhanced cooling system is being verified at Point-T for its long-term operation. The MC gas turbine, a 1630°C class next-generation gas turbine adopting this enhanced air-cooled system as the core technology, is being developed (Figure 10). Although the inlet temperature of the turbine becomes 50°C higher than that of the M501J, ultra-thick thermal barrier coating (TBC) developed based on the technology from the national project is adopted to achieve both high performance and reliability. In addition, by adopting a compressor with a high-pressure ratio design equivalent to that of the H-series gas turbine, the rise in the exhaust gas temperature at the gas turbine outlet is suppressed.
Figure 10 Characteristic of next-generation gas turbine using enhanced air-cooled combustor
We plan to close the existing demonstrator (T-point) and renew it as a new demonstration facility because it is necessary for conducting verification test operation of a newly-developed GTCC to renew not only the main body of the gas turbine, but also the main equipment such as the existing generator, the main transformer, the heat recovery steam generator, etc., to meet the specifications of the next-generation gas turbine. Figure 11 shows the expected completion of the new demonstration facility. Currently, we are carrying out development with the goal of starting verification in 2020. Similar to the past G- and J-series gas turbines, we will steadily verify the newly-developed gas turbine using the new demonstration facilities, and respond to social needs for further energy saving and the reduction of pollution.
Figure 11 Next-generation gas turbine demonstration facility and its schedule
5. Conclusion
For the improvement of the efficiency of GTCC, increasing the gas turbine temperature plays an important role. MHPS developed the highly-efficient M501J. which achieved the world's first turbine inlet temperature of 1600°C. utilizing the development results from the national project "1700°C class Ultrahigh-Temperature Gas Turbine Component Technology Development, which we have participated in since 2004, and has been steadily accumulating operating results. to further improve the efficiency and the operability of GTCC, we have devised the enhanced air-cooled system that enables air cooling of a high-temperature gas turbine. This enhanced air-cooled system was verified by actual an equipment demonstrator in the MHPS Takasago Work in 2015, and there was no problem in its operation. Since then, the system has been operating for long time to the present. Currently, we are developing the next-generation 1650°C class JAC gal turbine using this enhanced air-cooled system as a core technology. We will close the existing T-point demonstrator, and verification using a new demonstration facility will commence in 2020.
Development of Hydrogen and Natural Gas Co-firing Gas Turbine
The nonuse of fossil fuels through the introduction of hydrogen enemy is an effective option indispensable for the sustainable development of economic activity. The Mitsubishi Heavy Industries Ltd. (MHO Groin, is promoting the research and development of a large gas turbine for which a mixed fuel of natural gas and hydrogen can be used with support from the New Energy and Industrial Technology Development Organization (NEDO). Currently, with the newly developed combustor. etc, we succeeded in a co-firing test of 30 vol% of hydrogen. This co-firing makes it possible to reduce CO2 emissions during power generation by about 10% in comparison with conventional natural gas thermal power generation.
1. Introduction
In order to continue economic activities sustainably, it is essential to mane and supply energy that is stable and has low environmental impact. In response to issues such as global warming and the depletion of fossil fuels, the maximum acceleration of introduction and dissemination of renewable energy and the effective utilization of fossil fuels with maximum consideration for environmental impact are required. In addition to electricity and heat, hydrogen is expected to play a central role as future secondary energy, and the MHI Group is developing technology to fully utilize it.
Regarding the introduction of renewable energy, for example, the amount of wind power generation introduced globally has been increasing in a pace of 40.5 GW annually since 2011 and is predicted to expand to a maximum of about 2,500 GW in 2030. Because renewable energy has large output fluctuations, the utilization of surplus electric energy, in addition to the increase cf renewable energy power generation facilities, is considered to be an issue. In order to effectively utilize such surplus electric energy, energy storage technology that converts into a storage battery or hydrogen, etc., is necessary. In particular, when the fluctuation cycle is long and a signiflcant amount of energy capacity is required, it is considered effective to convert it to hydrogen, etc.
One promising power generation iuethod using hydrogen fuel is power generation with a gas turbine. Current gas turbines generally use natural gas that is distributed as a general-purpose product for fuel. Since CO2 generated during the combustion of natural gas is considered to be one of the factors of global warming, there is a movement to regulate its emission worldwide. Since tic combustion of hydrogen does not generate CO2, the amount of CO2 generated during power generation can be reduced by replacing a part of the hydrocarbon components in the fuel with hydrogen.
Figure 1 shows the hydrogen rich fuel operating experience in the MHI Group. Due to the fuel use of off gas (exhaust gas generated in refinery plants, etc.), the use results include fuels with various hydrogen content ratios. In addition, at the time of participation in World Energy NETWORK, the MHI Group succeeded in a combustion test of pure hydrogen fuel firing. However, these are results from small power generation facilities. In order to realize the full-scale introduction of hydrogen in the power generation field, large-scale and high-efficiency energy conversion methods are required like the current natural gas.
Therefore, the MHI Group is promoting the development of a large gas turbine capable of co-firing natural gas and hydrogen at the introduction stage of hydrogen infrastructure. This paper presents the outline and future prospects of technological development enabling hydrogen co-firing.
Figure 1 Hydrogen rich fuel operating experience
2. Issue of hydrogen co-firing
The Dry Low NOx (DLN) combustor installed in our large gas turbine adopts the premixed combustion method to reduce NOx (nitrogen oxide causing acid rain). Figure 2 compares the premixed combustor and the diffusion combustor. Since premixed combustion can reduce the flame temperature compared with diffusion combustion, NOx can be reduced without steam/water spraying, and it is a technology currently widely applied to low NOx combustor. On the other hand, the stable combustion range is narrower than that of the conventional diffusion combustor. and the flashback phenomenon tends to occur. Flashback is a phenomenon in which a flame moves upstream in the fluid when the propagation speed of the flame (hereinafter referred to as the combustion speed) is higher than the speed of the fluid (hereinafter referred to as the flow velocity). If flashback occurs inside the gas turbine combustor, there is a possibility of burning the upstream non-cooled part, so it is important to prevent its occurrence. Figure .3 provides an overview of tit flashback phenomenon.
When natural gas and hydrogen are mixed, the properties of the flame change due to the change in the fuel component. Particularly, in order to stably operate the gas turbine, it is necessary to develop a technology to deal with the change in the combustion speed. It has been confirmed that hydrogen has a higher combustion speed rate in comparison with natural gas. For this reason, when hydrogen is mixed, it is considered that the risk of the flashback phenomenon is higher compared with the case where only natural gas is burned. Therefore, for the development of a hydrogen co-firing gas turbine, the improvement of the combustor for the prevention of flashback occurrence is important.
Inside the MHI Group's DLN combustor, swirling flow is formed to promote the mixing of fuel and air. Several articles reported that in order to prevent the occurrence of flashback in such swirling flow, it is necessary to raise the flow velocity at the center portion of the swirling flow beyond the rise in the combustion speed.
Figure 2 Comparison of combustion type
Figure 3 Overview of flashback phenomenon
3. Outline of flashback prevention technology
3.1 Concept of new combustor
Figure 4 illustrates the outline of a combustor newly developed with the purpose of preventing an increase in the risk of flashback caused by hydrogen co-firing. The air supplied from the compressor to the interior of the combustor passes through the swirler and becomes a swirling flow. Fuel is supplied from a small hole provided on the blade surface of the swirler and mixed rapidly with the surrounding air due to the swirling flow effect. On the other hand, it is clear that a region with a low flow velocity exists in the central part (hereinafter referred to as swirling center) of the swirling flow. It is considered that the flashback phenomenon in the swirling flow is caused by the flame moving upstream in the portion of the swirling center where the flow velocity is slow. In the new combustor, in order to increase the flow velocity at the swirling center, air is characteristically injected from the tip of the nozzle. The injected air compensates for the low flow velocity region of the swirling center and prevents flashback
Figure 4 Outline of new combustor
3.2 Verification by non-combustion test
In order to confirm the effect of the new combustor, flow velocity distribution was measured with an air flow test. Figure 5 is a photograph of the equipment used for the air flow test. The swirling center does not remain at a certain position, and its position changes from moment to moment. For this reason, in flow velocity measurement, it is necessary to perform measurement at the moment when the flow velocity lowers while the swirling center passes through the measurement point. Therefore, by applying a hot wire current meter (Kanomax 7000 Ser and 𝞿5 𝞵 I-type linear probe made of tungsten) for the flow velocity measurement and by achieving high time resolution, the evaluation of the instantaneous minimum flow velocity at the measurement position was made possible.
Figure 6 compares the flow velocity distributions of the conventional combustor and the new combustor in the region close to the swirling center. Paying attention to the minimum flow velocity, which is thought to dominate the occurrence of the flashback phenomenon, it was confirmed that the new combustor realized a flow velocity of 2.5 limes or higher than that of the conventional combustor. Since the new combustor injects a very small amount of air from a small hole provided at the tip of the nozzle. regions other than the vicinity of the swirling center arc hardly affected, and the flow velocity distribution is the same as that of the conventional combustor.
Figure 5 Photograph of air flow test equipment
Figure 6 Comparison of flow velocity distributions in region close to swirling center
3.3 Confirmation of combustion characteristics by actual pressure combustion test
Representative items related to combustion characteristics of a gas turbine combustor induct NOx and combustion vibration. Since NOx is one of the factors of acid rain, there is a regulation on the amount of emissions in terms of the environmental aspect. On the other hand, combustion instability needs to be kept below a certain level in order to operate gas turbines stably. Since both NOx and combustion instability are affected by the combustion pressure conditions, testing under pressure conditions corresponding to the actual machine is necessary. Therefore. through the actual machine pressure combustion test (hereinafter referred to as the actual pressure combustion test) using one full-scale combustor (in the actual machine 16 to 20 combustors are used), the influence of hydrogen co-firing on combustion characteristics was confirmed. For the actual pressure combustion test, an actual pressure combustion test facility at the Mitsubishi Hitachi Power Systems, Ltd. Takasago Plant was used. Figure 7 gives the facility configuration of the actual pressure combustion test equipment. The high pressure and high temperature air used in the combustion test equipment is supplied by a two-shaft gas turbine and is guided to a test sector simulating the casing shape of the gas turbine (for one combustor) installed in the combustion test pressure vessel. The exhaust gas after combustion is discharged from the exhaust tower together with the exhaust gas of the compressor driving gas turbine. In order to simulate the fuel of the actual plant, hydrogen is added in the upstream part of the natural gas supply line and supplied to the actual pressure combustion test facility. Since hydrogen is added sufficiently upstream of the test facility, it is evenly mixed with natural gas before reaching the combustor.
Figure 7 Configuration of actual pressure combustion test equipment
Figure 8 shows the change in NOx with respect to the hydrogen mixing ratio under conditions equivalent to the rated conditions of a turbine inlet temperature 1600-degree class gas turbine. It was confirmed that as the hydrogen mixing ratio increased, NOx tended to increase slightly. This is thought to be because of the fact that the combustion speed increased due to the mixing of hydrogen in the fuel and the flame position in the combustor moved upstream. However, it was confirmed that even under the conditions with the hydrogen mixing ratio of 30 vol%, NOx was within the operable range. Figure 9 provides the change in combustion instability pressure level under the same conditions. It was confirmed that combustion instability pressure level was not significantly affected by the change in the hydrogen mixing ratio. From the above results, it can be considered that gas turbine operation under up to 30 vol% hydrogen co-firing conditions without the occurrence of flash back or a significant increase in the internal pressure fluctuation is ma& possible by applying the new combustor, even though there is an increase in NOx due to the increase in the hydrogen mixing ratio.
Figure 8 Change in NOx with respect to hydrogen mixing ratio
Figure 9 Change in internal pressure fluctuation level with respect to hydrogen mixing ratio
4. Future prospects
In outer to realize a hydrogen and natural gas co-firing gas turbine plant, it is necessary to further consider other auxiliary equipment attached to the plant and operation methods in parallel with the development of a combustor. Since current gas turbines mainly use natural gas distributed as a general-purpose product, piping materials and plant auxiliary equipment are selected on the premise of using natural gas. Hydrogen tends to leak and is easy to diffuse in comparison with natural gas, so it is necessary to devise safety measures suitable for the characteristics and to reselect specifications. In addition, since the hydrogen content rate may not be stable in actual plant operation, we will also work on the development of plant operation technology that can deal with an unsteady change in the hydrogen mixing ratio.
5. Conclusion
In order to respond to the use of hydrogen fuel targeting reduced CO, emissions in the field of thermal power generation, the MHI Group is working on the development of a hydrogen and natural gas co-firing gas turbine with support from the New Energy and Industrial Technology Development Organization (NEDO). For the prevention of the occurrence of the flashback phenomenon caused by hydrogen co-firing, a new combustor that suppresses the generation of the low flow velocity in the swirling center region was developed, and the prospect for gas turbine operation under 30 vol% hydrogen co-firing conditions was obtained. We are planning to develop plant operation technology in the future and to promote the development of a gas turbine that enables further higher concentration hydrogen co-firing for plant verification operation targeted to be implemented in fiscal 2025.
Hydrogen-fired Gas Turbine Targeting Realization of CO2-free Society
Gas turbine combined cycle power generation (GTCC) is clean and highly efficient and accounts for a large proportion of power generation today. Therefore, for the realization of a CO2-free society, it is important to use hydrogen for large power generation gas turbines on a largescale. Mitsubishi Heavy Industries group is proceeding with the development of natural gas and hydrogen co-fired and hydrogenfired large gas turbines, and has succeeded in a 30 vol% hydrogen co-firing test. In addition, we also started research on the use of ammonia, which shows promise as one of the energy carriers of hydrogen, in GTCC carriers, and are participating in a GTCC plant hydrogen firing conversion project in Europe. Through these activities, Mitsubishi Hitachi Power Systems, Ltd. (MHPS) will contribute to the realization of a hydrogen society by leading the establishment of an international hydrogen supply chain for the supply, transportation, and storage of hydrogen.
1. Introduction
To handle the rapid increase in electricity demand since the 1980s, GTCC power generation using natural gas/LNG (liquefied natural gas) as fuel has attracted attention, and its capacity and efficiency improvement have been promoted. GTCC power generation is the cleanest and most efficient facility among the thermal power generation systems using fossil fuels. In Japan, primary energy is convened mainly to electricity, which accounts for as much as 43% of the total. Among this total, the proportion of electricity supply from thermal power generation is as high as 85% (as of 2015). For this reason, GTCC power generation is required to continue to handle lively energy demand and to further reduce CO2 for the effective use of resources and the realization of a low-carbon society.
In Japan, as a basic hydrogen strategy for a low carbon society, the commercialization of hydrogen power generation around 2030 has been targeted. To more realistically promote commercialization atom the development of technologies to the introduction of equipment to electric power companies) in a short term of 10 or more years, we devised a system that can carry out hydrogen power generation using existing gas turbine equipment. This system does not require a large-scale renewal of power generation equipment other than gas turbine combustors. Therefore, it is expected to lower the cost hurdle for hydrogen conversion and to promote a smooth shift to a hydrogen society. Currently, with the support of the New Energy and Industrial Technology Development Organization (NEDO), we have succeeded in developing a combustor that can use 30% hydrogen mixed with LNG fuel for large power generation gas turbines. The emission cf NOx, which is a concern along with the combustion of hydrogen, can be suppressed to the conventional level. This technology can handle output equivalent to 700,000 kW (GTCC power generation with a turbine inlet temperature of 1,600°C), and the CO2 emissions during power generation can be reduced by approximately 10% in comparison with conventional GTCC power generation. This is a big step toward building a hydrogen society. This report presents our efforts toward realizing a hydrogen society, centered on hydrogen-fired gas turbines.
2. Large power generation gas turbines and hydrogen society
Efforts toward achieving the greenhouse gas reduction targets in the "Paris Agreement" adopted at the 2015 United Nations Climate Change Conference (COP 21) have begun in countries around the world, and the introduction of renewable energy has been accelerating. Figure 1 a) shows the forecast of the total global CO2 reduction amount from the present to 2060 in the IEA (International Energy Agency) report. The reduction of CO2 emissions using renewable energy is estimated to account for about 30% of the total.
Figure 1 Forecast of total global CO2 reduction amount from the present to 2060
Power generation using renewable energy such as wind power generation, photovoltaic power generation, and hydroelectric power generation requires flexible and stable power production and supply systems for the efficient utilization of such electric power because the power generation amount fluctuates depending on the climate and weather conditions and the time zone (day and night), and the power generation amount is unevenly distributed around the world. On the other hand, it is considered that converting renewable energy into hydrogen for storage, transportation, and usage is effective against energy fluctuations. Even in Japan, which is far away from large-scale power generation areas using renewable energy, it is important and urgent to build a hydrogen supply chain and develop relevant technologies.
In addition, in the previous report, it is expected that the use of hydrogen produced by reforming fossil fuels including natural gas will start to increase from around 2030 and will account for 14% of the cumulative CO2 reduction amount to 2050. Together with carbon dioxide capture and storage (CCS), which collects CO2 generated in large quantities at the time of manufacturing and stores it in the ground, technology for the utilization of hydrogen produced front a combination of fossil fuel reforming and CCS is also required in the transition period of shifting to a renewable energy-based society.
As illustrated in Figure 2, we are working on maximizing the utilization of hydrogen derive) from renewable energy and fossil fuel and applying power generation products, one of our major strengths, to the hydrogen value chain. Among these efforts, large gas turbines for power generation can not only generate power with high efficiency, but can also use low-purity hydrogen (with relatively low hurdles of manufacturing cost and technology), which leads to largo and stable hydrogen demand. As the hydrogen usage vision, including the expansion of infrastructure and various methods of utilization toward realizing a hydrogen society, has been presented, the role of our large gas turbines for power generation will increase further in the future.
Figure 2 Relationship between our hydrogen pearl generation technologies and hydrogen network
3. Combustor for hydrogen gas turbine
The development of large gas turbines for power generation has advanced up to now, while the turbine inlet temperature (combustion temperature) has been raised to achieve high efficiency. To handle the NOx emissions increasing exponentially along with the rise in the combustion temperature, a premixing combustion method is adopted for the Dry Low NOx (DLN) combustor installed in our large gas turbines for power generation.
The premixing combustion method mixes fuel and air in advance to put than into the combustor. Since the flame temperature can be made uniform compared with the diffusion combustion method, steam or water injection for NOx reduction is unnecessary and a decrease in the cycle efficiency does not occur. On the other hand, the stable combustion range is narrow, there is a risk of the occurrence of combustion oscillation and backfire (flashback), and unburned hydro carbons tend to be easily discharged.
Depending on the hydrogen mixing ratio, the fuel component changes, resulting in a change in the flame property Hydrogen has a higher combustion speed in comparison with natural gas, so the risk of flashback phenomenon in the case of natural gas and hydrogen co-firing is higher than that in the case of natural gas firing. Therefore, for the development and practical realization of combustors for hydrogen gas turbines, the reduction of NOx and the stabilization of combustion centering on improvements for the prevention of flashback together with improvements in marketability (low colt, long cervices life, etc.) are necessary.
The development status of our combustors for hydrogen-fired gas turbines that can be used for the co-firing and firing of hydrogen is described below. Figure 3 provides an overview.
Figure 3 Our combustors for hydrogen gas turbines
(1) Dry Low NOx (DLN) multi-nozzle combustor for hydrogen co-firing
Figure 4 gives an overview of a newly developed combustor for hydrogen co-firing based on the conventional DLN combustor with the aim of preventing an increase in the occurrence risk of flashback because of hydrogen co-firing. The air supplied from the compressor to the inside of the combustor passes through a swirler and forms a swirling flow. Fuel is supplied from a small hole provided on the wing surface of the swirler and mixed rapidly with the surrounding air due to the swirling flow effect. On the other hand, it is clear that a region with a low flow rate exists in the center part of the swirling flow (hereafter the vortex core). A flashback phenomenon in a swirling flow is considered as flame moving back in a slow-flow velocity portion of the vortex core. The new-type combustor characteristically injects air from the tip of the nozzle to raise the flow velocity of the vortex core. The injected air compensates for the low flow velocity region of the vortex core and prevents the occurrence of flashback.
As a result of a combustion test under the actual engine pressure using one full-scale new combustor, NOx was within the operable range even under the condition where 30 vol% of hydrogen was mixed in. so it was found that operation without the occurrence of flashback or a remarkable increase of combustion oscillation is possible.
Figure 4 Outline of new combustor for hydrogen co-firing
(2) Multi-cluster combustor for hydrogen firing (Figure 5)
The higher the concentration of hydrogen is, the higher the risk of flashback becomes. To mix fuel and air using swirling flow like a hydrogen co-firing DLN combustor, a relatively large space is necessary and the risk of flashback increases, so it is necessary to mix them in a short time in a narrow space. Therefore, we devised a mixing system that disperses the flame and blows out the fuel smaller and more finely. Based on the multi-cluster combustor illustrated in Figure 5 with a greater number of nozzles than the fuel supply nozzles (eight nozzles) of a DLN combustor, for the hole of one nozzle, we adopted a system where the nozzle hole was made smaller, air was fed in, and hydrogen was blown in for mixing. It is possible to mix az and hydrogen at a smaller scale without using swirling flow, which may allow for the compatibility of high flashback resistance and low NOx combustion. We are currently studying the basic structure of the fuel nozzle.
(3) Diffusion combustor
A diffusion combustor injects fuel to air into the combustor. Compared with a premixed combustion method, a region with a high flame temperature is likely to be formed, and the amount of NOx generated increases, so a measure for NOx reduction using steam or water injection is necessary. On the other hand, the stable combustion range is relatively wide, and the allowable range for the fluctuation of the fuel property is also large.
Figure 6 is our diffusing combustor. This combustor has actual results with fuels with a wide range of hydrogen content (up to 90 vol%) through the utilization of offgas (exhaust gas generated in refinery plants, etc.) as fuel in small to medium size gas turbine power generation facilities, and also succeeded in a hydrogen-fired combustion test when taking part in the International Clean Energy Network Using Hydrogen (World Energy NETWORK (WE-NET) technological research and development project.
Figure 5 Multi-cluster combustor (under development)
Figure 6 Diffusion combustor
4. Ammonia cracking GTCC
To make it possible to stably use the large amount of hydrogen required for a large-sized gas turbine for power generation, it is a prerequisite that a supply chain that produces. transports, stores, etc., hydrogen is established. The transportation and storage of hydrogen presented in the Hydrogen Basic Strategy(2) includts not only a method of liquefying hydrogen before transporting and storing, but also the utilization of energy carriers such as ammonia and organic hydride.
MHPS has been participating in the SIP (Strategic Innovation Promotion Program) of the Cabinet Office and studying gas turbine systems using ammonia as an energy earner since fiscal 2017. Ammonia has a volumetric hydrogen density 1.5 times higher than that of liquefied hydrogen, and has the feature that existing transportation and storage infrastructure for liquefied petroleum gas can be used. In the program, studies have been made to directly hum ammonia as a fuel in a micro gas turbine) and a small gas turbine. However, there are problems as can be seen in Table 1 with its application to large gas turbines. Therefore, as noted in Figure 7, we are studying a system that thermally cracks ammonia to hydrogen and burns it in a gas turbine. To crack ammonia, it is necessary to introduce a heat of reaction of 46 kJ/mol per 1 mole of raw ammonia while heating ammonia to high temperature under catalytic contact. since this neat or the reaction results in an increase in the heat value of hydrogen (chemical recuperation), there is no efficiency reduction in principle. Since a trace amount of residual ammonia remaining after cracking causes NOx formation in the combustor, the configuration of a cracker capable of reducing the amount cf residual ammonia, the selection of the cracking catalyst, etc., are being promoted through the program.
Table 1 Characteristics of ammonia combustion And consideration for large gas turbines
Figure 7 Concept of ammonia decomposition gas turbine cycle
As presented in Table 2, this system can be characteristically applied to high-efficiency and large-capacity GTCC systems with a relatively small number of modifications, thereby contributing to a large amount of CO2 reduction by using CO2-free ammonia. By applying this system, it is possible to not only utilize a hydrogen combustor for gas turbines currently under development, but also to use the developed ammonia cracker as a component of a general-purpose hydrogen supply chain.
Table 2 Characteristics of ammonia cracking gas turbine system
5. Efforts in overseas projects
Overseas, a comprehensive hydrogen utilization plan that covers the supply, transport, storage, and use of hydrogen is proposed, snub as a system that processes CO2 generated dining the production of fossil fuel-derived hydrogen using CCS. Especially in Europe where there is an advantage that existing natural gas pipelines have been developed, hydrogen utilization projects are underway as cross-border comprehensive infrastructure.
Among them, we are participating in a project to convert a natural gas-fired gas turbine combined cycle (GTCC) power generation plant with 1.32 million kW-class output operated by N.V. Nuon, a Dutch energy company, to hydrogen-fired power generation. 'Ibis project calls for the conversion of one of the three units of the M701F gas turbine power generation plant, which we delivered to the Nuon Magnum power plant (Figure 8) located in the state of Groningen in the northernmost part of the Netherlands, to a 100% hydrogen-fired power generation plant by 2023. We have carried out an initial feasibility study where we examined the application of a diffusion combustor, which is existing technology, and verified that the conversion to hydrogen-fired power generation is possible. Natural gas-fired power generation emits approximately 1.3 million tons of CO2 annually per system of 440,000 kW GTCC power generation, most of which can be reduced by conversion to a hydrogen-fired power generation plant. We will continue to handle the feasibility study in the field of gas turbine technology and will continue to cooperate toward the realization of the project including planning specific modification ranges, etc.
6. Conclusion
The contents described in chapter 3 of this paper are part of the outcome of the project "Technology Development for the Realization of a Hydrogen Society" of the New Energy and Industrial Technology Development Organization (NEDO). In this grant project, we worked on the development of combustors for hydrogen and natural gas co-fired gas turbines and found that gas turbine operation under a 30 vol% co-firing condition is possible. We are continuing with the development of hydrogen-fired systems.
The contents described in chapter 4 of this paper are part of the outcome of the Council for Science. Technology and Innovation (CTSI), Cross-ministerial Strategic Innovation Promotion Program (SIP), "Energy Carriers" (Funding agency: JST). With this research, we began the development of ammonia cracking GTCC systems using ammonia, which is promising as one of the energy carriers for hydrogen.
Our hydrogen-fired gas turbines play a major role in the realization of a global CO2-free hydrogen society using renewable energy by 2050 and in the utilization of fossil fuel-derived hydrogen combined with CCS in the transition period. We will continue to lead the construction of an international hydrogen supply chain with hydrogen power generation that produce a large and stable supply of hydrogen to contribute to the realization of a CO2-free hydrogen society.
Development of Next-Generation Large-Scale SOFC toward Realization of a Hydrogen Society
1. Introduction
In order to solve global warming problems, energy problems and economic problems at the same time, it is indispensable to reduce carbon emissions from energy sources and to increase efficiency in energy use. Therefore, to reduce omissions of CO2, one of the major greenhouse effect gases, it is necessary to combine decentralized power sources rationally according to location and capacity on the basis of the present state of an electric power base infrastructure established with a centralized power source of high efficiency thermal power generation. etc.. and then. to introduce new energies including renewable energies in the most economical and rational way possible. And, partly for global preservation of energy resources, it is indispensably and urgently required to use fossil fuel as effectively as possible by developing and quickly diffusing a high efficiency power generation system.
This article introduces the current development status of MHPS's SOFC, the status of the demonstrations of the SOFC-MGT hybrid system, which is a combined power generation system of the SOFC and a MGT, being conducted through the project of the National Research and Development Agency New Energy and Industrial Technology Development Organization (NEDO), and future developments.
2. Composition of SOFC combined power generation system
2.1 Cell stack
Figure 1 illustrates the structure of a cell stack of MHPS's tubular type SOFC. On the outer surface of the substrate tube, which is a structural member, a cell (anode, electrolyte, and cathode) reacting to generate power is formed and an electron-conductive ceramic used as an interconnector connects these cells in series. By selecting components with similar thermal expansion coefficient; and the adoption of integral sintering through the improvement of manufacturing technology, the production cost has been reduced, the bonding strength of components has been increased, and the performance and durability have been improved.
Figure 1 Structure of cell stack
MHPS has been developing out own high performance cell stacks. The Model 10 cell stack raised the number of cells to 85, and at the same time, the power output per cell stack has been enhanced by 30% by optimizing the interconnector composition, adjusting the cathode, etc. In the Model 15 cell stack, with which we have been attempting to further improve efficiency, the interface between the electrodes and the electrolyte has been improved to further increase the output density by 50% compared with Model 10 (Figure 2).
Figure 2 Tubular cell stack for SOFC
2.2 Cartridge
A cartridge that outputs electricity of several tens of kW by binding the cell stacks is formed and a set of cartridges with the necessary capacity, which is collectively contained in a pressure vessel, constitutes a module (Figure 3).
Figure 3 Composition of SOFC-MGT hybrid system
The adoption of such a layered structure seeks systematization by taking installation and even maintainability into consideration. In addition, since the electric output can be adjusted by the number of cartridges or the number of modules, a required wide range of electric output can be covered.
For the cartridge, higher per unit volume output density is aimed at. The higher packing density is accompanied by a higher heating density, but the heat transfer/cooling design of cartridges controls the heat transfer characteristics, ensuring the conventional level of heat transfer in the power generating area as well as in the heat exchange area across the power generation area. In Model 15, the reduction of the diameter and increase of the length of a cell stack enable an increase in the output density per unit volume and reduction of the system installation area (Figure 4).
Figure 4 Development of cell stack/cartridge for low-cost mass production
2.3 System
The hybrid system shown in Figure 5 generates electric power by the SOFC and the MGT in two steps. By installing waste heat recovery equipment on the exhaust gas line, it can function as a co-generation system that supplies steam and hot water at the same time.
Figure 5 SOFC-MGT hybrid system
3. Market introduction plan for the hybrid system
3.1 Demonstration at Tokyo Gas Co., Ltd. (Model 10 demonstration system)
Based on the achievements thus far, from fiscal 2011 to 2014, we conducted the development and evaluation of the Model 10 250 kW-class SOFC-MGT hybrid demonstration system, under the NEDO project at Tokyo Gas Cu., Ltd.'s Steaks Techno Station. An MGT made by Toyota Turbine and Systems Inc. was adopted (Figure 6).
Figure 6 Model 10 SOFC-MGT hybrid system for demonstration
With this demonstration system, we pinpointed problems toward promotion of initial introduction of the SOFC-MGT hybrid system and the examination of deregulation for promotion of its introduction. At present, in particular, because the SOFC-MGT hybrid system is a pressurized system with a fuel gas pressure of 100 kPa or more and is rated as a power generation system that has to be monitored at all times, we are targeting the necessary reconsideration of the regulation requirements for continuous monitoring so that the system would be diffused in earnest. Therefore, we obtained the technical data necessary for deregulation including the grounds for system safety design and the system long-term durability test data, as well as the operation data such as emergency measures on assumed starting and stopping, load change and system problems and verified the system's reliability and safety.
Figure 7 Result of durability test for SOFC-MGT hybrid system
We conducted the evaluations of various kinds of examinations and test data and the deregulation activities, receiving cooperation from the Fuel Cell Commercialization Conference cf Japan, Japan Gas Association and Japan Electrical Manufacturers' Association and other entities.
For the system's long-term durability, continuous operation for over 4,100 hours was conducted till the planned shutdown. As a result, no time deterioration was observed under the condition of a constant rated load, and the voltage degradation rate was stable at 0% in 1,000 hours (Figure 7).
3.2 Model 15 demonstration system at Kyushu University
Based on the achievements of the Model 10 demonstration system, we designed a Model 15 demonstration system, and it was set up at the Ito Campus of Kyushu University (Nishi-ku, Fukuoka City) in March 2015. In the future, it is planned that the Model 15 demonstration system will be used in verification studies and related basic research for improvement of performance, durability and reliability of SOFC at the Green Asia International Strategic Comprehensive Special Zone "Verification of a Smart Fuel Cell Society" in the "Next-Generation Fuel Cell Research Center (NEXT-FC)*" (Figure 8).
*Next-Generation Fuel Cell Research Center (NEXT-FC): The institution established with the objective of promoting indusny-acadenia collaboration toward earnest diffusion of SOFC.
Figure 8 SOFC-MGT hybrid system for demonstration delivered to Kyushu University
Table 1 Specifications of the system
3.3 SOFC market introduction plan
Taking advantage of the high efficiency, co-generation, quietness, environmental feasibility and other outstanding characteristics of the SOFC-MGT hybrid system, we henceforth intend to introduce it to distributed power sources for business purposes and industrial applications to hospitals, hotels, banks, data centers, etc. The specifications of the system are shown in Table 1.13 fiscal 2015, we are going to proactively introduce the SOFC-MGT hybrid system as a sample machine on the market for customers' evaluation. Toward the start of its full-fledged introduction on the market in 2017, we are going to make efforts to improve durability, transportability, Mob, based on evaluations and findings obtained with the sample machine, improve the system specifications to increase marketability, and bring down costs.
4. Approaches to a hydrogen society
4.1 Multi-energy station (Quatrogent)
Toward a future low-carbon society/hydrogen society, operations using a hybrid system as noted below are under examination. The SOFC generates electricity and heat using hydrogen and carbon monoxide that are produced by internal reforming of city gas as shown in Figure 9 (a). Ea addition, as shown in Figure 9 (b), some of the hydrogen produced by internal reforming may be directly extracted and used without being used for electricity generation. Therefore, electricity, heat and hydrogen can be simultaneously supplied, making it possible to realize Quatrogen, which also supplies city gas as fuel. By applying this mechanism to hydrogen stations, fuel can be simultaneously supplied not only to FCVs (fuel cell electric vehicles), but also to low carbon vehicles such as EVs (electric vehicles) and CNGVs (compressed natural gas vehicles). As a result, an increase in station profitability can be expected (Figure 9 (c)).
Figure 9 Image of Quatrogen. (a)Supply of electricity and heat by conventional SOFC (b)Hydrogen production by internal reforming (c)Application to n hydrogen station.
4.2 Local production of energy for local consumption (use of renewable energy)
It is expected that digestive gas generated at sewage treatment plants in urban areas can be used for the generation of electricity. Furthermore, methane generally constitutes about 60% of digestive gas. Accordingly, it is also considered that the use of the CO2 separation technique enables high-efficiency digestive gas power generation using high-purity methane as fuel. The application of the aforementioned Quatrogen enables the production of "hydrogen produced in urban areas" derived from digestive gas, and therefore, the "local production of energy for local consumption in urban areas" can be expected (Figure 10).
With the erection of these added values through the hybrid system, we would like to accelerate the introduction of SOFC into the market.
Figure 10 Image of digestive gas power generation
5. Conclusion
The Strategic Road Map for Hydrogen and Fuel Cells of the Ministry of Economy, Trade and industry was developed in June 2014. in the roadmap, the introduction of stationary fuel cells for commercial and industrial use on the market in fiscal 2017 was also explicitly stated. MHPS would like to steadily establish the SOFC-MGT hybrid system and expedite its commercial application, thus greatly contributing to the development of "a safe and sustainable energy/environmental society."
Efforts toward Introduction of SOFC-MGT Hybrid System to the Market
Toward a flame low-carbon society, the development of the SOFC-MGT hybrid system,in which a Solid Oxide Fuel cell (SOFC) that can generate power with high efficiency and a gas turbine are combined, has been promoted. In a program subsidized by the National Research and Development Agency New Energy and Industrial Technology Development Organization (NEDO) starting in fiscal 2015, 250 kW class demonstration systems were set up at four locations in Japan. The verification of durability and demonstrations of start/stop tests and load change tests under an actual load environment were conducted toward introduction to the market, and stable operation was verified. As a result, the introduction of the 250 kW class system to the market started in 2017. Furthermore, since fiscal 2016, in another NEDO commissioned project, the verification of the 1 MW class system, which features increased capacity, has been conducted, and the demonstration test is currently being conducted at the Nagasaki Works of Mitsubishi Hitachi Power Systems, Ltd. (MHPS).
1. Introduction
Recently, the energy situation in Japan has reached a major turning point, and it seems that awareness of high-efficiency power generation and power security has increased. To strike a balance between CO2 reduction to mitigate global warming and the stable supply of power, which is indispensable in modem society. it is important to combine an advanced power grids constructed with centralized power sources such as thermal power plants and high-efficiency distributed power sources or new energy sources such as renewable energy in the best mix in terms of both quality and quantity. To preserve global energy resources, it is also a necessary and urgent issue to ensure the effective use of fossil fuel through the development and early adoption of high-efficiency power generation systems. In Japan, the industrial sector accounts for more than 40% of all energy consumption. and the consumer and industrial sectors account for slightly more than 60% combined. It is considered that the spread of the use of fuel cells in the commercial field is one effective measure for improving the Japanese energy situation.
MHPS has focused on developing the high-efficiency SOFC hybrid power generation system with a very wide range of power output. The system covers everything from medium-capacity (259 kW class) distributed power sources to large-capacity centralized power sources including Gas Turbine Fuel Cell (GTFC) combined cycle and Integrated Coal Gasification Fuel Cell (IGFC) combined cycle technologies, which are advocated by the "Council for promoting the early achievement of next-generation thermal power generation" of the Ministry of Economy, Trade and Industry.
2. Composition of SOFC-MGT hybrid system
Figure 1 illustrates the structure of a cell stack which is a power generation element of tubular type SOFC. On the outer surface of the substrate tube, which is a structural member made of ceramics, an element (laminated anode, electrolyte, and cathode) reacting to generate power is formed and an electron-conductive ceramic interconnector connects these elements in series. Several hundred cell stacks are bound to form a cartridge, and several cartridges are contained in a pressure vessel. This is called an SOFC module (Figure 2).
Figure 1 Structure of cell stack
Figure 2 Composition of hybrid system
This system consists of the SOFC, Micro Gas Turbine (MOT), recycle blower, etc. Power is generated in the two stages of the SOFC and MGT. Furthermore, when a waste heat recovery device is installer; on the exhaust gas line., it can he utilized as a co-generation system that supplies steam or hot water at the same time (Figure 3).
Figure 3 Hybrid system
3. Efforts with 250 kW class
In fiscal 2015, under the NEDO-subsidized project "Technical demonstration of commercial system using solid oxide fuel cells," demonstration tests under an actual load environment were started toward introduction to the market.
The demonstration sites consist of four bases: Motomachi Plant of Toyota Motor Corporation, Komaki Plant of NGK Spark Plug Co., Ltd., Senju Techno Station of Tokyo Gas Co., Ltd. and Technology Center of Taisei Corporation (Figure 4).
Figure 4 Operation and planning status for the fuel cell SOFC
In this subsidized project, the respective main subjects/verification items have been set at each site and the demonstration tests are being carried out. The details of the demonstration test at each site are as described below. At each site, the effects of changes in power demand and start/stop operation on the performance and durability are assessed.
- The demonstration system for Toyota Motor Corporation: The start/stop operation test (once a month) is continuing.
- The demonstration system for NGK Spark Plug Co., Ltd.: The continuous durability test is continuing.
- The demonstration system for Tokyo Gas Co., Ltd.: The start/stop operation test (once a week) was conducted 31 times.
- The demonstration system for Taisei Corporation: The self-sustaining function verification test was completed.
Based on the results of the demonstration tests, the introduction of the 250 kW class system to the market commenced in 2017. The results of the demonstrations at the four sites have been reflected in the models to be introduced to the market. The first commercial system was delivered to the Marunouchi Building owned by Mitsubishi Estate Co., Ltd. and its operation will commence by the end of the current fiscal year. As of August 2018. the installation of the main body has been completed.
For the NEDO Research and Development Project "Research on coal gas application for fuel cell module" which was implemented by Electric Power Development Co., Ltd. (1-POWER), the 250 kW class system was delivered to Wakamatsu Laboratory of J-POWER in fiscal 2017.
Source: Mitsubishi Hitachi Power Systems, Ltd
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