Mitsubishi Heavy Industries Technical Review Vol. 55 No. 2 (June 2018)
1Development ofHydrogen and Natural Gas Co-firing Gas Turbine

KEI INOUE*1

KENJI MIYAMOTO*2

SHOHEI DOMEN*2

ISSEI TAMURA*3

TOMO KAWAKAMI*4

SATOSHI TANIMURA*5

The nonuse of fossil fuels through the introduction of hydrogen energy is an effective option
indispensable for the sustainable development of economic activity. The Mitsubishi HeavyIndustries Ltd. (MHI) Group is promoting the research and development of a large gas turbine forwhich a mixed fuel of natural gas and hydrogen can be used with support from the New Energy andIndustrial 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 withconventional natural gas thermal power generation.

|1. Introduction
In order to continue economic activities sustainably, it is essential to secure 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 anddissemination 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 at a pace of 40.5 GW annually since 2011 and ispredicted to expand to a maximum of about 2,500 GW in 2030. Because renewable energy haslarge output fluctuations, the utilization of surplus electric energy, in addition to the increase ofrenewable 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 significant
amount of energy capacity is required, it is considered effective to convert it to hydrogen, etc.
One promising power generation method 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 oneof the factors of global warming, there is a movement to regulate its emission worldwide. Since thecombustion 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 withhydrogen.
*1*2*3*4*5Combustion Research Department, Research & Innovation Center
Large Frame Gas Turbine Engineering Department, Gas Turbine Technology & Products Integration Division, Mitsubishi Hitachi
Power Systems, Ltd.
Combustion Research Department, Research & Innovation Center
Chief Staff Manager, Large Frame Gas Turbine Engineering Department, Gas Turbine Technology & Products Integration Division,
Mitsubishi Hitachi Power Systems, Ltd.
Senior Manager, Large Frame Gas Turbine Engineering Department, Gas Turbine Technology & Products Integration Division,
Mitsubishi Hitachi Power Systems, Ltd.

Mitsubishi Heavy Industries Technical Review Vol. 55 No. 2 (June 2018)
2Figure 1 shows the hydrogen rich fuel operating experience in the MHI Group. Due to thefuel use of off gas (exhaust gas generated in refinery plants, etc.), the use results include fuels withvarious 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 ofco-firing natural gas and hydrogen at the introduction stage of hydrogen infrastructure. This paper
presents the outline and future prospects of technological development enabling hydrogenco-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 thepremixed 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 thecombustion 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 theflashback phenomenon.
When natural gas and hydrogen are mixed, the properties of the flame change due to thechange 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 confirmedthat 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 ahydrogen 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 offuel and air. Several articles1, 2 reported that in order to prevent the occurrence of flashback in suchswirling flow, it is necessary to raise the flow velocity at the center portion of the swirling flow
beyond the rise in the combustion speed.

Mitsubishi Heavy Industries Technical Review Vol. 55 No. 2 (June 2018)
3

Figure 2 Comparison of combustion typeFigure 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 fromthe 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 aregion 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 causedby 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 ischaracteristically 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

Mitsubishi Heavy Industries Technical Review Vol. 55 No. 2 (June 2018)4

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. Theswirling center does not remain at a certain position, and its position changes from moment tomoment. 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 themeasurement point. Therefore, by applying a hot wire current meter (Kanomax 7000 Ser and φ5 μI-type linear probe made of tungsten) for the flow velocity measurement and by achieving hightime 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 thenew 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 wasconfirmed that the new combustor realized a flow velocity of 2.5 times or higher than that of theconventional 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 are
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 include
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 underpressure conditions corresponding to the actual machine is necessary. Therefore, through the actualmachine 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 influenceof hydrogen co-firing on combustion characteristics was confirmed. For the actual pressureMitsubishi Heavy Industries Technical Review Vol. 55 No. 2 (June 2018)
5combustion test, an actual pressure combustion test facility at the Mitsubishi Hitachi PowerSystems, Ltd. Takasago Plant was used. Figure 7 gives the facility configuration of the actualpressure combustion test equipment. The high pressure and high temperature air used in thecombustion 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 theactual plant, hydrogen is added in the upstream part of the natural gas supply line and supplied tothe actual pressure combustion test facility. Since hydrogen is added sufficiently upstream of thetest 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 underconditions equivalent to the rated conditions of a turbine inlet temperature 1600-degree class gasturbine. It was confirmed that as the hydrogen mixing ratio increased, NOx tended to increaseslightly. This is thought to be because of the fact that the combustion speed increased due to themixing 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 pressurelevel 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 canbe 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 madepossible by applying the new combustor, even though there is an increase in NOx due to theincrease in the hydrogen mixing ratio.

Figure 8 Change in NOx with respect tohydrogen mixing ratio

Figure 9 Change in internal pressure
fluctuation level with respect tohydrogen mixing ratio

Mitsubishi Heavy Industries Technical Review Vol. 55 No. 2 (June 2018)
6|4. Future prospects
In order to realize a hydrogen and natural gas co-firing gas turbine plant, it is necessary tofurther consider other auxiliary equipment attached to the plant and operation methods in parallelwith 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 thepremise of using natural gas. Hydrogen tends to leak and is easy to diffuse in comparison withnatural gas, so it is necessary to devise safety measures suitable for the characteristics and toreselect 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 withan unsteady change in the hydrogen mixing ratio.

|5. Conclusion
In order to respond to the use of hydrogen fuel targeting reduced CO2 emissions in the fieldof thermal power generation, the MHI Group is working on the development of a hydrogen andnatural 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 thelow 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 thatenables further higher concentration hydrogen co-firing for plant verification operation targeted tobe implemented in fiscal 2025.

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B.Dam, G.Corona, M.Hayder, A.Choudhuri, “Effects of syngas composition on combustion inducedvortex breakdown (CIVB) flashback in a swirl stabilized combustor”, Fuel, vol.90, pp.3274-3284, 2011