Combustion Emissions from NH3 Fuel

Gas Turbine Power Generation Demonstrated

O. Kurata1*, N. Iki1, T. Inoue1, T. Matsunuma1,

T. Tsujimura2, H. Furutani2, H. Kobayashi3, A. Hayakawa3

1National Institute of Advanced Industrial Science and Technology (AIST), Japan2The Fukushima Renewable Energy Institute, AIST (FREA), Japan3Tohoku University, Japan

2017 AIChE Annual Meeting

October 29 – November 3, 2017, Minneapolis, MN, USA

Topical Conference NH3 Energy+ - Enabling Optimized, Sustainable Energy and Agriculture

560a NH3 Fuel End Use

• To protect against global warming, a massive influx of renewable energy is expected.

• Although hydrogen is a renewable media, its storage and transportation in large quantity

has some problems.

• Ammonia, however, is a hydrogen energy carrier and carbon-free fuel, and its storage and

transportation technology is already established.

• As ammonia utilization, ammonia combustion and ammonia fuel cell are expected.

2

Transportation Storage

NH3 production using renewable energy

C T

Combustor

Gen.

NH3 comb.

NH3

NH3 as a hydrogen energy carrier

SL of NH3-air laminar premixed flame

(Hayakawa,2015)

NH3-air combustion

• NH3-air combustion is difficult because the laminar burning velocity is much lower than that

of conventional hydrocarbon fuels.

• In 1967, Pratt examined an NH3-fired gas-turbine combustor, and concluded that

combustion efficiencies were unacceptably low.

• Verkamp showed that the pre-cracking of NH3 and the additives improved the flame stability

• Because of those difficulties, the research and development of NH3-fueled gas turbines were

abandoned, and it has not been retried until recently.

3

Solar model T-350 engine (Solar, Final Technical

Report, DA-44-009-AMC-824, 1968)

Recent work of NH3 fueled gas turbine

• Recent demand for hydrogen energy carrier revives the interest of NH3 fuel.

• Evans proposed NH3-air combustion gas turbine using pre-cracked NH3.

• Valera tested NH3-CH4-air gas turbine combustors.

• AIST successfully performed ammonia-kerosene co-fired gas turbine power generation in

2014, and ammonia-fired gas turbine power generation in 2015.

• AIST plans developing a low NOx combustor using combustor test rig.

• Since emission characteristics of test rig combustor differ from that of gas turbine, emission

data of gas turbine re-characterized with the other parameters is needed.

4

NH3-kerosene-air micro gas turbine in our

institute (AIST)NH3-air combustion gas turbine (Evans, 2013)

Emissions of NH3 and NOx

• In the case of NH3-air combustion, most products are N2 and H2O.

• Small amounts of NH3 and NO are detected as pollutant emissions.

• If the emission of unburnt NH3 increases, combustion efficiency decreases; this is

prone to occur because the laminar burning velocity of NH3-air pre-mixture is very

low. Combustion efficiency had been unacceptably low in the 1960s.

• In order to improve combustion efficiency, unburnt NH3 must be minimized.

• The emission of NOx is thought to increase because NH3 is the source of fuel-NO.

• A small amount of NH3 has been used for additives to study combustion chemistry

of NOx formation.

5

NH3,

AirCombustion

N2, Pollutant emissions

H2O, NH3, NO, …

Unburnt NH3 ↓ → Combustion efficiency ↑

NH3 fuel → Source of fuel-NO

6

Gas turbine

Loading equipment

Gas compressor SCRVaporizer NH3 1ton cylinder

Gas turbine power generation demonstrated

Ammonia 1ton cylinder

VaporizerFuel gas compressor

50kW gas turbine

SCR

FTIRPortable gas analyzer

Methane cylinders

Kerosene tank

Heated probe

Fig. 1 Schematic of ammonia combustion gas turbine power plant

Loading equipment

• The demonstration

facility consists of an

NH3 fuel-supply system,

NH3 gas compressor,

50 kWe-class micro gas

turbine, SCR NOx-

reduction apparatus,

and loading equipment.

Regenerator-heated gas turbine

• Micro gas turbines utilize a regenerative heat exchanger to improve the thermal

efficiency of the gas turbine cycle.

• Regenerative heat exchangers transfer exhaust heat after the turbine into combustion

air after the compressor.

• Thus, the combustor inlet temperature increases to around 500 °C.

• This high combustor inlet temperature enhances the flame stability of NH3-air

combustion and reduces the unburnt NH3.

7

Fig. Heat-regenerative-cycle gas turbine

Combustor

8

• A diffusion-type combustor was employed with the expectation of

realizing a higher flame stability.

• NH3 gas was injected from 12 holes located around the kerosene

injector, and an air swirler was positioned around the NH3 gas-injection

holes.

Prototype NH3 fueled gas turbine combustor

238mm

12

8m

m

Emission after SCR

• NOx reduction equipment using SCR was placed after the micro gas turbine.

• The NH3 addition to the SCR for NOx reduction was carried out in the piping, after the

micro gas turbine combustor.

• Although NOx emission after the micro gas turbine combustor is sufficiently high, the

SCR NOx reduction equipment can reduce it below the regulation limit

9

Fig. NOx emission after the SCR

Combustion emissions from gas turbine

• Although NOx emission after SCR is below the regulation limit, the NOx

emission from a micro gas turbine combustor is so high that it requires a

large-size SCR.

• If a low NOx combustion method is developed, the size of the facility could

be reduced.

• In order to achieve low NOx combustion, a combustor test rig was built in

the same place with a common NH3 fuel supply facility.

• Meanwhile, in the gas turbine, the results arise from the restriction of the

eigen balance of fuel, air, and heat, because the compressor and turbine

are connected by a single shaft.

• It is difficult to characterize combustion emissions from the combustor test

rig with the former parameters because there is no restriction of the quantity

of fuel, air, and combustor inlet temperature.

• Thus, this paper reports combustion emissions of the NH3 fuel gas turbine

before SCR, re-characterized with the other parameters, such as fuel flow

rate, overall equivalence ratio, combustor pressure, and combustion

temperature.

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Eigen balance of fuel and air

• Meanwhile, in the gas turbine, the results arise from the restriction of the eigen

balance of fuel, air, and heat, because the compressor and turbine are connected by

a single shaft.

• It is difficult to characterize combustion emissions from the combustor test rig with

the former parameters because there is no restriction of the quantity of fuel, air, and

combustor inlet temperature. 11

0

500

1000

1500

0 100 200 300

ow70000rpm

ow72000rpm

ow75000rpm

ow78000rpm

ow80000rpm

Heat input LHV [kJ/s]

Air [m

3/h

]

Combustor with observation window (ow)

NH3-air combustion

Gas turbine

Test rig

Former reports on emissions

• In the case of NH3-air combustion, the NH3 and NO emissions strongly

depend on the combustor inlet temperature.

• In the case of CH4-NH3-air combustion, the emissions depend on the NH3

ratio.

12

0

500

1000

1500

2000

2500

3000

400 500 600 700

ow70000rpm

ow75000rpm

ow80000rpm

ow70000rpm

ow75000rpm

ow80000rpm

Combustor inlet temperature CIT [℃]

NH

3,

NO

(16%

O2)

[ppm

]

NH3

NO

Combustor with observation window (ow)

NH3-air combustion

0

500

1000

0

500

1000

1500

2000

0.0 0.5 1.0

NO

CIT

NO2

N2O

NH3

NO

(16%

O2)

[ppm

]

Com

busto

r in

let te

mpera

ture

CIT

[℃

]

NH3 ratio NH3_LHV / (CH4+NH3_LHV)

Combustor with observation window (ow)

CH4-NH3-air combustion

Electric power output: 31.4 kWe

Rotating speed: 75000 rpm

NH

3,

NO

2, N

2O

(16%

O2)

[ppm

]

NO2 and N2O emissions

• The global warming potential (GWP) of N2O is 298, and thus, N2O emission

needs to be minimized.

• The N2O emission decreases with increase of combustor inlet temperature,

i.e., electric power output, and stays below 46 ppm at a combustor inlet

temperature of 560 °C.

13

0

60

120

0

300

600

400 450 500 550 600 650

ow70000rpm

ow75000rpm

ow80000rpm

ow70000rpm

ow75000rpm

ow80000rpm

Combustor inlet temperature [℃]

N2O

(

16

% O

2)

[

pp

m]

NO

2(1

6%

O2)

[

pp

m]

NO2

N2O

Combustor with observation window (ow)

NH3-air combustion

Combustion emissions re-characterized

with the other parameters

• The emissions of NO and NH3 characterized by the fuel flow rate show one set of

emission pattern repeated in three heat input ranges.

• The overall equivalence ratio for 70000, 75000, and 80000 rpm were in the range

0.107–0.137, 0.117–0.157, and 0.132–0.142, respectively, which have overlaps.

• It is shown that the equivalence ratio alone does not determine the combustion

emissions.

14

0

500

1000

1500

2000

2500

3000

100 150 200 250 300

ow70000rpm

ow75000rpm

ow80000rpm

ow70000rpm

ow75000rpm

ow80000rpm

Heat input LHV [kJ/s]

NH

3,

NO

(1

6%

O2)

[pp

m] NH3

NO

Combustor with observation window (ow)

NH3-air combustion

0

500

1000

1500

2000

2500

3000

0.1 0.15 0.2

ow70000rpm

ow75000rpm

ow80000rpm

ow70000rpm

ow75000rpm

ow80000rpm

Overall equivalence ratio Φ

NH

3,

NO

(1

6%

O2)

[pp

m]

NH3

NO

Combustor with observation window (ow)

NH3-air combustion

Combustion emissions re-characterized

with the other parameters

• The combustor pressures for 70000, 75000, and 80000 rpm were in the range 285–292, 327–

337, and 369–371 kPa abs, respectively.

• It shows one set of emission patterns repeated in three pressure ranges.

• The temperature of the combustor liner is dependent upon the temperatures of the combustor

inlet and combustion.

• Although the dependency is most apparent in the former reports on emissions, it arises from the

eigen balance of fuel, air, and heat.

• It is expected that the accuracy of the results can be improved in the future combustor rig tests.

15

0

500

1000

1500

2000

2500

3000

250 300 350 400 450

ow70000rpm

ow75000rpm

ow80000rpm

ow70000rpm

ow75000rpm

ow80000rpm

Combustor pressure abs [kPa]

NH

3,

NO

(16%

O2)

[ppm

]NH3

NO

Combustor with observation window (ow)

NH3-air combustion

0

500

1000

1500

2000

2500

3000

600 700 800 900

ow70000rpm

ow75000rpm

ow80000rpm

ow70000rpm

ow75000rpmow80000rpm

Combustor liner temperature [℃]

NH

3,

NO

(1

6%

O2)

[pp

m]

NO

NH3

Combustor with observation window (ow)

NH3-air combustion

Acknowledgement

• This work was supported by the Council for Science, Technology and Innovation (CSTI), the

Cross-ministerial Strategic Innovation Promotion Program (SIP), “Energy Carriers” (Funding

agency: Japan Science and Technology Agency (JST)).

• The authors also thank “Toyota Turbine and Systems Inc.” for their assistance with the

operation of the micro gas turbine system.

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Thank you for your attention !!

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