Mitsubishi Heavy Industries Technical Review Vol. 59 No. 4 (December 2022)
1Development of Ammonia Co-firing Technology forCoal-fired Boilers toward Decarbonized Society
TAKATOSHI YAMASHITA*1 TAKESHI AMARI*2

YUICHIRO URAKATA*3TADASHI SUMIDA*4TERUYUKI OKAZAKI*5

AKIMASA TAKAYAMA*6

Thermal power generation utilizing hydrogen and ammonia as fuels is considered one of theleading options for decarbonization to achieve carbon neutrality by 2050. In particular, thedecarbonization of coal-fired boilers by ammonia co-firing is presented in the national roadmapfor the establishment of a fuel ammonia supply chain. Mitsubishi Heavy Industries, Ltd. (MHI) isdeveloping technologies to enable higher ammonia co-firing rate for both circular firing andopposed firing systems of coal-fired boilers in order to meet various customer requirements. This
report presents findings on the combustion characteristics of ammonia obtained to date and aschedule for future development toward realizing the practical use of this technology.

|1. Introduction
The Japanese government set a new target of reducing greenhouse gas emissions by 46% by
fiscal 2030 and submitted a Long-term Strategy as a Growth Strategy under the Paris Agreement (1)to the United Nations in October 2021. Toward this reduction target, the Green Growth Strategy
Through Achieving Carbon Neutrality in 2050 (2) associated with carbon neutrality by 2050 showsthat the development for increasing the ammonia co-firing rate used for coal-fired power plants will
be promoted, along with a growth strategy process chart for fuel ammonia. The Sixth Strategic
Energy Plan (3) includes measures with regard to thermal power generation, which is a major sourceof CO2 emissions, to reduce its power generation amount itself in order for decarbonization, but it
is also stated that an appropriate portfolio of thermal power generation, including coal, will bemaintained.
Thermal power generation is an important power supplier that supports a stable supply ofelectricity and electric power resilience, and it also has an important function as a power regulator
that compensates for the variability of power generated by wind and solar power generation.
Therefore, there is a need to reduce CO2 emissions from thermal power generation while
maintaining these functions, and one approach is to use ammonia, which emits no CO2 whenburned, for thermal power generation.
We have declared "MISSION NET ZERO", which includes contribution to the reduction ofCO2 emissions from customers' existing facilities. This report introduces the technologicaldevelopment that we have been working on to achieve higher ammonia co-firing rate in existingcoal-fired boilers.

*1

Deputy Director, Boiler Engineering Department, Steam Power Maintenance Innovation Business Division, Energy Systems,*2

Chief Staff Manager, Boiler Engineering Department, Steam Power Maintenance Innovation Business Division, Energy Systems,*3Boiler Engineering Department, Steam Power Maintenance Innovation Business Division, Energy Systems, Mitsubishi Heavy*4Manager, Power Systems Project Engineering Department, Steam Power Maintenance Innovation Business Division, Energy*5Senior Researcher, Combustion Research Department, Research & Innovation Center, Mitsubishi Heavy Industries, Ltd.

*6Combustion Research Department, Research & Innovation Center, Mitsubishi Heavy Industries, Ltd.

Mitsubishi Heavy Industries, Ltd.
Mitsubishi Heavy Industries, Ltd.
Industries, Ltd.
Systems, Mitsubishi Heavy Industries, Ltd.

Mitsubishi Heavy Industries Technical Review Vol. 59 No. 4 (December 2022)
2|2. Ammonia co-firing in coal-fired boilers
The development of ammonia co-firing technology for coal-fired boilers is being considered
for practical use, as the needs of electric power companies are increasing to achieve both a stablesupply of electricity and decarbonization.

2.1

Use of ammonia as boiler fuelFigure 1 shows the technological issues in modifying a coal-fired boiler to an ammonia
co-fired boiler in consideration of the characteristics of ammonia. In order to put ammonia co-firedboilers into practical use, it is necessary to plan modifications based on the results of technologicalstudies and verifications to solve these issues.
(1) Technological issues in development of ammonia-fired burner
Ammonia burns at a low speed (about 1/5 that of methane) and includes nitrogen.
Therefore, firing ammonia is accompanied by the issue of reducing unburned ammonia
downstream of the boiler and NOx emissions. To solve this issue, it is essential to realize stable
ignition of the ammonia burner and to control the combustion area with appropriate air
distribution. To achieve stable ignition, it is necessary to optimize the fuel-air mixing, airvelocity, and flame stabilization structure. To suppress NOx increase and unburned ammonia, it
is important to create a high-temperature reducing atmosphere near the burner to promote NOx
reduction, and to prevent unburned ammonia from flowing out by employing a two-stage
combustion air injection method at the upper part of the furnace and by optimizing the flowrate.
(2) Technological issues of boiler plant itself
In terms of boiler performance, it is necessary to study the effects of changes in radiation
heat transfer characteristics caused by changes in flame temperature and combustion gas
properties on the heat absorption of the furnace and bank sections. It is also necessary to study
the effects of changes in exhaust gas properties and gas volume on downstream equipment of
the boiler and draft systems such as fans, to consider start-up methods and handling uponemergency shutdown, as well as to examine the specifications required for plant operation fromthe standpoints of performance and safety. In addition, it is important to consider measures toprevent ammonia leakage, such as the additional installation of ammonia detoxificationequipment and fuel purge systems, and the formulation of an operation policy in the event offuel shutdown.

Figure 1

Technological issues in modifying coal-fired boiler to ammonia co-fired boiler

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2.2

Approach to higher ammonia co-firing rate

When coal and ammonia are co-fired, it is necessary to consider the mutual effects ofcombustion reactions. When coal and ammonia are co-fired in each burner, it becomes difficult tocontrol NOx and unburned fuel emissions when the combustion conditions required for both coaland ammonia cannot be maintained simultaneously due to a higher ammonia co-firing rate. On theother hand, if the coal burner and ammonia burner are independent (single-fuel) burners, it is easy
to control the air ratio of each, and NOx emissions can be controlled even at higher ammonia
co-firing rate. In addition, the co-firing rate can be altered to any level by adjusting the number ofoperating burners and the burner load.
MHI offers two types of boiler systems: opposed firing and circular firing systems. Figure 2
shows the concept of increasing the ammonia co-firing rate using single-fuel burners for eachsystem. The opposed firing system fires fuel with burners arranged facing each other at the front
and rear of the boiler. The figure shows a boiler with a total of six stages, three at the front andthree at the rear in the height direction, and four burners in each stage. The circular firing systemfires fuel with burners installed at the four corners of the boiler and swirls the flame. The figure
shows a boiler with six stages of burners arranged in the vertical direction. Each stage has one coalmill. Conversion to ammonia co-firing is done by replacing the coal burner with an ammonia
single-fuel burner for each burner stage according to the ammonia co-firing rate. The co-firing rate
can be adjusted to any level by the selection of the stage in which the burners are to be replaced andthe operating burner load. For example, the conversion to an ammonia co-firing rate of 20 cal.%can be achieved by replacing one stage of burners, which correspond to one mill, with ammoniasingle-fuel burners.
The selection of the stage at which the ammonia single-fuel burners are installed and theoperating burner load region will be studied for each operational need, such as the specifications ofindividual units and the co-firing rate, after the base design concept has been established, reflecting
the results of future development as appropriate.

Figure 2 Concept of higher ammonia co-firing rate for boilers with opposedfiring and circular firing systems
These are examples of arrangements for a co-firing rate of 50 cal.%, indicating that the coalburners in three of the six stages are replaced by ammonia single-fuel burners.

|3. Combustion characteristics of ammonia
In evaluating the boiler performance with modified burners, a combustion performance(NOx, unburned combustible in ash, unburned ammonia, etc.) prediction model for coal-ammonia
co-firing is needed to be incorporated into the boiler combustion simulation. To build this model,
we have accumulated data on the oxidation and thermal decomposition of ammonia and reactions
during coal-ammonia co-firing using a basic combustion test furnace. In addition, we conduct
combustion tests to select burner types for the burner development of both opposed firing andcircular firing systems. Based on the results of these tests, we will validate the combustion
performance of the selected burners through large-scale combustion tests on a full-scale burner

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equivalent to actual equipment, and also verify the accuracy of the combustion performance
prediction model.
This chapter presents the combustion test results obtained from the basic combustion test
furnace and small-scale combustion test furnace.

3.1

Combustion test results obtained from basic combustion test furnace

The basic combustion test furnace is a two-stage electric furnace (DTF) (4) that simulates thehigh-temperature environment inside a boiler, and as shown in Figure 3, the amount of combustion
air and temperature in the upper and lower stages can be adjusted independently. As shown in thefigure, combustion conditions can be set for the upper stage of the two-stage electric furnace tosimulate the burner combustion area of a boiler and for the lower stage to simulate the complete
combustion area.

Figure 3Basic combustion test furnace (two-stage electric furnace (DTF))

Figure 4 shows the trend of NOx generation at the combustion furnace outlet when coal andammonia are mixed in the basic combustion test furnace and the co-firing rate and the upper-stage
air ratio are varied at a given temperature.

Figure 4 Relationship between ammonia co-firing
rate and NOx generation

The amount of NOx generation was suppressed by lowering the air ratio in the upper stage.
The amount of NOx increased with an increase in the ammonia co-firing rate, with a tendency toreach a maximum value at about 50 cal.%. It was found that, in the case where coal and ammonia

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were mixed and then fired, the air ratio setting around the burner was important because thesensitivity to the air ratio was high. Therefore, to increase the ammonia co-firing rate, the methodof burning coal and ammonia using single-fuel dedicated burners for each and then co-firing themin the boiler is considered to provide better control of the combustion performance than the methodof mixing coal and ammonia and then burning the mixture using a single burner. As reported in theprevious section, the advantage from increasing the ammonia co-firing rate was produced by using
burners that burn coal and ammonia separately.

3.2

NOx emission characteristics obtained from small-scale combustion test
furnace

Using a small-scale combustion test furnace, a combustion test was conducted with the coalburner and ammonia burner installed separately as single-fuel burners. Coal-ammonia co-firing andsingle-fuel ammonia-firing tests were conducted for several burner types assuming both circularand opposed firing systems.
Figure 5 shows the relationship between the ammonia co-firing rate and the amount of NOx
generation in co-firing with coal single-fuel and ammonia single-fuel burners. Even when theammonia co-firing rate was increased, NOx generation could be suppressed to the same level orless as in the case of single-fuel coal-firing. In addition, stable combustion was confirmed for eachburner type, and unburned ammonia was not detected at the furnace outlet. By setting the optimal
combustion conditions for each fuel type in the coal single-fuel burner and ammonia single-fuelburner, it was confirmed that NOx generation could be suppressed even when the ammonia
co-firing rate was increased, and that a trend similar to the test results obtained from the basic
combustion furnace was shown.
Based on these test results, we plan to proceed with the trial design of a burner to be applied
to the actual boiler, select a burner type through burner combustion tests, and validate it throughcombustion test with full-scale burner equivalent to actual equipment.

Figure 5 NOx emission characteristics obtained from small-scale combustion test
furnace|4. Schedule for practical application
We are currently working on the development and demonstration of high-ratio ammonia
co-firing technology in coal-fired boilers under the Green Innovation Fund Project / Fuel Ammonia
Supply Chain Establishment of the New Energy and Industrial Technology Development
Organization (NEDO), with the aim of high-ratio ammonia co-firing (5). As shown in Figure 6, we
aim to develop an ammonia single-fuel burner by FY2024 through combustion tests with full-scaleburner equivalent to actual equipment. In addition, we are also working on a basic equipment planand feasibility study for the demonstration of an ammonia co-firing boiler in an actual plant incooperation with JERA Co., Inc., aiming to validate more than 50% ammonia co-firing in twounits, a circular firing system and an opposed firing system, in the demonstration operation in theactual plant.

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Figure 6

Schedule for practical application|5. Conclusion
In order to realize the decarbonization of coal-fired boilers, the development of ammonia
co-firing technology is important to promote both decarbonization and stable power supply.
Against this background, this report presented technological issues in the use of ammonia as aboiler fuel and efforts toward its practical application in the future. We have been developing anammonia single-fuel burner that can be applied to high-ratio ammonia co-firing in the future, andpresented our approach to high-ratio ammonia co-firing and the combustion characteristics ofammonia-coal co-firing that we have obtained so far. We will work hard on such development tocontribute to the decarbonization of boiler users in Japan and abroad as well as to the constructionof ammonia supply chains. Through this development, we will achieve our "MISSION NET
ZERO" and contribute to the realization of a carbon neutral society.
In addition, the developments shown in chapter 4 are the New Energy and Industrial
Technology Development Organization (NEDO) JPNP21020 Green Innovation Fund Project / FuelAmmonia Supply Chain Establishment / High-ratio co-firing and single-fuel firing needed forammonia power generation / Development and demonstration of high-ratio ammonia co-firingtechnology (including single-fuel firing technology) in coal-fired boilers / Demonstration project ofhigh-ratio ammonia co-firing in the commercial coal-fired power plants utilizing ammonia
single-fuel burners”.

References
(1)
(2)
(3)
(4)
(5)

Long-term Strategy as a Growth Strategy under the Paris Agreement, Oct. 22, 2021,
https://www.mofa.go.jp/mofaj/files/100285601.pdf
Green Growth Strategy Through Achieving Carbon Neutrality in 2050, June 6, 2021,
https://www.meti.go.jp/press/2021/09/20210914003/20210914003-b.pdf
Strategic Energy Plan, Agency for Natural Resources and Energy, Oct. 6, 2021,
https://www.enecho.meti.go.jp/category/others/basic_plan/pdf/20211022_01.pdf
Taniguchi, M. et al., Staged Combustion Properties for Pulverized Coals at High Temperature,
Combustion and Flame, Vol. 158, Issue 11（2011）p.2261-2271
JERA and MHI Start a Demonstration Project to Develop Technology to Increase the Ammonia Co-firing
Rate at Coal-fired Boilers, Mitsubishi Heavy Industries, Ltd. Press release (2022),
https:// www.mhi.com/jp/news/22010702.html