Mitsubishi Heavy Industries Technical Review Vol. 60 No. 3 (September 2023)
1Initiatives Biomass Combustion Technology forSteam Power Plants to Achieve Carbon Neutrality
KAZUTOSHI AIYOSHIZAWA*1 MASAYUKI KATO*1

SHOTA KAMIGUCHI*2

TOSHIHIRO KAWAKAMI*2

YUYA UEDA*2

YUKI KONDO*2

For achieving carbon neutrality, Mitsubishi Heavy Industries, Ltd. (MHI) has accumulated
experience in biomass co-firing and 100% biomass firing for pulverized coal-fired steam power
plants of various types and output ranges in Japan as well as overseas. As the latest example, large(1,000-MW-class) ultra-supercritical steam power plants in which pulverized coal is fired havestarted biomass co-firing operation at the ratio of 10% or more (calorie basis).

|1. Introduction
In order to fulfill our national goal of reducing carbon dioxide (CO2) emissions by 46% fromthe 2013 baseline by 2030 and achieving carbon neutrality by 2050, the electric power companies
and business operators with independent electric power generation facilities are employing various
measures to cut CO2 emissions. The steam power plants, which especially emit CO2 in large
quantities, are strongly required to decrease the usage of fossil fuel. The use of biomass as analternative fuel is expanding because of its good availability and economic advantage. Being
characterized by their large capacity as a power source and high load-following capability, thepulverized coal-fired steam power plants serve as a power source to balance power supply anddemand. If the fuel is switched from coal to biomass, or high ratio biomass co-firing or 100%
biomass firing is introduced, CO2 emissions can be substantially reduced while retaining theadvantages of pulverized coal-fired steam power plants. Furthermore, as the 100% biomass firing
technology has already been established in Europe, it is also the center of attention mainly among
the Japanese business entities aiming to reduce CO2 emissions from their steam power plants assoon as possible (by 2030).
This report presents the characteristics of biomass firing technology for steam power plants
and the latest application examples.

|2. Our biomass pulverization/combustion system
In terms of burning biomass in pulverized coal-fired steam power plants, either of thefollowing technologies is applied: (1) a mixed pulverization/combustion system (with the use ofwood chips or pellets) in which biomass is fed into the same mill as coal and is pulverized together
before being fired in the same burner as coal, or (2) a dedicated pulverization/combustion system(with wood pellets), which is equipped with a mill and a burner dedicated to pulverizing and firing
biomass. In the mixed pulverization/combustion system, biomass has to be pulverized as finely ascoal to ensure the flammability of coal, whereas the dedicated pulverization/combustion systemallows biomass to be pulverized more coarsely than coal owing to the high flammability ofbiomass. Being less bound by the mill’s operational restrictions, the latter system can process morebiomass, and therefore can increase the co-firing ratio more easily. Table 1 summarizes thecharacteristics of both systems.
*1

Chief Staff engineer, Engineering Department, Steam Power Maintenance Innovation Business Division, Energy System, Mitsubishi*2Engineering Department, Steam Power Maintenance Innovation Business Division, Energy System, Mitsubishi Heavy Industries,Heavy Industries, Ltd.
Ltd.

Mitsubishi Heavy Industries Technical Review Vol. 60 No. 3 (September 2023)
2

Table 1
Pulverization/combustion system(1) Mixedpulverizationand combustion(2) Dedicatedpulverizationand combustion

Biomass pulverization/combustion system (per burner)
Co-firing ratio*

System configuration

Up to several %(calorie basis)

Approx. 10 to 20%(calorie basis)× number of mills*: Biomass co-firing ratio in boiler, not per burner

In the dedicated pulverization/combustion system, the biomass co-firing ratio can be further
increased by adding a minimum set of devices/equipment suitable for the use of biomass without
performing substantial specification changes or remodeling the existing facilities of pulverizedcoal-fired steam power plants. In this system, the vertical mill with many proven records forapplication in pulverized coal-fired steam power plants and the low-NOx burner with superior
ignition stability are incorporated in the combustion equipment. By optimizing the vertical mill andthe low-NOx burner for biomass application, the reliability of the equipment can be enhanced. Our
combustion equipment, i.e., the mill and the burner, has been developed/designed, considering
separately the situations in which the fired fuel is 100% biomass, or either coal or biomass.
Biomass is higher in volatile matter content than coal and, as wood pellets, has a lower fuelmoisture content than other solid fuels. The minimum ignition energy is lower than coal. In thededicated pulverization/combustion system, in which the concentration of biomass in the millbecomes especially high, concerns are mainly raised about spontaneous ignition in the mill andrapid combustion. As such, the mill and the pulverized fuel chute are equipped with a rapid
combustion protection system (consisting of a container fille pressure vessel at an early stage. Withbiomass having a low minimum ignition energy a d with fire extinguishing media, pressure sensors,etc.) to detect and stop an excess s mentioned above, sparks generated by contact with metals, etc.,
may serve as a source of ignition. So, it is also important that safety measures should be taken
upstream of the combustion equipment including removal of foreign matter such as metals in thefuel handling system.

|3. Biomass co-firing technology application examples
3.1

Taketoyo Thermal Power Station Unit 5This is the boiler delivered to JERA Power Taketoyo LLC. Coal and wood pellets are
co-fired in this boiler. The biomass co-firing ratio is about 17% (calorie basis) (at a power output of
1,070 MW). The feed rate of wood pellets is approximately 90 t/h. Of its six mills, one is for
exclusive use of biomass. The pellets pulverized by this mill are fired in six burners that are used
only for biomass (a mill and single-stage burners). The power output from this plant is one of thelargest in Japan. The scale of biomass combustion is also one of the largest among the units wehave delivered. Table 2 shows the boiler specifications of the Taketoyo Thermal Power Station
Unit 5 and Figure 1 gives the exterior of this boiler plant.
The combustion system is two-stage combustion with the opposed firing system, using MPS
mills and HT-NR3B burners (Figure 2). It is characteristically equipped with a specialized
large-capacity mill and burners for exclusive use of biomass (wood pellets). This mill and burners
for biomass use have been optimized from the perspectives of operational management andMitsubishi Heavy Industries Technical Review Vol. 60 No. 3 (September 2023)
3structure. Specifically, consideration is given to the facilitation of pulverized biomass discharge forthe former and the realization of stable ignition over a wide range of burner loads for the latter.
Table 2Boiler design specifications (Taketoyo Unit 5)

OutputMaximum evaporation capacity
Turbine inlet main steam pressure / temperature
Fuel
Co-firing ratio
Vertical mill model
Burner model

1,070 MW3,210 t/h
26.4 MPa (g) / 600°C
Coal, wood pellets≈17% (calorie basis)
MPS-280BH
HT- NR3B

Figure 1 Exterior view of boiler plant(Taketoyo Unit 5)

Figure 2 Dedicated biomass burner(Taketoyo Unit 5)

3.2

Misumi Power Station Unit 2 of Chugoku Electric Power Co., Inc.

This is the boiler delivered to Chugoku Electric Power Co., Inc., in which wood pellets andcoal are co-fired. The biomass co-firing ratio is about 10% (calorie basis) (with a power output of1,000 MW). The feed rate of wood pellets is approximately 50 t/h. The power output from thisplant is one of the largest in Japan. The scale of biomass firing is also one of the largest among theunits we have delivered. Table 3 shows the boiler specifications of the Misumi Power Station Unit
2 and Figure 3 gives the exterior of this boiler plant.
Table 3 Boiler design specifications (Misumi Unit 2)
OutputMaximum evaporation capacity
Turbine inlet main steam pressure / temperature
Fuel
Co-firing ratio
Vertical mill model
Burner model

Figure 3 Exterior view of boiler plant(Misumi Unit 2)

1,000 MW
2,900 t/h
24.5 MPa (g) / 600°C
Coal, wood pellets≈10% (calorie basis)
MVM32RL
M-PM burner

Figure 4 Burner usable for either
biomass or coal (Misumi Unit 2)

The combustion system is two-stage combustion with the circular firing system, using MV
mills and Multiple Pollution Minimum (M-PM) burners (Figure 4). It is characteristically equippedwith a total of six mills, of which two can be switched between coal and biomass for exclusiveMitsubishi Heavy Industries Technical Review Vol. 60 No. 3 (September 2023)
4pulverization. These two mills are connected with 16 burners (two mills and two-stage burners),
which can be used for combustion of either coal or wood pellets.

|4. Conclusion
We have accumulated experience in biomass co-firing since the start of commercial
operation of the 110 MW class pulverized coal and biomass co-fired steam power plants in Japan,
which we delivered between 2018 and 2019. The 1,000 MW class pulverized coal-fired steam
power plants have started using the country’s first dedicated pulverization/combustion system forbiomass, which is suitable for the operation at a high biomass co-firing ratio. This dedicatedpulverization/combustion system has been in operation at the two units which are Taketoyo
Thermal Power Station Unit 5, and Misumi Power Station Unit 2. Their capacities are one of thelargest among the facilities we have delivered. Augmented by this experience with the two units,
our product line-up for steam power plants is now available over a wide plant output range of 110
MW to 1,070 MW (Figure 5).

Figure 5

Our delivery record of biomass plant/100% biomass-fired burners

Moving forward, we will introduce the use of biomass, expand the co-firing ratio, and workout a plan for eventual 100% biomass firing by applying the design and test-operation results
shown in this report to other existing plants (Figure 6). While meeting the needs of electric powercompanies and business operators with independent power generation facilities, we will contributeto the achievement of a carbon-neutral society.

Figure 6

Our biomass plant/co-firing ratio data and prospect of development

Mitsubishi Heavy Industries Technical Review Vol. 60 No. 3 (September 2023)
5References
(1)
(2)
(3)

Tatsuo Yokoshiki et. al, Operating Results of Coal and Biomass Fuel Fired Boiler, Mitsubishi Heavy
Industries Technical Review Vol.55 No.4 (2018)
Tatsuo Yokoshiki et. al, Biomass Fuel Fired Boiler Technology of MHPS Group, Mitsubishi Heavy
Industries Technical Review Vol.54 No.3 (2017)
Akihiro Ikeda et. al, Efforts Toward Steam Power Plant Utilized Pulverized Biomass Exclusive Firing
Technology, Mitsubishi Heavy Industries Technical Review Vol.56 No.3 (2019)