Operation Results of HighTemperature and -Pressure
Fluidized Bed Boiler withRecycled Waste Fuels
YOSHINORI TERASAWA*1
EIJI TAKAHASHI*2
TATSUO YOKOSHIKI*3

TAKEHIKO SHIRAHATA*2
MANABU NAGATOMI*2
RYO YAMAZAKI*3

This is a bubbling fluidized bed boiler that is highly adaptable to the environment and which operates on recycled
waste fuels such as cut tires, wood products, sludge, RPF (refuse paper & plastic fuel) as substitute for fossil fuels.
This plant is able to generate high-temperature and high-pressure steam with reduced fossil fuel consumption andlower CO2 emission. Steel wires contained in tires can be safely and continuously discharged from the fluidized bed
furnace without accumulating on the furnace bottom. Further, even when a mixture of different recycled waste fuels
is combusted, NOx and dioxins reduction can be achieved simultaneously by M-STAR (the Mitsubishi multi-stage airre-firing) combustion method, a combustion system(1) patented by Mitsubishi Heavy Industries, Ltd. (MHI). At present,
two fluidized bed boilers are commercially operating with recycled waste fuels containing cut tire at Nagoya Pulp
Corporation and Mitsubishi Paper Mills Limited.
must be continuously discharged from the furnace without accumulating in the fluidized bed. In this way, stablecombustion can be achieved even when multiple recycled
waste fuels are used simultaneously. Therefore, MHI
has developed its proprietary high-temperature andhigh-pressure fluidized bed boiler that operates on recycled waste fuel combining the waste materials
fluidized combustion technique for environmental systems and the high-temperature and high-pressure
fluidized bed boiler technique for power generation systems. This paper gives an outline of the engineeringand operation performance of this kind boilers that havebeen delivered to Nagoya Pulp Corporation and
Mitsubishi Paper Mills Limited.

1. Introduction
While the reduction of greenhouse gases (such as CO2)
is being promoted for prevention of global warming, 130
million tires (approximately 1.03 million tons) were discarded in Japan in 2003, of which 44% (451 thousandtons) was utilized for the purpose of thermal recovery
and electric power generation (2). It is also reported thatwoody biomass (wood chips, lumber from thinning, waste
wood derived from construction work, etc.) has a potential supply capacity of approximately 8 million tons per
year (3). Accordingly, if these materials were used to replace fossil fuels, not fuel costs and but CO 2 emissions
could be reduced.
However, as tires contain about 10% to 20% of steel
wires (hereinafter called wires), in order to ensurestable combustion of tires on the fluidized bed, the wires

2. Characteristics of recycled fuels
Table 1 shows the properties of various fuels.

Table 1 Properties of various recycled waste fuels
Nagoya PulpFuelContents

Mitsubishi Paper Mills

ReferenceCut tires

Woodproducts

RPF

Woodproducts

PS

Coal

0.56

23.3

2.41

13.2

58.4

9.00

Moisture(%)

Ash(%)

2.46

1.91

4.73

1.34

44.1

13.85

Combustibles

(%)

97.54

98.09

95.27

98.66

55.9

86.15

Carbon

(%)

81.3

48.9

63.1

43.0

25.0

71.0

Hydrogen

(%)

7.47

6.34

9.64

6.51

3.52

4.56

Nitrogen

(%)

0.37

0.69

0.74

0.21

0.93

1.72

Total sulfur

(%)

1.72

0.06

0.07

0.09

0.15

0.52

Total chlorine

(%)

0.14

0.15

0.23

0.41

0.18-Oxygen, etc.

(%)

6.54

41.95

21.49

48.44

26.12

8.35

Higher heating value (kJ/kg)

38 72019 42029 60019 0108 6 2028 870Lower heating value

37 05018 00027 42017 5407 830

28 110Notes(kJ/kg)Moisture is on an arrival basis, and others on a dry basis.
oAsh and combustibles are based on 800 C x 2 h.

*1 Yokohama Research & Development Center, Technical Headquarters*2 Yokohama Dockyard & Machinery Works*3 Power Systems Headquarters

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 42 No. 4 (Nov. 2005)1

(1) Cut tiresThe higher heating value of cut tires is 38 720 kJ/kg, which is approx. 30% higher than that of coal,
which is 28 870 kJ/kg. Cut tires are cheap and suitable as an alternative to coal. However, their sulfur
content is 1.72%, which is comparable to that of heavy
oil, so that consideration must be given to related
problems of corrosiveness. In addition, tires contain
10-20% of wires which can accumulate on the fluidized bed and hinder fluidization. Therefore,
prevention of such defective fluidization that could
cause inadequate combustion on the fluidized bed is
an important objective. Further, as shown in Fig. 11,small-size tires are cut into 16 pieces (approx. 200mm each) and large-size tires are cut into 32 pieces(approx. 330 mm each). These pieces, though comparatively large in size, must be made to combust stably
in the fluidized bed.
Steel cord

(2) Wood-product fuels (wood chips)
Moisture content is 10-20%, which is comparatively low, the higher heating value is as high as 19 000
kJ/kg, the ash content is only 1-2% and its combustibility is excellent. The sizes of chips to be charged
are, as shown in Fig.2
Fig.2, about 50 mm or less on thel o n g e r s i d e s . Wo o d c h i p s a l s o c o m e w i t hincombustibles such as stones and metal pieces (wires,nails, pieces of iron, etc.) which also need to be prevented from accumulating in the fluidized bed.
(3) Others
RPF is a solid fuel made of waste plastics and industrial type waste paper, whose moisture content isonly 2-3% and higher heating value 29 600 kJ/kg,
which is as high as that of coal and next to that of cut
tires. The higher heating value of paper sludge (PS)is 8 620 kJ/kg, which is lower than that of any otherfuel; its moisture content and ash content are as highas 58.4% and 44.1%, respectively, making this material hard to burn.

Steel cord

3. System characteristics
Beadwire

Beadwire

Approx. 200 mm

Approx. 330 mm

Table 2 shows the main elements of boiler engineering, and Fig. 3 shows the boiler configuration.

Fig. 1 Appearance of cut tire
Small-size tires are cut into 16 pieces of approx. 200 mm each andlarge tires into 32 pieces of approx. 330 mm each (car tires at left
and truck tires at right).

Secondarysuperheater
Primarysuperheater

Economizer

Fig. 2 Appearance of wood products (wood chips)
Charging size is about 50 mm or less on longer sides.
Table 2 Boiler planning main elements
Nagoya Pulp

Mitsubishi
Paper Mills

Main steam
flow rate(t/h)

117.5

77

Main steampressure (MPag)

12.65(superheater outlet)

10.20(superheater outlet)

Main steam
otemperature ( C)541
(superheater outlet)

515(superheater outlet)

Wood products,
cut tires, RPF,
kerosene

Wood products,
cut tires, sludge,
other combustibles,
AC blend oil(for starting andaiding combustion)

Item

Evaporator(in-bed)Heating tube in bed

Tertiary superheater(in-bed)
Fuels

Fig. 3 Boiler assembly
In case of higher temperature and pressure conditions, a final
superheater protected by refractories is installed in the fluidizedbed (an example at Nagoya Pulp Corp.).

User(for starting andaiding combustion)

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 42 No. 4 (Nov. 2005)

2Fig. 4 shows an example of an overall plant system
configuration. The boiler delivered to Nagoya Pulp Corporation, which is a bubbling fluidized bed boiler,
achieves high power generation efficiency through application of highest class high-temperature andhigh-pressure steam condition (12.65 MPag x 541oC) inJapan. In the meantime, the boiler delivered toMitsubishi Paper Mills Limited is operating on cut tires
as the main fuel, occupying approximately 75% of thetotal heat input. Both of these power generators arefriendly to the environment.
In the case of higher temperature and pressure conditions, an superheater (final superheater) protected by
Fuel feedng chute

Boilerrefractories, as shown in Fig. 55, is installed in the fluidized bed to reduce corrosion from sulfur content andabrasion by sand, enabling high-efficiency heat recovery (MHI patent). In addition, a stepped inclined furnacebottom structure, as shown in Fig. 66, has been adopted
and the air supply near the bed drain extraction section
has been made adjustable to discharge wires smoothly.
Incombustibles such as wires has been discharged fromthe fluidized bed along the bed ash treatment system,
7 and wires has been separated andas shown in Fig. 7,
recovered from the sand by magnetic separators. Other
incombustibles will be segregated subsequently by a vibrating sieve, discharged from the system and recovered.

Primary air heater

Secondary
air heater

Bag filter

U-AA
L-AA
OFA

CycloneInduced draft fan
Gas recirculation(GR) system

Secondary
air draft fan

Bed ashcoolerSteam gas
air heater

Primary air Suction steam
draft fangas air heater

SuctionsilencerAshconveyor
blowerSuctionsilencer
Desulfurization

Recovery system

Fly ash siloFig. 4 Total plant system configuration
An example of plant delivered to Mitsubishi Paper Mills. The plant delivered to Nagoya Pulp operates on a smaller amount of cut tires
so exhaust gas (SOx) in the downstream stage is treated by a dry-type treatment method (dry-type desulfurization by bag filter).
Bucket conveyor

Upper tube header in bed
Tube inbed

2nd step magnetic separator
3rd step magnetic separator

Tube

Vibrating sieve
Wire

Refractories

WireLower tubeheader

Fluidized bed boiler

Tube outer surfaces areprotected from abrasionby casters and studs.

Fluidized material
feeding conveyor
Ash cooler(screw conveyor)

Fig. 5 Outline of superheater structure in bed
Abrasion and corrosion are prevented by installing an in-layer superheater protected by refractories.

Ash cooler(screw conveyor)

1st stepmagnetic
separator

Wire

Fluidizedmaterial
conveyor

Wire
Wire

1st stepmagnetic
separator
Ash cooler(screw conveyor)

Bed drain

Stepped inclined furnace bottom

Fig. 7 Bed ash treatment system
Incombustibles containing wires and sand discharged from the furnacebottom are cooled on a water-cooled conveyor. Wires and other incombustibles are separated from sand, respectively, by magnetic separators
and a vibrating sieve, allowing the sand to return inside the furnace.

Fig. 6 Stepped inclined furnace bottom structure
The furnace bottom is inclined so as to discharge steel wires from thefurnace without their accumulating.

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 42 No. 4 (Nov. 2005)3

By optimizing the feeding rate of the secondary air
supplied from three stage ports at the free board, low
NOx and low dioxins can be attained simultaneously evenin the case of multiple type recycled waste fuel combustion by the M-STAR combustion method.

ently tended to become stabilized as the supply of fuels
was stabilized, and when the fluidized bed average temperature was 842oC, the exhaust gas contained 146 ppmof NOx, 2 mg/m3N of soot (both @ O2 6% dry), 122 ppm ofSOx (@ actual concentration of O 2 dry) and 74 ppm of
CO (@O 2 12% dry), their guaranteed values wareachieved. In the case of mixed fuel combustion, including cut tires, wood products and PS, at Mitsubishi PaperMills, stabilized combustion was also attained. When thefluidized bed average temperature was 821oC, the NOx
concentration was 66 ppm, the soot concentration 0.9 mg/
m 3N, the CO concentration 50 ppm, dioxins concentration less than 0.098 ng-TEQ/ m3N (so far @ O2 12% dry)
and the SOx concentration 35 ppm (@ actual concentration of O2 dry), their guaranteed values were achieved.

4. Operating conditions
4.1 Combustion stability
Fig. 8 shows the time trends of temperatures, boiler
evaporation and exhaust gas concentration during theperformance test. Table 3 shows the results of the performance test.
In the case of mixed recycled waste fuel combustion
including cut tires, wood products and RPF (at NagoyaPulp), both evaporation and steam temperature appar-

Table 3 Boiler performance test results

Target value

Test result

Target value

Test result

(t/h)

117.5

117.5

77.0

79.5

NOx(ppm)

150

146

80

66

Soot

3(mg/m N)

50

2100.9SOx(ppm)

140

122

100

35(ng-TEQ/m3N)--0.098

0.098 or less(ppm)

100

74100

50

Evaporation

CORemarksTemperature/NOx, COo( C/ppm)
Main steam flow rate (t/h)

10Fluidized bed temperature

8oRated steam temperature 541 C
Main steam temperature

6O24CO(@O212%)

NOx(@O2 6%)20150.0
Wood products
120.0

Main steam flow rate

20

Rated steam volume 117.5t/h
90.0Main steam pressure
60.00.0

1510Rated steam volume 12.65 MPag

30.0

RPF
01NOx, soot, dioxin and CO values
are as converted to O2 12% dryvalues.

NOx and soot values are asconverted to O2 6% dry values,and CO value as converted toO2 12% dry value.

5

Cut tires
2Time (h)340

Main steam pressure (MPag)/ Furnace outlet O2 concentration (%)
fuel supply amount (t/h)
Temperature/NOx, CO
Main steam flow rate (t/h)
o( C/ppm)

Dioxins10

1 000
Fluidized bed temperature
800

oRated steam temperature 515 C

6Main steam temperature

600

O2400
200

84NOx(@O212%)

CO(@O212%)

200

150.0

15PS

120.0

Main steam pressure 12
Main steam flow rate

90.0

Cut tires

60.0

Rated steam volume 77 t/h 6
Wood products30.00.0Rated steam volume 10.20 MPag 9012Time (h)3304Main steam pressure (MPag)/ Furnace outlet O concentration (%)
2fuel supply amount (t/h)

Item

1 000
900
800700600500
4003002001000

Mitsubishi Paper Mills

Nagoya Pulp

User

Fig. 8 Time trends of temperatures, boiler evaporation and exhaust gas concentration
Stable combustion was attained and the performance guaranteed values were achieved both in the caseof mixed fuel combustion involving cut tires, wood products and RPF, and mixed fuel combustion involving
cut tires, wood products and PS (Nagoya Pulp at left and Mitsubishi Paper Mills at right).

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 42 No. 4 (Nov. 2005)

4

Target feeding rate 3.8 t/h

1.6

4.8

1.2

3.6

0.8

2.4

0.4

1.2
: Wire discharge: Tire supply
Wire discharge rate = Wire discharge/Average steady wire discharge
024364860
72

00122

Under adjusting operation

4Target feeding rate 2.4 t/h

1.5

3120.5: Wire discharge: Tire supply
Wire discharge rate = Wire discharge/Average steady wire discharge

0012243648

60728496

108120132

144

Tire supply (t/h)

Under adjusting operation

1Tire supply (t/h)

Wire discharge rate (-)
Wire discharge rate (-)62(a) Wires about 60 mm long arerecovered by upstream
magnetic separator

0156

Time (h)Fig. 9 Time trends of wire discharge
Stable steel wire discharge was confirmed in both cases of mixed fuel combustion(upper figure: Mitsubishi Paper Mills, lower figure: Nagoya Pulp).

Fig. 10 Appearances of wires
recovered by magnetic separators

Table 4 Wire recovery rates by magnetic separator
Nagoya Pulp

Mitsubishi
Paper Mills

87.8

84.9

Downstream magnetic
separator recovery
rate (%)

6.9

9.1

Total recovery rate (%)

94.7

94.0

User

Item

Upstream magnetic
separator recovery
rate (%)

Remarks(b) Wires pulverized into pieces
about 2 mm long are recoveredby downstream magnetic
separator

As can be understood from Table 4, in both cases, thewire recovery rate indicates more than 94%, the discharged wires are almost recovered.
Fig. 10 shows the appearances of wires recovered by
the magnetic separators installed upstream and downstream. Compared with the wires recovered by theupstream separators, those recovered by the downstream
separators are finer. Approximately 6% of wires not recovered by the downstream separator seem to have been
oxidized in the fluidized bed, further pulverized and finally discharged together with combustion exhaust gas.

One downstream
Total recovery rate
magnetic separator
indicates value ofoutlets of two magnetic installed.
separators installedat downstream.

5. Conclusion
4.2 Wire dischargeability
Fig. 9 shows the time trends of wire discharge during
the wire dischargeability verification test. The wire discharge variation related on the tire supply changes during
the initial adjustment time, but as the tire supply wasstabilized, the wire discharge took place at a more or lessconstant rate and the capability of smooth wire discharge
was confirmed. Also, no wire deposit was found on thefurnace bottom during the inspection period.
4.3 Wire recovery performance
Table 4 shows the wire recovery rates of magnetic
separators installed in the bed ash treatment systems.

Yoshinori Terasawa

Takehiko Shirahata

High-efficiency power generation through applicationof highest class temperature and pressure steam conditions in Japan to the bubbling fluidized bed boiler wasverified, and adaptability to the environment/energy of
MHI's proprietary high-temperature and high-pressure
fluidized bed boiler technology utilizing a mixture of recycled fuels such as cut tires, wood chips, RPF and PS
was also confirmed. In future, MHI will continue its efforts to ascertain the clients' needs and offer products
excelling in adaptability to the environment with a viewto global warming prevention and efficient utilization of
the earth's limited energy resources.

Eiji Takahashi

Manabu Nagatomi

Tatsuo Yokoshiki

Ryo Yamazaki

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 42 No. 4 (Nov. 2005)

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