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80 MW of Electricity from Biofuel in
Kymin Voima
Asko Rantee
Kvaerner Power Oy
Finland
Jouni Kinni
Kvaerner Power Oy
Finland
Antti Rainio
Kymin Voima Oy
Finland
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1. POWER PLANT PROJECT
Kymin Voima made the investment decision for a new 80MW electricity and 180 MW heat
producing biomass power plant in June 2000. The main equipment was purchased in August
and in less than two years, in summer 2002, the new power plant was in operation. The
project was spread over ten main contracts and dozens of smaller delivery agreements. The
project team was assembled from UPM-Kymmene’s project and mill personnel. PVO
Engineering and Projekti-insinöörit acted as the main engineering consultants. The main
equipment suppliers and the project time schedule are shown below.
Table 1: Main equipment suppliers:
Bubbling fluidized bed boiler plant:
Kvaerner Power Oy
Fuel handling:
BMH Wood Technology Oy
Back pressure turbine and generator:
Alstom Finland Oy
LP and HP feed water heat exchangers:
Andritz-Ahlstrom Oy
Feed water pumps:
KSB
Demineralized water plant:
YIT Environment Oy
HP and connecting piping:
YIT Power Oy
LP and heating piping:
Steka Oy
Electrification:
Vaasa Engineering Oy, ABB Industry Oy,
Siemens Osakeyhtiö
DCS:
Metso Automation Oy
Table 2: The Kymin Voima project time schedule
Investment decision:
June 2000
Main equipment purchases:
August 2000
Start of construction:
March 2001
End of erection:
March - June 2002
Commissioning:
June - August 2002
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Kymin Voima is the company that was established for this power plant. Pohjolan Voima, a
Finnish forest industries power company, owns 76% of Kymin Voima. Kouvolan Seudun
Sähkö, a local utility company, owns the rest. The power plant is located in the UPMKymmene’s Kymi Paper mill in Kuusankoski. The towns of Kuusankoski and Kouvola, with
a combined population of around 50,000, are located within 5 kilometres of the plant. Each of
these towns has its own district heating networks.
Figure 1: Kymin Voima Power plant
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2. COMBINED HEAT AND POWER PRODUCTION
Kymi Paper is the third largest pulp and paper mill in Europe with an annual paper
production of 920,000 tons and pulp production of 520,000 tons. The mill uses 2.3 million
cubic meters of wood annually as raw material. The bark from this wood accounts for
approximately half of the fuel used in the new power plant.
The heat demand from the mill and the towns forms the basis for the operation of the power
plant. At nominal load it produces 125 MW of process steam and 15 MW of hot water for
Kymin Voima as well as 40 MW of district heat for the area. At this load the power
production is 76 MW and fuel input to the boiler is 290 MW. The plant achieves an overall
efficiency of over 88% and the power to heat ratio is 0.42.
The Kymin Voima power plant is connected to the Kymi Paper medium and low-pressure
steam networks for distributing the process steam to the three paper machines and other heat
consumers at the mill. In addition to the new plant, the two existing recovery boilers produce
at maximum 94 kg/s of steam for two older turbines with nominal capacities of 28 and 15
MW. As a back-up, the mill has a natural gas fired boiler producing medium pressure steam.
The mill steam network is shown in figure 2.
KYMIN VOIMA
Kymi Paper Oy
SK1
110 t/h
114 bar
540°C
KPA
265 MWf
385 t/h
SK2
250 t/h
MK
120 t/h
84 bar
84 bar
480°C
480°C
G
GT1
G
GT2
MAX
15 MW
0 – 20 t/h
16 bar
200°C
230 t/h
110 t/h
MAX
85 MW
G
MAX
28 MW
0-50 t/h
0-15 t/h
13,5 bar
0 – 10 t/h
Accumulator
3,5 bar
115-300 t/h
OWN
USE
OWN
USE
OWN
USE
Kouvola +
Kuusankoski
0-40 MW
4,5 bar
COOKING
C3 ja PK7
KYMI
Hydro
power plant
Koskela
0 - 15 MW
3,5 bar
Kni. heating
Pk1/2,
FC,Ky.läm
CONDENSOR 0-60 t/h
PK9
PK8
PK7
KAL
COOKING EVAP.
DRYING
Figure 2: Kymin Voima Power plant and Kymi Paper steam network.
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3. FUELS
The main fuel for the new boiler will be bark from the pulp mill’s debarking plant. It will
cover about half of the expected 2100 GWh annual fuel demand. UPM-Kymmene’s nearby
saw mills produce saw dust and wood residue, which are also combusted in Kymin Voima.
The mill’s waste water treatment plant produces sludge, which needs to be burned off. After
mechanical drying the sludge gets a positive heating value and produces energy in the boiler.
In the first years the main fuel purchased will be peat, covering about 28% of the annual fuel
energy. However, the target is to reduce the peat consumption and increase the share of forest
residue and whenever its production in the area increases.
Table 3: Expected fuel usage 2100 GWh / year
Bark
49 %
Forest residue
6 % initially
Saw dust and wood residue
12 %
Sludges
3%
Peat
3%
Natural gas
28 %
2 % start up and back up fuel
The moisture content and heating value of the bark varies according to the species of wood
and the time of year. The moisture is at its highest during winter time, when the boiler load is
also at maximum. This situation provides the dimensioning basis for the boiler. Peat and
forest residue somewhat level off the variation in heating value. Natural gas is used as startup fuel. It can be used as an auxiliary fuel with load burners, in the case of any disturbances
in the solid fuel handling system.
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Table 4: Fuel properties
Moisture %
LHV, MJ/kg
Bark
50-59
(44-65)
6.6-10.2
Peat
45
(40-60)
11.3
Forest residue
55
(40-60)
7.4
Biosludge
70
(60-70)
2.5
Bark and water treatment sludge are conveyed from the Kymi Paper mill via belt conveyors
to Kymin Voima’s 5000 m3 field storage. Wood fuels from the sawmills and forest residues
are fed to the same storage. Before passing through to the storage they go though a screening
and crushing station. Two screw feeders at the bottom of the wood fuel storage feed the fuel
to a belt conveyor taking it to the boiler house.
Peat comes to a separate receiving station and it is also screened, and larger pieces crushed
before passing to the 2000 m3 field silo. The peat is conveyed from this field silo to its own
feeding silo in the boiler house.
BMH Wood Technology
Figure 3: Outside fuel handling
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4. HYBEX BOILER
During the last 20 years Bubbling Fluidized Boiler technology has become a dominant boiler
technology in applications where a variaty of wet biofuels is combusted and high availability
and low emissions are sought. Kvaerner Power Oy was selected as the supplier for the Kymin
Voima project. When commissioned in summer 2002, the HYBEX boiler was the largest
biofuel-fired BFB boiler in the world.
Figure 4: Side view of the Kymin Voima HYBEX boiler
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4.1 Boiler systems
The steam parameters of the boiler are 107 kg/s, 114 bar and 541 °C. With these parameters
the boiler capacity is 269 MWth. The furnace width is 12 m, depth 11,4 and height 33 m. The
boiler has three-stage superheating, the two last stages being made from high chromium alloy
AC66.
The boiler is equipped with a hydrobeam floor. The coarse removal system consists of 12
hoppers, three screw conveyor, one drag conveyor and a sieving station.
Figure 5: Coarse removal system
The Kymin Voima boiler is equipped with two independent fuel feeding line. Each line
serves three fuel feeding points and has a capacity of up to 70 % MCR. In this project special
attention was paid to the fuel feeding system in order to achieve accurate and even fuel
feeding. Each feeding line has its own bark silo. There is a common peat silo in between the
bark silos. Peat is mixed with the other fuels in a mixing screw. The drag conveyor has a
special levelling chamber for the mixing and equalisation of fuel flow. Each feeding point is
equipped with a feeding screw.
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The separate peat silo at the boiler house makes it possible to adjust the heating value without
delay when there is a variation in the moisture content of the main fuel.
Figure 6: Fuel feeding system
The air system consists of a primary air fan, a secondary air fan, steam coils and flue gas air
preheaters. The boiler has a staged after-air system and the design is based on CFD
modelling.
The has four start-up and four load burners as an auxiliary and reserve firing system.
The load burner capacity is designed for 200 MW, and the burners are combined natural gas
/ oil burners.
The boiler is equipped with two ESPs and flue gas fans on the flue gas side.
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5. OPERATING EXPERIENCE
5.1 Start-up
Boiler commissioning started in spring 2002. The first solid fuel firing was on 10.5.2002 and
the boiler was handed over on 1.8.2003, two months ahead the original time schedule. The
boiler has been running continuously since the end of July.
5.2 Operation mode
The heat demand from the mill and the towns forms the basis for the operation of the power
plant. Loads were therefore low during the summer. Towards the end of 2002 load demand
had been increasing. The new HYBEX boiler also handles the load swings at the mill, while
the two recovery boilers are running at constant load. This means that there is a great deal of
daily load variation, as can be seen in Figure 7.
100
KYMIN VOIMA OY - BOILER LOAD SINCE START-UP
HYDRO TEST
11.1.2002
FIRST GAS FIRING
9.4.2002
FIRST SOLID FUEL FIRING 10.5.2002
75
50
25
0
Figure 7: Boiler load variation
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5.3 Fuels
The boiler has been operated with different fuel mixtures since start up. On a daily basis the
fuel mixture varies a lot, as does the moisture content. Figure 9 shows the fuel usage. The
natural gas consumption is exceptional due to the commissioning period.
NATURAL GAS
7%
PEAT
33 %
HEAVY FUEL
OIL
<1%
BARK
+FOREST
RESIDUES
59 %
Figure 8: Fuel usage after start up
5.4 Emissions
The official plant performance test was carried out during the last week of January 2003. The
official test report will be published after submittal of this paper. Preliminary results shows,
however, that the boiler performance appears to be according to design in terms of aspects
such as overall process design, boiler adjustability, controllability and flue gas emissions. The
guaranteed emissions for the boiler are 150 mgNO2/MJ, 15 mgN2O/MJ, 250 mgCO/nm3 (6 %
O2 dry) and dust 30 mg/nm3 (6 % O2 dry).
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EMISSION [mg/Nm3 at 6% O2]
STEAM FLOW [kg/s]
250
STEAM FLOW
CO
NOx
O2 after boiler
4.0
EMISSION AVERAGES:
NOx 188 mg/Nm3 @ 6% O2
CO 25 mg/Nm3 @ 6% O2
3.5
200
3.0
2.5
150
2.0
100
1.5
1.0
50
0.5
0
OXYGEN AFTER BOILER [Vol-% wet]
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0.0
0
10
20
30
40
50
60
70
80
90
100
110
120
MINUTES
Figure 9: Emissions during a test run
5.5 Other experiences
The start up and operation of the Kymin Voima HYBEX boiler has proceeded very smoothly.
The boiler is the fourth new boiler in this size class (under 300 MW) to be delivered in the
last seven years. This signifies that the design for this size of boiler has become very
standardised, and the designers were able to utilize all the experiences gained from the earlier
deliveries.
It is well known that in a fluidized bed boiler operation the key factor in load and emission
control is the fuel feeding system. Special attention was paid to the fuel feeding system in this
project and the results so far are very positive.
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6. CONCLUSION
The pulp industry has traditionally utilised biofuels to produce a large portion of their energy
demand. The Kymin Voima project is a good example of the co-operation between a pulp
mill and the surrounding communities in the co-generation of heat and power utilizing
different kinds of biofuels.
In large-scale biofuel firing, the fuel is typically a mixture of different kinds of fuels with
different properties. This emphasises the role of the mixing and equalisation of fuel in
emission and load control.