-
Advanced coal-fired technology for Meri-Pori To meet increasing
electricity demand Finland is building a 560 MWe power station
known as Meri-Pori. Once complete, it will be one of the world's
cleanest and most efficient coal-fired power plants. The project
which is being funded by Imatran Voima Oy (IVO) and Teollisuuden
Voima Oy (TVO), is scheduled for completion in late 1993.
K e v i n D o d m a n
Finland needs more generating capacity, to meet an expected 3000
MW g r o w t h in e n e r g y demand during the period up to the
year 2000. Of this 3000 MW, it is anticipated that 1500 MW will
need to be base load capacity, while the rest will only be needed
during the winter months.
To help meet th is demand a new 560 MWe c o a l - f i r e d p
lant called Meri-Pori is being built, near the town of Pori, 250 km
north-west of Helsinki in Fin land. The new plant will use an
advanced design of s team tu rb ine to ach ieve an overall
efficiency of 43.5 per cent.
It has been designed for base load operat ion and will have an
annual output of 3.6 TWh. A combi-nation of low-NO x burners and a
flue gas cleaning plant will result in emissions that will be
within the recently determined regulatory lim-its of 70 m g / M J
for N O x , 140 mg/MJ for S 0 2 and 20 mg/MJ for particulates.
Joint funding The overal l cost estmate for
Meri-Pori is FIM 2.5 billion ($650 mil l ion), including f
inancing and interest charges. Of this, 45 per cent is being
financed by TVO, the rest by IVO. TVO will have a 250 MW share of
the power generated by the plant in exchange for its investment,
whi le IVO has been responsible for construction of the plant and
will own and oprate it when completed.
IVO owns and operates a range of nuclear , foss i l fue l f i
red and
hydroelectr ic power plants. The company is Finland's largest
sup-plier of heat and power to industrial and ut i l i ty c o m p a
n i e s , meet ing some 45 per cent of the national energy
consumption.
TVO is owned by a number of individual industrial groups,
includ-ing IVO which has a 25 per cent shareholding in TVO. It
supplies power to industry and owns and o p e r a t e s the O l k i
l u o t o nuc lear power plant.
The decisin to build the Meri-Pori plant was taken at the end of
1989, pre l iminary p lanning was c o m p l e t e d in 1990 , and
IVO ordered the main equipment for the power station at the end of
May that year.
Construction work started at the end of 1990 and equipment
instal-lat ion c o m m e n c e d a year later.
Commissioning is scheduled for summer 1993, with commerc ia l
operation to follow in November. Power will be fed into the local
400 kV grid.
P o w e r n e e d e d u r g e n t l y To meet the anticipated
growth
in demand for power in Finland, three types of power generating
capacity were considered: natural gas, nuclear and coal. Natural
gas. It was felt that a sta-ble supply of natural gas could only be
g u a r a n t e e d by bu i l d ing a pipeline either from Norway
or from the Baren ts Sea. Both o p t i o n s would be uneconomic
under cur-rent conditions. Nuclear. There are four nuclear units in
Finland - two at Loviisa and two at Olkiluoto - all of which have
been operating successfully
Figure 1. The Meri-Pori power station will be one of the world's
c leanest and most efficient coal-fired power plants
March 1993 19
-
for a number of years. Government approval would be needed
before further nuclear capacity could be built and a proposal has
been put forward to build a fifth unit. No final dec is in has yet
been reached about whether to proceed with it but even if it is
approved, it will take around seven years to construct, so o ther f
o rms of g e n e r a t i n g capacity are needed in the short to
mdium term. Coal is already used extensively for power generation
in Finland. Coal-f ired power stations can be built relatively
quickly and by using the latest emission control technol-ogy,
environmental emissions can be minimized.
P l a n t c o n s t r u c t i o n The new plant is being built
near
the city of Pori, next to the existing Tahkoluoto power plant.
Factors nfluencing the cho ice of Pori i nc luded the fact that the
s i te already has a deep water harbour. Also, many facilities from
the exist-ing power plant, such as the cool-ing-water channel and
road and railway infrastructure, are being re-used.
The first stage of con-s t r u c t i o n i nvo l ved s i te m o
d i f i c a t i o n w o r k . The building office of the City of
Pori g ranted bu i ld ing p e r m i s s i o n in O c t o b e r
1990, and w o r k on the foundations began the fol-lowing
month.
The largest construc -tion contractor at Meri-Pori is the Haka
Group. They have undertaken the con-c re te w o r k and s u p p l e
-mentary structures for the main buildings. In al l , over a
hundred s u b c o n t r a c t o r s have been employed, and during
the installa-t ion phase , a round 700 people have worked at the
site.
E m i s s i o n c o n t r o l The emission control system
for
Meri-Pori was selected at the end of 1990, on the basis of the
sulphur removal requirements then prevail-ing, and the p roposed n
i t rogen ox ide lev is , in l ine w i th Government
guidelines.
The system has cost around $125 million and includes low-NO x
burners, plus catalytic converters for further reduction of NO x
levis, electrostatic precipitators to remove particulates, and a
wet-type desul-phurization system. This combina-tion of systems is
the first to be fit-
ted to a coal-fired power station in Finland.
In May 1 9 9 1 , the F inn ish Supreme Court ruled on the
emis-sion levis that would apply, and these were in line with the
original guidelines. The levis set by the Supreme Court are 140
mg/MJ for sulphur dioxide, 70 mg/MJ for nitro-gen dioxide and 20
mg/MJ for par-ticulate emissions during normal operation of the
plant. Wet desulphurization: The desul-phurization plant will be a
wet sys-t e m , s u p p l i e d by O u t o k u m p u Ecoenergy of F
in land and L&C Steinmller of Germany, with the bulk of the
equipment manufac-tured in Finland. It will comprise an absorption
reactor, together with water, washing liquor, end product and ash
treatment systems.
The flue gases will be fed via the electrostatic precipitators
and the heat e x c h a n g e r into the absorption reactor, where
the S 0 2 in the flue gas will react with an alkaline washing
liquor made up of powdered limestone and water, to form gypsum.
The washing liquor will be fed into the sump of the reactor and
pumped from there into the reac-tor's spraying zone. Flue gases
will be fed into the reactor abov the s u m p c o n t a i n i n g
the w a s h i n g liquor. As the gases move upward, the washing
liquor will be sprayed into the tower from a quadruple battery of
overlapping spray banks. This will ensure efficient mixing of the
gases and the washing liquor. The liquor will collect in the bottom
of the reactor, where the reactions will be supported by aeration
and agitation.
The upper part of the tower incorporates droplet separators to
prevent droplets from leaving the reacto r w i th the f lue gas .
The cooled, water-rich gases will be fed to the exit stack through
a gas-gas heat exchanger.
appeenranta
The process will remove over 90 per cent of the sulphur
contained in the f lue gas. The site 's sulphur dioxide emissions
on an average annual basis w i l l be be low the Finnish Government
's guidel ine
valu of 140 mg/MJ with all grades of coal.
The slurry accumulat-ing in the bottom of the reactor w i l l be
fed to hydro cyclones, which will increase the solid matter conten
from about 10 per cent to 50 per cent. The lighter, smal ler gypsum
crystals will be fed from the cyclones to a recy-cling tank and
from there back into the reactor. The concentrated slurry
gen-erated by the cyc lones
will then travel to a vacuum belt fi l -ter, after which the
solid content will be 90 per cent.
The Meri-Pori plant will produce about 60 000 t/yr of gypsum and
it is planned that this will be used in the construction industry.
Between 4 and 10 t /h of limestone will be used under norma l c o n
d i t i o n s , depending on the purity of the lime-stone and the
sulphur content of the coal being burned. Some 100 t/h of seawater
will also be used, as well as 8 t/h of potable water for gypsum
cleaning. Burners: The boiler at Meri-Pori is equipped with a
two-stage low-NO x combustin system, incorporating a total of 30
low-NO x burners. The burners s u p p l i e d by T a m p e l l a
Power are of the Babcock-Hitachi HTNR (High T e m p e r a t u r e N
O x Reduction) type. This design was
Figure 2. The plant is situated near the town of Pori, 250 km
north-west of Helsinki
Figure 3. Meri-Pori during construction
Varch 1993 21
-
chosen for opt imum fuel efficiency and NO x reduc-tion. These
swirl burners can run on pulverised coal or oil, and yleld N 0 2
con-c e n t r a t i o n s of b e t w e e n 100 and 200 m g / M J
depending on the type of coal used.
The design was inf lu -enced by a n u m b e r of requirements:
To maximize the rate at which the volatile elements are evolved
from the fuel. To provide an initial oxygen-defi-cient zone to
minimize NO x forma-tion, but provide sufficient oxygen to maintain
a stable fame To optimise both the residence time and the
temperature under fuel - r ich condit ions, to minimize NO x
formation To maximize char residence time under fuel-rich
conditions, to reduce the potential for the formation of char
nitro-gen oxide To add the remaining air in such a way that c o m
-plete fuel b u r n - o u t s ensured.
A further requirement is that the fame should have an oxidising
envelope, to minimize possible corro -sin of the furnace wall.
Key e l e m e n t s of the HTNR burner design are the in t
roduct ion of axia l swirl generation, which is inherently more
stable than radial generation, and the use of a stabilizing ring to
promote rapid and stable ignition.
Staged combustin, as used in the HTNR burner, is widely
regard-ed as the most effective way to minimize N O x p roduct ion
in the boiler, as it promotes localised fuel-rich conditions and
reduces the for-mation of both thermal and fuel -derived NO x .
The burners will yield N 0 2 con-centrat ions of between 100 and
200 mg/MJ in the flue gas leaving the boiler. These levis will be
reduced by subsequent catalytic con-versin. Catalytic converters:
Catalytic converters are fit-ted to reduce the NO x lev-is further.
The Babcock-Hitachi system supplied by Tampella Power includes an
ammon ia process ing unit, a network of spray jets and a catalyt ic
con -verter , wh ich is located
between the feedwater preheater and the air preheater. The
temper-ature in this rea is around 350C, which is the optimum
temperature for the reaction. Additional catalyt-ic layers should
be installed after 3-4 years, and the total expected life of the
catalyst is seven years.
Ammonia will be fed into the flue gas flow prior to the
converter and the process has been designed to keep ammonia
concentrations in the post-converter stage as low as
Figure 5. The desulphuriza-tion process
possible, to no more than 4 ppm, which will have no impact on
out-side air quality.
After passing through the cat-alytic converter, the flue gas
will have an N 0 2 content of no more than 70 mg/MJ and it is
expected that overall, the system will achieve an 80 per cent
reduction in nitrogen oxide levis compared to older boil-er
designs. Removal of particulates: Following the cata lyt ic
converter , the f lue gases will be fed to the electrostat-
ic precipitators for dust Figure 4. remova l . These wi l l be
Additional dual -chamber, four- f ield coal delivery systems and
after pass- equipment ing t h r o u g h t h e m , the has been dust
content of the flue added to the gas will be a mximum of existing
100 mg/nm 3 (wet). facilities that
A p r o p o r t i o n of the dellver coal r e m a i n i n g p a
r t i c u l a t e to the matter wi l l be removed Tahkoluoto
dur ing the d e s u l p h u r i z a t i o n power plant process,
after which the particulate content will be no more than 50 mg /nm
3 (wet), which is equivalent to 20 mg/MJ.
Overall, 99.5 per cent of the fly ash in the flue gas stream
will be removed. This will be around 150 000 t/yr and it will be
held in two silos, each with a volume of 3000 m 3 , prior to being
recycled either for use in the construction industry, or for
disposal in a landfill site.
B o i l e r The boiler at Meri-Pori
is a Benson once-through supercritical design and has been s u p
p l i e d by T a m p e l l a Power of Finland. It will burn
pulver-ized coal, with oil used for start-up, and will produce
440 kg/s of live steam at 240 bar and 540C, while reheat steam
conditions will be 48 bar and 560C.
The boiler house is 77 m high and the boiler's
size means that pulverized fuel is the best option. This also
has the advantages of good combust in efficiency and low operating
cost.
The 30 burners arranged at five levis will be fed with
pulverized coal by five MPS milis manufac-tured by Deutsche
Babcock, each with a capacity of 52 t /h . These feature a rotary
classifier for better particle separation.
At full boiler load four milis will be used mostly, with the
fifth as a s tandby . The coal wi l l be pur -
chased w o r l d w i d e , but Figure 6. The main ly f rom C o l
u m b i a boiler is fitted and Poland. The boiler with 30 HTNR has
been designed for 16 burners, six at different bituminous coal each
burner t y p e s , w h i c h wi l l have level ca lo r i f i c v a
l e s in the range 26.0 - 32.1 MJ/kg.
S t e a m t u r b i n e The s t e a m t u r b i n e ,
which is being supplied by ABB Stal, comprises f ive react ion
ax ia l - f low turbine sections:
March 1993 23
-
Figure 7. The burners feature axial swirl-generation and a
stabilizing ring to promote rapid and stable ignition
one single-f low high pressure (HP) section one double - f low
intermedate pressure (IP) section three double-flow low pressure
(LP) sections.
These are connected coaxially, by integral forged coupling
flanges, to the generator and the slip-ring unit. The whole train
is supported on eight bearing pedestals; one at each end of the
rotor train and one oetween each individual rotor and slip-ring
shaft.
Each bearing pedestal, except the one between the HP and IP
sections, has a single Journal bear-ng and is fixed to the
foundation in
all directions. The HP/IP pedestal can move axially, and carries
the axial thrust bearing, integrated with the journal bearing
The HP and IP casings are sup-ported vertically and guided
trans-versely by the bearing pedestals. The casings are axially
connected via the thrust bear ing pedesta l , which is free to move
axially on the 'oundation.
At the side towards the first LP rasing, the IP casing is fixed
axially to its bearing pedestal , which in turn is fixed to the
foundation. Thus when warming up, the IP casing, the thrust bearing
pedestal and the HP casing will be able to slide axi-al ly. The
rotor t ra in fo l lows the movement of the thrust bearing and thus
the axial clearance in the LP turbines can be reduced. Steam path:
Live steam will enter the HP turb ine through the two valve casings
flanged to the outer casing. Each valve casing contains a stop
valve and a control valve.
After expansin through the sin-g le - f low b lad ing , the
steam wil l eave the exhaust rea for reheat-ng, with some being
extracted for
'eedwater heating. The reheated steam will be admitted to the IP
tur-bine through the connections to the two combined stop and
intercept .alves located on each side of the turbine.
Af ter expans in th rough the double-flow IP turbine blading,
the steam wil l enter the IP exhaust rea. A g a i n , s o m e s
team f rom
ging of combustin air low-NO x burners
Overfire air
Fuel and
primary air
1000C
1200C Completion of
combustin
800C
CO+ I2 O2 CO2
Secondary Tertiary air a i r NO
Nh N2 + O2 Fuelj<
nitrogen N 0 \ N 2NO
S
-
Figure 10. The steam turbine which features HP, IP and LP stages
is mounted on spring bases to reduce dynamic loads on the
foundation structure
C o n t r o l s y s t e m The automation system at Meri-
Pori was supplied by Siemens and is based on the c o m p a n y '
s "e leperm ME technology, devel -:oed for power plant use.
The system is made up of intelli-gent l/O modules, which enable
a modular f o r m a t i o n of f u n c t i o n groups to be
assembled, depend-i g on the mechanical structure a~d operation of
the power plant. In :rs way, the Teleperm ME system :an be applied
to all apsects of rower plant automation, including : r otect ion ,
interlocking, measure-ment, and closed and open loop controls.
The Meri-Pori system comprises tne following elements: Main
automation system, includ-ng automation for the boiler, tur-bine
and turbine-related process :a-ts
Automation of the desulphuriza-ron plant Coal t r a n s p o r t
s y s t e m =Jtomation
Burner and sootblower automa-tion (acting as a subcontractor to
the boiler supplier)
i Auxiliary switchgear automation It includes two different bus
sys-"s; the CS275 bus and the sys-
m coupling bus, both of which nave redundant st ructures . The
system coupl ing bus is used to
nnect all the process stations t need data exchange, such as
rxotection signis and interlocking signis.
The CS275 bus connects the AS 220 EA automation systems, ttie
OS256-6 operating systems, t re Simatic S5 programmable logic
:ontrol lers f i tted to the auxil iary ooiler plant and the water
treatment plant, the workstations for system -a intenance, and the
information system (process computer).
Both main systems (boiler and ine) and the auxiliary systems
sulphurization, coal transport, _c) have the i r own buses
and
rating systems. The two buses
ing system, one for the information system and one for the
process computer.
The whole plant is operated and controlled via the monitors,
using the OS256 -6 operat ing system. The OS system also includes
a
. Absolute f x point, bearing I 9 casing/outer casing V anchored
on foundation
Relative fix point, inner casing fixed inside outer casing
Relative fix point, O positionof rotor train in
thrust bearing casing
Inner "casing ^Outer
casing _ Rotor
train
are linked via a bus connector for data exchange.
C o n t r o l r o o m The control room is designed to
be manned by one operator and one supervisor. However, the
con-trol desk s designed so that during start up and shut down, a
second operator can be accommodated. Both parts of the contro l
board have four monitors for the operat
Sicomp M56 computer, with the IS information system for
displaying and storing such information as alarms and limit switch
signis. It is also used for displaying curves and functional
operating points and as a gateway to other systems.
Due to this extensive automa-tion, when it enters service
Meri-Pori will require only around forty operating personnel, plus
mainte-
Figure 11. Thermal expansin of the steam turbine train
nance staff. Figure 12. The power plant control room
1993 27
-
Schematic diagram
-
| Schematic diagram
HT-NR BURNER
Coal and prlmary air Tertiary Fame
air stabilizing ring
A. Combustin zone of volatile matter B. Production zone of
reducing species C. NOx decomposition D. Char oxidizing zone
MERI PORI FINLANDIA 560 MWe
Key 1 Coal yard 23 Gypsum silo 2 Coal conveyor 24 Ash silo 3
Coal silo 25 Main condnsate pump 4 Coal feeder 26 Low-pressure
preheater 5 Coal mili 27 Feed-water tank (FW) 6 Coal burners 28
Turbine driven FW-pump 7 Forced-draught fan 29 High-pressure
preheater 8 Mill-airfan 30 Economiser 9 Air preheater 31
Evaporator
10 Ammonia supply 32 Superheater 11 NOx catalyst 33 HP turbine
12 Electrostatic precipitator 34 Reheater 13 Induced-draught fan 35
IP-turbine 14 Desulphurization absorber 36 LP-turbine 15 Absorbent
circulation 37 Condenser 16 Demisters 38 Cooling water pump 17 Flue
gas reheater 39 Turbogenerator 18 Stack 40 Main transformen 19
Gypsum dewatering 41 Control room 20 Effluent 42 Boiler house 21
Process Water 43 Turbine hall 22 Limestone silo 44 Switch yard