AEROSOL EMISSIONS FROM DUTCH COAL-FIRED POWER STATIONS
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AEROSOL EMISSIONS FROM DUTCH COAL-FIRED POWER STATIONS
R. Meij, B.H. te Winkel, H. Spoelstra and J.J. Erbrink
KEMA; Utrechteseweg 310, 6812 AR Arnhem, the Netherlands
+31-26-3 56 22 25, Fax +31-26-4 45 46 59, ruud.meij@kema.com
Keywords: coal-fired power station, coal fly ash, emissions, fugitive dust, combustion aerosols,
PM10, PM2.5
ABSTRACT
Particulate emissions from coal-fired power stations in the Netherlands have decreased considera-
bly. Before 1980 the particulate loadings (PL) wereThe Netherlands Ministry of Economic Affairs strongly urged the owners of the power stations to
reintroduce coal for the generation of electricity. Six existing units were reconverted for firing coal,
four units were converted form gas/oil firing to coal firing and five new power stations were erected
between 1980 and 1991.
The source of the coal supplies in the nineteen-fifties and earlier was mainly the Dutch mines,
which produced anthracite. The Dutch collieries were closed in the nineteen-sixties. Nowadays, all
the coal is imported from all over the world, resulting in a greater variation in the composition, and
in particular coal with a higher content of volatile matter (bituminous coal).
Description of coal-fired power stations in the Netherlands
Eight coal-fired power units, aged between 16 and
26 years old, are in operation at present in the
Netherlands; seven units are conventional and
one unit is an Integrated Shell coal Gasification
Combined Cycle (IGCC) unit. Essent, Nuon,
E.ON, EPZ (Essent and Delta) and Electrabel are
the owners of the units. The total installed net ca-
pacity of these coal-fired plants is 4,173 MWe. It is
expected that the units providing this capacity will
remain in service for the coming years. Nuon,
E.ON and Electrabel foresee expansion of coal-
fired generating capacity. Reducing CO2 emis-
sions is the goal nowadays. An agreement was
made between the Dutch government and the
electricity producing companies to reduce the CO2
emissions by 3 million tons in 2008. In practice,
Figure 1 Materials flows associated with a this means that about 13% of the coal by energy
coal-fired power station with a net or about 20% by dry mass will need to be re-
capacity of 600 MWe placed by secondary fuel. A typical unit is shown
in Fig. 1.
pulverised fly dust Pathway of ash through the power sta-
fuel ash (stack) tion
87,8% 0,04% When coal is burned in the boiler, non-
combustible materials are left behind in the
form of ash. On average, the coal fired in
the Netherlands consists of 14 per cent
non-combustible materials. These materi-
Boiler
als are principally sand and stony residues
ash in + fly ash 0,2% FGD left in the coal. If the ash cakes together
coal ESP
and becomes sufficiently heavy it will drop
to the bottom of the boiler where it is
caught in water. When the lumps of ash
cool off they disintegrate to form bottom
bottom gypsum and ash or slag. The remainder of the ash is
ash 12% sludge made up of particles that are so fine that
0,16% they are captured in the flue gases and “fly
away”. This ash is consequently known as
fly ash. The ratio of bottom ash to fly ash is
Figure 2 The distribution of ash flows about 12 to 88. The captured fly ash
reaches temperatures of between 1000
-2-and 1500 °C causing it to melt. As a result, the ash forms glassy globules which are then largely
removed from the flue gases using filters. All the flue gas filters used in the Netherlands are of the
high efficiency electrostatic type, or ESPs. A very high proportion of the fly ash, on average
99.75 per cent, can be removed by installing several such filters in series. The associated particu-
late loadings in the flue gas are on average 25 mg•m-3. The collected fly ash is referred to as pul-
verised fuel ash, while the portion which remains in the flue gases is simply termed fly ash. During
combustion, nearly all the sulphur in the coal is converted into sulphur dioxide (SO2). An average
of 90-92 per cent of this sulphur dioxide is removed from the flue gases using a flue gas desul-
phurisation (FGD) system. Other substances, such as fly ash and other gaseous compounds, are
also removed. About 80 per cent of the fly ash entering an FGD system is extracted. Between
them, therefore, the ESPs and the FGD system remove 99.96 per cent of all fly ash, so that only
about 0.04 per cent of the fly ash from the coal is ultimately released into the atmosphere. The as-
sociated flue gas concentration is on average 5 mg•m0-3.
Use of an FGD system involves the creation of additional materials flows. Calcium or limestone is
used, while gypsum and waste water are produced. The waste water is treated in a waste water
treatment (purification) plant (WWTP) before discharge into surface waters. The waste water treat-
ment plant in turn produces sludge. The various materials flows associated with a 600 MWe (net)
coal-fired power station and the distribution of the ash are shown in Fig. 2. The present generation
of coal-fired power stations in the Netherlands is fitted with various modern systems for cleaning
flue gases (DeNOx, ESP and FGD) enabling coal to be used to generate electricity in a responsi-
ble manner with minimal adverse environmental consequences. The generating process has a
number of by-products: bottom ash, pulverised fuel ash and gypsum. These by-products are used
as building materials: bottom ash as foundations in road building, pulverised fuel ash mainly in the
cement and concrete industry and gypsum in plasterboard and gypsum floors. The various ash
flows together with their principal properties are listed in Table 1. Distribution between the different
flows is indicated in both Table 1 and Fig. 2. Summarizing, the largest ash flow is that from the
ESP. This (fly) ash is referred to as pulverised fuel ash (PFA), partly to make it clear that it comes
from pulverised coal boilers and partly to distinguish it from the material released into the atmos-
phere from the stack. The latter is referred to as fly ash or fly dust. The term “fly ash” is used to re-
fer to material from plants without FGD systems (of which there are no longer any in the Nether-
lands), while the term “fly dust” is applied to material from plants with FGD systems. In the interna-
tional literature PFA is mostly called coal fly ash (CFA). It will be apparent from Table 1 that the
various ash types differ from one another greatly in terms of particle size.
Table 1 Nomenclature applied in the Netherlands to ash flows from coal-fired power stations
Term Definition Percentage of Particle size
all ash
Bottom ash Collected at bottom of Coarse
boiler
Pulverised fuel ash Removed from flue 50% of the overall mass
(ESP ash), mostly gases by ESP made up of particles
called coal fly ash smaller than 30 µm
(CFA) in interna-
tional literature
Fly ash In flue gases after pass- 50% of the overall mass
ing through ESP and (in made up of particles
plants without FGD sys- smaller than 3 µm
tem) in the stack
Fly dust In flue gases in the stack 50% of the overall mass
(after passing through made up of particles
FGD system) smaller than 0.3 µm
-3-The contributions made by coal-fired power stations to the ambient air fine dust concentrations for
a) the stack emissions and b) the fugitive dust of coal fly ash storages, coal piles and biomass are
discussed in this paper.
METHODS
The particle size distribution of the fly dust in the stack was determined with an Anderson cascade
impactor, type MARK III, and the particle size distribution of the PFA (CFA) was determined by la-
ser granulometry (Malvern). STACKS calculated the dispersion and depositions. This model has
been described in a thesis [Erbrink, 1995]. The meteorological data for Schiphol for the five-year
period 1995-1999 was used. The calculations were carried out for an area of 40 x 40 km around
the power station. The distance between grid points was 2000 metres, thus 441 grid points were
taken into consideration. The KEMA 3D Model® (3D=Dust, Dispersion, Deposition) was used to de-
termine the atmospheric concentrations of airborne pulverised fuel ash and coal and the associated
depositions. This model is derived from STACKS. The emission factors used in the model are
based on a long term measuring programme at the Maasvlakte power station.
RESULTS AND DISCUSSION
Historical view of stack emissions of particulates
Fly ash was removed from the flue gases in the nineteen-fifties and sixties of the last century by
cyclones, modaves (a kind of wet scrubbers) and electrostatic precipitators (ESP). Their removal
efficiencies and the final particulate concentrations in the stack are given in Table 2. All particulate
concentrations quoted in the paper apply to an oxygen concentration in the flue gases of 6% and at
standard conditions (P, T).
Table 2 Different types of dust collectors with their removal efficiency and final particulate con-
centrations (yearly averaged values)
Period type of dust collector removal efficiency final particulate concentra-
tions in mg•mstd-3
cyclones 90%
1960-1980 modaves 95%about one per cent of the emissions in 1965. The introduction of FGD has resulted in a drastic re-
duction of 95% since 1980.
12,000
10,000
8,000 PM oil
ton/year
PM coal
6,000
4,000
2,000
0
1980 1982 1984 1986 1988 1990 1992 1994 199 1998 2000 2002 2004 2006
6
year
Figure 3 Particulate emissions from the Dutch power stations between 1980-2005
Particulate matter loadings downstream of high efficiency ESPs
In the early nineteen-eighties KEMA performed a great deal of research into emissions of fly ash
from Dutch coal-fired power stations [Meij et al., 1985]. It appeared that:
a) there is no relation between the ash content of the coal and emissions,
b) the most important parameter is the resistivity of the ash. Where there is high resistivity the dust
layer will act as an insulator and where there is low resistivity the dust layer is difficult to re-
move.
The dominating factor is the sulphur content of the coal. With sulphur content of less than 0.6% in
the coal other compounds become more important in this respect, while at sulphur contents of
about 0.4% the ESP operates less efficiently. SO3 addition could be a solution. The collection effi-
ciency is influenced positively where S >> Na > Fe, K and negatively by Ca, Mg > Si and Al [Meij et
al., 1985; Meij et al., 2005]. In general it can be said that it becomes critical if S (in the coal) < 0.4-
0.6% and if Na2O + K2O < 1–1.5% and/or MgO + SiO2 + Al2O3 + CaO > 85% applies for the ash.
The collection efficiency can be influenced by temperature, water vapour content of the flue gases,
supply of particulate matter and particle size distribution as well as these chemical influences. It
appears that the annual average concentrations for most of the installations are ~20±10 mgmstd-3
downstream of the ESP. When coal which produces ash with a high resistivity is fired, concentra-
tions can sometimes be as high as 50 mg•mstd-3. Technical problems of the ESP can sometimes
also cause an increase in the concentrations to 50 mg•mstd-3. There is always a low probability of
particulate loadings reaching 100 mg•mstd-3 when adverse circumstances accumulate (both low re-
sistivity ash and technical problems).
Particulate loadings downstream of wet FGDs
It appeared that between 80-90% of particulates is removed from the flue gases in a wet FGD.
Measurements were performed at concentrations between 1 and 100 mgmstd-3 upstream of the
FGD. In the latter case these concentrations were achieved by closing down several sections of
the ESP. Elaborated studies of particulates emitted downstream of the FGD have been carried out
four times by KEMA for full coal firing in 1986 [Meij, 1989] and for >10% co-combustion in 2003
[Meij and Te Winkel, 2004a], 2004 [Meij, 2006] and 2006 [Meij, 2007]. It was demonstrated then
-5-that the particulate loadings are drastically lowered (70-90%) in the FGD plant with a concomitant
decrease in particle size distribution. The concentrations of the macro elements, except for Ca,
were lowered drastically (by a factor of about 2). The original fly ash is diluted with other dust
sources, such as evaporated droplets and gypsum and/or limestone particles. On average 50% of
the fly dust consists of fly ash. Therefore, one can no longer speak of fly ash and the term "fly dust"
was introduced for this purpose. The conclusion is that the working of the demisters is the most
important factor for the particulate loadings in the stack and that there is no relation anymore with
the fuel composition, provided that the particulate loadings upstream FGD are low.
Particulate loadings downstream of wet FGDs during co-combustion of secondary fuels
The research of the past ten years has concentrated on the question of what happens if secondary
fuels are co-combusted. After all co-combustion of secondary fuel, such as biomass, is daily prac-
tice. However, not many changes could be observed. This is not surprising since the influence of
fuel composition is in most cases no longer important.
100
aerodynamic diameter in µm
10
1
0,1
0.1 1 2 5 10 20 30 50 70 80 90 95 98 99 99.9
Cumulative smaller than [%]
Figure 4 Log probability plot of the particle size distribution upstream and downstream of FGD at
Gelderland power station on day 1[Meij, 1989]
The present particulate loadings
The present particulate loadings on an annual average basis are < 5 mg•mstd-3 with a range up to
80% of 100 mg•mstd-3 equal to 20 mg•mstd-3 (see discussions in the previous sections). It is not pos-
sible to provide accurate figures below 5 mg•mstd-3 (see discussions in Meij and Te Winkel, 2005).
These figures are in agreement with AEL values (Associated Emission Levels) of 5-20 mg•mstd-3,
which are linked to the Best Available Technique (BAT) and mentioned in documents of the Inte-
grated Pollution Prevention and Control (IPPC) guidelines of the EU concerning existing coal-fired
stations. The EU guideline for large combustion plants (LCP) mentions particulate loadings of
30 mg•mstd-3. The Dutch implementation of the LCP, which is named the BEES-A (Besluit Emissie-
Eisen Stookinstallaties Milieubeheer), has a more stringent value of 20 mg•mstd-3. A further de-
crease is technically and economically not possible for the existing installations. The Waste Incin-
eration Directive (WID), which is also more stringent in the Netherlands (named the Besluit Ver-
-6-branden van Afval (BVA)), also applies to co-combustion. The mixing rule has to be used, with a value of 20 mg•mstd-3 for the share of the coal and 7.5 mg•mstd-3 for the share of the biomass part. Only the fine particles remain given the existing high degree of removals (99.96%). The particulate loading is entirely in the PM2.5 category (see Fig. 4). However, the share of the very harmful ultra fine particles (
The secondary aerosols (NH4)2SO4 and NH4NO3 also contribute to the PM10 level. These com-
pounds are conversion products from the original gaseous emissions of SO2, NOx and NH3. The
conversion rate is slow, so the effect occurs over a longer period of time. This means that there is
no local influence on the PM10 ambient air concentrations. After 100 km no more than 3 per cent
has been converted and the flue gases are completely diluted [Meij and Erbrink, 2001]. The sec-
ondary aerosols are more of a problem at a continental level. Therefore, KEMA calculated the in-
fluence of secondary aerosols originating from all of the power stations (coal, oil and gas) in the
European Union on the ambient PM10 levels. If the SO2 and NOx emissions from all of these power
stations for the year 1990 had been reduced by 50 per cent, the model predicts that, on average,
the PM10 concentrations would have been reduced by 10 per cent. The influence of secondary
aerosols emitted by power stations on the PM10 level is of secondary importance [Erbrink et al.
1997; Meij and Erbrink, 2001]. Model calculations performed by RIVM confirmed these results
[Aben et al., 2002]. Exposures of rats to these secondary aerosols did not show any effects [Aben
et al., 2002], so it appears that secondary aerosols do not play an important role in the adverse
effects of fine dust.
Total wet and dry fly dust deposition over a 40 x 40 kilometres square area around the power sta-
tion averages 1.7 milligrams per square metre per year, with a maximum of 25 milligrams per
square metre per year. Depositions of this order will not cause any nuisance and are negligible
[Meij and Te Winkel, 2003 and 2004a].
Coal fly ash storage
The pulverised fuel ash (PFA or coal fly ash (CFA)) is normally stored in closed silos. Ash that
does not meet the specifications for applications or when the silos are full are the only reasons for
a temporary storage of PFA on the premises of the power station. Blow away is prevented by good
housekeeping and wetting of the surface of the storage.
The particle size distribution in pulverised fuel ash was determined on the basis of the internation-
ally accepted differentiation between an inhalable fraction (PM50, consisting of larger particles), a
fine fraction (PM10) and a respirable fraction (PM4). An additional very fine fraction was also de-
fined (PM2.5) in order to assess the implications for high-risk groups, such as small children and
CNSLD sufferers, [Meij et al., 2001b and 2001c]. The results are presented in Table 3.
Table 3 Particle size distribution of PFA (coal fly ash) expressed in terms of aerodynamic
diameter
aerodynamic particle size distribution part of total PFA (%) PM4/PM50
diameter D10 D50 D90 PM2.5 PM4 PM10 PM50 %
(µm) (µm) (µm)
mean 6.5 31.0 131.0 1.3 4.6 19.9 54.7 8.4
stand. dev. 0.3 4.8 15.6 0.2 0.5 1.8 2.8 0.6
v (%) 5 16 12 12 11 9 5 7
minimal 5.8 23.2 104.8 1.2 4.1 17.1 49.1 7.6
maximal 7.0 43.0 157.5 1.7 5.9 24.0 59.9 9.8
N 17 17 17 17 17 17 17 17
range according to 95% confidence interval
mean–2*std 5.9 21.3 99.7 1.0 3.6 16.2 49.2 7.3
mean+2*std 7.2 40.6 162.3 1.7 5.6 23.5 60.3 9.5
Ten per cent of the mass of pulverised fuel ash is accounted for by particles of less than
4.5 micrometres in diameter (± 0.2 micrometres). Fifty per cent of the mass consists of particles of
less than 21.4 micrometres (± 3.2 micrometres). Particles of less than 90.4 micrometres
-8-1000
300 900
800
250
700
200 600
µg/m3 150 500 m
400
100
300
50
200
250-300
900
0 100
600200-250
1000
µg.m -3 0
800
150-200
0
100
200
300
400
500
600
700
800
900
1000
300
600
m
100-150
400
m 0 m
200
50-100
0
0-2 2-4 4-6 6-8 8-10
0-50
Figure 6 Annual ground level concentrations of inhalable PFA on and around an open storage of
PFA in µg•m-3
(± 10.8 micrometres) make up 90 per cent of the mass. The diameters are expressed as their
geometric or projected diameters. The proportions of the mass accounted for by inhalable
particulate material (PM50), fine particulate material (PM10), respirable particulate material (PM4) and
very fine particulate material (PM2.5) average 55 per cent, 20 per cent, 5 per cent and 1 per cent,
respectively.
Model calculations of the airborne dispersal of pulverised fuel ash at and near a storage site indicate
that, in the area where people work, concentrations of the inhalable suspended pulverised fuel ash
average 0.07 milligrams per cubic metre. Concentrations of the respirable fraction average
0.006 milligrams per cubic metre. In the course of a year, the highest hourly average
concentrations of the inhalable fraction in that area are between 0.8 and 7.5 milligrams per cubic
metre depending on the precise location, while concentrations of the respirable fraction are
between 0.1 and 0.9 milligrams per cubic metre. The TLV for inhalable particulate material is
10 milligrams per cubic metre and the corresponding figure for respirable particulate material is
5 milligrams per cubic metre. These TLVs are eight-hour average figures; transient concentrations
up to twice these values are permitted. The model calculations indicated that neither TLV was
exceeded in any hour or at any location.
Around the perimeter of the site, where members of the public may be exposed, the annual average
concentrations of fine particulate pulverised fuel ash are up to 2.6 micrograms per cubic metre. The
highest hourly average concentration in the course of a year is at the northern perimeter, where
meteorological conditions could result in 31 micrograms per cubic metre being reached. This would
increase the annual average background concentration of fine particulate material by up to 6.5 per
cent. This is within the range of natural variations in background concentrations and therefore
negligible. The results concerning the inhalable fraction are presented in Fig. 6 and the results
concerning the PM10 concentrations are presented in Table 5 [Meij et al., 2001c].
-9-Table 5 Statistical results of yearly averaged suspended PM10 PFA in µg•m-3 with their percen-
tiles, based on percentiles of daily averaged values at 500 metres from the centre of the
storage (for X and Y see Fig. 5).
number of days in 3 years 545 109 54 22 3 1
number of days in 1 year 183 37 18 1 week 1 day
µg.m-3 mean P50 P90 P95 P98 P99.7 max.
x y PM10 of PFA (coal fly ash)
0 1000 0.9 0.00 2.9 5.5 9 15 26
100 1000 1.0 0.00 2.8 5.9 10 20 23
200 1000 1.0 0.00 3.5 5.8 11 19 22
300 1000 1.3 0.00 4.6 7.5 12 18 25
400 1000 1.7 0.00 5.9 8.8 13 22 33
500 1000 2.3 0.07 7.1 11.3 16 31 48
600 1000 2.5 0.45 8.3 11.0 16 24 31
700 1000 2.6 0.70 8.0 10.5 16 23 27
800 1000 2.0 0.53 6.2 8.2 12 17 22
900 1000 1.4 0.40 4.3 6.5 9 16 24
1000 1000 1.2 0.33 3.4 5.1 7 13 20
Deposition five hundred metres from the centre of the source is between 0.4 and 1.9 grams per
square metre per month, i.e. around the subjective nuisance threshold. The HESP model was used
to calculate what the consequences of prolonged deposition (i.e. deposition over a period of a
hundred years) of pulverised fuel ash on the soil would be for human health. For the purpose of the
calculations, it was assumed that meat, milk, eggs and vegetables from the deposition area would
be consumed. The calculations indicated that the acceptable daily intake (ADI) values for the
various elements found in pulverised fuel ash would not be exceeded. Small children form a
special group in relation to exposure via deposition, because of their inclination to put anything
they find in their mouths. On the basis of worst case assumptions, it was calculated that a small child
could swallow as much as 0.1 grams of pulverised fuel ash. Given the composition of pulverised fuel
ash, the insolubility of the ash particles and the leachable nature of the elements concerned, it is
believed that effective intake by the body would be too small for adverse effects to result [Meij et al.,
2001c].
The number of particles is also an important factor for health studies. An estimate of the numbers
of particles present in PFA has been made based on the density, shape and particle size. The re-
sults are presented in Table 6 [Meij et al., 2001c].
Table 6 Number of particles per kilogram PFA
class fraction % based on weight number of particles per kg PFA
TSPM 100 3.63•1012
PM2.5 1.3 8.26•1011
PM4 4.6 1.90•1012
PM10 19.9 3.17•1012
PM50 54.7 3.31•1012
- 10 -Table 7 Relative distribution of different particle sizes of suspended coal
fraction abbreviation % of TSP
inhalable PM50 41
fine dust PM10 2
respirable PM4 0.7
very fine dust PM2.5 0.4
ratio PM4 / PM50 0.02
ratio PM10 / PM50 0.04
Coal storage
Airborne coal dust is relatively coarse with a particle size up to 260 µm. At a distance of tens of
metres from the source 50% of the mass is accounted for by particles greater than 50 - 100 µm
(aerodynamic diameter). The health-related harmful effects are associated with the fine particles.
This means that the inhalable portion (PM50), the fine portion (PM10), the respirable portion (PM4)
and the very fine portion (PM2.5) are of importance. On average, these portions account for 41%,
2%, 0.7% and 0.4% respectively (see Table 7).
A coal-fired power station of net 600 MWe consumes about 1.2 million tons of coal a year. During
transfer, about 0.0014% could blow away, equal to 13 - 16 metric tons a year. Coal dust particles
are relatively coarse so that the majority will be deposited on the site itself. Furthermore, fugitive
dust can be generated by wind erosion of stored coal, the quantities involved being comparable to
those associated with transfer (13 metric tons a year). Emission prevention measures at the coal
store at Gelderland Power Station prevented KEMA making any airborne dust measurements.
However, it should be noted that the measurements related to a relatively short time period only.
People living in the vicinity of a coal-fired power station can be exposed to airborne coal dust. The
maximum exposure occurs at least 500 metres from the source. At this distance, the annual aver-
age overall coal dust concentration in the air is 0.5 micrograms per cubic metre, with a maximum
daily average value of 9 micrograms per cubic metre. A limit value of 40 micrograms per cubic me-
tre exists for the fine fraction (PM10) in the ambient air. Coal dust is rather coarse, consisting of
only about 2% fine dust. At a distance of 500 metres from the source, the proportion of fine dust
will be greater, but it is plausible that the dispersal of coal dust does not lead to the recommended
limits for fine particulate material being exceeded. The deposition of coal dust is calculated to be
2.8 grams per square metre at a distance of 500 metres from the source. These values are not suf-
ficient for the dust to be perceived as a nuisance.
Secondary fuel storage
Secondary fuel or biomass, predominantly stored in closed silos, is co-combusted at almost all
coal-fired power stations on a routine basis. In some rare cases this fuel is mixed with the coal in
the coal yard but covered by a coal layer. No fine dust of this origin will be blown away in the envi-
ronment.
CONCLUSIONS
• The emission of particulate matter from the stack of a coal-fired power station influences the
local environment by increasing the atmospheric concentrations and the levels of wet and dry
deposition of the substances in question. However, the currently prevailing concentrations and
levels of deposition are only to a small extent attributable to such emissions.
• People living in the vicinity of a coal-fired power station with an open pulverised fuel ash storage
facility may be exposed to airborne pulverised fuel ash. In absolute terms, the concentrations
involved are low and negligible in relation to normal background levels. Hence, the airborne
- 11 -dispersal of pulverised fuel ash does not lead to the recommended limits for fine particulate
material being exceeded. The amount of pulverised fuel ash deposited near to the perimeter of
the site could be perceived as a nuisance, but is not sufficient to constitute a health hazard.
• Airborne coal dust is relatively coarse, therefore dispersion does not take place over large dis-
tances. Calculations indicate that the levels of exposure beyond the power station site are low.
Furthermore, the levels of deposition are sufficiently low so that no nuisance is to be expected.
• Biomass is stored in silos and no blow away will occur.
ACKNOWLEDGEMENTS
The project described in this paper was carried out within the framework of the Technical Service
Agreement placed with KEMA by the five electricity generating companies in the Netherlands:
Electrabel Nederland N.V., E.ON Benelux, EPZ, Essent Energie Productie and Nuon Power Gen-
eration.
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