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Environmental Issues and Kiln Firing.

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Dev. Chem. Eng. Mineral Process., 7(5/6), pp.463-482, 1999.
Environmental Issues and Kiln Firing
N. Syred
School of Engineering, CardiHUniversity, PO Box 685, The Parade,
CardiH CF2 3TA, South Wales, UK
It is not necessary to repeat the well known concerns about environmental issues
and how they affect the design and operation of combustion processes. In this
paper I wish to describe recent experiences in this area and how engineers can
react to the associated issues. A UK content will be used and discussions will be
made about how this relates to the global situation.
Introduction
Environmental concerns are generally formed on the basis of human health effects
of pollutants, acidification, smogs, plant/wildlife effects and global warming.
Sulphur dioxide and oxides of nitrogen are established contributors to human
respiratory conditions as well as directly related to the long range acidification of
lakes, rivers and land. Carbon dioxide is a major contributor to global warming.
Fine particulate matter is suspected as a factor in respiratory illness and contains
heavy metals from the combustion of coal wastes and oil. Some of the pollutants
emitted in lesser quantities such as polyaromatic hydrocarbons are known to be
carcinogenic. Releases to water may include metals and their salts, many of
which are harmful to wildlife and may also affect subsequent use of the water.
The heat rejected in the cooling water returned to rivers can have a significant
effect on their ability to support fish populations. The need to dispose of ash
and/or wastes imposes a significant environmental effect on the land and may be
463
N. Syred
augmented, for example, by the need to mine limestone and dispose of waste from
abatement processes.
It is clear that there is a need for control of releases from kiln processes to all
three environmental media. There may be choices to be made between media and
control measures aimed at reducing pollution in one may have effects in another.
General information on plant performance is available on the Public Register, held
by the Health & Safety Executive, UK [HSE].
The UK and European Experience
In Britain, integrated pollution control was introduced in 1990 by the
Environmental Protection Act [EPA90]. The act requires the use of the best
available techniques not entailing excessive cost [BATNEEC] to prevent or, if
that is not practicable, to minimise the release of prescribed substances; also to
render harmless any prescribed substances which are released or any other
substances which might cause harm. When a process is likely to involve releases
to more than one medium, the best practicable environmental option [BPEO] must
be achieved by the use of BATNEEC to ensure the least effect on the
environment.
The Environment Act 1995 transferred the implementation of these
requirements to the Environment Agency in England and Wales and to the
Scottish Environmental Protection Agency in Scotland. It also introduced into
law the concept of sustainability which may widen the boundaries within which
control of a process is excercised.
In England and Wales, the responsibility for the control of pollution to air by
the smaller, less polluting processes rests with the local authorities. The 1990 Act
also requires conformance with any legal environmental quality standard or
Directive.
Other countries are moving towards integrated control and in particular the
recently adopted Integrated Pollution Prevention and Control Directive will affect
all EU countries. It closely reflects British experience, but prescribes a somewhat
464
Environmental issues and kiln firing
wider range of processes for control. It covers the energy industries, production
and processing of metals, the minerals and chemicals industries, waste
management and a wide range of other activities including some food processing
and animal rearing.
Within combustion, it covers installations with a rated
thermal input exceeding 50 MW.
The United Nations Economic Commission for Europe W C E ] was
responsible for the 1979 Convention on Long Range Transboundary Air
Pollution. The 1985 Protocol on the Reduction of Sulphur Emissions committed
the parties to a 30% cut in emissions by 1993, based on 1980 levels. The 1994
Protocol commits the United Kingdom to an 80% cut by 20 10 based on the 1980
levels.
The 1988 Protocol concerning the Control of Emissions of Nitrogen Oxides
committed the parties to reducing their emissions back to 1987 levels by 1994. A
second Protocol on nitrogen oxides is in preparation. The Protocols are based on
the environmental effects of the emissions which include acidification and harm to
human health. The work on acidification is based on the neutralising capacity of
soil and water and hence the “critical loads”.
The European Commission is responding with a proposed Community
Strategy to Combat Acidification which envisages a closing of the gap between
actual emissions and critical loads. Substantial further reductions in emissions
would be required to achieve these proposal.
A Directive on the Sulphur Content of Fuel Oils is proposed as a contributor
to the strategy. This would limit the sulphur content of heavy fuel oil to 1% with
a derogation for plant fitted with abatement equipment which comply with the
Large Combustion Plant Directive [LCPD].
The LCPD dates from 1988 and covers plant in excess of 50 MWth. It gives
emission concentration limits for particulates. sulphur dioxide and oxides of
nitrogen for new plant. Existing plant is included in national annual tonnage
limits for sulphur dioxide and oxides of nitrogen. These are implemented in the
UK through a national plan administered by the Environment Agencies. The
465
N. Syred
Directive is currently under review and there are some interesting implications for
operators and plant suppliers in the
draft
revision. The emission limits are
tightened and are closely in line with what is considered achievable by the
Environment Agency. Clauses on energy efficiency and the usefulness of wastes
are included. There is also a proposal to include gas turbines in the Directive for
the first time.
In Britain, under EPABO, the operator of a proposed process must submit an
application for authorisation and advertise it. The application is made publicly
available for comment. The Inspector assesses the application to ensure that it
meets the requirements of the Act and, when satisfied, writes an authorisation
which contains the emission limits and other conditions which must be met. Each
authorisation is reviewed at not more than four yearly intervals.
In assessing the application, the Inspector uses published Environment
Agency guidance on, for example, BPEO, dispersion and monitoring as well as
the process guidance. Site specific considerations taken into account include
whether the plant is new or existing, its size, local air quality, topography and
housing and the presence of any conservation habitat.
The use of energy in abatement processes, the possible need for chemical
reagents and the disposal of wastes are all potentially environmentally harmful. I
intend to discuss the above in the context of kiln and other firing systems by using
generic examples publically available in the UK.
It is useful here to describe the sort of processes by which emissions from
large plant are characterised. Where, as is usual, releases of pollutants are to more
than one medium, BPEO must be achieved by the use of BATNEEC to ensure the
least effect on the environment as a whole. In the context of existing plant there
are inevitably compromises and differences which have to be settled as the
demand for ever improving efficiency and emission performance increases. Plant
operators are seeking to reduce costs, especially those involving fuel by burning
materials such as scrap tyres, various forms of liquid fuels manufactured from
wastes, petroleum coke, municipal and other wastes. The use of such materials in
466
Environmental issues and kiln firing
existing or indeed new plant gives rise to concerns about emissions which can
only be met by means of the previously discussed BPEO and BATNEEC
approach, and indeed brings conflicts of purpose when dedicated incinerators
have been separately constructed.
A conventional BPEO assessment using the Methodology proposed by the
old HMIP (Her Majesties Inspectorate of Pollution now superseded by the
Environment Agency) normally entails a preliminary assessment of the base case
(the existing situation in the case of established operations) followed by the
generation and assessment of various control options. The approach is modified
when operation with a new fuel is to be considered such that the new modes are
assessed side by side with the base case, whilst still complying with the proposed
methodology.
Assessment of plant performance in terms of BPEO and BATNEEC is based
on analytical data obtained from both test run sampling, analysis programmes as
well as continuous monitoring of results.
During a preliminary assessment the following tasks are carried out:1)
emissions to air, water and land are measured and described;
2)
these are compared to emission levels given in appropriate guidance notes
[CIGN] - this determines the level of control required;
3)
determine the appropriate stack height for emissions to air and determine the
level of control required (if any);
4)
determine Predicted Environmental Concentrations [PECs] of emissions to
air, water and land and compare these with the appropriate Environmental Action
Levels [EALs].
The above process is long, expensive to carry out and extremely complex to
report. I wish to highlight certain areas of the analysis which give pointers to the
future direction of technological development.
467
N.Syred
Table 1 Comparison of Existing, Typical Plant Emissions with .NewPlant CIGN
Values
Substance
CIGN
CoavPet Coke
Release
Concentration
(mp/m3)
Actual Emission
IPR 3/1
Total particulate
matter
Oxides of sulphur
Concentration
(mg/m3)
40% Waste Liquid
Fuel
Actual Emission
Concentration
(mgh’)
50
-15
-15
750
-230
160
(as so3
Oxides of nitrogen
1,500
-630
(as NO#’’
Reference condition for emission conceneations are 273K,
(a)
101.3 Wa,no correction for water vapour or oxygen content.
Semi-dry process, long kiln, no pretalciner
@)
550
The above table shows a typical result comparing CoaVPetroleum Coke
burning with a case where waste liquid fuel at 40% substitution rate was used.
The measurements of course represent long term averages, but show the effect of
the efficiency of well operated electrostatic dust precipitators and burners/plant set
up for low NO, operation. The variations in sulphur emission arise fiom the 40%
substitution of coaYpetroleum coke with waste liquid fuel of very low sulphur
content
The results show considerable benefit from the use of waste liquid fuel in
respect of SOx and NO,, although no comparison is made with a real base case
of 100% firing of a low sulphur bituminous coal.
However in general overall levels of heavy metal emissions (when
normalised by factors which allow - controversially - for their varying toxicity)
increase substantially with such waste liquid fuels. This problem has been
controversially allowed for via a calculation of overall emission indice whereby
increased normalised emissions of heavy metals are traded off against reduced
NOx and sometimes SOx
An important series of parameters are the Environmental Assessment Levels
[EALs] for various pollutants and these are the levels which should be allowed to
468
Environmental issues and kiln firing
occur at ground level. These are divided into long and short term effects with the
greatest emphasis normally occurring with long term effects.
Mandatory Ambient Air Quality Standards
Mandatory ambient air quality standards exist in the UK for four of the pollutants
(i.e. sulphur dioxide, particulates, nitrogen dioxide and lead). These standards are
derived from European Community Directives and are implemented under the Air
Quality Standards Regulations. European Community Directive limit and guide
values for sulphur dioxide, particulates, nitrogen dioxide and lead are summarised
in Table 2.
Long Term Air Quality Guidelines
In the absence of standards applicable to the other substances which may be
emitted from the facility, the following sources of guidelines may be applied in
the following order of preference in accordance with the draft BPEO
methodology:
Air Quality Guidelines for Europe, the World Health Organization
WHO1
These guidelines, published in the WHO Regional Publications European
Series No 23 (1987), are intended to provide background and guidance to
governments in making risk management decisions, particularly in setting air
quality standards.
Other International Organisations
Relevant National Organisations For example, the US EPA IRIS database.
Occupational Exposure limits [OELs] OELs are exposure limits prepared
by the Health and Safely Executive [HSE] designed to protect workers over an
8 hour, 5 day week.
Environmental Assessment Levels [EALs] for the substances where
mandatory standards or nationaVinternationa1 guidelines are not available have
been derived from the HSE exposure limits. A summary of EALs for the
469
N.Syred
Table 2
UK Air Quality Standards based on EC Directives 80/779/EEC,
85/203/EECand 85/2lOEEC
Substance
Sulphur dioxide
Reference Period &
Limit Value
Median of daily mean
values over a year
80 (particulates >40)
120 (particulates 140)
Arithmetic mean of daily
mean values over a year
40-60
98th percentile of daily
mean values over a year
250 particulates>l50)
350 (particulates 4 5 0 )
24 hour daily mean value
Nitrogen dioxide
50th percentile of hourly
mean values over a year
-
98th percentile of hourly
mean values over a year
Lead
Annual mean
concentration
Suspended
particulates (as
measured by the
OECD black
smoke method)
98th percentile of daily
mean values over a year
100-150
50
200
250
40-60
80
,
24 hour daily mean value
470
135
2
Arithmetic mean of daily
mean values over a year
Annual median of daily
mean values over a year
Guide
Value
(pg m’)
-
100-150
Environmental issues and kiln firing
pollutants of interest are presented in Table 3. These do of c o m e change as new
findings and information become available.
The next step in the analysis is to:
1)
use existing data fiom the site/general area to predict background
concentrations of all pollutants arising fiom industry, traffic, agriculture, etc,
2)
use stack emission data to predict environmental concentrations PECs] of
pollutants at ground level in terms of annual and maximum 1 hour mean
increments to ground level concentrations. A typical model used is the All
Terrain Dispersion Model [ATDM]. This model has been developed and
validated for use in complex terrain by the US Environmental Protection
Agency [EPA]. Like many dispersion models currently used for assessment
work, it is based on the concept of the time averaged lateral and vertical
concentration of pollutants in a plume.Topography and terrain effects as well
as the prevailing wind direction are included. Building downwash effects
are another parameter which affects dispersion, and can be incorporated if
sufficient data is available.
Key input parameters required for the ATDM model are as follows:
0
pollutant emission rate and stack height;
0
building dimensions and terrain elevations;
0
temperature and velocity of gas at stack exit and stack parameter;
0
stack diameter.
The latter three parameters are required for calculation of the plume rise.
These are assessed both in terms of the plume’s thermal buoyancy and
momentum; whichever of these factors is dominant, the model selects for use in
its plume rise equations.
ADTM is a model requiring hourly sequential meteorological data. To
calculate annual mean concentrations it is necessary to use one year of hour
meteorology data and to average all the predicted hourly concentrations at each of
the selected receptor locations. Hourly average meteorological data over a four
471
N. Syred
Table3 Long Term Environmental Assessment Levels [EALs]
(referenced to Ground Level)
EAL (pg m')
Source
Nitrogen dioxide
50
EC Directive 85/203/EEC
Suspended particulates
80
EC Directive 80/779/EEC
Sulphur dioxide
80
EC Directive 80/779/EEC
Carbon monoxide
550
HSE (OES1100)
Chloride (as HCI)
7
US EPA IRIS
Fluoride (as HF)
25
HSE (OES/100)
Cadmium
0.005
WHO
Thallium (')
1
HSE (OES/lOO)
Mercury
1
WHO
Antimony
5
HSE (OES/lOO)
0.2
HSE (MEUSOO)
5
HSE (OES/l 00)
Cobalt
0.2
HSE (OES/IOO)
Copper
2
HSE (OES/IOO)
Lead
2
EC Directive 82/884/EEC
Manganese
1
WHO
Nickel
0.2
HSE (MEUSOO)
Tin
20
HSE (OES/I 00)
Vanadium
2.8
HSE (OES/lOO)
Pollutant
Arsenic
Chromium (Ill)
472
Environmental issues and kilnfiring
year period fiom a local meteorological station are used. Often such stations are
greater than 15 - 20 lan away and hence in the UK with very variable topography
and wind results are open to question. Predicted Ground Level Concentrations
[GLCs] are then added to the background concentration to give a PEC value. This
is then compared to the EAL value for a very wide range of materials including
NOz, particulates, SO2, HCI, HF, dioxin & furan I-TEQ, mercury, cadmium,
copper, lead, maganese, nickel, tin vanadium, as well as various hydrocarbons, viz
methane, toluene, butane, dichloromethane, propane, n-hexane, benzene, pentane.
Emissions to water are not normally significant with most kiln operations.
Emissions to land are most likely to occur locally as a result of dry
deposition of gases or particles. The contribution from wet deposition close to the
source is normally small as chemical and physical interactions are required prior
to wet removal processes. Wet deposition is most significant for particulates and
hence both dry and wet deposition are considered for this type of emission.
Stack emissions are investigated for the following reasons.
0
The deposition of acidic compounds (SOz, NOx and their products of reactions
in the atmosphere, H2S04 and HNOj) can result in an excess of hydrogen ions
or nitrogen above the tolerable environmental level. A threshold level exists
above which this input causes an effect known as the critical load.
0
The deposition of trace metals can cause a long term accumulation of
concentrations in soils with potential effects on plants, animals and humans.
Although both of the above are important, the available data and knowledge
is greater for acidic deposition than for the accumulation of metal concentrations.
Furthermore, the deposition of acidic compounds can be treated on an
instantaneous basis rather than as an accumulation over time and is much more
dependent on local factors such as geology. Some soils can tolerate considerable
amounts of acid deposition, others can tolerate less. Conversely, plants, animals
and humans display adverse effects to increasing exposure to trace metals.
473
N. Syred
The proposed BPEO assessment methodology for deposition to land
involves predicting the Maximum Deposition Rate
W R ] for each substance of
interest. The MDR is the quantiv of a pollutant which can be added to the soil
daily over a 100 year period before the selected soil quality criteria is exceeded,
and are equivalent to the EAL.
In the case of SO2 and NOz long term
accumulations are not an issue, and MDRs are not presented for these substances.
MDRs are normally considered for some metallic compounds present in the
particulate emissions.
The assessment methodology generally adopted when considering such acid
pollutants is the critical loads approach noted above.
The proposed BPEO
methodology does not currently incorporate a method for assessing critical loads,
therefore the potential impact of deposition of acid emissions to land is not fully
considered in the UK at the moment.
Nonetheless indications are that emissions of all acid gases in the case
discussed, except HF which has the lowest emission concentration, are lower for
the 40% waste liquid fuel firing mode of operation than for 100% coaVpet coke
firing. It therefore follows that the potential impact of acid deposition for this
mode of operation is also likely to be smaller.
The analysis considers dry and wet deposition (as appropriate) to soil,
predicts fluxes of substances to soil, includes background flux, then compares the
total to the MDR figure. With a well operated unit, the plant contribution to the
overall flux is normally insignificant compared to background levels.
Derivation of Integrated Environmental Index Emissions to Air
The Environmental Quotient for emissions to air (EQJ
for each mode of
operation is derived from EALs and GLCs for each substance emitted. A typical
result is shown overleaf in Table 4.
474
Environmental issues and kiln firing
Table 4
Derivation of Typical Environmental Quotients for Emission to Air
Substance
EAL'.)
CoaVPet coke Fired
EQ
GLC'"
GLCEAL
40% Waste Liquid Fuel
GLP
EO
GLC~EAL
Nitrogen Oxides (NO3
50
18.8
0.375
16.1
0.323
Particulates'"'
80
0.48
0.0060
0.42
0.0052
Sulphur Dioxide(S02)
80
6.9
0.086
4.8
0.060
Carbon Monoxide (CO)
550
8.5
0.0 16
9.83
0.018
Hydrogen Chloride (HCI)
7
0.12
0.017
0.050
0.0072
Hydrogen Fluoride (€IF)
25
0.015
0.00059
0.047
0.00019
Dioxin & Furan I-TEQ
3 x lo9
3
Merculy
1
0.000057
Cadmium
0.005
0.000022
0.0044
0.00001 1
0.0023
Thallium
1
0.00048
0.00048
0.0000045
0.0000045
Antimony
5
0.000152
0.000030
0.0000047
0.00000094
Arsenic
0.2
0.00012
0.00062
0.0000051
0.000026
Chromium
5
0.000 10
0.000020
0.00029
0.000058
0.000057
0.00071
0.00071
Cobalt
0.2
0.000036
0.00018
0.0000086
0.000043
Copper
2
0.000084
0.000042
0.00019
0.000093
Lead
2
0.003 1
0.0016
0.0013
0.00067
Manganese
1
0.00012
0.00012
0.000040
0.000040
Nickel
0.2
0.00021
0.0010
0.00010
0.00052
Tin
20
0.00046
0.000023
0.0000050
0.00000025
Vanadium
2.8
0.00025
0.000088
0.000063
0.000023
Methane
Toluene
0.25
1880
0.2648
0.2 1
0.000 I 1
0.1869
0.000 10
0.3202
0.000022
Butane
14300
0.25
0.000018
Dichloromethane
700
0.19
0.00027
0.058
Propane
0.1033
n-Hexane
0.7
0.047
0.0674
0.0634
0.09 1
Benzene
3.25
0.0089
0.0027
0.044
0.014
Pentane
I8000
0.067
0.0000037
0.1 561
0.0000087
Total EQA,~
0.5799
0.5238
(a) All concentrations expressed in pg m'
475
N.Syred
Emissions to Land
The Environmental Quotient for emissions to land (EQLand) for each mode of
operation is derived fiorn MDRs and an estimate of the deposition of pollutants to
land resulting fiom site emissions, Table 5.
Table 5
Derivation of Environmental Quotientfor Emissions to Land
CoaUPet coke Fired
Substance
MDR'"
Mercury
Cadmium
0.008
Thallium
0.006
Antimony
Flux "'
40% Waste Liquid Fuel
EQ
EQ
Flux[MDRl
Flux")
Flux(MDR1
0.000022
0.0037
0.00028
0.047
0.000021
0.0026
0.000011
0.0014
0.00039
0.0000036
0.00011
0.0000034
Arsenic
0.10
0.000072
Chromium
0.6
0.000088
0.00015
0.00026
0.00043
Cobalt
0.16
0.000021
0.00013
0.0000049
0.000030
Copper
0.32
0.000058
0.00018
0.00013
0.00040
Lead
0.52
0.0031
0.0069
0.0013
0.0025
Manganese
0.00072
0.00012
0.0000030
0.000030
0.000039
Nickel
0.2
0.00013
0.00067
0.000067
0.00025
Tin
0.160
0.00031
0.0019
0.0000034
0.000021
Vanadium
0.00022
Total EQtmd
0.000057
0.0170
0.0520
(a) All units expressed in mg2 day-'
Integated Environmental Index [IEI] for both modes of operation can be
calculated using the following formula:
476
Environmental issues and kiln firing
The EQs for both modes of operation are summarised in Table 6 along with
their corresponding IEIs @QW*
Table 6
= 0).
Integrated Environmental Indexes QEIs]
Coal/Pet Coke Fired
Waste Liquid Fuel
EQ*U
0.580
0.524
EQLand
0.017
0.052
0.597
0.576
IEI
It is clear that the analysis depends on the relative weighting placed on NO,
and SO,, particulates versus heavy metals deposited on land. A further point is
that the IEI for 100% bituminous coal firing lower of order 0.5310.54.
Short Term Effects
Again a similar analysis is carried out with the use of maximum measured
concentrations during normal operating conditions (in conjunction with worst case
atmospheric conditions) to give a credible worst case scenario. Generally NO2,
SO2 and particulates are monitored continuously and one hour maximum average
values are used for calculation purposes. As data is generally not available
regarding short term air quality, the long term air quality data is used. Ground
level concentrations [GLCs] are predicted using short term air dispersion models
with the results added to that from long term air quality data.
Short Term Environmental Assessment Levels [EALs]
Environmental Assessment Levels P A L S ] for short term exposure are derived in a
similar manner to long term EALs. Short term EALs are derived from the
following sources in the order of preference given:
0
Mandatory air quality standards
477
N.Syred
HSE Occupational Exposure Short Term (10 minute) Exposure Limits divided
by 10.
0
HSE Maximum Exposure Limits, Short Term Exposure Limits (10 minutes)
divided by 50.
0
For substances for which a Short Term Exposure limit is not listed the
Occupational Exposure Limit (8 hr TWA) multiplied by three may be used.
EALs for the pollutants of interest are presented in Table 7.
Predicted Environmental Concentrations [PECs]
The maximum predicted hourly average ground level concentrations [GLCs] are
again determined using the ATDM dispersion model which acknowledges terrain
and other important conditions. A comparison between the resultant GLCs, PECs
and their corresponding short term EALs is again made for both modes of
operation.
As there is no data available regarding short term ambient
concentrations for the substances concerned the PECs are determined using longterm ambient background and the short term GLCs.
The GLCs are calculated as maximum hourly averages and, therefore are
more representative of the 100th percentile. However, the EALs are expressed in
a number of ways, maximum, 98th percentiles, 95th percentiles and 98th
percentile of 24 hour means. Therefore, they are not directly comparable to the
dispersion model predictions. For the cases reported it is hardly surprising that all
maximum predicted hourly average GLCs are below their respective EALs owing
to the lack of continuous monitoring of data for many pollutants. For NO, GLCs
exceed EALs and indeed for SO2 with coaVpetroleum coke.
Although the frequency at which maximum hourly average GLCs may occur
is very small only under certain atmospheric conditions it is clear that plant
operators will need to be better informed in hture about combinations of
circumstances which give rise to these conditions.
478
Environmental issues a.nd kiln jiring
Short Term Environmental Assessment Levels [EALs]
Table 7
Pollutant
Nitrogen dioxide
EAL (up m 3
Source
WHO
200 (1 hr average)
150 (24 hr average)
Suspended particulates
250
EC Directive 80/779/EEC("
Sulphur dioxide
250
EC Directive 80/779EEC@'
350
33,000
HSE@)
Chloride (as HCI)
700
HSE@)
Fluoride (as HF)
250
HSE@)
Cadmium
7.5
HSE'~)
Carbon monoxide
HSE(~)
Thallium
Mercury
15
HSE'"
Antimony
150
HSE(*)
Arsenic
30
HSE(*)
Chromium (111)
150
HSE(~)
Cobalt
30
HSE(*)
Copper
Lead
20
HSE@)
2
EC Directive 82/884/EEC("
Manganese
150
HSE(~)
Nickel
Tin
30
HSE(~)
400
HSE'~)
I
WHO
Vanadium
Toluene
8,000
WHO
n-Butane
178.000
HSE(~'
3,000
WHO
n-Hexane
21,000
HSE")
n-Pentane
225,000
HSE")
Dichloromethane
(a)
95th percentile limit value. Mandatory air quality standard.
(b)
98th percentile limit value. Values presented are for
particulates > 150 and 150 ug m' respectively. Mandatory air quality
standard.
(c) HSE short term exposure limit/lO.
(d)
HSE long term exposure limit x 3/10.
(e)
Annual mean.
479
N. Syred
Other considerations include:
Global Warming Potential
The BPEO methodology identifies two pollutants C02 and CH4 as being relevant
in this kiln context, allowing for the significant decarbonisation of limestone in
addition to combustion.
Ozone Formation Potential
VOCs are sampled and presented with data pertaining to those pollutants able to
exert an effect on levels of ozone. These emissions are then multiplied by a factor
given in guidance notes relating to that substance’s capability to create
-
photochemical smogs Photochemical Ozone Creation Potential CpOCP].
Dioxins and Furans
In a well operated plant these do not appear to be a problem and all measurements
the author has seen appear to be below the critical threshold value in terms of
Toxic Equivalent Factor.
Waste Generated
Normally the only wastes arising are the cement kiln dust [CKD] collected by the
electrostatic dust precipitators. In the UK up to recently this dust has often not
been normally returned to the process owing to its high alkalinity. However, this
dust has significant non-toxic organics related to dioxins and furans.. A final
hazard score is calculated based on the annual quantity produced and a unit hazard
score which is a measure of the potential toxicity of the waste component. Since
the UK Government imposes charges on the landfilling of such materials kiln
operators appear now to be recycling the material (or most of it) in the kiln.
480
Environmental issues and kiln firing
Discussion and Conclusions
There are many issues raised by this type of analysis which will inevitably become
more detailed and rigorous with time. Despite the associated costs and complexity
major issues which these analyses highlight include:
Despite the low cost of petroleum coke there are clear environmental issues
raised by its use with this type of analysis in terms of increased sulphur and
heavy metal emissions. Increases in fuel sulphur and heavy metal content
generally give rise to increased backend emissions.
100% petroleum coke can be efficiently burnt with low NO, providing the
appropriate grind of fuel, burner set up and air preheat is achieved, as recent
work at the International Flame Research Foundation, The Netherlands, has
shown.
There is bound to be an increasing trend for plant operators to gather a much
wider range of data on a continuous or near continuous basis. Inevitably
much of the anlaysis will be sharpened up and operators will have to learn to
operate plant in the context of local geography, meteorology, raw materials
and fuel supplies to ensure that appropriate standards are met both on a short
and long term basis.
Low cost fuel solutions are less likely to include petroleum coke or waste
liquid fuels unless fuel specifications or clean-up is improved. Scrap/waste
tyres, if properly fed, would appear to offer good long term potential as a
low cost, low emission fuel, as indeed would forestry and agricultural wastes
providing they are available in sufficient quantities.
Acronyms
EPA
Environmental Protection Act 1990 (EPA90)
BATNEEC
Best available techniques not involving excessive cost
BPEO
Best practical environmental option
LCPD
Large Combustion Plant Directive
UNECE
United Nations Economic Commission for Europe
481
N. Syred
HMIP
Her Majesty’s Inspectorate of Pollution (UK).
Now
superseded by the Environment Agency
CIGN
Guidance notes produced by HMIPEnvuonment Agency
defining allowable emission levels for pollutants
EALs
Environmental Action Levels
OELs
Occupational Exposure Levels
PECs
Predicted Environmental Concentrations (of pollutants)
HSE
Health and Safety Executive, UK
EPA
Environmental Protection Agency, USA
ATDM
All Terrain Dispersion Model
GLCs
Ground Level Concentrations
CKD
Cement Kiln Dust
482
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