The Cement Kiln Portal
All around the world communities are fighting cement kilns. With the current drive to reduce CO2 emissions, save on the cost of fuel and get rid of all kinds of waste, many cement companies are burning, or considering burning, what are politely called "alternative fuels" but should really be called waste. This site aims to consolidate information pertaining to cement kilns, especially those burning waste, and the communities that are opposing this practice.
General
Overview
Concrete, a vital element of which is cement, is the second most
consumed substance in the world. Only water is used in greater
quantities
(ref).
Apparently, almost one ton of concrete is used for each person
in the world each year
(ref).
The amount of concrete used in construction around the world is
more than double that of the total of all other building materials,
including wood, steel, plastic and aluminium
(ref).
Currently, production of cement is in the region of 1.5 billion tons
per annum
(ref),
with a projected 2 billion tonnes (2000 megatonnes) production
by 2010
(ref).
This should be of grave concern to all, as the manufacturing of
cement is intrinsically unsustainable, and has serious environmental
impacts.
At the moment sixteen cement companies, which together represent
more than 50 percent of the cement manufacturing capacity outside
of China, have formed the
Cement Sustainability
Initiative (CSI),
a member sponsored program of the
World Business Council for
Sustainable Development (WBCDSD).
Core members of the CSI are
Holcim
and
Lafarge.
The Cement Sustainability Initiative has put out a
great many documents
CSI Documents:
- The Cement Sustainability Initiative (Brochure)
- Agenda for Action
- Toward a Sustainable Cement Industry (Executive Summary)
- Guidelines for the Selection and Use of Fuels and Raw Materials in the Cement Manufacturing Process (Draft)(443 kb)
- Formation and Release of POPs in the Cement Industry (2nd Edition)
- Safety in the cement industry: Guidelines for measuring and reporting
- The Cement CO2 Protocol: CO2 Accounting and Reporting Standard for the Cement Industry (Guidance Document)
- The Cement Sustainability Initiative: Progress report
- The Cement CO2 Protocol: CO2 Accounting and Reporting Standard for the Cement Industry (Spreadsheet)
- Environmental and social impact assessment (ESIA) guidelines
- Guidelines for Emissions Monitoring and Reporting in the Cement Industry
- Health & safety in the cement industry: Examples of good practice
- Go to the CSI Document Page...
,
all of which avoid the central truth – that cement can
never be sustainably produced. While the industry is fond of saying
that cement is the glue which holds society together, it generally
neglects to point out that the industry is also responsible for a
disproportionate volume of CO2 and other green house gas emissions,
for massive fossil fuel consumption, for the creation of huge volumes
of particulate matter, for the emission of large amounts of mercury
and for environmental impacts through the mining of quarries and so on.
While, in fairness, the industry is making some genuine environmental
adjustments, we should not lose sight of the fact that a more honest
approach to sustainability would be to make real investments in
research into sustainable alternatives to cement, and to building
methods which do not require concrete or cement, and which are less
harmful to the environment.
An area where the cement industry is particularly focussed at present
is the use of what they term “alternative fuels”, which translates
to the use of waste as a fuel. We must also not allow the industry’s
current attempts to paint the use of “alternative” fuels and waste
materials green to go unchallenged – in the end, the use of waste in
the cement industry is no more sustainable than current practices, and
potentially brings with it a number of new problems.
This section last checked or updated: 15 July 2008
Manufacturing Process
Cement is essentially a binding agent which is used in concrete,
mortar and plaster. It consists of four elements, calcium, silica,
alumina and iron, which are found in limestone, clay and sand. To
manufacture cement, four main processes are followed.
Firstly, raw materials are quarried and transported to a cement facility.
These materials would include lime, shells or chalk, silica or fly ash
from coal combustion, alumina from clay or shale or fly ash from coal
combustion and iron oxide from iron ore or from iron containing
by-products.
Next, these raw materials are milled into a fine powder and are mixed
thoroughly. This mixing may be done using water or compressed air.
The next step is to heat the elements at very high temperatures
(between 1400° and 1500°C), in a cement kiln. What is placed in the
kiln can be either wet or dry. In the dry process, raw materials are
in a fine dust form, and in the wet process in a slurry form.
Generally, wet kilns are older and dry kilns are more modern and fuel
efficient.
The kiln is an enormous sloped cylinder which slowly rotates.
Temperatures increase over the length of the cylinder to very high
temperatures – around about 1500°C - and the fuel is fed directly into
the kiln, meaning that the fuel residues are incorporated into the
final product. The temperature has to remain regulated, because if it
is too low the product will not become sintered (i.e. the small
particles of the raw materials will not adhere to one another correctly)
and if it is too high the particles will melt and fuse into large
glass-like lumps.
There are four thermal zones through which the raw materials travel
in the kiln. The first is known as the Calcining zone, and it is here
that limestone undergoes a chemical conversion to become lime. This
occurs at about 900°C and the liberation of a CO2 molecule from the
limestone (calcium carbonate - CaCO3) to form lime (calcium oxide - CaO)
is known as calcination. The second zone is known as the Upper-transition
zone, and here the temperature of the materials is increased to about
1200°C. In the third zone, the Sintering or Burning zone, the temperature
is increased to about 1450°C, and it is at this point that the clinker,
grey, glass-hard pellets, is formed. The last few meters of the kiln
form the fourth zone, the Cooling or Lower-transition zone, and here
the clinker is cooled to around 1250°C. The clinker then drops into
a cooler and is taken for storage, where it can be kept for a number
of years before being used.
In the final step of cement manufacture, about two percent gypsum
(calcium sulphate), along with various other materials, is added to
the clinker to improve the cement’s setting and handling qualities,
and everything is then finely ground into a powder which will react
to the addition of water.
Find out more...
This section last checked or updated: 15 July 2008
Environmental Problems with Cement Manufacture
Energy and Fuel
Because the process of turning limestone into clinker requires high
temperatures, the cement industry is one of the most energy intensive
industries, consuming about 10 times more energy than the average
required by industry in general. Modern dry-process kilns, however,
require far less energy than the older, wet-process kilns
(ref),
and the use of pre-burners and the re-use of air from the clinker
coolers can further reduce the amount of energy required. However,
in the US in 2003, 25 kilns at 14 plants used hazardous waste as
a fuel and most of these used the older, wet process
[Commission for Environmental Cooperation, p. 36].
Historically, fuels used to fire cement kilns include pulverised coal,
petroleum coke, which is a by-product of oil refining, and natural gas.
More recently, “alternative fuels” such as used solvents, spent tyres,
waste oil, paint residue, biomass such as wood chips, treated wood and
paper, and sewerage sludge have also been used [ibid, p. 36].
The burning of hazardous and non-hazardous waste is also
euphemistically known as co-processing, secondary materials
co-processing or energy recycling. Waste fuels are very attractive
to the industry as energy makes up the major cost in the manufacture
of cement and such fuels are generally cheaper than the traditional
fuels. Tyres and used industrial solvents are particularly attractive
as they have calorific (energy) values similar to that of coal.
Sometimes, waste can have an added benefit in that the kiln operator
may, in fact, be paid for incinerating the waste. In certain countries,
because the use of waste fuels reduces the use of oil and gas, carbon
dioxide emission credits can be claimed [ibid, p. 36].
The cement industry suggests that the use of tyres as a fuel is
beneficial to all. They try to convince us that a tyre will be completely destroyed in
six seconds, and we are led to believe that virtually nothing will be
emitted as a result. Research performed by Carrasco et al.
indicated, however, that while there were improvements in some areas,
the emission of some pollutants was exacerbated by the inclusion of
tyres. The following table comes from the report
Gaseous Contaminant Emissions as Affected by Burning Scrap Tyres in Cement Manufacturing.
† PM = particulate matter; PAH = polycyclic aromatic hydrocarbons
Clearly, emissions from a kiln will vary with exactly what is
being burned, and there would never be a standard emission pattern
for all kilns, or even for one kiln at all times.
The industry generally characterises the burning of waste in
cement kilns as “an internationally accepted practice”. But,
in 2003 in Mexico less than five percent of fuel used was alternative
fuel, even though all cement kilns in Mexico are licensed to burn
waste, while alternative fuels accounted for eight percent in Canada
and nine percent in the United States
[Commission for Environmental Cooperation, p. 36].
Should the practice, in fact, be “accepted”,
then it is unlikely that there would be as many organisations
militating against the use of such fuels as there are .
Greenhouse gas emissions
According to the cement industry itself, it is
responsible for about 3% of the world’s total greenhouse gas emissions
and for 5% of CO2 emissions
[Humphreys and Mahasenan, p. 2].
This equates to about 1.4 Gt (1 Gt = 1 gigatonne = 109 metric tonnes =
100 000 000 tonnes
(ref)). These emissions come from the burning
of fossil fuels in kilns (40%), transport of raw materials (5%),
fossil fuels required for electricity (5%) and the conversion of
limestone (CaCO3) to calcium oxide (CaO) (50%). These are estimates,
however, as the cement industry does not collect this data in a
systematic manner [Humphreys and Mahasenan, p. 4].
Japan has managed to reduce their CO2 emissions to .73kg CO2 for
each kilogram of cement produced, the best CO2 emission record for
cement kilns in the world but, having made great improvements with
their early efforts, have been unable to further reduce them.
Similarly, cement factories in Britain showed sharp improvement when
first addressing the problem in the 1990s, but a levelling off in
2003 and 2004. It is felt that
only fundamental technology breakthroughs or changes in market
incentives will allow for further meaningful reductions in emissions
[Humphreys and Mahasenan, p. 4].
The industry uses the potential reduction of CO2 emissions as a reason
for the use of waste derived fuels. However, given that half of the CO2
emissions result from the calcification of limestone, changes in fuel
will have no impact on these particular emissions, and even if the
industry were to be able to reduce their fuel related emissions of CO2
to nothing, they would still be responsible for more than 2.5% of the
world’s total CO2 emissions – or round about 84 million tonnes every
year.
Mercury emissions
Mercury is classified as a persistent, bioaccumulative
toxic (PBT) chemical. It can cause neurological and developmental
problems, particularly in children.
In a letter
“Mercury is a serious threat to public health. The health effects
of exposure to mercury pollution are well documented. Methylmercury,
an organic form of mercury that bioaccumulates in a number of fish and
marine mammal species commonly eaten by humans, is known to be highly
toxic and can adversely affect several organ systems, including the
cardiovascular system, and especially the brain and central nervous
system.
The nervous systems of children, infants, and above all the developing
fetus are the most sensitive to mercury exposures. Methylmercury
easily passes via the placenta from mother to fetus, where it readily
penetrates the fetal brain. Neurological and development impairment
can occur from both high dose and low dose exposures during fetal
development. High dose exposures have been demonstrated to result
in low birth weight, severe mental retardation, small head
circumference, cerebral palsy, deafness, blindness, and seizures.
Low dose exposures can result in lowered IQ, decreased performance
on tests of attention, fine motor function, and language, and
developmental delays, such as delayed walking. Such effects can take
place even at exposure levels where the mother remains healthy or
suffers only minor symptoms due to mercury exposure.
Mercury pollution is ubiquitous. In its assessment of the toxicological
effects of methylmercury, the National Research Council
concluded that mercury is both widespread and persistent in the
environment.11 According to the National Listing of Fish Advisories
(NLFA), 2,436 mercury advisories were issued by 44 states, 1
territory, and 2 tribes and a total of 13,183,748 lake acres and
765,299 river miles were under advisory for mercury in 2004.12
Additionally, Oklahoma, one of the six states not listed on the
2004 NLFA (along with Alaska, Iowa, Kansas, Utah, and Wyoming)
issued a statewide mercury advisory after the time of data release,
bringing the total number of states under mercury advisory in
2004 to 45. Also, in 2005, the State Departments of Health and
Environmental Quality, the Division of Wildlife Resources, and
the U.S. Fish and Wildlife Service (FWS) in Utah jointly issued
a no-consumption advisory for two duck species found to have toxic
levels of mercury in their flesh.
This pervasiveness of mercury contamination in the environment
presents a serious health risk to those who eat contaminated fish,
marine mammal, and wildfowl species. In January 2003, the Centers
for Disease Control and Prevention (CDC) found that nearly eight
percent of women of child bearing ages (16 to 49) are exposed to
levels of mercury that exceed the EPA reference dose (RfD) considered
safe for a fetus—0.1 micrograms per kilogram (µg/kg) of body weight
per day and 5.8 micrograms per liter (µg/L) of blood. A more recent
analysis by EPA scientists raised that estimate to more than 15%
of women, based on peer-reviewed studies showing that cord blood
concentrates mercury at significantly higher levels than maternal
blood. Using 2000 census data to extrapolate across the entire U.S.
population, this could mean that as many as 630,000 newborns each
year are at risk of serious congenital neurological and development
impairment.”
to the United States Environmental Protection Agency,
protesting the fact that the EPA had elected not to place limits on the
mercury emissions of cement kilns, the group Physicians for Social
Responsibility explain the effects of mercury pollution.
In Northern America in 2003, cement kilns, which represent less than
one percent of industries reporting, reported about nine percent of the
total mercury released in air emissions
[Commission for Environmental Cooperation, p. 56]
in North America. This equates to approximately
5.75 tons of mercury and mercury compounds, about 5.23 tons of which
were emitted to the air.
In view of the high and unregulated emissions, Physicians for Social
Responsibility calls on the EPA to more stringently monitor cement kiln
stacks. The letter also suggests that the reporting methods used by the
cement kilns are flawed, and that the actual emissions from these kilns
may be significantly higher. A
recent report appears to confirm this.
Controlling mercury emissions from cement kilns is particularly
troublesome as the high temperature of the kilns makes it impossible
to use the bag houses used in other industries. A bag house traps dust
from the boiler and an activated carbon injection system is used to
extract the mercury. The bags would melt in a cement kiln environment,
and carbon injection is not effective where there is a lot of dust.
Luc Robitaille of Holcim cement says that there is no technology that
exists in the cement industry to control mercury emissions [Shapley,
16 July 2006].
Dioxins, Furans and Products of Incomplete Combustion
Dioxins and Furans are inadvertently created through
combustion and industrial activities and are considered to be persistent,
bio-accumulative toxic compounds. Some are carcinogenic and are
suspected to be neurological, developmental and reproductive toxicants
or endocrine disruptors. They may be produced when exhaust gases cool,
and cooling these gases quickly through the critical temperature range
of 450 to 200°C has been demonstrated to reduce dioxin and furan
formation in cement kilns
[Commission for Environmental Cooperation, p. 60].
Combustion upsets are par for the course in any
kind of kiln or incinerator. Because of the very hot raw mix, a
cement kiln must run through each combustion upset or process
malfunction. This means that it is possible for the cement kiln to
contain products of incomplete combustion (PICs), even though they
may be required by regulations to stop feeding new matter into the
kiln should there be an upset [p13]. This presents a real risk to
surrounding communities as upset emissions have been shown to be more
toxic than the original waste being burned through the creation of
harmful products of incomplete combustion [Neil Carmen, 23 April 2004].
In 1995, at an EPA workshop, it was indicated that the cement industry
was responsible for 17% of all dioxin emissions in the United States,
and that those kilns burning hazardous waste were responsible for 99%
of the cement industry’s dioxin emissions
(ref),
and in 1998, in their
report “The inventory of Sources of Dioxin the United States”, they
say that kilns that burn hazardous waste have 80 times higher dioxin
emissions in the stack gases than those which use only conventional
fuels
[USEPA, p. 5].
In addition, USEPA also reports that dioxins
are found in the Cement Kiln Dust (CKD) of both kilns which burn
conventional fuel and those that burn hazardous waste, but that
concentrations of dioxins in the CKD of those burning hazardous waste
are almost 100 times greater than those not doing so.
A more recent study,
Use of Continuous Isokinetic Samplers for the Measurement of Dioxins and Furans in Emissions to Atmosphere
shows that continuous sampling shows higher levels of dioxin emissions than
certified manual sampling. This study, however, shows low levels of dioxin emissions.
You may also wish to read comment
on the report.
Ozone
Ozone (O3) is “good” when it is high up in the
atmosphere, in the region known as the stratosphere, but “bad” when
found close to the earth in the troposphere
(ref).
Too much ozone can
cause respiratory problems in humans. The electrostatic precipitator
(ESP) is a particulate collection device that removes particles from
air or flowing gas through the force of an induced electrostatic charge,
and which tends to create ozone
(ref).
A study showed that maintenance
workers who suffered from respiratory and eye irritations when working
in a cement kiln were being affected by the ozone being generated by
the ESP
(ref).
In 2004, two activist groups, Downwinders and Blue Skies, Midlothian
citizens groups which have long been fighting the three enormous cement
factories in Texas, sued the US Environmental Protection Agency (USEPA)
“to do its job”, and force the cement factories to reduce their
emissions, especially ozone which is thought to be causing the
extremely high incidence of asthma in the areas downwind from the
plants
(ref).
A settlement was reached in 2005 whereby a cement kiln
study would be conducted. This study concluded that emissions,
including ozone, could be considerably reduced through the installation
of new technology known as selective catalytic reduction (SCR). This
is, however, quite expensive and the cement industry, who generally
deny that their plants are any sort of problem at all, are resisting
the installation of SCRs.
Cement Kiln Dust and Particle Emissions
Dust emissions are one of the primary problems
faced by the cement industry. However, according to industry, these
emissions “have been reduced considerably in the last 20 years, and
state-of-the-art abatement techniques now available (electrostatic
precipitators, bag filters) result in stack emissions which are
insignificant in a modern and well managed cement plant”
[CSI, January 2006, p. 47].
This statement not withstanding, a
continuous monitoring system run by the NGO Emission-Watch, at
Castle Cement’s brand-new plant at Padeswood in Flintshire, North
Wales, indicates frequent upsets where particulate matter exceeds
the regulatory limit of 50ug/m3
(ref).
Most materials which are burned at very high temperatures will
vaporise. However, when this vapour is cooled, the aerosols could
have changed from the original materials to a previously unknown
compound, which might have unpredictable consequences for people’s
health and for the environment. Even materials that are generally
considered to be chemically inert may become reactive and electrically
charged when they are changed into small particles and at times
these particles may be of a novel configuration
(ref).
Large amounts of fine material are given off during the cement making
process. This material is carried out of the kiln by the flow of hot
gas generated inside the kiln, and is not incorporated into the clinker
as the raw materials have not been fully processed. This dust, CKD,
therefore becomes a waste by-product
(ref).
In many cases, CKD is
recycled back into the kiln and is ultimately incorporated into the
clinker. The problem with this is that heavy metals can become
concentrated in the CKD as some of it will pass through the kiln many
times (ref).
Where it is not recycled, it is stored in piles at the
facility, and ultimately transferred to landfill. There have been
allegations that this dust has contaminated both surface and ground
water.
Off-gassing
It is currently unknown what the effects of
incorporating the combusted waste matter will have. Conceivably
some of these, too, may off-gas. And certainly, when the cement
is used, or the concrete or mortar for which it has been used is
later broken up, it is more than possible that contaminants will be
“set free”.
Products
As the residues from the fuel which is used to fire
the kiln are ultimately incorporated into the clinker, the clinker and
cement produced from the clinker will obviously contain the same types
of metals and organic compounds which are found in the CKD and in the
air emissions (ref).
Concern has been expressed as to whether cement produced by kilns which
burn alternative fuels will contain unacceptable levels of metals.
It is possible that, should metals be present in great enough quantities,
the integrity of the cement could be threatened. It is also possible
that these materials could leach out from the finished cement, or could
be released when the cement is later broken up for whatever reason.
While researching their Cement Kiln Dust Report, the EPA found that
some clinker samples from waste burning kilns contained certain
materials in quantities which exceeded the Land Disposal Restrictions
for hazardous waste. This means that this clinker could technically
be considered hazardous waste. Other research, however, has indicated
that there is very little difference between the concentrations of
metal in cement produced by kilns burning hazardous waste and those
not doing so (ref).
It should be remembered, however, that what is
being burned at any one time will impact on what is
incorporated into the cement.
This section last checked or updated: 1 October 2008
Conclusion
While the industry has spent a great deal of time,
energy, money and imagination on putting a positive spin on the
production of cement, there are a number of issues which pose serious
problems for the industry, for the people who live near the manufacturing
plants and the people who ultimately use, or are surrounded by, cement
products.
Even without the introduction of alternative fuels to the scenario,
industry emissions are problematic and, while there is as yet little
firm data to back this up, it is probable that the burning of hazardous
waste will introduce additional concerns.
Through burning waste, cement kilns become simply incinerators in
disguise. Even though this is so, cement kilns are generally not subject
to the same stringent emission standards that waste incinerators are.
This is clearly an unreasonable situation as it not only means that
cement kilns are in a position to pollute the community with relative
freedom, but also that they have an unfair competitive advantage over
the incinerators which, no matter how we may view them, are at least
required to remain within certain standards.
The use of waste in kilns represents for the industry the kind of
operating savings which can make an appreciable difference to their
bottom line – assuming that they do not intend to pass these savings
on to the consumer – or to their ability to be competitive in the market.
The key elements of the industry argument are that it is better to burn
waste in a cement kiln than in a conventional incinerator as they burn
hotter and for longer, they exist already, and the energy from the waste
is “recycled”. These are fallacious but, are likely to carry weight
with both communities and government.
Ideally, the making of cement should be phased out altogether,
although this is clearly a long-term option and would require a great
deal of innovation and imagination from the industry and from society
in general. In the short-term, however, communities should be pushing
for more stringent standards to be imposed upon the industry, and for
the burning of waste to be disallowed completely.
This section last checked or updated: 17 July 2008
Alternative Fuels & Raw Materials (AFRs)
Overview
The term "Alternative Fuels" is generally a euphemism for waste. The waste that
is most often considered as fuel for cement kilns includes used tyres, rubber, paper waste,
waste oils, waste wood, paper sludge, sewage sludge, plastics and spent solvents and spent
potliners.
Arguments that the cement industry use to justify the use of waste as a fuel
are pretty standard. They generally include:
Conservation of a non-renewable resource
The industry points out that substituting coal with unwanted materials that
need to be disposed of would save coal, a non-renewable resource.
This implies that waste is a renewable resource, which it certainly should not be. Any process
which relies on a constant (and in the case of cement kilns, large) stream of
waste is intrinsically unsustainable and can only encourage an increase in waste
generation rather than any attempts to reduce it.
Energy recovery from waste materials
As all the energy is used directly in the kiln for clinker
production, the use of alternative fuels maximises the recovery of energy
from waste. The recovery of the non-combustible parts of the waste is
also maximised as the inorganic part is a substitute for raw materials in
the cement and the need for disposal of slag or ash is eliminated.
If we accept that there is no option but to both generate and burn waste, then
this argument holds true. The incorporation of heavy metals and other toxins
in the cement should, however, be a cause for concern rather than celebration.
Increased environmental performance
Because of high temperatures, long residence times, high
turbulence, a high PH environment, termal stability and the elimination of
ash residues, cement kilns are more efficient and have a lower environmental
impact than traditional incinerators.
Once again, the premise is that waste is a given, and that it must be burned is a given.
It is true that if, indeed, there is no alternative to producing waste and burning
it, it is better that it be burned at very high temperatures, leaving little residue. It
must be remembered, however, that the waste burned contains heavy metals and toxins,
and that these don't just simply disappear. Instead they either go up the stack or are
incorporated into the cement.
Overall greenhouse gas emissions will be reduced
After considering the emissions from incinerators and landfills, there is an
overall decrease in greenhouse gas production if waste is co-processed in cement
kilns, because the kilns take these emissions over and no new emissions
are generated.
Once again, this argument is based on the idea that waste is inevitable and
must be burned, so it might as well be burned in cement kilns.
There is a reduced risk of soil and groundwater contamination"
By burning waste in cement kilns there is a reduced requirement
for landfills and potentially hazardous waste will be incinerated and incorporated
into the cement instead of being sent to landfills either as is or in the form of
ash from a traditional incinerator.
We are led to believe that there are no alternatives to waste or what could
be done to it, and it is better to have the waste residues trapped in the
cement and its products than elsewhere.
The use of AFRs will not significantly change emissions
If the basic rules of secondary and raw material usage are
followed (for example, feeding via the correct firing path, storing the waste
correctly, sourcing it from trustworthy sources and setting limits on the quality)
there should be no significant change in emissions from the cement kiln.
There is evidence to suggest that, under perfect operating conditions, emissions are
largely limited. Unfortunately, however, perfect conditions rarely persist and
during start-up and shut-down situations, as well as upsets during normal operation,
emissions have been shown to be problematic.
An industry view can be found in
Alternative Fuels in Cement Manufacture - Technical and environmental review.
This section last checked or updated: 26 June 2008
Tyres
Waste tyres are a popular fuel for cement kilns. They are a real problem in
waste terms, and are attractive to kilns because they have a high energy content.
In many instances tyres are the only "alternative" fuel that a kiln might use.
Some cement kilns can accept whole tyres, while others require that the tyres
first be chipped.
A Friends of the Earth report,
Gone to Blazes
reports that tests of tyre burning at four California kilns showed the following emission increases
when compared to coal:
| Emission | % Increase | Number of Tests |
|---|---|---|
| Dioxins | 53% - 100% | 4/4 |
| PAHs* | 296% - 2230% | 3/4 |
| Lead | 59% - 475% | 3/4 |
| Chromium | 727% | 1/3 |
A significant increase of zinc and lead input to the kiln, and between a two
to five times increase in dioxin emissions were found in a German study of a
Belgian kiln burning tyres.
There is plenty of tyre burning information
here. A report, Options for the use and disposal of waste tyres,
examines both the problems with burning tyres and alternative uses for waste tyres in
the South African context.
Although about a test burn case at a paper mill facility, the note
International paper and a boiler full of tyres
has some interesting legal perspectives on test burns of tyres.
Although about a dedicated tyre incinerator,
a letter to the Dixie County Advocate newspaper summarises very nicely
a community's concerns about tyre burning.
This section last checked or updated: 24 February 2009
Blended and Processed Fuels
Blending plants take waste a create fuel products from them. They are given
fancy names like Cemfuel, Climafuel and Profuel to make them sound green and
to disguise the fact that they are
actually just waste, often hazardous, in a different form. Manufacturers
of such fuels claim that they are helping to recycle waste that otherwise
cannot be recycled.
Some of these products are known as SLFs (Secondary Liquid Fuels).
SLFs are a blend of organic and solvent wastes. Materials used in such fuels
include Oils, Non Halogenated Solvents, Halogenated Solvents, Organic Acids.
Glycols, Distillation Residues, Solvent Based Inks, Paints and Adhesives,
Aqueous/Organic Mixtures, Viscous Organic Liquids, Toxic Solvents,
Organic Sludges and Amines/Alkali. Such fuels can replace up to 40% of the
traditional fuels used in the kilns. They are used by injecting them into
the kiln burner.
One of the best known SLFs is Cemfuel, produced by a Castle Cement affiliate
company in Britain. Castle had hoped that, once waste had been turned into Cemfuel, it would be
classed as a fuel and would therefore no longer be seen to be waste. This
would mean that it would not be subject to the trade restrictions imposed
upon waste through mechanisms such as the Basel Convention.
This hope was, however, for the moment at least, dashed in a
court case where
the judge deemed that Cemfuel remained waste until such time as it was burned
and the energy recovered.
Fuels such as Climafuel and Profuel are made from cardboard, paper, plastics,
textiles, carpet and other
fibrous wastes that are expensive or difficult to recycle and would, says
the industry, otherwise be disposed of in landfill sites. The materials
are shredded and ground to pieces of about 20mm in size, and then mixed.
Meat and Bone Meal (MBM) products are produced at animal rendering plants
through the high temperature processing of animal remains, largely waste
from abattoirs. The fuel is the granular solid residue that is left after
the tallow (fat) has been rendered out.
Processed Sewerage Pellets (PSP) are made from the sludge from sewerage
works. The sludge is treated by drying and then the application of heat
to produce a sterile, glassy, pelletised material.
This section last checked or updated: 17 July 2008
Communities
All around the world communities are opposing cement kilns. This site is intended to bring those communities together and any additional information regarding groups that are working against cement kilns would be gratefully received. Please e-mail team@groundwork.org.za with any information that you might have.
South Africa
United Kingdom
United States
This section last checked or updated: 17 July 2008
Abstracts
Usage of cement kiln dust in cement products
Maslehuddin, M., O. S. B. Al-Amoudi, et al. (2008). Usage of cement kiln dust in cement products - Research review and preliminary investigations. Construction and Building Materials 22(12): 2369-2375.
Abstract:
Large quantity of dust, commonly known as cement kiln dust (CKD), is produced
during the production of Portland cement. In order to meet environmental
requirements, CKD is disposed off in land fills. Recently, there has been
a trend of utilizing it for soil stabilization, treatment of sewage, etc.
Also, attempts were made at using it in cement products. This paper reviews
the work conducted on the latter aspect and reports results of tests
conducted by the authors to investigate the properties of cement-CKD
combination. Results indicate that CKD does not adversely affect the
properties of cement mortar. However, the implication of high chloride
concentration and alkalinity of CKD on concrete durability needs to be studied.
Taiwan: dioxin emission factors during
start-up and normal operations of MSW incinerator
Chen et al., 2008. Polychlorinated dibenzo-p-dioxins/dibenzofuran mass distribution in both start-up and normal condition in the whole municipal solid waste incinerator. Journal of Hazardous Materials. Article in Press. doi: 10.1016/j.jhazmat.2008.02.077
Abstract:
Although many researches focused on the polychlorinated dibenzo-p-dioxins/
dibenzofuran (PCDD/F) emissions from stack, in the bottom ash and in the
surrounding environment, researches focused on PCDD/F mass distributions in
the whole incineration plant have seldom been addressed. This study
determined PCDD/F emissions in the whole plant. A high-resolution gas
chromatograph/high-resolution mass spectrometer was utilized for analyzing
17 PCDD/F species. Experimental results displayed that PCDD/Fs were formed
during fly ash from super heater (SH), economizer (EC), semi-dryer absorber
(SDA) and fabric filter (FF) was transferred to fly ash pit. Mass
distribution ratios of PCDD/Fs in g I-TEQ (Toxicity Equivalency Quantity)
per week from stack, SH, EC, SDA, FF, generation and bottom residue (BR)
in start-up operations were 14.6%, 0.1%, 8.3%, 1.0%, 41.7%, 33.4% and 0.9%,
respectively. Above results indicated that main PCDD/F source in the MSWI
was from fly ash. However, the fly ash is easily controlled and PCDD/F
emitted from stack flue gases will be difficult to be handled. Therefore, we should pay more attention on PCDD/F emission from flue gases especially from start-up procedure. Besides, fly ash should be controlled by sodium hypophosphite before being landfilled. MSWI did require further detoxification treatments for the solid residues and flue gases.
[from body of text]:
The stack samples and ash samples were collected from KS MSWI, located in southern Taiwan. There are four incinerators, each of which includes own heat recovery systems (350 degrees C), selective non-catalytic reduction, dry scrubber (250–230 degrees C), activated carbon injection, fabric filter (180–160 degrees C) and stack. The treatment processes are the most common ones in Taiwan, which are recognized as the most effective technique for PCDD/F emission control.
Operation of the KS MSWI began in 2000 and its total capacity is 1800 ton/day with lower heating value of 2500 kcal/kg-waste
Experimental results displayed that the averaged PCDD/F equivalent concentration was 0.0511 ng I-TEQNm-3. The averaged PCDD/F contents for ash samples from the bottom residue, super heater, economizer, semi-dryer absorber, fabric filter and fly ash pit were measured to be: 17.2, 37.9, 4180, 620, 5020 and 6410 ng I-TEQ kg-1, respectively. The total PCDD/Fs emission factors were stack (8.47mg ton-waste-1; 0.454mg I-TEQ ton waste-1), BR (58.2 mg ton-waste-1; 3.54 mg I-TEQ ton-waste-1), SH (4.40 mg ton-waste-1; 0.306 mg I- TEQ ton-waste-1), EC (961 mg ton-waste-1; 31.9 mg I-TEQ ton-waste-1), SDA (100 mg ton- waste-1; 3.66 mg I-TEQ ton-waste-1), FF (1870 mg ton-waste-1; 160 mg I-TEQ ton-waste-1) and FAP (3610 mg ton-waste-1; 323 mg I-TEQ ton-waste-1), respectively. Theoretically the PCDD/F emission factor in FAP should be equal to summation of that in SH, EC, SDA and FF because fly ash from SH, EC, SDA and FF were transferred to fly ash pit. In other words, the PCDD/Fs might be formed (674 mg ton-waste-1; 128 mg I-TEQ ton-waste-1). As a result, the temperature of transmission system should be maintained at a level of 105–110 degrees C to prevent formation of PCDD/Fs and save energy as well. Recently, several studies have focused on the high PCDD/F emission during the start-up of incinerators. Therefore, the total emission amount of PCDD/Fs from stack, BR, SH, EC, SDA, FF and generation were 0.596, 0.0377, 0.00326, 0.340, 0.0390, 1.70 and 1.36 g I-TEQ week-1 with considering the start-up operations, respectively. Mass distribution ratios of PCDD/Fs in g I-TEQ week-1 from stack, SH, EC, SDA, FF, generation and BR in start-up operations were 14.6%, 0.1%, 8.3%, 1.0%, 41.7%, 33.4% and 0.9%, respectively. It could be seen that the main PCDD/F source in the MSWI was from fly ash although start-up procedure can generate 60% of the PCDD/F emissions from stacks for one whole year of normal operations.
Specific emergy of cement&concrete
Pulselli et al., 2008. Specific emergy of cement and concrete: An energy-based
appraisal of building materials and their transport. Ecological Indicators 8: 647 – 656.
Abstract:
Use and production of building materials, such as cement and concrete, is a major cause of
global ecological problems with special reference to the overexploitation of non-renewable
natural resources due to high temperature production processes, fossil fuels combustion,
extraction of raw materials and non-recycling. In this paper, an environmental accounting
method was applied to the production of cement and concrete in order to evaluate its
dependence on natural resources even non-renewable and heavily relied on external
inflows. The main steps of the production process (1) cement production, (2) transport of
materials and (3) concrete mixing, were assessed by the emergy analysis (spelled with an
‘‘m’’). This was performed to measure the amount of environmental resource use in terms of
equivalent solar energy, extending the energy hierarchy principle to building materials. The
resulting unit emergy values of cement and concrete were compared with previous emergy
assessments in order to highlight how emergy analysis is sensitive to local context and
reference system’s boundaries. An Emergy Investment Ratio (EIR) was assessed and presented as a synthetic indicator of sustainability. Results showed a high dependence of
cement and concrete production on external resource flows. Furthermore, the high value of
EIR suggested a weak competitive capacity due to a high sensitivity to external instabilities.
[from body of text]:
In this paper, an evaluation of building materials sustainability was presented through an emergy evaluation. The specific emergy of cement and concrete are 3.04 x 10 to the 9 sej/g and 1.81 x 10 to the 9 sej/g, respectively, in the Italian context. The emergy analysis of cement and concrete production
takes into account various steps in the process. More than procedures for materials production, the results highlight the impact of the use of quarry materials. These are seen as mineral resources with high specific emergy provided by natural sedimentary cycles and accounted in sej. In the case of cement, materials (limestone, chalk, shale, clay and sand) are about 84% of the total emergy, while emergy for the blast
furnace is about 15%. In the case of concrete, materials (sand, gravel, crushed stone, cement) are about 97% of the total emergy. Thus emergy highlights the critical role of overuse of non-renewable resources in the building industry, since it accounts for the work of nature (sedimentary cycle), not only human work for quarrying (the only process accounted in economic analysis). The dominant contribution of mineral resources underlines the un-sustainability of the building industry. Non-renewable and non-recyclable materials such as cement and concrete are undergoing depletion.
Burning RDF in cement kilns
Genon, G. and E. Brizio (2008). "Perspectives and limits for cement kilns as a destination for RDF." Waste Management 28(11): 2375-2385
a: Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy
b: A.R.P.A. Piemonte, Via Vecchia di Borgo 11, 12100 Cuneo, Italy
Abstract:
RDF, the high calorific value fraction of MSW obtained by conventional separation systems, can be employed in technological plants (mainly cement kilns) in order to obtain a useful energy recovery. It is interesting and important to evaluate this possibility within the general framework of waste-to-energy solutions. The solution must be assessed on the basis of different aspects, namely: technological features and clinker characteristics; local atmospheric pollution; the effects of RDF used in cement kilns on the generation of greenhouse gases; the economics of conventional solid fuels substitution and planning perspectives, from the point of view of the destination of RDF and optimal cement kiln policy. The different experiences of this issue throughout Europe are reviewed, and some applications within Italy are also been considered. The main findings of the study are that the use of RDF in cement kilns instead of coal or coke offers environmental benefits in terms of greenhouse gases, while the format ion of conventional gaseous pollutants is not a critical aspect. Indeed, the generation of nitrogen oxides can probably be lower because of lower flame temperatures or lower air excess. The presence of chlorinated micro-pollutants is not influenced by the presence of RDF in fuel, whereas depending on the quality of the RDF, some problems could arise compared to the substituted fuel as far as heavy metals are concerned, chiefly the more volatile ones.
[from body of text]:
Some studies reported 1.8 million t/y of secondary fuels co-incinerated in cement kilns in Europe in 1997, which is expected to increase by 15% by 2003. The related strategy for the cement industry is to rely on alternative fuels to reduce its high energy bill (energy costs typically represent 30–40% of manufacturing costs of Portland cement), as well as for sustainable development. This is also an important consideration from the point of view of carbon dioxide emissions and the consequent possibility to benefit from
carbon emission credits.
Hazardous wastes (1 million t/y) and tyres (550,000 t/y) are the most frequently used secondary fuels. However, future attention should be switched to biomass-based fuels including wastepaper and sewage sludge for carbon emission credits.
On the contrary, an increase in chlorine (0.3–0.5% in RDF, very low values less than 0.1% in coke) can lead to some problems arising from reactions between alkali and chlorine, the volatilisation of chlorides and recycling with dust, and the necessity to operate a bypass (extraction of part of the flue-gas) in order to limit the chlorides in the final clinker ( Kurdowski, 1983 ).
The presence of heavy metals in secondary fuels can lead to a transfer in the produced clinker
… A final important aspect for the proposed substitution of secondary fuels is the low density of this material in comparison with conventional fuels. Taking into account the transport and storage costs, the cost of substituted fuels per unit of heat produced is higher than the cost of coke or coal.
… The use of RDF in cement manufacturing kilns seems to be positive, as the combustion of RDF
allows for a reduction of about 1.61 kg of CO2 per kg of utilised RDF compared to conventional combustible materials (coal). This is due to the chemical composition of the combustible material. When RDF is used in specifically set up combustion systems with energetic recovery, taking into consideration the energetic mix for the production of electric energy and the efficiency of the electric production, the
substitution of the combustible material involves an increase in the production of CO2 of about 0.15 kg per kg of RDF.
… The negative impact of the emission of atmospheric pollutants from the raw composition of burned RDF consists of the possible transfer of substances contained in the waste
to the atmosphere or the produced clinker.
In any case, it is evident that the use of RDF instead of traditional fuels in a cement kiln could be dangerous in terms of the presence of larger amounts of heavy metals in the waste gas, so the quality and the quantity of RDF
… It is important to underscore that the transfer factors can change according to the composition of the fuel (for example, which molecules mercury forms around), to the presence of halogens (for example, Pb, Ag, Ni are much more volatile as chlorides) and to the occurrence of a reducing or oxidising atmosphere.
… As far as the possible formation of dioxin is concerned, a complete study has been conducted on the emissions from the co-combustion system ( SINTEF, 2004 ). The main results of this study are as follows:
- there is no correlation between dioxin emissions and the type of alternative combustible material used ( Fig. 4 );
- the formation of dioxins can occur in a thermal window between 200 and 450 _C, zones that are encountered in fume cooling systems before the final separator of the fumes;
- potential precursors released by combustible material introduced into the pre-calcination zone can react with the chlorine not retained by the alkaline matrix of the clinker, in the presence of metallic catalysts present in the transported powders, giving rise to emissions of dioxin where de-novo synthesis occurs;
- while the dioxin concentrations are, in most cases, lower than 0.1 ng/Nm3, concentrations of PCB at least a thousand times higher are possible. In this sense, they constitute a significant source of precursors that are able to generate micro-pollutants where the aforementioned kinetic conditions allow this to happen.
Based on our experience, some problems can arise for cement kilns when using secondary raw materials containing micro pollutants or precursors (PCB, PAH).
Read Full ReportThis section last checked or updated: 1 October 2008
Jargon
| Term | Definition |
|---|---|
| AFR | Alternative Fuels & Resources |
| Alternative Fuels | Waste |
| CKD | Cement Kiln Dust |
| Co-processing | Burning waste along with coal or other fuels |
| CSI | Cement Sustainability Initiative |
| CV | Calorific Value |
| EIA | Environmental Impact Assessment |
| Emergy | The energy of one kind, usually solar energy, which is required to make a service or product |
| ESP | Electrostatic Precipitator |
| MBM | Meat and Bone Meal |
| MBT | Mechanically and Biologically Treated |
| MSW | Municipal Solid Waste |
| OPC | Ordinary Portland Cement |
| PFA | Pulverised Fuel Ash |
| PAH | Polycylclic Aromatic Hydrocarbon |
| PIC | Product of Incomplete Combustion |
| Product of Incomplete Combustion | Organic compounds formed by combustion at too low a temperature |
| PSP | Processed Sewerage Pellets |
| RDF | Refuse Derived Fuels |
| Refuse Derived Fuels | Waste |
| RFO | Recovered Fuel Oil |
| RHC | Rapid Hardening Cement |
| RoD | Record of Decision |
| SCR | Selective Catalytic Reduction |
| Secondary materials | Waste |
| SLF | Secondary Liquid Fuel |
| SRF | Solid Recovered Fuel |
| TDF | Tyre Derived Fuel |
| WLF | Waste Liquid Fuel |
