Use of alternative fuels in cement industry

Abstract

Cement production has advanced greatly in the last few decades. The traditional fuels used in
traditional kilns include coal, oil, petroleum coke, and natural gas. The substitution of fossil fuels by
alternative fuels (AF) in the production of cement clinker is of great importance both for cement
producers and for society because it conserves fossil fuel reserves and, in the case of biogenic
wastes, reduces greenhouse gas emissions. In addition, the use of alternative fuels can help to
reduce the costs of cement production. Energy costs and environmental concerns have encouraged
cement companies worldwide to evaluate to what extent conventional fuels can be replaced by
waste materials, such as waste oils, mixtures of non-recycled plastics and paper, used tires, biomass
wastes, and even wastewater sludge. The clinker firing process is well suited for various alternative
fuels; the goal is to optimise process control and alternative fuel consumption while maintaining
clinker product quality. The potential is enormous since the global cement industry produces about
3.5 billion tons that consume nearly 350 million tons of coal-equivalent fossil and alternative fuels.
This study has shown that several cement plants have replaced part of the fossil fuel used by
alternative fuels, such waste recovered fuels. Many years of industrial experience have shown that
the use of wastes as alternative fuels by cement plants is both ecologically and economically
justified.

Full text

Proceedings of the 12th International Conference on Protection and Restoration of the Environment
Editors: A. Liakopoulos, A. Kungolos, C. Christodoulatos, A. Koutsopsyros
ISBN 978-960-88490-6-8
521
Use of alternative fuels in cement industry
N. Chatziaras1, C.S. Psomopoulos 1, 2*, N.J. Themelis2
1T.E.I. Piraeus, Dept. of Electrical Engineering, 250 Thivon str & P. Rali Ave, GR-12244, Egaleo, Greece
2Global WTERT Council and Earth Engineering Center, Columbia University, 500 West 120th St., #925,
New York, NY 10027, U.S.A.
*Corresponding author: E-mail: cpsomop@teipir.gr, Tel +302105381182, Fax: +302105381321
Abstract
Cement production has advanced greatly in the last few decades. The traditional fuels used in
traditional kilns include coal, oil, petroleum coke, and natural gas. The substitution of fossil fuels by
alternative fuels (AF) in the production of cement clinker is of great importance both for cement
producers and for society because it conserves fossil fuel reserves and, in the case of biogenic
wastes, reduces greenhouse gas emissions. In addition, the use of alternative fuels can help to
reduce the costs of cement production. Energy costs and environmental concerns have encouraged
cement companies worldwide to evaluate to what extent conventional fuels can be replaced by
waste materials, such as waste oils, mixtures of non-recycled plastics and paper, used tires, biomass
wastes, and even wastewater sludge. The clinker firing process is well suited for various alternative
fuels; the goal is to optimise process control and alternative fuel consumption while maintaining
clinker product quality. The potential is enormous since the global cement industry produces about
3.5 billion tons that consume nearly 350 million tons of coal-equivalent fossil and alternative fuels.
This study has shown that several cement plants have replaced part of the fossil fuel used by
alternative fuels, such waste recovered fuels. Many years of industrial experience have shown that
the use of wastes as alternative fuels by cement plants is both ecologically and economically
justified.
Keywords: alternative fuels, municipal and industrial waste, cement industry, cement production, raw
materials
1. INDRODUCTION
Cement is the key construction material for global housing and infrastructure needs. The cement
industry worldwide is facing growing challenges in conserving material and energy resources, as
well as reducing its CO2 emissions. Cement producers are striving to increase energy efficiency and
also the use of alternative raw materials and fuels. Therefore the use of alternative fuels has already
increased significantly, but potential for further increases still exists [1].
The role of the cement industry in resource conservation and environmental protection has
increased in recent years because of the rapid economic growth of large regions, such as China,
India and Southeast Asia [2]. The cement industry is an energy-intensive industry with energy
typically accounting for 30–40% of production costs. Figure 1 presents the distribution of electricity
demand in each stage of the cement production process. The energy consumption is estimated at
approximately 2% of world total, and 5% of industry total. The fuel mix in the industry is carbon
intensive, and the calcination process itself produces CO2, so that in total the cement industry
contributes 5% of the global CO2 emissions [1,3].
The 2008 production of cement in the European Union was 200 Mt, approximately 7% of the world
production. In Europe, 158 Mt of CO2 were emitted in 2008 from cement plants which corresponds
to 38.5% of all industrial emissions in Europe or 3.2% of the total European CO2 emissions. In a
modern cement plant, 60% of the CO2 emitted by a cement plant results from the calcinations of
limestone, 30% from combustion of fuels in the kiln and 10% from other downstream plant

522
operations [4].
Figure 1 Use of electrical energy in cement production [1,4]
Energy efficiency improvements (use of energy efficient equipment, process modifications, etc.),
fuel switching to waste as alternative fuel, and, cement blending using industrial by-products have
helped decrease the CO2 emissions associated with energy conversion [1-4]. This paper presents a
review of the basic alternative fuels used in cement industry.
2. MATERIALS AND METHODS
2.1 Classification of alternative fuels
Cement kilns use different sources of energy to produce the high temperatures necessary for the
formation of clinker. The most common sources of fuel for the cement industry are: coal, fuel oil,
petroleum coke, and natural gas [5].
Alternative fuels are another source of energy used by cement producers around the world. These
fuels are usually derived from the mixtures of industrial, municipal and hazardous wastes [6].
Alternative fuels used in cement industries can be solid or liquid. They are required to have an
appropriate chemical content depending on the type of components and their organic contents.
There are four groups of solid alternative fuels [3].
These fuels generally include:
• Agricultural biomass residues
• Non-agricultural biomass residues
• Petroleum based wastes
• Miscellaneous wastes and
• Chemical and hazardous wastes
The main part of fuel consumption, and consequently CO2 generation, takes place in the calciner
and clinker forming kiln. The utilization of low-carbon content fuel with high hydrogen-to-carbon
(H/C) ratio instead of conventional fossil fuels can remarkably diminish the rate of CO2 emissions
in the process. In addition to producing a smaller amount of CO2, the use of alternative fuels has
been shown to improve refractory life and also reduce pressure drop in preheater tower [7].
Various types of alternative fuels can be used in a cement plant, with the adequate equipment
installed for the utiliszation. The use of alternative fuels in cement plants also reduces emissions
from landfills [8]. Therefore, it has been estimated that the utilization of this type of fuel will

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increase at the rate of 1% per year worldwide [1,6,7,9].
2.2 Alternative fuels
Alternative fuel utilization in the cement industry started in the 1980s. Starting in calciner lines, up
to almost 100% alternative fuel firing at the pre-calciner stage was very quickly achieved.
Alternative fuels are mainly used tires, animal residues, sewage sludges, and waste oil, as can be
seen in Table 1. The last are solid recovered fuels retrieved from industry waste streams, and to a
growing extent also from municipal sources. These refuse-derived fuels are pre-treated light
fractions processed by mechanical or air separation. Waste-derived fuels consist of shredded paper,
plastics, foils, textiles and rubber and also contain metal or mineral impurities. Alternative fuel
utilization in cement kilns is still progressing. While in some kilns up to 100% substitution rates
have been achieved, in others, local waste markets and permitting conditions do not allow for
higher rates of AFR. In any case, AFR utilization requires the adaptation of the combustion process.
Modern multi-channel burners designed for the use of alternative fuels and thermograph systems
allow control of the flame shape to optimize the burning behavior of the fuels and the burning
conditions for the clinker. Table 2 presents the calorific values of varius fuels used in cement
industry, while figure 2 presents a comparison with fossil fuels [9-12].
Table 1 Alternative fuels options for the cement industry [1, 9-12]
Liquid waste fuels Solid waste fuels Gaseous waste
petrochemical waste battery c ases Landfill gas
asphalt slurry plastic residues pyrolysis gas
paint waste wood waste
Petroleum coke rubber residues
Table 2 Wastes used for alternative fuel sources and their energy content [11, 12]
Wastes Energy (MJ/kg)
Used tir e 23.03
Husk 19.93
Industrial plastic 18.21
Waste oil 14.65
Scrap paper 14.23
Contaminated wast e 14.23
RDF plastic 11.72
Sewage s ludge 8.37
Figure 2 Comparison of the calorific values of various alternative fuels [3, 9, 10]
2.2.1. Refuse derived fuel (RDF)
The product of municipal solid waste (MSW) processing is typically referred to as “refuse derived

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fuel” (RDF), and is a common fuel alternative in many European countries. Italy, Belgium,
Denmark and The Netherlands are among the countries that have at least one cement kiln
processing RDF. MSW must be sorted to remove there cyclable and inert, and sometimes wet
fractions before it is input into cement kilns. The remaining material accounts for about 20–50% of
the original MSW weight can be incinerated directly or pelletized. Using RDF as a supplemental
fuel in cement production is an economically viable option to minimize fuel costs and landfill
disposals. The effect of using RDF on economy is changing with the cost of capital, coal and
landfill disposal prices [12-14].
There are many advantages of RDF such as minimizing CO2 emission and ash residue, producing
more homogeneous fuel, having higher calorific value content and a lower moisture content. It is
reported that for a net carbon offset through the replacement of coal with RDF, water content must
be less than 15% and in this case net reduction in emissions is obtained as 0.4 tons CO2/ton coal
[15].The basic issue regarding the use of RDF by cement kilns is the chlorine content since chlorine
weakens the cement and increase the risk of corrosion of steel bars in reinforced concrete structures.
Alternative fuels that have high amount of chloride like PVC should be used in limited amounts and
fuel mix optimization is very critical in terms of sufficient heat value in kiln and cement quality [16,
17].
The utilisation of RDF in cement industry is common practice since 1993 in EU while in Austria,
Belgium, Denmark, Italy and Netherlands are some of the indicative countries. According to
literature [18] around 115,000 tpa of MSW were co-incinerated in cement kilns in Europe in 1997
and more than 300,000 tpa of RDF in 2003 [18]. Also in Turkey according to a recent publication
[19] the target for a single cement plant is 35000t/y the usage of RDF [18, 19].
2.2.2. Tire derived fuel (TDF)
Tires are one of the most promising alternatives to the traditional fuels used in the incineration
process in the cement industry. The high temperature in a cement kiln ensures the complete
destruction of end-of-life tires (ELT). Moreover, tires are one of the most powerful alternative fuels
because of their high energy content (above 30 MJ/kg), low degree of material diversification, and
low moisture levels. The technical, environmental and economic viability of using tires in cement
manufacturing processes has been analysed in recent years [17, 20]. Consequently, it is
demonstrated that the amount of coal or petcoke required is reduced and thus the costs associated
with their use is also reduced. In regards to atmospheric emissions of GHGs and pollutants, it is
observed that the CO and total hydrocarbon emissions from the combustion of ELT-fuel mixtures
are slightly higher compared to those from non-ELT firing kilns. [17, 20].
The environmental benefits of utilizing scrap tires as a supplemental fuel in the Portland cement
manufacturing process are multifold. When whole tires are combusted in cement kilns, the steel
belting which is the wire mesh supporting the rubber tire becomes a component of the clinker,
replacing some or all of the iron required by the manufacturing process [15]. Since tires contain no
component deleterious to the quality of cement and, as proven from long experience in checking the
quality of the product, there is no change in the quality of cement caused by feeding tires.
Combustion residues of both tire and steel are not found in the finished cement [15]. None of the
differences in the emission data sets between tire derived fuel (TDF) versus non-TDF firing kilns
for sulfur dioxide, nitrogen oxides, total hydrocarbons, carbon monoxide, and metals were
statistically significant [12, 15, 22].
Many studies conducted by the U.S. governmental agencies and engineering consulting firms have
also indicated that TDF firing either reduces or does not significantly affect emissions of various
contaminants from cement kilns [22]. Tires have some limitations when they are introduced into the
kiln directly because of the large quantity of Zn that remains in the ashes, which can modify the

525
cement composition dramatically. To avoid this problem, replacement ratios under 30% are
suggested for the kiln fuel [23].
TDF is one of the most commonly used AF in the cement industry in Europe with regular utilisation
in 10 countries across EU. In Finland, Luxembourg and Portugal, TDF is the only AF utilised in
cement kilns. According to literature [18] around 550,000 tpa of TDF is co-incinerated in cement
kilns in Europe. Also in Turkey according to a recent publication [19] a single cement company
have disposed 12.2 millions of scrap tires within last 7 years in three kilns [18, 19].
2.2.3 Sewage sludge
The disposal of sewage sludge generated for sewage treatment plants is causing an important waste
management problem. Cement companies are able to use sewage sludge with calorific energy
potential as one of the alternative fuel sources. Therefore, dried sludge is also used as an alternative
fuel in its rotary kilns.The use of sewage sludge does not generate additional emissions also of all
proven technologies the co-processing of sewage sludge in a cement kiln offers the largest reduction
of CO2 equivalents per ton of dry sludge [24].
Sewage sludge (SS) has high water content. This is an important aspect to be considered when SS is
used in gasification and, especially, in combustion processes. The SS is dried before being used as
an alternative fuel or raw material and the cost of this process is important. Normally, SS is dried
using the waste heat from the cement kiln. It is placed in the main furnace of the cement kiln and
burned as a fuel, or it is gasified beforehand and the gas produced is used as an alternative fuel in
cement kilns, heaters, or pre-calciners. In both cases, the residual non-combustible components of
the sludge are used as raw materials in cement production. If utilized properly, sewage sludge
creates very little to zero environmental impacts [11, 24].
Dewatered SS is utilised in the Europe’s cement industry in 3 countries at least. According to
literature [18] around 50,000 tpa of SS is co-incinerated in cement kilns in Europe. Also in Turkey
according to a recent publication [19] a single cement company is using 45000 tons of SS annually.
[18, 19].
2.2.4. Municipal solid waste (MSW)
MSW production is increasing notably in Europe, and MSW has become a common alternative fuel
in the cement industry. However, most cement plants do not directly burn unsorted MSW due the
heterogeneous nature of the waste and the presence of components that could pose quality and
environmental concerns. Istead they use RDFs like the ones mentioned above. The RDFs from
MSW have different physical and chemical properties depending on their sources, especially with
respect to their ash, chlorine, sulphur, and water contents. There are notable differences among
RDFs, and certain physical and chemical properties can cause difficulties in the kiln combustion
process in cases where the RDF is introduced directly [6, 10, 12, 18].
2.2.5. Waste Derived Fuel PASr
Waste Derived Fuel named PASr is a product used in Malogoszcz Cement Plant, located in Poland.
This fuel is produced by shedding the following types of waste to a grain size of 0-70 mm or 0-40
mm: paper, cardboard, foil, cloth, textile, plastic containers, tapes, cables and cleaning agent. The
waste may be contaminated with oil, fat, lubricants, paint, etc. The fuel is characterised by the
following quality parameters:
1. average heating value—24 MJ/kg (value dependent on fuel composition)
2. average humidity content—3.19%
3. average ash content—7.98%
4. average chlorine content—0.42%
5. average sulphur content—0.23%

526
PASr fuel was fed to the furnace inlet and through the main burner of the furnace. The tests had
positive results despite the technical and technological problems which occurred. After the tests
were conducted, the following was noted:
1. An increased CO2 content in emissions when the fuel is fed to the furnace inlet, hence the fuel
must be fed to the main burner of the furnace
2. The content of the main oxide components and the phase composition of clinker produced
during the tests of PASr fuel is similar to clinkers produced without the addition of the fuel.
3. Emissions to air, meeting the requirements of the approval decision
After the appropriate installations have been constructed, the fuel will be fed to the furnace through
the main burner (since June 2002). The target combustion will amount to ca.45 thousand tonnes of
fuel annually [6, 25].
2.2.6. Waste Derived Fuel PASi
Waste Derived Fuel named PASr is a product used in Malogoszcz Cement Plant, located in Poland.
The fuel is the result of mixing the sorbent, in the form of sawdust or tobacco dust, with waste
originating from paint, varnish, heavy post-distillation fractions, diatomaceous earth contaminated
with petroleum-based waste, etc. The fuel is characterised by the following quality parameters:
1. average heating value —9.1 MJ/kg (value dependent on fuel composition)
2. average humidity content—30.45%
3. average ash content—24.13%
4. average chlorine content—0.24%
5. average sulphur content —0.28%
The PASi alternative fuel was fed to the lift chamber of the furnace. The tests had positive results
despite, as in the case of the PASr fuel, the technological problems. As in the case of PASr, it was
stated that the content of the main oxide components and the phase composition of the clinker
produced during the tests on the combustion of PASr fuels are similar to those for clinkers produced
without the addition of the fuel. The target is to burn ca. 35 thousand tones of the alternative fuel
(PASi) annually [6, 25].
3. RESULTS AND DISCUSSION
3.1 Adaptability of alternative fuels
The burning of various types of wastes requires the detailed control and adaptation of technological
processes to each type of waste. For this reason, alternative fuels are derived from wastes having
similar composition and properties. Following properties should be examined before the burning of
alternative fuels is undertaken:
• physical state of the fuel (solid, liquid, gaseous),
• content of circulating elements,
• toxicity (organic compounds, heavy metals),
• composition and content of ash,
• volatile content ,
• calorific value,
• physical properties (scrap size, density, homogeneity),
• grinding properties,
• humidity content,
• Proportioning technology.

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As a mixture of various wastes, alternative fuels must be produced in conformity with certain rules.
The chemical quality of the fuel must meet regulatory standards assuring environmental protection,
is the first rule. The calorific value must be stable enough to allow the control of the energy supply
to the kiln, the objective being to arrive at a fairly homogeneous composition, and the physical form
must allow easy handling of the material for transportation and a stable, adjustable flow of material
in the cement plant [12, 26, 27].
3.2 Benefits of burning alternative fuels
3.2.1. Ecological benefits
Several years of experience with the use of waste as alternative fuels by the cement industry have
shown that their application is justified both from an economic and an ecological point-of-view.
Firstly, the reduction of the use of non-renewable fossil fuels such as coal as well as the
environmental impacts associated with coal mining. Furthermore, the contribution towards a
lowering of emissions such as greenhouse gases by replacing the use of fossil fuels with materials
that would otherwise have to be incinerated with corresponding emissions and final residues. All
the energy is used directly in the kiln for clinker production [1, 14, 18, 26].
The use of alternative fuels in cement furnaces is also dictated by the broadly understood term
environmental protection, as not only primary sources of energy are spared, but also waste is used,
which would otherwise have to be disposed of on waste disposal sites, or burnt in specially
constructed incineration plants. Application of alternative fuels made from waste may allow one to
reduce the amount of waste to be disposed of by up to 50%. Both incineration plants and waste
disposal sites may have significant negative impacts on components of the environment. One must
be aware that the acquisition of primary sources of energy also negatively influences the
environment [1, 14, 18, 22, 26].
3.2.2. Technological benefits
Flame temperature at 2000C and material temperature at around 1400C which together with
residence time of 4–5 seconds in an oxygen rich atmosphere ensures destruction of organic
components in any residues .The neutralization of any acid gaseous formed during combustion by
the alkaline nature of raw material and subsequent incorporation in the clinker. Interaction of flue
gases and the raw material present in the kiln ensures that the non-combustible part, if any is
reduced. On total life cycle concept, it is superior in comparison with the specialized incinerator or
any other mode. There are many social benefits such as the implementation in rural area would
contribute to overall development of the area and employment. In addition generates additional
revenue for economically backward and frequent drought affected farmers of the region and aids
rural upliftment & ameliorating their economic status [1, 18, 22, 26].
3.2.3. Economic benefits
The use of alternative fuels by the cement industry is related to the energy-consuming process of
clinker production. On average, the energy required for the production of one tonne of cement
amounts to some 3.3 GJ, which corresponds to about 120 kg of coal. The costs of energy consist
about 30–40% of the total costs of cement production. Applications of alternative fuels will
therefore allow one to reduce the production costs. The use of fuels made from waste in cement
plants results not only in financial benefits for the industry, but also for society. Owing to such
waste management, smaller quantities of waste will be disposed of in, or directed to, incineration
plants. This will lead to a reduced number of new disposal sites, a limitation of the expansion of
existing sites and will avoid the necessity to build incineration plants [1, 2, 18, 26].
4. CONCLUSIONS
Many years of experience have shown that the use of wastes as alternative fuels by cement plants is

528
both ecologically and economically justified. The use of alternative fuels will help reduce the costs
of cement production. The average energy demand for the production of 1 ton of cement is about
3.3. GJ, which corresponds to 120 kg of coal with a calorific value of 27.5 MJ per kg. Energy costs
account for 30–40% of the total costs of cement production. The substitution of alternative fuels for
fossil fuels will help reduce energy costs, providing a competitive edge for a cement plant using this
source of energy. Furthermore, less waste will have to be dumped or burnt, which will mean less
dumping sites. Therefore, the use of waste-derived alternative fuels by cement plants will be also
beneficial to the environment. The conditions in rotary kilns, such as high temperature, the high
speed of the gas stream and the long particle-storage period, guarantee that the use of alternative
fuels is ecologically safe. Co-processing in the cement industry is the optimum way of recovering
energy and material from waste. It offers a safe and sound solution for society, the environment and
the cement industry, by substituting non renewable resources with societal waste under strictly
controlled conditions. The desired waste material, to be used as a fuel, is available within the state.
The cost of waste being used as fuel does not exceed the cost of fossil fuels.
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