Journal of Cleaner Production 181 (2018) 8e16
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Journal of Cleaner Production
journal homepage: www.elsevier.com/locate/jclepro
Use of non-recycled plastics and paper as alternative fuel in cement
production
A.C. (Thanos) Bourtsalas a, *, Jiao Zhang a, M.J. Castaldi b, N.J. Themelis a
a
b
Earth Engineering Center, Columbia University, New York, NY, 10027, USA
Earth Engineering Center, City College of New York, New York, NY, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The global cement industry produces over four billion tonnes annually. In recent years, the quest for
increasing energy efficiency has led this industry to test and use “waste” materials as alternative fuels
(AF). The objective of this study was to examine the use, as alternative fuel, of the shredded non-recycled
plastics and paper residue (NRPP) of a materials recovery facility at the Balcones plant in San Antonio,
Texas; this material has a Lower Heating Value (LHV) of about 17 MJ/kg and is called “engineered fuel”
(EF). The results showed that EF consists of mostly paper fiber, a biogenic material, so its use helps to
decrease CO2 emissions from cement production. In the US, on an average about 4.3 MJ of thermal energy
are used to dry, decompose, and sinter the carbonate minerals to produce one kg of “clinker” that is then
ground to cement powder and mixed with other compounds. If the maximum amount of EF that can be
used by the U.S. cement industry (83 million tonnes of cement per year) were to be separated at Material
Recovery Facilities and used as alternative fuel in cement kilns, the diversion of non-recycled paper and
plastics from landfills would amount to 17.7 million tonnes of EF. The general methodology used for the
Life Cycle Assessment (LCA) is Eco-indicators 99 that uses the SimaPro database and four scenarios were
assessed. The corresponding chemical structure of the EF was calculated and the associated emissions
during combustion were determined. The laboratory analyses determined the average makeup of the
sampled fuels consisted of 20% fossil based carbon and 80% biogenic. The use of EF in the cement industry reduces greenhouse gas emission by up to 3 tonnes of CO2 per tonne of EF used in place of a highquality coal. The study also found that use of EF in cement production has no adverse effect on the stack
emissions of cement plants, nor on the quality of cement produced. The mercury concentration in the
stack gas of U.S. cement kilns is well below the U.S. standard and the total dioxin emissions of all cement
plants amount to only 0.05% of the dioxins emitted by all U.S. sources. Furthermore, the cement process
incorporates the residual ash in the EF into the final clinker, thus resulting in both energy and materials
recovery.
© 2018 Elsevier Ltd. All rights reserved.
Keywords:
Cement production
Energy
Non-recycled plastics
Plastic waste
Paper waste
Alternative fuel
Environmental effects
1. Introduction: characteristics of global and US cement
production
The cement industry is one of the largest in the world and,
typically, about 3e5 MJ of thermal energy are used to dry, decompose, and sinter the carbonate minerals to produce one kg of
“clinker” that is then ground to cement powder, and mixed with
other components. For the first time in history, the annual output of
cement exceeded 4 gigatonnes (Gt) in 2015. China, with an output
* Corresponding author.
E-mail address: ab3129@columbia.edu (A.C. (Thanos) Bourtsalas).
https://doi.org/10.1016/j.jclepro.2018.01.214
0959-6526/© 2018 Elsevier Ltd. All rights reserved.
of 2.4 Gt or 57.3% of the total global production is the world's
leading producer, followed by India 6.6% of world production and
the U.S. (2.0%), as presented in Fig. 1.
In the period between 1993 and 2005, U.S. cement production
increased from 67 million tonnes to a maximum of 99 million
tonnes in 2005. It decreased to a low of 65 million tonnes in 2009,
due to the economic crisis and then recovered to 83 million tonnes
by 2015. The estimated clinker capacity for 2015 was 106 million
tonnes of clinker. Therefore, the average energy consumption was
calculated at about 4.5 MJ/kg of cement in 2013, and was about the
same since 1993 as presented in Fig. 3 (USGS, 1993e2016; Bye,
2011; Marceau, 2006).
Fossil fuels have been used in cement production but the
A.C. (Thanos) Bourtsalas et al. / Journal of Cleaner Production 181 (2018) 8e16
Fig. 1. World cement production in 2015, total 4.1 billion tonnes (USGS, 1993e2016).
Fig. 2. . Replacement ratios of fossil fuels with alternative fuels (AF) in European
countries. The average for EU-27 is 30.5% (Zhang, 2013).
increasing pressure for lower operating cost and reduced environmental impact has led the global cement industry to use
“waste” materials as alternative fuels (AF). AF used in cement
production include a variety of waste fuels, such as automobile
shredder residue (ASR), carpet residue, textiles, wax residue, meat
and bone meal, landfill gas, and fuels derived from municipal solids
waste (MSW) streams. It is desirable for the properties of AF to be
close to petcoke since the process has been optimized for that fuel.
Petcoke is a solid carbon material, which is a by-product of the oil
refining process. Table 1 (Nasrullah et al., 2015; Gallardo et al.,
2014; Rada and Ragazzi, 2014; Zhang, 2013; Zhou et al., 2013;
Patel et al., 2012; Ahn et al., 2013; Garg et al., 2007; Skodras
et al., 2006; Grammelis et al., 2009; Piao et al., 2000; Dai et al.,
2001; Conesa et al., 2004; Wan et al., 2008; Hassan et al., 2009;
Scala and Chirone, 2004; Senneca et al., 2002; Zou et al., 2007;
Ayllon et al., 2006; Kaantee et al., 2004; Wang et al., 2004; Trent
et al., 1982; Brady and Hatch, 1997; NETL, 2012; Littlefield, 2009;
Aho and Ferrer, 2005; Borgianni et al., 2002; Liu et al., 2001;
Jannelli and Minutillo, 2007) shows that many of the AF materials
meet one or two specifications, e.g., moisture and ash content, but
not others, such as Cl concentration and heating value. Tires and
Tire Derived Fuels (TDF) have a similar high heating value to petcoke (34.4e36.2 MJ/kg) while refuse derived fuels (RDF) are lower
9
in heating value than petcoke and coal.
The use of waste materials in cement plants has increased in
recent years. In 2012, over two thirds of the nearly 270 cement
plants in the European Union used some alternative fuels. The
average use of AF was about 30% of the total thermal energy, with
the highest levels of 62% in Germany, 63% in Austria, and 83% in the
Netherlands (Fig. 2 (Zhang, 2013)).
The typical heating values of the various fuels used in the US
cement production are shown in Table 2 (US EPA, 2008; IPCC, 2006;
United Nations, 2010). The units of all fuels are expressed in MJ/kg.
The total energy consumption of the US cement industry is calculated at 3.8 MJ/kg of cement and 4.2 MJ/kg of clinker for the year
2014 and is slightly reduced as compared to 1993, which was about
4.3 MJ/kg of cement and 4.4 MJ/kg of clinker. Fig. 4 shows the kinds
of fossil and alternative fuels used by the U.S. cement industry, in
the period 1993e2014, expressed as a percent share of fuels in the
total energy consumption. In the U.S., the use of AF (tires, RDF,
wood, liquid wastes, etc.) in the cement industry increased from
8.7% to 18.9% of the total energy consumption (USGS, 1993e2016).
The AF used are divided into three big categories: tires, other solid
waste and liquid waste. Both “other solid waste” and “liquid waste”
may include several materials and their LHV varies widely. The use
of “other solid wastes” in the U.S. cement industry increased from
90 thousand tonnes in 1993 to 1.3 million tonnes in 2014 which, at
an assumed LHV of 18 MJ/kg, represented about 39.4% of the AF
energy used in cement production (7.4% of the total fuel used)
(USGS, 1993e2016). The liquid waste, with an assumed LHV of
15 MJ/kg, contributed to about 39.6% of the AF energy used in
cement manufacturing (7.5% of the total) and tires, with a LHV of
32.6 MJ/kg, contributed at about 21.1% to the AF energy produced
for cement production (3.9% of the total). The use of coal, with LHV
of 26.3 MJ/kg, dramatically decreased from 82.8% in 1993 to 56.7%
in 2014 of the total energy used in the US cement industry. The
contribution of petcoke (34 MJ/kg) to the total energy used was
slightly increased from 14.1% in 1995 to 17.1% in 2014. However,
there is a tendency of the cement industry to move away from the
use of fossil fuels and use AF instead. This is associated with the
observed steady increase of the ‘other solid waste’ fuels use since
1993 (USGS, 1993e2016).
However, there is often a negative public perception for the use
of AF in combustion processes, mainly associated with the chlorine
content of these fuels and the formation of dioxins and furans
during combustion. Dioxins and furans and other organic pollutants of environmental concern emissions are negligible, mainly
associated with the long residence time of the fuel to the cement
kiln and the level of temperature inside the kiln. An inventory by
Columbia University (Dwyer and Themelis, 2015) of all controlled
(i.e. industrial) and non-controlled (i.e. landfill fires, back yard
burning, etc.) sources of dioxins in the U.S. showed that the total
annual dioxin emissions of the U.S. cement industry amounted to
18 g TEQ, corresponding to 0.05% of all U.S. sources of toxic dioxins
(Dwyer and Themelis, 2015). Also, a survey (WBCSD, 2006) of
nearly 2200 worldwide dioxin emissions data, from 1990s to 2005,
of cement kilns co-combusting AF concluded that the use of AF had
a negligible effect on dioxin emissions; in some cases where AF
contained trace amounts of heavy metals, they were stabilized in
the clinker or entrapped by the Air Pollution Control (APC) systems,
thus resulting in negligible difference of heavy metal emissions
between plants combusting only fossil fuels and those cocombusting AF (Kara, 2012; Schneider et al., 2011; Shih et al.,
2005; WBCSD, 2006).
The energetic and environmental impacts of using AF for
cement and clinker production have been extensively examined
with Life Cycle Analysis (LCA) models, laboratory studies and industrial surveys (Kajaste and Hurme, 2016; Gursel et al., 2014; Li
10
A.C. (Thanos) Bourtsalas et al. / Journal of Cleaner Production 181 (2018) 8e16
Fig. 3. Clinker and cement production (primary axis: million tonnes) and energy consumption (secondary axis: MJ/kg), U.S. 1993e2014 (USGS, 1993e2016).
Table 1
Proximate and ultimate analysis and heating values of fuels used in cement production. Notes to Table 2 shown in following page: a) Pine wood and waste wood, b) Refuse
Derived Fuel from Municipal Solid Waste, c) Tire Derived Fuel, d) Meat and Bone Meal, e) Poly-Ethylene, f) Poly-Vinyl-Chloride, g) American coal, (*) calculated. The Low
Heating Values (LHV) are frequently used in Europe.
Fuel Type
Wooda
(12), (18)
RDFb
(4)e(11), (14),
(19),
(20), (21), (31),
(32)
Tires
(15), (16), (23),
(28)
TDFc
(19), (20)
Pecan Shells
(28)
MBMd
(22), (23)
(29)
PEe
(20), (24)
PVCf
(13), (24), (30)
Sewage Sludge
(19), (23)
Pet. Coke
(21), (23)
Coalg
(19, 25e27)
Proximate Analysis (wt. %, as received)
Ultimate Analysis (wt. %, dry basis)
Moisture Volatile
Matter
Fixed
Carbon
Ash
C
5.6e6.3
69.5e78.5
15e16.1
0.5e8.8
3.7e20
71.9e76
3.9e13.2
10.2
e13.8
46e51.3 5.7
e5.8
41.7
4.4
e50.2
e7.8
0.7e4
63.8e68.7
24e31.1
2.2e8.2
76.7
e89.4
0.9e1.9
63.4e64
30.4e30.7
3.3e4.4
14.6
n/a
n/a
2.32
83.8
e86.7
46.84
1.4e8.1
64.5e79.7
7.2e9.7
10.4
e28.3
42.1
e55.7
z0
z0
e0.06
1e7.6
86
35.9e38 4.4e5 0e0.11
H
Alkali
N
S
Cl
O
0.07
e3.8
0.75
e1.65
0.01
e0.05
0.1
e0.76
z0
35.4e36 z0
0.7
e1.13
28.5
e36.3
7e7.8 0.2e0.5
0.8e2.2
z0e0.1 0.4e4.5
6.9
0.3e0.6
1.9e2
z0
5.41
0.44
n/a
5.8e8 7.2e8.9
14
K
HHV
MJ/kg MMBTU/ MJ/kgMMBTU/
ton
ton
17.1*-22.5*
14.7e19.4
0
0
15.9*-17*
e0.93 e0.37 13.7e14.6
18.6e23.9
16.0e20.6
17.5e18.4
15.1e15.9
0e0.9 0e1.1 32e35.6
28.4e30.7
34.6*-37.3
29.8e32.1
0.9e2.3
n/a
n/a
n/a
n/a
n/a
n/a
0.05
e0.4
0.2
15.3
e38.4
1.5
0.3
31.8e36.8
27.4e311.7
18.2*
15.7
19.6e28.8*
16.9e24.8
33.5*-38.4*
28.9e33.1
19.8
17.1
21*-30.6
18.1e26.4
z0
z0
z0
n/a
n/a
z0
57
z0
n/a
n/a
0.1e0.6
z0-1
22
z0
z0
44.6
38.4
17.1*
14.7
9.3e15.8
8.0e13.6
44.9*
38.7
18.1
15.6
10.4*-17.5
9.0e15.1
1.2e1.7
1.5e4
z0
1.1e1.2
z0
1.2
e1.41
0.6e5.5
z0
e0.33
5.9
e12.5
z0
99.8e100
e0.17
z0e0.2 85.9e91
6.3e9
5.2e5.6
40.5e85
5e10.1
17.9
e29.5
36.4
e40.5
4.7e7 0.84
e5.0
0.8e1.5
7.6e10
88.6e89.6
0.5e1
1.1e3.3
23e35.3
44.2e66.8
6.4
e15.5
89.5
e92.7
65.3
e80.9
2.4
e3.7
3.7
e5.1
et al., 2014; Valderrama et al., 2012; Chen et al., 2010; Huntzinger
and Eatmon, 2009; Galvez-Martos and Schoenberger, 2014; De
Queiroz Lamas et al., 2013; Strazza et al., 2011; Rovira et al., 2010;
Genon and Brizio, 2008; Mokrzycki et al., 2003; VDZe.V. V.D.Z.,
1996; Karstensen, 2008; Dwyer and Themelis, 2015; Kara, 2012;
Schneider et al., 2011; Shih et al., 2005; WBCSD, 2006; European
Commission, 2003; Montejo et al., 2011). However, there are no
Na
LHV
z0
z0
33.5e35.4*
28.9e30.5
25.4e31.8*
0
0
e0.03 e0.19 21.9e27.4
z0
34.4*-36.2
29.6e31.2
26.3*-32.9
22.7e28.3
studies on the use of non-recycled plastics and paper (NRPP) as AF
in cement production and the associated potential of advancing
waste-to-energy in a nation. The objective of this study is to fill this
gap. Data were obtained from the Balcones cement plant in San
Antonio, Texas, which receives engineered fuel (EF) comprised of
NRPP from a Materials Recovery Facility located nearby.
A.C. (Thanos) Bourtsalas et al. / Journal of Cleaner Production 181 (2018) 8e16
Table 2
LHV of fuels used in U.S. cement industry [33e35].
Fuels
LHV (MJ/kg)
Coal
Petcoke
Tires
Coke from coal
Fuel Oils
Natural Gas
Other solid waste
Liquid waste
26.3
34.0
32.6
28.2 (IPCC, 2006)
40.0 (IPCC, 2006)
53.5 (United Nations, 2010)
18.0
15.0
Fig. 4. Energy use by different fuels in U.S. cement industry, 1993e2014 (USGS,
1993e2016).
2. Characteristics of Balcones plant and alternative fuels used
The Balcones plant operates with a rotary kiln, 54 m long, and a
kiln, where secondary combustion takes place, 74 m long. Fig. 5
depicts a schematic of the two kiln lines, both having the flow
path for solids and gases. The rotary kiln is equipped with a 5-stage
preheater precalciner with raw gas temperatures of about
11
310e320 C. The calciner is designed for a long retention time to
ensure that AF are effectively combusted and that CO and VOC
emissions are kept to the minimum. The air pollution control (APC)
system of Balcones includes selective non-catalytic reduction for
NOx emissions (SNCR; ammonia injection), and baghouse fabric
filter for particulate matter (PM) control.
At the Balcones facility, the typical AF used are: “Engineered
fuel” (NRPP), wood, tires and pecan shells. EF is provided to the
cement plant by a materials recovery facility (MRF) in San Antonio
where source-separated recyclables are sorted out to marketable
paper, plastic, metal, and glass. The Balcones MRF was built in 2012
on a 10.6-acre site with a capital investment of $ 24 million or $278
per ton of MSW. The gate fee of the facility is about $35 per ton of
MSW. The total inbound tons of all residential, commercial, direct
feed fiber and plastics averages 7200 tons per month of which
about 4000 tonnes are residential waste. The residential single
stream is being processed at 25 tonnes per hour and the commercial single stream is being processed at 15e17 tons per hour.
Balcones is currently operating a single 8.5-h shift Monday through
Saturday. In 2013, the production of EF amounted to about 3000
tonnes (Zhang, 2013).
The Balcones process involves mixing of the as-received MSW to
specific plastic-to-fiber ratios depending on waste availability,
process requirements, and customer needs. The mixed MSW is
shredded before being fed at a controlled rate into two parallel fuel
extruders with adjustable dies that control the extrusion dimensions. The fuel extrusion process is primarily accomplished
using pressure. Heat can also be added with the use of resistance
heating elements. Once extruded, the fuel pellets fall onto a
conveyor and stored in truck containers ready for delivery.
The residue consists primarily of non-recycled plastics and paper fiber (NRPP) with a calorific value of 17.5 MJ/kg, which is similar
to the US average of ‘other solid fuels’ (18 MJ/kg). It is shredded and
transported by truck to the cement plant. A typical flow diagram of
the NRPP production process is shown in Fig. 6.
The monthly composition of the AF combusted at the Balcones
plant, in 2013, is presented in Fig. 7. In February 2013, the facility
reached a monthly record of NRPP (12.5% of total fuel used) used as
AF. Also, in April 2013, Balcones site reached a peak in the use of
energy from AF (38.9% of total fuel used), which was significant
higher than the US average usage of AF (19.7%).
3. LCA study and calculation of greenhouse gas effects of
using NRPP
The emissions of CO2 by the U.S. cement industry in 2013 were
calculated to be about 60.7 million tonnes, i.e., 0.87 tonnes of CO2
per tonne of clinker produced (USGS, 1993e2016). Table 3 compares the U.S. MSW and cellulose (paper fiber) compositions. The
molecular weight and the heat of formation of the various compounds were obtained from HSC 9.1 software. The corresponding
chemical structure of the first three materials was calculated using
the atomic composition of each material (Zhang, 2013). The most
biogenic material, poplar wood, contains 4.2 atoms of oxygen for
every 6 atoms of carbon; while the highest fossil-based material,
TDF, contains very little oxygen.
The combustion of the NRPP fraction is associated with the
following reaction:
C6 H11.7 O2.7 þ 7.57 O2 / 6 CO2 þ 5.85 H2O
Fig. 5. Flow diagram of cement process. Fig. 5 depicts a schematic of the two kiln lines,
both having the flow path for solids and gases (Zhang, 2013).
which is a highly exothermic reaction with 23.8 MJ of energy
released/kg of fuel, which is higher than the calculated value of
MSW, 17.9 MJ/kg, as attenuated. However, the reported heating
value of the NRPP used at the Balcones plant was 17.5 MJ/kg. The
12
A.C. (Thanos) Bourtsalas et al. / Journal of Cleaner Production 181 (2018) 8e16
fuels, except for waste tires.
The general methodology used for the Life Cycle Assessment
(LCA) is Eco-indicators 99 that uses the SimaPro database. Four
different scenarios were considered to determine the carbon dioxide emissions of using NRPP in place of coal in the cement production process:
- Scenario 1 (best case): 75% of the thermal energy is derived
from NRPP and 25% from coal.
- Scenario 2: 50% of the energy is derived from NRPP and 50%
from coal.
- Scenario 3: 25% of the energy is derived from NRPP and 75%
from coal.
- Scenario 4 (worst case): 100% of the energy is derived from
coal.
The functional unit was 1 tonne of clinker production and the
assumptions made for the CO2 calculation were as follows:
- Total energy demand of 4500 MJ/tonne of clinker produced.
- Heating value of 26.3 MJ/kg, for coal, and 17.5 MJ/kg, for NRPP.
- Transport distance from MRF to cement plant of 50 km, using
7.5e16-tonne truck.
- Transport distance from coal mine to cement plant: 300 km via
rail.
80% of carbon in NRPP is biogenic (paper fiber, etc.) and 20%
fossil based (non-recycled plastics).
- The carbon-based compounds in NRPP are diluted with 20%
moisture plus non-combustible materials.
Fig. 6. Production process of EF, which consists of non-recycled plastics and paper
fiber (NRPP), used at Balcones plant. The input waste to the Materials Recovery Facility
(MRF) for the recovery of EF-NRPP is Commercial and Industrial Waste (C&I). In 2013,
the total inbound tons of all residential, commercial, direct feed fiber and plastics
averages 7200 tons per month of which about 4000 tonnes are residential waste. In the
same year, the EF production was about 3000 tons.
losses are mainly associated with the moisture and the impurities
contained in the NRPP fraction.
The CO2 emissions were calculated by the above chemical
equation, which gives 1.93 kg of CO2 per kg of NRPP. MSW combustion is associated with 1.68 kg of CO2 and tires with 3.10 kg of
CO2 per kg of fuel, as presented in Table 3. Also, the combustion of
pet coke is associated with 3.56 kg of CO2 per kg of pet coke combusted, as a result of the significant higher amount of carbon contained in petcoke compared to NRPP/RDF, MSW and other waste
The alternative fuel used was sampled and analyzed at EEC|
CCNY laboratory using standard ASTM protocols. The analyses
determined the average makeup of the sampled fuels consisted of
20% fossil based carbon and 80% biogenic. (Zhang, 2013).
Since the ash of both NRPP and coal is absorbed in the clinker
the boundaries of the LCA study are defined from the production of
the fuel input to the cement production process and the CO2-eq
emissions were calculated. In accordance with the international
protocol (IPCC, 2006), only the fossil-based CO2 emissions are
considered as contributors to the greenhouse gases (GHG) causing
climate change. The GHG emissions are based on the SimaPro
database and the Ecoinvent program and U.S. input-output database for coal mining, production of NRPP (electricity from waste
allocation from Simapro), transportation (coal freight and lorry for
coal ash and NRPP), and landfill avoidance for NRPP.
For the production of NRPP-EF, the energy consumption was
assumed to be 2580e3840 MWh/year. The annual energy costs
were calculated to be $180,000 e $192,000/year at an electricity
rate of 5e7 ¢/kWh. At a production rate of 36,000 tonnes of NRPPEF per year, the energy intensity of producing NRPP-EF is estimated
at 864e1272 kWh of electricity per ton of NRPP-EF produced. In this
case, the energy cost is about $5/tonne of EF (Zhang, 2013). The
estimated electricity consumed was used as an input to the
Ecoinvent and U.S. input-output database to obtain the CO2-eq
emissions per ton of EF (Cleary, 2009).
The results of the LCA analysis are shown in Table 4. It is
assumed that, when the NRPP is not used in cement production, it
is disposed in a sanitary landfill where 75% of the methane (CH4)
generated by the organic fraction of the NRPP is captured and 25% is
emitted to the atmosphere (Zhang, 2013). Under these circumstances, the SimaPro LCA program assigns an additional GHG
benefit of 1.31 kg CO2 per kg of NRPP used in cement production.
The use of one tonne of NRPP in the cement production results
in the reduction of about 1.6 tonnes of CO2. The beneficial effect of
using NRPP in place of coal, when the avoided landfill emissions are
13
A.C. (Thanos) Bourtsalas et al. / Journal of Cleaner Production 181 (2018) 8e16
45
40
35
% of fuels used
30
EF
Tires
25
Wood
Pecan
20
Tire Fluff
15
Total AF
10
5
0
Jan Feb Mar April May June July Aug Sept Oct Nov Dec
Fig. 7. Average monthly composition of AF used at the Balcones plant. Data from JaneDec 2013
Table 3
C, H, and O concentration in five dry materials and petcoke coal.
Composition
Tire derived fuel
RDF and NRPP
U.S. MSW
Poplar wood
Cellulose
Petcoke
%C
%H
%O
All other (%)
Calculated CeHeO structure
Formula weight (g/mol)
Carbon emissions during combustion (kg/kg of fuel)
85.20%
7.30%
0.50%
7.00%
C6 H6.2 O0.03
78.79
3.10
48.80%
7.80%
29.20%
14.20%
C6 H11.7 O2.7
127.06
1.93
38%
5.21%
33.33%
23.96%
C 6 H10 O4
146.14
1.68
47.50%
6.10%
44.50%
1.90%
C6 H9.2 O4.2
148.53
1.66
44.40%
6.20%
49.40%
0.00%
C 6 H10 O5
162.14
1.51
90.00%
3.00%
1.20%
5.8%
C6H2.4O0.06
74.08
3.56
Table 4
LCA calculation of GHG emissions for four EF-coal combustion scenarios for functional unit: 1 tonne of clinker.
Energy needed MJ/tonne clinker
Kilograms fuel per tonne clinker
Mining of coal, kg CO2/tonne clinker
Production of EF, kg CO2/tonne cl.
Coal transport, kg CO2/tonne clinker
EF transportation (kg CO2/tonne clinker)
Combustion emissions, kg CO2/tonne clinker
Subtotal kg CO2/ton clinker
Total EFþcoal, for scenario, kg CO2/tonne clinker
Kg CO2 avoidance due to EF use in cement
Total GHG Including landfill, kg/tonne clinker.
Scenario A: 75% EF
Scenario B: 50% EF
Scenario C: 25% EF
Scenario D: 0% EF
EF
Coal
EF
Coal
EF
Coal
Coal
3375
193
1125
43
4.3
2250
129
2250
86
8.6
1125
64
3375
128
12.8
4500
171
17.1
1.6
2.1
456
470.4
609
628.2
628.2
0
0
0.25
0.17
0.5
0.03
372
372.3
530.1
98.1
351.1
153
157.8
included in the comparison of GHG emissions, results in an additional reduction of 1.3 tonnes of CO2 per tonne of NRPP, making a
total of about 2.9 tonnes of CO2.
4. Limits for AF use for replacing fossil fuels in cement
production
One of the basic specifications of the characteristics of the
feedstock to the cement kiln is the maximum amount of chlorine
content, which should be <0.7%. Higher amounts of chlorine may
0.08
1.1
0.01
249
249.2
564.9
63.3
232.3
306
315.7
0.008
124
124.1
594.5
33.7
117.5
result in the excessive formation of salts (cement kiln dust) that are
volatilized in the kiln and then solidify and can foul and corrode the
downstream unit (in the direction of gas flow) of the calciner
(Ahling, 1979). This section discusses the corresponding upper limit
of AF that can be used to replace fossil fuels in cement production.
The data for the chlorine content of different fuels were
collected from different sources and small discrepancies were
noted. The results are shown in Table 5. Coal and petcoke have the
lowest chlorine content. The chlorine in petcoke is about
0.005e0.032%. There are high chlorine coals (>0.3%) produced in
14
A.C. (Thanos) Bourtsalas et al. / Journal of Cleaner Production 181 (2018) 8e16
Table 5
Chlorine contents of different fuels.
Fuel type
Chlorine (%)
Coal
0.04 (CIWMB, 1992)
Petcoke
MSW
RDF
0.005e0.032 (DOE's)
0.3e0.8 (CIWMB, 1992)
Wood
pellet
Tires
EF
a
b
0.01e0.03 (DOE's)
0.01e0.2 (National Research Council, 0.12e0.54 (Dept. of Energy,
2007)
1993)
0e1.56 (0.726)b (Valkenburg, 2008)
0.36e1.29 (0.7)b (European commission,
2003)
0.010e0.126 (0.048)b (Obernberger and Thek, 0.01e0.05 (0.02)b (Vassilev, 2010)
2004)
0.07e0.2 (CIWMB, 1992)
0.15 (Rubber manufacturers association,
2016)
0.74a
Balcones Plant.
Number in parenthesis is the mean value.
Illinois, but the usual chlorine found in coals ranges between 0.01
and 0.04%. Wood pellets (0.01e0.126%) and tires (0.07e0.2%) have
higher chlorine content than coal and petcoke, but lower than RDF
(0.36e1.29%). MSW is reported to range from 0.3 to 1.56% but the
typical range of the U.S. MSW is 0.4e0.6% and of the Engineered
Fuel- NRPP (0.74%) (CIWMB, 1992; Rubber manufacturers
association, 2016; DOE's; National Research Council, 2007; Dept.
of Energy, 1993; Valkenburg, 2008; European commission, 2003;
Obernberger and Thek, 2004; Vassilev, 2010; Ahling, 1979; UNEP,
2005). Therefore, all types of AF, including the NRPP used at Balcones, can potentially substitute fossil fuels in cement production.
5. Potential for increasing the U.S. WTE capacity using AF
The 2013 use of AF in the cement industry effectively increased
the total waste-to-energy (WTE) capacity of the U.S. from 27.4
million to 28.5 million tonnes, i.e. by 3.9%. If all energy for cement
production in the US (310.5 billion MJ) was provided by EF similar
to these used at Balcones facility (17.5 MJ/kg of NRPP), then about
17.7 million tonnes of the NRPP fuel would be needed. Therefore,
the increase in the WTE capacity of 2013 or avoidance to landfill
would be about 64.5%.
To quantify this benefit, it will be assumed that the current recovery from U.S. households of 33 million tonnes of paper fiber and
2.3 million tonnes of plastic wastes (Dolly, 2014) will be decreased
by 17.7 million tonnes of NRPP, to be used in U.S. cement plants,
similarly to the use of NRPP at the Balcones cement plant. This
option will be compared with two alternatives: Landfilling the
NRPP, as is done presently, and building additional WTE capacity
for 17.7 million tonnes of MSW.
It is assumed that the NRPP collected and used in cement plants
will consist of two thirds paper fiber (i.e. 11.8 million tonnes) and
one third plastic wastes (5.9 million tonnes). Landfilling of 10
tonnes of MSW requires 1 m2 of land (Dolly, 2014). Therefore, the
use of the assumed amount of NRPP in the cement industry is
associated with the conservation of 1.7 million square meters or
420.1 acres of land surface, plus the avoidance of about 53 million
tonnes of CO2-eq (2.9 tonnes CO2-eq per tonne of NRPP).
For the comparison with WTE since the current capital cost of
WTE power plants is between $600 and $800/tonne of MSW processed, the 2014 use of 17.7 million tonnes of NRPP in the U.S.
cement industry would avoid the investment of $10.6 to $14.2
billion in new WTE capacity. However, the combustion of 17.7
million tonnes of MSW in WTE facilities would produce about
8.9 GWh of electricity and about 35 GWh of district heating/cooling
or low-pressure steam for industrial uses (Zhang, 2013). Also, with
WTE the recovery of about 10 wt% of ferrous and non-ferrous
metals from the bottom ashes is possible. Metals are typically
with the highest value and demand in the market, which can go up
to $700 for non-ferrous aluminum. However, WTE is linked with
the hazardous disposal of the fly ash produced, which will be at a
small amount (0.17e0.89 million tonnes at an assumed 1 to 5 wt%
of fly ash produced from the combustion of MSW), but the cost of
processing and disposal is often up to $50 to $100 per tonne of fly
ash. Although the production of NRPP requires some investment in
mechanical processing, at MRFs and feeding systems at cement
plants, it is evident that increasing the use of waste-derived fuels in
cement production is economically more attractive than adding
WTE capacity (Energy Recovery Council, 2016; Advancing
Sustainable Materials Management, 2013). The cost of collection,
transport and processing the NRPP at MRF facilities would be
covered by the avoidance of landfill gate fee. Regarding energy
benefits, the use of NRPP in cement production would avoid the
mining of about the same tonnage of coal.
6. Conclusions
Cement production is one of the largest solids processing hightemperature process worldwide and it is associated with the
emission of high amounts of CO2-eq during production. The
expanded use of AF in cement kilns will reduce the use of fossil
fuels and the amount of wastes that need to be landfilled. This
study has shown that the combustion of AF in the cement kiln
system is being applied widely and offers definite environmental
and energy advantages. The major findings of this study were:
1. The total energy consumption of the US cement industry is
calculated at 4.2 MJ/kg of clinker for the year 2014 and is slightly
reduced as compared to 1993, which was about 4.4 MJ/kg of
clinker. The use of AF (tires, RDF, wood, liquid wastes, etc.) in the
cement industry increased from 8.7% in 1993 to 18.9% in 2014 of
the total energy consumption. Much higher levels have been
reached in Germany (62%) and the Netherlands (83%). The use of
“other solid wastes” in the U.S. cement industry increased from
90 thousand tonnes in 1993 to 1.3 million tonnes in 2014 which,
at an assumed LHV of 18 MJ/kg, represented about 39.4% of the
AF energy used in cement production (7.4% of the total fuel
used).
2. On the assumption that the NRPP used at Balcones (17.5 MJ/kg)
were to be used throughout the U.S. cement industry, the increase in the U.S. WTE capacity, and corresponding reduction in
landfilling, would be about 17.7 million tonnes of NRPP, i.e. a
64.5% increase of the current U.S. WTE capacity.
3. The use of about 17.7 million tonnes of NRPP in the cement industry would be associated with the conservation of 1.7 million
square meters or 420 acres of land surface, plus the avoidance of
A.C. (Thanos) Bourtsalas et al. / Journal of Cleaner Production 181 (2018) 8e16
about 53 million tonnes of CO2-eq. Increasing the capacity of the
U.S, WTE industry by 18 million tonnes would require a capital
investment of $11 to $14 billion. Although the production of
NRPP will require some investment in mechanical processing, at
MRFs, and feeding systems at cement plants, it is evident that
use of waste-derived fuels in cement production is economically
more attractive than adding WTE plant capacity.
4. The dioxin emissions examined in this study were an order of
magnitude lower than the U.S. and E.U. standard (0.1 ng TEQ/
Nm3 of stack gas). In a separate EEC study (Dwyer and Themelis,
2015), an inventory was created of all controlled (i.e. industrial)
and non-controlled (i.e. landfill fires, back yard burning, etc.)
sources of dioxins in the U.S. The results showed that the annual
dioxin emissions of the entire U.S. cement industry amounted to
18 g TEQ, corresponding to 0.5% of all U.S. sources of toxic
dioxins.
5. The carbon dioxide emissions of four fuel scenarios were
calculated using standard LCA methodology; they ranged from
100% high quality coal to 25% coal-75% engineered fuel. The
results showed that the major GHG impact was the CO2 generated during combustion of the fuel. The GHG benefit of using EF
amounted to 3 tonnes of CO2 per tonne of EF used in place of
coal, when the avoidance of landfill gas emissions was included.
The GHG emission is reduced from 390 kg CO2 per tonne clinker
for 100% coal to 137 kg for 75% EF and 25% coal.
6. The overall conclusion from this study was that the use of MSWderived fuels in cement production has no adverse impact on
the cement production process or the quality of the product.
Acknowledgments
The authors would like to acknowledge the contribution of the
Balcones plant personnel and the provision of operating data by
Balcones engineers. The authors are also very grateful to Mr. Jose B.
Martinez Madero of CEMEX for engaging the Earth Engineering
Centers of Columbia University and City College of New York in this
study.
Notation
AF
APC
ASR
EF
GHG
LCA
LHV
MRF
MSW
NRPP
PM
RDF
SNCR
TDF
WTE
Alternative fuel
Air pollution control
Automobile shredder residue
Engineered fuel: shredded non-recycled plastics and
paper residue (NRPP)
Greenhouse gases, expressed in CO2-eq
Life cycle analysis
Lower heating value
Materials recovery facility
Municipal solid waste
non-recycled plastics and paper residue (NRPP).
Processed AF, called EF
Particulate matter
Refuse derived fuels
Selective non-catalytic reactor
Tire derived fuels
Waste-to-energy
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