Simulation model for the calcination process of cement.

Idalia Flores(a)Guillermo Perea(b)

(a) Facultad de Ingeniería, UNAM
(b) Facultad de Ingeniería, UNAM
(a)
idalia@unam.mx, (b)guillermo.perea@live.com.mx

Abstract
Simulation is an important tool when a
phenomenon or input-output relationships of
a system makes its operation or testing
impossible, expensive, dangerous or
impractical. This paper develops a simulation
model for the burning process of Portland
cement. The methodology used is the one
used in simulation, which establishes the
definition of the problem, analysis of the
variables to be modeled, executes a basic
model, a detailed model development,
Figure 1 Cement components
validation, reports and conclusions.

Keywords: Simulation, calcinations, clinker, 2. Manufacturing process.

Cruz Azul cement, Arena, Simio. 2.1 Obtaining raw materials.
The cement manufacturing process begins
1. Introduction with the extraction of raw materials that
Cement is one of the main inputs in the are found in deposits, usually in open
construction industry in Mexico; quarries. The quarries are operated by
domestic production was 42 million tons controlled blasting in the case of hard
in 2010. The calcinations of cement unit materials such as limestone and slates,
is a system consisting of a Preheater, Kiln while excavators are used to dig out the
and Cooler (PHE), which raises the soft materials (clays). Once the material is
temperature of the limestone powder to extracted and classified, it is then crushed
1.450° C, causing physicochemical to a particle size suitable for the mill
changes and the formation of silicates in a product and is transported by conveyer
granular mixture called clinker. belt or truck to the factory for storage in
Simulating the system PHE will allow us the prehomogenization pile.
to analyze the formation of clinker
through a mass-energy balance. 2.2 Homogenization and grinding of
To optimize this process we require a model raw.
that allows us to manipulate the different In the prehomogenization pile, the
variables of the system. The aim of this paper crushed material is stored in top layers to
is to build a simulation model of the be selected later in a controlled manner.
calcination process in cement production, The blending bed can prepare the proper
assessing the behavior of the input, dosage of components by reducing
distribution of the process, and output
variability.
variables.
Figure 1 shows some components of the Subsequently, these materials are ground
cement. in ball or vertical mills to make them
smaller and thus make it easier to fire

150
them in the kiln. In the vertical mill, the the balls collide, crushing the clinker and
material is crushed by the pressure of its additives to a fine homogeneous rawmix:
roller on a turntable. From there, the raw cement.
material (powder or rawmix) is stored in a
silo to increase the uniformity of the 2.5 Distribution.
mixture. Finally, the cement is stored in silos,
separated according to its various classes
2.3 Preheater, kiln and cooler (PHE). before being bagged or loaded onto a
The kiln is powered by means of the truck for transport by road or rail.
cyclone preheater that heats the feedstock
to facilitate firing. Ground material or 3. The simulation model for the
rawmix is inserted through the top of the cement.
tower and drops through it. Meanwhile, 3.1. Calcination process analysis.
the gases from the kiln, which are at a The reactions that occur in the calcination
high temperature, rise against the current, process are:
thus the rawmix is preheated before
entering the kiln. • Evaporation of water from the mixture.
As the rawmix progresses in the kiln • Elimination of combined water in the
while it rotates, the temperature increases clay.
to reach 1.500 ° C. At this temperature • Dissociation of magnesium carbonate.
complex chemical reactions occur that • Dissociation of calcium carbonate.
result in the clinker. • Reaction in the kiln, mixing the lime
To achieve the temperatures required for and clay.
firing the raw materials and the
production of clinker, the kiln has a main The kiln (heat exchanger-cooler) is the
flame that burns at 2, 000 º C. In some equipment that determines the production,
cases there is also a secondary flame being the most important part of the
located in the combustion chamber in the process.
preheater tower. The clinker is produced by heating the
Once the clinker leaves the kiln, a cooler properly dosed rawmix at high
is introduced in inject cold air to lower temperatures in an oxidizing atmosphere
the temperature from 1.400 ° C to 100 º generally. The reactions of clinker
C. The hot air generated in this device is produced essentially four main elements:
returned to the kiln to support CaO, SiO 2 , Al 2 O 3 , Fe 2 O 3 to form
combustion, thereby improving the silicates with hydraulic properties. In
energy efficiency of the process. overall, the clinker formation process can
be divided into four parts:
2.4 Grinding of the clinker.
Once the clinker is obtained, it is mixed
in a cement mill with gypsum and
additives, in the right proportions. Inside,
the materials are ground, mixed and
homogenized.
The mills can consist of (horizontal and
vertical) rollers or balls. The later consists
of a large rotating tube with steel balls
inside. Thanks to the rotation of the mill,

151
Temperature Reactions ferroaluminato
(ºC)
1260-1450 3CaO + SiO 2 » 3CaO.SiO 2
20-100 CaCO 3 .MgCO 3 .Al 2 O 3 .SiO 2 .Fe 2 O 3 .H 2 O
Formation of tricalcium silicate (C3S)
» CaCO 3 .MgCO 3 .Al 2 O 3 .SiO 2 .Fe 2 O 3 +
from C2S and free lime CaO +
H 2 O (V)
2CaO.SiO 2 » 3CaO.SiO 2
Dehydration of the mixture(evaporation
of free water) Table 3 Sintering and clinker

100-400 Al 2 O 3 .2SiO 2 .H 2 O » Al 2 O 3 + SiO 2 + Temperature Reactions

2H 2 O (v) (ºC)
It expels water of crystallization (water 1450 Belita Formation of and Alita
removal combined with clay)
1300-1240 Crystallization of aluminates and
400-900 Chemical water is released. ferrites
Table 1 Drying Table 4 Cooled
3.2 System mass balance-preheater
kiln-cooler (PHE).
Temperat Reactions PHE Process is developed in the
ure (ºC) following steps:
500-900 CaCO 3 » CaO + CO 2 3.2.1. Precalcination of the raw
Decarbonation mixture. The preheater has a preheater,
MgCO 3 » Mg + CO 2 which heats the raw mixture of 60-70 ° C
Dissociation of magnesium to 800-850 ° C, usually fueled by natural
carbonate gas as fuel and use the waste gases from
CO 2 is expelled the kiln.
Debajo de CaO + Al 2 O 3 » CaO.Al 2 O 3
800 Formation of calcium aluminate 3.2.2. Formation of clinker.
CaO + Fe 2 O 3 » CaO.Fe 2 O 3 The formation of the clinker takes place
Formation of ferrous oxide in the rotary kiln, which is fed with the
800-900 CaO + SiO 2 » CaO.SiO 2 raw mixture from the preheater and, in
Formation of calcium silicate turn, introduces hot air (secondary)
900-950 5CaO + 3Al 2 O 3 » 5CaO.3Al 2 O 3 cooler.
Formation of calcium
trialuminato 3.2.3. Cooling of clinker.
950-1200 2CaO + SiO 2 » 2CaO.SiO 2 The cooler consists of fans with variable
Formation of dicalcium silicate flow through variable speed drives.
(C2S)
Table 2 Calcination 3.2.4 Cooling gases.
The waste gases are cooled in a cooling
Temperature Reactions tower, which is constituted by a system of
(ºC)
nozzles and decanting to separate the oil
1200-1300 3CaO + Al 2 O 3 » 3CaO.Al 2 O 3 carried by the gases. However, decanting
Formation of tricalcium aluminate is not enough, so an electrostatic filter is
(C3A) also used.
1260 4CaO + Al 2 O 3 + Fe 2 O 3 »
4CaO.Al 2 O 3 .Fe 2 O 3 3.2.5. Separation of dust from waste
Formation of Tetracalcium
gases.

152
An electrostatic precipitator, consisting of
plate-rapping systems and electric fields, Due to the complexity and automation of
is used to separate or precipitate dust most processes in the Cooperativa La
from raw waste gases. Cruz Azul SCL, it is somewhat difficult
to find areas of opportunity for
3.2.6. Separation of dust from the improvement. At the present time, Cruz
cooler. Azul has project engineering areas and an
It uses an electrostatic filter that separates optimization department whose job is to
the particles of dust from clinker cooler constantly search for innovative
air technologies or technical information that
would maximize existing resources,
Mass balance: evaluate the replacement of equipment,
The aforementioned integrated process is performance and energy fuels and, if
summarized in the following block necessary, to supervise the construction
diagram: of an entirely new factory. Usually these
areas (or project optimization) work
separately and there is a significant
difference between the scope of each of
them.

However, in both the Project area and the

area of optimization, the firing is the key
process in cement manufacturing. From
the roasting process is designed the size
and capacity of the kiln, which in turn
determines the capacity of the preheater
building itself and, in consequence, the
Figure 2 Mass balance various skills of the teams that will take
part in the design of a production line or a
To calculate the mass flow rates, the complete plant.
incidence matrix for mass was developed,
according to the mass flows that get in The following questions arise:
and out of the equipment: • Why not analyze the input-output flows
under a controlled environment of mass-
energy and time?
• Why not gradually change the way
people work in the process engineering
Table 5 Incidence matrix for mass department, using a scientific
methodology provided by simulation?
3.3 Simulation model for calcination
unit No. 9 of Cruz Azul cement plant, The system to be analyzed consists of a
Hidalgo, Mexico. combustion process as show below.
Cooperativa La Cruz Azul S.C., a
homegrown company from the Mexican
state of Hidalgo, currently ranks third in
national cement production after Cemex
and Apasco.

153
3.3.1 Collecting the information.
Solving the system of mass balance
equations with real data of the calcination
unit No.9, we have:

Figure 4 Basic model with Arena

3.3.3. Complete Model.

From the calculated mass balance, we
developed a new model from the inputs
and outputs, by considering mass and the
stoichiometric analysis of the raw
materials and the heat capacity of the fuel.
APE software was used.
Table 6 Mass flow of calcination unit 9
3.3.4 Flowcharts
3.3.2 Basic model. According to the block diagram in which
The basic model was developed in Arena, inputs and outputs represent the mass, we
which is an initial flowchart where the proceeded to develop flow charts for the
flow of rawmix fed into the Preheater- calcination process.
Kiln-Cooler system (PHE), and the
chaotic movement is undergoes in the
cyclone preheater (allocation probability)
determines, in a linear fashion, both the
consumption of fuel and electrical power.

Figure 5 Flowchart for the calcination process

3.3.5 Display
We subsequently assigned the variables
Figure 3 Flow chart for the PHE representing the masses (m 1 , m 2 , m 3 ...) to
form the input-output system mass. The
arrival of a continuous entity called
rawmix is determined to simulate a power
of 265 Ton / hr within the system.

154
 Figure 6 Simulations with SIMIO Figure 7 Simulation experiments
As a result, we obtained the following
We observe in the Arena model that there data:
is a chaotic movement of rawmix
particles in the cyclone, so that we
determine that they are probability
fluxes (approximately 65% -35%). The
temperature is monitored at the inlet to
the Preheater, and at the inlet , center and
outlet from the kiln, at the inlet and outlet
of the clinker cooler. Fuel consumption is
based on the flow of rawmix, which has
already been decarbonated in order to
achieve more efficient calcination. It
simulates the consumption of coke
(petroleum), whose consumption is
approximately 7.500 kg / hr in the
preheater (preheating) and 8.800 kg / hr
in the main burner (kiln). The flow in the
supply of rawmix is between 64.7 - 65
Ton / hr, so we used the linear function L
(64.7-65) to simulate the behavior.

3.3.6 Experiments
In order to have more results, 10
experiments were performed, as shown
below:

Table 7 Simulation experiments

3.3.7 Model Validation

In order to validate the model, we
consider the nominal production of the
calcination unit No.9 Cruz Azul,
according to the information provided by
the area of new projects, nominal output

155
is 157.65 tons / hr of clinker. Considering of this operation on the final quality of
this fact, along with the 10 experiments the cement. It has been demonstrated to
and the linear nature of a controlled simulate a controlled continuous
process, we can validate the statistical production process (24 hours a day 360
behavior of the production of clinker days a year) finally yields results that are
simulated by using the Student t test as very close to reality, regardless of the
shown in the following table: number of variables involved. The
simulation that we developed was a
process "in constant motion".

There are several international companies

that develop the engineering and
construction for cement plants, using
very complex mass and energy balances
to determine the specific capacity of each
piece of equipment to be installed,
though, of course, the heart of the system
is the installed kiln capacity and overall
clinker production rate of the calcination
unit. Simulation can give different
scenarios for the future and allows the
company to change or modify important
parameters in the production of the
cement.

References
Aguilar Barona Byrthzee Rubén. Tesis de
Maestría: “La Simulación de Sistemas
en la mejora de procesos de
manufactura y servicios”. Facultad de
Ingeniería UNAM. Año 2004.
Barceló Jaime. “Simulación de Sistemas
Discretos”. Primera Edición. Año 1996.
Editorial Isdefe. Madrid España.
García Dunna Eduardo, García Reyes
Using the t-test, the mean and the standard Heriberto y Cárdenas Barrón Leopoldo.
deviation is calculated with a sample of the “Simulación y análisis de sistemas con
10 experiments: ProModel”. Primera Edición. Editorial
Prentice Hall, México 2006.
Kelton David, Sadowski Randall y Sturrock
David. “Simulación con Software
Arena”. Cuarta edición. Editorial Mc
4. Conclusions
The linearity of an industrial process such Graw Hill. Año 2008.
as cement calcination represents very Rivett Patrick. “Construcción de modelos
slight changes in control variables, para análisis de decisiones”. Primera
because of the importance and criticality

156
 Edición. Año 1983. Editorial Limusa. (UPIICSA), currently studying a Masters
México D.F. in Systems Engineering with
Deolalkar S P. “Handbook for Designing specialization in Operations Research at
Cement Plants”. Añ0 2009. BS the National Autonomous University of
Publications. Mexico (UNAM). He has worked in the
Ackoff Russell L., Sasieni Maurice W. cement industry in the planning and
“Fundamentos de Investigación de control of projects specifically in
Operaciones” Sexta Edición. Año 1984. Cementos Cruz Azul. Within the concrete
Editorial Limusa. México D.F. industry in the same group has developed
databases and applied statistical tools that
have increased the efficiency of the
Web sites information in the technical area He is
http://canacem.org.mx/canacem.htm currently coordinator of new projects.
http://www.cruzazul.com.mx
http://www.holcim.com.mx
http://www.ieca.es
http://minerals.usgs.gov/minerals/pubs/mc
s/2011/mcs2011.pdf
http://www.investigacion-
operaciones.com/Historia.htm
http://www.vaticgroup.com/unlimitpages.a
sp?id=81&pid=-1
http://www.flsmidth.com

AUTHORS BIOGRAPHY
Dra. Idalia Flores de la Mota…
Dr. Idalia Flores de la Mota is
mathematics at the Faculty of Sciences of
the UNAM and studied the Masters and
Ph.D. in Operations Research at the
Faculty of Engineering of the UNAM.
She has published notes, chapters in
books, booklets and articles disclosed in
international journals. He has been referee
of the journals, Simulation, the Journal of
Accounting and Administration,
Computing Reviews online and Revista
Iberoamericana de Automática e
Informática Industrial. It belongs to the
Institute for Operations Research and the
Management Science and is Director of
the Center for Simulation McLeod in
Mexico.

Ing. Guillermo Perea Rivera.

Industrial engineer, graduated from the
National Polytechnic Institute

157