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Heat Transfer and Renewable Sources of Energy 2012
INFLUENCE CONSTRUCTION OF SUSPENSION PREHEATER ON ENERGY
CONSUMPTION PROCESS DURING BURNING IN ROTARY KILN
JERZY DUDA*, MAREK WASILEWSKI**
Opole University of Technology, Faculty of Production Engineering and Logistics
ul. Ozimska 75, 45-370 Opole, Poland
*) e-mail: j.duda@po.opole.pl, **) e-mail: m.wasilewski@po.opole.pl
ABSTRACT: In this article are presented directions of the modernization of suspension preheaters and
influence these changes on thermal efficiency, consumption of electrical energy on drive of kiln fans
and also effectives of dust dedusting. In his articel is presented plan of research, which define optimal
variants of modification of construction cyclones for first stage and which are used in the clinker
burning process. Range of research includes: experimental research on test station, digital image
analyze (by using fast digital camera), CFD modeling (packet Ansys 14). In the next step results will
be compared with dates which are in reality in installation in the cement industry.
NOMENCLATURE
h - enthalpy, J/kg,
- enthalpy of a gas stream, J/s,
- enthalpy of a dust stream, J/s,
- enthalpy of a raw material stream, J/s,
i - stage of suspension preheater,
- stream of gas, m3/s,
- stream of dust, kg/s,
- stream of raw material, kg/s,
- mass balance, kg/s,
- number of stage of suspension preheater,
- gas temperature, K,
- raw material temperature, K,
- dust temperature, K,
- stream of heat losses, J/s,
- inlet gas temperature, K,
- difference between inlet temperature of gases and outlet temperature of the raw
material, K,
- difference between the temperature of the exhaust gas and the raw material, K,
- average difference between gas temperature at the inlet and raw material temperature
at the exit from each stage or the suspension preheater, K,
- degree of separation.
Jerzy Duda, Marek Wasilewski
2
1. INTRODUCTION
External preheater are one of the most important elements of kiln installation in the
clinker burning process using the dry method. Energy consumption of the burning process has
significant influence on the costs of cement production. Costs connect with clinker burning
give about 50% costs of energy in cement production process. In connection with problem
lower energy consumption costs of production is defined as basic modernization action.
These actions mainly refer to design of suspension preheater and clinker cooler and also
another device cooperating with rotary kiln. Design and efficiency these devices have a large
influence on energy efficiency of cement production process and investment costs of rotary
kiln. Cyclones are one of the most common used devices in an external suspension
preheater. Compared with another constructions (ex. shaft preheater) they are characterized by
a simple construction, low production and exploitation costs and also possibility work in
different conditions. Figure 1 is presented development of the construction of kiln installation,
which had place in last years, together with application the suspension preheater.
Fig. 1. Influence of suspension preheater on the design of rotary kiln and temperature distribution
The use of multi-stage suspension preheater apart from considerable depending on the
number of stages reduce fuel consumption (30-50%), it also allowed on implementation two
- stage firing klin, so-called initial decarbonization. Efficiency both thermal (heat transfer
released in burning process in a rotary kiln and precalciner to raw material) as well as
dedusting (effectiveness of the separation participles with gas), depends mainly on the design
and number of cyclones (number of stages of suspension preheater) located in tower of
preheater.
The clinker burning process is characterized by a low thermal efficiency (about 50%).
The greatest loss (which is more than 50% of thermal losses) is enthalpy of exhaust gases
from the kiln. One method to improve the thermal efficiency of the burning process is
Influence construction of suspension preheater on energy consumption process during burning in rotary kiln
3
modernization of the suspension preheater by adding additional stages. For example using of
the 6-stage suspension preheater in place 4-stages reduces the heat consumption average
about 200 kJ/kg kl, this is to the one-leap level of energy consumption, what gives 2930 kJ/kg
kl [4]. Expansion of the suspension preheater by additional stages requires new design of
cyclones which are characterized by lower pressure loss and higher efficiency. Each
additional stages of cyclone is connected with higher resistance of suspension preheater
(about 0,8-1,6 kPa). Approximately 90% of the total exploitation costs of the kiln is
associated with delivering energy (gas kiln fan drive exhauster) required to compensate of
pressure drops in the suspension preheater. Therefore, each modernization of the suspension
preheater requires a preliminary analysis possibility of superstructure by using additional
stages and estimation of influence on investment and exploitation costs of kiln installation.
2. DIRECTIONS OF THE MODERNIZATION OF SUSPENSION PREHEATERS
The application of modern techniques for clinker burning in kiln with systems of initial
decarbonization requires the expansion of the classical 4-stage suspension preheater by using
additional stage 5 or 6. Application additional stages require using new construction of
suspension preheater, characterized by a lower hydraulic resistance and higher dust dedusting
efficiency. For example - the modernization of the clinker burning installation connected with
extension of the traditional 4-stage suspension preheater by using additional (fifth) stage,
allowed to obtain the following results [2,3]:
lower hydraulic resistance of the entire installation of suspension preheater in spite of
extending it to a fifth stage. Decrease of pressure drop in suspension preheater from
6,45 kPa to 6,1kPa,
reduce heat consumption about 200 kJ/kg kl, what gives 6 % total requirement
reduction of energy consumption about 0,6 kWh/t (fan drive of kiln exhaustor).
Modernization of suspension preheater may depend not only on increasing the number
of stages, but also on using innovative design of cyclones. An example of this is Hurriclon
technology proposed by the Austrian A-TEC Company. Hurriclon (Fig. 2) is a specially
designed cyclone with two dip pipes instead of one (two outlet connector pipes of cleaned
gas) [5].
Fig. 2. Hurriclon cyclone
Jerzy Duda, Marek Wasilewski
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One is located at the top of the cyclone (the convectional solution), while the second is
in the bottom of the cyclone. Additionally, by the inlets to these pipes installed
Hurrivane. As a result of installation two Hurriclon cyclones in cement plant Cimpor
Alhandra in Portugal, was observed pressure drop to 910 Pa (before modernization 1700 Pa).
The efficiency of the kiln increased about 347 t/d, this is more than 12%, while
efficiency of particle separation of the cyclone for 1 stage is 93 % [1].
3. MODEL RESEARCH OF SUSPENSION PREHEATER
Cyclone in kiln installation in cement industry is using as dedusting device and
preheater. The principle of operation of the suspension preheater is similar to the classical
preheater in suspension state. Raw material ( ) flows successive through stages of cyclones
from top to bottom to the inlet of the kiln. On the other hand the hot gases from the kiln (
flow through vertical ducts (connecting individual stages of cyclones) and cyclones in the
opposite direction to the flow of material up. A typical, the most common solution of
preheater is system composed of four stages of cyclones. The graph (Fig. 3) shows the
temperature of the burned material and gases at the characteristic points of the kiln installation
with an external, 4-stage of the suspension preheater.
Fig. 3. Diagram of gases temperature and material in the clinker burning installation
Influence construction of suspension preheater on energy consumption process during burning in rotary kiln
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In the suspension preheater, apart from heating and the drying of material has place
already partially the process of decarbonization of raw material. In 4- stage suspension
preheater, process of decarbonization of raw material does not exceed 40%. However in the
installation with the system of the preliminary calcination (precalciner), stege of
decarbonization of raw material at the inlet to the rotary kiln is over 90%.
Realized research of the suspension preheater have a different form. Starting from
theoretical works, through identification examinations on the object and finishing on
numerical research. Particularly these recent research are widely used in solving the problem
of flow and heat transfer. This possibility gives access to the more and more efficient
computational hardware and software. However, due to the complexity of conditions in
suspension preheater (various physical and chemical processes), it is necessary to analyze
each case individual or the use of several methods and subsequent their verify.
Practically in each stage of preheater occur similar processes of heat exchange between
the gases and the raw material and separately - separation of material from the gas. Therefore,
for the mathematical description of the individual stages of the preheater, it is possible to
accept some simplifications concerning balance relations. Figure 4 shows scheme of the
cyclone, along with the main streams of material ( , dusts and gases and also
enthalpies (H) of these streams. The difference between the stages of cyclones depend only on
chemical transformations, which occur at different stages of the preheater (at different
temperatures).
Fig. 4 Scheme of the cyclone with streams
According to data on figure 4, can determine (from balance of mass) particular streams
of material in cyclone ex.
(1)
(2)
Jerzy Duda, Marek Wasilewski
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degree of separation of material from the gases:
(3)
Thermal balance for i-th stage can define from the relation:
(4)
Similarly, it can define temperatures of material and gases for i-th cyclone or
suspension preheater. Based on foreign and own experience, it is possible to assume a
constant difference between the temperature of the exhaust gas and the raw material from i-ih
cyclone, what it describes below relation:
Difference between inlet temperature of gases to cyclone and outlet temperature of the
material from cyclone can define as:
(5)
From the above relation can be determined temperature of raw material and gases at
particular stages of preheater and average difference
, between gas temperature at the
inlet and raw material temperature at the exit from each stage or the suspension preheater.
As the example, kiln gas temperature at the inlet (
to four-stage preheater (N=4), can
be defined from the relation:
(6)
However presented a mathematical description of the particular stages of suspension
preheater has application only in the limited range. This method does not let on optimization
the shape of the suspension preheater. The answer on influence of cyclone design, shape of
the inlet, depth of the immersion and diameter of dip pipe on value of pressure drop, energetic
and dedusting efficiency, can be obtained based on model research.
Planning research on these issues it is decided to divide in three stages (fig. 5).
Fig. 5. Plan of research
The aim of research is determine optimal variants of new construction of cyclones for first
stage (dedusting), used in the clinker burning process.
Influence construction of suspension preheater on energy consumption process during burning in rotary kiln
7
The research are conducted at using Ansys 14 packet. With the purpose of the first stage
of these work is comparison of the results received from the working installation with the
results obtained from numerical calculations. The calculation are conducted in parallel for the
two computational models - Reynolds Stress Model (RSM) and kThis let to
select the optimal numerical model for further research. Additionally trajectories of particles
movement of raw material are appointed at using Discrete Phase Model (DPM).
The first stage was defined three-dimensional (fig. 6a) geometrical model (Ansys
Design Modeler program). This model was designed based on two-dimensional technical
drawing prepared on the basis of the characteristics of the cyclone for the first stage. This
cyclone is working in one cement plant in Poland. Successively, it was selected computational
grid (program Ansys Meshing) - figure 6b. Definition of boundary conditions, selection of
proper computational models and finally the calculations are carried out in Ansys Fluent
program.
Fig. 6. a) Geometrical model of the cyclone, b) Hexagonal computational grid of the cyclone
Based on data coming from the industrial practice and data from professional literature
and also taking into consideration implemented criteria of similarity, was designed model of
the cyclone and experimental installation. On prepared installation will be carried out series of
the measurements for real raw material. Using mass-heat balance was defined value of mass
intensity of raw material and range of changes of velocity at the inlet. For these calculations
used capacity of kiln, consumption of raw material, quantity of exhaust gases and distribution
of temperature in suspension preheater. The research will be conducted on the cold model,
where flow of exhaust gases will be simulated stream of cold air. Using cold model it is
possible to obtain qualitative data as well as quantitative, concerning conditions of the flow in
the model device. Quantitatively it can determine pressure drop and distribution of velocity in
various parts of the device. While qualitative data obtains in relation to character, turbulence
of the flow of exhaust gases and ranges in which can occur excessive erosion of refractory
materials.
Test station enables both changes of particular elements of cyclones and their
dimensions and measurement of all parameters influencing on dust dedusting efficiency and
hydraulic resistance. Experimental research will be accompanied the process of registering the
flow of the mixture by using fast digital camera coupled with a portable computer performing
the role of the programmer, as well as the register. Examined cyclone applied to registration
will be illuminated by using laser. Observed flow in cyclone after registration will be
transmitted to DPIV analyze (bitmaps). Successively, based on this analyze will be
Jerzy Duda, Marek Wasilewski
8
determined field of velocity and trajectories of particles movement. By using video sequence
will be conducted identification of place of deposition particles and places exposed to
excessive erosion.
4. CONCLUSION
After analysis of literature and practical examples of functioning installations in cement
industry it was claimed that exist also simpler methods improving work of suspension
preheater. Obviously must be eliminated here modernization requiring long-term
disengagement of the entire installation from the utility (ex. expansion of the next steps
towers of suspension preheaters). Therefore in this work is decided that the main attention
will be concentrated on the optimization of the design of cyclones for the first stage, in
particular will be examined influence of the inlet geometry, depth immersion of the outlet dip
pipe (on pressure losses and dedusting and thermal efficiency. In this place it should be
underline that cyclones of the first stage characterize large capacity to dust dedusting
compared with another cyclones used in lower stages.
Planned research will be helpful to define optimal geometrical dimensions of cyclone,
depending on conditions in udner which it will be working (capacity, temperature,
technological conditions). Taking into consideration fact that each installation working in
industry has own characteristic technological conditions, it must be determined for these local
conditions optimal parameters of devices guaranteeing appropriate and economical duty.
REFERENCES
[1] A TEC, Preheater optimization in the cement industry; 2006 r.,
[2
[3] Duda J., Sobala J.: Modernization and increase in capacity at Malogoszcz Cement plant, World
Cement, No 6/1996, pp. 4-8
[4] Igawa T., Hatano H.: Energieersparnis durch Umbau eines 4 stufigen Zyklonvorwarmers in einem
5 stufigen Warmetauscher, Zement-Kalk-Gips, 1986 No. 12, pp.661-663
[5] Schwaiger G.; Pressure loss reductions and energy saving created by insertion of vortex finder
vanes into preheater and grinding circuit cyclones, and installation of Hurriclon cyclones; Europe
Cement Conference 1999, Paper 9
EINFLUSS DER KONSTRUKTION DES ZYKLONWÄRMETAUSCHERS AUF DEN
ENERGIEAUFWAND DES BRENNPROZESSES IM DREHOFEN
ZUSAMMENFASSUNG: Im Artikel wurden die Modernisierungsrichtungen von
den elektrischen
Energieverbrauch der Ventilatorenantriebe und auf die Effizienz der Endstaubung beschrieben. Der
Untersuchungsplan in Richtung Ausarbeitung optimaler Modifikationsvarianten der Konstruktion von
Zyklonen der I Stufe im Klinkerbrennprozess wurde vorgestellt. Der Bereich der Untersuchungen
umfasst: experimentiele Untersuchungen am Untersuchungsstand, Computer-Bild-Analyse (schnelle
Digitalcamera), numerische Untersuchungen (Ansis -Packet 14) und Verifizierung der Ergebnissen
mit Daten aus funktionierenden Anlagen in der Zementindustrie.
