2. FEBRUARY 2016 ICR
either to the raw mill or to the fuel mill or
directly into the calciner. As the carbon
portion of HiCAlis dead-burnt graphite
and as such is less reactive than even the
lowest volatile petcoke, proper combustion
of the mineraliser needs to be ensured.
To better understand the combustion
behaviour of the burnable portion of high-
carbon HiCAIproducts when injected in a
calciner, different scenarios (see Table 2)
were evaluated in collaboration with CINAR
by Mineral Interactive - Computational
Fluid Dynamics {Ml-CFD) modelling. The
scenarios consider an input of 0.2 per cent
F to clinker from HiCAI and are compared
to a base case without HiCAl.The influence
of HiCAI particles size distribution and its
inlet location are evaluated as follows:
•co-grinding of HiCAI with the other raw
materials in the raw mill and feeding it
together with the meal to the calciner
{Wll)
WISWl4
~
Max.3.15mm
Wl3
Table 1: compositionand calorific value of Regain HiCAlproducts
Element/compound HiCAl-R HiCAl40
Calorific value (GJ/t) N/A >12
Carbon - as C (%) 2-7 40-45
Silica - as Si02 (%) 30-37 6-12
Alumina - as Al,03 (%) 25-30 16-21
Iron - as Fe,03 (%) 2-6 2-7
Calcium - as Cao(%) 1-4 1-3
Magnesium- as MgO (%) 0-2 0-1
Sulphur - as S03 (%) 0-2 0-2
Potassium - as K,O (%) 0-2 0-1
Sodium - as Na,O (%) 18-23 14-19
Total fluoride(%) 8-12 8-12
Whereas low-carbon products like
HiCAl-R are designed to be dosed to the
raw mill via a dedicated feeder, high-
carbon products like HiCAI 40 can be dosed
wlmeal 31.3% >90µm
Wl2
w/petcoke
Wl1
@97%
Burnout
1.00
0.90
0.80
0.70
060
0.50
0.40
0.30
0.20
0.10
0.00
Figure 1: HiCAl trajectories coloured with burn-out in each scenario. Dark blue indicates phase
before combustion while red shows complete volatile release or complete combustion of the
volatiles in the gas-phase. Forchar combustion, first blue colours indicate the initiation of char
combustion in the solid-phase and the red indicates completion of char combustion
((
CINAR
nu
@99% @99%
Mineralisers for enhanced
cement production
Regain HiCAI products (listed in Table 1)
are safe, high-quality mineral products that
are manufactured from residual materials
of the primary aluminium industry to
enhance the efficiency of Portland clinker
and cement manufacture as well as reduce
production cost and emissions.
A
s generally known by the cement
industry, fluoride reduces
combinability temperature and boosts
the alite formation in clinker, resulting
in improved clinker quality and enabling
reduced clinker factors. This leads to a
significant reduction in specific energy
consumption and greenhouse gas
emissions from cement production.
Furthermore, alkalis in clinker bind
to excessive sulphur, reducing sulphur
cycles in kiln systems, dust generation and
build-up formation as well as enhancing
clinker reactivity in terms of early-strength
development. If a carbon containing
mineraliser is used, carbon contributes
to the fuel mix and substitutes traditional
fuels like coal or petcoke.
Mineralisers such as fluoride help to produce cement in a more efficient way, reducing
energy requirements and GHG emissions. In case a carbon-containing mineraliser is fed
to the preheater, a good burn-out of the carbon portion must be ensured. In this article,
several scenarios are evaluated with the help of Ml-CFOmodelling.
• by Barbara Borges Fernandes, CINAR Brasil Ltda, Brazil, Dr Tom M Lowes, Optimum Process, UK, and
Dr YvesC Zimmermann, Regain Services Pty Ltd, Australia
KILN OPTIMISATION •
Better burn-outs
3. CINAR
lmm
<212µm
I /
Figure 3: HiCAl particle trajectories coloured by size
Wl2W11BC
(02] lkg/kg)
0.23
0.21
0.18
0.16
0.14
0.11
0.09
0.07
0.05
0.02
0.00
indicates the
region where
the fuel is
burning
The lower 02 tM•!!lii!!i--1
concentration
in dark blue
colour
Figure 2: oxygen concentration profile contours and fuel trajectories -
petcoke in black and HiCAl in purple
ICR FEBRUARY 2016
Assumptionsand
boundaryconditions
Ml-CFD simulates the combustion
aerodynamics and heat transfer between
the kiln gases, tertiary air, petcoke, HiCAl
and calciner meal in the complex non-
linear process that takes place in the
calciner.
The simulations were carried out in
a modern nominal 5000tpd FLSmidth
calciner, with a fuel consumption of
3200kJ/kg clinker, firing 100 per cent high-
sulphur petcoke, with a 42/58 per cent
kiln/calciner fuel split and eight seconds
calciner gas residence time.
Experience has shown that an unburnt
carbon fraction in the hot meal of >0.05 per
cent can exacerbate S03 cycles if there is an
excess of S03 over alkalis in the hot meal.
For the purposes of the simulations
HiCAlhas been assumed to have 10 per
cent F and a calorific value of 13GJ/t. This
means 4tph of HiCAlwas used to substitute
some 14 per cent of petcoke in the calciner.
To ensure that the HiCAlused does not
drive the so3 cycles, a burn-out of 95 per
cent exiting the calciner is required.
•co-grinding of HiCAlwith petcoke in the
fuel mill and feeding it together with
fine petcoke into the calciner (W12)
- separate grinding of HiCAl to different
finenesses and separate feeding at
different locations into the ca lei ner
(Wl3-Wl6).
"... the calcinergeometry
and process conditions
together with the HiCAI
PSD and inletlocation
play a decisive role
in the behaviour of
HiCAI combustion, as it
determines the oxygen
and temperatureprofile."
Scenario Wll Wll Wl3 Wl4 WIS WIG
Front wall
Back wall Backwall Top of tertiary
HiCAlinjection location With meal With petcoke at petcoke
burners level
above cone below cone air duct
78.2% >90µm
HiCAl PSD Meal PSD Petcoke PSD 37.3% >90µm 37.3% >90µm 37.3%>90µm (top size -
3.lSmm)
Table 2: identification of HiCAI particle size distribution (PSD)and injection location in each scenario
KILN OPTIMISATION
4. FEBRUARY 2016 ICR
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•
Conclusions
Ml-CFDmodelling is an efficient way to optimise the injection
location and the required particle sizedistribution for high-
carbon HiCAlproducts.
For this state-of-the-art calciner, the HiCAlinjection to the
kiln system is possible together with the raw meal, with the
main fuel (petcoke) or separately and in all casesit is possible
to achieve the required burn-out.
It should be noted that the calciner geometry and process
conditions together with the HiCAl PSD and inlet location play
a decisive role in the behaviour of HiCA! combustion, as it
determines the oxygen and temperature profile.
In the meal injection mode, its location relative to the
tertiary air is crucial for the fast combustion of HiCAl, while
the introduction of HiCAlwith petcoke needs the full calciner
residence time for a good burn-out.
For optimised injection locations into the calciner, fineness
of HiCAlcan be as low as 37 per cent residue on 90µm. A top
size up to SOOµm seems possible for 9S per cent burn-out in
casesof unconventional injection points such as from the top
of the tertiary air duct. •
Results
HiCAlinjection with the meal (Wll) and petcoke (Wl2) as well as
the two optimised injection locations with separate injection of
coarser HiCAl(Wl4 and WIS) readily meet the 9S per cent burn-
out requirement (see Figure 1).
Wll injection with the meal shows a complete burn-out in
around four seconds. The good burn-out with the meal was
not expected due to meal quenching effects. However, the
high injection temperature at 800° C combined with a high
local oxygen concentration due to the feeding location relative
to the position of tertiary air (see Figure 2) and favourable
aerodynamics near the meal injection point in this calciner
overcome the meal quenching potential issue.
Wl2 injection with the petcoke needs the full calciner
residence time for complete burn-out even though the residue
on 90µm was only three per cent. Dueto the injection location,
the HiCAl particles compete with the petcoke particles for
the oxygen, while travelling through regions with low 02
availability. Therefore, care needs to be taken with the petcoke/
HiCAlinjection location for smaller calciners.
The two optimised injection locations Wl4 and WIS
showed a high burn-out level(> 9S per cent), especially when
considering that the residue on 90µm of HiCAlis 37 per cent
and this is much higher than any petcoke would ever be
prepared for injection into a calciner. This shows the value of
the knowledge gained from Ml-CFD where the high oxygen
and temperatures will be to optimise the injection location.
Wl3 in the first place did not give a good combustion level for
example.
W16 looked at the possibility of using even coarser HiCAl
product and dropping it into the tertiary air duct. The top size
was 3.lSmm and only achieved an average burn-out of 61
per cent. However, with the tracking power of Ml-CFD it was
possible to look at the behaviour of different sizefractions (see
Figure 3). The 212µm fraction and all the smaller sizes burnt out
completely just above the tertiary air duct and even the SOOµm
fraction was burnt out by the end of the calciner. The Ml-CFD
also indicates potential wall impingement of the >SOOµm sizes,
which could lead to refractory damage and build-up.
KILN OPTIMISATION
