ICR Feb 2016 Better burn-outs

• FEBRUARY 2016 International

FEBRUARY 2016 ICR

either to the raw mill or to the fuel mill or directly into the calciner. As the carbon portion of HiCAl is 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 HiCAI products 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 Hi CAI 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)

WIS Wl4 ~ Max.3.15mm

Wl3

Table 1: composition and calorific value of Regain HiCAl products

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. For char 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.

As 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-CFO modelling.

• by Barbara Borges Fernandes, CINAR Brasil Ltda, Brazil, Dr Tom M Lowes, Optimum Process, UK, and Dr Yves C Zimmermann, Regain Services Pty Ltd, Australia

KILN OPTIMISATION •

Better burn-outs

CINAR

lmm

<212µm

I /

Figure 3: HiCAl particle trajectories coloured by size

Wl2 W11 BC

(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

Assumptions and boundary conditions 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 HiCAl has been assumed to have 10 per cent F and a calorific value of 13GJ/t. This means 4tph of HiCAl was used to substitute some 14 per cent of petcoke in the calciner. To ensure that the HiCAl used does not drive the so3 cycles, a burn-out of 95 per cent exiting the calciner is required.

•co-grinding of HiCAl with 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 calciner geometry and process conditions together with the HiCAI PSD and inlet location play a decisive role in the behaviour of HiCAI combustion, as it determines the oxygen and temperature profile."

Scenario Wll Wll Wl3 Wl4 WIS WIG

Front wall Back wall Backwall Top of tertiary

HiCAl injection 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

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FEBRUARY 2016 ICR

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Conclusions Ml-CFD modelling is an efficient way to optimise the injection location and the required particle size distribution for high- carbon HiCAl products.

For this state-of-the-art calciner, the HiCAl injection to the kiln system is possible together with the raw meal, with the main fuel (petcoke) or separately and in all cases it 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 HiCAl with petcoke needs the full calciner residence time for a good burn-out.

For optimised injection locations into the calciner, fineness of HiCAl can 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 cases of unconventional injection points such as from the top of the tertiary air duct. •

Results HiCAl injection 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. Due to 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/ HiCAl injection 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 HiCAl is 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 size fractions (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