use of F to enhance cement quality, reduce NOx and fuel and increase output

2. The use of Fluorine in Cement
Manufacture
Tom Lowes

3. The Use of Fluorine in Cement Manufacture
Background
 Mineralised clinker with high early strength (HES) characteristics
was first patented by Blue Circle in 1976. The essential features of
the active clinker are:
 A fluorine level of ~0.2%
 An SO3 level of 2.5 - 3.5%
 A controlled alkali level (up to ~1.2% eq Na2O the higher the alkali
level the higher the early strengths)
 A high C3S level (70%)
 The concept is that F acts as a mineraliser that together with SO3
acts to lower the temperature that any raw material needs to be
heated to combine and produce clinker, PLUS improves the
reactivity and % of C3S for any clinker chemistry as explained on
the next slide

4. What Happens Chemically with F
 The Fluoride addition to raw mix causes the viscosity and surface
tension of the clinker melt or liquid phase to reduce facilitating the
faster production of Alite.
 The F- ions find their way into the crystal structure of Alite replacing
O2- in the crystal structure and dragging Al2+ with them displacing
Si3+ to get the charge balance right. The Alite structure has become
more disordered. The Si, Al and F components are more randomly
distributed in the chemical system which increases the Entropy and
reduces the Gibbs Energy of the system and stabilises Alite. Alite
with F and Al substitution becomes the lowest or preferred energy
state.
 The displaced Si can form additional Alite to the advantage of late
strength and the substituted Al can reduce the C3A to the detriment
of setting time.
 The crystal structure with F substitution is Rhombohedral which is
the more reactive form of Alite.
 The impact of F is therefore multi layered

5. What Happens Chemically with F
To summarise the impact of F addition:
 Reduces surface tension and viscosity of the melt or liquid phase
facilitating Alite formation
 Increases the Entropy and lowers the Gibbs Energy of the chemical
system stabilising the equilibrium between Alite, Belite and Free
Lime facilitating Alite formation.
 Causes Si to be substituted by Al to ensure a charge balance in the
Alite structure thereby enabling the formation of additional Alite.
Approximately 0.2% F would result in the formation of an additional
1.6% Alite by this mechanism alone.
 Reduces the C3A in the system. Approximately 0.2% F would result
in the reduction in C3A of 2%.
 Causes the Alite crystal structure to move to Rhombohedral, thought
to be more reactive.
Hence 102 LSF clinker can readily be burnt to @ 1% free
lime with a higher and more reactive C3S

6. The Use of Fluorine in Cement Manufacture
 Typically with 0.2% F a 6% higher LSF clinker can be burnt for the
same combination temperature.
 The technology was applied to Aalborg that produced a clinker with:
 A fluorine of 0.23 %
 SO3 of 1.8%
 C3S of 67
 Which resulted in
 27 and 57 N/mm2 1 and 7 day mortar strengths with: -
 14% chalk and a +45u of 0.3%
 This clinker represents 30% of the Danish Market and represents a
big CO2 saving.
 BCI did not develop HES in the UK although it was a major project
in the 80's with the idea of an HES /PFA with 60/40 mix to improve
kiln capacity. The poor extended cement market in the UK and the
need to develop new standards stopped the project progressing.
 A summary of the BCI work is in the embedded ppt and word doc.

7. The Use of Fluorine in Cement Manufacture
Other Applications
 Italcementi have used CaF2 to reduce SO3 cycles and achieve 100%
petcoke on many plants with even as much as 0.3% F on a plant with 2.5%
SO3 in the clinker. Typically 0.2% F reduces the combinability temperature
by 80C and the fuel consumption by @ 70 kcals/kg
 The impact of various parameters clinker parameters on combinability
temperature can be ascertained via the embedded excel sheet
 A drop in NOx emission of close to 50% can occur with a drop in
combinability temperature of 80C
 Holcim have had several applications, notably in Mexico where CaF2 was
used to allow a higher C3S and hence a higher early strength to be
achieved
 During this work Holcim discovered one of the downsides of the use of
F, is that it can cause bleeding and longer setting times, unless care is
taken to ascertain the maximum F addition plus then adequate blending
control on a cement specific basis
 This was discovered in BCI - by default - at its Hope works that had a
natural F in the raw materials that varied from 0.1 to 0.5% in clinker -
where the general limit was put at 0.2%, which resulted in no quality
problems for Hope works even in the winter.

8. The Use of Fluorine in Cement Manufacture
Drawbacks
 Quality
 Needing to take care of bleeding and longer setting times, by identifying
plant specific %F limits in clinker (guideline 0.2%)
 One of the problems is that not only does the early strength increase
with a higher C3S, but also the late strength due to more active belite.
Hence one sometimes needs to grind coarser to met 28 day standards,
hence the increase in setting time and bleeding tendencies.
 Process
 There is occassionally an issue with a Fluoro – Spurrite based build up
at @ 700C, which needs the temperature zone to be shifted to a less
prone for build up location, via a water spray if it persists
Availability
 The International price for CaF2 is @ $400 /tonne FOB. for 80% purity
 However wastes exists with F in them: -
 Some currently being used in cement production
 SPL contains 15% F
 Wastes from CaF2 mines are rich in F and can be used

9. The Use of Fluorine in Cement Manufacture
Conclusions
 F addition to the raw materials has many benefits: -
 More petcoke
 Lower SO3 cycles
 Lower NOx
 Better cement strength
 More extender
 Limestone cements
 Lower CO2
 The problems associated with bleeding and setting time can be
managed
 Availability and Price limits its use
 It should be one of the aims of all AFR programmes to locate
suitable waste F sources, one of which is normally SPL which is a
hazardous source of F and attracts a significant disposal fee which
should be developed for use in the Cement Industry

10. 10
Typical Spent Potliner Composition
Constituent 1st cut only 1st and 2nd cut
Carbon 55 + 5% 30 + 5%
Fluoride 13 + 3% 15 + 3%
Sodium 12 + 5% 15 + 3%
Aluminum 10 + 2% 15 + 5%
Cyanide (total) 50 -10,000 ppm (0.2% average)
Silicon 3% 4%
Calcium 3% 4%
Sulfur 0.2 + 0.1% 0.2 + 0.1%
PAH 0-300 ppm
Moisture <3% <3%
BTU/lb 8000 4500
Hazardous and needs crushing or grinding

11. HiCal – A refined SPL non Haz F source
Adding HiCal at 2%
will give 0.2% F, plus
50 to 70 kcals/kg
from the CV and no
hazardous handling
issues