characteristics & performance of portland cement...
TRANSCRIPT
Characteristics & Performance of
Portland Cement Made from Looped
Sorbent from the CaL Process
Thomas Hills1,2*, Liya Zheng1, Nick Florin3 & Paul Fennell1
1Department of Chemical Engineering, Imperial College London2Grantham Institute – Climate Change and the Environment
3Institute for Sustainable Futures, University of Technology, Sydney
Outline
• Why calcium looping for the cement industry?
• Method of cement synthesis
• Compressive strength via miniaturisation
– Method
– Results
• Caveats
• Conclusions
Why CCS? Why Calcium Looping?
• Other decarbonisation efforts can provide -40 %
specific CO2 reduction
– CCS is only method which can get lower
• Both plants handle hot solids including CaCO3/CaO
• Waste sorbent used as an alternative cement feedstock
– Integration has been discussed by Ozcan et al. (2013) &
Rodriguez et al. (2012), and Hornberger yesterday
• But is the resulting cement suitable?
What we know so far…
• Alite concentrations in CaL cement similar to
normal– Dean et al. (2011)
• Burnability of CaL raw mixes similar to normal, if
not better– Telesca et al. (2015)
• Hydration products similar to normal– Telesca et al. (2015)
Extra information provided by this study
1. The ‘dry method’
2. Compressive strength
3. QPA via XRD (not discussed here)
So this study builds on Dean et al. (2011), and is
complementary to that of Telesca et al.
Method for making cement
1. Calcination of limestone2. Blending & compression
3. Clinkering & dry quenching
4. Clinker product
5. Grinding & gypsum addition 6. Cement tests
Effect of variables on cement product
Number
of cycles
(0, 5, 10)
Gaseous
atmosphere
(15% CO2,
CaL)
Raw
materials
(Pure oxides,
clay)
Use of
FBR
Compressive strength test - methods
• Current European and US standards require
large amounts of cement (450g / batch)
– We make only 40 g at a time!
• The standards were ‘miniaturised’
– 26 g cement used in one batch of 12 cubes
Compressive strength test - results
Error bars represent ± 1 standard deviation based on max.
12 cubes for each sample, and 2-5 samples per cement type
31.034.9
37.8
44.5
37.0 35.5
28.2
39.4
24.7
0
5
10
15
20
25
30
35
40
45
50
CEM 1 L-0-C C-0-C C-5-C O-5-C O-5-F C-5-F I-5-C C-10-C
Co
mp
ress
ive
Str
en
gth
at
7 d
ays
(MP
a)
But what about the particle size distribution?
• Anderegg & Hubbell (1929): After 7 days, the
reaction depth is ca. 1.7 – 2.6 µm
• Thus, a shifted particle diameter to larger sizes
lower strengths at 7 days.
y = -1.5185x + 51.921R² = 0.3445
10
15
20
25
30
35
40
45
50
6 8 10 12 14 16 18
Co
mp
ress
ive
Str
en
gth
, 7 d
ays
(MP
a)
Particle diameter, surface area weighted mean (µm)
Particle size distribution effects
One outlier (7.54 MPa, 23.6 µm) and CEM 1 excluded
Student’s t-test was applied; the gradient
is statistically significant (α = 0.05)
Strength tests – Effect of composition
𝜎𝑥=10 =𝜎𝑥=𝑟
𝐸(𝜎𝑥=𝑟)∗ 𝐸(𝜎𝑥=10)
31.037.0
44.539.4
27.737.8
44.837.0
0
10
20
30
40
50
60
Cemex CEM 1 (O-5-C) 5 cycles,oxides
(C-5-C) 5 cycles, clay (I-5-C) 5 cycles,wrong clay ratio
Co
mp
ress
ive
Str
en
gth
at
7 d
ays
(MP
a)
Effect of composition
Original Standardised
Strength tests – discussion (1)
The use of clay as a raw material produces stronger cement than using pure oxides
• Better availability of trace elements for substitution?
• Better flux properties?
• Better psd?
• Raw meal compounds more conducive to clinker formation?
31.037.0
44.539.4
27.737.8
44.837.0
0
10
20
30
40
50
60
Cemex CEM 1 (O-5-C) 5 cycles, oxides (C-5-C) 5 cycles, clay (I-5-C) 5 cycles, wrongclay ratio
Co
mp
ress
ive
Stre
ngt
h a
t 7
day
s (M
Pa)
Original Standardised
Strength tests – Effect of FBR, looping
31.0 33.337.8
44.5 41.8
27.733.0
38.444.8
36.6
0
10
20
30
40
50
60
Cemex CEM 1 (L-0-C) FromLimestone, clay
(C-0-C) 0 cycles,clay
(C-5-C) 5 cycles,clay
(C-10-C) 10cycles, clay*
Co
mp
ress
ive
Str
en
gth
at
7 d
ays
(MP
a)
Original Standardised
Strength tests – discussion (2)
Calcium looping may produce stronger clinker
• 5-cycle cement seems to be stronger than 0-
cycle or 10-cycle
• Thus, it may have an effect
– Probably not a negative one
31.0 33.337.8
44.5 41.8
27.733.0
38.444.8
36.6
0
10
20
30
40
50
60
Cemex CEM 1 (L-0-C) FromLimestone, clay
(C-0-C) 0 cycles, clay (C-5-C) 5 cycles, clay (C-10-C) 10 cycles,clay*
Co
mp
ress
ive
Str
en
gth
at
7 d
ays
(MP
a)
Original Standardised
Some caveats
• The line of best fit is not based on many observations (< 30)– the coefficients (and shape) are therefore not
particularly certain
• 2 – 5 samples per condition is not enough to make any definitive conclusions
• The clinker synthesis method is batch-wise– Very different conditions from real clinker manufacture
Conclusions
1. Clinker made from calcium looped CaOappears to be suitable for use in commercial cement
2. The number of cycles may have a small positive influence on the compressive strength but no definite trend can be discerned
33.3 37.8 37.044.5 41.8
33.0 38.4 37.844.8
36.6
0
10
20
30
40
50
60
From Limestone,clay (L-0-C)
0 cycles, clay (C-0-C)
5 cycles, oxides(O-5-C)
5 cycles, clay (C-5-C)
10 cycles, clay*(C-10-C)
Co
mp
ress
ive
Str
engt
h a
t 7
day
s (M
Pa)
Effect of FBR, calcium looping
Original Standardised
Conclusions
3. Cement made in the lab has a higher
compressive strength than commercial cement
4. The type of raw material affects the strength as
well as its elemental make-up
31.037.0
44.539.4
27.737.8
44.837.0
0
10
20
30
40
50
60
Cemex CEM 1 5 cycles, oxides (O-5-C)
5 cycles, clay (C-5-C) 5 cycles, wrong clayratio (I-5-C)
Co
mp
ress
ive
Str
engt
h a
t 7
day
s (M
Pa) Effect of composition
Original Standardised
Conclusions
5. The effects of particle size distribution variability should be taken into account when measuring the compressive strength of the cement.
6. Batch-wise cement production seems to produce variable product
41.835.8 32.8
41.040.6 36.8 35.940.5
0
10
20
30
40
50
19 20 21 23
Co
mp
ress
ive
Str
en
gth
, 7 d
ays,
M
Pa
C-0-C samples
Original Standardised
Acknowledgements
I gratefully acknowledge funding and support from:
• Grantham Institute – Climate Change and the
Environment, Imperial College London
• Climate-KIC
• Cemex Research Group AG
References
• Cement Sustainability Initiative: Cement Technology Roadmap 2009. WBCSD/IEA
• Ozcan et al (2013): Process integration of a Ca-looping carbon capture process in a cement plant. Int. J. GHG Control (19) 530-540
• Rodriguez et al (2012): CO2 Capture from Cement Plants Using Oxyfired Precalcination and/or Calcium Looping. Environ. Sci. Tech. 46 (4) 2460-2466
• Dean et al. (2013): Integrating Calcium Looping CO2 Capture with the Manufacture of Cement. Energy Procedia 37 7078-7090
• Telesca et al (2015): Calcium Looping Spent Sorbent as a Limestone Replacement in the Manufacture of Portland and Calcium Sulfoaluminate Cements. Environ. Sci. Technol. 49 (11) 6865-6871
Extra slides
Where do the CO2 emissions come from?
• Ca. 800 kg CO2/t CEM 1
• 60 % from calcination of limestone
• 40 % from fuel combustion
80% of emissions from
precalciner (step 5)
What we know so far…
• Dean et al (2011):
Alite concentrations are similar in cycled sorbent
cement and non-cycled cement
– Trace element levels differ if coal is burned in the
fluidised bed
What we know so far…
• Telesca et al. (2015):
CaL raw mixes are of similar burnability to
normal cement; hydration of the cements is
similar
Meal type BI (CaCO3) BI (CaO)
1 52.3 58.5
2 50.7 62.2
3 69.9 64.4
Fluidised bed reactor
Cement composition
• All clinkers were designed to have:
– Lime saturation factor (LSF) = 0.95
– Silica ratio (SR) = 2.5
– Alumina ratio (AR) = 1.5
– Composition of feedstocks determined by XRF (bead)
• Cement was produced by grinding the clinker
and mixing it with 5 wt% gypsum
– Equivalent to CEM 1 (as in EN 197-1)
Compressive strength test - methods
• No direct comparison to standard tests can be
made
• Several tests with CEMEX CEM 1 were
performed as a benchmark cement.
• Silicone mini ice cube trays (1/2” cubes) were
used instead of steel moulds
– Easier to demould
– Cheaper
Compressive strength test - methods
• 12 cubes per cement batch (allows s.d. calculation)
• 26 g : 26 g : 13 g
Cement : sand : water
• Sand was SiO2 40-100 mesh (150 – 400 µm)
• Demoulding after 24h (± 15 min)
• Testing after 7 days (± 1 h)
What steps affect the cement product?
Several different methods tested to try to
understand this:
• Limestone blended with other raw materials (RMs),
pressed into a brick and clinkered
– As similar to traditional synthesis as possible
• CaO calcined once in fluidised bed (FB), blended,
pressed, clinkered
• CaO cycled in FB, blended, pressed, clinkered.
Analysis of variance (ANOVA) - Repeats
• ANOVA used to identify any significant differences between repeats– 90 % Confidence interval
• Yes, the repeats aren’t particularly similar
Type No. samples F P-value F critCemex 3 12.23 0.01% 2.47
1 3 6.15 0.54% 2.473 2 0.93 34.51% 2.954 3 16.14 0.00% 2.475 3 224.59 0.00% 2.506 2 39.09 0.00% 2.957 3 41.18 0.00% 2.219 3 126.71 0.00% 2.47
11 2 22.60 0.01% 2.95
ANOVA – between cement types
Variable to change
Constants Number of ‘types’ P-value
Atmosphere Oxides; 5 cycles; Method
2 0.82
Atmosphere Clay; 5 cycles; Method
2 0
Composition CaL atmos.; 5 cycles; Method
3 0
Method CaL atmos.; 0 cycles; Clay
2 0
Cycles CaL atmos.; Clay; Method
3 0
N.B. These results are for the normalised data
PSD effects – t-test
• Hypothesis that the gradient of the line of
regression was 0 was tested using one-sided
Student t-test:
– i.e. β0 = 0
– t-score = 10.7
– Critical t-value (22,0.05) = 1.7
– Hypothesis rejected
• Gradient is statistically significant
Calculating standardised values
• Develop regression equation
• Use equation to calculate expected strength
• Divide strength by expected strength to get a
ratio
• Multiply expected strength at 10 µm by the ratio
to determine standardised strength
𝜎𝑥=10 =𝜎𝑥=𝑟
𝐸(𝜎𝑥=𝑟)∗ 𝐸(𝜎𝑥=10)
Mean strengths, all samples
0
10
20
30
40
50
60
Cem
ex0
1
Cem
ex0
2
Cem
ex0
3
02
03
04
05
06
07
08
09
10
11
12
13
14
15
17
18
19
20
21
22
23
24
27
L01
L03
L04
Co
mp
ress
ive
Str
en
gth
at
7 d
ays
(MP
a) Mean strengths, all samples
Actual Normalised
0%
10%
20%
30%
40%
50%
60%
70%
Alite Belite C3A C4AF
002 003 006
007 008 009
010 011 012
013 014 015
XRF results
Boxes represent typical
percentages as suggested
by HFW Taylor: ‘Cement
Chemistry’ (1990)
Phase percentages calculated using GSAS II. Toby &
Von Dreele (2013) J. App. Cryst. 46(2) 544-549
Strength tests – Effect of atmosphere
37.0 35.5
44.5
27.7
37.8 38.244.8
34.0
0
10
20
30
40
50
60
(O-5-C) Oxides, CaL (O-5-F) Oxides, 15% (C-5-C) Clay, CaL (C-5-F) Clay, 15%
Co
mp
ress
ive
Str
en
gth
at
7 d
ays
(MP
a)
Effect of atmosphere
Original Standardised
Strength tests – discussion (2)
Calcium looping atmospheres may provide stronger
clinker
Mechanical properties of CaO calcined in different
atmospheres may affect its grindability
– This may be useful for cement plants
• Or a pain – they might need new mills!
37.0 35.544.5
27.737.8 38.2
44.834.0
0
10
20
30
40
50
60
(O-5-C) Oxides, CaL (O-5-F) Oxides, 15% (C-5-C) Clay, CaL (C-5-F) Clay, 15%
Co
mp
ress
ive
Str
engt
h a
t 7
day
s (M
Pa)
Original Standardised