characteristics & performance of portland cement...

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