Measurements of the Quality of Cement Produced from Looped LimestoneCharles Dean, Prof. Denis Dugwell and Dr. Paul Fennell*

Department of Chemical Engineering and Chemical Technology, Imperial College London.Funded by EPSRC and Cemex.

IEA GHG Solid Looping Cycles Network, Vienna 2011.

*p.fennell@imperial.ac.uk

Presentation Outline

• Background to the Project• Objectives• Methods• Some Results

Benefit to Cement Manufacture of Using Spent Sorbent

kg / tonne clinker

Assuming energy demand of 3.7GJ/tonne clinker, pet coke use at calciner and bituminous coal at kiln.

Data taken from: Alsop, P. A., 2007, Cement Plant Operations Handbook

kg / tonne clinkerTherefore possible to mitigate ~ ¾ cement CO2 emissions by using spent sorbent from Ca-loop.

Assuming energy demand of 3.7GJ/tonne clinker, pet coke use at calciner and bituminous coal at kiln.

Data taken from: Alsop, P. A., 2007, Cement Plant Operations Handbook

Benefit to Cement Manufacture of Using Spent Sorbent

Cement Chemistry Overview

CaO is used to produce calcium silicates→ upon hydration these crystals form an interlocking microstructure which provide the bonding strength.

KILN REACTIONS900-1200 2CaO+SiO2 → 2CaO.SiO2 – ‘Belite’

CaO + Clay → Calcium Aluminates (‘Interstitial phases’)

1250-1500 CaO+2CaO.SiO2 → 3CaO.SiO2 – ‘Alite’

Final Proportions: ~ 60 % Alite, ~ 25 % Belite, ~ 15 % interstitials.

< 1 yr strength

> 1 yr strength

The Role of Trace Elements in Cement

e.g. Effect of MgO e.g. Effect of ZnO

Some elements are beneficial between certain limits, detrimental outside of those limits.e.g. MgO > 2 %.

Formation of calcium silicates strongly influenced by trace elements in clinker:

Objectives of the Project

• To identify chemical changes in sorbent (concentration of trace elements) upon repeated cycling under different conditions.

→ Repeated cycling will lead to chemical and physical changes in the sorbent. In particular combustion products and ash from fuel use in calciner will potentially be retained in the sorbent.

• To relate chemical changes in sorbent to possible changes in cement quality/composition.

→ In this project, cement quality is being inferred from aliteproduction (as the most prevalent phase).

Objectives of the Project

• To identify chemical changes in sorbent (concentration of trace elements) upon repeated cycling under different conditions.

→ Repeated cycling will lead to chemical and physical changes in the sorbent. In particular combustion products and ash from fuel use in calciner will potentially be retained in the sorbent.

• To relate chemical changes in sorbent to possible changes in cement quality/composition.

→ In this project, cement quality is being inferred from aliteproduction (as the most prevalent phase).

Research Methodology

1. Produce sorbent using different fuels and numbers of cycles.

2. Analysis of sorbent (ICP).3. Production and analysis of clinkers

(XRD).

Sorbent Production and Analysis

Sorbent Production – 3kW Spouted Bed Reactor

CO

2co

ncen

tratio

n

15 % CO2 (balance air), 5 l/m, LongcalP25 limestone, 425 – 500 µ.

2g coal / cycle – based on modeling work (essentially is amount req’d at calciner based on 30 % split fuel use).

Fluidising gasFuel

Bed

Tem

pera

ture

(◦C

)Time (s)

Sorbent Production – RDF Fuel Feeding System

Methods: Trace Element Analysis of Fuels & Sorbent

• Sorbent prepared for ICP – hot nitric acid digestion followed by filtration.

• Efficacy of digestion checked using standard reference materials.

0

500

1000

1500

2000

2500

Mg Fe K S Sr Mn P

Sam

ple

Con

c. (p

pm)

Ref. Exp.

SRM 1d - Limestone

[Units – ppm]

SRM 1547 – Biomass (Peach Leaves)

Clinker Production and Analysis

Clinker Production

Once sorbent is removed from reactor:• Homogenised with other oxides in DI water then dried.• Pressed into a brick using 100 atm pressure.• Then fired in tube furnace at 1500°C for 2hrs.

Clinker Production

• The brick is then pushed directly from the furnace into an air cooled chamber – 25 l/m applied evenly across brick until ambient temp.

• This is to prevent decomposition of alite to belite which can take place if clinker is allowed to cool at its own rate.

Methods – Qualitative Assessment of Clinkers

• First, qualitative assessment of phases present in the clinker –indicates that correct phases are present.

25 30 35 40

0

400

1600

3600

6400

Inte

nsity

(cou

nts)

Blue – BeliteGreen – AlitePink - Interstitial

Alite

Belite

Interstitial phases

• % alite is achieved by mixing clinker samples with corundum (Al2O3) in 1:1 ratio. This enables changes in alite peaks to be converted to % by comparing to corundum peak (using RIR value – taken from ICDD database).

Methods – Quantitative Assessment

Xa = (Ia/Ic)*(Irelc/Irela)*(Xc/RIR)26.5 27.0 27.5 28.0 28.5 29.0 29.5 30.0 30.52Theta (°)

0

100

400

900

1600

2500

Inte

nsity

(cou

nts)

Main Results -% Alite

Main Results - % Alite – No Fuel & La Jagua Coal

C. Dean, D. Dugwell, and P.S. Fennell.Energy & Environmental Science, 2011. 4(6): p. 2050-2053.

0102030405060708090

100

1 5 10 15

% A

lite

No. Cycles

No Fuel 2 g / cycle

All results average of 3 replicate experiments

Sorbent trace element levels after 5 cycles

5 cycles, La Jagua Colombian coal – 2 g / cycleAverage of 3 replicate experiments

**

Increase in most elements. However largest increase is Ba and Cr.(Decrease in Mg and Sr – assume that other increases over-ride these losses).

↑↓

La Jagua

Long-cliffe

5cyc Sorbent

ppm ppm ppmB 13.88 0.00 9.73Ti 69.77 0.35 6.60Zn 6.17 0.00 5.14

Ba 80.34 12.00 27.99Cr 2.97 2.50 47.26Cu 31.50 4.50 10.64Ni 2.89 0.35 0.30Mg 114.31 1500.00 1295.29Mn 6.57 45.00 57.54Sr 56.85 135.00 112.82

Elements Detrimental to Alite Formation

Elements Beneficial to Alite Formation

5 cycles, La Jagua Colombian coal – 2 g / cycleAverage of 3 replicate experiments

Drop in the level of trace element concentrations after 1 cycle indicates that most elements are first lost before being replenished. This could explain drop in % alite upon repeated cycling without fuel.

Sorbent trace element levels after 5 and 1 cycle

↑↓

La Jagua

Long-cliffe

5cyc Sorbent

1cyc Sorbent

ppm ppm ppm ppmB 13.88 0.00 9.73 9.81Ti 69.77 0.35 6.60 0.00Zn 6.17 0.00 5.14 4.87

Ba 80.34 12.00 27.99 6.59Cr 2.97 2.50 47.26 3.82Cu 31.50 4.50 10.64 13.76Ni 2.89 0.35 0.30 0.00Mg 114.31 1500.00 1295.29 1399.19Mn 6.57 45.00 57.54 43.98Sr 56.85 135.00 112.82 84.23

Conclusions on cement from cycled sorbent

Repeated cycling without fuel - appears to impact negatively on alite production. Trace element results after 1 cycle indicate that this could be due to loss of impurities / trace elements.

For the case of La Jagua – repeated cycling appears to improve alite formation. Trace element results after 5 cycles indicate this could be due to replenishment of impurities from fuel, esp. Ba and Cr.

However further work needed – esp. producing clinker from raw materials containing a more realistic baseline of trace elements (i.e. clay) to see if repeated cycling with fuel takes trace element concentrations past any ‘tipping points’.

Further Results –Trace Element Partitioning

Partitioning of Trace Elements

Partitioning of Trace Elements

Partitioning of Trace Elements after 5 cycles: RDF

0

50

100

150

200

250

300

350

400

450

Ti Ti Cu B V Al

Ba Cr

Mn Fe Na K S Zn Sr Ni

Mo

Mg

Pb P Co

Cd As

Sb

% R

ecov

ered

% Recovered in Solid Streams

Average of 3 repeats

• Heavier elements closer to 100 %. • More volatile elements lost.• Contamination from Ti and Cu.

Partitioning: Implications for Cement Manufacture

S

Na K

18,000ppm!

+148 %+43 %

+ 579 %

20,000ppm!RDF

█ - Sorbent █ - Fly Ash █ - Fines █ - Lost

RDF Trace Element Conc.

Conclusions on RDF trace element partitioning

• Heavier elements / elements with lower boiling points tend to reside in sorbent and therefore potentially also in the cement. Volatile elements tend to collect in fines / fly ash or exit as gas.

• Partitioning shows that Na, K and S could cause problems in use of RDF-derived sorbent, both in cement application (i.e. aggregate/concrete) and in Ca-loop / cement plant operation.

• Climafuel feeding: contamination issues need resolving before producing cement!

ThankyouQuestions