Download ppt - Ruth Allington 1 How to make cement-raw material requirements RUTH ALLINGTON

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Ruth Allington

How to make cement-raw material requirements

RUTH ALLINGTON

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Ruth Allington

Structure of the presentation• What is cement and how is it made?• Structure of the cement industry and relationship

to its main markets• What is its chemistry and what is it made of?• How much raw material do we need?• How much of each raw material do we need?

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Ruth Allington

Cement manufacture• Clay and limestone materials with a combined CaCO3

content at between 78% and 80% (and constraints on Fe2O3, Al2O3 and SiO2), heated in a kiln to temperatures greater than 1,200°C to produce CLINKER.

• Clinker ground finely in mills and with the addition of gypsum and/or other materials to produce CEMENT.

• Cement clinker is predominantly calcium silicate. Limestone is burnt, releasing CO2, and combined with silica to produce calcium silicate (with iron and alumina combined with calcium as minor constituents).

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The structure of the cement industry and its relationship to its market

CEMENT WORKS ADJACENTTO RAW MATERIALS RESERVES LASTING

20-30 YRS

COAL OR OTHER FUELDELIVERED TO CEMENT

WORKS VIA RAIL, ROAD, OR (FOR GAS) VIA PIPELINE

CLINKER

CEMENT

GRINDING PLANT

READY MIXDISTRIBUTED IN A 30km RADIUS

BAG (MERCHANT)MARKET

200km

IMPORTS

OTHER RAW MATERIALSe.g. GYPSUM, IRON OXIDE,SAND

CONCRETEPRODUCTS

ON-SITE MIXING EXPORTS

AGGREGATES (bulky commodity - high transport costs)

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Clinker chemistry

Example: Project “Grenze” (Poland)

SiO2 21%

Al2 O3 5.5%

Fe2 O3 3%

CaO 64%

SO3 0%

MgO 2.5% (must be less than 6% in cement)

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Cement raw material requirements

• Raw materials required such that clinker chemistry and key ratios are within the following target ranges:– SR = 2.2-2.8 {S/(A+F)}

– LSF = 0.92-0.98 {(C-0.7SO3)/(2.8S+1.2A+0.65F)}

– AF = 1.6-2.2 {A/F}

– C3S = 0.5-0.68 {4.07C-7.6S-6.72A-1.4F-2.85SO3}

– C2S = 0.10-0.30 {2.87S-0.754C3S}

– C3A = 0.08-0.12 {2.65A-1.69F}

– C4AF = 0.06-0.10 {3.04F}

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Relationship between raw material chemistry and clinker

chemistryWhen limestone is burnt in a cement kiln, carbon dioxide is produced. The reduction in mass on burning is known as the Loss on Ignition or LOI. If LOI for a limestone were 40%, then an alumina content in the dry limestone of 2% would equate to an alumina content in the clinker of 2% of 60% (i.e. 12%).

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Amount of raw material required per tonne of clinker

The amount of dry raw material required per tonne of clinker produced depends on the weighted average LOI of the raw materials. The conversion factor is given by 1/(1-LOI) and is typically around 1.5 - 1.6. For chalk, the moisture content may be around 23% (Ww/(Ww+Ws)).

On this basis, around 2 tonnes of as-dug raw material is required per tonne of clinker.

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Silica Ratio = SR = SiO2/(Al2O3 + Fe2O3)

Weighted average SR for three raw materials:

x% of limestone, y% of clay, and z% of oxide additives.

If:

Slmst = SiO2 content of limestone

Almst = Al2O3 content of limestone

Flmst = Fe2O3 content of limestone etc ……

SR of the raw mix is given by:

Equation 1 - Silica Ratio

zFyFxFzAyAxA

zSySxSSR

oxidesclaylmstoxidesclaylmst

oxidesclaylmstrawmat ******

***

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Ruth Allington

Rearranging the equation:

Equation 1 - Silica Ratio

0***

******

***

*******

zSFSRASR

ySFSRASRxSFSRASR

zSySxS

zFyFxFzAyAxASR

oxidesoxidesrawmatoxidesrawmat

clayclayrawmatclayrawmatlmstlmstrawmatlmstrawmat

oxidesclaylmst

oxidesclaylmstoxidesclaylmstrawmat

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Lime Saturation Factor = LSF =

(CaO-0.7SO3)/(2.8SiO2+1.2Al2O3+0.65Fe2O3)

Weighted average LSF for three raw materials:

x% of limestone, y% of clay, and z% of oxide additives

If:

Slmst = SiO2 content of limestone

Almst = Al2O3 content of limestone

Flmst = Fe2O3 content of limestone

Clmst = CaO content of limestone

SO3lmst = SO3 content of limestone etc ……

LSF of the raw mix is given by:

Equation 2 - Lime Saturation Factor

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Ruth Allington

Rearranging:

Equation 2 - Lime Saturation Factor

zFASyFASxFAS

zSOCySOCxSOCLSF

oxidesoxidesoxidesclayclayclaylmstlmstlmst

oxidesoxidesclayclaylmstlmstrawmix 65.02.18.265.02.18.265.02.18.2

37.037.037.0

037.065.0*2.1*8.2*

37.065.0*2.1*8.2*

37.065.0*2.1*8.2*

zSOCFLSFALSFSLSF

ySOCFLSFALSFSLSF

xSOCFLSFALSFSLSF

oxidesoxidesoxidesrawmatoxidesrawmatoxidesrawmat

clayclayclayrawmatclayrawmatclayrawmat

lmstlmstlmstrawmatlmstrawmatlmstrawmat

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x + y + z = 1

where:x is the proportion of limestone in the raw mix

y is the proportion of clay in the raw mix

z is the proportion of oxide additives in the raw mix

Equation 3

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Spreadsheet for proportioning cement raw material mixes

cement raw materials.xls

1. Enter raw material chemistries in first worksheet. Worksheet allows for three grades of limestone (high, medium and low), and later calculations assume a mix of high and low carbonate materials. It also assumes that the fuel will be coal and that the coal ash will combine with the clinker thus affecting its chemistry.

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2a. Vary the bold italic numbers at the top of page 2 of the ‘raw mix calculations’ sheet:

Vary raw mix SR until clinker SR is within the required range

Vary raw mix LSF until clinker LSF is within the required range

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2b. Vary the proportion of constituents in the additive mix (in the example, ceramic clay and iron oxide)

Vary the proportion of high carbonate limestone in the high/low carbonate limestone mix (if there are only two grades of limestone, either enter 100% or 0% and give the same analysis to both)

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2c. Whilst varying these values, have the screen split so that the clinker chemistry and ratios are displayed at the same time. Continue varying the values until all of the ratios and the clinker chemistry is within the desired ranges.

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Skills and experience relevant to cement raw materials evaluation

• Geological investigation and modelling• Geochemical investigation and modelling• Quality scheduling to meet defined chemical

targets for the raw material• Quarry and mine design incorporating quality and

quantity release scheduling meeting the requirements of the process

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Cement raw material resource evaluation e.g. in a due diligence

studyKEY ISSUES

• Resource/reserve size and locations

• Resource/reserve chemistry

• Working/quality release constraints

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Data

• Published data - geological and topographic maps, plans and aerial photography

• Official documentation

• Monitoring and site investigation data

• Data collected during site visits and in discussion with Works staff

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Geochemical modelling

• Borehole records and geochemical information availability

• Geological structure and relationship to chemistry

• Approaches to modelling at the due diligence stage

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Resource measurement and classification

• Constraints on resource size– Geology– Geotechnics– Hydrogeology– Land ownership and permitting– Working methods and existing mine layouts– Quality release requirements

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Resource measurement and classification

• Constraints on resource life– Availability of balancing materials– Expected clinker production rates