Understand Cement Production - Home — · PDF fileUnderstand Cement Production Module 3....

A GIZ-Holcim Public Private Partnership managed by FHNW

Understand Cement Production

Module 3

Module 3: Understand Cement Production

Learning targets

� Participants generally have a basic knowledge of the

chemical, process-technological and environmental

aspects of cement production.

� They also have the basic knowledge to understand and

discuss the environmental dynamics of a modern

cement kiln system.

2

cement kiln system.

v3.1, 31.01.2011A GIZ-Holcim Public Private Partnership managed by FHNW


List of contents

� Cement production: chemistry

� Cement process technology

� Environmental features and aspects of cement

production

3v3.1, 31.01.2011A GIZ-Holcim Public Private Partnership managed by FHNW


Cement is made from „raw materials“

� Four main categories of raw materials for cement/

clinker production

� CaO = C, SiO2 = S, Al2O3 = A, Fe2O3 = F

� Corrective materials provide main elements deficient in the

(locally) available raw materials.

Raw mix will be dried, ground to raw meal and burnt to

Cement production: chemistry

4

� Raw mix will be dried, ground to raw meal and burnt to

clinker (minerals) C3S, C2S, C3A, C4AF

� Mineral components

� Set controllers

� Clinker, set controllers (and mineral components) are

ground to cement




Examples of raw materials I

Material Category Origin Examples

Raw materials (main) Natural Limestone, marly limestone,

calcareous

marl…clay…coal ash

Alternative Industrial lime/sludge, fly

ash

Corrective materials Natural High grade limestone,


5

Corrective materials Natural High grade limestone,

quartz sand, bauxite, iron

ore

Alternative Foundry sand, pyrite ash

Set controllers Natural Gypsum

Alternative Desulfurization gypsum

Mineral compounds Natural Pozzolana

Alternative Blast furnace slag, fly ash




Examples of raw materials II Cement production: chemistry

6




Raw materials naturally include also

minor and trace elementsHeavy metals (HM): ranges of Holcim 2004 clinker compounds

Main elements (oxides) Minor elements (oxides) Trace elements (WID-list)

CaO 620-650-700 MgO 6-18-50 Hg 0-0-0

SiO2 190-210-240 SO3 1-8-21 Tl <0.5-<0.5-<0.5

Al2O3 32-51-64 K2O 0-7-14 Cd <0.1-0.43-2.1

Fe2O3 2-35-77 Na2O 0-2-10 As 1.3-14-265


7

TiO2 0-3-10 Co 4.0-13-65

Mn2O3 0-1-12 Ni 4.0-42-360

Cr2O3 Sb <0.1-??-60

P2O5 0-2-6 Pb <1.0-20-127

Cl- 0-0.1-0.3 Cr 18-58-263

F- 0-3 Cu 3.2-61-299

Pyritic S 0 Mn ??-??-??

Organic C 0 V 20-95-353

NH3 0

TOTAL [g/kg] Ca. 950 g TOTAL [g/kg] Ca. 50g TOTAL [mg/kg] Ca. 300 mg




To turn raw materials into clinker, they

need to undergo several treatments� Storage/pre-blending

� Chemical analysis

� Proportioning to meet mix calculation targets

� Mixing, drying, grinding (in the raw mill)


8

� Mixing, drying, grinding (in the raw mill)

� Precalcining to transform CaCO3 into CaO and CO2,

(CO2 emits to the atmosphere)

� Burning clinker minerals (rotary kiln)

� Rapid air cooling to stabilize the clinker minerals




Thermal processes in the kiln system

� Decarbonization, clinker

mineral formation and

first clinker cooling is

performed in the high

temperature zone of the

kiln system with:


9

kiln system with:

� Material temperature

between 800 and

1,450°C

� Combustion air and

combustion gas

temperatures between

800 and 2,000°C




Cement making today: the process flow

chartCement process te

chnology

10

Cement process te

chnology



Clinker production today: the kiln flow

chart

Exhaust airdedustingSuspension preheater

Exhaust gasdedusting

DOM

300°°°°C250°°°°C100°°°°C

Cement process te

chnology

11

Rotary kiln

Clinker cooler

Precalciner

Raw mill

Coolingtower

Tertiary air duct

DOM duct

100°°°°C

Cement process te

chnology



Firing a cement kiln: feeding continuous streams

of uniform quality combustible materials

� The example of mineral coal as the generic case for all (natural and alternative) fuels:

1 2 3

Arrow = transport processes

Fuel preparation� drying� grinding

Fuelsourcing

Fuelproportioningto feed points

Cement process te

chnology

12

Arrow = transport processes

1 = Storage of raw coal

2 = Fine coal silo

3 = Kiln system

Desired characteristics of cement kiln fuels:

� Continuous availability in large quantities

� High and uniform quality

� Low water and ash content / fineness appropriate for feed point

� Good flowability / metrability for low excess air combustion

� Environmental soundness

Cement process te

chnology



Fuel feed point in cement kiln systems

Precalciner firing

or secondary firing (SP kilns)

Cement process te

chnology

13

Main firingKiln inlet firing

Cement process te

chnology



Cement and concrete production:

blocks and numbers [tonne / tonne clinker]

1Burning

process2

Cement

grinding3

Ready mix

concrete

plant4

1.65

0.15

1.5

0.12

0.5+0.3

1.0

0.33

1.33

8.0 0.66

10.0

(4 m3)

Raw materials� Proportioning� Drying� Grinding

Cement process te

chnology

14

Natural and

alternative

raw materials

preparation

5

Natural and

alternative

fuels

preparation

6 7

Natural and

alternative

min. comp.

preparation

Natural and

alternative

aggregates

preparation

8

1 = Raw meal homogenizing and storage silo 5 = Raw material pre-blending and storage halls

2 = Clinker silo 6 = Prepared fuel silos

3 = Cement silo 7 = Storage silos or halls

4 = Concrete construction 8 = Storage stocks or silos

Cement process te

chnology



Special characteristics

� No. 1: high to very high system temperatures

� No. 2: process inherent multi-stage fluidized bed gas cleaning technology

� No. 3: high retention capacity for SO2 and Cl

� No. 4: atmospheric emissions largely given by roasting off of volatile raw material compounds

Environmental features and aspects

15

raw material compounds

� No. 5: all mineral compounds transformed into product

� No. 6: all trace elements (heavy metals) safely embedded in final product

� No. 7: high thermal efficiency of process

� No. 8: reduction of country CO2 emissions through alternative fuels utilization




No. 1: high to very high system

temperatures� Result in complete combustion down to traces of CO in the rotary kiln: all organic input is reliably destroyed (oxidized)


16

Note: Even the most stable organic compound can not survive temperatures exceeding slightly more than 800 °C




No. 2: process inherent multi-stage

fluidized bed gas cleaning technology

� Six scrubbing „stations“ in series,


17

� Six scrubbing „stations“ in series,

working at different

temperatures (850, 750, 650,

500, 320 and 100°C)

� Last stage (raw mill) particularly

effective due to:

� Newly generated active surface

� Lowest temperature

� Highly efficient bag filter (>10 mg/Nm3 clean gas dust)




No. 3: huge retention capacity for SO2and ClEnvironmental features and aspects

18




No. 4: atmospheric emissions largely given by

roasting off of volatile raw material componentsEmission component of

importance in the

cement industry

Range of

emissions found

[mg/Nm3]

European ELV

acc. to WID

[mg/Nm3]

Origin of emissions

SO2 0 – 300 - 3000 50 plus Pyritic S in raw materials

NOx 300 - 2000 200?/500/800 Main flame in rotary kiln +

fuel NO

VOC 0- 50 - 500 10 plus Organics in raw materials


19

HCl 1 – 15 10 Raw materials and fuels

NH3 1 – 15 – 40 None Raw materials and possible

SNCR

Benzene (C6H6) 1 -2 - …. 5 Organics in raw materials

PCDD/DF 0 – 0.02 ng ITE 0.1 Organics in raw materials

Hg 0 - 1 0.05 Raw materials and fuels

Tl and Cd traces 0.05 Raw materials

Other 9 heavy met. Σ< 0.5 0.5 Raw materials

Clean gas dust 1 – 20 – 50 - 150 30 Raw materials




No. 5: all mineral input turned into

product� All main and minor elements (particularly also those imported

with alternative materials) are used to form clinker minerals or

are incorporated in clinker minerals

Exceptions in case of bypass dust generation:

� Incorporation in hydration products (concrete)

� Landfilling 20

0

80

100

4


20

Legend

� Clinker

� Limestone

� Marl

� Foundry sand

� Pyrite ash

� Coal ash

� Lignite ash

� Sewage sludge ash

� Tire ash

� Landfilling

100

80

40

Al2O3+Fe2O3 (%)20 80 1000

0

20

40

9

8

7

6

5

3

2

1




No. 6: all trace elements (heavy metals)

safely embedded in final product (I)� All heavy metals (HM) are

� incorporated in the clinker minerals (except Hg and Tl)

� bound in hydration products (also Tl and much of Hg)

� encapsulated in the concrete structures

Concrete is a multi-barrier system preventing migration

(leaching) of heavy metals to the living environment


21

Leaching tests Test results

Monolithic concretes, all leaching test methods

All HM below or close to detection limit even of most sensitive leaching test method

Crushed concrete, most aggressive test method

Leached concentrations of chromium, aluminum and barium may come close to drinking water standards. Conclusion: limit chromium input to the minimum

(leaching) of heavy metals to the living environment




No. 6: all trace elements (heavy metals)

safely embedded in final product (II)

� To prevent abuse (of concrete as a final storage facility

for HMs), do not exceed, e.g., the following HM

concentrations in alternative fuels (AF)


22

Tl Cd Be Cr As Sb Sn Co Pb Ni Cu V Hg

50 50 50 250 400 500 500 500 800 1000 1000 1000 5




No. 7: high thermal efficiency of process

� Specific heat consumption of process: 3,000 – 3,300 kJ/kg cli

� Theoretical heat demand of clinker formation: 1,750 kJ/kg cli

� Thus, thermal efficiency: 53 – 58 %

� Thermal efficiency at maximum waste heat utilization (kiln exhaust gas and cooler exhaust air: 80 -90 %


23

� Example of a kiln system heat balance (orders of magnitude only):

� Clinker formation 1,750

� Exhaust gas heat content 700

� Exhaust air heat content 400

� Radiation and convection losses 250

� Clinker heat content 100

Total: 3,200 kJ/kg of clinker




No. 8: reduction of country CO2 emissions

through alternative fuels (AF) utilization

1 2 3 4

No use of AF in CI Use of AF in CI


24

1 2 3 4

AF to

landfill

AF to

incineratorCement

industryor

AF to cement

industry

1. Landfill gas (CO2 and CH4)

2. CO2 from incineration

3. CO2 from fossil fuels in CI

4. CO2 from both systems if AF used in CI

Other options for CO2 reduction:

� Reduction of cli/cem factor

� Process improvements (including waste heat utilization)




Emission abatement techniques

Emission Available abatement methods

Stack dust Well maintained bag filters or electrostatic precipitators

SO2 Hydrated lime injection to top riser duct (max.1200 � 500)

Wet sulfur scrubber (for large emissions, up to 3000 � < 200)

NOx SNCR with NH3 injection

VOCs Nothing really satisfactory (activated carbon absorbers, catalytic converters , thermal oxidisers)


25

DOM = Direct Operation Mode of kiln/raw mill system

HCl Indirectly via kiln and DOM dust bypass to CM

NH3 Indirectly via DOM dust bypass to CM

C6H6 Nothing reasonable for the time being

PCDD/DF No emission problems. In the rare case of elevated emissions: Indirectly via DOM dust bypass to CM and reduction of precursors

Hg/Tl Input control and limitation, indirectly via DOM dust to CM

Other HM No emission problems




Annex

� Historic cement making

processes

� SO2, NOx, VOC, heavy metal,

HCl emissions

� Measuring emissions

26

�

� Conversions

� Basic design of an air quality

protection regulation

� Air quality limit values

� Components of an air quality

protection system



Historic cement making processes (still in

use): wet processAnnex



Historic cement making processes (still in

use): semi-dry processAnnex



Other historic or rarely used cement

making processes

� Semi-wet process, using precalcination and external

drier technology or using grate preheater (Lepol-)

technology

� Semi-dry process, using long kilns with cross heat

exchangers or vertical shaft kilns

Annex

29

exchangers or vertical shaft kilns

� Dry process, using long kilns with chain heat exchangers



SO2 emissions� Effects

� Attacks muscous membranes through formation of sulfuric acid

� 5 -10 ppm: irritation of eyes and respiratory tract

� 400-500 ppm: lethal damage to respiratory system possible

� 2520 ppm: LD50 (inhalation, rats)

� Acidifies rain, surface waters and soils, and thus kills water life (plants, animals) and forests

� Destroys the built environment (e.g. historic building facades)

Annex

30

� Characteristics

� Colorless, toxic gas with a pungent smell and acid taste

� Odor threshold: between 0.01 and 0.3 ppm

� Maximum workplace concentration: 1.3 ppm

� Historic case: the big London smog from December 5 to 9, 1952 with particles and SO2 from coal fires; killed 12,000

� Origin of SO2: In the cement industry with SP/PC kilns from raw materials only (oxidation and partial release to the atmosphere)



NOx emissions� Effects

� NO from combustion processes reacts in the atmosphere to form NO2

� Contributes to acidification and eutrophication (nutrient overload)

� Contributes to ozone formation, Los Angeles smog formation, ozone layer destruction.

� NO2 inhalation may cause pulmonary edema (death possible, lethal concentration: 200 ppm)

Characteristics

Annex

31

� Characteristics

� NO is a colorless, odorless, toxic gas

� NO2 is a brownish/red, toxic gas with a pungent smell

� Maximum workplace concentration: 5 ppm

� Origin of NOx

� Thermal NOx from oxidation of N2 (combustion air) in the hot flame

� Fuel NOx from oxidation of organically bound N in the fuel

� Cement kiln NOx emission: 95 to 98% NO, 2 to 5% NO2



Volatile Organic Components (VOC) emissions

� Effects

� Contribute to summer (Los Angeles) smog and ozone formation

� Some are persistent and tend to accumulate in the food chain (bio-accumulation).

� In living organisms they might develop carcinogenic or teratogenic effects.

� Characteristics: toxic, flammable, explosive, persistent, bio-accumulative, carcinogenic, teratogenic, etc.

Annex

32

accumulative, carcinogenic, teratogenic, etc.

� Origin of VOC: in cement industry from (poss. contaminated) raw materials, rarely from overloaded secondary and precalciner firing, never from main firing.

Note: This issue is too complex even for a fairly detailed summary. VOC is the general term, sub-classes are, e.g., BTEX (benzene, toluene ethyl-benzene, xylene), PAH (polyaromatic hydrocarbons), PCB (polychlorinated biphenyls), HFHC, PCDD/DF, etc.

Cement kiln emissions are normally far below any emission limits



Heavy metal (HM) emissions� Effects

� Toxic to humans and animals in case of bio-accumulation (cacerogenic and teratogenic effects)

� But Cr, Fe, Co, Cu, Mn, Mo, Ni, V, Zn and Sn are essential trace elements in humans

� Characteristics (the cement industry distinguishes three classes of HM)

� Non-volatile HM: completely incorporated in clinker. No emission at all (i.e. below DL)

Annex

33

all (i.e. below DL)

� Semi-volatile HM (Tl, Cd, Pb): completely retained in the kiln system and incorporated in concrete, emissions can occur in special cases

� Volatile HM (Hg): no incorporation in clinker and partial incorporation only in concrete, elevated emissions possible

� Historic cases

� Tl-case of Lengerich/1979, Itai-Itai-desease in Japan, a Cd-case

� Pb concentrations along main roads: leaded fuels

Note: HM are in all raw materials and fuels. In the case of AFR input must be strictly limited to avoid abuse (of cement as a HM landfill) and to avoid emissions in the case of Hg



HCl Emissions Annex

� Effects:

� HCl is caustic and toxic at high concentrations

� Contributes to acidification

� If inhaled, it can irritate mucous membranes and the pulmonary system (bronchitis and pneumonia possible)

� Characteristics: colourless gas with a pungent smell

� Historic case: major emission component from first generation garbage incinerators

34

� Historic case: major emission component from first generation garbage incinerators

� Origin of HCl

� In the cement industry from some raw materials and from alternative (mainly plastic waste derived) fuels

� Clinker can carry max. 0.03%, cement 0.1% Cl, more needs to be landfilled (the latter two require the implementation of bypass technology

Note: HF emissions are negligible in the cement industry



Measuring emissions from a cement kiln

� Today‘s status at Holcim:

� Continuously measured emission components

� Always, mandatory: Dust, SO2, NOx (NO), VOC

� Occasionally: NH3, HCl, HF, Hg, benzene etc.

� Discontinuously measured emission components

� Always mandatory: NH , HCl, benzene, PCDD/DF, 12

Annex

35

� Always mandatory: NH3, HCl, benzene, PCDD/DF, 12

heavy metals (including Hg, Tl, Cd, …)

� Details of measuring campaigns according to Holcim EMR

manuals

� Baseline emission measurements as well as trial burn

emission measurements use this same approach



Conversion of ppm to mg/Nm3

(1013 mbar, 273,15 °K)Annex

Emission component ppm mg /Nm3

SO2 1 2.86

NO 1 1.34

NO as NO2 1 2.05

NO 1 2.05

36

NO2 1 2.05

VOC (CH4 Equiv.) 1 0.54

VOC (C3H8 Equiv.) 1 1.61

CO 1 1.25

HCl 1 1.58

HF 1 0.89

NH3 1 0.76



Basic design of an air quality protection

regulationAnnex

Transmission

Emissions

Emission limit values

Imission

Air quality limit values

Air quality

37

Emission limit valuesDynamization

Air quality

observation

network



Air quality limit values: example,

Switzerland (I)

� Definition: Imissions are air pollutants acting in various

ways on humans, animals, plants and material goods

� Gaseous imissions are quantified in concentration

values: g/Nm3, mg/Nm3,µg/Nm3

Annex

38

� Depositing dust is quantified in g/m2d or mg/m2d.



Air quality limit values: example

Switzerland (II)Pollutant Immission

limit

[../Nm3 dry]

Statistical

definition

Total suspended

dust

70 µg

<150 µg

A

F

Pb in suspended

dust

1 µg A

Annex

Pollutant Immission

limit

[../Nm3 dry]

Statistical

definition

SO2 30 µg

<100 µg

<100 µg

A

B

C

NO2 30 µg

<100 µg

A

B

39

Cd in suspended

dust

10 µg A

Total dust deposition

Pb in total dust

Cd in total dust

Zn in total dust

TI in total dust

200 mg

100 µg

2 µg

400 µg

2 µg

A

A

A

A

A

A = Yearly arithmetical mean valueB = 95% of all ½ h mean values/aC = All-1 24 h mean values/aD = 98% of all ½ mean values/monthE = All-1 1h mean values/aF = 95% of all 24h mean values/a

<100 µg

<80 µg

B

C

CO 8 mg C

O3 <100 µg

<120 µg

D

E



Components of an air quality protection

systemRequired are:

1. General air quality or immission standards

2. General emission standards

3. Linkage between immission and emission standards by

Annex

40

3. Linkage between immission and emission standards by the precautionary approach

4. Special standards specific to industries or sectors

5. Dynamization possibilities

6. National air quality observation network

7. Prescriptions for measurement and reporting


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