Fully Integrated Simulation of a Cement Plant with a ... · PDF fileFully Integrated...

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Fully Integrated Simulation of a Cement Plant with a Carbon Capture Ca-looping Process

Dursun Can Ozcan, Hyungwoong Ahn, Stefano Brandani

Institute for Materials and Processes School of Engineering

University of Edinburgh 2012/20/08

The 4th IEAGHG Technical Workshop on HTSLC in Beijing

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Carbon Capture for Cement Industry

CO2 Emission from Cement Industry • Cement is a key construction material (3.78 billion tons in 2012). • Large industrial source of CO2 emission (5% of worldwide emission). • Around 50% of the total emission accounts for calcination of limestone in raw

material. • Energy efficiency improvements are limited, essential to deploy a carbon capture

technology to reduce CO2 emission up to 90%. Technical Options for Carbon Capture • Oxy-combustion

Technical uncertainty in operating cement kiln under the condition of oxy-combustion • Post-combustion amine process

Stripper steam should be generated with an external boiler. new boiler, FGD, SCR • Post-combustion Ca-looping process

The absorbent is one of the cement raw materials purge CaO can be used for cement manufacture

The operating condition of a carbonator can be found in cement plant. The 4th IEAGHG Technical Workshop on HTSLC in Beijing

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Chemical Reactions

Ref. Cement Chemistry, H F W Taylor, 2nd ed. 1997.

Reaction ∆H (kJ) For 1kg of

CaCO3 (Calcite) CaO + CO2(g) +1782 CaCO3

AS4H (pyrophyllite) α-Al2O3 + 4SiO2(quartz) + H2O(g) +224 AS4H

AS2H2 (kaolinite) α-Al2O3 + 2SiO2(quartz) + 2H2O(g) +538 AS2H2

2FeO⋅OH (goethite) α-Fe2O3 + H2O(g) +254 FeO⋅OH

2CaO + SiO2 (quartz) ß-C2S -734 C2S

3CaO + SiO2 (quartz) C3S -495 C3S

3CaO + α-Al2O3 C3A -27 C3A

6CaO + 2 α-Al2O3 + α-Fe2O3 C6A2F -157 C6A2F

4CaO + α-Al2O3 + α-Fe2O3 C4AF -105 C4AF

o The enthalpy of formation of 1kg of a Portland cement clinker is around +1757 kJ/kg.


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Phase Change in Cement Plant

Ref. Cement Chemistry, H F W Taylor, 2nd ed. 1997.

Pre-heaters • 30% sulphur reacts with oxygen • Partial CaCO3 calcination • Partial clay minerals

decomposition Pre-calciner

• CaCO3 calcination (>90%) and clay mineral decomposition completed.

• Partial conversion of CaO to C2S.

Kiln • C2S to C3S conversion. C3A and

C4AF formed. • Aluminate and Ferrite melting.

Preheaters out

Pre-Calciner Kiln


Mass and Energy Balances


Mass in kg/s Mass out kg/s Raw meal 52.41 Clinker 31.45 Air 99.71 Flue gas Fuel From fuel drying 4.53 Wet coal to pre-calciner 2.25 From raw mill 75.57 Wet pet-coke to kiln 1.18 Excess Air 44.00 Total in 155.55 Total out 155.55

Enthalpy in [GJ/h] Enthalpy out [GJ/h] Sensible

Heat Heat by

combustion Sensible

Heat Heat of

Reaction Raw Meal 1.82 Clinker 5.09 Air 3.23 Flue gas Fuel From fuel drying 4.63 Wet coal to pre-calciner 0.12 218.78 From raw Mill 74.13 Wet pet-coke to kiln 0.05 141.06 Excess Air 46.30

Heat lost by radiation and convection 53.29

Overall heat of reaction 181.62

(1.60 MJ/kg) Total in 365.06 Total out 365.06

Energy Balance

Mass Balance

oThe required thermal energy for unit clinker production is 3.18 MJ/kg clinker.

o 1.67 kg/s of raw meal is required to produce 1 kg/s of clinker.

Clinker Composition

Mineral

Bogue

calculation

…[wt %]

Simulation

[wt%]

Alite (C3S)

Belite (C2S)

Tricalcium Aluminate (C3A)

Tetracalcium Aluminate (C4AF)

Free CaO

CaO⋅SO3

Ash

Total

60.6

17.5

11.0

8.6

0.0

2.3

0.0

100.0

60.4

17.2

10.9

8.2

0.0

2.5

0.8

100.0

The simulated clinker compositions are in a good agreement with those estimated by Bogue equation.


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Selection of an Optimal Feed Stream for Ca-looping Process

Raw Mill 1st Preheater

2nd Preheater

3rd Preheater

4th Preheater Pre-Calciner Kiln Cooler

Bag Filter Bag FilterFuel Drying

Bag Filter

CoalPet Coke

Air In-leak Air In-leak Air In-leak Air In-leak Air In-leak Air In-leak

Secondary Air

Cooling Air

Tertiary Air

Primary Air

Raw MealClinker

Collected Dust

Air In-leak

To Atmosphere

To Atmosphere

To Atmosphere

• The flue gas temperature and CO2 mole fraction varies over the process • The optimal flue gas stream for the capture process should be selected taking the operating condition of a selected capture unit, ease of heat integration, and CO2 partial pressure into account.


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Process Integration in Retrofit Case

0

10

20

30

40

CO

2 con

cent

ratio

n

(mol

e%)

1st Preheater 2nd Preheater 3rd Preheater 4th Preheater Precalciner Kiln Raw mill

The flue gas at the 3rd preheater exit has a higher CO2 concentration (~35 vol%)

The CO2 concentration at the end-of-pipe stream is ~22 vol%

0

200400

600

800

10001200

1400

1600

Tem

pera

ture

[C]

Raw Mill 1st Preheater 2nd Preheater 3rd Preheater 4th Preheater Pre-Calciner Kiln Cooler

Gas Flow

Solid Flow

Flue gas temperature is around 650°C no preheating is required.

Flue gas needs to be heated up to 650°C. Relatively low CO2 concentration. The 4th IEAGHG Technical Workshop on HTSLC in Beijing

Raw Mill 1st Preheater

2nd Preheater

3rd Preheater

4th Preheater

Pre-calciner Kiln Cooler

Bag Filter

Fuel Drying

Bag Filter

CoalPet Coke

Air In-leak Air In-leak Air In-leak Air In-leak Air In-leak Air In-leak

Secondary Air

Cooling Air

Tertiary Air

Primary Air

Raw Meal

Collected Dust

Air In-leak

To Atmosphere

To Atmosphere

Carbonator Calciner

CaCO3

CaO

PetCoke

CO2 Compression

Oxygen

Make-upCaCO3

Steam Cycle

Compressed

Purge

Qcarbonator

Blower Bag Filter

Clinker

Excess Air

Gas Flow

Solid Flow

Excess Air

Heat stream

ASU

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Process Integration in Retrofit Case

1) The flue gas from 3rd Preheater is diverted to Ca-looping process for carbon capture.

2) CO2 depleted flue gas from carbonator is routed to the 2nd Preheater for the raw material preheating.

3) Part of excess air from the cooler is used for additional raw material heating. 4) Purge from the carbon capture calciner is sent to the kiln.


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Ca-Looping Process

• Calciner needs to operate at 930oC for 100% calcination while carbonator operates at 650oC.

• CaO loses its capacity over the cycles theoretical capture rate is determined by two flowrate ratios: FR/FCO2 and F0/FCO2.

• The operation conditions inside carbonator and calciner are also favourable to the SO2 capture (effects of sulfidation on the maximum carbonation degree).

Calciner

gas flow

solid flow

Air Separation

Unit

O2

Carbonator

CO2 degraded flue gas

CO2-rich flue gas

Make-up (CaCO3)

N2

Flue gas from power plant

Purge to cement plant(CaO, CaSO4, ash)

Fuel

Heat extraction (Q3)

Blower

Q1

Q2

Q4

CO2 Compression

Compressed CO2


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Carbonator Model

Two mathematical models for carbonator have been compared in the study; • The simple model (all active fraction of CaO reacts with CO2) • The rigorous model1: * CFB model operates in the fast fluidization regime * Particle distribution part has been applied from K-L model; lower

dense region and upper lean region * The CO2 concentration at the exit has been estimated from the

gaseous material balance by considering the first order kinetic law of carbonation degree.

The effect of sulfidation was considering by adjusting the k and Xr constants corresponding to sulfidation level of Piaseck limestone 2 (valid up to1% sulfidation)


1 Romano, M.C. Modelling the carbonator of a Ca-looping process for CO2 capture from power plant flue gas. Chem. Eng. Sci. 2012, 69 (1), 257-269 . 2 Grasa, G.S.; Alonso, M.; Abanades, J.C. Sulfidation of CaO particles in a carbonation/calcination loop to capture CO2. Ind. Eng. Chem. Res. 2008, 47, 1630-1635.

1

2

3

4

5

6

0 1 2 3 4 5 6

F R/F

CO

2

F0/FCO2

Rigorous model (w/ S) Rigorous model (w/o S) Simple model

F0/FCO2 Sulfidation levels (%) 0.2 0.22 0.25 0.25 0.3 0.28 0.4 0.33 0.6 0.42 0.8 0.50 1.2 0.62 1.6 0.70 3.5 0.90 5.8 1.00

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Carbonator Model


lower limit

upper limit

• To keep sulfidation rate maximum at 1%, the S content of fuel has been adjusted. (5.3% → 3.6%)

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Carbonator Model

o All the mathematical models for the carbonator have been solved in Matlab, and the carbonator unit was incorporated into the Unisim process simulation (Unisim Matlab Unisim)

Unisim User Unit Operation for Carbonator Simulation

The interface of the model in Unisim


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Simulation – Retrofit Case

Simulation Basis • Target: 90% CO2 recovery in the carbonator and 95+% CO2 purity. • The total clinker production rate is kept constant. • ASU : 95% O2 purity. • CO2 product is compressed up to 150 bar.


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Results

• The thermal requirement for the pre-calciner and kiln decrease reduction in

calcite fed to raw mill, and calcite is completely calcined in the calciner. • The heat requirement for the calciner shows a minimum. • The energy requirement for ASU and blower has decreasing trend less gas

flow into the carbonator.

0

1

2

3

4

5

6

7

8

9

10

0 1 2 3 4 5 6

The

rmal

ene

rgy

cons

umpt

ion

per

unit

clin

ker [

GJ t

h/ton

]

F0/FCO2

Total energy input (Fuel + ASU+Blower) Total fuel input Fuel input to calciner Fuel input to pre-calciner and kiln


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• The gross power generation efficiency is estimated as 46 %. • It is predicted that the power generated in steam cycle can exceed the power

demand in the cement plant integrated with a Ca-looping process up to 2.9 F0/FCO2.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 1 2 3 4 5 6

Pow

er p

er u

nit c

linke

r [M

Wh/

ton]

F0/FCO2

Gross power generation

Total power consumption

CO₂ compressor power

Cement plant power

ASU+Blower power


0

2

4

6

8

10

12

88

90

92

94

96

98

100

0 1 2 3 4 5 6

Incremental energy consum

ption per C

O2 avoided [G

J/ton CO

2 ]

CO

2 rec

over

y (a

void

ed) [

%]

F0/FCO2

Carbon Dioxide Recovery At oxy-calciner Energy Consumption without Heat Recovery At oxy-calciner Energy Consumption with Heat Recovery At oxy-calciner

• The percentage of CO2 avoided is between 92 – 99 %. • Oxy-calciner only no carbonator and all calcites are calcined in the calciner. • The incremental energy consumption for 5.8 case is 5.3 GJ/ton CO2 while that value

can be estimated as 4.6 GJ/ton CO2 for integrated MEA process. • With heat recovery, the resulting energy consumption decreases to 2.3 GJ/ton CO2

for 5.8 case. The 4th IEAGHG Technical Workshop on HTSLC in Beijing

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Conclusions

• A way of capturing CO2 from cement plants by integrating it with a Ca-looping process has been investigated.

• The clinker composition is in a good agreement with the Bogue equation. • The gas stream leaving the 3rd preheater was selected to be a feed suitable for

Ca-looping capture unit since o it does not have to be preheated o it has a higher CO2 partial pressure and lower total volumetric flow rate o a simpler design of steam cycle for heat recovery is possible

• Low sulphur fuel is required to minimize CaO circulation.


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Conclusions

• Given the 90% carbon capture in the carbonator, the CO2 avoided in overall process ranges from 92% to 99% depending on the F0/FCO2 ratio.

• The fuel consumption of 2.3 to 3.0 GJ/ton CO2 avoided which depends on the F0/FCO2 ratio with a heat recovery system is estimated.

• The estimation of heat recovery can be made more accurate by a follow-up study on a detailed steam cycle.


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