Process Integration of Ca -Looping Process with a … Integration of Ca -Looping Process with a Cement Manufacturing Plant ... due to infiltration air ... Raw Mill 1. st. nd Preheater

The 3rd IEAGHG Technical Workshop on HTSLC in Vienna 1

Process Integration of Ca-Looping Process with a Cement Manufacturing Plant

Hyungwoong Ahn, Dursun Can Ozcan, Stefano Brandani

Institute for Materials and ProcessesSchool of Engineering

University of Edinburgh2011/08/30


Carbon Capture for Cement Industy

CO2 Emission from Cement Industy• Large industrial source of CO2 emission (5% of worldwide emission)• The CO2 emission rate is around 0.72 – 0.98 ton CO2/ ton cement• Over 60% of the total emission accounts for mineral dissociation. The reduction

of CO2 emission by improving its energy efficiency is highly limited.)

Technical Options for Carbon Capture • Oxy-combustion

Limited CO2 product purity (80 v%) due to infiltration air CO2 purification required.• Post-combustion amine process

CO2 vol.% is as high as 20-30% and MEA is saturated with CO2 below this CO2 level. 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. No pre-

conditioning of feed stream is required.


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

The enthalpy of formation of 1kg of a Portland cement clinker is around +1757 kJ/kg and the total heat requirement in dry process kiln is around 3306 kJ/kg clinker.


Phase Change in Cement Plant

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

Pre-heaters • 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. (The Bogue calculation)

• Aluminate and Ferrite melting.

Preheaters out

Pre-Calciner Kiln


Base Case Simulation

• Steady-state process simulation by Honeywell Unisim R390.

Comparison of heat loss in a cement plant [kJ/kg clinker]Heat loss by radiation and

convectionThis

study Reference

Preheater 35 40

Calciner 22 20

Rotary Kiln 253 237

Tertiary air duct 27 27

Cooler+kiln hood 30 14

Total 367 338

Ref. VDZ, Execution and Evaluation of Kiln Performance Tests, 1992, Ali et al., 2010.

* Net heat of melting is around 104.7 kJ/kg.

-1.25E+06

-1.20E+06

-1.15E+06

-1.10E+06

-1.05E+06

-1.00E+060 200 400 600 800 1000 1200 1400 1600 1800 2000

Temperature [K]

Enth

alpy

[J/m

ol]

Comparison of CaCO3 enthalpies between reference and Unisim simulation.


Carbonate Looping Process

• Calciner needs to operate at 930oC for 100% calcination while carbonator operates at 600 – 750 oC

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

• Purge can be utilized in the cement industry as long as the cement spec is met. (CaSO4 limit: 10 wt.%, Ash limit: 30 wt.%)

• The heat of reaction for calcination (–175 kJ/mol) is higher than amine process (–154 kJ/mol for MEA) but the exothermic heat can be recovered by steam cycle (electricity).


0

200400

600

800

10001200

1400

1600

Tem

pera

ture

[C]

Selection of an Optimal Feed Stream for Ca-looping Process

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

Gas Flow

Solid Flow

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

Flue gas temperature is around 650°C no preheating is required.Higher CO2 concentration,

Flue gas needs to be heated up to 650°C. Relatively low CO2concentration.


Process Integration in Retrofit Case

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

2) CO2 depleted flue gas from the 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. the required

amount of fuel for the kiln needs to be increased.

Raw Mill 1st Preheater

2nd Preheater

3rd Preheater

4th Preheater Pre-Calciner Kiln Cooler

Bag Filter 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 MealClinker

Collected Dust

Air In-leak

To Atmosphere

To Atmosphere

To Atmosphere

Carbonator Calciner

CaCO3

CaO

Coke

CO2 Compression

Oxygen

CaCO3 M/U

Steam Cycle CompressedCO2

Purge

Raw Material

Pre-heater


Carbonator Model

1-D Fast Fluidisation Model in CFB

1) Particle Distribution (Lean/Dense Region) • The volume fraction of solids in a

dense region is fixed.2) Carbonation Reaction Rate

• Calculation of active CaO fraction.• Calculation of carbonation rate in

terms of boundary layer diffusion and chemical reaction.

3) CO2 absorption efficiency• Implemented Matlab code into

Unisim Design Suit R390 through a COM interface

0

20

40

60

80

100

0 10 20Cap

ture

Eff

icie

ncy

(%)

Height (m)

Unisim User Unit Operation for Carbonator Simulation

Carbonator Simulation Result


Carbonator Model

Parameters for the carbonator model FCO2: 200 kmol/h, FCaO: 325 kmol/h, uo: 6m/s

80828486889092949698

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575 600 625 650 675 700 725

Cap

ture

Eff

icie

ncy

(%)

Temperature (oC)

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50

100

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250

6000 7000 8000 9000 10000 11000

Pres

sure

Dro

p (m

bar)

Solid Inventory (kg)

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0 0.1 0.2

Hei

ght (

m)

Solid Fraction

Solid Inventory6600 kg

80828486889092949698

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500 1000 1500 2000 2500

Cap

ture

Eff

icie

ncy

(%)

FCaO in the purge (kgmole/h)

Results of parametric study on carbonator model


Simulation – Retrofit Case

Simulation Basis• Target: 90% CO2 recovery and 95+% CO2 purity.• ASU : 95% O2 purity.• CO2 product is compressed up to 150 bar. • The flowrates of both CaO circulation and CaCO3 make-up were determined

such that FR/FCO2 = 3.9 and FO/FCO2 = 0.1 in order to accomplish 90% CO2

capture.• 10% excess oxygen is fed to the calciner for complete combustion.


Steam Cycle and CO2 Compression

Ref. Cement Chemistry, H F W Taylor, 2nd ed. 1997.14 Rodriguez et al., 2009; 15 Rodriguez et al., 2010

Sub-critical Rankine cycle• Heat source: Heat extracted from

the carbonator and heat from a hot CO2 stream from the calciner

• Steam cycle efficiency: 35%

CO2 Compression• Multistage Turbo Compressor with

intermediate cooling.• Inlet temperatures were fixed as

45oC.• Adiabatic efficiency of each

compressor is 85%.


Simulation Results – Retrofit Case

Simulation Result

Base Case Retrofit Case

Raw Meal [kg/s] 52.4 52.4 + 5.8

Clinker Product [kg/s] 31.6 34.8

Energy input per kg of clinker [kJ/kg] 3,081 7,221

CO2 emitted per kg of clinker [kg/kg] 0.806 0.075

Gross power generation [MWe] N/A 50

Energy consumption in CO2 compression [MWe] N/A 15

*Energy consumption in ASU [MWe] N/A 10

Energy consumption per kg of captured CO2 [kJ/kg] N/A 3,527*ASU power consumption : 200 kWh/ton O2.

• Energy consumption per unit mass of clinker in retrofit case is more than double that in base case.

• The required electricity for CO2 compression and ASU can be produced by a steam cycle being driven by the heat recovery from Ca-looping process.


Conclusions

• Cement process has been successfully simulated by a steady-state process simulator considering typical chemical reactions. The simulation will be refined to reflect a more detailed reactions.

• A User Unit Operation for 1-D Carbonator has been developed in order to estimate its CO2 capture rate and the dimension of reactor. Develop user defined unit operations for calciner and kiln.

• Optimal feed stream for carbon capture Ca-looping process was selected as 3rd

preheater outlet based on the feed temperature and COz concentration.• The heat from the flue gas leaving the carbonator is integrated with cement

plant by feeding it to 2nd preheater.• The purge of deactivated CaO can be mixed with calcined material from pre-

calciner and sent to the kiln. Increasing the production by approximately 10 %. need to determine the optimums of the two flowrate ratios: circulating CaO to CO2 and CaCO3 make-up to CO2.


Conclusions

• Steam cycle has been simulated independently to estimate the power generation by heat recovery Investigate the further integration with steam cycle. Need a detailed air separation unit simulation for the estimation of the utilities consumption.

• The required energy for unit clinker in retrofit case is more than double that in base case but additional electricity can be generated. Full comparison with amine and oxyfuel (Unisim flowsheets from IGSCC project), Economic analysis for the evaluation of various capture processes.

Documents

Process Integration of Ca -Looping Process with a … Integration of Ca -Looping Process with a Cement Manufacturing Plant ... due to infiltration air ... Raw Mill 1. st. nd Preheater