172 v. kumar

Presented by

Vinod Kumar Singh

Ph.D. Research Scholar

A

Presentation

on

Carbon Dioxide Capture and Sequestration by Adsorption on Activated Carbon

Guided by

Dr. E. Anil Kumar

Assistant Professor

Discipline of Mechanical Engineering

Indian Institute of Technology Indore

OUTLINE

Introduction

Objective of the Study

Mathematical Modeling

Results and Discussions

Conclusions

Scope of Future Work

Significance

Limitations

Definition

CO2 Capture

Technology

Importance

of AC

Physical

Model

Kinetic

Models

Governing

Equations

Discretization

Equations

Validation

Parametric

Analysis

CCS

Introduction

With the rapid development of modern civilization, the widespread use of fossil

fuels within the current energy infrastructure is considered as the largest source of

anthropogenic emissions of CO2, which is largely responsible for global warming

and climate change

The International Panel on Climate Change (IPCC) predicts that, by the year 2100,

the atmosphere may contain up to 570 ppm CO2, causing a rise in the mean global

temperature of around 1.9 C

CCS is not the „silver bullet‟ that in and of itself will solve the climate change

problem, it is powerful addition to the portfolio of technologies that will be needed

to address climate change

12/11/2013 Discipline of Mechanical Engineering, IIT Indore 1

Source: Martinez et al. (2013), IPCC (2007) and Bernstein et al. (2006)

Table : Fossil fuel emission levels (Pounds/Billions BTU of energy input)

Pollutant Natural Gas Coal Oil

Carbon dioxide 117000 208000 164000

Carbon Monoxide 40 208 33

Nitrogen oxide 92 457 448

Sulphur dioxide 1 2591 1122

Particulates 7 2744 84

Mercury 0 0.016 0.007

Total 117140 214000 165687

IPCC Climate Change: Impacts, Adaptation and Vulnerability

Discipline of Mechanical Engineering, IIT Indore12/11/2013 2

Fig. Atmospheric CO2 concentration during 1958-2012

Source: Carbon dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of

Energy


Fossil fuels will continue to be used in absence of any fast and easy alternatives

used at large scale

CCS enables to continue use of fossil fuels with reduced emissions while other

alternatives are being developed

CO₂ capture technologies are commercial and widely used in industrial processes

mainly in petroleum industries, ammonia processing and natural gas refining

Applied to several gas fired and coal fired boilers but at smaller scales than current

power plants

Significance of Carbon Capture andSequestration (ccs)


Source: Special Report on “Carbon dioxide capture and storage.” Chapter 3, Intergovernmental Panel on

Climate Change (IPCC), (2006)

• Small Scale: Demonstrated in several industrial applications but not yet at a modern

electric power plant of capacity of as high as 500 MW

• Energy Penalty & High costs involved for the implementation of CCS (CO₂separation, compression, delivery in pipeline and injection of compressed CO₂ in

geologic reservoirs)

Limitations of ccs


Source: IPCC (2006)

Carbon dioxide Capture and Sequestration (CCS)

- Post – combustion - Pipeline - Depleted oil/gas fields

- Pre - combustion - Tanker - Deep Saline formations

- Oxyfuel combustion - Unmineable coal seams

- Deep Ocean

- Mineralization

- Reuse

Power Plant

or Industrial

Process

CO2

Capture &

Compress

CO2

Transport

CO2 Storage

(Sequestration)

USEFUL

PRODUCTS

(e.g., electricity, fuels,

chemicals, hydrogen)

Fossil

Fuels;

Biomass

Air or

Oxygen

CO2

Fig. Schematic of a CCS system, consisting of CO2 capture, transport and storage

Definition of CCS


Source: Rubin, E.S. (2010)


Fig. Schematic CO2 Capture Options (Source: Figuerea et al. (2008))

Fig. Technical options for CO2 capture (The choice of method depends strongly on the

particular application)

CO2 Separation and Capture

Absorption Adsorption Cryogenics Membranes Microbial/Algal

Systems

Chemical

Physical

Adsorber

Beds

Gas Absorption

Regeneration

Method

Gas Separation

Ceramic Based

Systems

MEA

Caustic

Other

Selexol

Rectisol

Other

Alumina

Zeolite

Activated Carbon

Pressure Swing

Temperature Swing

Washing

Polyphenyleneoxide

Polydimethylsiloxane

Polypropelene

CO2 Capture Technologies


Source: Rao, A.B. et al (2002)

Importance of Activated Carbons (AC)

• High Thermal Stability

• Favorable Adsorption Capacity

• Wide Range of Starting Materials for Production of Activated Carbons

• Leads to Lower Raw Material Costs

• Large Adsorption Capacity at Elevated Pressures

• Desorption can Easily be Accomplished by the Pressure Swing Approach


Source: Spigarelli, B.P. et al. (2013)

Objective of the Study

To select as a suitable adsorbents for the CO2 capture and a numerical analysis is

carried out to study the rate of adsorption of the gas

A one dimensional mathematical model is proposed based on the Dubinin‟s

Theory of volume filling of Micropore, and analyzed along with the unsteady

heat transfer

A parametric analysis is carried out to study the effect of various crucial

parameters like thickness of bed, cooling fluid temperature, supply temperature

and heat transfer coefficient on the adsorption amount


Mathematical Modeling

Problem Formulation And Solution Methodology

Physical Model

Fig. Physical model of adsorption system Fig. Side view of the reactor bed


D

Assumptions

1. Reactor is one dimensional i.e. only radial variations are considered.

2. Variation of porosity with adsorption is negligible inside the bed. There is no

swelling of the solids.

3. Thermo-physical properties of both the gas and solid phases are constant.

4. Local thermal equilibrium exists between the gas and solid. The gas velocities in

the bed are small. Hence, the gas and solid phase have sufficient time to attain

equilibrium.

5. Carbon dioxide acts like an ideal gas inside the bed.

6. Natural convection and radiation effects are neglected.

7. CO2 pressure within the bed is uniform (at any given instant; no radial variations).

8. Cooling fluid temperature is taken to be constant throughout the process with

convection occurring for cooling of the bed.

9. Other gases in stream have a very low ppm hence no effect on the adsorption of

CO2 by AC. Sorption capacity of AC towards moisture is very low.


Kinetic Model for ACs

Dubinin Astakhov (D-A) and Radushkevich (D-R) Equation

n

a ao

0

2

0

0

AN N exp

E

AW W exp

E

Dubinin Astakhov Equation

Dubinin Radushkevich Equation

Where;

Na = Amount adsorbed at relative pressure P/Ps

Nao = Limiting amount of gas adsorbed in micropores where W0 = NaoVm

A = Thermodynamic potential RT ln (Ps/P)

Eο = Characteristic energy for a given adsorbent system

β = Scaling factor depending on adsorbate

Wο = Micropore volume

Vm = Molar volume at specified pressure and temp.


Source: Stoeckli, F. et al. (1995, 2001)

Properties of Activated Carbons

S.

No

Name of

Activated

Carbon

Micropore

Volume

Wo (cm3/g)

Surface area

of

Micropore

Smi (m2/g)

Average

Micropore

width

Lo (nm)

Characteristic

Energy

Eo (kJ/mol)

1. PSAC

(coal tar)

0.26 413 1.25 20.04

2. Commercial AC

MAXSORB 30

(petroleum

coke)

0.34 2250 0.97 22.5

3. ACP-750-2.0

(coconut shell)

0.40 1018 0.78 25.14


Source: Guillot, A. et al. (2001), Linares (2005)

Empirical Relations Used to calculate the Characteristic Energy Eo

(Assuming single slit shaped micropore)


Source: Stoeckli, F. et al. (1995)

Governing Equations


Boundary Conditions


Solution through Discretization of Equations


Internal Node Equation Surface Node Equation


S.N. Parameter Activated

Carbon (AC)

Carbon

Dioxide (CO2)

(1) Density (Kgm-3) 530 1.98

(2) Specific heat (JKg-1K-1) 0.92

(3) Effective thermal conductivity (Wm-1K-1 ) 0.25

(4) Diffusivity (m2s-1) 5e-7

(5) Heat of adsorption (kJmol-1) 15

(6) Universal gas constant (Jmol-1K-1) 8.314

(7) Characteristic Energy (KJmol-1) 25

(8) Scaling Factor 0.36

(9) Limiting amount adsorbed (mol) 0.000755

(10) Saturation Pressure (atm) 1.1

(11) Inlet Pressure of CO2 (atm) 0 - 1


Table: Thermophysical Properties of AC and CO2

Source: Guillot, A. et al. (2001), Linares (2005), Martin, C.F. et al. (2010)

S.N. Parameter Range of Value

(1) Initial temperature of bed T0* (K) 313 - 373

(2) Diameter of the bed D* (m) 0.15 – 0.70

(3) Cooling fluid temperature Tf *(K) 273 - 303

(4) Heat transfer coefficient h* (Wm-2K-1) 50 - 250

Table: Operational parameters (* representsvariable quantities)


Results and Discussions

Validation of Kinetic Model

Nao = Wo/Vm (Vm = Molar Volume)

T = 50 C

Ps = 1.1 atm

Eo = 25 kJ/mol

βCO2= 0.36

Wo = 0.4 cm3/g

Vm = 530 cm3/g

Average Relative Error: 2.8%

Fig. Graphical comparison of Theoretical and Experimental results for stream at 40°Cand 0-1 atm (Experimental values: Chang et al., 2006 )


Parametric study of carbon dioxide capture system

Radial Variations of Temperature &Adsorption Amount of CO2

Process conditions:

Initial Temperature of bed: 80 C Heat Transfer Coefficient: 150 W/m2K

Cooling fluid temperature: 10 C Dimensions: 0.30 m diameter

Fig. Radial variations of Temperature Fig. Radial variation of Adsorption

Quantity (mol kg-1 of adsorbent)


Effect of Radius on amount of CO2 adsorbed withtime

• Maximum quantity of CO2

adsorbed does not vary

significantly while changing

the diameter

• Time to reach the max.

adsorbed state increases as

the bed thickness is increased

• Bed with lesser thickness

facilitates heat conduction

faster

• At any given time, the lower

thickness bed would have

cooled down more than the

one with more thickness

Process conditions:

Initial bed temperature: 80 C

Cold fluid temperature: 10 C

Fig. Variation of CO2 adsorption with time for

different radii (packing density kept same)


Effect of Cold Fluid Temperature on amountadsorbed

• Higher cooling fluid

temperature values, the heat

is dissipated faster with

more adsorbed CO2 at any

given time due to the lower

average bed temperatures

• Time to reach maximum

adsorption state does not

vary significantly

Process conditions:


Heat transfer coefficient: 150 W/m2K

Fig. Variation of CO2 adsorption with cooling fluid temperature


Effect of Heat transfer coefficient on amountof CO2 adsorbed with time

Process conditions:



• Maximum adsorption state is

reached faster for higher „h‟

values

• Amount adsorbed does not

increase significantly after h =

100 W/m2K

Fig. Variation of CO2 adsorption with time for different heat transfer coefficient


Effect of Initial Bed Temperature on amountof CO2 adsorbed with time

• For higher initial temperatures,

the maximum amount of CO2

adsorbed is more, though

insignificant differences exists

• Time to reach that state is also

almost the same in all cases

Process conditions:

Heat transfer coefficient: 150 W/m2K


Fig. Variation of CO2 adsorption with different inlet bed temperatures


Conclusions

Conclusions

1. The adsorption model (rate as a function of temperature & pressure) for AC is

best described by Dubinin‟s Theory of Volume Filling of Micropores (TVFM)

2. Lower reactor bed radii are preferred to minimize the time required to reach the

maximum adsorption state although the CO2 adsorbed does not have significant

differences. Hence, a bed diameter of D = 30 cm is selected

3. Higher heat transfer coefficient results in faster adsorption as well as higher

amount of CO2 adsorbed. But after h = 100 Wm-2K-1, the maximum amount

adsorbed tends to be the same. Hence, an „h‟ value of 150 Wm-2K-1 is selected

4. Lower cooling fluid temperature results in faster adsorption. Hence, a value of

10 C is selected for the operation

5. Higher initial bed temperature results in greater amount of CO2 adsorbed with

the steady state being reached in same time. It leads to the selection of To=

353K as the preferred value. Although, temperature should not be increased to a

level which tends to degrade the material of the reactor bed


Scope for Future Work

• 1D study can be extended to a 2D and 3D model followed by practical

implementation to realize the real-time difficulties associated with the model

• AC used in the present work have the basic form without the impregnation of basic

functionalities like amines. This study can thus be used to incorporate those

modifications and then analyze the system

• Mathematical approach discussed in the present work can be used to carry out the

comparison of different adsorbents


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