Capture of Carbon Dioxide from Flue Gas Using a Cyclic Alkali

Carbonate-Based Process

Research Triangle Park, North Carolina

Second Annual Conference on Carbon Sequestration

Alexandria, Virginia May 2003

Research Triangle Institute

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Project Team

� RTI– David A. Green – Raghubir P. Gupta– Santosh K. Gangwal

� LSU– Douglas P. Harrison

� Church & Dwight– Robert Berube– Steve Lajoie

� DOE/NETL– Michael K. Knaggs

– Brian S. Turk– William J. McMichael– Jeffrey W. Portzer

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Objectives

To develop a carbon dioxide separation technology that is� Regenerable sorbent-based� Applicable to both coal and natural gas-based power plants� Applicable as a retrofit to existing plants, as well as to new

power plants� Compatible with the operating conditions in current power

plant configurations� Relatively simple to operate � Less expensive than currently available technologies

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Integration of the “Dry Carbonate” Process in a Combustion Facility

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Concept Evaluation(Sodium Bicarbonate Sorbent – “Baking Soda”)

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Time (min)

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ght F

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ture

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Temperature

Mass

Calcination/Regeneration:130 °C in HeCarbonation:11% CO27% H2O74%N27% O2

Inexpensive CO2getler identified

Getler is readily regenerated

Low temperature process

Convenient for flue gas treatment

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Materials Screened

� Sodium bicarbonate (SBC) – NaHCO3– Grade 1– Grade 2– Grade 3– Grade 5– Spherical

� Trona--Na2CO3•NaHCO3•2H2O– Grade T-50– Grade T-200

� Potassium Carbonate – K2CO3– Analytical Grade– Commercial Grade– Jet-milled

� Supported Sorbents– 40% K2CO3/60% support– 10% K2CO3/90% support– 20% Na2CO3/80% support– 40% Na2CO3/60% support

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Sorbent Characterization and Testing

� Physical– Particle Size Distribution (RTI)– Surface Area (RTI & C&D)– Attrition Resistance (RTI)– Pore Size Distribution (RTI)– Bulk Density (RTI)– X-ray Diffraction (C&D)– Scanning Electron Microscopy (C&D)– Fluidization Characteristics (RTI)

� Chemical– Thermogravimetry (RTI & LSU)– Fixed Bed Testing (LSU)– Fluidized Bed Testing (RTI)

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Sodium Carbonate Chemistry

30.82NaHCO3 X Na2CO3 +CO2 +H2O

32.15 NaHCO3 X Na2CO3•3NaHCO3 +CO2 +H2O

32.82/3 Na2CO3•3NaHCO3 X 5/3 Na2CO3 +CO2 +H2O

∆ HKcal/gmol CO2

Reaction

� CO2 removal is exothermic

� Sorbent regeneration is endothermic

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Fundamental Kinetic andThermodynamic Studies

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ensi

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t 60°C

70°C

80°C

8%CO2

16%H2O76%He

Na2CO3·3NaHCO3

SBC Grade #3 Sorbent

First order reaction kinetics– CO2

– H2OTemperature sensitive kinetics

– NaHCO3 product at 60 °C– Intermediate product

(WS) at 70 °C– Higher temperatures

decrease CO2 removalPotential temperature control strategies

– Cold diluents → solids– Liquid H2O addition

(∆ HVAP = 10 Kcal/gmol)

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Sorbent Operating Temperature Ranges

� Sodium Carbonate– Carbonation: 60 – 80 °C– Regeneration (decarbonation; calcination): > 120 °C

� Potassium Carbonate– Carbonation: up to 120 °C– Regeneration (decarbonation; calcination): > 140 °C

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TGA Cyclic Reactivity Testing

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Sorbent: 40% supported potassium carbonate

Temperature: 70 °C (Isothermal)

Gas: Carbonation 7.5% CO2, 5.7% H2O, He

Regeneration 100% He

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Fixed-Bed Reactor System at LSU

N2

O2

CO2

Syringe Pump (H2O)

Vent

BPR : BackPressureRegulator

COND : CondenserCV : Check valveD : DryerF : FilterMFC : Mass Flow ControllerPI : Pressure

IndicatorPRV : Pressure

Relief valve

Furnace

BPR

To GCCOND

PRV MFC

CV F

D

MFC

CV F

D

D

MFC

CV FPI

PI

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Fixed-Bed Testing of SBC

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Time (minutes)

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bon

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xide

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oval

(%) Cycle 1

Cycle 2Cycle 3Cycle 4Cycle 5

Sorbent: SBC Grade #3Regeneration

Temp: 120 °CGas: He

CarbonationTemp: 60 °CGas: 8% CO2, 16%

H2O in He

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SBC Sorbent Interaction with HCl and SO2

� Hydrogen Chloride– 1-inch Fluidized-bed testing – 100 ppm HCl in simulated flue gas– >98% removal with 1.2 sec superficial residence time

� Sulfur Dioxide– TGA tests and 1-inch fluidized-bed testing– 1000 ppm SO2 in simulated flue gas– >95% removal– Irreversible at temperatures ≤ 200 °C

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RTI’s Bench-Scale Fluid-Bed Test Unit

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Fluid-Bed Testing of 40% Supported Sodium Carbonate

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rage

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ture

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Carbonation in 7% Carbon Dioxide, 6% Water Vapor

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Conceptual Transport Reactor System

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Transport Reactor Approach

� Advantages– Low pressure drop (<1 psi [< 30 in. W.C.])– Reliable and effective solid sorbent movement – Superior temperature control

� Sorbent design challenges– High sorbent reactivity required

• Short residence times (2-6 seconds)– Highly attrition-resistant sorbent required

• High sorbent flux rate

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Engineering Design Challenges

� Heat integration– Capturing low-grade, low-value heat in the steam cycle for

sorbent regeneration– Minimizing parasitic power consumption– Heat transfer:

• Removal of carbonation heat of reaction• Addition of regeneration energy

� Low pressure drop of flue gas stream– Minimizing additional power requirements of the I.D. fan

� Sorbent Transfer– Efficiently move sorbent between carbonation reactor and

regenerator

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Heat Integration Analysis

� Goal: Minimize process energy requirements

� Target: Regeneration– Largest energy requirement– Low-level heat (120-140 °C)

� Solutions– Steam usage– Low-level heat sources

• Recover flue gas heat• Extract heat from cooling water• Alternative air preheating schemes

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Comparison of Coal Fired Power Plants With and Without CO2 Removal

Heat Require- Auxiliary Plantment for CO2 Sor- Gross Plant Power Net Plant Efficiency

bent Regeneration, Power Requirement Power (HHV)Case Btu/lbmol CO2 kWe kWe kWe %

EPRI BaseCase 7CCoal Fired Steam Not Applicable 491,108 29,050 462,058 40.5Plant; no CO2Removal

EPRI Case 7AMEA CO2 71,140E 402,254 72,730 329,524 28.9Removal

EPRI Case 7ARe-calc’d 103,400A 362,178 72,730 289,448 25.4

Comparison CaseNa2CO3-based 60,000 416,144 72,730 343,414 30.1Dry CO2 Removal90% CO2 Removal for Applicable CasesFor all cases: Heat input = 1,140,155 kWheat (HHV)EEPRI, Evaluation of Innovative Fossil Fuel Power Plants with CO2 Removal, 2000AAlstom Power, Engineering Feasibility and Economics of CO2 Capture on an Existing Coal-Fired Power Plant, 2001

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Summary of Research Findings

� The sodium and potassium carbonate sorbents react readily to remove CO2

� The materials can be cycled repeatedly without appreciable loss of activity

� The carbonate/carbon dioxide reaction may be limited by considerations of heat removal from the sorbent particle

� The high initial rates of reaction may be suitable for short residence time transport reactor systems

� Regeneration of sorbent can be carried out in an essentially pure carbon dioxide stream

� Supported materials provide suitable activity and attrition resistance

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Technology Development Plan

Evaluate concept

Kinetic studiesMaterial screeningSorbent developmentProcess modelingPreliminary economics

Scale-up of sorbent productionSorbent evaluation

– Reactivity– Capacity– Attrition– Stability

� Energy analysis– Heat requirements– Temperature constraints

� Economic evaluation

Thermodynamic Analysis

& Lab Testing

Bench-scale

Testing

Pilot-Plant

Testing

Slip Stream

Testing

Demonstration

TestingCOMMERCIAL

IMPLEMENTATION

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Acknowledgements

� U.S. DOE/NETL Cooperative Agreement No. DE-FC26-00NT40923

� Project Manager: Michael K. Knaggs

� Sequestration Project Manager: Scott M. Klara